2000 Progress Report: The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama

EPA Grant Number: R827072C013
Subproject: this is subproject number 013 , established and managed by the Center Director under grant R827072
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).

Center: Alabama Center For Estuarine Studies (ACES)
Center Director: Shipp, Robert L.
Title: The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama
Investigators: Pennock, Jonathan R. , Kiene, Ronald P. , Lehrter, John
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1999 through September 30, 2000
Project Period Covered by this Report: October 1, 1999 through September 30, 2000
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text |  Recipients Lists
Research Category: Ecological Restoration , Targeted Research


The overall goal of this study is to compare the effect of different predominant land-use/land-cover complexes on non-point source nitrogen (N) and phosphorus (P) loading, biogeochemical nutrient processing and ecosystem response in coupled watershed-estuarine ecosystems. The project is being carried out in three sub-estuaries of Mobile Bay with distinctly different land-use and land-cover (Dog River, Fowl River and Fish River/Weeks Bay) utilizing a watershed-ecosystem approach that incorporates both empirical data and modeling efforts.

Progress Summary:

To examine nutrient loading dynamics, we are sampling 10 low and high order streams in each watershed approximately twice monthly and during peak freshwater discharge. These samples are analyzed for dissolved inorganic nitrogen (measured components are NO3, NO2, and NH4), dissolved organic nitrogen, particulate organic nitrogen, dissolved inorganic phosphorus (PO4), dissolved organic phosphorus, and particulate organic phosphorus. These measurements, in concert with gauged and modeled river flow rates applied to un-gauged portions of each watershed, are subsequently used to estimate nutrient loading rates (mmol/m3/d). The manner in which biogeochemical processes respond to nutrient loading is being determined during bimonthly collection of hydrographic data and water-column and sediment process measurements, including water-column primary production, sediment denitrification, sediment oxygen flux, and sediment dissolved inorganic nitrogen and phosphorus flux. Subsequently, sub-estuarine ecosystem response will be assessed by integrating these rate processes with estimates of water residence time and mixing, calculated from a 3-D hydrodynamic model implemented for each system.

To date, we have completed 26 of our scheduled 40 watershed surveys during which nitrogen and phosphorus samples are collected. Results thus far indicate that there are significant differences in the concentration of N and P species among the watersheds. In the highly agricultural watershed (Fish River/Weeks Bay), NO3 concentrations routinely exceed 100 µM in high order streams and the dissolved inorganic nitrogen component far exceeds the organic component. In the predominantly forested watershed (Fowl River), the majority of the flux is in the form of organic nitrogen and phosphorus. Results from our urban estuary (Dog River) show concentrations of N and P comparable to the forested watershed. The ratio of dissolved inorganic nutrients to organic nutrients (e.g. DIN:DON) is a good indicator of the predominant source of nutrient. Our results thus far indicate that non-point source nutrients are the largest source in Weeks Bay, while in Fowl River the primary nutrient source is derived from decomposed terrestrial plant material. Not only do these ratios tell us something about the source of nutrients, they also elucidate how the receiving aquatic ecosystems carbon cycles are operating. For instance in the Fowl River system the high load of dissolved organic nutrients delivers a recalcitrant (not easily utilizable) form of nutrient to the estuary. However, in the Weeks Bay system the estuary receives high concentrations of DIN that are directly utilizable by macrophytes and phytoplankton and thus there is the potential for subsequent eutrophication effects. The fact that we do not see eutrophication effects, such as hypoxia or die-off of submerged aquatic vegetation, in Weeks Bay is more a factor of the basin morphometry of Weeks Bays, i.e. a very shallow and well-mixed system. This leads to the necessity of examining the eutrophication process not only in terms of nutrient loading and biological response but also estuarine physics that are examined in this study using a hydrodynamic model.

