Increasing dissimilarity of water chemical compositions in a warmer climate

Understanding variability patterns of biogeochemical conditions in water is a key issue for water management strategies. Here a unique homogeneous data set of 1041 Swedish boreal lakes, sampled during three lake inventories along an 8 degrees latitudinal temperature gradient, revealed a systematic increase in the variability of the water chemical composition between lakes with increasing temperatures. The variability pattern was consistent on a spatial and temporal scale and became especially apparent for water chemical variables showing an in-lake biological process-driven seasonality, such as nitrogen, pH, silica, and organic carbon. The degree of dissimilarity in the chemical composition between lakes was well related to the duration of the main growing and runoff season (D-T > 0), both on a spatial scale (R-2 = 0.57-0.79, P < 0.05) and a temporal scale (R-2 = 0.99, P < 0.05). It is suggested that D-T > 0 is a very suitable proxy to explain biogeochemical variability patterns between lakes. According to this study, a further temperature increase will result in an increased biogeochemical dissimilarity between lakes.