2002 Progress Report: PULSES - The Importance of Pulsed Physical Events for Watershed Sustainability in Coastal Louisiana

EPA Grant Number: R828009
Title: PULSES - The Importance of Pulsed Physical Events for Watershed Sustainability in Coastal Louisiana
Investigators: Day, John , Cable, Jaye , Fry, Brian , Justic, Dubravko , Kemp, Paul , Reyes, Enrique , Templet, Paul , Twilley, Robert
Institution: Louisiana State University - Baton Rouge , University of Louisiana at Lafayette , University of New Orleans
Current Institution: Louisiana State University - Baton Rouge , University of Southwestern Louisiana
EPA Project Officer: Hiscock, Michael
Project Period: February 28, 2000 through February 27, 2003 (Extended to August 27, 2004)
Project Period Covered by this Report: February 28, 2002 through February 27, 2003
Project Amount: $899,995
RFA: Water and Watersheds (1999) RFA Text |  Recipients Lists
Research Category: Water and Watersheds , Water

Objective:

The overall objective of this research project is to evaluate multiple effects of different scales of river inputs in one coastal watershed; the Caernarvon Watershed, just south of New Orleans, where river inputs have been ongoing since the 1991 opening of a gated river diversion structure. The specific physical science objectives are to: (1) monitor hydrodynamic responses to river inputs and climatic factors; and (2) evaluate marsh accretion responses to different levels of river inputs. The specific ecological science objectives are to: (1) evaluate marsh plant growth responses to river inputs that bring both sediments and nutrients; (2) monitor water quality changes at the landscape level at different scales of water diversion; (3) evaluate the function of wetland soils and benthic sediments at nutrient sinks in response to repeated flooding events with river water; (4) assay effects of river inputs on fish, shrimp, and oysters using stable isotopes; and (5) monitor phytoplankton responses to pulsed riverine freshwater and nutrient inputs. Subsequently, we will develop and implement: (1) an integrated physical/biological water quality model of the Caernarvon system; and (2) a regional-level simulation model to understand freshwater discharge and nutrient dynamic interactions. The specific social science objectives are to provide an interface between the natural and human systems of the region within the context of sustainable development through: conceptual model building, cost/benefit analysis, energy analysis, and multicriteria/stakeholder analysis.

Progress Summary:

The high-pulsed discharges (6,500 cubic-feet-per-second, cfs) occurred for the two 2-week periods of early spring in 2003. We have monitored physical and ecological trends of the watershed area before, during, and after the discharges.

We have completed a total of 32 water quality transects in the Breton Sound estuary since September 2000. We used a flow-through system to continuously measure chlorophyll a, total suspended sediments (TSS), salinity, and temperature as we traveled by boat along major bayous and channels leading from the Caernarvon diversion to Breton Sound Bay. Discrete water samples were taken at 20 locations in the estuary and later analyzed for nitrate nitrite, ammonium, total nitrogen, total phosphorus, phosphate, and silica. Preliminary results suggest the estuary to be a strong sink for nitrogen phosphorus, especially inorganic forms, as well as silica and TSS. These reductions in nutrient concentrations appear to cause a change in stoichiometric nutrient ratios as water passes through the estuary, with an overall decrease in the dissolved N:P ratio and an increase in the Si:N ratio. Discharge from the diversion structure controls salinity throughout the estuary, especially during large ‘pulses,’ when almost the entire estuary freshens.

We used the stable isotope method to test the hypothesis that Mississippi River water has a strong impact on fisheries and organic matter cycling in the Caernarvon Watershed. Specifically, we are examining how C, N, and S cycling change in downstream food webs. We analyzed anchovies, shrimp, barnacles, and particulate organic matter in the water column between September 2000 and August 2002. We found very strong gradients in C, N, and S isotope distributions; with low S and high C and N isotope values associated with the upper estuary. Although S isotopes are strongly related to salinity, C and N are mainly reflecting the signal from the Mississippi River water. With a time delay of about 1 to 2 months, the riverine related isotope signals appear in anchovies, shrimp, and barnacles. These primary consumers are common prey for higher trophic levels and, hence, we expect that the riverine signal will be transmitted to higher trophic levels.

