Nitrogen and carbon interactions between boreal soils and lakes

In this study, we used a large data set on nitrogen (N) and carbon (C) from Swedish boreal soils and lake waters to investigate N and C interactions between soils and lake waters. To link thousands of soils sites with hundreds of lake sites distributed all over Sweden, we gridded the data and found a significant relation between gridded C:N ratios of the organic soil layer and the ones of lake waters. We also found evidence of N deposition having depressed the C:N ratios of lake waters more than the ones of organic soil layers. In lake waters N strongly increased toward southern Sweden, mainly in the form of nitrate‐nitrogen (NO 3 − ‐N) which we primarily attribute to an increased NO 3 − ‐N input from the boreal soils into the lakes. In contrast to N we found a much weaker direct relationship for C between soils and lake waters over Sweden. Instead, lake C was strongly related to lake morphometry and catchment characteristics. Our results indicate that large‐scale variations in soil C content are not directly linked to C concentrations in lake waters, whereas soil N seems to leach in small amounts from the soils directly into the lakes in form of NO 3 − ‐N. Such differences in N and C interactions between soils and lake waters give important insights into the global biogeochemical cycling of N and C.