Agriculture doesn’t affect export of dissolved carbon

Posted on September 22, 2010

Over the last forty years there has been a clear increase in concentrations of dissolved organic carbon (DOC)  in streams of Western Europe andNorth America.  Possible causes of this increase include practices such as manure spreading, which increases the supply of organic matter, and land drainage, which increases soil aeration and rates of organic breakdown.  Because DOC acts as a focus for micropollutants (e.g., heavy metals, pesticides), high DOC levels can create a need for more costly water treatment systems. DOC management relies on an understanding of sources and movements of DOC during floods.  Researchers used concentrations of DOC, nitrate, sulphate and chloride to follow patterns of water mixing during eight storm events in a lowland headwater catchment inWestern France.  Most (up to 86%) of the DOC in streams came from flushing of the surface layers of riparian wetlands.  Instream, groundwater and rainwater sources of DOC were relatively insignificant.  Although intensive farming led to high concentrations of nitrate concentrations in the stream, comparisons with the results of previous studies in alpine and forested regions suggest that at the catchment scale, agriculture practices have no significant effect on the dynamics of DOC export.

Reference:  Morel, B., Durand, P., Jaffrezic, A., Gruau, G. & Molenat, J.  2009.  Sources of dissolved organic carbon during stormflow in a headwater agricultural catchment.    Hydrological Processes 23, 2888–2901.