Document Type

Technical Report

Publication Date

6-1-1995

Keywords

Zebra mussel, Arkansas river, Reservoir ecosystem

Abstract

Zebra mussels recently invaded southern waterways including the Arkansas River. Exponential population growth and high filtration capacity of dense populations could alter reservoir ecosystem function. Furthermore, they attach to hard surfaces; thus, threatening normal operations of many artificial structures. We designed this study to provide baseline data prior to high population levels of zebra mussels in Lake Dardanelle. The characterization of spatial and temporal variability in water quality, zooplankton, phytoplankton, and macrophytes will allow testing of several hypotheses. We sampled zebra mussel density and zooplankton at four fixed sites and the other key variables at three of these sites biweekly from August 1994 through June 1995. Turbidity was high, averaging 22.5 NTU and Secchi disk depths were typically less than 0.8 m. The main lake had the highest average turbidity and the Illinois Bayou bay of the lake had the lowest (29.0 and 16.4 NTU, respectively). Chlorophyll a was the dominant chlorophyll type (mean of 15.8 ug/L) and it was lowest in winter (< 8 ug/L) when water temperatures and solar infiltration were the lowest. Turbidity was high during this period due to above average flows and higher loading of sediments. Total suspended solids were also high (mean of 16.7 mg/L) and followed the same pattern as turbidity. Concentrations of major ions increased during fall anddeclined sharply in early winter. In the bay areas, these ions were somewhat diluted by tributary flow compared to those in the main lake {e.g., conductivity was 318 verses 420 us/cm, respectively). Rotifers numerically dominated the zooplankton community. Their density was similar among sites and often exceeded 40/L. Mean density of larval zebra mussels in 1993 remained less than 0.1/L; whereas, in 1994 density was over 10/L for much of the summer and exceeded 50/L on two sampling dates. The 1995 summer peak in larval zebra mussel density may still be in progress and our most recent samples analyzed (July 9) document a mean density exceeding 32/L. We found only 2.5 to 37.5% coverage of emergent vegetation (especially water willow) in shoreline sample areas and no submergent vegetation. Increased light penetration (resulting from high filtration rates) could allow dense beds of emergent and submergent vegetation, which could drastically influence fish population dynamics and negatively impact boating. The study will be continued to test this and related hypotheses.

Report Number

PUB 171

Page

86

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