Source: UNIVERSITY OF NORTH CAROLINA submitted to NRP
MANDATED NITROGEN LOADING REDUCTIONS TO THE HYDRODYNAMICALLY VARIABLE NEUSE RIVER ESTUARY, NC: IMPLICATIONS FOR PHYTOPLANKTON COMMUNITY...
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
NRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
0186477
Grant No.
00-35101-9281
Cumulative Award Amt.
(N/A)
Proposal No.
2000-00609
Multistate No.
(N/A)
Project Start Date
Sep 1, 2000
Project End Date
Aug 31, 2004
Grant Year
2000
Program Code
[(N/A)]- (N/A)
Recipient Organization
UNIVERSITY OF NORTH CAROLINA
(N/A)
MOREHEAD CITY,NC 28557
Performing Department
INST OF MARINE SCIENCE
Non Technical Summary
Eutrophication and associated declines in water quality in the Neuse River Estuary, NC, have been linked to growing inputs of non-point source nitrogen (N), half of which are of agricultural origin. In response to public concern, a 30% reduction in N loading to the Neuse Estuary was legislatively mandated to be in place by 2003. General agreement exists that such a reduction is appropriate, but the ecological ramifications are unknown. Our prior USDA-supported research indicates that the timing and magnitude of N inputs are strong determinants of ecosystem response to N loading. Using a complementary combination of experimental and field-based research, we will examine potential impacts on ecosystem structure and function at the base of the food web. This will allow us to better predict short and long term ecosystem responses to the proposed nutrient reductions. Overall, our work will yield a better understanding of, and rationale for, evaluating nutrient management strategies designed to reverse eutrophication and restore natural ecosystem function to estuarine ecosystems experiencing excessive nutrient loading.
Animal Health Component
50%
Research Effort Categories
Basic
50%
Applied
50%
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1120210107050%
1120210110325%
1120210119025%
Knowledge Area
112 - Watershed Protection and Management;

Subject Of Investigation
0210 - Water resources;

Field Of Science
1103 - Other microbiology; 1070 - Ecology; 1190 - Limnology;
Goals / Objectives
Our overall hypothesis is that a mandated 30% reduction in total dissolved nitrogen input will lead to an overall reduction in phytoplankton productivity and growth, and that differential responses to reductions in specific forms of nitrogen will lead to group-specific phytoplankton growth responses (resulting in variations in phytoplankton community structure). These effects, in turn, will affect higher trophic levels (e.g. zooplankton grazing). We will evaluate the impacts of total and compound specific (nitrate, ammonium) reductions on N uptake kinetics, primary productivity and growth of phytoplankton under seasonally and inter-annually varying hydrologic and climatic condtions in the NRE. These effects will be manifested as differences in phytoplankton community structure (algal group composition) and function (nutrient cycling, oxygen dynamics). We will also examine the potential effects of alterations in phytoplankton community structure on zooplankton grazing. Finally, we will provide information on phytoplankton group specific growth and loss (by grazing) responses to nitrogen reductions for the development and validation of the Neuse Estuary Eutrophication Model.
Project Methods
Neuse River Estuary water samples will be manipulated in bioassays to assess changes in nitrogen and carbon utilization resulting from a range of exogenous nitrogen load reduction scenarios. Nitrogen reductions (nutrient dilution bioassays) will be compared to treatments reflecting no reductions and further enrichment (nutrient enrichment bioassays). Measurements of phytoplankton community structure and function will include primary productivity (14C uptake), nutrient uptake kinetics (15N enrichment) and taxanomic composition (diagnostic photopigment analysis). Counting both zooplankton and their eggs will assess effects on trophic transfer to zooplankton. Bioassays will be conducted bimonthly on phytoplankton communities from two sites representative of the freshwater (0 psu) and mesohaline (5-15 psu) regions of the estuary. This will allow us to assess both temporal and spatial variabillity in ecosystem structure and function.

