@article{nickels_genereux_knappe_2023, title={Improved Darcian streambed measurements to quantify flux and mass discharge of volatile organic compounds from a contaminated aquifer to an urban stream}, volume={253}, ISSN={["1873-6009"]}, DOI={10.1016/j.jconhyd.2022.104124}, abstractNote={Quantifying VOC transport from contaminated groundwater to streams is challenging and important for understanding off-site migration of VOCs, cross-media contamination (groundwater to surface water and eventually air), and potential impacts on downstream ecosystems and human populations. A streambed point sampling approach was used to quantify fluxes of water and 14 VOCs from groundwater to an urban stream in North Carolina, USA, during summer (June 2015) and winter (January 2016). The approach is unique in coupling measurements of vertical hydraulic conductivity, vertical hydraulic head gradient, and groundwater VOC concentration at each individual sampling point, reducing or eliminating some potential concerns with other Darcian methods for quantifying VOC inputs to streams. Most results were consistent with discharge of two main VOC plumes on opposite sides of the stream. Plume 1 from the west side was dominated by cis-1,2-dichloroethene (cDCE) and vinyl chloride (VC) at mean concentrations of 19 and 11 μg L-1, respectively. Plume 2 from the east side was dominated by benzene (mean concentration 56 μg L-1). Plume 2 was not previously known, and the improved sampling approach allowed VOC discharge from both plumes to be quantified simultaneously. For 13 of the 14 detected VOCs, the mean VOC flux from groundwater to the stream (fVOC) was higher in January 2016 than in June 2015, mainly because groundwater flux was higher in January. The only exception was cDCE, the most abundant VOC in Plume 1, which had mean fVOC values of 9.8 and 9.5 mg m-2 d-1 in June 2015 and January 2016, respectively. Benzene was the most abundant VOC in Plume 2 and had mean fVOC values of 11 and 37 mg m-2 d-1 in June 2015 and January 2016, respectively. High groundwater flux drove almost all the occurrences of high VOC flux. For a given VOC, the flow-weighted mean concentration (with each VOC concentration weighted by the upward groundwater flux at the VOC sampling point) was generally larger than the unweighted mean concentration. Thus, flow-weighting of concentrations gave a more accurate indication of the average VOC concentration in net groundwater discharge to the stream. An estimate of total VOC mass discharge from groundwater to the study reach of the stream, 3.6 kg of VOC per year, was based on the fVOC results and streambed area in the reach. The bulk of this discharge was due to benzene, cDCE, and VC, with individual mass discharges of 2.1, 0.83, and 0.40 kg yr-1, respectively. Estimates of maximum potential VOC degradation in the streambed suggest that the 3.6 kg yr-1 estimate of mass discharge was not sensitive to potential degradation of VOCs in the streambed sediments above the groundwater sampling depth.}, journal={JOURNAL OF CONTAMINANT HYDROLOGY}, author={Nickels, J. L. and Genereux, D. P. and Knappe, D. R. U.}, year={2023}, month={Feb} }
 @article{zeyrek_mittelstet_gilmore_zlotnik_solomon_genereux_humphrey_shrestha_2023, title={Modeling groundwater transit time distributions and means across a Nebraska watershed: Effects of heterogeneity in the aquifer, riverbed, and recharge parameters}, volume={617}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2022.128891}, journal={JOURNAL OF HYDROLOGY}, author={Zeyrek, Caner and Mittelstet, Aaron R. and Gilmore, Troy E. and Zlotnik, Vitaly and Solomon, D. Kip and Genereux, David P. and Humphrey, C. Eric and Shrestha, Nawaraj}, year={2023}, month={Feb} }
 @article{genereux_2022, title={Addendum to "Quantifying Uncertainty in Tracer-Based Hydrograph Separations" for Three-Component Mixing Problems}, volume={58}, ISSN={["1944-7973"]}, DOI={10.1029/2022WR031987}, abstractNote={Water mixing problems are common in hydrology. A 1998 paper describing uncertainty analysis in tracer-based mixing problems is widely cited but does not present the equations needed for three-component problems. This Commentary presents the equations needed to compute the uncertainties in the mixing fractions for a three-component water mixing problem based on tracer data.}, number={2}, journal={WATER RESOURCES RESEARCH}, author={Genereux, David P.}, year={2022}, month={Feb} }
 @article{jensen_genereux_gilmore_solomon_mittelstet_humphrey_macnamara_zeyrek_zlotnik_2022, title={Estimating groundwater mean transit time from SF6 in stream water: field example and planning metrics for a reach mass-balance approach}, ISSN={["1435-0157"]}, DOI={10.1007/s10040-021-02435-8}, journal={HYDROGEOLOGY JOURNAL}, author={Jensen, Craig R. and Genereux, David P. and Gilmore, Troy E. and Solomon, D. Kip and Mittelstet, Aaron R. and Humphrey, C. Eric and MacNamara, Markus R. and Zeyrek, Caner and Zlotnik, Vitaly A.}, year={2022}, month={Jan} }
 @article{marzolf_small_oviedo-vargas_ganong_duff_ramirez_pringle_genereux_ardon_2022, title={Partitioning inorganic carbon fluxes from paired O-2-CO2 gas measurements in a Neotropical headwater stream, Costa Rica}, volume={7}, ISSN={["1573-515X"]}, url={https://doi.org/10.1007/s10533-022-00954-4}, DOI={10.1007/s10533-022-00954-4}, abstractNote={The role of streams and rivers in the global carbon (C) cycle remains unconstrained, especially in headwater streams where CO2 evasion (FCO2) to the atmosphere is high. Stream C cycling is understudied in the tropics compared to temperate streams, and tropical streams may have among the highest FCO2 due to higher temperatures, continuous organic matter inputs, and high respiration rates both in-stream and in surrounding soils. In this paper, we present paired in-stream O2 and CO2 sensor data from a headwater stream in a lowland rainforest in Costa Rica to explore temporal variability in gas concentrations and ecosystem processes. Further, we estimate groundwater CO2 inputs (GWCO2) from riparian well CO2 measurements. Paired O2–CO2 data reveal stream CO2 supersaturation driven by groundwater CO2 inputs and large in-stream production of CO2. At short time scales, CO2 was diluted during storm events, but increased at longer seasonal scales. Areal fluxes in our study reach show that FCO2 is supported by greater in-stream metabolism compared to GWCO2. Our results underscore the importance of tropical headwater streams as large contributors of carbon dioxide to the atmosphere and show evaded C can be derived from both in-stream and terrestrial sources.}, journal={BIOGEOCHEMISTRY}, publisher={Springer Science and Business Media LLC}, author={Marzolf, Nicholas S. and Small, Gaston E. and Oviedo-Vargas, Diana and Ganong, Carissa N. and Duff, John H. and Ramirez, Alonso and Pringle, Catherine M. and Genereux, David P. and Ardon, Marcelo}, year={2022}, month={Jul} }
 @article{petre_salk_stapleton_ferguson_tait_obenour_knappe_genereux_2022, title={Per- and polyfluoroalkyl substances (PFAS) in river discharge: Modeling loads upstream and downstream of a PFAS manufacturing plant in the Cape Fear watershed, North Carolina}, volume={831}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2022.154763}, abstractNote={The Cape Fear River is an important source of drinking water in North Carolina, and many drinking water intakes in the watershed are affected by per- and polyfluoroalkyl substances (PFAS). We quantified PFAS concentrations and loads in river water upstream and downstream of a PFAS manufacturing plant that has been producing PFAS since 1980. River samples collected from September 2018 to February 2021 were analyzed for 13 PFAS at the upstream station and 43-57 PFAS downstream near Wilmington. Frequent PFAS sampling (daily to weekly) was conducted close to gauging stations (critical to load estimation), and near major drinking water intakes (relevant to human exposure). Perfluoroalkyl acids dominated upstream while fluoroethers associated with the plant made up about 47% on average of the detected PFAS downstream. Near Wilmington, Σ43PFAS concentration averaged 143 ng/L (range 40-377) and Σ43PFAS load averaged 3440 g/day (range 459-17,300), with 17-88% originating from the PFAS plant. LOADEST was a useful tool in quantifying individual and total quantified PFAS loads downstream, however, its use was limited at the upstream station where PFAS levels in the river were affected by variable inputs from a wastewater treatment plant. Long-term monitoring of PFAS concentrations is warranted, especially at the downstream station. Results suggest a slight downward trend in PFAS levels downstream, as indicated by a decrease in flow-weighted mean concentrations and the best-fitting LOADEST model. However, despite the cessation of PFAS process wastewater discharge from the plant in November 2017, and the phase-out of perfluorooctane sulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) in North America, both fluoroethers and legacy PFAS continue to reach the river in significant quantities, reflecting groundwater discharge to the river and other continuing inputs. Persistence of PFAS in surface water and drinking water supplies suggests that up to 1.5 million people in the Cape Fear watershed might be exposed.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Petre, M-A and Salk, K. R. and Stapleton, H. M. and Ferguson, P. L. and Tait, G. and Obenour, D. R. and Knappe, D. R. U. and Genereux, D. P.}, year={2022}, month={Jul} }
 @article{humphrey_solomon_genereux_gilmore_mittelstet_zlotnik_zeyrek_jensen_macnamara_2022, title={Using Automated Seepage Meters to Quantify the Spatial Variability and Net Flux of Groundwater to a Stream}, volume={58}, ISSN={["1944-7973"]}, DOI={10.1029/2021WR030711}, abstractNote={We utilized 251 measurements from a recently developed automated seepage meter (ASM) in streambeds in the Nebraska Sand Hills, USA to investigate the small-scale spatial variability of groundwater seepage flux (q) and the ability of the ASM to estimate mean q at larger scales. Small-scale spatial variability of q was analyzed in five dense arrays, each covering an area of 13.5–28.0 m2 (169 total point measurements). Streambed vertical hydraulic conductivity (K) was also measured. Results provided: (a) high-resolution contour plots of q and K, (b) anisotropic semi-variograms demonstrating greater correlation scales of q and K along the stream length than across the stream width, and (c) the number of rows of points (perpendicular to streamflow) needed to represent the groundwater flux of areas up to 28.0 m2. The findings suggest that representative streambed measurements are best conducted perpendicular to streamflow to accommodate larger seepage flux heterogeneity in this direction and minimize sampling redundancy. To investigate the ASM's ability to produce accurate mean q at larger scales, seepage meters were deployed in four stream reaches (170–890 m), arranged in three to six transects (three to eight points each) per reach across the channel. In each reach, the mean seepage flux from ASMs was compared to the seepage flux from bromide tracer dilution. Agreement between the two methods indicates the viability of a modest number of seepage meter measurements to determine the overall groundwater flux to the stream and can guide sampling for solutes and environmental tracers.}, number={6}, journal={WATER RESOURCES RESEARCH}, author={Humphrey, C. Eric and Solomon, D. Kip and Genereux, David P. and Gilmore, Troy E. and Mittelstet, Aaron R. and Zlotnik, Vitaly A. and Zeyrek, Caner and Jensen, Craig R. and MacNamara, Markus R.}, year={2022}, month={Jun} }
