Eutrophication processes in the Azul and Quemquemtreu rivers, Lago Puelo sub-basin, Argentina
DOI:
https://doi.org/10.25260/EA.25.35.1.0.2335Keywords:
conservative variables, nutrients, limiting nutrients, trophic state, periAbstract
Conservative variables and nutrients were analyzed in the Azul river basin from August 2019 to July 2020 to study their bimonthly variations, in relation to natural characteristics and anthropic impacts. Electrical conductivity (EC) and pH were measured in situ, and samples were taken for analysis of total alkalinity (AT), ammonium (NH4+), nitrites + nitrates (NO2- + NO3-), phosphates (PRS), nitrogen and total phosphorus (NT, PT) in four sites located on the Quemquemtreu river and two sites on the Azul river. During the same period, precipitation and temperature data were analyzed. Nutrients, EC and AT values were significantly different (P<0.05) between sites in the entire Azul-Quemquemtreu system, while mean pH values varied significantly between samplings (P<0.001), indicating the influence of precipitation, spring thaw and periphytic coverage. The greatest anthropic impacts were observed in sites downstream of the urban area, associated with household discharges, soil washing and effluents from the sewage treatment plant (PTLC), mostly during the summer season. Nutrient values of the middle Azul River were largely recovered in the lower reach of the river, downstream of the mouth of the Quemquemtreu River, by dilution and self-purification processes; this reach presented a notable increase of periphytic coverage. The limiting nutrient was nitrogen (N) in pristine sites, and phosphorus (P) in sites with anthropogenic impact. In general, the trophic state of the basin is oligotrophic; only the lower reaches of the Quemquemtreu river were classified as eutrophic to mesotrophic. The annual average values of NT and PT in the Azul-Quemquemtreu system between 1995/6 and 2019/20 increased significantly by 710% and 120%, respectively.
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