Synchronous variation in water chemistry for 80 lakes in southern Sweden

Variation in water chemistry was studied in 80 lakes in southern Sweden. The lakes had forest dominated catchments. The length of the time series was 14 years. Synchrony was calculated as Pearson's product moment correlation coefficients for all combinations of lakes, i.e. 3160 lake-pairs. The chemical variables studied were non-marine sulphate (SO4*), non-marine calcium (Ca*), absorbance and acid neutralising capacity (ANC). Statistically significant synchrony occurred in 93% of all lake-pairs for SO4*, and between 58 and 67% for absorbance, Ca* and ANC. In 70% of all lake-pairs, the synchrony was > 0.71 for SO4*, which means that more than half of the variation in one lake could be explained by the variation in the other lake. For absorbance, Ca* and ANC, about 25% of the lake-pairs had a synchrony > 0.71. The relatively high synchrony for SO4* occurred during an overall downward trend in SO4* concentration. The degree of synchrony in our study was at a level comparable to other studies in northern America and England. However, our study included lakes in a much larger area, with distances of up to 500 km between the lakes, while earlier studies were made on small lake districts with lakes located within approximately 50 km. In contrast to these earlier studies, there was no correlation between synchrony and distance, lake characteristics or catchment characteristics. However, when a small subset of 15 lakes in the southeast of Sweden was selected, such relations were found.