@article{burkholder_touchette_allen_alexander_rublee_2008, title={Environmental conditions, cyanobacteria and microcystin concentrations in potable water supply reservoirs in North Carolina, USA}, volume={619}, journal={Cyanobacterial harmful algal blooms: state of the science and research needs}, author={Burkholder, J. M. and Touchette, B. W. and Allen, E. H. and Alexander, J. L. and Rublee, P. A.}, year={2008}, pages={293–294} }
 @misc{touchette_burkholder_2007, title={Carbon and nitrogen metabolism in the seagrass, Zostera marina L.: Environmental control of enzymes involved in carbon allocation and nitrogen assimilation}, volume={350}, ISSN={["0022-0981"]}, DOI={10.1016/j.jembe.2007.05.034}, abstractNote={This study experimentally examined influences of environmental variables on the activities of key enzymes involved in carbon and nitrogen metabolism of the submersed marine angiosperm, Zostera marina L. Nitrate reductase activity in leaf tissue was correlated with both water-column nitrate concentrations and leaf sucrose levels. Under elevated nitrate, shoot nitrate reductase activity increased in both light and dark periods if carbohydrate reserves were available. When water-column nitrate was low, glutamine synthetase activity in leaf tissue increased with environmental ammonium. In contrast, glutamine synthetase activity in belowground tissues was statistically related to both nitrate and temperature. At the optimal growth temperature for this species (ca. 25 °C), increased water-column nitrate promoted an increase in glutamine synthetase activity of belowground tissues. As temperatures diverged from the optimum, this nitrate effect on glutamine synthetase was no longer evident. Activities of both sucrose synthase and sucrose-P synthase were directly correlated with temperature. Sucrose-P synthase activity also was correlated with salinity, and sucrose synthase activity was statistically related to tissue ammonium. Overall, the enzymatic responses that were observed indicate a tight coupling between carbon and nitrogen metabolism that is strongly influenced by prevailing environmental conditions, especially temperature, salinity, and environmental nutrient levels.}, number={1-2}, journal={JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY}, author={Touchette, Brant W. and Burkholder, JoAnn M.}, year={2007}, month={Nov}, pages={216–233} }
 @article{touchette_burkholder_allen_alexander_kinder_brownie_james_britton_2007, title={Eutrophication and cyanobacteria blooms in run-of-river impoundments in North Carolina, USA}, volume={23}, ISSN={["1040-2381"]}, DOI={10.1080/07438140709353921}, abstractNote={Abstract We compared monthly data taken during the dry summer growing season of 2002 in 11 potable water supply reservoirs (19–85 years old based on year filled) within the North Carolina Piedmont, including measures of watershed land use, watershed area, reservoir morphometry (depth, surface area, volume), suspended solids (SS), nutrient concentrations (total nitrogen, TN; total Kjeldahl nitrogen, TKN; nitrate + nitrite, NO3− + NO2−; total phosphorus, TP; total organic carbon), phytoplankton chlorophyll a (chla) concentrations, cyanobacteria assemblages, and microcystin concentrations from monthly data taken during the dry summer 2002 growing season. The reservoirs were considered collectively or as two subgroups by age as “mod.” (moderate age, 19–40 years post-fill, n = 5) and “old” (74–85 yr post-fill, n = 6). The run-of-river impoundments were meso-/eutrophic and turbid (means 25–125 μg TP/L, 410–1,800 μg TN/L, 3–70 μg chla/L and 5.7–41.9 mg SS/L). Under drought conditions in these turbid systems, there was a positive relationship between chla and both TN and TP, supported by correlation analyses and hierarchical ANOVA models. The models also indicated significant positive relationships between TN and TP, and between SS and both TP and TN. Agricultural land use was positively correlated with TKN for the reservoirs considered collectively, and with TN, TKN, TP, and chla in mod. reservoirs. In models considering the reservoirs by age group, TN:TP ratios were significantly lower and NO3− + NO2− was significantly higher in old reservoirs, and these relationships were stronger when reservoir age was used as a linear predictor. Cyanobacteria assemblages in the two reservoir age groups generally were comparable in abundance and species composition, and comprised 60–95% (up to 1.9 × 106 cells/mL) of the total phytoplankton cell number. Potentially toxic taxa were dominated by Cylindrospermopsis raciborskii and C. philippinensis. Although known microcystin producers were low in abundance, microcystin (< 0.8 μg/L) was detected in most samples. TP and chla were significant predictors of total cyanobacterial abundance. The data suggest that at present these turbid, meso-/eutrophic reservoirs have moderate cyanobacteria abundance and low cyanotoxin (microcystin) levels over the summer growing season, even in low-precipitation seasons that favor cyanobacteria. Accelerated eutrophication from further watershed development is expected to promote increased cyanobacterial abundance and adversely affect the value of these reservoirs as potable water supplies.}, number={2}, journal={LAKE AND RESERVOIR MANAGEMENT}, author={Touchette, Brant W. and Burkholder, Joann M. and Allen, Elie H. and Alexander, Jessica L. and Kinder, Carol A. and Brownie, Cavell and James, Jennifer and Britton, Clay H.}, year={2007}, month={Jun}, pages={179–192} }
