Surface water chemistry: the key to partitioning dissolved matter sources and assessing carbon cycle parameters

Abstract

For the first time, the contributions of surface water base cation sources, such as atmospheric deposition, weathering and organic matter mineralisation were estimated using only water chemistry data. Estimations were based on a comparison of acid neutralising capacity (ANC) and dissolved organic carbon (DOC) export ratios measured for the ice-covered and the ice-free periods. The highest export of cations from both atmospheric and organic origin was observed during mid-summer, when the maximum precipitation coincides with maximum temperature, which favours organic decomposition. Organic matter contribution decreases from spring to autumn, contrary to the increase in weathering contribution. In the first half of the ice-free period, this is conditioned by the optimisation of soil conditions favourable to weathering, and in the second half it is mostly due to the decrease in precipitation and, consequently, in lateral flow. Since the ANC represents cations released due to carbonic and carboxylic acid reactions and organic mineralisation, it can also be considered a parameter of the carbon cycle. The export value of mineralisation-derived cations can serve as the basis for evaluating the CO2 emission from soil.