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

Abstract

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 R2 value of 0.73.

Keywords

• eutrophication
• phosphorus
• Sierra Nevada Mountain alpine lakes
• stocked fish