EFFECTS OF RESERVOIR TYPE (RUN OF RIVER VS. STORAGE) ON NATIVE AND INVASIVE ZOOPLANKTON ASSEMBLAGES

Impoundments (dams and their resulting reservoirs) hydrologically alter riverine systems by lengthening water residence time and altering water quality. Zooplankton are vital primary and secondary consumers in these systems and are an important prey base for the economically and ecologically important salmonids of the Pacific Northwest. The NSF (DISES-DAMS) project aims to determine the ways in which run of river (ROR) and storage reservoirs differ ecologically, including how zooplankton i) assemblage structure, ii) seasonal abundance, and iii) occurrence of invasive species differ between reservoir type. We undertook a two-year field study of four impoundments within the Columbia River Basin, including two ROR (Bonneville, The Dalles) and two storage (Cougar, Detroit) reservoirs. Replicate zooplankton and associated environmental samples were collected at each site bimonthly. We found zooplankton absolute abundances to be higher in storage reservoirs than in ROR reservoirs (with marked seasonal variability). Additionally, relative abundance was also different between storage and ROR reservoirs, with taxa more evenly distributed in ROR systems and dominated by copepods in storage systems. Temperature and conductivity were found to be significant factors associated with zooplankton assemblage structure, which may be due to their effects on phytoplankton productivity. Lastly, invasives (e.g., the copepod Pseudodiaptomus forbesi) were only found in the ROR sites, likely due to the mainstem Columbia fostering invasive introductions via shipping.

Presentation Preference: Oral

Primary Presenter: Jess Mitchell, Washington State University (jess.mtchell@gmail.com)

Authors:

Jess Mitchell, Washington State University  (jess.mtchell@gmail.com)

Stephen Bollens, Washington State University  (sbollens@wsu.edu)

Gretchen Rollwagen-Bollens, Washington State University  (rollboll@wsu.edu)