Progress 09/01/00 to 08/31/04

Outputs
The Neuse River Estuary (NRE) and Pamlico Sound (PS) have been subjected to significant anthropogenic nutrient stress. North Carolina has adopted a nitrogen (N) loading cap and mandated a 30% reduction in N loading to the system by 2003. Nutrient bioassays were conducted to assess changes in the phytoplankton community that may result from changing nutrient conditions. Experiments compared the response to an increase or decrease in the concentration of a limiting nutrient and the addition of all probable limiting compounds except that nutrient. In the NRE phytoplankton productivity and biomass data showed that N availability was primarily limiting and phosphorus availability was only occasionally secondarily limiting. Data from these bioassays indicated that the phytoplankton community in PS is primarily nitrogen (N) limited. Dissolved inorganic nitrogen concentrations in PS were relatively stable during this study. The biology of its estuarine tributaries, as has been shown for the Neuse River Estuary (NRE), acted as an effective filter for most of the nutrients transported from upstream. We found stoichiometric predictors of phytoplankton community nutrient limitations (e.g. N:P ratios) to be reliable in some instances, but inaccurate in others. Results indicated that changes in the PS phytoplankton community could result from changes in nutrient regime, and changes may not be consistent across phytoplankton taxonomic groups. Unlike the NRE where pulses of riverine N have significant effects on phytoplankton community structure, the PS phytoplankton community did not appear to be subjected to these periodic N enrichments. Data from these bioassays assessed the relationship of the NRE and PS phytoplankton communities and current nutrient conditions, and will allow prediction of changes that may occur in the future. The uptake rates of ammonium, nitrate and urea were measured during the spring, summer and autumn (2001) in the NRE. Ammonium was the dominant form of N taken up during the study, contributing approximately half of the total measured N uptake throughout the estuary. Nitrate uptake declined significantly with distance downstream. While, urea uptake contributed least to the total pool in the upper estuary, but increased in importance in the middle and lower estuary. The importance of regenerated N for fuelling phytoplankton productivity in the mesohaline sections of the NRE was demonstrated. The contribution of urea to the regenerated N pool suggests that internal regeneration of DON may support a large proportion of the phytoplankton primary production and biomass accumulation in the middle and lower NRE. These results suggest that N-budgets based on DIN uptake rates alone may under estimate phytoplankton N uptake.

Impacts
Data generated by this study are contributing to a better understanding of the effects of variations in Neuse River Estuary nutrient conditions on the native phytoplankton community. This information provides scientific validation for nutrient control strategies to control unwanted phytoplankton growth.

