2000 Progress Report: Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem

EPA Grant Number: R827072C010
Subproject: this is subproject number 010 , 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: Effects Of Variation in River Discharge and Wind-Driven Resuspension on Lower Trophic Levels of the Mobile Bay Ecosystem
Investigators: Kiene, Ronald P. , Cowan, Jean , Pennock, Jonathan R. , Thomas, Florence
Current Investigators: Kiene, Ronald P. , Cowan, Jean , Pennock, Jonathan R.
Institution: University of South Alabama
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 1999 through August 31, 2002
Project Period Covered by this Report: September 1, 1999 through August 31, 2000
Project Amount: Refer to main center abstract for funding details.
RFA: Alabama Center For Estuarine Studies (ACES) (1999) RFA Text |  Recipients Lists
Research Category: Ecological Restoration , Targeted Research


Proper management of the Mobile Bay estuary and its living resources requires a fundamental understanding of current ecosystem structure and function. We are carrying out an integrated study of trophic linkages in the microbial food web (phytoplankton and bacterioplankton) in the water column and sediments of Mobile Bay. We are working closely with another group that is focusing on coupling in higher trophic levels. Our aim to understand patterns of primary and secondary productivity and how they are affected by natural perturbations such as pulsed freshwater flow and wind-driven sediment resuspension. The following major study questions are being addressed in our study: 1) What is the spatial and temporal variation in net carbon production in the Mobile Bay system? 2) How do variations in freshwater delivery and sediment resuspension affect trophic efficiency in the phytoplankton and bacterioplankton communities? 3) How does advective or wind-driven shear affect sediment resuspension, nutrient exchanges and particulate carbon redistribution?

Progress Summary:

In the first year of this project we sampled three stations along the main axis if the Bay on a monthly basis as part of a characterization of the Mobile Bay system. The sampling period (March 2000-February 2001) covered a time of low precipitation in the watershed resulting in anomalously high salinities, as high as 20 and 26 in the upper Bay and lower Bay, respectively. Inorganic nutrient concentrations were generally low throughout the Bay except for the March - April period in 2000. For example, nitrate concentrations were generally less than 0.3 µM except for April when concentrations surpassed 15 µM. Ammonium concentrations were generally less than 1 µM except during the early spring and winter when they exceeded 3 µM. Urea concentrations ranged from 0.2 - 1.0 µM suggesting that urea could be an important source of labile nitrogen during much of the year. Phytoplankton primary production rates displayed a modest seasonal cycle, ranging from minimum rates of 25-42 mmolC m-2 d-1 in the early spring and December, to maximum rates of 125-167 mmolC m-2 d-1 in mid-summer. Phytoplankton chlorophyll values ranged between <1 and 20 µg l-1 with generally higher values near the head of the Bay, however, these patterns were random and did not display any obvious seasonal cycle.

Bacterial secondary production was measured in surface and bottom waters at each of the three stations. Differences in rates between surface and bottom, and between stations were relatively small. Highest rates (10-13 mmol C L-1 d-1) were measured during the period May through August. Minimum rates (0.5-2.0 mmol C L-1 d-1) in the two lower bay sites (WB-5 and FM-7) were observed in November - December, whereas minimum values for the upper bay site (DR-5) were observed in February. Temperature differences between these sites may largely explain the seasonal patterns. Estimates of the annual water column bacterial secondary production for the three stations are 5.5, 4.4 and 4.6 mol C m-2 y-1 for DR-5, WB-5 and FMS-7 respectively.

Experimental work revealed that a large fraction of the bacterial biomass production (determined in 1 h incubations) could be removed by gentle filtration through 20 mm nitex screens, suggesting that particle attached bacteria are important in secondary production. In apparent contrast we found that respiration rates (determined in 24 h incubations) were highest in the <20 mm size fraction. Approximately 50% of respiration activity was however in the 1 - 20 mm size fraction. Measurements of hydrolytic enzyme activities also supported an important role of particle attached bacteria.

Sediment cores were collected for whole core flux experiments as well as for analyses of sediment PC/PN (1 cm depth by 0.5 cm intervals), sediment Chl-a profiles (6 cm depth by 0.5 cm intervals), and sediment nutrient porewater profiles (10 cm depth by 1 cm intervals), and sediment water exchange of oxygen, NH4+, NO3-+NO2-, NO2-, and PO4.

Sediment PC/PN was fairly constant at all 3 stations over the annual cycle. There was a summer peak in chlorophyll-a concentration in the top 0.5 cm sediment at all stations, and a smaller fall peak at station DR5. This is a departure from results obtained in 1993 and 1994 (Cowan et al. 1996) when no discernable pattern was found, possibly because river flow patterns were altered by drought conditions in 2000.

Results from all stations generally show a positive relationship between NH4+ and PO4 flux and temperature, and a negative relationship between NO3-+NO2-, NO2-, and DO flux and temperature. The opposite patterns hold for relationships between these chemical parameters and bottom water dissolved oxygen concentration. Temperature and DO concentration have such an effect on nutrient fluxes because of their effect on biological processes such as nitrification and denitrification, and physico-chemical processes such as phosphate sorption/desorption to particles. The generally negative relationship between DO flux and temperature is driven by the fact that bottom water DO concentrations decreased to hypoxic levels in the summer months at two of the three stations.

Release rates of dissolved inorganic nitrogen tended to be greatest and of similar magnitude at stations DR5 and FM7. Station WB5 had the lowest release rates of DIN, and on occasion uptake of NO3-+NO2- was observed at this station. Phosphate fluxes were far greater at station DR5 than at either of the lower bay stations; lowest PO4 fluxes were measured at station WB5. Preliminary results suggest that porewater profiles follow a similar pattern.

The large amount of data collected during this project adds substantially to knowledge of the food web and biogeochemical dynamics in Mobile Bay. Analysis of the data is ongoing and further intensive studies targeting resuspension events and high flow conditions will be carried out in the second year of the project. Information on dynamics of the lower trophic levels will be integrated with information from a companion project that is focused on higher trophic levels. The long-term goal of this work is to generate a model of trophic dynamics in Mobile Bay that can ultimately be used to guide further research on this system.

Journal Articles:

No journal articles submitted with this report: View all 4 publications for this subproject

Supplemental Keywords:

estuarine research, coastal ecosystem, watersheds, aquatic ecosystems, river discharge, nutrients, trophic levels, biomass., RFA, Scientific Discipline, Geographic Area, Water, ECOSYSTEMS, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Ecology, estuarine research, Ecosystem Protection, Ecosystem/Assessment/Indicators, Restoration, Ecological Effects - Environmental Exposure & Risk, Aquatic Ecosystem, Aquatic Ecosystems, Ecological Monitoring, Ecology and Ecosystems, Ecological Risk Assessment, Aquatic Ecosystem Restoration, Ecological Indicators, Gulf of Mexico, trophic levels, river discharge, coastal ecosystem, Mobile Bay, estuaries, watersheds, nutrients, phytoplankton, biomass, ecosystem, environmental indicators, estuarine waters, water quality, wind-driven resuspension, sediment dynamics

Progress and Final Reports:

Original Abstract
  • 2001
  • 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