We studied the nutrient processing capabilities of wetland soils and benthic sediments in response to repeated pulsed Mississippi River water discharge events at the Caernarvon diversion structure, because sediment input helps build marshes, but accompanying high riverine nutrient levels potentially cause eutrophication and harmful algal blooms.

Repeated experiments at Big Mar, a body of open water close to the diversion structure, indicate a strong temporal variability of fluxes. Our data compilation shows that the estuary cores have the potential to induce high nitrate/nitrite fluxes out of the water column under certain conditions, indicating that these estuarine sediments can function, at least temporarily, as nutrient sinks.

Denitrification rates, measured in the same experiment, indicate consistently increasing denitrification with increasing distance from the diversion and thus increasing ambient water temperature in the field. At Big Mar, the rate was low with a mean around 15 µmol N2 m-2 h-1, but with a high variability between the tested 3 replicate cores. The rates at the other stations consistently increased from a mean around 50 to approximately 160 µmol N2 m-2 h-1 for the warmest location. During the colder weather condition of the February 2002 diversion event, no denitrification was determined for Big Mar, but rates for the warmer stations further away from the diversion site were comparable to the rates measured in March 2002.

Sediment nutrient fluxes are strongly influenced by a variety of factors. With sufficient carbon supply, dissolved nutrient concentrations may be determining potential uptake rates during warmer seasons. Temperature effects may dominate the potential rates during colder winter/spring months. Larger benthos organisms, like the mussel Rangia, strongly affect the observed rates and cause strong variability between replicate cores. At times of high density of plankton organisms, sediment uptake rates may be reduced because of competition for the dissolved nutrients in the water column.

We have been conducting two different spatial modelings to assess impacts of the pulsed riverine inputs into the Caernarvon Watershed. First, we developed an integrated physical-biological water quality model of the Caernarvon Watershed. In developing this model, our primary goal was to describe the coupling between riverine nutrient loads, nutrient ratios, and eutrophication in coastal watersheds. We have developed a general framework for the implementation of a 2-dimensional (2-D) finite-element hydrodynamic model in the Caernarvon diversion area. In a parallel effort, we have developed and calibrated an estuarine eutrophication model that includes multiple N, Si, and P uptake of the Monod type and multiple algal assemblages, whose productivity is simultaneously dependent on nutrient concentrations, nutrient ratios, and ambient light intensity. The eutrophication model is designed to run either as a stand-alone module or as a component of a larger 2-D hydrodynamic model.

The model has been tested using environmental data collected during the 2001 PULSES project experiment. Predicted flows, salinity distributions, nutrient concentrations, and chlorophyll a levels generally have shown a good agreement with the measured values.

Another spatial modeling effort is to simulate habitat changes of the watershed, because of riverine inputs. An environmental data set was created to coordinate the time-series parameters. This database facilitates retrieval and analysis of more than 20,000 records. The length of this database expands from 1956 to 1998. Several federal and state agencies were consulted to compile the environmental information. Most time-series parameters include records for precipitation, air temperature, and solar irradiance. Water quality parameters were provided by the U.S. Geological Survey and include water temperature, river stage, and diversion discharge. Records of biological parameters, such as nutrient loading and uptake were compiled using data collected by Louisiana State University (LSU) researchers in previous and concurrent field studies. Spatially distributed data include topological and vegetation maps for the area. The spatial data comprised three habitat maps for the years 1956, 1978, and 1988, and a thematic satellite image for 1993. A bathymetric map for the coastal areas was obtained. This bathymetry was merged with topographic elevations surveyed by this project and information provided by the National Resource Conservation Service. This topological map, in combination with the respective habitat map, forms the basis for the spatial initial conditions, in which the landscape model is run.

