Date of Award

1983

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Abstract

A two-year survey of the aquatic plants and invertebrates in the Des Allemands Swamp was designed to determine the ecological effects of altered hydrologic regimes. The aquatic invertebrate community in an impoundment was compared with a control site subject to "normal" overflow flooding and a crawfish farm where high rates of water exchange are maintained by a system of pumps and artificial levees. Swamp hydrology for the years 1914-1980 was modeled using Thornthwaite and Mather components. Time-series analysis found no evidence of any long-term cyclical behavior. High evapotranspiration and drainage during summer decrease water levels to zero in natural swamp areas. However, summer evapotranspiration alone cannot remove winter surpluses, and areas where drainage is hindered tend to maintain high water levels all year. Swamps that do not dry out develop large openings in an otherwise uniform tree canopy; accumulate thick mats of floating vegetation; develop highly anaerobic sediments in late summer; maintain very large numbers of macroinvertebrates in mats of floating vegetation; decrease in community complexity and diversity; and sustain a biological seasonality different from that of natural or managed areas. Average density in the "normal" swamp was 10,508 individuals/sq m in the floating vegetation (FV) and 5,690 individuals/sq m in the sediment. However, the average biomass was greater in the sediment (8.4 gAFDW/sq m) than in the FV (4.2 gAFDW/sq m). Seasonal patterns of species frequency and abundances were related to the hydrologic regime of each station. Organic flows and the mechanisms controlling backswamp invertebrate populations were simulated with CSMP. The models predict macrofaunal seasonal fluctuations as a function of hydrology, temperature, and oxygen. Simulating a decrease in the artificial levee height from 500 mm to 50 mm increased surface runoff from 44.0 mm/mo to 65.6 mm/mo and increased export of organic matter from 33.9 g/sq m/mo to 48.5 g/sq m/mo.

Pages

296

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