Publications

  • Peierls, B.L., R.R. Christian and H.W. Paerl. 2003. Water Quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem. Estuaries 26:1329-1343.
  • Paerl, H.W. J. Dyble, L. Twomey, J. L. Pinckney, J. Nelson and L. Kerkhof. 2002. Characterizing man-made and natural modifications of microbial diversity and activity in coastal ecosystems: Antonie van Leeuwenhoek 81:487-507.
  • Paerl, H.W. 2002. Connecting atmospheric deposition to coastal eutrophication. Environ. Sci. Technol. 36, No.15:323A-326A.
  • Piehler, MF, J. Dyble, PH Moisander, JL Pinckney and HW Paerl. 2002. Effects of modified nutrient concentrations and ratios on the structure and function of the native phytoplankton community in the Neuse River Estuary, North Carolina USA. Aquatic Ecology 36: 371-385.
  • Paerl, H.W., L. M. Valdes, A.R. Joyner, M. F. Piehler and M.E. Lebo. 2004. Solving problems resulting from solutions: The evolution of a dual nutrient management strategy for the eutrophying Neuse River Estuary, North Carolina, USA. Environmental Science and Technology 38: 3068-3073.
  • Walker, J.T., D.R. Whitall, W Robarge, and H.W. Paerl. 2004. Ambient ammonia and ammonium aerosols across a region of variable ammonia emission density. Atmospheric Environment 38:1235-1246.
  • Swackhamer, D.L., H.W. Paerl, S.J. Eisenreich, J. Hurley, K.C. Hornbuckle, M. McLachlan, D. Mount, D. Muir, and D. Schindler. 2004. Impacts of atmospheric pollutant on aquatic ecosystems. Issues in Ecology 12, Ecological Society of America, Washington, DC.
  • Whitall, D., B. Hendrickson and H. W. Paerl. 2003. Importance of atmospherically deposited nitrogen to the annual nitrogen budget of the Neuse River estuary, North Carolina. Environment International 29:393-399.
  • Paerl, H.W. and T.F. Steppe 2003. Scaling up: The next challenge in environmental microbiology. Environmental Microbiology 5(11): 1025-1038.
  • Piehler, MF, SP Thompson, J Dyble, PH Moisander, J Fear and HW Paerl. 2002. Biologically mediated nitrogen cycling in the Neuse River Estuary. UNC Water Resources Research Institute Report #339.
  • Paerl, H.W., R. S. Fulton, P.H. Moisander and J. Dyble. 2001. Harmful Freshwater Algal Blooms, With an Emphasis on Cyanobacteria. The Scientific World 1:76-113.
  • Paerl, H.W., J. D. Bales, L.W. Ausley, C.P. Buzzelli, L.B. Crowder, L.A. Eby, J. M. Fear, M. Go, B.L. Peierls, T.L. Richardson and J.S. Ramus. 2001. Ecosystem impacts of 3 sequential hurricanes (Dennis, Floyd and Irene) on the US largest lagoonal estuary, Pamlico Sound, NC. Proceedings of the National Academy of Science. USA. 98(10):5655-5660.
  • Paerl, H. W, R. L. Dennis and D. R. Whitall. 2001. Atmospheric deposition of nitrogen: Implications for nutrient over-enrichment of coastal waters. Estuaries (In press).
  • Pinckney, J. L., T. L. Richardson, D. F. Millie, H. W. Paerl. 2001. Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates. Organic Geochemistry 32:585-595.
  • Richardson, T.L., J.L. Pinckney and H. W. Paerl. 2001. Responses of estuarine phytoplankton communities to nitrogen form and mixing using microcosm bioassays. Estuaries 24(6A): 828-839.
  • Paerl, H. W. (2000). Primary Productivity and Producers. In C. J. Hurst (ed.) Manual of Environmental Microbiology (2nd Ed.). ASM Press, Washington, DC.
  • Paerl, H. W., J. D. Bales, L. W. Ausley, C. P. Buzzelli, L. B. Crowder, L. A. Eby, M. Go, B. L. Peierls, T. L. Richardson, and J. S. Ramus. 2000. Hurricanes hydrological, ecological effects linger in major US estuary. EOS 81(40):457-462.
  • Pinckney, J. L., H. W.Paerl, E. Haugen and P. A. Tester. 2000. Repsonse of phytoplankton and Pfiesteria-like dinoflagellate zoospores to nutrient enrichment in the Neuse River Estuary, North Carolina, USA. Marine Ecology Progress Series 192:65-78.
  • Twomey, LJ, MF Piehler and HW Paerl. 2004. Phytoplankton uptake of ammonium, nitrate and urea in the Neuse River Estuary, NC, USA. In press, Hydrobiologia.
  • Piehler, MF, LJ Twomey, NS Hall and HW Paerl. 2004. Impacts of inorganic nutrient enrichment on the phytoplankton community structure and function in Pamlico Sound, NC USA. Estuarine, Coastal and Shelf Science 61(2) 197-209.
  • Paerl, H.W., J. Dyble, J.L. Pinckney, L.M. Valdes, D.F. Millie, P.H. Moisander, J.T. Morris, B. Bendis, and M.F. Piehler. 2004. Using microalgal indicators to assess human and climatically induced ecological change in estuaries. Estuarine Indicators, S.A. Bartone (Ed). CRC Press, Boca Raton, Florida.


