MEASUREMENT OF NUTRIENT SPIRALING IN A MEDITERRANEAN STREAM - COMPARISON OF 2 EXTREME HYDROLOGICAL PERIODS

Uptake length and uptake rate of nitrate-N, phosphorus, calcium and po tassium were measured in a second order Mediterranean stream of SW Spa in, in November 1991 and May 1992. This study compared two disturbance phases of an annual hydrological cycle: at initiation of surface flow and at the end of continuous flow (drying-pool). At both times nitrat e-N and calcium were the elements with lowest uptake length followed b y phosphorus and potassium. A higher uptake rate occurred for all elem ents during continuous surface flow, indicating that in this phase of the hydrological cycle, there was a higher retention capacity by the e cosystem. This higher uptake rate occurred despite the lower temperatu re, higher discharge and higher water velocity during surface flow, in dicating that in Montesina streams, these variables were not the most important mechanisms regulating element uptake, at least in these two extremes hydrological phases. The shorter uptake length of nitrate-N t han phosphorus suggests N-limitation in this stream.