Grantee Research Project Results
Final Report: CISNet: Nutrient Inputs as a Stressor and Net Nutrient Flux as an Indicator of Stress Response in Delaware's Inland Bays Ecosystem
EPA Grant Number: R826945Title: CISNet: Nutrient Inputs as a Stressor and Net Nutrient Flux as an Indicator of Stress Response in Delaware's Inland Bays Ecosystem
Investigators: Ullman, William J. , Krantz, David E. , McKenna, Thomas E. , Madsen, John M. , Scudlark, Joseph R. , Andres, A. Scott , Wong, Kuo-Chuin
Institution: University of Delaware , University of Toledo
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1998 through September 30, 2001 (Extended to September 30, 2002)
Project Amount: $600,000
RFA: Ecological Effects of Environmental Stressors Using Coastal Intensive Sites (1998) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
This research project focused on the Delaware Inland Bays watershed, a member of the common, but understudied, class of shallow estuarine ecosystems. The objective of this research project was to document the fluxes of nutrients (nitrogen [N], phosphorus [P], and organic carbon) to and from the Bays. This watershed receives excessive nutrient fluxes from agricultural, municipal, domestic, and industrial sources. These inputs lead to a number of undesirable consequences of eutrophication in the Bays. The specific objectives of this research project were to: (1) determine the sources, magnitudes, and spatial and temporal variability of nutrient fluxes to the Bays; (2) assess the magnitude of nutrient sinks in this system; and (3) develop conceptual and simple quantitative models that relate these nutrient inputs and outputs to more easily measured and monitored hydrological forcing parameters, such as precipitation, temperature, wind speed and direction, season, groundwater levels, and surface-water discharge.
Summary/Accomplishments (Outputs/Outcomes):
Previous work on nutrient loadings from tributaries to the Inland Bays have used land-use/land-cover information together with estimated land-use loading rates to determine annual loads. The present work has tried to use recently available estimates of baseflow and storm loads to verify or improve on these estimates. Most recently, we used a more explicit hydrographic separation of baseflow and storm loadings from which to estimate monthly, seasonal, and annual nutrient loads associated with baseflow and storm discharges. At the best-studied stormwater site, Bundicks Branch, a hydrographic separation technique that takes into account the reduction of baseflow loads during and immediately after storms was applied successfully to estimate (N) and (P) loads. At this site, however, nutrients also flow under the gauging/sampling station through the permeable coastal plain sediments of this watershed. The underflow component of discharge was estimated based on the hydrological balance at the Millsboro Pond station, where it is reasonable to assume, based on the size of the watershed, that there is negligible underflow. Evapotranspiration rates estimated at Millsboro Pond then were applied to Bundicks Branch to estimate underflow. On the basis of this analysis and studies of the time variation of nutrient concentrations, dissolved N loads may be estimated with a precision of approximately 10 percent and dissolved P and dissolved organic carbon (DOC) loads with a precision of 15 percent. Particulate species, however, are substantially more variable and the precision of particulate loads is typically about 40 to 50 percent. Measured annual loads of N from Bundicks Branch are similar to those estimated by previous studies of land use using regional land-use loading factors. Measured loads of P, however, are substantially lower than previous estimates based on land use. Assuming that Bundicks Branch is a good model for the Rehoboth Bay watershed, these results were used to calculate the monthly, seasonal, and annual loads of P and N to this bay. On an annual basis, the watershed typically contributes less than 75 percent of the N reaching Rehoboth Bay, while atmospheric deposition and the Rehoboth Beach Wastewater Treatment Plant (RBWTP) contribute 17 and 4 percent of the N load, respectively. These results are similar to previously reported estimates. For P, however, annual loads to Rehoboth Bay come about equally from the watershed and the RBWTP, with 14 percent contributed from atmospheric deposition. In the summer, when discharges from the watershed are at their minimum and the discharge from RBWTP is at its maximum, RBWTP may contribute up to 78 percent of the total load to the bay. These results confirm our hypothesis that the RBWTP is responsible for the high levels of P (in excess of available N based on the Redfield stoichiometry) found in Rehoboth Bay during the summer.