 @article{petre_genereux_koropeckyj-cox_knappe_duboscq_gilmore_hopkins_2021, title={Per- and Polyfluoroalkyl Substance (PFAS) Transport from Groundwater to Streams near a PFAS Manufacturing Facility in North Carolina, USA}, volume={55}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.0c07978}, abstractNote={We quantified per- and polyfluoroalkyl substance (PFAS) transport from groundwater to five tributaries of the Cape Fear River near a PFAS manufacturing facility in North Carolina (USA). Hydrologic and PFAS data were coupled to quantify PFAS fluxes from groundwater to the tributaries. Up to 29 PFAS were analyzed, including perfluoroalkyl acids and recently identified fluoroethers. Total quantified PFAS (ΣPFAS) in groundwater was 20-4773 ng/L (mean = 1863 ng/L); the range for stream water was 426-3617 ng/L (mean = 1717 ng/L). Eight PFAS constituted 98% of ΣPFAS; perfluoro-2-(perfluoromethoxy)propanoic acid (PMPA) and hexafluoropropylene oxide dimer acid (GenX) accounted for 61%. For PFAS discharge from groundwater to one tributary, values estimated from stream water measurements (18 ± 4 kg/yr) were similar to those from groundwater measurements in streambeds (22-25 ± 5 kg/yr). At baseflow, 32 ± 7 kg/yr of PFAS discharged from groundwater to the five tributaries, eventually reaching the Cape Fear River. Given the PFAS emission timeline at the site, groundwater data suggest the abundant fluoroethers moved through the subsurface to streams in ≪50 yr. Discharge of contaminated groundwater may lead to long-term contamination of surface water and impacts on downstream drinking water supplies. This work addresses a gap in the PFAS literature: quantifying PFAS mass transfer between groundwater and surface water using field data.}, number={9}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Petre, Marie-Amelie and Genereux, David P. and Koropeckyj-Cox, Lydia and Knappe, Detlef R. U. and Duboscq, Sandrine and Gilmore, Troy E. and Hopkins, Zachary R.}, year={2021}, month={May}, pages={5848–5856} }
 @article{solomon_humphrey_gilmore_genereux_zlotnik_2020, title={An Automated Seepage Meter for Streams and Lakes}, volume={56}, ISSN={["1944-7973"]}, DOI={10.1029/2019WR026983}, number={4}, journal={WATER RESOURCES RESEARCH}, author={Solomon, D. Kip and Humphrey, Eric and Gilmore, Troy E. and Genereux, David P. and Zlotnik, Vitaly}, year={2020}, month={Apr} }
 @article{stewart-maddox_frisbee_andronicos_genereux_meyers_2018, title={Identifying the regional extent and geochemical evolution of interbasin groundwater flow using geochemical inverse modeling and Sr-87/Sr-86 ratios in a complex conglomeratic aquifer}, volume={500}, ISSN={["1878-5999"]}, DOI={10.1016/j.chemgeo.2018.07.026}, abstractNote={Abstract Interbasin groundwater flow (IGF) occurs when water that is recharged in one watershed or basin discharges into an adjacent watershed or basin. IGF can directly impact the water and solute mass discharged from a watershed and consequently, skew estimates of watershed-scale weathering rates. It is extremely difficult to determine the impact of IGF on weathering processes in adjacent watersheds because it is difficult to differentiate between solute mass originating within the watershed from solute mass transported into the watershed from sources outside the watershed. We quantify the regional extent of IGF in three watersheds (Canjilon, El Rito, and Vallecitos) draining the Tusas Mountains of northern New Mexico, USA (sites where IGF has been shown to occur) using spatial trends in 87Sr/86Sr in springs and streams and geochemical modeling using PHREEQC. 87Sr/86Sr ratios show a strong connection from the Canjilon watershed to the El Rito watershed and suggest that the IGF connection may extend to the Vallecitos watershed. Geochemical modeling constrained by XRD analysis of aquifer mineralogy indicates that IGF from the Canjilon watershed is the dominant control on perennial flow in springs and streams in the adjacent El Rito watershed. However, the geochemical signature of an IGF connection from El Rito to the Vallecitos watershed is weak to non-existent. The maximum possible IGF contribution from El Rito to Vallecitos is during snowmelt, contributing as much as 20% of the water and solute mass to Vallecitos. However, the maximum IGF contribution is}, journal={CHEMICAL GEOLOGY}, author={Stewart-Maddox, Noah S. and Frisbee, Marty D. and Andronicos, Christopher L. and Genereux, David P. and Meyers, Zachary P.}, year={2018}, month={Nov}, pages={20–29} }
 @article{osburn_oviedo-vargas_barnett_dierick_oberbauer_genereux_2018, title={Regional Groundwater and Storms Are Hydrologic Controls on the Quality and Export of Dissolved Organic Matter in Two Tropical Rainforest Streams, Costa Rica}, volume={123}, ISSN={2169-8953}, url={http://dx.doi.org/10.1002/2017JG003960}, DOI={10.1002/2017jg003960}, number={3}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Osburn, Christopher L. and Oviedo-Vargas, Diana and Barnett, Emily and Dierick, Diego and Oberbauer, Steven F. and Genereux, David P.}, year={2018}, month={Mar}, pages={850–866} }
 @article{koh_genereux_koh_ko_2017, title={Relationship of groundwater geochemistry and flow to volcanic stratigraphy in basaltic aquifers affected by magmatic CO2, Jeju Island, Korea}, volume={467}, ISSN={["1872-6836"]}, DOI={10.1016/j.chemgeo.2017.08.009}, abstractNote={Abstract Groundwater from pristine volcanic rock aquifers on dormant Jeju Island, Korea, was investigated to identify sources and geochemical processes of dissolved inorganic carbon (DIC) and related solutes along with characteristics of groundwater flow using a multi-isotope approach. δ 18 O, δ 2 H, and 3 H of groundwater indicated the water is of meteoric origin, and is mainly derived from recent recharge, except Na-rich mineral water which has a significant contribution of 3 H-free old water. 87 Sr/ 86 Sr of dissolved Sr suggests that solutes in groundwater were mainly derived from old alkali basalt in the lower part of lava flows. δ 13 C CO2(g) calculated using δ 13 C DIC and measured hydrogeochemical parameters indicated that (1) biogenic soil CO 2 is a dominant source of DIC in low mineralized water, (2) CO 2 -rich water had mostly mantle-derived magmatic CO 2 , and (3) mineral water contained both biogenic and magmatic CO 2 . δ 13 C CO2(g) in mineral water was affected by precipitation of calcite, which complicated the estimation of the contribution of CO 2 sources to DIC. Concentrations of mobile elements were mainly controlled by the amount of magmatic CO 2 and groundwater residence time. δ 13 C CO2(g) and 3 H content were used to distinguish four types of groundwater with different spatial patterns of occurrence in relation to the volcanic stratigraphy of Jeju Island. Groundwater types I and II are low mineralized water with lower levels of DIC from biogenic CO 2 , composed of either recent recharge ( 3 H (> 60 years, type II). Type III is Mg-rich mineral water with significant recent recharge while type IV is Na-rich mineral water with older residence time. Types III and IV had somewhat elevated levels of DIC (up to 7.6 mM) with mixed signatures of magmatic and biogenic CO 2 , while CO 2 -rich water (a subset of type III) had DIC up to 100 mM with signatures of mantle-derived magmatic CO 2 . Groundwater in the eastern area of Jeju Island is mostly type I, which can be attributed to a lack of both low-permeability rocks and recent volcanic rocks in that area. Types III and IV were found in the western area where the latest volcanic rocks are distributed. In the southwestern area, type III is associated with permeable basaltic aquifers with a contribution of magmatic CO 2 and type IV is from the younger lava flows dissected by older massive trachytic rocks and shallower hydrovolcanic tuffs, which led to the higher degree of mineralization. A conceptual model is proposed to integrate the chemical and isotopic constraints of groundwater with volcanic stratigraphy and suggest the processes that generated groundwater types with different residence times and chemical compositions. This study may contribute to understanding the processes of groundwater flow and mineralization in volcanic aquifers affected by deep-source CO 2 and variable residence time of groundwater in both dormant and active volcanic areas.}, journal={CHEMICAL GEOLOGY}, author={Koh, Dong-Chan and Genereux, David P. and Koh, Gi-Won and Ko, Kyung-Seok}, year={2017}, month={Sep}, pages={143–158} }
 @article{solder_gilmore_genereux_solomon_2016, title={A Tube Seepage Meter for In Situ Measurement of Seepage Rate and Groundwater Sampling}, volume={54}, ISSN={["1745-6584"]}, DOI={10.1111/gwat.12388}, abstractNote={We designed and evaluated a “tube seepage meter” for point measurements of vertical seepage rates (q), collecting groundwater samples, and estimating vertical hydraulic conductivity (K) in streambeds. Laboratory testing in artificial streambeds show that seepage rates from the tube seepage meter agreed well with expected values. Results of field testing of the tube seepage meter in a sandy-bottom stream with a mean seepage rate of about 0.5 m/day agreed well with Darcian estimates (vertical hydraulic conductivity times head gradient) when averaged over multiple measurements. The uncertainties in q and K were evaluated with a Monte Carlo method and are typically 20% and 60%, respectively, for field data, and depend on the magnitude of the hydraulic gradient and the uncertainty in head measurements. The primary advantages of the tube seepage meter are its small footprint, concurrent and colocated assessments of q and K, and that it can also be configured as a self-purging groundwater-sampling device.}, number={4}, journal={GROUNDWATER}, author={Solder, John E. and Gilmore, Troy E. and Genereux, David P. and Solomon, D. Kip}, year={2016}, pages={588–595} }
