WATER
RESOURCES
Louisiana’s coastal
water resources are challenged by an unstable landscape, invading
species, nutrient-rich runoff, declining groundwater supplies
and numerous waste discharges. Louisiana Sea Grant sponsors research
focusing on water treatment technology, best management practices,
and water quality issues to advance the nation’s clean water
and environmental quality standards.
Evaluation
of the Impact of Domestic Wastewater on the Surface and Subsurface
Environments of Coastal Marshes: Refining the Marshland Upwelling
System (MUS) to Achieve Net Nitrogen System Reductions
Gambrell, R., Louisiana State University,
Wetland Biogeochemistry Institute
Thousands of recreational camps in coastal Louisiana are located
in isolated, rural areas that lack sewer systems and have soil
conditions that render treatment of household wastes by means
of septic tanks or other conventional gravity systems impractical.
Traditionally, many camp owners have simply discharged untreated
household wastes into a nearby canal, bayou or marsh surface without
treatment. The MUS system was initially developed for use in coastal
locations underlain by shallow sand deposits and brackish groundwater,
where wastewater could be pumped into the ground and treated through
contact with saltwater as it percolated upward to the water table.
Although pilot tests of the MUS at marsh sites without sand deposits
have not been as successful as the coastal sites, there is strong
regulatory agency interest in pursuing the upwelling concept for
more general use and certification. This project represents an
effort to study and characterize system performance in terms of
fundamental scientific and economic factors that may ultimately
serve as the basis for a rational design capability.
Coastal waters
and wetlands in proximity to campsites that lack conventional
septic systems are vulnerable to eutrophication caused by discharge
of untreated household wastes and yard run-off. This project will
refine the MUS system for overall nitrogen reduction from wastewater
from coastal dwellings. Objectives include: determination of the
nitrogen mass reduction potential of the MUS, which leads to overall
lower input of nitrogen into the environment; determination of
the extent of wetland plant growth enhancement due to nutrient
input into the subsurface environment; an estimation of the extent
to which addition of nitrate enhances the anaerobic degradation
of organic matter contained in the wastewater and cost analysis
to determine the incremental increase in system fixed cost and
operational cost required to achieve a net reduction in nitrogen.
Development
of a Fate and Transport Model for Pathogen Tracking in Coastal
Subsurfaces Impacted by Anthropogenic Pollutant Sources
Tsai, F., Louisiana State University, Civil
& Environmental Engineering
The Marshland
Upwelling System (MUS) was developed to treat and dispose of sanitary
wastes from recreational camps by injecting them into a shallow,
permeable saltwater aquifer. Investigations associated with pilot
field installations at several locations indicate that effluents
pumped into a saline aquifer tend to spread laterally and migrate
back towards the ground surface in response to the differential
buoyancy between the freshwater effluent and the saline groundwater.
At the same time, groundwater near the injection point may be
displaced laterally and diluted by mixing with the injected liquid.
Field data show that a plume forms through mixing, diffusion and
laminar flow within the soil pores and pollutants including viral
and bacterial organisms disperse throughout the mixing zone. Contact
with saltwater is believed to significantly retard the mobility
of the polluting organisms in sediment due to ionic attraction.
For engineering purposes, characterization of this system as a
mathematical model is a logical next step that will provide the
detailed understanding of key process interactions needed to design
and predict performance of MUS installations with confidence.
The project will address this requirement through development
and utilization of a “fate and transport model.” The
principal investigator will employ a variety of geophysical and
biological methods, laboratory tests, experiments and mathematical
modeling techniques to achieve the desired understanding of anthropogenic
pollutant interactions within coastal groundwater systems and
yield a practical modeling tool for design and prediction of system
performance.
Landscape
Patterns of Denitrification in Marsh and Subtidal Sediments of
Breton Sound During River-Pulsing Events Using Isotopic Methods
Twilley, R., Louisiana State University,
Wetland Biogeochemistry Institute
Currently there is
limited information on rates at which dissolved nitrogen compounds
in different habitats are converted to nitrogen gas during river-pulsing
events. Modeling efforts to determine the impact of excess nitrogen
inputs on water quality at the landscape level require these denitrification
rates to calibrate box and processes-oriented models; these will
be used to forecast eutrophication levels at the ecosystem scale
with various restoration alternatives. Comprehensive spatial coverage
of denitrification rates will be undertaken simultaneously in
two habitat types (subtidal and intertidal) in a major restoration
site, using direct 15N-N isotope methods. The principal investigator
anticipates that project results will contribute to determining
the relative role of denitrification as a nitrogen sink in coastal
Louisiana.
