Transformation and Loss of Nitrate in an Agricultural Stream

ABSTRACT

Mass balances of nitrate nitrogen were determined for an agricultural stream receiving non-point inputs of inorganic nitrogen. Primary production and respiration of stream reaches were estimated from analyses of diurnal changes in dissolved oxygen and temperature. Substantial in-stream losses of nitrate were observed, averaging 0.66 g N m⁻² day⁻¹. The estimated nitrogen requirements to support observed rates of primary production ranged between 0.15 and 0.27 g N m⁻² day⁻¹. Laboratory investigations measuring nitrate nitrogen loss rates from stream water overlying intact sediment cores suggest that algal assimilation of inorganic nitrogen contributes to the overall nitrate decline in these systems.