@article{baker_showers_2019, title={Hysteresis analysis of nitrate dynamics in the Neuse River, NC}, volume={652}, ISSN={["1879-1026"]}, DOI={10.1016/j.scitotenv.2018.10.254}, abstractNote={Anthropogenic activities have caused N saturation in many terrestrial ecosystems. The transfer of nutrients and sediments to freshwater environments has resulted in water quality impairments including eutrophication, increased turbidity, ecosystem acidification, and loss of biodiversity. Storm events account for the transport of a large proportion of nutrients and sediments found in watersheds on an annual basis. To implement effective water-quality management strategies, the importance of surface and subsurface flow paths during storm events and low flow conditions need to be quantified. The increased availability of optical in-situ sensors makes high-frequency monitoring of catchment fluxes practical. In this study, we present a high-resolution nitrate monitoring record over a 10-year period in the Neuse River Basin near Clayton, North Carolina. The relationship between discharge and nitrate concentration for 365 storm events are categorized into hysteresis classes that indicate different transport mechanisms into the river. Storm events over the entire period of this study are divided between clockwise, counter-clockwise, and complex hysteresis patterns, indicating multiple nitrate flow paths during different seasons and years. Logistic regression of a suite of environmental variables demonstrates that antecedent soil moisture is a significant factor in determining the storm hysteresis class, with the odds of counter-clockwise hysteresis increasing by 10.3% for every 1 percentage point increase in the soil moisture. There is also an overlying seasonal effect, which indicates that dry soil conditions and frequent small storms during summer leads to greater nitrate transport on the rising limb, in contrast to slower, groundwater-driven inputs during the rest of the year.}, journal={SCIENCE OF THE TOTAL ENVIRONMENT}, author={Baker, Evan B. and Showers, William J.}, year={2019}, month={Feb}, pages={889–899} }
 @article{hurley-sanders_levine_nelson_law_showers_stoskopf_2015, title={Key metabolites in tissue extracts ofElliptio complanataidentified using1H nuclear magnetic resonance spectroscopy}, volume={3}, ISSN={2051-1434}, url={http://dx.doi.org/10.1093/conphys/cov023}, DOI={10.1093/conphys/cov023}, abstractNote={We used 1H-NMR to describe the freshwater mussel metabolome. Muscle, digestive gland, mantle and gill tissues yielded profiles with possible biomarkers of physiologic function. These preliminary studies provide evidence for potential use of digestive gland and mantle tissue for studying physiological impacts of location, sex and reproductive condition on Elliptio complanata.}, number={1}, journal={Conservation Physiology}, publisher={Oxford University Press (OUP)}, author={Hurley-Sanders, Jennifer L. and Levine, Jay F. and Nelson, Stacy A. C. and Law, J. M. and Showers, William J. and Stoskopf, Michael K.}, year={2015}, pages={cov023} }
 @article{hurley-sanders_stoskopf_nelson_showers_law_gracz_levine_2015, title={Tissue extraction methods for metabolic profiling of a freshwater bivalve, Elliptio complanata}, volume={33}, ISSN={0740-2783 2162-2698}, url={http://dx.doi.org/10.4003/006.033.0209}, DOI={10.4003/006.033.0209}, abstractNote={Abstract: 
 Much is still unknown about why freshwater mussels (Unionidae) are particularly sensitive to environmental change. A better understanding of freshwater mussel metabolism is needed, and the field of environmental metabolomics holds the promise to inform these questions. A number of protocols exist for the extraction of metabolites for identification from animal tissues. As a first step in the application of environmental metabolomics to the study of freshwater mussels, we compared extraction protocols using an inorganic oxidizing acid (perchloric acid), an organic nitrile (acetonitrile), and a salt/water solution (Ringer's solution) to establish an uncomplicated, robust, repeatable and inexpensive tissue extraction protocol for freshwater mussel tissue. Perchloric acid resulted in notable extraction of energy-related nucleotides (AMP/ADP/ATP), yet had the lowest peak count of the three extraction methods and showed poor repeatability. Acetonitrile and Ringer's solution yielded metabolite extraction results similar to each other with Ringer's solution having the greatest number of peaks particularly in the 3.0–4.5 ppm sugar/amino acid range. Ringer's solution is simple to use, safe and consistent and bears consideration when selecting an extraction protocol for 1H nuclear magnetic resonance experiments.}, number={2}, journal={American Malacological Bulletin}, publisher={American Malacological Society}, author={Hurley-Sanders, J.L. and Stoskopf, M. and Nelson, S.A.C. and Showers, W. and Law, J.M. and Gracz, H.S. and Levine, J.F.}, year={2015}, pages={185–194} }
 @article{bucci_levine_showers_2011, title={Spatial variability of the stable isotope (δ15N) composition in two freshwater bivalves (Corbicula fluminea and Elliptio complanata)}, volume={26}, ISSN={0270-5060 2156-6941}, url={http://dx.doi.org/10.1080/02705060.2011.553817}, DOI={10.1080/02705060.2011.553817}, abstractNote={We compared the isotopic composition in freshwater bivalves (Corbicula fluminea and Elliptio complanata) from streams with different nitrate concentrations in a North Carolina river basin. Nitrogen isotopic (δ 15N) tissue values of C. fluminea and E. complanata were significantly higher in an agricultural land-use stream site compared to urban and forested samples (p < 0.05). Nitrogen (δ 15N) tissue values for both species were significantly (p < 0.001) associated with land-use type or patterns. The potential use of resident, non-native bivalves as biomonitors of potentially harmful nitrogen levels was implied.}, number={1}, journal={Journal of Freshwater Ecology}, publisher={Informa UK Limited}, author={Bucci, John P. and Levine, Jay F. and Showers, William J.}, year={2011}, month={Mar}, pages={19–24} }
 @article{corliss_brown_sun_showers_2009, title={Deep-sea benthic diversity linked to seasonality of pelagic productivity}, volume={56}, ISSN={["1879-0119"]}, DOI={10.1016/j.dsr.2008.12.009}, abstractNote={Latitudinal gradients in biodiversity are found in both terrestrial and marine environments, but little agreement exists on the mechanisms or ecological causes creating these patterns. Marine biodiversity patterns have been particularly challenging to document, because of the lack of appropriate data sets from ocean basins. We document latitudinal patterns of North Atlantic deep-sea benthic foraminifera and show that seasonality of primary productivity, as estimated from SeaWiFS satellite imagery, has a significant effect on diversity indices, with generally lower values of H(S), species ♯, and species equitability found with high seasonality between 40 and 60°N. High foraminiferal diversity is not found in areas with phytodetritus deposition in the North Atlantic basin, which indicates that patch dynamics, biological disturbance, and sediment heterogeneity resulting from phytodetritus deposits do not create high deep-sea foraminiferal diversity. Annual resource stability, reflecting the timing of organic carbon flux and the mode of sedimentation, accounts for the benthic foraminiferal patterns found in this study and is an important variable structuring the deep-sea benthic foraminiferal community.}, number={5}, journal={DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS}, author={Corliss, B. H. and Brown, C. W. and Sun, X. and Showers, W. J.}, year={2009}, month={May}, pages={835–841} }
