Determining the Influence of Land-Use On Urea Sources and Transport within the Chesapeake Bay Watershed.

Urea, a form of organic nitrogen found in fertilizers, manures and septic waste, has increasingly been discovered in surface waters throughout the Chesapeake Bay watershed and similar coastal systems. This nutrient is gaining recognition as a driver for the development of Harmful Algal Blooms (HABs) that produce the deadly toxin domoic acid.  Mounting evidence demonstrates that environmentally significant urea loadings are delivered from headwaters to estuaries; however, the types of sources, transport pathways, and in-stream processes that affect urea within the river network are poorly understood.  The main objective of this research is to identify spatial and temporal relationships between land-use and urea loading in the Manokin River, an agricultural watershed with intensive poultry production that drains directly into the Chesapeake Bay.  Preliminary results from synoptic baseflow sampling conducted at 20 sites throughout the watershed in March and April 2010 revealed that urea concentrations in surface water were generally low (<1.0 μM L^-1).  Intensive sampling at one headwater agricultural site during a storm event in late March 2010 produced slightly higher urea concentrations (1 – 2 μM L^-1) than those measured in baseflow, which suggested that stormflow may be an important period for urea mobilization and transport.  The results of this study will shed light on spatial and temporal patterns of urea delivery to river networks and quantify sources of urea to surface waters.  This information will be critical to the development of nutrient management plans and restoration efforts aimed at protecting aquatic life in the Chesapeake Bay Watershed.