Trophic Cascade Effects on Algae Blooms in Washington State

Herrera conducted a study of the trophic cascade effects of trout stocking on algae blooms and cyanobacteria (blue-green algae) toxins in Washington lakes for the Liberty Lake Sewer and Water District with funding provided by the Washington State Freshwater Algae Control Grant Program. Study questions and hypotheses were developed from the compilation and review of 65 relevant publications, which generally showed that trophic cascade effects are most prevalent in lakes with high trout stocking rates and low amounts of algae. Existing water quality, cyanobacteria toxin, and trout stocking data were compiled and relationships among the key variables were evaluated on a seasonal and annual basis using principal component analysis (PCA) and multiple regression (MR). A detailed analysis of Liberty Lake, located in eastern Washington, was performed using an 18-year water quality database that included phytoplankton and zooplankton species abundance data. In addition, trophic state parameter data were compiled from ambient monitoring programs for 96 lakes with over 10 years of data in western Washington. A technical committee consisting of 15 lake experts from the University of Washington and various state and county agencies provided input in the study design and data evaluation.