Stream production and decomposition processes in contrasting environments in Argentina

GIORGI, ADONIS; VILCHES, CAROLINA; TAGLIAFERRO, MARINA; TORREMORELL, ANA; ALBARIÑO, RICARDO

Dublin (virtual)

Simposio; Symposium for European Freshwater Sciences; 2021

European Federation for Freshwater

We estimated whole metabolism and leaf litter decomposition in two Argentina ecoregions, the Pampas and Patagonia. Pampean streams have mild weather, high irradiance, moderate temperatures, high nutrient concentrations and low slopes. Patagonian streams have lower irradiance, temperature and nutrient concentrations and higher slopes. Changes in dissolved oxygen were measured in twelve streams during austral spring at both ecoregions with the two station method along selected reaches. Using these values and those of re-aeration, whole stream metabolism was estimated. Decomposition was estimated by the litter bag method, in twelve stream reaches with coarse and fine mesh sizes (20 and 0.5mm diameter, respectively) filled with 5 g of Populus nigra leaf litter. Bags were fastened to stream bottoms and retrieved at different dates to estimate decay rates by a negative exponential model against cumulative degree days (dd-1) obtained from water temperature series. Both production and decomposition differed by one order of magnitude between the two ecoregions. Estimated production was 1-8 g O2 m-2 d-1 in Pampean streams and 0.027-0.397 g O2 m-2d-1 in Patagonia streams. Decay rates in Pampean were 0.00400 dd-1 and 0.00089 dd-1 in Patagonian streams. Our findings suggest that Pampean streams function as autotrophic ecosystems while Patagonian streams behave as heterotrophic, mostly ruled by regional contrasts determining different carbon sources and the capability to process them Such differences in stream functioning were diminished in high nutrient and less dense riparian plant canopy environments.