Evaluating the hydrological, geothermal and anthropic factors in the Baños tarn (Spanish Pyrenees)

Abstract

Baños tarn is a low-altitude Pyrenean glacial lake with both geothermal and surface influxes and significant local anthropic stressors. Its water was seasonally sampled from 2010 to 2013 to study its dynamics and evaluate the main factors affecting its hydrochemical trends. Main surface and thermal streams draining into the water mass were also assessed and a detailed characterisation of the study site was made. The large catchment area of the Baños tarn implies a huge water input, a short water retention time and a high water mass mixing that reduces the natural stratification of the lake. The hydrochemical features of the Baños tarn are primarily determined by a slightly alkaline pH and fluctuating medium–high ionic and nutrient contents. Hydrological changes affecting lake tributaries are the foremost factors driving seasonal changes in the ionic composition of the lake. Resuspension of organic matter and nutrients trapped in floor sediments by a century-long history of untreated waste water inputs is supposed to be the main nutrient source to the Baños water mass. Other anthropic activities, such as tourism, dam and withdrawal pipe management, as well as shoreline reforestation, also affect the trophic dynamics of the Baños tarn. These results present herein are scientifically novel because of the uncommon features of the Baños tarn and may broaden our understanding of factors affecting glacial lake dynamics on a global scale.