Evaluation of pollutant sources in the circumlacustrine ring of Lake Titicaca (Peruvian sector), 2017

Abstract

Lake Titicaca with river contributions (tributaries) considered endorheic, is an ecosystem that plays different functions and hosts great biodiversity. It is important to evaluate pollutants, especially the addition of nutrients, to evaluate the pollutant sources in the circumlacustrine ring of Lake Titicaca through the exploration of physicochemical parameters, considering the state of water quality, the contribution of the pollutant load, and variability between areas and periods evaluated. In April and September/October 2017, two campaigns were carried out and the monitoring stations were in areas where the tributary inflow drains into the lake, and at effluent entry points that capture wastewater. We considered 39 stations (20 in bays and river mouths, 10 in river tributaries, and 9 in wastewater effluent points of treatment plants - WWTPs). Wastewater discharges yielded high levels of BOD5, nitrogen, and total phosphorus, exceeding the maximum permissible limits (D.S. 003-2010-MINAM) for thermotolerant coliforms in all effluents, except for the Tilali oxidation pond, did not show significant differences (p> 0.05) between evaluation periods. As for rivers, we observed that the daily discharge with the highest pollutant contribution occurred in April (total nitrogen 15.70 t/day, total phosphorus 3.54 t/day, TSS 921.69 t/day, and BOD5 42.02 t/day), while in September/October it was reduced, the greatest contributions were recorded at the confluence of the Ramis and Huancané, Coata and Ilave rivers. There was an increase of 0.65 (total nitrogen) and 0.94 (total phosphorus) compared to 1981-1982. According to the WQS category 3 for rivers, pH exceeded in all the zones evaluated, BOD5 was higher for the Coata River, and thermotolerant coliforms were high for the Desaguadero River. Regarding the bays and mouths of Lake Titicaca (Peruvian sector), nutrients showed high values in the bay of Puno and Yunguyo. According to WQS – category 2 and 4 (D.S. Nº 004-2017-MINAM), the electrical conductivity, total phosphorus, and total nitrogen were exceeded in most of the evaluated areas, while in the inner bay of Puno and Yunguyo, chlorophyll-a, BOD5, TSS were found above the permissible ranges, presenting hypertrophic levels according to the trophic status of the OECD (1982). No significant differences (p>0.05) were found between the periods evaluated, based on the statistical analysis.