Passive samplers were used to monitor gaseous ammonia, (NH3[g]), concentrations around some poultry houses in the Inland Bays watershed. The results of the passive sampling of NH3(g) were compared with the results of a well-established gas scrubber method and found to give essentially identical results to the more common method. The samplers can be used over the wide range of concentrations found in agricultural regions by varying the deployment interval. The results of sampling at one poultry house were used together with measured and estimated ventilation rates to determine that 19 ± 3 g of NH3-N is released to the atmosphere per chicken in a 6-week production period, a value similar to previous reports. Confined animal feeding operations are a well-known source of NH3(g) to the atmosphere and the deposition of NHx (gaseous and particulate ammonia + particulate ammonium) to the nearby estuary is potentially important during the summer when deposition is at its maximum, and other sources of bioavailable N to the estuary are at their minimum. Although atmospheric deposition of N to the Inland Bays represents only about 15 percent of the total N-load annually (see above), up to 51 percent of the N-load to the Inland Bays during the summer may come from the atmosphere, when watershed contributions are at a minimum.
There are two modes of groundwater discharge from the watershed to the Inland Bays. The first mode is largely confined to the coastal margins of the Bays by Ghyben-Herzberg dynamics and can be detected using airborne thermal imagery. However, significant groundwater discharge bypasses the coastal margins due to the impermeability of near-surface sediments and may discharge in the open waters of the Bays or in the adjacent coastal ocean. This second mode of discharge was identified in a horizontal resistivity survey of the margins of Indian River Bay, and further studied using seismic techniques and coring. The resistivity survey, conducted in collaboration with the U.S. Geological Survey, found a plume of fresh groundwater discharging beyond the margin of Indian River Bay due to the presence of a confining layer deposited at the base of a Pleistocene paleochannel. This plume was tracked from the margin to the center of the Bay by coring, water sampling, and vertical geophysical logging. The results of this survey suggest that the plume of fresh groundwater slowly mixes with estuarine water in the bottom sediments as the plume moves offshore. Both mixing with more permeable adjacent units (perhaps due to Ghyben-Herzberg exchange) and diffusive exchange through the confining layer contribute to the dissipation of the plume with distance from the shoreline. The mixing between oxic and NO3--rich waters originating from upland aquifers and anoxic estuarine sediments and pore waters provides an ideal setting for N removal by denitrification.
The subtidal exchange of estuarine water with the coastal ocean is largely controlled by wind-driven processes. Inputs from the coastal ocean are driven by shore-parallel northeast winds and, to a lesser extent, by nearshore easterly winds. Discharges to the coastal ocean are driven by regional southwesterly winds and local westerlies. Typical storm events with northeasterly winds initially drive water into the Bays and then, on relaxation of the wind field, lead to large discharge rates. The impact of this process is rapid episodic flushing of the Bays independent of surface and groundwater discharges from the watershed. The nutrient fluxes associated with tidal and wind-driven exchange can be quantified based on a simultaneous analysis of salt and nutrient budgets. The effects of wind stress on water and nutrient exchange between the Bays, between Rehoboth and Delaware Bays through the Lewes-Rehoboth Canal, and between Indian River Bay and Little Assawoman Bay through the Assawoman Canal are still under investigation. These results have application to the questions of canal dredging, flushing of dead-end lagoons, and proposals to open new inlets between the Bays and the adjacent coastal ocean.
The results of surface water sampling are being used to determine the predictable seasonal patterns of nutrient distributions in Indian River and Rehoboth Bays. Among the questions addressed are the patterns of nutrient availability and limitation. Generally, the Inland Bays are P limited in the fresher waters due to the high N concentrations and ratios of dissolved N/P in both surface and groundwater inputs from the watershed. However, there is a distinct difference in N/P ratios of more saline waters of Indian River and Rehoboth Bays during summer. Rehoboth Bay is potentially limited by N (apparently due to wastewater contributions of excess P). As a result, groundwater and atmospheric inputs of N that bypass the tributaries and the coastal margins could significantly contribute to primary production in this Bay. In contrast, Indian River Bay is potentially limited by P, and therefore inputs of P from Rehoboth Bay, from the coastal ocean, and potentially from atmospheric deposition could increase total primary productivity in this Bay. These results suggest that different management practices may be appropriate for the two Bays and at different times of the year. These results also support the management decision to remove all point source effluents, the principal allochthonous input to the ecosystem, from the Inland Bays and its tributaries.
