The Benthos-Plankton Relationship Upstream and Downstream of a Blackwater Impoundment

Abstract

ABSTRACT The phytoplankton, zooplankton, and the macroinvertebrate snag communities of Black Creek, South Carolina, upstream and downstream of an impoundment were Investigated during 1982. Phytoplankton and zooplankton densities upstream of the impoundment were very low. The reservoir outflow contributed a large part of the zooplankton of all sizes to the stream immediately below the impoundment. Large copepods and cladocerans were almost absent from the community 2.2 km downstream leaving mainly nauplii, small cladocerans, and rotifers. The reservoir also released a moderate amount of phytoplankton into the stream which was only slightly reduced further downstream. The macroinvertebrate snag community upstream of the impoundment was diverse and was dominated by the filter feeders Simulium and Rheotanytar-sus. The community immediately downstream of the impoundment displayed decreased diversity and was dominated by the filter-feeding caddisflies Hydropsyche and Neureclipsis crepuscularis. Further downstream, the community showed Increased diversity and a community structure resembling that above the impoundment with Rheotanytarsus dominating the filter feeders. The filter feeders above the impoundment utilized mainly ultrafine particulate organic matter (UPOM) which was probably In the form of bacteria or detritus. Immediately below, the caddisfly community utilized larger fine particulate organic matter and developed as a response to the input of large plankton entering the system. Further downstream, the return of a more diverse community utilizing UPOM paralleled the absence of large zooplankton and the retention of phytoplankton and small zooplankton in the system.