Identifier

etd-1119102-163547

Degree

Master of Science (MS)

Department

Renewable Natural Resources

Document Type

Thesis

Abstract

Nearly 35,000 ha are used to grow crawfish in southwest and south-central Louisiana, and many of these ponds discharge into impaired water bodies. In 2002, proposed guidelines were published by the United States Environmental Protection Agency (USEPA) assigning effluent limitations and standards for some aquaculture production systems and exempting others (e.g. crawfish ponds). This research had three objectives relative to crawfish ponds: develop water discharge models; final drawdown effluent quality and seasonal mass loading of solids and nutrients; and identification of Best Management Practices (BMPs) that could reduce effluent discharge and improve effluent quality. Models for south-central and southwest Louisiana with a 15 cm storage capacity showed that excess precipitation overflow (final drawdown not included) can be decreased by 28% for a high precipitation year, 61% for an average precipitation year, and 100% for a low precipitation year. The major sources of effluent from crawfish ponds are (1) overflow during winter – when precipitation exceeds evaporation, evapotranspiration, and infiltration – and (2) discharge during the summer drawdown period. Pond evaporation and evapotranspiration combined are the greatest sources of water loss (68%) during a crawfish production cycle. During final drawdown, solids were high during the first 5% of pond water discharge due to poorly consolidated sediment in and around the drain and high during the last 20% of pond water discharge due to the poorly consolidated pond bottom sediments. During final drawdown: total suspended solids were reduced over a distance of 268 m by 28% at the Aquaculture Research Station (wide, shallow, non-vegetated ditch); total suspended solids increased over a distance of 268 m by 15% at the Rice Research Station (narrow, non-vegetated ditch); and total suspended solids were reduced over a distance of 268 m by 80% at the University of Louisiana at Lafayette Model Sustainable Agricultural Complex (deep vegetated ditch). To reduce solid and nutrient mass loading in crawfish pond discharge, ponds should be slowly drained from the top of the water column and avoid draining the last 20% of the pond volume. If that is not possible, then it is recommended to treat the last 20% of the pond volume by sending the discharge through deep vegetated ditches, settling basins, or constructed wetlands with a residence time of 4 d to 14 d.

Date

2002

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Robert P. Romaire

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