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: R826945
Title: 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
Current 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


In the proposed project, we will evaluate nutrient (N and P) delivery and dynamics in Rehoboth and Indian River Bays, two members of Delaware's Inland Bays ecosystem. These two small, shallow Bays are interconnected, with restricted exchange to the coastal ocean, but differ markedly in flushing and circulation. The Inland Bays are representative of a common, but understudied, class of coastal estuarine ecosystems along the East and Gulf coasts of the U.S. The objectives of this study are to:

  • determine the sources, magnitudes, and spatial and temporal variability of nutrient (N and P) fluxes to Rehoboth and Indian River Bays, the primary stressor in this system;
  • assess the magnitude of nutrient sinks in this system; and
  • develop conceptual and simple quantitative models that relate these inputs and outputs to more easily measured and monitored forcing parameters, such as precipitation, temperature, season, ground-water levels and surface-water discharge.
This study will determine the gross fluxes of nutrients into and out of the Inland Bays system and the net annual and seasonal fluxes to the Bays as an indicator of the impact of the nutrient-flux stressor. The models developed in this study will be available for calculations of fluxes to the Bays (and perhaps other analogous systems) under future environmental conditions.


The field-study portion of this project is designed to quantify the fluxes from each of the primary sources delivering water and nutrients to the Inland Bays: atmospheric deposition, surface water, ground water, and exchange with the coastal ocean and the relationship between hydrological and hydro-meteorological conditions and these fluxes. The study will also evaluate the seasonal role of estuarine waters and sediments as nutrient reservoirs.

Atmospheric deposition will be measured at the Cape Henlopen AirMon site. Surface water inputs from ten tributary streams will be monitored biweekly to determine the seasonality of baseflow discharge of fresh water and associated nutrients into the Bays. Storm discharges of nutrients will be measured at one of these sites, Millsboro Pond. Sites of focused ground-water discharge will be identified by evaluating thermal infrared images of the Bay margins for thermal anomalies. Several of these discharge areas will be instrumented to measure seasonal and annual ground-water and associated nutrient fluxes to the estuary. Ground-water discharge will be related to the underlying geology using ground-penetrating radar on land and high-resolution marine seismics.

The outflow of water and associated nutrients from the Inland Bays ecosystem through Indian River Inlet will be determined using an acoustic Doppler current profiler to measure water flow and biweekly analyses of nutrient concentrations in waters moving through the inlet. Additional advective fluxes of water and nutrients will be determined at Massey's Ditch, the connection between the two Bays, and in the Lewes/Rehoboth Canal, the connection between Rehoboth Bay and Delaware Bay to the north.

The internal cycling of nutrients within the Bays will be evaluated from nutrient mixing curves based on regularly collected samples from both Bays. The change in water-column storage of nutrients will be determined from the same data set. The loss of nutrients to sediments and the extent of temporary nutrient storage in these sediments will be studied in a suite of cores from the Bays available in the Delaware Geological Survey core collection.

The seasonal and temporal variability of all sources and sinks will be determined and conceptual and simple quantitative models describing these relationships and the effect of external forcing parameters, such as precipitation, temperature, surface and ground water discharge on component and net nutrient fluxes will be developed. These models will make it possible to determine the magnitude of gross fluxes (stressor) and net fluxes (stress response) characteristics under future sets of environmental forcing parameters.

Expected Results:

The expected results include: (1) a data set describing spatial and temporal variability in nutrient fluxes (2) an analysis of the magnitude of and the relationship between the hydrological and meteorological forcing parameters impacting the estuary; and (3) a set of conceptual and simple quantitative models that can be incorporated into the Hydrodynamic/Water Quality model currently used to set discharge limits and determine best management practices for the Inland Bays estuary and watershed. These conceptual models will also permit the magnitude of gross (stressor) and net fluxes (stress response) to be determined under future environmental conditions from more easily monitored and available sets of hydrological and hydro-meteorological forcing parameters.

Although the proposed work is designed to focus on the Inland Bays ecosystem that is well-known to the investigators, it is likely to have additional impacts on similar small, shallow, and agriculturally impacted estuarine ecosystems on the Atlantic coastal plain and elsewhere.

Publications and Presentations:

Publications have been submitted on this project: View all 92 publications for this project

Journal Articles:

Journal Articles have been submitted on this project: View all 6 journal articles for this project

Supplemental Keywords:

Estuary, watershed, groundwater, chemical transport, ecological effects, nutrients, indicators, environmental chemistry, marine science, hydrology, geology, oceanography, surveys, monitoring, Mid-Atlantic, DE., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Hydrology, Nutrients, Ecology, Water & Watershed, Ecosystem/Assessment/Indicators, Ecosystem Protection, Chemistry, State, Monitoring/Modeling, Ecological Effects - Environmental Exposure & Risk, 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, groundwater

Relevant Websites:

Progress and Final Reports:

  • 1999 Progress Report
  • 2000 Progress Report
  • 2001 Progress Report
  • Final Report