 @article{bucci_showers_genna_levine_2009, title={Stable oxygen and carbon isotope profiles in an invasive bivalve (Corbicula fluminea) in North Carolina watersheds}, volume={73}, ISSN={0016-7037}, url={http://dx.doi.org/10.1016/j.gca.2009.03.023}, DOI={10.1016/j.gca.2009.03.023}, abstractNote={The modern invasive bivalve Corbicula fluminea was collected in 2006 from three sites with different land uses located in a North Carolina River Basin. The primary objective was to describe the δ18O and δ13C profiles of C. fluminea shells under various land use conditions. An additional aim was to evaluate whether growth patterns of C. fluminea form seasonally. Annual shell growth patterns were measured from the umbo to the margin and co-varied with estimates of ambient water temperature, corresponding to seasonal variation. The C. fluminea growth patterns as translucent bands (slower growth) appeared to form during winter months and opaque bands (rapid growth) formed during summer. A mixed model analysis (ANOVA) showed a significant site level effect of δ18O and δ13C profiles examined among sites (F = 17.1; p = 0.003). A second model showed a borderline significant site effect among profiles with variability more pronounced at the urban site, Crabtree Creek (p = 0.085). Previous habitat assessment ratings and water chemistry measurements suggested that the urban site was more impacted by storm water runoff. Understanding δ18O and δ13CSHELL profiles and shell growth patterns of the invasive bivalve (C. fluminea) may help establish a framework for using these animals as biomonitors to record water temperature and nutrient pollution.}, number={11}, journal={Geochimica et Cosmochimica Acta}, publisher={Elsevier BV}, author={Bucci, John P. and Showers, William J. and Genna, Bernie and Levine, Jay F.}, year={2009}, month={Jun}, pages={3234–3247} }
 @article{occhipinti_aneja_showers_niyogi_2008, title={Back-trajectory analysis and source-receptor relationships: Particulate matter and nitrogen isotopic composition in rainwater}, volume={58}, ISSN={["1047-3289"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-53849144360&partnerID=MN8TOARS}, DOI={10.3155/1047-3289.58.9.1215}, abstractNote={Abstract The southeastern portion of North Carolina features a dense crop and animal agricultural region; previous research suggests that this agricultural presence emits a significant portion of the state’s nitrogen (i.e., oxides of nitrogen and ammonia) emissions. These findings indicate that transporting air over this region can affect nitrogen concentrations in precipitation at sites as far as 50 mi away. The study combined nitrate nitrogen isotope data with back-trajectory analysis to examine the relationship between regional nitrogen emission estimates independent of pollutant concentration information. In 2004, the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model was used to determine potential sources of nitrogen in rainwater collected at an urban receptor site in Raleigh, NC. The δ15N isotope ratio signatures of each sample were used to further differentiate between sources of the rainwater nitrate. This study examined the importance of pollution sources, including animal agricultural activity, and meteorology on rainfall chemistry as well as the implications in fine particulate matter (PM2.5) formation. Samples that transited the dense crop and animal (swine) agricultural region of east-southeastern North Carolina (i.e., the source region) had lower δ15N isotope ratios in the nitrate ion (average = −2.1 ± 1.7‰) than those from a counterpart nonagricultural region (average = 0.1 ± 3‰.) An increase in PM2.5 concentrations in the urban receptor site (yearly average = 15.1 ± 5.8 μg/m3) was also found to correspond to air transport over the dense agricultural region relative to air that was not subjected to such transport (yearly average = 11.7 ± 5.8 μg/m3).}, number={9}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Occhipinti, Chris and Aneja, Viney P. and Showers, William and Niyogi, Dev}, year={2008}, month={Sep}, pages={1215–1222} }
 @article{showers_genna_mcdade_bolich_fountain_2008, title={Nitrate contamination in groundwater on an urbanized dairy farm}, volume={42}, ISSN={["0013-936X"]}, DOI={10.1021/es071551t}, abstractNote={Urbanization of rural farmland is a pervasive trend around the globe, and maintaining and protecting adequate water supplies in suburban areas is a growing problem. Identification of the sources of groundwater contamination in urbanized areas is problematic, but will become important in areas of rapid population growth and development. The isotopic composition of NO3 (delta15N(NO3) and delta18O NO3), NH4 (delta15N(NH4)), groundwater (delta2H(wt) and delta18O(wt)) and chloride/bromide ratios were used to determine the source of nitrate contamination in drinking water wells in a housing development that was built on the site of a dairy farm in the North Carolina Piedmont, U.S. The delta15N(NO3) and delta18O NO3 compositions imply that elevated nitrate levels at this site in drinking well water are the result of waste contamination, and that denitrification has not significantly attenuated the groundwater nitrate concentrations. delta15N(NO3) and delta18O(NO3) compositions in groundwater could not differentiate between septic effluent and animal waste contamination. Chloride/ bromide ratios in the most contaminated drinking water wells were similar to ratios found in animal waste application fields, and were higher than Cl/Br ratios observed in septic drain fields in the area. delta18O(wt) was depleted near the site of a buried waste lagoon without an accompanying shift in delta2H(wt) suggesting water oxygen exchange with CO2. This water-CO2 exchange resulted from the reduction of buried lagoon organic matter, and oxidation of the released gases in aerobic soils. delta18O(wt) is not depleted in the contaminated drinking water wells, indicating that the buried dairy lagoon is not a source of waste contamination. The isotope and Cl/Br ratios indicate that nitrate contamination in these drinking wells are not from septic systems, but are the result of animal waste leached from pastures into groundwater during 35 years of dairy operations which did not violate any existing regulations. Statutes need to be enacted to protect the health of the homeowners that require well water to be tested prior to the sale of homes built on urbanized farmland.}, number={13}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Showers, William J. and Genna, Bernard and McDade, Timothy and Bolich, Rick and Fountain, John C.}, year={2008}, month={Jul}, pages={4683–4688} }
