Phosphates in Lake Chapala, Mexico

Lake Chapala, the most important lake in Mexico, has suffered from cultural eutrophication problems for many years, manifested by the growth of aquatic vegetation and an increase in primary productivity. It was found that about 70% of the total phosphorus entering Lake Chapala is orthophosphate, thus increasing the biological availability of nutrients in the lake. In addition, the hydrologic imbalance in the lake, caused by the over‐use of water resources along the Lerma–Chapala basin, has significantly increased the hydraulic residence time of the inflow waters, thus increasing the effects of the added phosphorus, and creating conditions that increase the lake’s eutrophication status. The shallow characteristics of the lake and the action of the wind forces produce rapid changes in water quality, especially in the distribution of phosphate. The focus of this paper is on the development of a historical orthophosphate balance in Lake Chapala, quantifying the main point and non‐point sources that contribute to the enhancement of this nutrient in the lake. The estimation of the amount of phosphate in the lake can be used to determine appropriate management practices to reduce the phosphate loads on the lake.