Bioclimatic influence on water chemistry and dissolved organic matter in shallow temperate lakes of Andean Patagonia: A gradient approach

Abstract

We addressed the influence of bioclimatic variables (precipitation, temperature and vegetation) on physicochemical properties, carbon (C) and nutrients dynamics in shallow temperate lakes in the northern Patagonian Andes. Four shallow lakes (mean depth < 15 m) located along the Andean Patagonian bioclimatic gradient, and characterised by a west‐to‐east decrease in precipitation, increase in temperature and changes in vegetation type, were studied during wet and dry periods. Physicochemical variables, total nitrogen and phosphorus (TN and TP) and particulate and dissolved organic matter (POM and DOM) were analysed. Multivariate analyses were performed to evaluate the influence of environmental variables on lake water chemistry and to identify the main factors associated with spatial and temporal differences in lake DOM pools. Spatial and seasonal decreases in precipitation and warming were reflected in reduced hydrological connectivity of the lakes. The reduced connectivity resulted in increased conductivity, pH, alkalinity, dissolved organic carbon (DOC) and TN concentrations. Such conditions favoured the loss of lake DOM aromaticity, humic content and molecular weight/size, and increased the degradation signals and the biologically produced DOM fraction. Lakes responded uniformly to changes in climate variables along the Andean Patagonian gradient. Differences among lakes in water chemistry and DOM composition, were associated at the gradient scale with variation in precipitation, temperature and catchment vegetation, which may provide insights into C and water chemistry trajectories under forecasted climate trends. Our results suggest that drought and warming trends could result in less hydrological connectivity, shrinking terrestrial DOM fluxes to lakes while concomitantly increasing internal degradation processes.