 @article{michalski_kasem_rech_adieu_showers_genna_thiemens_2008, title={Uncertainties in the oxygen isotopic composition of barium sulfate induced by coprecipitation of nitrate}, volume={22}, ISSN={["1097-0231"]}, DOI={10.1002/rcm.3687}, abstractNote={Coprecipitation of nitrate and sulfate by barium has probably resulted in significant error in numerous studies dealing with the oxygen isotopic composition of natural sulfates using chemical/thermal conversion of BaSO(4) and analysis by isotope ratio mass spectrometry. In solutions where NO(3) (-)/SO(4) (2-) molar ratios are above 2 the amount of nitrate coprecipitated with BaSO(4) reaches a maximum of approximately 7% and decreases roughly linearly as the molar ratio decreases. The fraction of coprecipitated nitrate appears to increase with decreasing pH and is also affected by the nature of the cations in the precipitating solution. The size of the oxygen isotope artifact in sulfate depends both on the amount of coprecipitated nitrate and the delta(18)O and Delta(17)O values of the nitrate, both of which can be highly variable. The oxygen isotopic composition of sulfate extracted from atmospheric aerosols or rain waters are probably severely biased because photochemical nitrate is usually also present and it is highly enriched in (18)O (delta(18)O approximately 50-90 per thousand) and has a large mass-independent isotopic composition (Delta(17)O approximately 20-32 per thousand). The sulfate delta(18)O error can be 2-5 per thousand with Delta(17)O artifacts reaching as high as 4.0 per thousand.}, number={19}, journal={RAPID COMMUNICATIONS IN MASS SPECTROMETRY}, author={Michalski, Greg and Kasem, Michelle and Rech, Jason A. and Adieu, Sabine and Showers, William S. and Genna, Bernie and Thiemens, Mark}, year={2008}, month={Oct}, pages={2971–2976} }
 @article{bucci_showers_levine_usry_2008, title={Valve Gape Response to Turbidity in Two Freshwater Bivalves (Corbicula flumineaandLampsilis radiata)}, volume={23}, ISSN={0270-5060 2156-6941}, url={http://dx.doi.org/10.1080/02705060.2008.9664229}, DOI={10.1080/02705060.2008.9664229}, abstractNote={ABSTRACT In a laboratory study with a simulated storm event, we found a significant difference (p<0.05) in valve gape response to the turbidity between Corbicula fluminea and Lampsilis radiata. Valves of C. fluminea opened more intensively during the peak turbidity period and closed significantly more during a following chronic turbidity period. L. radiata exhibited little change in valve gape response with change in turbidity.}, number={3}, journal={Journal of Freshwater Ecology}, publisher={Informa UK Limited}, author={Bucci, John P. and Showers, William J. and Levine, Jay F. and Usry, Brian}, year={2008}, month={Sep}, pages={479–483} }
 @article{bucci_rebach_demaster_showers_2007, title={A comparison of blue crab and bivalve delta N-15 tissue enrichment in two North Carolina estuaries}, volume={145}, DOI={10.1016/j.envpol.2006.03.009}, abstractNote={Stable isotope analyses (delta(15)N) were used to examine invertebrate tissue enrichment in two North Carolina estuaries with differing amounts of nutrient loading. Bivalves collected from a nutrient sensitive estuary yielded a significant difference in mean nitrogen isotopic composition of tissue (10.4 per thousand+/-0.82; N=66) compared to bivalves collected from a less nutrient sensitive estuary (6.4 per thousand+/-0.63; N=45). Similarly, blue crabs from nutrient sensitive sites had a nitrogen isotopic composition of 11.4 per thousand (+/-1.3, N=77), which was significantly different (P<0.001) than the tissue of less nutrient sensitive blue crabs (9.6 per thousand+/-0.6; N=77). The results showed that an inverse relationship exists between invertebrate tissue enrichment and indicators of water quality across estuarine sites. This study suggests that a relationship may exist between nutrient sources and subsequent energy transfer to estuarine consumers in two North Carolina estuaries.}, number={1}, journal={Environmental Pollution}, author={Bucci, J. P. and Rebach, S. and Demaster, D. and Showers, W. J.}, year={2007}, pages={299–308} }
 @misc{johnson_needoba_riser_showers_2007, title={Chemical sensor networks for the aquatic environment}, volume={107}, ISSN={["1520-6890"]}, DOI={10.1021/cr050354e}, abstractNote={Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, California 95039, School of Oceanography, University ofWashington, Seattle, Washington 98195-7940, Department of Marine, Earth and Atmospheric Sciences, North Carolina State University,Raleigh, North Carolina 27695Received July 14, 2006}, number={2}, journal={CHEMICAL REVIEWS}, author={Johnson, Kenneth S. and Needoba, Joseph A. and Riser, Stephen C. and Showers, William J.}, year={2007}, month={Feb}, pages={623–640} }
 @article{bucci_showers_rebach_demaster_genna_2007, title={Stable isotope analyses (delta N-15 and delta C-13) of the trophic relationships of Callinectes sapidus in two north Carolina estuaries}, volume={30}, ISSN={["1559-2731"]}, DOI={10.1007/BF02841395}, number={6}, journal={ESTUARIES AND COASTS}, author={Bucci, J. P. and Showers, W. J. and Rebach, S. and DeMaster, D. and Genna, B.}, year={2007}, month={Dec}, pages={1049–1059} }
 @article{gustafson_showers_kwak_levine_stoskopf_2007, title={Temporal and spatial variability in stable isotope compositions of a freshwater mussel: implications for biomonitoring and ecological studies}, volume={152}, ISSN={["1432-1939"]}, DOI={10.1007/s00442-006-0633-7}, number={1}, journal={OECOLOGIA}, author={Gustafson, Lori and Showers, William and Kwak, Thomas and Levine, Jay and Stoskopf, Michael}, year={2007}, month={May}, pages={140–150} }
 @article{showers_williams_jennings_2006, title={Impact of large poultry operations on groundwater: Stable 15N isotopes of nitrate assessment}, volume={5}, ISBN={1682-8356}, DOI={10.3923/ijps.2006.318.329}, number={4}, journal={International Journal of Poultry Science}, author={Showers, W. J. and Williams, C. M. and Jennings, G. D.}, year={2006}, pages={318} }
 @article{corliss_sun_brown_showers_2006, title={Influence of seasonal primary productivity on delta C-13 of North Atlantic deep-sea benthic foraminifera}, volume={53}, ISSN={["1879-0119"]}, DOI={10.1016/j.dsr.2006.01.006}, abstractNote={The stable isotopic composition of benthic foraminifera has been widely used to reconstruct deep-ocean circulation, but questions have been raised about the influence of organic carbon flux on the carbon isotopic composition of deep-sea taxa. We show that annual and seasonality of primary productivity in the North Atlantic do not affect δ13C of Planulina wuellerstorfi, but that the intermittency or seasonality of primary production has a significant effect (0.9‰ change over 60° latitude) on δ13C of Epistominella exigua, reflecting the influence of pelagic-benthic coupling and microhabitat preferences on test geochemistry. These results support the use of δ13C of P. wuellerstorfi in paleocirculation studies and suggest that the δ13C of E. exigua can be used to reconstruct seasonality of productivity.}, number={4}, journal={DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS}, author={Corliss, B. H. and Sun, X. and Brown, C. W. and Showers, W. J.}, year={2006}, month={Apr}, pages={740–746} }
