Analysis of water clarity, dissolved oxygen, total ammonia, total phosphorus, and chlorophyll a of Oologah Lake, Oklahoma, after zebra mussel (Dreissena polymorpha) invasion

Oologah Lake, in Oklahoma, is a U.S. Army Corps of Engineers project; flows are controlled by dam releases for navigation and flood control purposes. Zebra mussels were discovered in Oologah Lake in June of 2003. Monthly water quality samples were taken at five stations within the lake for nine consecutive years (2000 - 2008). This data set allowed for analysis of the lake's water quality parameters pre- and post-zebra mussel invasion. Water samples were analyzed for Secchi depth, turbidity, total suspended solids, dissolved oxygen, total phosphorus, total ammonia, and chlorophyll a concentrations. Standard procedures and a YSI sonde unit were used to measure Secchi depth, dissolved oxygen and turbidity at each station; the other water quality parameters were measured using EPA and Standard Method procedures in the lab. Results for each parameter were analyzed using Analysis of Covariance (ANCOVA), significance determined at alpha=0.05, for lake-wide results and individual sampling stations. Hydraulic residence time was calculated for each sampling trip and used as the covariate in the ANCOVA. During the study period, three levels of treatment periods were used, before zebra mussel arrival, during zebra mussel presence, and after the zebra mussel die-off, which occurred in 2006.;ANCOVA results indicate that there were no significant differences between treatment means (Before, During, and After zebra mussels presence) in water clarity measurements, dissolved oxygen, total phosphorus, or chlorophyll alpha concentrations for the lake-wide analysis. There was, however, a significant difference between treatment means seen at individual sampling stations for total phosphorus, dissolved oxygen, and chlorophyll alpha concentration levels at individual sites (OOL-1, OOL-3, and OOL-5, respectively). Using hydraulic resident time as a covariate in this analysis helped to isolate the impacts that zebra mussels had on the system by accounting for the impact that Oologah Lake's hydrology has on each water quality parameter measurement. Proximity of water quality sampling station to the zebra mussel population location may be another factor in lack of direct impacts on Oologah Lake's water quality parameter concentrations.