 @article{oviedo-vargas_dierick_genereux_oberbauer_2016, title={Chamber measurements of high CO2 emissions from a rainforest stream receiving old C-rich regional groundwater}, volume={130}, ISSN={["1573-515X"]}, DOI={10.1007/s10533-016-0243-3}, number={1-2}, journal={BIOGEOCHEMISTRY}, author={Oviedo-Vargas, Diana and Dierick, Diego and Genereux, David P. and Oberbauer, Steven F.}, year={2016}, month={Oct}, pages={69–83} }
 @article{heilweil_solomon_darrah_gilmore_genereux_2016, title={Gas-Tracer Experiment for Evaluating the Fate of Methane in a Coastal Plain Stream: Degassing versus in-Stream Oxidation}, volume={50}, ISSN={["1520-5851"]}, DOI={10.1021/acs.est.6b02224}, abstractNote={Methane emissions from streams and rivers have recently been recognized as an important component of global greenhouse budgets. Stream methane is lost as evasion to the atmosphere or in-stream methane oxidation. Previous studies have quantified evasion and oxidation with point-scale measurements. In this study, dissolved gases (methane, krypton) were injected into a coastal plain stream in North Carolina to quantify stream CH4 losses at the watershed scale. Stream-reach modeling yielded gas transfer and oxidation rate constants of 3.2 ± 0.5 and 0.5 ± 1.5 d-1, respectively, indicating a ratio of about 6:1. The resulting evasion and oxidation rates of 2.9 mmol m-2 d-1 and 1,140 nmol L-1 d-1, respectively, lie within ranges of published values. Similarly, the gas transfer velocity (K600) of 2.1 m d-1 is consistent with other gas tracer studies. This study illustrates the utility of dissolved-gas tracers for evaluating stream methane fluxes. In contrast to point measurements, this approach provides a larger watershed-scale perspective. Further work is needed to quantify the magnitude of these fluxes under varying conditions (e.g., stream temperature, nutrient load, gradient, flow rate) at regional and global scales before reliable bottom-up estimates of methane evasion can be determined at global scales.}, number={19}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Heilweil, Victor M. and Solomon, D. Kip and Darrah, Thomas H. and Gilmore, Troy E. and Genereux, David P.}, year={2016}, month={Oct}, pages={10504–10511} }
 @article{gilmore_genereux_solomon_solder_2016, title={Groundwater transit time distribution and mean from streambed sampling in an agricultural coastal plain watershed, North Carolina, USA}, volume={52}, ISSN={["1944-7973"]}, DOI={10.1002/2015wr017600}, abstractNote={We measured groundwater apparent age (τ) and seepage rate (v) in a sandy streambed using point-scale sampling and seepage blankets (a novel seepage meter). We found very similar MTT estimates from streambed point sampling in a 58 m reach (29 years) and a 2.5 km reach (31 years). The TTD for groundwater discharging to the stream was best fit by a gamma distribution model and was very similar for streambed point sampling in both reaches. Between adjacent point-scale and seepage blanket samples, water from the seepage blankets was generally younger, largely because blanket samples contained a fraction of “young” stream water. Correcting blanket data for the stream water fraction brought τ estimates for most blanket samples closer to those for adjacent point samples. The MTT estimates from corrected blanket data were in good agreement with those from sampling streambed points adjacent to the blankets. Collectively, agreement among age-dating tracers, general accord between tracer data and piston-flow model curves, and large groundwater age gradients in the streambed, suggested that the piston flow apparent ages were reasonable estimates of the groundwater transit times for most samples. Overall, our results from two field campaigns suggest that groundwater collected in the streambed can provide reasonable estimates of apparent age of groundwater discharge, and that MTT can be determined from different age-dating tracers and by sampling with different groundwater collection devices. Coupled streambed point measurements of groundwater age and groundwater seepage rate represent a novel, reproducible, and effective approach to estimating aquifer TTD and MTT.}, number={3}, journal={WATER RESOURCES RESEARCH}, author={Gilmore, Troy E. and Genereux, David P. and Solomon, D. Kip and Solder, John E.}, year={2016}, month={Mar}, pages={2025–2044} }
 @article{burnette_genereux_birgand_2016, title={In-situ falling-head test for hydraulic conductivity: Evaluation in layered sediments of an analysis derived for homogenous sediments}, volume={539}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/j.jhydrol.2016.05.030}, DOI={10.1016/j.jhydrol.2016.05.030}, abstractNote={Summary The hydraulic conductivity (K) of streambeds is a critical variable controlling interaction of groundwater and surface water. The Hvorslev analysis for estimating K from falling-head test data has been widely used since the 1950s, but its performance in layered sandy sediments common in streams and lakes has not previously been examined. Our numerical simulations and laboratory experiments show that the Hvorslev analysis yields accurate K values in both homogenous sediment (for which the analysis was originally derived) and layered deposits with low-K sand over high-K sand. K from the Hvorslev analysis deviated significantly from true K only when two conditions were present together: (1) high-K sand was present over low-K sand, and (2) the bottom of the permeameter in which K was measured was at or very near the interface between high-K and low-K. When this combination of conditions exists, simulation and laboratory sand tank results show that in-situ Hvorslev K underestimates the true K of the sediment within a permeameter, because the falling-head test is affected by low-K sediment outside of (below the bottom of) the permeameter. In simulation results, the maximum underestimation (occurring when the bottom of the permeameter was at the interface of high K over low K) was by a factor of 0.91, 0.59, and 0.12 when the high-K to low-K ratio was 2, 10, and 100, respectively. In laboratory sand tank experiments, the underestimation was by a factor of about 0.83 when the high-K to low-K ratio was 2.3. Also, this underestimation of K by the Hvorslev analysis was about the same whether the underlying low-K layer was 2 cm or 174 cm thick (1% or 87% of the domain thickness). Numerical model simulations were useful in the interpretation of in-situ field K profiles at streambed sites with layering; specifically, scaling the model results to the maximum measured K at the top of the field K profiles helped constrain the likely ratio of high K to low K at field locations with layered heterogeneity. Vertical K values are important in field studies of groundwater–surface water interaction, and the Hvorslev analysis can be a useful tool, even in layered media, when applied carefully.}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Burnette, Matthew C. and Genereux, David P. and Birgand, François}, year={2016}, month={Aug}, pages={319–329} }
 @article{gilmore_genereux_solomon_farrell_mitasova_2016, title={Quantifying an aquifer nitrate budget and future nitrate discharge using field data from streambeds and well nests}, volume={52}, ISSN={["1944-7973"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85005896258&partnerID=MN8TOARS}, DOI={10.1002/2016wr018976}, abstractNote={Novel groundwater sampling (age, flux, and nitrate) carried out beneath a streambed and in wells was used to estimate (1) the current rate of change of nitrate storage, dSNO3/dt, in a contaminated unconfined aquifer, and (2) future [ NO3−]FWM (the flow-weighted mean nitrate concentration in groundwater discharge) and fNO3 (the nitrate flux from aquifer to stream). Estimates of dSNO3/dt suggested that at the time of sampling (2013) the nitrate storage in the aquifer was decreasing at an annual rate (mean = −9 mmol/m2yr) equal to about one-tenth the rate of nitrate input by recharge. This is consistent with data showing a slow decrease in the [ NO3−] of groundwater recharge in recent years. Regarding future [ NO3−]FWM and fNO3, predictions based on well data show an immediate decrease that becomes more rapid after ∼5 years before leveling out in the early 2040s. Predictions based on streambed data generally show an increase in future [ NO3−]FWM and fNO3 until the late 2020s, followed by a decrease before leveling out in the 2040s. Differences show the potential value of using information directly from the groundwater—surface water interface to quantify the future impact of groundwater nitrate on surface water quality. The choice of denitrification kinetics was similarly important; compared to zero-order kinetics, a first-order rate law levels out estimates of future [ NO3−]FWM and fNO3 (lower peak, higher minimum) as legacy nitrate is flushed from the aquifer. Major fundamental questions about nonpoint-source aquifer contamination can be answered without a complex numerical model or long-term monitoring program.}, number={11}, journal={WATER RESOURCES RESEARCH}, author={Gilmore, Troy E. and Genereux, David P. and Solomon, D. Kip and Farrell, Kathleen M. and Mitasova, Helena}, year={2016}, month={Nov}, pages={9046–9065} }
 @article{gilmore_genereux_solomon_solder_kimball_mitasova_birgand_2016, title={Quantifying the fate of agricultural nitrogen in an unconfined aquifer: Stream-based observations at three measurement scales}, volume={52}, ISSN={0043-1397}, url={http://dx.doi.org/10.1002/2015WR017599}, DOI={10.1002/2015wr017599}, abstractNote={We compared three stream-based sampling methods to study the fate of nitrate in groundwater in a coastal plain watershed: point measurements beneath the streambed, seepage blankets (novel seepage-meter design), and reach mass-balance. The methods gave similar mean groundwater seepage rates into the stream (0.3–0.6 m/d) during two 3–4 day field campaigns despite an order of magnitude difference in stream discharge between the campaigns. At low flow, estimates of flow-weighted mean nitrate concentrations in groundwater discharge ([ NO3−]FWM) and nitrate flux from groundwater to the stream decreased with increasing degree of channel influence and measurement scale, i.e., [ NO3−]FWM was 654, 561, and 451 µM for point, blanket, and reach mass-balance sampling, respectively. At high flow the trend was reversed, likely because reach mass-balance captured inputs from shallow transient high-nitrate flow paths while point and blanket measurements did not. Point sampling may be better suited to estimating aquifer discharge of nitrate, while reach mass-balance reflects full nitrate inputs into the channel (which at high flow may be more than aquifer discharge due to transient flow paths, and at low flow may be less than aquifer discharge due to channel-based nitrate removal). Modeling dissolved N2 from streambed samples suggested (1) about half of groundwater nitrate was denitrified prior to discharge from the aquifer, and (2) both extent of denitrification and initial nitrate concentration in groundwater (700–1300 µM) were related to land use, suggesting these forms of streambed sampling for groundwater can reveal watershed spatial relations relevant to nitrate contamination and fate in the aquifer.}, number={3}, journal={Water Resources Research}, publisher={American Geophysical Union (AGU)}, author={Gilmore, Troy E. and Genereux, David P. and Solomon, D. Kip and Solder, John E. and Kimball, Briant A. and Mitasova, Helena and Birgand, François}, year={2016}, month={Mar}, pages={1961–1983} }
