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Changes in soil dissolved organic carbon affect reconstructed history and projected future trends in surface water acidification

Jakub Hruška1, Pavel Krám1, Filip Moldan2, Filip Oulehle1, Christopher D. Evans3, Richard F. Wright4, Jiří Kopáček5, Bernard J. Cosby6
1 Czech Geological Survey
2 Swedish Environmental Research Institute
3 Centre for Ecology and Hydrology
4 Norwegian Institute for Water Research
5 Hydrobiological Institute AS CR
6 University of Virginia

P 7.11 in Controls of dissolved organic matter fluxes in ecosystems

Poster Session 1 on Monday, 16:30-18:30

Over the last two decades concentrations of dissolved organic carbon (DOC) have shown widespread increases in surface waters in several regions in Europe. The increases in DOC have been ascribed primarily to decreased acid deposition and the mechanism appears to be increased solubility of DOC due to decreased ionic strength of soil solution. Concentrations of DOC in acidified surface waters were thus probably higher in pre-industrial times relative to present-day levels and may increase further in the future if acid deposition continues to decline.

Pre-industrial (1850s) and future (2060) stream water chemistry of an anthropogenically acidified small catchment (Lysina, Czech Republic) was estimated using the MAGIC model for three different scenarios for dissolved organic carbon (DOC) concentrations and sources. The highest modeled pH = 5.7 for 1850´s as well as for 2060 (pH = 4.4) was simulated given the assumption that stream water DOC concentration was constant at the 1993 level. A scenario accounting for an increase of DOC as an inverse function of ionic strength (IS) of soil water and stream water resulted in much lower pre-industrial (pH=4.9) and future recovery to (pH=4.1) if the stream riparian zone was assumed to be the only DOC source. If upland soil water (where significant DOC increase was observed at 5 cm and 15 cm below soil surface) was also included, DOC was partly neutralized within the soil and higher pre-industrial pH=5.3 and future pH = 4.2 were estimated. The observed DOC stream flux was 2 – 4 times higher than the potential carbon production of the riparian zone, implying that this is unlikely to be the sole DOC source. Modeling based on the assumption that stream DOC changes are solely attributable to changes in the riparian zone appears likely to underestimate pre-industrial pH.

Letzte Änderung 19.06.2014