Relative role of transport and source-limited controls for estrogen, TDP, and DOC export for two manure application methods

Developing successful mitigation strategies for emerging contaminants can be difficult due to incomplete understanding of factors controlling their fate and transport. A variety of data analysis techniques can be used to assess the fate and transport behavior of pollutants in runoff water. Here, we use concentration-discharge, load-discharge, and coefficient of variation relationships to examine how two methods of dairy manure application (surface broadcast and shallow disk injection) affect the transport dynamics of estrogens, total dissolved phosphorus (TDP), and dissolved organic carbon (DOC). Nine surface runoff events were sampled from Oct 2014-June 2015 from 12 research plots (six with each application method) in Central Pennsylvania after fall application. The plots received inorganic fertilizer for 15 years, but only four manure applications since 2012. Both TDP and DOC exhibited similar transport behavior under both manure application methods that indicate transport-limited control of export, potentially due to legacy sources in soils. However, estrogen loads exhibited dilution responses, a sign of source-limited controls. The strength of the dilution response for estrogens was greater for surface applied manure relative to the injected manure, suggesting that manure application methods can be used to control the mobilization potential of estrogens. Additionally, results suggest the longer-term application history of inorganic fertilizer led to the transport-limited dynamics exhibited by TDP, while the short-term application history of manure caused estrogen transport to be source-limited. Our findings provide insight into how anthropogenic drivers (application type, method, and history) and natural drivers (hydrology, biogeochemistry) are interconnected in agricultural fields, and point to opportunities for protecting downstream water quality.