 @misc{sun_corliss_brown_showers_2006, title={The effect of primary productivity and seasonality on the distribution of deep-sea benthic foraminifera in the North Atlantic}, volume={53}, ISSN={["0967-0637"]}, DOI={10.1016/j.dsr.2005.07.003}, abstractNote={Deep-sea benthic foraminifera from 43 Holocene core tops in the North Atlantic were studied to evaluate the influence of primary productivity and the seasonality of primary productivity on the distributional patterns of species, faunal assemblages, and microhabitat groups. Two faunal assemblages, Epistominella exigua-Alabaminella weddellensis assemblage and Globocassidulina subglobosa-Epistominella umbonifera assemblage, were found to correlate with seasonality of primary productivity. The E. exigua-A. weddellensis assemblage is found at high latitudes and positively correlates with seasonality, while the G. subglobosa-E. umbonifera assemblage is generally found at low latitudes and has a negative correlation. Correlation analysis indicates that the relative abundance of one species alone (E. exigua or A. weddellensis) is not a strong indicator of either primary productivity or seasonality. No significant relationships are found between benthic foraminiferal species, faunal assemblages, or microhabitat groups and bottom water properties, which suggests that the deep-sea fauna may not be used to reconstruct bottom water properties in this region. Based on microhabitat preferences of individual species, the fauna is categorized into epifaunal, infaunal, and phytodetrital groups and is compared with primary productivity of the overlying surface waters and seasonality. No significant relationship was found between the relative abundance of the infaunal group and primary productivity or its seasonality, and only a weak correlation was found between these variables and the epifaunal group (r2=0.33; 0.46). However, the relative abundances of the phytodetrital group correlate relatively well with seasonal variability (r2=0.63), reflecting the association of these species with phytodetritus in regions marked by high seasonal variation in organic carbon flux. These results indicate that the relative abundance of the phytodetrital group may be used to reconstruct seasonality of productivity in the North Atlantic.}, number={1}, journal={DEEP-SEA RESEARCH PART I-OCEANOGRAPHIC RESEARCH PAPERS}, author={Sun, XC and Corliss, BH and Brown, CW and Showers, WJ}, year={2006}, month={Jan}, pages={28–47} }
 @article{gustafson_stoskopf_bogan_showers_kwak_hanlon_levine_2005, title={Evaluation of a nonlethal technique for hemolymph collection in Elliptio complanata, a freshwater bivalve (Mollusca: Unionidae)}, volume={65}, ISSN={0177-5103 1616-1580}, url={http://dx.doi.org/10.3354/dao065159}, DOI={10.3354/dao065159}, abstractNote={Hemolymph, the circulatory fluid of bivalves, transports nutrients, respiratory gases, enzymes, metabolic wastes, and toxicants throughout the body. Hemolymph can provide information pertinent to health assessment of animals or populations, but is not commonly used in freshwater bivalves partly because of the lack of tested, practical techniques for its nonlethal collection. The objective of this study was to evaluate the effect of hemolymph collection on the growth and survival of Elliptio complanata, a freshwater bivalve (Unionidae). We describe a simple technique for the collection of hemolymph from the anterior adductor muscle sinus of E. complanata. To evaluate the effect of hemolymph sampling on mussel survival and growth, 30 mussels sampled using the technique and 30 unsampled controls were followed for 3 mo post collection. Nine animals were sampled 3 times over 7 mo to monitor effects of repeated sampling. No negative impacts on survival or growth were observed in either the singly or repeatedly sampled animals. We also compared the composition of hemolymph collected from the adductor muscle sinus with that collected from the ventricle of the heart. Calcium levels and cell count of hemolymph obtained from the adductor sinus and ventricle were significantly different. There was no significant difference between collection sites for magnesium, phosphorus, ammonia, protein, sodium, potassium, or chloride. We conclude that collection of hemolymph from the adductor sinus is safe for sampled E. complanata and should be explored as a relatively non-invasive, and potentially useful, approach to the evaluation of freshwater mussel health.}, number={2}, journal={Diseases of Aquatic Organisms}, publisher={Inter-Research Science Center}, author={Gustafson, LL and Stoskopf, MK and Bogan, AE and Showers, W and Kwak, TJ and Hanlon, S and Levine, JF}, year={2005}, pages={159–165} }
 @article{israel_showers_fountain_fountain_2005, title={Nitrate movement in shallow ground water from swine-lagoon-effluent spray fields managed under current application regulations}, volume={34}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2004.0338}, abstractNote={Rapid increases in the swine (Sus scrofa domestica) population in the 1990s and associated potential for nitrate N pollution of surface waters led the state of North Carolina to adopt stringent waste management regulations in 1993. Our objectives were to characterize (i) nitrate N movement from waste application fields (WAFs) in shallow ground water, and (ii) soil, hydrologic, and biological factors influencing the amount of nitrate N in the adjacent stream. A ground water monitoring study was conducted for 36 mo on a swine farm managed under new regulations. Water table contours and lack of vertical gradients indicated horizontal flow over most of the site. Nitrate N concentrations in water from shallow wells in WAFs averaged 30 +/- 19 mg L(-1) and delta15N ratios for nitrate N were between +20 and +25 per mil. Nitrate N concentration decreased from field-edge to streamside wells by 22 to 99%. Measurement of delta18O and delta15N enrichment of nitrate in ground water throughout the WAF-riparian system indicated that denitrification has not caused significant 15N enrichment of nitrate. Over a 24-mo period, delta15N ratios for nitrate N in the stream approached delta15N ratios for nitrate N in ground water beneath WAFs indicating delivery of some waste-derived nitrate N to the stream in shallow ground water. Nitrate N concentrations in the stream were relatively low, averaging 1 mg L(-1). Dilution of high nitrate N water in shallow horizontal flow paths with low nitrate N water from deeper horizontal flow paths at or near the stream, some denitrification as ground water discharges through the stream bottom, and some denitrification in riparian zone contributed to this low nitrate N concentration.}, number={5}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Israel, DW and Showers, WJ and Fountain, M and Fountain, J}, year={2005}, pages={1828–1842} }