Progress 10/01/02 to 09/30/03

Outputs
Changes in phytoplankton community composition that may result from increased frequency and quantity of inorganic nutrient inputs could have negative ecological effects on Pamlico Sound (PS) in North Carolina. We conducted a series of nutrient bioassays to assess the relationship between increased inorganic nutrient concentration and phytoplankton community structure and function. Experiments were conducted on the native phytoplankton community of the southwest basin of PS. We utilized nutrient addition treatments and all-but-one nutrient treatments together in bioassays. This allowed the comparison of the effect of adding one potentially growth limiting nutrient (e.g. nitrogen) to adding all potentially limiting nutrients except one (e.g. all except nitrogen). Data from these bioassays indicated that the phytoplankton community in PS is primarily nitrogen (N) limited. Nutrient concentrations in PS were not very variable during this study. The biology of its estuarine tributaries, as has been shown for the Neuse River Estuary (NRE), acted as an effective filter for most of the nutrients transported from upstream. We found stoichiometric predictors of phytoplankton community nutrient limitations to be reliable in some instances, but inaccurate in others. Some taxa-specific responses to nutrient additions were observed, however there were not consistent patterns throughout the experiments. Results indicated that changes in the PS phytoplankton community could result from changes in nutrient regime, and changes may not be consistent across phytoplankton taxonomic groups. Phytoplankton community structuring in PS appeared to be largely unaffected by discharge related pulses of nutrients as seen in the NRE. Events like hurricanes and enhanced precipitation associated with El Nino Southern Oscillation are likely among the few events large enough to affect short-term phytoplankton community dynamics in the PS. Uptake rates of ammonium, nitrate and urea were measured during the spring, summer and autumn (2001) in the eutrophic, nitrogen (N) limited Neuse River Estuary, North Carolina. Ammonium was the dominant form of N taken up during the study, contributing approximately half of the total measured N uptake throughout the estuary. Nitrate uptake declined significantly with distance downstream comprising 33% of the total uptake in the upper estuary but only 11% and 16% in the middle and lower estuary respectively. Urea uptake contributed least to the total pool in the upper estuary (16%), but increased in importance in the middle and lower estuary, comprising 45% and 37% of the total N taken up respectively. The importance of regenerated N for fuelling phytoplankton productivity in the mesohaline sections of the NRE was demonstrated. The contribution of urea to the regenerated N pool suggests that internal regeneration of DON may support a large proportion of the phytoplankton primary production and biomass accumulation in the middle and lower NRE. These results suggest that N-budgets based on DIN uptake rates alone will seriously under estimate phytoplankton N uptake.

Impacts
Data generated by this study are contributing to a better understanding of the effects of variations in Neuse River Estuary nutrient conditions on the native phytoplankton community. This information provides scientific validation for nutrient control strategies to control unwanted phytoplankton growth.

Publications

  • Moisander, P.H., E. McClinton III and H.W. Paerl. 2002. Salinity effects on growth, photosynthetic parameters, and nitrogenase activity in estuarine planktonic cyanobacteria. Microb. Ecol. 43:432-442.
  • Paerl, H.W., J. Dyble, P.H. Moisander, R.T. Noble, M.F. Piehler, J.T. Pinckney, L. Twomey and L.M. Valdes. 2003. Microbial Indicators of Aquatic Ecosystem Change: Current Applications to Eutrophication Studies. FEMS Microbial Ecology 46 (3):233-246.
  • Paerl, H.W., L.M. Valdes, J.L. Pinckney, M.F. Piehler, J. Dyble and P.H. Moisander. 2003. Phytoplankton photopigments as Indicators of Estuarine and Coastal Eutrophication. BioScience 53(10) 953-964.
  • Paerl, H.W. and T.F. Steppe 2003. Scaling up: The next challenge in environmental microbiology. Environmental Microbiology 5(11): 1025-1038.
  • Paerl, H.W. and J. Kuparinen. 2002. Microbial aggregates and consortia. In: G. Bitton (Ed). Encyclopedia of Environmental Microbiology, Vol. 1, p. 160-181. John Wiley and Sons, Inc. New York, NY.
  • Paerl, H.W, R. L. Dennis and D. R. Whitall. 2002. Atmospheric deposition of nitrogen: Implications for nutrient over-enrichment of coastal waters. Estuaries 25:677-693.
  • Peierls, B.L., R.R. Chrtistian & H.W. Paerl. 2003. Water Quality and phytoplankton as indicators of hurricane impacts on a large estuarine ecosystem. Estuaries 26:1329-1343.
  • Whitall, D., B. Hendrickson and H. W. Paerl. 2003. Importance of atmospherically deposited nitrogen to the annual nitrogen budget of the Neuse River estuary, North Carolina. Environment International 29:393-399.


