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Farm Drainage Ditch Sediments Generate Urea


Harmful algal blooms can occur when noxious aquatic organisms grow in the presence of elevated urea concentrations. Urea-based fertilizers are ubiquitous, but decompose rapidly in soils. Thus, high urea concentrations found in discharge from agricultural watersheds following storm events during mid to late summer, weeks after fertilization, are unexplained by the transport of untransformed fertilizer from fields to waterways.

In a recent article in the Journal of Environmental Quality, researchers flooded sediments under controlled laboratory conditions to determine whether sediments from ditches draining different land use areas would generate high concentrations of urea in stagnant surface waters. Sediments from agricultural field ditches yielded higher urea concentrations than sediments from forested ditches, wetlands, and a control. Warmer temperatures also resulted in greater urea concentrations. In situ water samples from dry agricultural field ditches that were filled by summer rainstorms showed similar elevated urea concentrations. High urea concentrations in stagnant ditch water are likely due to microbial metabolism in the sediment.

Given the high urea concentrations observed and the expansive networks of ditches that drain agricultural fields, ditch sediments may constitute an important source of urea that may be flushed by storm events to downstream water bodies that are vulnerable to harmful algal blooms. 

Read the full open access paper in JEQ.