 @article{gustafson_stoskopf_showers_cope_eads_linnehan_kwak_andersen_levine_2005, title={Reference ranges for hemolymph chemistries from Elliptio complanata of North Carolina}, volume={65}, ISSN={["1616-1580"]}, DOI={10.3354/dao065167}, abstractNote={Hemolymph chemistries may be useful nonlethal measures of bivalve health. The prognostic value of hemolymph, however, depends on a comparison of chemistry results to reference ranges from healthy individuals. Currently, knowledge of expected hemolymph values in healthy and unhealthy freshwater mussels is extremely limited. The purpose of this study was to develop a set of reference ranges for clinical evaluation of hemolymph from a freshwater mussel species common to southeastern USA. We collected hemolymph from 380 Elliptio complanata from 19 apparently healthy populations from northwest of Raleigh, North Carolina, during May through July 2001. We present reference ranges for hemolymph parameters ammonia, glucose, calcium, magnesium, phosphorus, aspartate aminotransferase (AST), bicarbonate, protein and cell count, and for tissue glycogen. We compare the subpopulations of mussels from regions with an agricultural riparian buffer to those surrounded predominantly by forested lands. We further present correlations noted between hemolymph chemistries and physical or physiologic parameters. The only statistically significant differences between populations contiguous to agricultural and forested lands were in hemolymph calcium and glucose concentrations. Other statistically significant correlations identified were between gravidity and hemolymph protein concentration and tissue glycogen content, as well as between gravidity and parasite burden, and between shell length and hemolymph glucose, AST, calcium and bicarbonate concentrations. The results of this study will aid the interpretation of health measures from populations of E. complanata of similar geographic and seasonal origin.}, number={2}, journal={DISEASES OF AQUATIC ORGANISMS}, author={Gustafson, LL and Stoskopf, MK and Showers, W and Cope, G and Eads, C and Linnehan, R and Kwak, TJ and Andersen, B and Levine, JF}, year={2005}, month={Jun}, pages={167–176} }
 @article{karr_showers_jennings_2003, title={Low-level nitrate export from confined dairy farming detected in North Carolina streams using delta N-15}, volume={95}, ISSN={["1873-2305"]}, DOI={10.1016/S0167-8809(02)00103-2}, abstractNote={Animal waste-produced nitrate in streams can be detected with natural abundance nitrogen isotopes even when stream nitrate concentrations are low and derive predominantly from natural soil nitrate sources. The objective of this limited study was to demonstrate the utility of such an approach with a minimal number of samples and minimal supporting data. These constraints are important in terms of the usefulness of the small-scale isotopic approach as a component of long-term, large-scale watershed and river basin monitoring, given the expense of nitrate isotopic measurements. The study was able to identify a small animal waste nitrate export signal over a significant background signal of soil nitrate and possible fertilizer nitrate in the stream draining the site. During the course of a year, a second-order stream adjacent to a carefully managed research dairy farm near Raleigh, NC had mean nitrate–N of 0.4 mg l−1 with mean δ15N–NO3 values of +8.7‰ downstream of the farm. Secondary dairy lagoon liquids used for spray irrigation of nearby fields had a mean ammonium concentration of 87.5 mg l−1, and a mean δ15N of +20.7‰. A small, intermittent first-order stream draining the dairy sprayfields and emptying into the second-order stream had a mean nitrate–N level of 3.7 mg l−1 and mean δ15N–NO3 of +16.0‰. Even at the relatively low nitrate levels and slightly elevated δ15N–NO3 values of the second-order receiving stream, an observed increase in δ15N values with increasing nitrate concentration in this stream indicates that a small amount of animal waste-produced nitrate is being exported. This type of monitoring could be applied to many small watersheds as part of a larger watershed or river basin study where sampling density is constrained by logistical and economic factors. This is the case in the Neuse River Basin, where this study was an early part of a developing basin-wide Nitrogen Isotope Tracer Program. This type of monitoring can be particularly useful where identification of targets for reduction or stabilization of N export from livestock farms is desired, and the animal waste nitrate signal is superimposed on a larger natural background nitrate or fertilizer nitrate + natural background nitrate signal.}, number={1}, journal={AGRICULTURE ECOSYSTEMS & ENVIRONMENT}, author={Karr, JD and Showers, WJ and Jennings, GD}, year={2003}, month={Apr}, pages={103–110} }
 @article{spruill_showers_howe_2002, title={Application of classification-tree methods to identify nitrate sources in ground water}, volume={31}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2002.1538}, abstractNote={A study was conducted to determine if nitrate sources in ground water (fertilizer on crops, fertilizer on golf courses, irrigation spray from hog (Sus scrofa) wastes, and leachate from poultry litter and septic systems) could be classified with 80% or greater success. Two statistical classification-tree models were devised from 48 water samples containing nitrate from five source categories. Model 1 was constructed by evaluating 32 variables and selecting four primary predictor variables (delta 15N, nitrate to ammonia ratio, sodium to potassium ratio, and zinc) to identify nitrate sources. A delta 15N value of nitrate plus potassium > 18.2 indicated animal sources; a value < 18.2 indicated inorganic or soil organic N. A nitrate to ammonia ratio > 575 indicated inorganic fertilizer on agricultural crops; a ratio < 575 indicated nitrate from golf courses. A sodium to potassium ratio > 3.2 indicated septic-system wastes; a ratio < 3.2 indicated spray or poultry wastes. A value for zinc > 2.8 indicated spray wastes from hog lagoons; a value < 2.8 indicated poultry wastes. Model 2 was devised by using all variables except delta 15N. This model also included four variables (sodium plus potassium, nitrate to ammonia ratio, calcium to magnesium ratio, and sodium to potassium ratio) to distinguish categories. Both models were able to distinguish all five source categories with better than 80% overall success and with 71 to 100% success in individual categories using the learning samples. Seventeen water samples that were not used in model development were tested using Model 2 for three categories, and all were correctly classified. Classification-tree models show great potential in identifying sources of contamination and variables important in the source-identification process.}, number={5}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Spruill, TB and Showers, WJ and Howe, SS}, year={2002}, pages={1538–1549} }
