Menu
:
:



The role of dissolved organic nitrogen in a nitrate-rich agricultural stream

350 210 Stroud Water Research Center

Oviedo-Vargas D., and T.V. Royer. 2015. Journal of Environmental Quality 44(2):668–675.

doi: 10.2134/jeq2014.07.0314

Abstract

Agricultural activities have heavily altered the nitrogen (N) cycle in stream ecosystems draining croplands, particularly in the midwestern United States. However, our knowledge about dissolved organic N (DON) biogeochemistry in agricultural ecosystems is limited. From January 2011 to June 2012, we investigated DON dynamics in an agricultural headwater stream in the midwestern United States. We quantified the contribution of DON to the total dissolved N (TDN) pool and examined the role of DON as a source of N for microbial metabolism. For this we measured N-acquiring enzyme activities (aminopeptidases) and whole-stream DON uptake through short-term releases of amino acids. To investigate potential coupling between the N and C cycles occurring via simultaneous uptake of these two elements during assimilation of amino acids, seven of the short-term releases were performed concurrently with acetate. We found minimal contribution of DON to the TDN pool in this stream as a result of high concentrations of nitrate. Acetate uptake suggested that C was a limiting factor for microbial metabolism in this stream. In contrast, we were not able to detect amino acid uptake during any of the 13 short-term releases we conducted, likely as a result of high availability of dissolved inorganic N. Aminopeptidase (AMP) activity did not reflect N demand. Large spatial variability in AMP was observed within and among sites, possibly as result of physicochemical characteristics of the sediments. In contrast to other human-dominated streams, DON appeared to play a minor role in microbial metabolic processes and contributed minimally to the N pool of the study stream.

Give the Gift of Fresh Water

As you give thanks for the gifts in your life, we invite you to give the gift of water. Clean drinking water, good health, happy trout, productive soil, clean air, the simple joys of swimming, boating, fishing — our healthy freshwater ecosystems make these and so many other things possible.

Your donation today will help preserve and protect
the future of fresh water.