Alterations of the hydrologic regime and their effects in the phosphorus and phosphates in Lake Chapala, Mexico [modificaciones en el régimen hidrológico y sus efectos en la acumulación de fósforo y fosfatos en el Lago de Chapala, MéXico]

Abstract

As a result of water inflow reduction and contamination, as well as water volume loss due to water extraction, since several years ago Lake Chapala undergoes a process of cultural eutrophication due to excess of nutrients, placed in evidence by the grow of abundant aquatic vegetation in the mouth of the Lerma River and in the lake itself. Application of non conventional techniques based in a cell model to obtain a mass balance for phosphorus (P) and phosphates (PO4 -3) demonstrated that the main source of this nutrients in the lake is the Lerma River, due to the fact that this river receives municipal, agricultural, and industrial waste water discharges, with limited treatment, along the basin. This work proposes a rigorous method to assess P and PO4 -3 accumulation in Lake Chapala. The results show that the lake lost its ability to remove total P since 1983 and PO4 -3 starting in the period 1977-1978. At the same time it was estimated that the average amount of PO4 -3 in the lake represents 67.6% of total P, which maintains a high biological availability of this nutrient in the water column of the lake.