 @article{solomon_gilmore_solder_kimball_genereux_2015, title={Evaluating an unconfined aquifer by analysis of age-dating tracers in stream water}, volume={51}, ISSN={["1944-7973"]}, DOI={10.1002/2015wr017602}, abstractNote={The mean transit time (MTT) is a fundamental property of a groundwater flow system that is strongly related to the ratio of recharge rate to storage volume. However, obtaining samples for estimating the MTT using environmental tracers is problematic as flow-weighted samples over the full spectrum of transit times are needed. Samples collected from the base flow of a gaining stream in the North Carolina Coastal Plain (West Bear Creek) that were corrected for exchange with the atmosphere yielded environmental tracer concentrations (SF6 and CFC-11) very similar to flow-weighted values from nine or ten streambed piezometers that directly sampled groundwater during low streamflow. At higher streamflow on the falling limb of the hydrograph, stream tracer concentrations (after correction for gas exchange) were significantly higher than the flow-weighted mean from piezometers, consistent with dominance of the stream tracer signal by transient influx of surface water and/or younger subsurface water. The apparent MTT derived from SF6 in low flow stream water samples was 26 years, suggesting a groundwater recharge rate of about 210 mm/yr, that is consistent with vertical profiles obtained by sampling nested piezometers in the aquifer. When sampled under low flow conditions when streamflow consists of a high component of groundwater discharge, West Bear Creek appears to act as a flow-weighted integrator of transit times and, streamflow samples can provide fundamental information regarding groundwater recharge rate and MTT. Our study suggests that watershed-scale evaluation of some groundwater flow systems is possible without utilizing monitoring wells.}, number={11}, journal={WATER RESOURCES RESEARCH}, author={Solomon, D. K. and Gilmore, T. E. and Solder, J. E. and Kimball, B. and Genereux, D. P.}, year={2015}, month={Nov}, pages={8883–8899} }
 @article{ganong_small_ardón_mcdowell_genereux_duff_pringle_2015, title={Interbasin flow of geothermally modified ground water stabilizes stream exports of biologically important solutes against variation in precipitation}, volume={34}, ISSN={2161-9549 2161-9565}, url={http://dx.doi.org/10.1086/679739}, DOI={10.1086/679739}, abstractNote={AbstractGeothermally modified ground water (GMG) in tectonically active areas can be an important source of stream nutrients, and the relative importance of GMG inflows is likely to change with shifts in precipitation that are predicted to occur in response to climate change. However, few studies have quantified the influence of GMG inflows on export of biologically important solutes from watersheds across years differing in precipitation. We quantified N, soluble reactive P (SRP), and dissolved organic C (DOC) export during a year with high precipitation (6550 mm rain) and a year with average precipitation (4033 mm rain) in 2 gauged tropical streams at La Selva Biological Station in lowland Costa Rica. One stream receives extensive inputs of regional GMG, whereas the other is fed entirely by local runoff. In the stream fed only by local runoff, a 62% increase in precipitation from the dry year to the wet year led to a 68% increase in stream discharge, a 67% increase in export of SRP, DOC, dissolved organ...}, number={1}, journal={Freshwater Science}, publisher={University of Chicago Press}, author={Ganong, Carissa N. and Small, Gaston E. and Ardón, Marcelo and McDowell, William H. and Genereux, David P. and Duff, John H. and Pringle, Catherine M.}, year={2015}, month={Mar}, pages={276–286} }
 @article{oviedo‐vargas_genereux_dierick_oberbauer_2015, title={The effect of regional groundwater on carbon dioxide and methane emissions from a lowland rainforest stream in Costa Rica}, volume={120}, ISSN={2169-8953 2169-8961}, url={http://dx.doi.org/10.1002/2015JG003009}, DOI={10.1002/2015JG003009}, abstractNote={In the tropical rainforest at La Selva Biological Station in Costa Rica, regional bedrock groundwater high in dissolved carbon discharges into some streams and wetlands, with the potential for multiple cascading effects on ecosystem carbon pools and fluxes. We investigated carbon dioxide (CO2) and methane (CH4) degassing from two streams at La Selva: the Arboleda, where approximately one third of the streamflow is from regional groundwater, and the Taconazo, fed exclusively by local groundwater recharged within the catchment. The regional groundwater inflow to the Arboleda had no measurable effect on stream gas exchange velocity, dissolved CH4 concentration, or CH4 emissions but significantly increased stream CO2 concentration and degassing. CO2 evasion from the reach of the Arboleda receiving regional groundwater (lower Arboleda) averaged 5.5 mol C m−2 d−1, ~7.5 times higher than the average (0.7 mol C m−2 d−1) from the stream reaches with no regional groundwater inflow (the Taconazo and upper Arboleda). Carbon emissions from both streams were dominated by CO2; CH4 accounted for only 0.06–1.70% of the total (average of both streams: 5 × 10−3 mol C m−2 d−1). Annual stream degassing fluxes normalized by watershed area were 48 and 299 g C m−2 for the Taconazo and Arboleda, respectively. CO2 degassing from the Arboleda is a significant carbon flux, similar in magnitude to the average net ecosystem exchange estimated by eddy covariance. Examining the effects of catchment connections to underlying hydrogeological systems can help avoid overestimation of ecosystem respiration and advance our understanding of carbon source/sink status and overall terrestrial ecosystem carbon budgets.}, number={12}, journal={Journal of Geophysical Research: Biogeosciences}, publisher={American Geophysical Union (AGU)}, author={Oviedo‐Vargas, Diana and Genereux, David P. and Dierick, Diego and Oberbauer, Steven F.}, year={2015}, month={Dec}, pages={2579–2595} }
 @article{zanon_genereux_oberbauer_2014, title={Use of a watershed hydrologic model to estimate interbasin groundwater flow in a Costa Rican rainforest}, volume={28}, ISSN={["1099-1085"]}, DOI={10.1002/hyp.9917}, abstractNote={The watershed hydrologic model TOPMODEL was used to estimate interbasin groundwater flow (IGF) into a small lowland rainforest watershed in Costa Rica. IGF is a common hydrological process but often difficult to quantify. Four-year simulations (2006–2009) using three different model approaches gave estimates of IGF that were very similar to each other (10.1, 10.2, and 9.8 m/year) and to an earlier estimate (10.0 m/year) based on 1998–2002 data from a budget study that did not use a hydrologic simulation model, providing confidence in the new estimates and suggesting each of the three model approaches is viable. Results show no significant temporal variation in IGF during 2006–2009 (or between this period and the earlier study from 1998–2002). Simulations of the 16 consecutive 3-month periods in 2006–2009 gave 16 values of IGF rate with a mean (10.1 m/year, standard deviation = 0.6 m/year) very similar to the estimates above from the 4-year simulations. This suggests the modified version of TOPMODEL can be used to model stream discharge and estimate IGF for sub-annual time periods during which change in water storage is not necessarily equal to zero. Thus, simple watershed models may be used to estimate IGF based on even relatively short calibration periods, making such models useful tools in the study of this widespread hydrological process that affects water and chemical fluxes and budgets but is often difficult and costly to quantify. Copyright © 2013 John Wiley & Sons, Ltd.}, number={10}, journal={HYDROLOGICAL PROCESSES}, author={Zanon, Carlo and Genereux, David P. and Oberbauer, Steven F.}, year={2014}, month={May}, pages={3670–3680} }
 @article{genereux_nagy_osburn_oberbauer_2013, title={A connection to deep groundwater alters ecosystem carbon fluxes and budgets: Example from a Costa Rican rainforest}, volume={40}, ISSN={0094-8276}, url={http://dx.doi.org/10.1002/grl.50423}, DOI={10.1002/grl.50423}, abstractNote={[1] Field studies of watershed carbon fluxes and budgets are critical for understanding the carbon cycle, but the role of deep regional groundwater is poorly known and field examples are lacking. Here we show that discharge of regional groundwater into a lowland Costa Rican rainforest has a major influence on ecosystem carbon fluxes. This influence is observable through chemical, isotopic, and flux signals in groundwater, surface water, and air. Not addressing the influence of regional groundwater in the field measurement program and data analysis would give a misleading impression of the overall carbon source or sink status of the rainforest. In quantifying a carbon budget with the traditional “small watershed” mass balance approach, it would be critical at this site and likely many others to consider watershed inputs or losses associated with exchange between the ecosystem and the deeper hydrogeological system on which it sits.}, number={10}, journal={Geophysical Research Letters}, publisher={American Geophysical Union (AGU)}, author={Genereux, David P. and Nagy, Laura A. and Osburn, Christopher L. and Oberbauer, Steven F.}, year={2013}, month={May}, pages={2066–2070} }