Progress 10/01/01 to 09/30/02

Outputs
Experimental and field monitoring activities are continuing in the Neuse River Estuary (NRE). Nutrient bioassays in the system have continued to yield information about the relationship of nutrient regime and phytoplankton community structure and function. Considerable data have been generated using 15N labelled nitrogenous compounds to track the kinetics of form-specific utilization of nitrogen (N) by phytoplankton. Preliminary results indicate that the NRE can be separated into three types of phytoplankton populations, the upper estuary is dominated by freshwater species, the middle estuary by brackish species and the lower estuary is dominated by brackish/marine species. At any time the estuary may house a variety of different, spatially separate phytoplankton communities with very different cellular N requirements and abilities to take up various forms of N. Therefore, there is considerable spatial and temporal variability in N uptake in the NRE, which is dependent on changes to the physical, chemical and biological environment. Throughout the estuary N uptake was greatest during late spring, summer and early fall and lowest in the winter. In the upper estuary ammonium was taken up at higher rates than nitrate, and these forms were preferred to urea, which only contributed approximately 5% of the total measured N uptake in the upper estuary. In the mid-estuary ammonium dominated N uptake (approximately 60% annual N uptake) and urea was taken up at much greater rates than in the upper estuary, however there were often only very low concentrations of urea present. Urea constituted approximately 30-35% of total annual measured N uptake. Nitrate was least preferred and represented approximately 5-10% of the total annual measured N uptake. This was likely attributable to the concentration gradient of nitrate in the estuary, with much higher concentrations recorded in the upper estuary, and lower concentrations with increasing distance downstream. In the lower estuary phytoplankton showed similar preference for ammonium and urea, however ammonium uptake was greater and probably related to higher supply rates. Ammonium represented 50-55% of the total annual N uptake, urea 40-45% and nitrate 0-5%.

Impacts
Data generated by this study are contributing to a better understanding of the effects of variations in Neuse River Estuary nutrient conditions on the native phytoplankton community. This information provides scientific validation for nutrient control strategies to control unwanted phytoplankton growth.

Publications

  • Paerl, H.W. J. Dyble, L. Twomey, J. L. Pinckney, J. Nelson and L. Kerkhof. 2002. Characterizing man-made and natural modifications of microbial diversity and activity in coastal ecosystems: Antonie van Leeuwenhoek 81:487-507.
  • Paerl, H.W. 2002. Connecting atmospheric deposition to coastal eutrophication. Environ. Sci. Technol. 36, No.15:323A-326A.
  • Piehler, MF, J. Dyble, PH Moisander, JL Pinckney and HW Paerl. 2002. Effects of modified nutrient concentrations and ratios on the structure and function of the native phytoplankton community in the Neuse River Estuary, North Carolina USA. Aquatic Ecology 36: 371-385.
  • Piehler, MF, SP Thompson, J Dyble, PH Moisander, J Fear and HW Paerl. 2002. Biologically mediated nitrogen cycling in the Neuse River Estuary. UNC Water Resources Research Institute Report #339.
  • Richardson, T.L., J.L. Pinckney and H. W. Paerl. 2001. Responses of estuarine phytoplankton communities to nitrogen form and mixing using microcosm bioassays. Estuaries 24(6A): 828-839.