 @article{dietl_kelley_barrick_showers_2002, title={Escalation and extinction selectivity: morphology versus isotopic reconstruction of bivalve metabolism.}, volume={56}, DOI={10.1111/j.0014-3820.2002.tb01338.x}, abstractNote={Abstract Studies that have tested and failed to support the hypothesis that escalated species (e.g., those with predation-resistant adaptations) are more susceptible to elimination during mass extinctions have concentrated on the distribution and degree of morphological defenses in molluscan species. This morphological approach to determining level of escalation in bivalves may be oversimplified because it does not account for metabolic rate, which is an important measure of escalation that is less readily accessible for fossils. Shell growth rates in living bivalves are positively correlated with metabolic rate and thus are potential indicators of level of escalation. To evaluate this approach, we used oxygen isotopes to reconstruct shell growth rates for two bivalve species (Macrocallista marylandica and Glossus markoei) from Miocene-aged sediments of Maryland. Although both species are classified as non-escalated based on morphology, the isotopic data indicate that M. marylandica was a faster-growing species with a higher metabolic rate and G. markoei was a slower-growing species with a lower metabolic rate. Based on these results, we predict that some morphologically non-escalated species in previous tests of extinction selectivity should be reclassified as escalated because of their fast shell growth rates (i.e., high metabolic rates). Studies that evaluate the level of escalation of a fauna should take into account the energetic physiology of taxa to avoid misleading results. Corresponding Editor: D. Geary}, number={2}, journal={Evolution}, author={Dietl, G. P. and Kelley, P. H. and Barrick, R. and Showers, W.}, year={2002}, pages={284–291} }
 @article{showers_barrick_genna_2002, title={Isotopic analysis of dinosaur bones}, volume={74}, ISSN={["0003-2700"]}, DOI={10.1021/ac021968b}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVFeaturesNEXTPeer Reviewed: Isotopic Analysis of Dinosaur BonesA new pyrolysis technique provides direct evidence that some dinosaurs were warm-blooded.William J. Showers, Reese Barrick, and Bernard GennaCite this: Anal. Chem. 2002, 74, 5, 142 A–150 APublication Date (Web):March 1, 2002Publication History Published online1 March 2002Published inissue 1 March 2002https://doi.org/10.1021/ac021968bRIGHTS & PERMISSIONSArticle Views1803Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (10 MB) Get e-AlertscloseSUBJECTS:Anatomy Get e-Alerts}, number={5}, journal={ANALYTICAL CHEMISTRY}, author={Showers, WJ and Barrick, R and Genna, B}, year={2002}, month={Mar}, pages={142A–150A} }
 @article{karr_showers_hinson_2002, title={Nitrate source identification using delta N-15 in a ground water plume near an intensive swine operation}, volume={22}, ISSN={["1745-6592"]}, DOI={10.1111/j.1745-6592.2002.tb00314.x}, abstractNote={Nitrate‐contaminated ground water beneath and adjacent to an intensive swine (Sus scrofa domesticus) production facility in the Middle Coastal Plain of North Carolina was analyzed for δ15N of nitrate (δ15N‐NO3). Results show that the isotopic signal of animal waste nitrogen is readily identifiable and traceable in nitrate in this ground water. The widespread land application of animal wastes from intensive livestock operations constitutes a potential source of nitrogen contamination to natural water throughout large regions of the United States and other countries. The site of the present study has been suspected as a nitrate contamination source to nearby domestic supply wells and has been monitored for several years by government and private water quality investigators through sampling of observation wells, ditches, and streams. δ15N of nitrate allowed direct identification of animal waste‐produced nitrate in 11 of 14 wells sampled in this study, as well as recognition of nitrate contributions from non‐animal waste agricultural sources in remaining wells.}, number={2}, journal={GROUND WATER MONITORING AND REMEDIATION}, author={Karr, JD and Showers, WJ and Hinson, TH}, year={2002}, pages={68–75} }
 @misc{showers_genna_2002, title={Reply to comments on 'Isotopic analysis of dinosaur bones'}, volume={74}, DOI={10.1021/ac022060o}, abstractNote={ADVERTISEMENT RETURN TO ISSUEPREVDepartmentsNEXTLetters to the Editor: Reply to Comments on "Isotopic Analysis of Dinosaur Bones"William J. Showers and Bernard GennaCite this: Anal. Chem. 2002, 74, 13, 352 APublication Date (Web):July 1, 2002Publication History Published online1 July 2002Published inissue 1 July 2002https://doi.org/10.1021/ac022060oRIGHTS & PERMISSIONSArticle Views155Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (30 KB) Get e-AlertsSupporting Info (2)»Supporting Information Supporting Information SUBJECTS:Anatomy Get e-Alerts}, number={13}, journal={Analytical Chemistry}, author={Showers, W. J. and Genna, B.}, year={2002}, pages={352A} }
 @article{karr_showers_2002, title={Stable oxygen and hydrogen isotopic tracers in Amazon shelf waters during Amasseds}, volume={25}, ISSN={["0399-1784"]}, DOI={10.1016/S0399-1784(02)01183-0}, abstractNote={Abstract A detailed hydrographic survey of the water column of the Amazon shelf was performed using stable oxygen and hydrogen isotopes to determine the source and fate of waters on the shelf. δ 18 O-H 2 O and δ D measurements were made on water column samples from approximately 60 stations (three depths per station) which were each collected during four Amasseds (A Multidisciplinary Amazon Shelf SEDiment Study) cruises: I8909-August 1989, falling river discharge; I9002-March 1990, rising river discharge; I9004-May 1990, peak discharge; I9113-November 1991, minimum discharge. Isotopes were compared with salinity and temperature measurements in order to identify water masses and mixing. The characteristics (salinity, temperature, δ 18 O, δ D and d ) are proposed for the following end-number water masses: river water, open ocean surface water (0–100 m) and open ocean intermediate water (> 300 m). River water: salinity = 0; temperature ≈ 27–29 °C; δ 18 O = –4.2 to –6.8 per mil; δ D ≈ –22.1 to –38.9 per mil; d =  9.4 to 17.0 per mil (compare to d  = 10 for Meteoric Water Line). Open ocean surface water (≈ 0–100 m): salinity ≈ 35 to 37; temperature ≈ 25–29 °C; δ 18 O ≈ –1 to +2 per mil; δ D ≈ –3.6 to +10.2 per mil. Open ocean intermediate water (≳300 m): salinity = 34.6 to 35.0; temperature = 4.8 to 9.6 °C; δ 18 O = –0.2 to +0.3 per mil; δ D = –8.72 to –0.95 per mil. Amazon river water follows a seasonal isotopic cycle in response to basin hydrologic processes. River water mixes with equatorial surface ocean water and intermediate ocean waters originating in mid-to-high southern latitudes. Near-surface waters in the region of North Brazil Current retroflection were identical in isotope–salinity space to waters on the outer shelf during November 1991.}, number={2}, journal={OCEANOLOGICA ACTA}, author={Karr, JD and Showers, WJ}, year={2002}, pages={71–78} }