 @article{kennedy_murdoch_genereux_corbett_stone_pham_mitasova_2010, title={Comparison of Darcian flux calculations and seepage meter measurements in a sandy streambed in North Carolina, United States}, volume={46}, ISSN={["0043-1397"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77956498672&partnerID=MN8TOARS}, DOI={10.1029/2009wr008342}, abstractNote={[1] We compared two methods for estimating groundwater flux into a stream reach: seepage meters and Darcian flux calculations. Both methods were applied at the same 53 points on the streambed of a 62.5-m-long reach of West Bear Creek in the coastal plain of North Carolina. At each point, a seepage meter was used to measure groundwater flux, vmeter, and several minutes later the streambed hydraulic conductivity (K) and hydraulic head gradient (J) were measured. We compared the 53 paired point values of groundwater flux from each method (vmeter and vdarcy = KJ), the integrated volumetric groundwater flux to the stream reach from each method (Qdarcy and Qmeter), and the spatial distributions of vdarcy and vmeter on the streambed. Values of Qmeter (268 m3/d) and mean vmeter (0.66 m/d) were each about 0.70 × the corresponding Darcian flux quantities (Qdarcy = 375 m3/d and mean vdarcy = 0.92 m/d). Despite their differences, the two methods gave the same direction of groundwater flow (into the stream) at all 53 points, a result not found in all previous comparison studies and thus not to be taken for granted. Also, vdarcy and vmeter had similar spatial distributions on the streambed. The ratio vmeter/vdarcy = 0.70 is within the range of 0.3–7 from previous studies and is closer to 1 than in previous studies. The differences between the two methods are probably in part due to random measurement error and to the spatial scales for the Darcy and seepage meter measurements being of a slightly different size and offset several centimeters from each other on the heterogeneous streambed, but these effects are unlikely to produce the observed consistent bias. The mean bias between the methods (ratio of 0.70) may be related to gas bubbles in the streambed pore spaces (e.g., collection of gas bubbles in the seepage meters lowering vmeter and loss of gas from the streambed upon seepage meter removal or permeameter insertion increasing the subsequent vdarcy measurement).}, number={9}, journal={WATER RESOURCES RESEARCH}, author={Kennedy, Casey D. and Murdoch, Lawrence C. and Genereux, David P. and Corbett, D. Reide and Stone, Katie and Pham, Phung and Mitasova, Helena}, year={2010}, month={Sep} }
 @article{solomon_genereux_plummer_busenberg_2010, title={Testing mixing models of old and young groundwater in a tropical lowland rain forest with environmental tracers}, volume={46}, ISSN={["0043-1397"]}, DOI={10.1029/2009wr008341}, abstractNote={[1] We tested three models of mixing between old interbasin groundwater flow (IGF) and young, locally derived groundwater in a lowland rain forest in Costa Rica using a large suite of environmental tracers. We focus on the young fraction of water using the transient tracers CFC-11, CFC-12, CFC-113, SF6, 3H, and bomb 14C. We measured 3He, but 3H/3He dating is generally problematic due to the presence of mantle 3He. Because of their unique concentration histories in the atmosphere, combinations of transient tracers are sensitive not only to subsurface travel times but also to mixing between waters having different travel times. Samples fall into three distinct categories: (1) young waters that plot along a piston flow line, (2) old samples that have near-zero concentrations of the transient tracers, and (3) mixtures of 1 and 2. We have modeled the concentrations of the transient tracers using (1) a binary mixing model (BMM) of old and young water with the young fraction transported via piston flow, (2) an exponential mixing model (EMM) with a distribution of groundwater travel times characterized by a mean value, and (3) an exponential mixing model for the young fraction followed by binary mixing with an old fraction (EMM/BMM). In spite of the mathematical differences in the mixing models, they all lead to a similar conceptual model of young (0 to 10 year) groundwater that is locally derived mixing with old (>1000 years) groundwater that is recharged beyond the surface water boundary of the system.}, journal={WATER RESOURCES RESEARCH}, author={Solomon, D. Kip and Genereux, David P. and Plummer, L. Niel and Busenberg, Eurybiades}, year={2010}, month={Apr} }
 @article{genereux_webb_solomon_2009, title={Chemical and isotopic signature of old groundwater and magmatic solutes in a Costa Rican rain forest: Evidence from carbon, helium, and chlorine}, volume={45}, ISSN={["1944-7973"]}, DOI={10.1029/2008wr007630}, abstractNote={[1] C, He, and Cl concentrations and isotopes in groundwater and surface water in a lowland Costa Rican rain forest are consistent with the mixing of two distinct groundwaters: (1) high-solute bedrock groundwater representing interbasin groundwater flow (IGF) into the rain forest and (2) low-solute local groundwater recharged in the lowlands. In bedrock groundwater, high δ13C (−4.89‰), low 14C (7.98 pM), high R/RA for He (6.88), and low 36Cl/Cl (17 × 10−15) suggest that elevated tracer concentrations are derived from magmatic outgassing and/or weathering of volcanic rock beneath nearby Volcan Barva. In local groundwater, the magmatic signature is absent, and data suggest atmospheric sources for He and Cl and a biogenic soil gas CO2 source for dissolved inorganic carbon. Dating of 14C suggests that the age of bedrock groundwater is 2400–4000 years (most likely at the lower end of the range). Local groundwater has 14C > 100 pM, indicating the presence of “bomb carbon” and thus ages less than ∼55 years. Overall, data are consistent with a conceptual hydrologic model originally proposed on the basis of water budget and major ion data: (1) large variation in solute concentrations can be explained by mixing of the two distinct groundwaters, (2) bedrock groundwater is much older than local groundwater, (3) elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and/or rock, and (4) local groundwater has not interacted with volcanic rock. Tracers with different capabilities converge on the same hydrologic interpretation. Also, transport of magmatic CO2 into the lowland rain forest via IGF seems to be significant relative to other large ecosystem-level carbon fluxes.}, journal={WATER RESOURCES RESEARCH}, author={Genereux, David P. and Webb, Mathew and Solomon, D. Kip}, year={2009}, month={Aug} }
 @article{kennedy_genereux_corbett_mitasova_2009, title={Relationships among groundwater age, denitrification, and the coupled groundwater and nitrogen fluxes through a streambed}, volume={45}, ISSN={["1944-7973"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72149099351&partnerID=MN8TOARS}, DOI={10.1029/2008wr007400}, abstractNote={[1] The relationships among coupled groundwater and nitrogen (N) fluxes, groundwater age, and denitrification were examined for a section of West Bear Creek, an agricultural stream in the coastal plain of North Carolina, United States. Simultaneous streambed measurements of hydraulic conductivity (K) and hydraulic head gradient (J) and the concentrations of NO3− ([NO3−]), dissolved gases, and chlorofluorocarbons in groundwater were interpolated, mapped, and (for water flux v = KJ and nitrate flux fNO3 = v[NO3−]) integrated over the streambed area. Nitrate and dissolved organic N accounted for 92 and 8% of N flux through the streambed, respectively. Streambed maps show a band of greater groundwater age, and lower [NO3−] and fNO3, running through the center of most of the study reach. Nitrate flux (fNO3) exhibits this “center-low” pattern even though one of its controlling factors, groundwater flux (v), has on average the opposite “center-high” pattern. An inverse relationship between [NO3−] and age is indicative of fertilizer as the primary source of groundwater NO3−. Denitrification reduced mean fNO3 by ∼50%, from 370 mmol m−2 d−1 (what it would have been in the absence of denitrification) to 173 mmol m−2 d−1 (what it actually was). Measurement of both groundwater age and v made possible a new method for estimating flow-weighted mean groundwater age (τFWM), an important aquifer hydraulic characteristic related to groundwater storage and recharge rate. This method gives τFWM = 30 years, which, along with the overall distribution of groundwater ages, suggests the possibility of a significant time lag between changes in N fertilizer application rates and NO3− flux from groundwater to West Bear Creek. Differences in streambed groundwater chemistry between the left and right sides of the streambed suggest differences in agricultural practices on opposite sides of the stream.}, number={9}, journal={WATER RESOURCES RESEARCH}, author={Kennedy, Casey D. and Genereux, David P. and Corbett, D. Reide and Mitasova, Helena}, year={2009}, month={Sep} }
 @article{kennedy_genereux_corbett_mitasova_2009, title={Spatial and temporal dynamics of coupled groundwater and nitrogen fluxes through a streambed in an agricultural watershed}, volume={45}, ISSN={["0043-1397"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-72149089873&partnerID=MN8TOARS}, DOI={10.1029/2008wr007397}, abstractNote={[1] This paper presents results on the spatiotemporal dynamics of the coupled water flux (v) and nitrogen fluxes (fN = v[N], where [N] is the concentration of a dissolved N species) through a streambed in an agricultural watershed in North Carolina. Physical and chemical variables were measured at numerous points in the streambed of a 0.26-km reach: hydraulic conductivity (K) and head gradient (J) and the concentrations of NO3− and other N species in streambed groundwater, from which water flux (v = KJ) and N fluxes (e.g., fNO3 = v[NO3−]) through the streambed were computed, mapped, and integrated in space. The result was a novel set of streambed maps of the linked variables (K, J, v, and N concentrations and fluxes), showing their spatial variability and how it changed over a year (on the basis of seven bimonthly sets of maps). Mean fNO3 during the study year was 154 mmol m−2 d−1; this NO3− flux, together with that of dissolved organic nitrogen (fDON = 17 mmol m−2 d−1), accounted for >99% of the total dissolved N flux through the streambed. Repeat measurements at the same locations on the streambed show significant temporal variability in fNO3, controlled largely by changes in v rather than changes in [NO3−]. One of the clearest and most persistent aspects of spatial variability was lateral variability across the channel from bank to bank. K and v values were greater in the center of the channel; this distribution of K (ultimately a reflection of sediment dynamics in the channel) apparently focuses groundwater discharge toward the center of the channel. The opposite pattern (low values in the center) was found for J, [NO3−], and (to a lesser extent) fNO3. Overall, fNO3 was characterized by localized zones of high and low values that changed in size and shape over time but remained in basically the same locations (the same was true of K, J, and [NO3−], though less so for v), with 70% of NO3− flux occurring through about 38% of the streambed area. Lateral distributions of the physical hydrologic attributes (K, J, and v) were highly symmetrical across the channel, while those of [NO3−] and fNO3 showed higher values on the left than on the right, likely a reflection of different N use on opposite sides of the stream. The streambed-based approach taken here offers insights concerning the spatial and temporal dynamics of linked water and N fluxes through a streambed and their controls.}, number={9}, journal={WATER RESOURCES RESEARCH}, author={Kennedy, Casey D. and Genereux, David P. and Corbett, D. Reide and Mitasova, Helena}, year={2009}, month={Sep} }
