Daily variation of N and P uptake in a highly productive Pampean stream (Argentina)

MARTI EUGENIA; SABATER FRANCESC; FEIJOO CLAUDIA SILVINA; GANTES PATRICIA; GIORGI, ADONIS; VILCHES, CAROLINA; FERREIRO NICOLAS ANDRES; TORREMOREL ANA; RODRIGUEZ CASTRO CAROLINA; RANIERI MARIA CONSTANZA

Providence

Congreso; NABS 2011 ANNUAL MEETING: RESPONDING TO THE GLOBAL WATER CRISIS; 2011

NABS 2011 Annual Meeting: Responding to the Global Water Crisis

Pampean streams are characterized by low slopes, constrained channels, open canopy, potential P-limitation, and a high abundance of algae and macrophytes. In these streams, dramatic daily variations of dissolved oxygen concentration and high rates of ecosystem metabolism have been observed. We examined how N and P uptake varied daily in Las Flores, a Pampean stream. We hypothesized that autotrophic activity would control nutrient uptake; and expected higher rates at daytime than at night. We conducted 6 slug additions of phosphate and ammonium over 24 hours. Results showed that in-stream ammonium-N and phosphate uptake accounted for about 90% of what it was added in a 28-m reach, indicating a high stream nutrient uptake capacity. While P uptake was relatively constant over time, ammonium-N uptake was lower at night. This suggests that, besides N assimilation by primary producers, nitrification could also be relevant to whole-reach ammonium-N uptake but it may be constrained by redox conditions at night. These results contribute to expand our knowledge of nutrient cycling in highly productive streams and the role of primary producers on P and N uptake.