The modeling component of this study includes both watershed hydrologic models and estuarine hydrodynamic models. The data inputs for the watershed hydrologic model and hydrodynamic models have been incorporated into ArcInfo GIS coverages. For the hydrologic model these data layers include land-use/land-cover derived from Landsat TM imagery, digital elevation models (DEM), and soils all with 30 meter grid cell resolution and river reach and watershed delineations created from the DEMs using ArcInfo's hydrologic routines. The hydrodynamic model (HEM 3-D) data consists of gridded estuarine bathymetry, estuarine boundary files, and water level time series data collected with continuous recording pressure transducers.

The final elements of this study are the process measurements of sediment denitrification, sediment O2 consumption, sediment N and P flux, and water-column primary production across the salinity/nutrient gradient in each of the three sub-estuaries. We are making these measurements at six stations within each sub-estuary and, to date, have completed these process measurements twice for each sub-estuary. The sediment processes are measured by the change in the N2/Ar and O2/Ar ratio, respectively for denitrification and sediment O2 consumption rates, and by changes in concentration of DIN species and PO4. All of these measurements are made during static sediment core incubations with diver-collected sediments and overlying bottom water collected at each station. Water column production is measured using 14C radioisotope methods.

Examination of these coupled watershed-estuarine systems in this manner is producing data that allows us to ask and answer pertinent management questions pertaining to both local and global eutrophication problems. Locally, we are producing data products, GIS coverages, water quality data and process measures, which previously were non-existent for these systems. Once all these data are processed and analyzed we will be able to compare this dataset to the growing list of such estuarine datasets collected throughout the world and contribute to a better understanding of the sources, fates, and system response of nutrient over-enrichment of estuarine ecosystems.

Supplemental Keywords:

estuarine research, coastal ecosystem, human modifications, land and water use, watersheds, aquatic ecosystems, bay ecosystem, nutrients, land cover, nitrogen cycling., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Ecology, Aquatic Ecosystems & Estuarine Research, Ecosystem/Assessment/Indicators, Ecosystem Protection, Chemistry, State, Restoration, Aquatic Ecosystem, Ecological Effects - Environmental Exposure & Risk, Ecology and Ecosystems, Ecological Risk Assessment, Aquatic Ecosystem Restoration, Gulf of Mexico, Ecological Indicators, coastal ecosystem, anthropogenic stress, anthropogenic stresses, wetlands, estuarine research, water use, Mobile Bay, watersheds, nutrient loading, land cover, nitrogen cycling, nutrients, Alabama (AL), coastal environments, aquatic ecosystems, ecosystem, phosphorus, Fish River/Weeks Bay, water quality, bay ecosystem, human modifications, Dog River, land use, nitrogen

Progress and Final Reports:

Original Abstract
  • Final

  • Main Center Abstract and Reports:

    R827072    Alabama Center For Estuarine Studies (ACES)

    Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
    R827072C001 Fluorescent Whitening Agents As Facile Pollution Markers In Shellfishing Waters
    R827072C002 Red Snapper Demographics on Artificial Reefs: The Effect of Nearest-Neighbor Dynamics
    R827072C003 Stabilization of Eroding Shorelines in Estuarine Wave Eliminates with Constructed Fringe Wetlands Incorporating Offshore Breakwaters
    R827072C004 Interaction Between Water Column Structure and Reproduction in Jellyfish Populations Of Mobile Bay (SGER)
    R827072C005 Effects of Variation in River Discharge and Wind-Driven Resuspension on Higher Trophic Levels in the Mobile Bay Ecosystem
    R827072C006 Results of Zooplankton Component
    R827072C007 Benthic Study Component
    R827072C008 A Preliminary Survey of Macroalgal and Aquatic Plant Distribution in the Mobile Tensaw Delta
    R827072C009 Fisheries-induced changes in the structure and function of shallow water "nursery habitats": an experimental assessment
    R827072C010 Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem
    R827072C011 Evaluation of Alabama Estuaries as Developmental Habitat for Juvenile Sea Turtles
    R827072C012 Effects of Salinity Stress on Natural and Anthropogenically-Derived Bacteria in Estuarine Environments
    R827072C013 The Role of Land-Use/Land-Cover and Sub-estuarine Ecosystem Nitrogen Cycling in the Regulation of Nitrogen Delivery to a River Dominated Estuary; Mobile Bay, Alabama
    R827072C014 Environmental Attitudes of Alabama Coastal Residents: Public Opinion Polls and Environmental Policy
    R827072C015 Synthesis and Characterization of an Electrochemical Peptide Nucleic Acid Probe
    R827072C016 Determinants of Small-Scale Variation in the Abundance of the Blue Crab Callinectes Sapidus
    R827072C017 Effects of Estrogen Pollution on the Reproductive Fitness of the Gulf Pipefish, Syngnathus scovelli
    R827072C019 A Model for Genetic Diversity Aquatic Insects of the Mobile/Tensaw River Delta
    R827072C020 Evaluating Trophic Processes as Indicators of Anthropogenic Eutrophication in Coastal Ecosystems: An Exploratory Analysis
    R827072C021 Effects of Anthropogenic Eutrophication on the Magnitude and Trophic Fate of Microphytobenthic Production in Estuaries
    R827072C022 Characteristics of Ship Waves and Wind Waves in Mobile Bay
    R827072C023 Methods Comparison Between Stripping Voltammetry and Plasma Emission Spectroscopy for Metals in Mobile Bay
    R827072C024 Changes in Water Conditions and Sedimentation Rates Associated With Construction of the Mobile Bay Causeway
    R827072C025 Cold-Induced Hibernation of Marine Vibrios in the Gulf of Mexico: A Study of Cell-Cell Communication and Dormancy in Vibrio vulnificus
    R827072C026 Holocene Sedimentary History of Weeks Bay, AL: Human and Natural Impacts on Deposition in a Gulf Coast Estuary
    R827072C027 Shelter Bottlenecks and Self-Regulation in Blue Crab Populations: Assessing the Roles of Nursery Habitats and Juvenile Interactions for Shelter Dependent Organisms
    R827072C028 Predicting Seagrass Survival in Nutrient Enriched Waters: Toward a New View of an Existing Paradigm
    R827072C029 DMSP and its Role as an Antioxidant in the Salt Marsh Macrophyte Spartina alterniflora
    R827072C030 A Preliminary Survey of Aerial and Ground-Dwelling Insects of the Mobile/Tensaw Delta
    R827072C031 Natural Biogeochemical Tags of Striped Mullet, Mugil cephalus, Estuarine Nursery Areas in the North Central Gulf of Mexico
    R827072C032 Resolution of Sedimentation Rates in Impacted Coastal Environments Using 137Cs and 210Pb Markers: Dog River and Fowl River Embayments
    R827072C033 Investigation of the Use of Pulse Amplitude Modulated (PAM) Fluorometry as an Indicator of Submerged Aquatic Vegetation Health in Mobile Bay
    R827072C034 Influence of Invasive Plant Species in Determining Diversity of Aquatic Vegetation in the Mobile-Tensaw Delta
    R827072C035 The Influence of Shallow Water Hydrodynamics on the Importance of Seagrass Detritus in Estuarine Food Webs
    R827072C036 Food Web Interactions, Spatial Subsidies and the Flow of Energy Between the Mobile Bay Delta and Offshore Waters: A SGER Proposal to the Alabama Center for Estuarine Studies
    R830651C001 Meteorological Modeling of Hurricanes and Coastal Interactions: A Stability Study For Vertical Pressure Levels
    R830651C002 Characterization of Glycoprotein Cues Used by the Parasitic Rhizocephalan Barnacle Loxothylacus texanus To Identify Its Blue Crab Host, Callinectes sapidus
    R830651C003 Survey of Diamondback Terrapin Populations in Alabama Estuaries
    R830651C004 An Assessment of Environmental Contaminant Levels in Water and Dragonfly Larvae Tissues from the Mobile/Tensaw Delta