 @article{kennedy_genereux_mitasova_corbett_leahy_2008, title={Effect of sampling density and design on estimation of streambed attributes}, volume={355}, ISSN={["1879-2707"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-43949128733&partnerID=MN8TOARS}, DOI={10.1016/j.jhydrol.2008.03.018}, abstractNote={Summary Underlying questions that are central to field studies of the groundwater–surface water interaction are the extent of error in means and spatial distributions of streambed attributes such as groundwater seepage rate or solute flux, and the relation of this error to the number and location of point measurements. To investigate these questions, spatially intensive point measurements of five streambed attributes were made in two 63-m long stream reaches in the North Carolina Coastal Plain: hydraulic conductivity ( K ), hydraulic head gradient between groundwater and stream water ( J ), nitrate concentration in streambed groundwater ( C ), and groundwater seepage ( v  =  KJ ) and nitrate flux ( f  =  vC ) through the streambed. In all, 10 datasets (2 reaches, 5 attributes), each with 54 closely-spaced point values, were created (540-point values in all). For each dataset, subsets of 8- to 40-point values were selected from the 54 available to evaluate the effects of sampling density (the number of point values per reach, or per m 2 of streambed) and sampling design (the relative number of point values from the right side, left side, and center of the channel) on the mean and the spatial field of the streambed attribute. Specifically, we evaluated the following as a function of sampling density and sampling design: (1) the likelihood of error in the reach-average value of each streambed attribute, (2) the average magnitude of error and distribution of error in the reach-average value of each attribute, (3) the magnitude of error in the prediction of point values of each attribute, and (4) the geometry of interpolated surfaces of two attributes ( K and f ). In all cases, “error” in a value or interpolated surface based on a subset of points was taken as a deviation from the corresponding result based on the full dataset of 54 points. The probability ( p ) that error did not occur increased with sampling density for each sampling design and attribute in both reaches, though the effect of “diminishing returns” was evident for sampling densities greater than ∼24 points per reach (roughly 0.05–0.06 points per m 2 of streambed). Relative to sampling density, sampling design had little effect on values of p . Average error in streambed attributes was generally small (⩽10%) and less than the 95% confidence limits about the reach-average values of the attributes. The ability to estimate unknown point values by interpolation among other point values was poor using both 12- and 36-point subsets, though results suggest the 24 additional known point values (in going from 12 to 36) were helpful in one case in which there was some degree of autocorrelation between the additional known values and the values to be predicted in the interpolation. Visual inspection of 130 contour maps showed that those based on 36-point values were far more realistic in appearance than those based on 12-point values (where the standard for “realistic” appearance was the contour maps based on the full datasets of 54-point values).}, number={1-4}, journal={JOURNAL OF HYDROLOGY}, author={Kennedy, Casey D. and Genereux, David P. and Mitasova, Helena and Corbett, D. Reide and Leahy, Scott}, year={2008}, month={Jun}, pages={164–180} }
 @article{genereux_leahy_mitasova_kennedy_corbett_2008, title={Spatial and temporal variability of streambed hydraulic conductivity in West Bear Creek, North Carolina, USA}, volume={358}, ISSN={["1879-2707"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-48849088675&partnerID=MN8TOARS}, DOI={10.1016/j.jhydrol.2008.06.017}, abstractNote={Summary The hydraulic conductivity ( K ) of the streambed is an important variable influencing water and solute exchange between streams and surrounding groundwater systems. However, there are few detailed data on spatial variability in streambed K and almost none on temporal variability. The spatial and temporal variability of streambed K in a North Carolina stream were investigated with 487 field measurements of K over a 1-year period. Measurements were made bimonthly from December 2005 to December 2006 at 46 measurement locations in a 262.5 m reach (the “large reach”). To give a more detailed picture of spatial variability, closely-spaced one-time measurements were made in two 62.5 m reaches (the “small reaches”, one investigated in July 2006 and the other in August 2006) that were part of the large reach. Arithmetic mean K for the large reach was ∼16 m/day (range was 0.01 to 66 m/day). Neither K nor ln K was normally distributed, and K distributions appeared somewhat bimodal. There was significant spatial variability over horizontal length scales of a few m. Perhaps the clearest feature within this variability was the generally higher K in the center of the channel. This feature may be an important control on water and chemical fluxes through the streambed (e.g., other measurements show generally higher water seepage velocity, but lower porewater nitrate concentration, in the center of the streambed). Grain size analysis of streambed cores showed that layers of elevated fines (silt + clay) content were less common in the center of the channel (overall, the streambed was about 94% sand). Results also suggest a modest but discernable difference in average streambed K upstream and downstream of a small beaver dam: K was about 23% lower upstream, when the dam was present during the first few months of the study. This upstream/downstream difference in K disappeared after the dam collapsed, perhaps in response to re-mobilization of fine sediments or leaf matter that had accumulated in quiet waters ponded on the upstream side of the dam. Temporal variability was significant and followed a variety of different patterns at the 46 measurement locations in the large reach. Temperature data show that variation in streambed and groundwater temperature was not an important cause of the observed temporal variability in K . Measurements of changes in the elevation of the streambed surface suggest erosion and deposition played an important role in causing the observed temporal variability in streambed K (of which the change described above following collapse of the beaver dam was a special case), though other potentially time-varying factors (e.g., gas content, bioturbation, or biofilms in the streambed) were not explicitly addressed and cannot be ruled out as contributors to the temporal variability in streambed K . Temporal variability in streambed K merits additional study as a potentially important control on temporal variability in the magnitudes and spatial patterns of water and solute fluxes between groundwater and surface water. From the data available it seems appropriate to view streambed K as a dynamic attribute, variable in both space and time.}, number={3-4}, journal={JOURNAL OF HYDROLOGY}, author={Genereux, David P. and Leahy, Scott and Mitasova, Helena and Kennedy, Casey D. and Corbett, D. Reide}, year={2008}, month={Sep}, pages={332–353} }
 @article{kennedy_genereux_2007, title={C-14 groundwater age and the importance of chemical fluxes across aquifer boundaries in confined cretaceous aquifers of North Carolina, USA}, volume={49}, ISSN={["1945-5755"]}, DOI={10.1017/s0033822200043101}, abstractNote={Radiocarbon activity, He concentrations, and other geochemical parameters were measured in groundwater from the confined Black Creek (BC) and Upper Cape Fear (UCF) aquifers in the Coastal Plain of North Carolina. 14 C ages adjusted for geochemical and diffusion effects ranged from 400 to 21,900 BP in the BC, and 13,400 to 26,000 BP in the underlying UCF; ages increased coastward in both aquifers. Long-term average linear groundwater velocity is about 2.5 m/yr for the BC, and somewhat larger for the UCF. Aquifer-aquitard exchange is an important influence on the DIC concentration, 14 C activity, and estimated age of aquifer groundwater. Accounting for this exchange in 14 C age calculations places the groundwater samples with the lowest estimated recharge temperatures nearest in time to the last glacial maximum. Traditional geochemical correction models that do not account for aquifer-aquitard exchange significantly overestimate groundwater age. He concentration in groundwater varies with both age and stratigraphic position. Dissolved He data provide strong evidence of upward vertical He transport through the study aquifers; data from the UCF are broadly consistent with the pattern expected for a confined aquifer receiving a concentrated, localized He flux from below (based on a previously published model for this situation), in this case most likely from crystalline bedrock. He has potential as an indicator of groundwater age in the study aquifers, if interpreted within an appropriate analytical framework that includes the observed strong vertical transport. δ 18 O in the oldest groundwater is enriched (relative to modern groundwater) by 1 to 1.2‰, the opposite of the δ 18 O depletion found in many old groundwaters but consistent with the enrichment found in groundwater in this age range in Georgia and Florida.}, number={3}, journal={RADIOCARBON}, author={Kennedy, Casey D. and Genereux, David P.}, year={2007}, pages={1181–1203} }
