Oligotrophication Effects Following Diversion of Waste Effluent from an Embayment of Lake Martin, Alabama

Abstract

I examined the effects of nutrient diversion on water quality, phytoplankton, and macroinvertebrate and fish community structures over a 10-year period in Lake Martin, Alabama. In 2001, a pipeline began diverting treated effluent from Alexander City, Alabama out of Elkahatchee Creek Embayment (ECE) and into the mainstem of Lake Martin reservoir. Oligotrophication in ECE produced measurable responses within the biotic community, including: 1) decreased algal biomass; 2) a shifting black bass community; 3) decreased catch and condition of sunfish and crappie; and 4) altered structure and function of littoral macroinvertebrate communities. Elevated conductivity at the mouth of Dennis Creek Embayment (DCE), the reference site, suggested the encroachment of diverted effluent. No changes conclusive to nutrient enrichment were found with respect to: key nutrients, algal biomass, or macroinvertebrate assemblages. vi However, some Centrarchid fish responded in a manner consistent with eutrophication. Members of Lepomis expressed higher condition following diversion. In addition, the black bass dynamic shifted to favor longer largemouth bass (Micropterus salmoides) with higher relative weights, while spotted bass (Micropterus punctulatus) were fewer, shorter, and less robust. The aquatic communities in this study provided a measurable response to subtle changes in trophic status which underscores the sensitivity of the aquatic community. The ability to detect and predict these subtle changes enables reservoir managers to make more confident predictions and ultimately lead to improved design and management of reservoirs.