Journal Articles on this Report : 6 Displayed | Download in RIS Format
Other project views: | All 92 publications | 11 publications in selected types | All 6 journal articles |
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Type | Citation | ||
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Bratton JF, Bohlke JK, Swarzenski P, Manheim FT, Krantz DE. Ground water beneath coastal bays of the Delmarva Peninsula: Ages and Nutrients. Ground Water 2004;42(7):1021-1034, Oceans Issue. |
R826945 (Final) |
not available |
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Krantz DE, Manheim FT, Bratton JF, Phelan DJ. Hydrogeologic setting and ground water flow beneath a section of Indian River Bay, Delaware. Ground Water 2004;42(7):1035-1051, Oceans Issue. |
R826945 (Final) |
not available |
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Manheim FT, Krantz DE, Bratton JF. Studying ground water under Delmarva coastal bays using electrical resistivity: Ground Water. Ground Water 2004;42(7):1052-1068, Oceans Issue. |
R826945 (Final) |
not available |
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Roadman MJ, Scudlark JR, Meisinger JJ, Ullman WJ. Validation of Ogawa passive samplers for the determination of gaseous ammonia concentrations in agricultural settings. Atmospheric Environment 2003;37(17):2317-2325. |
R826945 (Final) |
not available |
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Ullman WJ, Chang B, Miller DC, Madsen JA. Groundwater mixing, nutrient diagenesis, and discharges across a sandy beachface, Cape Henlopen, Delaware (USA). Estuarine, Coastal, and Shelf Science 2002;57(3):539-552. |
R826945 (Final) |
not available |
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Wong K-C. On the wind-induced exchange between Indian River Bay, Delaware and the adjacent continental shelf. Continental Shelf Research 2002, Volume: 22, Number: 11-13 (JUL-AUG), Page: 1651-1668. |
R826945 (2001) R826945 (Final) |
not available |
Supplemental Keywords:
air, atmosphere, precipitation, estuaries, groundwater, watershed, ecological effects, bioavailability, stressor, nutrients, ecosystem, indicators, habitat, environmental chemistry, ecology, hydrology, geology, surveys, measurement methods, remote sensing, Atlantic coast, mid-Atlantic, Delaware, DE, EPA Region 3, agriculture., RFA, Scientific Discipline, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Water & Watershed, Hydrology, Ecology, Nutrients, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Chemistry, Ecological Effects - Environmental Exposure & Risk, Monitoring/Modeling, Air Deposition, Mid-Atlantic, Watersheds, bays, ecological exposure, aquatic ecosystem, environmental monitoring, fate and transport, coastal ecosystem, nutrient transport, stressors, meteorology, Delaware (DE), nutrient flux, coastal zone, public information, chemical speciation, CISNet Program, public reporting, Indian River Bay, soil, aquatic ecosystems, ecosystem, ecosystem health, water quality, nutrient cycling, stress responses, nutrients as stressors, Rehoboth Bay, nutrient transport model, atmospheric deposition, atmospheric chemistry, groundwaterRelevant Websites:
http://www.ocean.udel.edu/level1/facultystaff/faculty/wullman/index.html Exit
http://www.ocean.udel.edu/level1/facultystaff/faculty/kwong/index.html Exit
http://copland.udel.edu/~jmadsen/ Exit
http://www.eeescience.utoledo.edu/Faculty/Krantz/index.htm Exit
http://www.udel.edu/dgs/DGS/Staff/asa.html Exit
http://www.udel.edu/dgs/DGS/Staff/tmck.html Exit
http://www.udel.edu/dgs/ftp/cisnet/CHEMDATA Exit
http://www.udel.edu/dgs/Publications/pubform.html Exit
Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.