 @misc{burkholder_tomasko_touchette_2007, title={Seagrasses and eutrophication}, volume={350}, ISSN={["1879-1697"]}, DOI={10.1016/j.jembe.2007.06.024}, abstractNote={This review summarizes the historic, correlative field evidence and experimental research that implicate cultural eutrophication as a major cause of seagrass disappearance. We summarize the underlying physiological responses of seagrass species, the potential utility of various parameters as indicators of nutrient enrichment in seagrasses, the relatively sparse available information about environmental conditions that exacerbate eutrophication effects, and the better known array of indirect stressors imposed by nutrient over-enrichment that influence seagrass growth and survival. Seagrass recovery following nutrient reductions is examined, as well as the status of modeling efforts to predict seagrass response to changing nutrient regimes. The most common mechanism invoked or demonstrated for seagrass decline under nutrient over-enrichment is light reduction through stimulation of high-biomass algal overgrowth as epiphytes and macroalgae in shallow coastal areas, and as phytoplankton in deeper coastal waters. Direct physiological responses such as ammonium toxicity and water-column nitrate inhibition through internal carbon limitation may also contribute. Seagrass decline under nutrient enrichment appears to involve indirect and feedback mechanisms, and is manifested as sudden shifts in seagrass abundance rather than continuous, gradual changes in parallel with rates of increased nutrient additions. Depending on the species, interactions of high salinity, high temperature, and low light have been shown to exacerbate the adverse effects of nutrient over-enrichment. An array of indirect effects of nutrient enrichment can accelerate seagrass disappearance, including sediment re-suspension from seagrass loss, increased system respiration and resulting oxygen stress, depressed advective water exchange from thick macroalgal growth, biogeochemical alterations such as sediment anoxia with increased hydrogen sulfide concentrations, and internal nutrient loading via enhanced nutrient fluxes from sediments to the overlying water. Indirect effects on trophic structure can also be critically important, for example, the loss of herbivores, through increased hypoxia/anoxia and other habitat shifts, that would have acted as “ecological engineers” in promoting seagrass survival by controlling algal overgrowth; and shifts favoring exotic grazers that out-compete seagrasses for space. Evidence suggests that natural seagrass population shifts are disrupted, slowed or indefinitely blocked by cultural eutrophication, and there are relatively few known examples of seagrass meadow recovery following nutrient reductions. Reliable biomarkers as early indicators of nutrient over-enriched seagrass meadows would benefit coastal resource managers in improving protective measures. Seagrasses can be considered as “long-term" integrators (days to weeks) of nutrient availability, especially through analyses of their tissue content, and of activities of enzymes such as nitrate reductase and alkaline phosphatase. The ratio of leaf nitrogen content to leaf mass has also shown promise as a “nutrient pollution indicator” for the seagrass Zostera marina, with potential application to other species. In modeling efforts, seagrass response to nutrient loading has proven difficult to quantify beyond localized areas because long-term data consistent in quality are generally lacking, and high inter-annual variability in abundance and productivity depending upon stochastic meteorological and hydrographic conditions. Efforts to protect remaining seagrass meadows from damage and loss under eutrophication, within countries and across regions, are generally lacking or weak and ineffective. Research needs to further understand about seagrasses and eutrophication should emphasize experimental studies to assess the response of a wider range of species to chronic, low-level as well as acute, pulsed nutrient enrichment. These experiments should be conducted in the field or in large-scale mesocosms following appropriate acclimation, and should emphasize factor interactions (N, P, C; turbidity; temperature; herbivory) to more closely simulate reality in seagrass ecosystems. They should scale up to address processes that occur over larger scales, including food-web dynamics that involve highly mobile predators and herbivores. Without any further research, however, one point is presently very clear: Concerted local and national actions, thus far mostly lacking, are needed worldwide to protect remaining seagrass meadows from accelerating cultural eutrophication in rapidly urbanizing coastal zones.}, number={1-2}, journal={JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY}, author={Burkholder, JoAnn M. and Tomasko, David A. and Touchette, Brant W.}, year={2007}, month={Nov}, pages={46–72} }