 @article{stoskopf_barrick_showers_2001, title={Oxygen isotope variability in bones of wild caught and constant temperature reared sub-adult American alligators}, volume={26}, ISSN={["0306-4565"]}, DOI={10.1016/S0306-4565(00)00041-3}, abstractNote={(1) The mean delta18O(BP) ( per thousandSMOW) for any given bone sampled from captive alligators maintained at high constant temperature was lower (indicative of higher temperatures of bone deposition) than that of the same bone from wild alligators caught in Northern Florida, but these differences were only greater than two standard deviations from the mean for the thoracic vertebrae and metatarsal bones. (2) Inter-bone variability of delta18O(BP) ( per thousandSMOW) was similar for captive alligators maintained at constant temperatures and the wild alligators, but intra-bone variability was much greater in wild alligators. (3) The order of mean delta18O(BP) ( per thousandSMOW) of bones (from highest to lowest) differed between treatment groups. However, intra-bone variability obscured the significance of those differences. Nevertheless, the thoracic vertebra had the highest mean delta18O(BP) ( per thousandSMOW), indicative of lower temperatures, and the lowest variability of bones in both groups of alligators. Conversely, the tibia was one of the warmest and more variable bones in both groups of alligators. (4) The pattern of delta18O(BP) ( per thousandSMOW) values across sites within long bones were identical between alligator treatment groups for the femur and humerus but differed between groups for the tibia and metatarsus, and differed between different long bones. The predicted intra-bone pattern for long bones of increasing delta18O(BP) ( per thousandSMOW) indicative of lower temperatures in more distal sampling sites was only obtained from the femurs. (5) Paired cortical and cancellous bone samples from the same site from all individuals in both treatment groups were available for proximal humeri and distal femurs. delta18O(BP) ( per thousandSMOW) values from cortical bone were more variable than those from cancellous bone for both bones. (6) Cortical bone had lower delta18O(BP) ( per thousandSMOW) values indicative of warmer temperatures than cancellous bone at sites sampled on the proximal humeri and distal femurs of all three animals from both treatment groups.}, number={3}, journal={JOURNAL OF THERMAL BIOLOGY}, author={Stoskopf, MK and Barrick, RE and Showers, WJ}, year={2001}, month={Jun}, pages={183–191} }
 @article{bond_kromer_beer_muscheler_evans_showers_hoffmann_lotti-bond_hajdas_bonani_2001, title={Persistent solar influence on north Atlantic climate during the Holocene}, volume={294}, ISSN={["1095-9203"]}, DOI={10.1126/science.1065680}, abstractNote={Surface winds and surface ocean hydrography in the subpolar North Atlantic appear to have been influenced by variations in solar output through the entire Holocene. The evidence comes from a close correlation between inferred changes in production rates of the cosmogenic nuclides carbon-14 and beryllium-10 and centennial to millennial time scale changes in proxies of drift ice measured in deep-sea sediment cores. A solar forcing mechanism therefore may underlie at least the Holocene segment of the North Atlantic's “1500-year” cycle. The surface hydrographic changes may have affected production of North Atlantic Deep Water, potentially providing an additional mechanism for amplifying the solar signals and transmitting them globally.}, number={5549}, journal={SCIENCE}, author={Bond, G and Kromer, B and Beer, J and Muscheler, R and Evans, MN and Showers, W and Hoffmann, S and Lotti-Bond, R and Hajdas, I and Bonani, G}, year={2001}, month={Dec}, pages={2130–2136} }
 @article{karr_showers_gilliam_andres_2001, title={Tracing nitrate transport and environmental impact from intensive swine farming using delta nitrogen-15}, volume={30}, ISSN={["1537-2537"]}, DOI={10.2134/jeq2001.3041163x}, abstractNote={Natural-abundance delta15N showed that nitrate generated from commercial land application of swine (Sus scrofa domesticus) waste within a North Carolina Coastal Plain catchment was being discharged to surface waters by ground water passing beneath the sprayfields and adjacent riparian buffers. This was significant because intensive swine farms in North Carolina are considered non-discharge operations, and riparian buffers with minimum widths of 7.6 m (25 ft) are the primary regulatory control on ground water export of nitrate from these operations. This study shows that such buffers are not always adequate to prevent discharge of concentrated nitrate in ground water from commercial swine farms in the Mid-Atlantic Coastal Plain, and that additional measures are required to ensure non-discharge conditions. The median delta15N-total N of liquids in site swine waste lagoons was +15.4 +/- 0.2% vs. atmospheric nitrogen. The median delta15N-NO3 values of shallow ground water beneath and adjacent to site sprayfields, a stream draining sprayfields, and waters up to 1.5 km downstream were + 15.3 +/- 0.2 to + 15.4 +/- 0.2%. Seasonal and spatial isotopic variations in lagoons and well waters were greatly homogenized during ground water transport and discharge to streams. Neither denitrification nor losses of ammonia during spraying significantly altered the bulk ground water delta15N signal being delivered to streams. The lagoons were sources of chloride and potassium enrichment, and shallow ground water showed strong correlation between nitrate N, potassium, and chloride. The 15N-enriched nitrate in ground water beneath swine waste sprayfields can thus be successfully traced during transport and discharge into nearby surface waters.}, number={4}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Karr, JD and Showers, WJ and Gilliam, JW and Andres, AS}, year={2001}, pages={1163–1175} }
 @article{barrick_fischer_showers_1999, title={Oxygen isotopes from turtle bone: Applications for terrestrial paleoclimates?}, volume={14}, ISSN={["0883-1351"]}, DOI={10.2307/3515374}, abstractNote={The oxygen isotope values (8) of turtle-bone phosphate for two freshwater emydid genera from the United States vary linearly with isotopic values (8J of environmental water. Mud, box, and snapping turtles do not fall on this regression line, while a soft-shelled turtle and marine loggerhead and leatherback turtles do. Although ectothermic, emydid turtles depend upon basking to raise their body temperatures. The mean temperature of bone growth is similar (3133?C) in emydid individuals analyzed as indicated by their bone and body-water oxygen isotopes. Unlike regressions for mammals, the slope of 8p versus 8, for these emydid turtles is unity, suggesting that the divergence from equilibrium is due to simple fractionation between environmental water and body water. Thus, bone 8, values from these genera of turtles (and potentially others) may be used to reconstruct local meteoric water 8w values in the fossil record. Concurrent study of fossil freshwater fish or molluscs may then be used to reconstruct local paleotemperatures.}, number={2}, journal={PALAIOS}, author={Barrick, RE and Fischer, AG and Showers, WJ}, year={1999}, month={Apr}, pages={186–191} }
