Dissolved Organic Carbon (DOC) in Agricultural Runoff and Its Influence On Exports of Estrogens and Trace Elements.

Dissolved organic carbon (DOC) provides a reactive substrate that can facilitate the transport of organic and inorganic contaminants in runoff.  The aromatic fractions of DOC are especially important since contaminants are preferentially sorbed onto these fractions.  Agricultural practices such as land application of manure can provide substantial inputs of both DOC as well as associated contaminants to agroecosystems.  We explored the exports of DOC, estrogens and trace elements in surface runoff from agricultural plots receiving poultry litter.  The study was conducted on agricultural soils of the coastal plain in Delaware.  Estrogens included free forms: estrone, 17β–estradiol, and estriol; and their glucuronide and sulfate conjugates.  Trace elements studied were arsenic, copper, and zinc.  Litter treatments included raw litter, pelletized litter and control (no-litter).  Treatment plots were 5m wide and 12m long with reduced and no–tillage management practices.  The aromatic content of DOC was characterized using specific ultra violet absorbance (SUVA).  Surface runoff samples were collected for seven natural storm events over the summer (April-July, 2008).  Flow-weighted concentrations of DOC and SUVA from plots receiving litter were significantly (p≤0.10) greater than the control plots.  Plots in reduced tillage with raw litter yielded higher DOC concentrations and SUVA values (more aromatic) compared to plots with the pelletized litter.  No significant differences (p≤0.10) in DOC and SUVA were observed for litter treatments in no-tillage.  Mass exports of estrogens and the trace elements were positively and significantly (p≤0.10) correlated with DOC and SUVA, indicating that DOC, especially its aromatic fractions, played significant role in the exports of these contaminants.