 @article{touchette_burkholder_glasgow_2003, title={Variations in eelgrass (Zostera marina L.) morphology and internal nutrient composition as influenced by increased temperature and water column nitrate}, volume={26}, ISSN={["0160-8347"]}, DOI={10.1007/BF02691701}, number={1}, journal={ESTUARIES}, author={Touchette, BW and Burkholder, JM and Glasgow, HB}, year={2003}, month={Feb}, pages={142–155} }
 @article{touchette_burkholder_2002, title={Seasonal variations in carbon and nitrogen constituents in eelgrass (Zostera marina L.) as influenced by increased temperature and water-column nitrate}, volume={45}, ISSN={["0006-8055"]}, DOI={10.1515/BOT.2002.004}, abstractNote={Abstract Fluctuations in nitrogen and carbon compounds were examined over an autumn growing season in the submersed marine angiosperm Zostera marina L. (eelgrass). The experimental design included replicated controls (ambient NO3 −, typically < 2 μM), increased water-column nitrate (8 μMNO3 − above ambient, pulsed daily), increased environmental temperature (3 to 4 °C above 20-year weekly means), and combined increased water-column nitrate and temperature. Above- and belowground tissues were collected weekly to biweekly and assayed for total soluble carbohydrates, non-reducing carbohydrates, starch, α-cellulose, lipids, free amino acids, total protein, tissue nitrate, tissue nitrite, and tissue ammonium. Tissue nitrate declined, and amino acids, proteins, lipids, and cellulose increased as the growing season progressed in both control and treated plants. In addition, there were seasonal quadratic responses for tissue ammonium, soluble carbohydrates, and non-reducing sugars, with maxima during periods of optimal plant growth (mid- to late September). Increased temperature promoted periodic increases in amino acids and soluble carbohydrates, but decreased accumulation of α-cellulose by the end of the experiment. Moreover, increases in water-column nitrate led to periodic increases in tissue ammonium and amino acids, as well as decreases in non-reducing sugars. Toward the end of the experiment, increases in soluble carbohydrates for plants grown under higher temperatures may have been associated with an extension of the growing season. In contrast, decreased non-reducing sugars in nitrate-enriched plants may have resulted from an increased carbon demand during nitrate assimilation/reduction, as well as a reallocation of carbon to enhance amino acid synthesis.}, number={1}, journal={BOTANICA MARINA}, author={Touchette, BW and Burkholder, JM}, year={2002}, month={Jan}, pages={23–34} }
 @article{touchette_burkholder_2001, title={Nitrate reductase activity in a submersed marine angiosperm: Controlling influences of environmental and physiological factors}, volume={39}, ISSN={["0981-9428"]}, DOI={10.1016/S0981-9428(01)01278-5}, abstractNote={In plants, nitrate reductase (NR; EC 1.6.6.1) is considered to be a key enzyme in nitrate assimilation. Therefore, the activity of NR as influenced by major environmental factors may affect the survival of many aquatic nitrogen-limited plant species. In this study, the in vivo activity of NR following exposure to increased water-column nitrate was examined in a submersed marine angiosperm (eelgrass, Zostera marina L.). NR activity was primarily localized in new leaf tissue, and was related to light and/or soluble carbohydrate availability. Under extended periods of darkness (18 h), enzyme activity decreased by more than 60 %. Nevertheless, in vivo NR activity was induced during dark periods provided that water-column nitrate (≥ 8 μM NO3–) was available. Enzyme activities were lower in plants that were exposed to hypoxic conditions (< 3.5 mg O2·L–1 for 14 h), and/or elevated growth temperatures (3 to 4 °C above mean weekly temperatures). In contrast, exposure to the atmosphere for 90 min promoted a significant increase in in vivo NR activity. A temporal investigation (14 weeks in autumn) revealed that the intensity of in vivo NR response to water-column nitrate was directly correlated with the quantity of soluble carbohydrates within the leaf tissue. Many of the observed in vivo NR responses were likely related to carbohydrate availability. During periods where soluble carbohydrate availability was expected to be low, in vivo NR response to increased water-column nitrate was substantially compromised.}, number={7-8}, journal={PLANT PHYSIOLOGY AND BIOCHEMISTRY}, author={Touchette, BW and Burkholder, J}, year={2001}, pages={583–593} }
