Nitrate reductase activity in an eutrophic reservoir during the stratification cycle

Nitrate reductase activity was measured during the stratification cycle of the eutrophic reservoir La Concepcion. Nitrate was consumed in the epilimni on mainly through assimilatory reduction. and in the hypolimnion through di ssimilatory reduction triggered by anoxic conditions. Nitrate reductase act ivity (NR) scaled to particulate nitrogen (PN) was positively correlated wi th the external nitrate concentration and the NO3-/NH4+ ratio. Using NR as a toot for the assessment of the N cycle dynamics, it can be suggested that at the beginning of the stratification cycle, the phytoplanktonic communit y was mainly using NO3- as N source; and since N was not likely the limitin g nutrient at that time of the year, NR was close to its maximum possible.