Phosphorus loading rates in lakes with development and stocked fish in the Sierra Nevada Mountains, California, USA

Abstract In high‐elevation lakes of the Sierra Nevada Mountains of central California, USA , increases in P concentration suggest accelerated nutrient loading in these delicate aquatic ecosystems. Some of these lakes show signs of eutrophication due to increased P loading. Presently, fish stocking practices include introductions of non‐native as well as native fish, and sometimes in very large quantities. Stocked fish are fed diets that are often high in P and in turn excrete high P waste into lakes and/or die and decompose, potentially adding additional P to the system. The goal of this research was to determine the potential P contributions from residential shoreline developments and stocked fish. A seasonal, steady state P loading rate model was created to quantify P loading into nine lakes in the eastern Sierra Nevada. Lakes with no fish, stocked lakes, and lakes that have shoreline developments and stocked fish were compared using measured P concentrations. The greatest difference in P‐loading rates was between stocked and unstocked lakes, which yielded an average of 6.29 × 10 −3 (±6.39 × 10 −3 ) mg P·L −1 ·yr −1 and 6.87 (±5.41) mg P·L −1 ·yr −1 , respectively. Stocked lakes with shoreline development did not vary significantly from lakes with stocked fish and no shoreline development. The P‐loading rate showed a correlation with the annual frequency of stocking events with an R 2 value of 0.73.