 @article{touchette_burkholder_2000, title={Overview of the physiological ecology of carbon metabolism in seagrasses}, volume={250}, DOI={10.1016/S0022-0981(00)00196-9}, abstractNote={The small but diverse group of angiosperms known as seagrasses form submersed meadow communities that are among the most productive on earth. Seagrasses are frequently light-limited and, despite access to carbon-rich seawaters, they may also sustain periodic internal carbon limitation. They have been regarded as C3 plants, but many species appear to be C3-C4 intermediates and/or have various carbon-concentrating mechanisms to aid the Rubisco enzyme in carbon acquisition. Photorespiration can occur as a C loss process that may protect photosynthetic electron transport during periods of low CO(2) availability and high light intensity. Seagrasses can also become photoinhibited in high light (generally>1000 µE m(-2) s(-1)) as a protective mechanism that allows excessive light energy to be dissipated as heat. Many photosynthesis-irradiance curves have been developed to assess light levels needed for seagrass growth. However, most available data (e.g. compensation irradiance I(c)) do not account for belowground tissue respiration and, thus, are of limited use in assessing the whole-plant carbon balance across light gradients. Caution is recommended in use of I(k) (saturating irradiance for photosynthesis), since seagrass photosynthesis commonly increases under higher light intensities than I(k); and in estimating seagrass productivity from H(sat) (duration of daily light period when light equals or exceeds I(k)) which varies considerably among species and sites, and which fails to account for light-limited photosynthesis at light levels less than I(k). The dominant storage carbohydrate in seagrasses is sucrose (primarily stored in rhizomes), which generally forms more than 90% of the total soluble carbohydrate pool. Seagrasses with high I(c) levels (suggesting lower efficiency in C acquisition) have relatively low levels of leaf carbohydrates. Sucrose-P synthase (SPS, involved in sucrose synthesis) activity increases with leaf age, consistent with leaf maturation from carbon sink to source. Unlike terrestrial plants, SPS apparently is not light-activated, and is positively influenced by increasing temperature and salinity. This response may indicate an osmotic adjustment in marine angiosperms, analogous to increased SPS activity as a cryoprotectant response in terrestrial non-halophytic plants. Sucrose synthase (SS, involved in sucrose metabolism and degradation in sink tissues) of both above- and belowground tissues decreases with tissue age. In belowground tissues, SS activity increases under low oxygen availability and with increasing temperatures, likely indicating increased metabolic carbohydrate demand. Respiration in seagrasses is primarily influenced by temperature and, in belowground tissues, by oxygen availability. Aboveground tissues (involved in C assimilation and other energy-costly processes) generally have higher respiration rates than belowground (mostly storage) tissues. Respiration rates increase with increasing temperature (in excess of 40 degrees C) and increasing water-column nitrate enrichment (Z. marina), which may help to supply the energy and carbon needed to assimilate and reduce nitrate. Seagrasses translocate oxygen from photosynthesizing leaves to belowground tissues for aerobic respiration. During darkness or extended periods of low light, belowground tissues can sustain extended anerobiosis. Documented alternate fermentation pathways have yielded high alanine, a metabolic 'strategy' that would depress production of the more toxic product ethanol, while conserving carbon skeletons and assimilated nitrogen. In comparison to the wealth of information available for terrestrial plants, little is known about the physiological ecology of seagrasses in carbon acquisition and metabolism. Many aspects of their carbon metabolism - controls by interactive environmental factors; and the role of carbon metabolism in salt tolerance, growth under resource-limited conditions, and survival through periods of dormancy - remain to be resolved as directions in future research. Such research will strengthen the understanding needed to improve management and protection of these environmentally important marine angiosperms.}, number={1-2}, journal={Journal of Experimental Marine Biology and Ecology}, author={Touchette, B. W. and Burkholder, J. M.}, year={2000}, pages={169–205} }
 @misc{touchette_burkholder_2000, title={Review of nitrogen and phosphorus metabolism in seagrasses}, volume={250}, ISSN={["1879-1697"]}, DOI={10.1016/S0022-0981(00)00195-7}, abstractNote={Within the past few decades, major losses of seagrass habitats in coastal waters impacted by cultural eutrophication have been documented worldwide. In confronting a pressing need to improve the management and protection of seagrass meadows, surprisingly little is known about the basic nutritional physiology of these critical habitat species, or the physiological mechanisms that control their responses to N and P gradients. The limited available evidence to date already has revealed, for some seagrass species such as the north temperate dominant Zostera marina, unusual responses to nutrient enrichment in comparison to other vascular plants. Seagrasses derive N and P from sediment pore water (especially ammonium) and the water column (most nitrate). The importance of leaves versus roots in nutrient acquisition depends, in part, on the enrichment conditions. For example, a shift from reliance on sediment pore water to increased reliance on the overlying water for N and P supplies has been observed under progressive water-column nutrient enrichment. Seagrasses may be N-limited in nutrient-poor waters with sandy or (less so) organic sediments, and P-limited in carbonate sediments. On the basis of data from few species, seagrasses appear to have active