Dworshak Dam Resident Fish Mitigation

Résumé du livre

The Idaho Department of Fish and Game (IDFG) and the U.S. Army Corps of Engineers(USACE) initiated a five-year pilot project in 2007 to evaluate nutrient restoration as a management strategy for restoring the Dworshak Reservoir ecosystem and improving the fishery. The goal of the project was to restore lost productivity by improving the N:P ratios in the reservoir, thereby promoting the growth of desirable phytoplankton (i.e., edible by zooplankton). Increased abundance of edible phytoplankton was expected to lead to an increased abundance of zooplankton, therefore providing an improved forage base for fish. A moderate N nutrient restoration was hypothesized to benefit fish populations without degrading water quality (Stockner and Brandt 2006).3The project has been collaborative since its inception with the USACE applying the nutrients and IDFG conducting the monitoring. Advanced Eco-Solutions, a private consulting company, was contracted to assist in designing the monitoring program, interpret the results of the limnological data, and adjust the nutrient prescriptions as necessary. However, nutrient applications were suspended in late July of 2010 due to a legal challenge. At that time, the project was being conducted under the legal authority of a Consent Order issued by the Idaho Department of Environmental Quality (DEQ). The U.S. Environmental Protection Agency then determined that a National Pollutant Discharge Elimination System (NPDES) permit would be required for nutrient applications to continue. An NPDES permit was obtained in October of 2011,and the project resumed in 2012.This report summarizes reservoir data collected through 2022. These data were used to evaluate the action effectiveness of nutrient restoration for both limnological and fishery responses. The primary role of IDFG’s monitoring program was to evaluate the effectiveness oft he nutrient restoration program at improving the flow of carbon to the kokanee population in Dworshak Reservoir without adversely affecting water quality. Thus, limnological surveys were conducted to meet three major requirements. The first requirement was to ensure that water quality standards, as stipulated in the NPDES permit, were maintained. Secondly, limnological data were collected to make comparisons with pre-treatment conditions to determine the biological effects of the project, including changes to the plankton communities. Furthermore, data were provided to the consultant to actively manage the nutrient applications. Lastly, surveys we reconducted to monitor the kokanee population. The nutrient restoration program is expected to increase the average size of kokanee at any given population density.