Progress 10/01/00 to 09/30/01

Outputs
The Neuse River Estuary (NRE) and Pamlico Sound (PS) have been subjected to significant anthropogenic nutrient stress. North Carolina has adopted a nitrogen (N) loading cap and mandated a 30% reduction in N loading to the system by 2003. Nutrient bioassays are being conducted to assess changes in the phytoplankton community that may result from changing nutrient conditions. Experiments compared the response to an increase or decrease in the concentration of a limiting nutrient and the addition of all probable limiting compounds except that nutrient. Bioassays included nutrient addition, nutrient dilution and all but one treatments at a mesohaline NRE site. HPLC diagnostic photopigment analyses and microscopic voucher counts are being conducted to determine the effects on phytoplankton community composition. Phytoplankton productivity and biomass data show that N availability was primarily limiting and phosphorus availability was only occasionally secondarily limiting in the NRE. Data from these bioassays assessed the relationship of the NRE phytoplankton community and current nutrient conditions, and will allow prediction of changes that may occur in the future. Estimates of N uptake by the phytoplankton community provide important process information to enable evaluation of phytoplankton physiological, functional and compositional responses to different N forms. Using 15N labeled substrates, estimates of phytoplankton community uptake of ammonium, nitrate and urea were conducted at bi-weekly intervals at three sites in NRE. Measurements of N concentration uptake kinetics were made at quarterly periods throughout the year to evaluate concentration dependent uptake rates and to determine the potential in situ and maximum uptake rates. Preliminary results suggest that in the NRE-PS ammonium was taken up more rapidly than nitrate and urea. Urea was taken up at a rate similar to supply and nitrate was taken up at much lower rates. We will continue nutrient bioassays and nutrient uptake experiments. The zooplankton component of the project will be further developed and integrated, and the nutritional analyses of phytoplankton will continue to assess trophic impacts of changing nutrient regimes. Our progress has matched or exceeded the goals outlined in our proposal.

Impacts
Details about the relationship between phytoplankton growth and composition and nutrient concentrations in the Neuse River Estuary and Pamlico Sound will allow better predictions of the effectiveness of the current nutrient management strategy. Additionally, this information will be valuable to support any modifications of the nutrient management plans that may be required.

Publications

  • Paerl, H. W. (2000). Primary Productivity and Producers. In C. J. Hurst (ed.) Manual of Environmental Microbiology (2nd Ed.). ASM Press, Washington, DC (in press).
  • Paerl, H. W., J. D. Bales, L. W. Ausley, C. P. Buzzelli, L. B. Crowder, L. A. Eby, M. Go, B. L. Peierls, T. L. Richardson, and J. S. Ramus. 2000. Hurricanes' hydrological, ecological effects linger in major US estuary. EOS 81(40):457-462.
  • Pinckney, J. L., H. W.Paerl, E. Haugen and P. A. Tester. 2000. Repsonse of phytoplankton and Pfiesteria-like dinoflagellate zoospores to nutrient enrichment in the Neuse River Estuary, North Carolina, USA. Marine Ecology Progress Series 192:65-78.
  • Paerl, H.W., R. S. Fulton, P.H. Moisander and J. Dyble. 2001. Harmful Freshwater Algal Blooms, With an Emphasis on Cyanobacteria. The Scientific World 1:76-113.
  • Paerl, H.W., J. D. Bales, L.W. Ausley, C.P. Buzzelli, L.B. Crowder, L.A. Eby, J. M. Fear, M. Go, B.L. Peierls, T.L. Richardson and J.S. Ramus. 2001. Ecosystem impacts of 3 sequential hurricanes (Dennis, Floyd and Irene) on the US's largest lagoonal estuary, Pamlico Sound, NC. Proceedings of the National Academy of Science. USA. 98(10):5655-5660.
  • Paerl, H. W, R. L. Dennis and D. R. Whitall. 2001. Atmospheric deposition of nitrogen: Implications for nutrient over-enrichment of coastal waters. Estuaries (In press).
  • Pinckney, J. L., T. L. Richardson, D. F. Millie, H. W. Paerl. 2001. Application of photopigment biomarkers for quantifying microalgal community composition and in situ growth rates. Organic Geochemistry 32:585-595.