Poultry manure runoff and its influence on fluorescence characteristics of dissolved organic matter (DOM)

Land application of poultry manure as a substitute for synthetic fertilizer is a common practice in states like Delaware which have a surplus of this animal waste. However, this practice can generate large amounts of labile DOM and nutrients in agricultural runoff that can cause eutrophication of downstream aquatic ecosystems. We determined the concentrations of dissolved organic carbon (DOC) and dissolved inorganic nitrogen (DIN) and the quality of DOM for a cropland receiving poultry manure in the coastal plain soils of Delaware. Manure was applied at the rate of 9 Mg ha-1 in the spring (March 10) of 2010 to an agricultural field planted in corn. Sampling was performed for surface runoff and soil waters at four landscape positions - field edge, upper and lower riparian zones and the stream. Sampling was conducted for eight storm events, one before manure application and seven after (March through July spanning over 100 days). DOM quality was characterized using spectrofluorometric techniques and the development of a site-specific PARAFAC model. DOC and DIN concentrations in surface runoff ranged from 18.1 to 77.2 mg/l and 4.2 to 22.6 mg/l, respectively. The percent of protein-like and humic-like DOM in surface runoff ranged between 3.9 to 23.5% and 12.3 to 41.6%, respectively. Highest concentrations of DOC and DIN were observed at the field edge and lowest in the stream. Protein-like and humic-like DOM decreased from the field edge to stream in surface runoff and soil waters. Temporally, both humic-like and protein-like DOM showed significant increases in storm runoff following manure application. After manure application, humic-like DOM increased by 70% while protein-like DOM increased by more than 200% in surface runoff indicating elevated content of labile DOM in poultry manure. These concentrations remained high for more than 60 days following manure application. Protein-like DOM was significantly correlated with nitrate-nitrogen (r = 0.43; p < 0.05) concentrations indicating a coupling of labile DOM and nutrients. Our results suggest that runoff from cropland receiving animal manure can contain elevated concentrations of DOC and DIN and labile DOM (as indicated by the content of protein-like DOM). The potential for loss of these nutrients in surface runoff is especially high for storm events that immediately follow manure application.