Using our spatially descriptive model, we prepared a series of scenarios. The calibration and results of the simulation of alternative management scenarios for three unit models: a fresh marsh and a brackish marsh at the Caernarvon marshes, and an open water environment with an oyster community in the Breton Sound Estuary. The unit models were connected sequentially to represent the fresh marshes located near the Caernarvon diversion outlet with little tidal influence, and the brackish marsh with an oyster community as its principal trophic consumer. We ran calibration runs for a 3-year period with a 1-hour time step.

The scenarios included: normal Caernarvon diversion discharge, no freshwater discharge, increased freshwater discharge (double the current conditions, which match a prior level of operation), and water discharge pulsing scenarios. Results indicated that any further increases in salinity for any of the sites creates deleterious conditions for the communities. Only the scenarios with freshwater discharge seem to contribute to maintaining the favorable conditions for these ecosystems.

Regarding the social sciences, we have been developing a conceptual model of the interaction of the natural and economic systems and will use it with the empirical data generated from the natural science part of the project. The purpose is to provide decisionmakers and ecosystem manager system-level models that conceptually illustrate the interactions between natural and human systems. Our hypothesis is that natural systems, such as watersheds, contribute to human well being by contributing resources and services, and by accepting wastes. Human actions that diminish these natural capital services also diminish social capital. Improving natural capital, as the Caernarvon diversion will do, improves social and economic capital. Economic capital is man made capital and includes the stock of revenue generating assets. Social capital is the accumulation of those aspects of our human culture that contribute to a higher quality of life. For example, social capital is composed of educational attainment, social cohesion, low crime, volunteerism, participation in government at all levels, longevity, access to restoration, esthetics, good income and low poverty, housing, access to quality medical care, and other factors. All of these factors contribute to a high quality of life, which has become a primary driving force in economic development. Some of these factors are clearly related to natural capital (e.g., access to recreation and esthetics), but other relationships between natural and social capital are not so clear.

During the reporting period, we have continued to research the connection between the environment and the economy to show how economies partition energy, both commercial energy and natural energy, into goods and services or waste (Templet, 2002). Those economies that partition more to goods are more efficient and their social and financial capital are higher. Putting more natural energy, like the energy generated by the Caernarvon diversion, into an economic system will create more goods. Improving the efficiency of the economic system (i.e. partititioning more of the energy to goods) also will improve the social and economic capital.

Finally, we have completed a questionnaire–based stakeholder analysis for experts and local people, and interviews with members of the Caernarvon Interagency Advisory Committee, which is an institutionalized stakeholder meeting representing federal, state, and local governments/agencies, local fishers, recreational sportsmen, and land owners.

Preliminary results of the survey and interviews revealed that: (1) there is a high level of agreement on the significance of coastal land loss; (2) local people tend to make judgments based on heuristics (e.g., personal experience for generalization); (3) significantly different responses exist among decisionmakers, experts, and local people, (4) channels to accommodate public opinion are available, but not actively used and therefore, (5) diverse opinions and conflicts exist that may affect project successes that are not being addressed adequately.

Future Activities:

During the no-cost extension period, we will conclude sample measurement and data analysis for the study of marsh denitrification and benthic sediments. We will prepare a manuscript about the results of our studies, which should be submitted before project closure. The maintenance of the marsh mesocosms will be continued and various treatments will be used to study biogeochemical cycling of nutrients in this type of long-term setup.

Future modeling activities will concentrate on optimizing pulsing events with respect to the two key elements of estuarine eutrophication, nitrate removal potential, and algal bloom potential, and proposing management alternatives for sustainable management of coastal watersheds in the Mississippi Delta. Uncertainty analysis will be conducted for key ecological parameters under low flow conditions and high flow conditions. Knowing the variability associated with model predictions and the importance of individual parameters will help focus the future field experiments. Also, model predictions that explicitly include uncertainty will be more useful to environmental managers than simple point value predictions.

