2002 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.
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, 2001 through August 31, 2002
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 hypothesized that variations in river discharge and wind-driven sediment resuspension in this shallow estuary have dramatic effects—not only on the biological community and trophic structure—but also on the way in which anthropogenic materials are processed by the estuarine ecosystem. We are conducting an integrated study of trophic linkages in the microbial food web (phytoplankton and bacterioplankton), and how they are affected by natural perturbations such as pulsed freshwater flow and wind-driven sediment resuspension. The objectives of this research project are to determine: (1) the spatial and temporal variation in net carbon production in the Mobile Bay system ; (2) how variations in freshwater delivery and sediment resuspension affect trophic efficiency in the phytoplankton and bacterioplankton communities; and (3) how advective or wind-driven shear affects sediment resuspension, nutrient exchanges, and particulate carbon redistribution. In collaboration with a companion project focused on higher trophic levels, we are examining the relationships between multiple levels of the food web up to juvenile fish. The data gathered in this study are being used to construct a model of trophic dynamics of the Mobile Bay ecosystem that will be useful for guiding future research and resource management.

Progress Summary:

The first phase of this research project was a thorough characterization of system-state variables and processes rates. We sampled three sites monthly, on an annual cycle, along the main axis of Mobile Bay, spanning the oligohaline and polyhaline regions. As expected, salinity regimes and sediment resuspension conditions were considerably varied during the sampling period. Somewhat unexpectedly, the March 2000-2001 period was characterized by exceptionally low rainfall in the watershed. This resulted in salinities that were at the extreme upper end of the monthly 10-year averages for the different stations. In terms of the annual cycle, salinities in the Bay were low when sampling first commenced, but then increased and remained high throughout the rest of the sampling period. Temperatures ranged from 7.5°C in January 2001 to 30.5°C in August 2001. Suspended sediments (seston) in surface waters ranged over an order of magnitude from 10-150 mg L-1, illustrating the high degree of variability in resuspension of bottom sediments that occurs in this shallow system. Despite the large variations in seston, measurements of primary production, bacterial secondary production, and community respiration showed little relationship to seston load. In contrast, these biological processes were strongly related to temperature, with salinity and nutrient loading having less impact on the overall patterns in these rates.

Primary production was low in the spring, despite high freshwater flow and nutrient delivery (see Figure 1). With diminishing freshwater flow and seasonal advance toward summer, primary production increased and remained high (60-160 mmol C m-2 d-1) until the fall, when rates declined, despite continued nutrient availability. Bacterioplankton secondary production averaged 34 percent of primary production, and there was a significant correlation (P < 0.001) between these parameters. Estimated bacterial carbon utilization in the water column approximately balanced primary production. Total system respiration (water column + sediments) also closely followed the annual production cycle (see Figure 1). This was a result of the tight coupling of water column respiration with primary production; sediment respiration was not strongly coupled with water column primary production. Sediment respiration averaged 26 percent of the total annual carbon processing, but contributed up to 40-60 percent of total carbon flow during the fall-winter, when freshwater inflow and water column heterotrophic activity were low. Annual primary production ranged from 22-27 mol C m-2, but all stations displayed net-heterotrophy on an annual basis with total respiration (water column + sediments) exceeding primary production by 19-25 percent (4.2 to 6.2 mol C m-2 y-1) (see Table 1). Station FM-7 was the most heterotrophic over the annual cycle, but the differences between stations were small.

Figure 1. Annual Cycle of Depth-Integrated Primary Production, Bacterial Secondary Production, and Total Respiration for Three Stations in Mobile Bay, Alabama. All stations are along the central axis of the Bay. Station DR-5 was the farthest upstream, WB-5 was in mid-Bay, and FM-7 was near the mouth of the Bay. Total respiration includes water column community respiration and sediment respiration.

Table 1. Annual Integrated Primary Production or Respiration at Three Stations in Mobile Bay, Alabama. Values are in mol C m-2 y-1.

1° Prod
Water Column Respiration
Sediment Respiration
Net as % of 1° Prod

Size fractionation experiments showed that 30-60 percent of bacterial secondary production and community respiration was associated with particles greater than 20 mm in size. This suggests that attached bacteria were very important in this turbid system. This finding has implications for the trophic transfer of bacterial secondary production because this production may be directly available to detritivores and macrozooplankton. The high rates of particle-associated bacterial activity were somewhat surprising because bacterial production was not correlated with seston load. This may be because high seston loads diminish primary production (by limiting light penetration) on which bacterial production seems to depend strongly.

A closer examination of how resuspension affects trophic dynamics was conducted by sampling intensively over a 1-month period, during which several resuspension events occurred. Again, no relationship between bacterial secondary production or community respiration was observed with suspended sediment load. More detailed analysis of the event sampling data is ongoing.

Future Activities:

Most of the major field work of this project is now completed, with the exception of mesocosm experiments, which currently are in progress. The first of these has been conducted, and the rest will be conducted in spring and summer 2003. The mesocosm experiments are being conducted by Ms. Carolanne Russel, an M.S. student. Data analysis and synthesis are ongoing. One of the remaining tasks is to integrate data from the Alabama Center for Estuarine Studies (ACES) Lower Trophic Level study with that of the ACES Higher Trophic Level study into an EcoPath-EcoSim model describing the trophic linkages in Mobile Bay. This activity will take place in summer and fall 2003.

Journal Articles on this Report : 2 Displayed | Download in RIS Format

Other subproject views: All 4 publications 2 publications in selected types All 2 journal articles
Other center views: All 86 publications 5 publications in selected types All 5 journal articles
Type Citation Sub Project Document Sources
Journal Article Kiene RP, Aikens M, Linn L, Axell M. Factors affecting bacterial production and growth efficiency in a large estuary subject to frequent sediment resuspension. Aquatic Microbial Ecology. R827072C010 (2002)
not available
Journal Article Osland M, Kiene RP. Influence of natural sediment resuspension events on size fractionated plankton respiration in lower Mobile Bay, Alabama. Estuaries. R827072C010 (2002)
not available

Supplemental Keywords:

ecosystem, ecosystem protection, environmental exposure, risk, geographic area, water, aquatic ecosystem, estuarine research, chemical engineering, chemistry, ecology, ecological effects, human health, ecological indicators, assessment, indicators, environmental chemistry, Alabama, AL, artificial reef design, coastal ecosystem, coastal environments, estuaries, estuarine waters, fishery sampling, human modifications, land use, water use, phytoplankton, bacterioplankton, freshwater, sediment resuspension., 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, coastal ecosystem, river discharge, trophic levels, estuaries, watersheds, Mobile Bay, nutrients, phytoplankton, biomass, ecosystem, environmental indicators, water quality, estuarine waters, wind-driven resuspension, sediment dynamics

Relevant Websites:

http://www.southalabama.edu/aces/ Exit
http://www.disl.org Exit

Progress and Final Reports:

Original Abstract
  • 2000 Progress Report
  • 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