 @article{schlunz_schneider_muller_showers_wefer_1999, title={Terrestrial organic carbon accumulation on the Amazon deep sea fan during the last glacial sea level low stand}, volume={159}, ISSN={["0009-2541"]}, DOI={10.1016/S0009-2541(99)00041-8}, abstractNote={Sediment cores from the Amazon deep sea fan recovered during R/V Meteor cruise 16-2 show in detail the modern areal distribution of sedimentary organic carbon, stable organic carbon isotopes of the organic matter (OM), as well as variations in the depositional processes. In addition, we studied up to 300 m long drilled sediment records recovered during ODP Leg 155 which allow evaluation of temporal variations on the Amazon fan. Our results reveal new evidence for a very rapid change of fan depositional processes and organic carbon source at times of sea-level change over the middle and lower Amazon fan. To estimate the amount of terrestrial organic carbon stored in sediments from the last glacial in the Amazon fan we used stable organic carbon isotopes of the OM (δ13Corg), organic carbon content (Corg), and age models based on oxygen isotopes, faunal data, and magnetic excursions. Following our results, the organic carbon accumulation on the Amazon deep sea fan is controlled by glacio-eustatic sea-level oscillations. Interglacial sea-level high stand sediments are dominated by marine OM whereas during glacial sea-level low stands terrestrial organic carbon is transported beyond the continental shelf through the Amazon canyon and deposited directly onto the Amazon deep sea fan. Glacial sediments of the Amazon fan stored approximately 73×1015 g terrestrial Corg in 20,000 years or 3.7×1012 g terrestrial Corg yr−1 (equivalent to 7–12% of the riverine organic carbon discharge; assuming constant paleo discharge), which is about the same amount of terrestrial organic carbon as deposited on the Amazon shelf today (3.1×1012 g terrestrial Corg yr−1 or 6–10% of the modern riverine organic carbon discharge).}, number={1-4}, journal={CHEMICAL GEOLOGY}, author={Schlunz, B and Schneider, RR and Muller, PJ and Showers, WJ and Wefer, G}, year={1999}, month={Jul}, pages={263–281} }
 @article{barrick_stoskopf_marcot_russell_showers_1998, title={The thermoregulatory functions of the Triceratops frill and horns: Heat flow measured with oxygen isotopes}, volume={18}, ISSN={["0272-4634"]}, DOI={10.1080/02724634.1998.10011103}, abstractNote={ABSTRACT Variability of body temperature within fossil vertebrates can be measured by the oxygen isotopie composition of bone phosphate (δp). Intrabone and interbone δp variations indicate heat flow within an individual and can be used to establish thermoregulatory strategies such as homeothermy and regional heterothermy. This method is applied to an individual Triceratops skeleton where the results suggest very high and uniform heat flow through the parietal frill, maintaining mean frill temperatures between 0–4°C below the body core. Heat flow to the postorbital horn-core is much more variable. The frill and horn cores of Triceratops were used as thermoregulatory structures with the horn cores interpreted as being especially important in the stabilization of brain temperatures at extreme ambient temperatures and the frill serving a more consistent role in body temperature regulation.}, number={4}, journal={JOURNAL OF VERTEBRATE PALEONTOLOGY}, author={Barrick, RE and Stoskopf, MK and Marcot, JD and Russell, DA and Showers, WJ}, year={1998}, month={Dec}, pages={746–750} }
 @article{bond_showers_cheseby_lotti_almasi_demenocal_priore_cullen_hajdas_bonani_1997, title={A pervasive millennial-scale cycle in North Atlantic Holocene and glacial climates}, volume={278}, ISSN={["0036-8075"]}, DOI={10.1126/science.278.5341.1257}, abstractNote={Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what is conventionally thought to have been a relatively stable Holocene climate. During each of these episodes, cool, ice-bearing waters from north of Iceland were advected as far south as the latitude of Britain. At about the same times, the atmospheric circulation above Greenland changed abruptly. Pacings of the Holocene events and of abrupt climate shifts during the last glaciation are statistically the same; together, they make up a series of climate shifts with a cyclicity close to 1470 ± 500 years. The Holocene events, therefore, appear to be the most recent manifestation of a pervasive millennial-scale climate cycle operating independently of the glacial-interglacial climate state. Amplification of the cycle during the last glaciation may have been linked to the North Atlantic's thermohaline circulation.}, number={5341}, journal={SCIENCE}, author={Bond, G and Showers, W and Cheseby, M and Lotti, R and Almasi, P and deMenocal, P and Priore, P and Cullen, H and Hajdas, I and Bonani, G}, year={1997}, month={Nov}, pages={1257–1266} }
 @article{showers_schneider_mikkelson_maslin_1997, title={Isotopic stratigraphy of Amazon fan sediments}, volume={155}, number={1997}, journal={Proceedings of the Ocean Drilling Program}, author={Showers, W. J. and Schneider, R. and Mikkelson, N. and Maslin, M.}, year={1997}, pages={281–303} }
 @article{betzer_showers_laws_winn_ditullio_kroopnick_1984, title={PRIMARY PRODUCTIVITY AND PARTICLE FLUXES ON A TRANSECT OF THE EQUATOR AT 153-DEGREES-W IN THE PACIFIC-OCEAN}, volume={31}, ISSN={["0198-0149"]}, DOI={10.1016/0198-0149(84)90068-2}, abstractNote={Abstract Primary productivity (14C) and mass flux measurements using a free-drifting sediment trap deployed at 900 m were made at four stations in the Pacific Ocean between 12°N and 6°S at 153°W. The latitudinal variations in productivity were consistent with historical patterns showing the equator as a zone of high production and the oligotrophic waters north of the equatorial region as an area of low productivity. The correlation coefficient between the two sets of independent measurements was 0.999, indicating that in this oceanic area the activity of the primary producers was closely related to the total mass flux. A re-examination of historical data suggests that the downward flux of particulate organic carbon varies in direct proportion to the quotient of surface primary production raised to the 1.4 power and depth raised to the 0.63 power.}, number={1}, journal={DEEP-SEA RESEARCH PART A-OCEANOGRAPHIC RESEARCH PAPERS}, author={BETZER, PR and SHOWERS, WJ and LAWS, EA and WINN, CD and DITULLIO, GR and KROOPNICK, PM}, year={1984}, pages={1–11} }