Energy analysis and multi-criteria analysis will be completed using empirical data collected by the PULSES project teams.


Journal Articles on this Report : 6 Displayed | Download in RIS Format

Other project views: All 109 publications 18 publications in selected types All 17 journal articles
Type Citation Project Document Sources
Journal Article Justic D, Turner RE, Rabalais NN. Climatic influences on riverine nitrate flux: implications for coastal marine eutrophication and hypoxia. Estuaries 2003;26(1):1-11. R828009 (2001)
R828009 (2002)
R828009 (Final)
R827785E02 (Final)
  • Abstract: Springer - Abstract
    Exit
  • Journal Article Lane RR, Day JW, Reyes E, Justic D, Day JN, Hyfield E. Chlorophyll, suspended sediment, salinity, and temperature dynamics measured with a flow-through system in the Breton Sound estuary during the spring pulse of 2001. Journal of Coastal Research. R828009 (2002)
    not available
    Journal Article Lane RR, Day JW, Justic D, Reyes E, Marx B, Day JN, Hyfield E. Changes in stoichiometric Si, N and P ratios of Mississippi River water diverted through coastal wetlands to the Gulf of Mexico. Estuarine, Coastal and Shelf Science 2004;60(1):1-10. R828009 (2002)
    R828009 (Final)
  • Full-text: Science Direct PDF
    Exit
  • Abstract: Science Direct
    Exit
  • Other: Science Direct HTML
    Exit
  • Journal Article Lane RR, Day Jr. JW, Marx BD, Reyes E, Hyfield E, Day JN. The effects of riverine discharge on temperature, salinity, suspended sediment and chlorophyll a in a Mississippi delta estuary measured using a flow-through system. Estuarine, Coastal and Shelf Science 2007;74(1-2):145-154. R828009 (2002)
    R828009 (Final)
  • Full-text: Science Direct
    Exit
  • Abstract: Science Direct
    Exit
  • Other: Science Direct PDF
    Exit
  • Journal Article Templet PH. Partitioning of resources in production: an empirical analysis. Journal of Cleaner Production 2004;12(8-10):855-863. R828009 (2001)
    R828009 (2002)
  • Full-text: Science Direct
    Exit
  • Abstract: Science Direct
    Exit
  • Other: Science Direct PDF
    Exit
  • Journal Article Xu Z, Cheng G, Chen D, Templet PH. Economic diversity, development capacity and sustainable development of China. Ecological Economics 2002;40(3):369-378. R828009 (2001)
    R828009 (2002)
    R828009 (Final)
  • Full-text: Science Direct
    Exit
  • Abstract: Science Direct
    Exit
  • Other: Science Direct PDF
    Exit
  • Supplemental Keywords:

    watershed, estuary, restoration, ecosystem, integrated assessment, decision making, survey, ecology, modeling, monitoring, Gulf Coast, Louisiana, LA, sustainable management, EPA region 6., RFA, Scientific Discipline, Geographic Area, Water, Ecosystem Protection/Environmental Exposure & Risk, Nutrients, Water & Watershed, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Ecological Effects - Environmental Exposure & Risk, Southeast, Environmental Monitoring, Ecological Risk Assessment, Watersheds, nutrient transport, coastal ecosystem, eutrophication, ecological exposure, flood plains, coastal watershed, economics, marsh plant growth, river inputs, watershed sustainablity, sediment transport, fisheries, conservation, Louisiana (LA), Louisiana, pulsed physical events, tropical storms, aquatic ecosystems, watershed sustainablility, riverine ecosystems , water quality

    Relevant Websites:

    http://www.lsu.edu/aeg/pulses/pulses.html Exit
    http://www.ucs.louisiana.edu/~rrt4630/pulses.html Exit

    Progress and Final Reports:

    Original Abstract
  • 2000 Progress Report
  • 2001 Progress Report
  • 2003
  • Final Report