Nitrate Reductase Activity in an Eutrophic Reservoir duringthe Stratification Cycle

Nitrate reductase activity was measured during the stratification cycle of the eutrophic reservoir La Concepcion. Nitrate was consumed in the epilimnion mainly through assimilatory reduction, and in the hypolimnion through dissimilatory reduction triggered by anoxic conditions. Nitrate reductase activity (NR) scaled to particulate nitrogen (PN) was positively correlated with the external nitrate concentration and the NO3 ‐ /NH4 + ratio. Using NR as a tool for the assessment of the N cycle dynamics, it can be suggested that at the beginning of the stratification cycle, the phytoplanktonic community was mainly using NO3 ‐ as N source; and since N was not likely the limiting nutrient at that time of the year, NR was close to its maximum possible.