uptake systems for NO3− and PO4−3, but NH4+ uptake may involve both low- and high-affinity systems. Pi uptake affinities reported thus far are much lower than values for active ammonium uptake, but comparable to values for nitrate uptake by leaf tissues. Beyond such basic information, seagrass species have shown considerable variation in nutritional response. Dominance of acropetal versus basipetal nutrient translocation appears to vary among species as an innate trait. While some species follow classic Michaelis–Menten kinetics for Ni uptake, others have exhibited sustained linear uptake with limited or negligible product feedback inhibition, perhaps in adaptation to oligotrophic environments. Zostera marina also is able to maintain nitrate reductase (NR) activity during dark periods if adequate carbohydrate reserves and substrate are available. Thus, this species can respond to nitrate pulses throughout a diel cycle, rather than being limited as most plants to nitrate uptake during the light period. Further adaptations may have occurred for seagrasses in extremely nitrate-depauperate conditions. For example, Halophila decipiens and H. stipulacea lack inducible NR and apparently have lost the ability to reduce nitrate; and a biphasic rather than hyperbolic Pi uptake curve, with ‘surge’ uptake, has been described for Zostera noltii. Many seagrasses respond favorably to low or moderate N and/or P enrichment. However, excessive Ni loading to the water column can inhibit seagrass growth and survival, not only as an indirect effect by stimulating algal overgrowth and associated light reduction, but—for some species—as a direct physiological effect. The latter direct impact has been most pronounced for plants growing in sandy (nutrient-poor) sediments, and is exacerbated by elevated temperatures and/or light reduction. Ammonia toxicity, known for many vascular plants, has been reported in seagrasses Ruppia drepanensis and Z. marina (125 μM water-column NH4+, 5 weeks). Z. marina has shown to be inhibited, as well, by pulsed water-column nitrate enrichment (as low as 3.5–7 μM NO3−, 3–5 weeks), which is actively taken up without apparent product feedback inhibition. Inhibition by elevated nitrate has also been reported, with description of the underlying physiological mechanisms, in certain macroalgae and microalgae. In Z. marina, this effect has been related to the high, sustained energy demands of nitrate uptake, and to inducement of internal carbon limitation by the concomitant ‘carbon drain’ into amino acid assimilation. In contrast, nitrate enrichment can stimulate growth of Z. marina when the sediment, rather than the water column, is the source. Because seagrass species have shown considerable variation in nutritional response, inferences about one well-studied species, from one geographic location, should not be applied a priori to that species in other regions or to seagrasses in general. Most of the available information has been obtained from study of a few species, and the basic nutritional physiology of many seagrasses remains to be examined and compared across geographic regions. Nonetheless, the relatively recent gains in general understanding about the physiological responses of some seagrass species to nutrient gradients already have proven valuable in both basic and applied research. For example, physiological variables such as tissue C:N:P content have begun to be developed as integrative indicators of nutrient conditions and anthropogenic nutrient enrichment. To strengthen insights for management strategies to optimize seagrass survival in coastal waters adjacent to exponential human population growth and associated nutrient inputs, additional emphasis is critically needed to assess the role of variable interactions—among inorganic as well as organic N, P and C, environmental factors such as temperature, light, and other community components—in controlling the physiology, growth and survival of these ecologically important marine angiosperms.}, number={1-2}, journal={JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY}, author={Touchette, BW and Burkholder, JM}, year={2000}, month={Jul}, pages={133–167} }
 @article{mallin_burkholder_mciver_shanks_glasgow_touchette_springer_1997, title={Comparative effects of poultry and swine waste lagoon spills on the quality of receiving streamwaters}, volume={26}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1997.00472425002600060023x}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Mallin, MA and Burkholder, JM and McIver, MR and Shanks, GC and Glasgow, HB and Touchette, BW and Springer, J}, year={1997}, pages={1622–1631} }
 @article{burkholder_mallin_glasgow_larsen_mciver_shank_deamer-melia_briley_springer_touchette_et al._1997, title={Impacts to a coastal river and estuary from rupture of a large swine waste holding lagoon}, volume={26}, ISSN={["0047-2425"]}, DOI={10.2134/jeq1997.00472425002600060003x}, abstractNote={Abstract}, number={6}, journal={JOURNAL OF ENVIRONMENTAL QUALITY}, author={Burkholder, JM and Mallin, MA and Glasgow, HB and Larsen, LM and McIver, MR and Shank, GC and Deamer-Melia, N and Briley, DS and Springer, J and Touchette, BW and et al.}, year={1997}, pages={1451–1466} }