 @article{kennedy_genereux_corbett_mitasova_2007, title={Design of a light-oil piezomanometer for measurement of hydraulic head differences and collection of groundwater samples}, volume={43}, ISSN={["1944-7973"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-35848960791&partnerID=MN8TOARS}, DOI={10.1029/2007wr005904}, abstractNote={[1] This paper describes a device (“piezomanometer”) that combines three components (an oil-water manometer, a pushable screened PVC probe, and a system for groundwater sample collection) into a single inexpensive ($130), easily built, reliable tool for rapid collection of shallow groundwater from a streambed or lake bed and accurate measurement of even very small head differences between this groundwater and overlying surface water. The piezomanometer has been tested with excellent results both in the lab and in a stream shallow enough for wading; in principle, it could be adapted for use in deeper water where work is done from a dock, boat, or other platform. The problem of gas bubbles collecting in the groundwater line (a common drawback of field manometers) was nearly eliminated by use of a three-way valve at a local elevation maximum in the groundwater line (gas bubbles in the groundwater line can be purged through this valve). Field application is illustrated here with data from a 2-day study using four piezomanometers in a North Carolina stream.}, number={9}, journal={WATER RESOURCES RESEARCH}, author={Kennedy, Casey D. and Genereux, David P. and Corbett, D. Reide and Mitasova, Helena}, year={2007}, month={Sep} }
 @article{genereux_jordan_2006, title={Interbasin groundwater flow and groundwater interaction with surface water in a lowland rainforest, Costa Rica: A review}, volume={320}, ISSN={["1879-2707"]}, DOI={10.1016/j.jhydrol.2005.07.023}, abstractNote={Abstract This paper reviews work related to interbasin groundwater flow (naturally occurring groundwater flow beneath watershed topographic divides) into lowland rainforest watersheds at La Selva Biological Station in Costa Rica. Chemical mixing calculations (based on dissolved chloride) have shown that up to half the water in some streams and up to 84% of the water in some riparian seeps and wells is due to high-solute interbasin groundwater flow (IGF). The contribution is even greater for major ions; IGF accounts for well over 90% of the major ions at these sites. Proportions are highly variable both among watersheds and with elevation within the same watershed (there is greater influence of IGF at lower elevations). The large proportion of IGF found in water in some riparian wetlands suggests that IGF is largely responsible for maintaining these wetlands. δ 18 O data support the conclusions from the major ion data. Annual water and major ion budgets for two adjacent watersheds, one affected by IGF and the other not, showed that IGF accounted for two-thirds of the water input and 92–99% of the major ion input (depending on the major ion in question) to the former watershed. The large (in some cases, dominating) influence of IGF on watershed surface water quantity and quality has important implications for stream ecology and watershed management in this lowland rainforest. Because of its high phosphorus content, IGF increases a variety of ecological variables (algal growth rates, leaf decay rate, fungal biomass, invertebrate biomass, microbial respiration rates on leaves) in streams at La Selva. The significant rates of IGF at La Selva also suggest the importance of regional (as opposed to small-scale local) water resource planning that links lowland watersheds with regional groundwater. IGF is a relatively unexplored and potentially critical factor in the conservation of lowland rainforest.}, number={3-4}, journal={JOURNAL OF HYDROLOGY}, author={Genereux, DP and Jordan, M}, year={2006}, month={Apr}, pages={385–399} }
 @article{genereux_jordan_carbonell_2005, title={A paired-watershed budget study to quantify interbasin groundwater flow in a lowland rain forest, Costa Rica}, volume={41}, ISSN={["0043-1397"]}, DOI={10.1029/2004wr003635}, abstractNote={[1] A paired-watershed budget study was used to quantify the annual water and major ion (sodium, potassium, magnesium, calcium, chloride, and sulfate) budgets of two adjacent lowland rain forest watersheds in Costa Rica. Interbasin groundwater flow (IGF) accounted for about two thirds of the water input and about 97% of the solute input (an average over the six major ions) to one watershed but little or none of the inputs to the adjacent watershed in which IGF was at most marginally distinguishable from zero. Results underscore the significance of IGF as a potential control on the hydrology and water quality of lowland watersheds, the spatial complexity of its occurrence in lowlands (where its influence may range from dominating to negligible on adjacent watersheds), and the importance of accounting for IGF in the design and execution of watershed studies and in water management.}, number={4}, journal={WATER RESOURCES RESEARCH}, author={Genereux, DP and Jordan, MT and Carbonell, D}, year={2005}, month={Apr} }
 @article{genereux_2004, title={Comparison of naturally-occurring chloride and oxygen-18 as tracers of interbasin groundwater transfer in lowland rainforest, Costa Rica}, volume={295}, DOI={10.1016/j.jhyfrol.2004.02.020}, number={04-Jan}, journal={Journal of Hydrology}, author={Genereux, D.}, year={2004}, pages={17–27} }
 @article{genereux_2004, title={Comparison of naturally-occurring chloride and oxygen-18 as tracers of interbasin groundwater transfer in lowland rainforest, Costa Rica}, volume={295}, ISSN={0022-1694}, url={http://dx.doi.org/10.1016/j.jhydrol.2004.02.020}, DOI={10.1016/j.jhydrol.2004.02.020}, abstractNote={Abstract δ 18 O data were used to test a two-end-member hydrologic mixing model previously published for an area of lowland rainforest in Costa Rica. The model distinguishes interbasin groundwater transfer from locally-recharged groundwater. The model was originally based on data for chloride (Cl) and other major ions and is fully consistent with new Cl data presented here. The mixing model was used to generate five predictions concerning δ 18 O at 13 groundwater and surface water sampling sites, on the premise that the model would be supported if δ 18 O data agreed with the predictions. Overall, the δ 18 O data are consistent with the predictions, giving reasonably clear support for 3 of the 5, and neither clearly supporting nor ruling out the other 2. The large intra-site temporal variability in δ 18 O precludes conclusive confirmation of the latter two predictions. This variability also affects the results of mixing calculations to quantify the proportions of each end member in water samples representing mixtures of the end members. Mixing calculations based on δ 18 O give different results and much higher uncertainties than those based on Cl. For δ 18 O data, intra-site variability is large relative to the difference between the two end member waters, leading to large uncertainty in δ 18 O-based mixing calculations. In this case, Cl appears to be the superior tracer for interbasin groundwater transfer, mainly because intra-site variability in Cl is small relative to the large Cl difference between end members.}, number={1-4}, journal={Journal of Hydrology}, publisher={Elsevier BV}, author={Genereux, David}, year={2004}, month={Aug}, pages={17–27} }
 @article{saiers_genereux_bolster_2004, title={Influence of calibration methodology on ground water flow predictions}, volume={42}, ISSN={["0017-467X"]}, DOI={10.1111/j.1745-6584.2004.tb02448.x}, abstractNote={We constructed a numerical model of transient ground water flow and solute transport for a portion of the Biscayne Aquifer in Florida, and calibrated the model with three different combinations of data from a 193-day period: head (h) data alone, data on h and ground water discharge to a canal (q), and data on h, q, and ground water chloride concentration (C). We used each of the three calibrated models to predict h and q during a 182-day test period separate from the calibration period. All three calibrated models predicted h equally well during the test period (r= 0.95, where r= 1 indicates perfect agreement between measured and simulated values), though the model calibrated on h alone had significantly different parameter values than the other two models. Predictions of q during the test period depended on calibration methodology; models calibrated with multiple targets simulated q more accurately than the model calibrated on h alone (r = 0.79 compared to r = 0.49). Based on the results of these simulations, we conclude: (1) Post-calibration prediction is important in assessing the value of different data types in automated calibration; (2) inverse-solution uniqueness is not a requirement for accurate h predictions; (3) relatively simple models can predict with reasonable accuracy transient ground water flow in a complex aquifer, and parameters governing this prediction can be estimated by nonlinear regression methods that incorporate both h and q data; (4) addition of C data to the calibration did not improve model predictive capacity because the information in the C data was similar to that in the q data, from the perspective of model calibration (the subsurface chemical signal in question was controlled mainly by seepage of high-chloride canal water into the low-chloride ground water system).}, number={1}, journal={GROUND WATER}, author={Saiers, JE and Genereux, DP and Bolster, CH}, year={2004}, pages={32–44} }
 @article{genereux_2003, title={Comparison of methods for estimation of 50-year peak discharge from a small, rural watershed in North Carolina}, volume={44}, ISSN={["0943-0105"]}, DOI={10.1007/s00254-002-0734-5}, number={1}, journal={ENVIRONMENTAL GEOLOGY}, author={Genereux, DP}, year={2003}, month={May}, pages={53–58} }
 @article{genereux_wood_pringle_2002, title={Chemical tracing of interbasin groundwater transfer in the lowland rainforest of Costa Rica}, volume={258}, ISSN={["1879-2707"]}, DOI={10.1016/S0022-1694(01)00568-6}, abstractNote={Chemical data from several hundred surface water and groundwater samples collected mainly during baseflow over 4.5 years were used to detect and quantify the natural interbasin transfer of deep groundwater into watersheds at La Selva Biological Station, a research site in the lowland rainforest of Costa Rica. Most of the variability in major ion concentrations at La Selva can be explained by mixing of two chemically and hydrologically distinct waters: high-solute bedrock groundwater, and low-solute local water draining from hillslope soils within the study watersheds. Several lines of evidence indicate that high-solute bedrock groundwater represents subsurface interbasin transfer into the study site. The fraction of water due to interbasin transfer (fwater) ranged from zero to about 0.49 for major streams at La Selva; fwater values were even higher (up to 0.84) for small riparian seeps and shallow groundwater near the Salto stream. The relative contribution of major ions by interbasin transfer was even more significant than of water itself. fwater values of 0.49 and 0.84 correspond to fCl values of 0.92 and 0.99, respectively (fCl, the fraction of dissolved chloride in a water sample that is due to interbasin transfer, is approximately equal to the fraction of all major ions contributed to the sample by interbasin transfer, given the observed linear correlation between Cl and other major ions). fwater and fCl of streams and riparian seeps varied on both long (monthly/seasonal) and short (storm event) time scales, in each case decreasing as conditions at La Selva became wetter. The high fwater values found in riparian groundwater and seeps indicate that local water and bedrock groundwater derived from interbasin transfer mix in the shallow subsurface at La Selva, not just in stream channels. With fwater values up to 0.84, it appears that some areas of riparian wetland may be maintained largely by interbasin transfer. This large interbasin transfer significantly affects both terrestrial (e.g. wetland) and aquatic ecosystems. Results suggest the importance of a regional approach to land use planning in this and similar environments. Complete protection of lowland streams, wetlands, and ecosystems in this hydrogeologic setting requires protection of a deep interbasin groundwater system whose precise volume, boundaries, and recharge areas are presently unknown.}, number={1-4}, journal={JOURNAL OF HYDROLOGY}, author={Genereux, DP and Wood, SJ and Pringle, CM}, year={2002}, month={Feb}, pages={163–178} }
