Spatial and temporal dynamics of the trophic state in a tropical high Andean lake in northern

Abstract

Perú. Lake Pomacochas is located in the montane forest region of northern Perú, in an area of great agricultural and fish farming importance, activities that represent the basis of the local economy. The population settled on its margins discharges part of its wastewater into the lake without treatment. The main aim of this study was to determine the spatio-temporal dynamics of this lentic ecosystem, evaluating the limnological and trophic conditions during the dry and rainy periods, and their relationship with each other. The following limnological variables were analyzed at 15 sampling sites: Transparency, chlorophyll ‘a’, temperature, pH, conductivity, oxygen saturation, turbidity, nitrates, nitrites, ammonium and soluble reactive phosphorus. Besides, the following trophic indices were calculated: Carlson’s trophic status index (TSIC), trophic status index modified by Aizaki et al. (TSIA), trophic status index modified by Toledo et al. (TSIT) and trophic status index by Vollenweider et al. (TRIX). The lake showed temporal, but not spatial, variation for both limnological variables and trophic indices. The dynamics of the limnological variables in the different climatic periods was also analyzed. The TSIC and TSIA indexes indicated that the lake can be characterized as α-mesotrophic to β-eutrophic, and according to TSIT index as α-mesotrophic to α-eutrophic. The TRIX showed the system has a poor water quality, highly productive, and a very high trophic level. The results reveal that the TSIA best described the trophic state of the lake, while the TSIC was the worst. All these results were statistically significant (P<0.05). The trophic indices evidenced that lake Pomacochas shows a strong tendency to the eutrophication due to agricultural activities. The study also showed that the system is conditioned by climatic seasonality.