 @article{genereux_bandopadhyay_2002, title={Reply to comment on "numerical investigation of lake bed seepage patterns: effects of porous medium and lake properties"' by Genereux, D., and Bandopadhyay, I., 2001. Journal of Hydrology 241, 286-303}, volume={258}, ISSN={["0022-1694"]}, DOI={10.1016/S0022-1694(01)00572-8}, abstractNote={Seawater intrusion (SI) is an increased threat to the groundwater resource in coastal regions. The cut-off wall is widely used to arrest the advance of a seawater wedge, but it is likely to cause groundwater contamination in landward aquifers. In order to alleviate the contamination problem, we proposed a new variable-permeability cut-off wall (VPFW) with a semi-permeable section at the bottom of the physical barrier. This study is the first to investigate the spatial distributions and transient behaviors of SI and nitrate pollution at field scale under the joint effects of physical barriers and denitrification. Results show the dissolved oxygen (DO) decreases almost synchronously with the intrusion of SW near the sea boundary, and the denitrification of NO3− and retreat of the dissolved organic carbon (DOC) wedge occurred in the inland aquifer. Notably, the freshwater discharge flux and nitrate discharge flux for the developed VPFW increase by 35% and 20%, respectively, while the enrichment ratio of specific volume of nitrate contamination zone (SVNR) went down by 15% on average compared with the traditional cut-off wall. Four indices were proposed to quantify the impervious barrier: heights (H), relative hydraulic conductivities (K*), and control effectiveness of SI and nitrate pollution. Moreover, we found the control effectiveness for SI and nitrate pollution was continually enhanced with the reduction of K* and increase of H; however, excessive reduction and increase may result in the opposite impacts. The optimal K* and H for the VPFW can be determined with the required value of the reduction rate of saltwater wedge length (SWR) and SVNR; but all cut-off wall cases fail to meet the demand. The results show that the VPFW is much more effective in controlling SI and nitrate pollution in comparison with the traditional cut-off wall.}, number={1-4}, journal={JOURNAL OF HYDROLOGY}, author={Genereux, D and Bandopadhyay, I}, year={2002}, month={Feb}, pages={265–266} }
 @article{genereux_guardiario_2001, title={A borehole flowmeter investigation of small-scale hydraulic conductivity variation in the Biscayne Aquifer, Florida}, volume={37}, ISSN={["1944-7973"]}, DOI={10.1029/2001WR900023}, abstractNote={Geostatistical analysis of closely spaced borehole flowmeter measurements was used to estimate the variance (2.53) and vertical and horizontal correlation lengths of ln K(0.57 and 7.3 m) in the Biscayne Aquifer, a limestone aquifer critical for Florida's water supply and for Everglades restoration efforts. The variance and correlation lengths of the Biscayne Aquifer are similar to some of the values for unconsolidated siliciclastic sediments (especially those at Columbus, Mississippi∥. The larger λh, for the Biscayne Aquifer (7.3 m) is thought to be due at least in part to the lower lateral variability of the carbonate platform depositional environment, compared to the fluvial environments in which the siliciclastic sediments were deposited. An improved down hole packer would allow for data with finer vertical resolution; the current system is adequate for work inside well screens but cannot adequately seal many spots in open, irregular rock boreholes. Research in rock presents additional logistical difficulties but is important for addressing fundamental questions about solute transport in a wider range of geological media, beyond unconsolidated siliciclastic deposits.}, number={5}, journal={WATER RESOURCES RESEARCH}, author={Genereux, D and Guardiario, J}, year={2001}, month={May}, pages={1511–1517} }
 @article{bolster_genereux_saiers_2001, title={Determination of specific yield for the Biscayne Aquifer with a canal-drawdown test}, volume={39}, ISSN={["0017-467X"]}, DOI={10.1111/j.1745-6584.2001.tb02368.x}, abstractNote={Data from a large-scale canal-drawdown test were used to estimate the specific yield (sy) of the Biscayne Aquifer, an unconfined limestone aquifer in southeast Florida. The drawdown test involved dropping the water level in a canal by about 30 cm and monitoring the response of hydraulic head in the surrounding aquifer. Specific yield was determined by analyzing data from the unsteady portion of the drawdown test using an analytical stream-aquifer interaction model (Zlotnik and Huang 1999). Specific yield values computed from drawdown at individual piezometers ranged from 0.050 to 0.57, most likely indicating heterogeneity of specific yield within the aquifer (small-scale variation in hydraulic conductivity may also have contributed to the differences in sy among piezometers). A value of 0.15 (our best estimate) was computed based on all drawdown data from all piezometers. We incorporated our best estimate of specific yield into a large-scale two-dimensional numerical MODFLOW-based ground water flow model and made predictions of head during a 183-day period at four wells located 337 to 2546 m from the canal. We found good agreement between observed and predicted heads, indicating our estimate of specific yield is representative of the large portion of the Biscayne Aquifer studied here. This work represents a practical and novel approach to the determination of a key hydrogeological parameter (the storage parameter needed for simulation and calculation of transient unconfined ground water flow), at a large spatial scale (a common scale for water resource modeling), for a highly transmissive limestone aquifer (in which execution of a traditional pump test would be impractical and would likely yield ambiguous results). Accurate estimates of specific yield and other hydrogeological parameters are critical for management of water supply, Everglades environmental restoration, flood control, and other issues related to the ground water hydrology of the Biscayne Aquifer.}, number={5}, journal={GROUND WATER}, author={Bolster, CH and Genereux, DP and Saiers, JE}, year={2001}, pages={768–777} }
 @article{genereux_bandopadhyay_2001, title={Numerical investigation of lake bed seepage patterns: effects of porous medium and lake properties}, volume={241}, ISSN={["0022-1694"]}, DOI={10.1016/s0022-1694(00)00380-2}, abstractNote={Abstract Three-dimensional steady-state numerical models were used to investigate the relative significance of several factors controlling lake bed seepage patterns: lake depth, lake bed slope, orientation of an asymmetric lake with respect to a regional hydraulic gradient, lake bed sediments, and heterogeneity and anisotropy of the porous medium. We considered both inflow and flow-through lakes, and our focus was on the details of seepage flux at the lake bed (not on the surrounding porous medium). While porous medium factors (anisotropy and heterogeneity) are important, we found several conditions where lake bed factors were nearly as important in controlling the distribution of seepage. Varying lake bed slope from 0.013 to 0.04 in different simulations had a significant effect on shoreline seepage (rates were 10–40% higher for lakes of low slope than lakes of steep slope). Also, significantly elevated seepage (in some cases, a local maximum) was observed offshore at the break in bed slope between the sloping side and flat central portions of the lake bed, whenever the surrounding porous medium had a high anisotropy (1000 or 100). For flow-through lakes in media of high anisotropy, the annual volume of groundwater inseepage was significantly higher (about 20%) in lakes with steep bed slope compared to those with low slope; this effect of slope was smaller at lower anisotropy. For an asymmetric flow-through lake (a lake with a steep bed slope on one side, moderate slope on the other) the percentage of lake bed experiencing inseepage was greatest when the steep side was downgradient, and the effect was larger at higher anisotropy. These effects illustrate the complex interaction between lake bed slope and the anisotropy of the surrounding porous medium in controlling lake:groundwater exchange. Adding low-conductivity lake sediments, and decreasing their conductivity, shifted groundwater seepage further offshore in inflow lakes; increasing the anisotropy of the surrounding porous medium had the same effect. Adding sediments and increasing anisotropy also decreased nearshore seepage in flow-through lakes, but without increasing offshore seepage; in this case, the net effect was a smaller annual volume of lake:groundwater exchange. At the same time, the percentage of the lake bed experiencing inseepage increased in flow-through lakes, even as the annual volume of inseepage was decreasing. Thus, for flow-through lakes, a larger area of inseepage may not be a good indicator of a greater volume of inseepage. Lake depth did not have a significant effect on the quantity or distribution of seepage to inflow or flow-through lakes. Many of the physical factors investigated here influence the amount of lake:groundwater exchange and the proportions of nearshore and offshore seepage; therefore, they are potentially significant to lake water quality and ecology in addition to hydrology.}, number={3-4}, journal={JOURNAL OF HYDROLOGY}, author={Genereux, D and Bandopadhyay, I}, year={2001}, month={Jan}, pages={286–303} }