Integrated study of metal behavior in Mediterranean stream ecosystems: a case-study.

The objective of the present work was to assess the ecosystem status of Francolí river (Catalonia, Spain), a Mediterranean stream basin with contrasting human influences. An integrated approach was designed by combining physicochemical, biological and ecotoxicological analyses. The content of metals (As, Cd, Cr, Co, Cu, Hg, Ni, Pb, and Zn) was analyzed in samples of water, benthic sediments and aquatic macroinvertebrates. In addition, the potentially bioavailable fraction of metals in water and sediments was determined by using diffusive gradient in thin-films (DGTs) and sequential extraction of sediments (BCR), respectively. The biological quality was evaluated through aquatic macroinvertebrate communities, while the ecotoxicological status was assessed by Microtox(®) with Vibrio fischeri. Finally, an analysis of acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) was performed to evaluate the sediment toxicity associated to metal content. According to the results, DGTs and BCR are suitable methodologies to predict the potential bioavailable fraction of metals in freshwater systems. Moreover, ecotoxicity evaluation by means of V. fischeri, in combination with the chemical characterization and the biological quality assessment, should be complementarily used to get a better diagnose of freshwater systems.

Point-source effects on N and P uptake in a forested and an agricultural Mediterranean streams.

We examined the effect of point-source inputs from wastewater treatment plants (WWTP) on in-stream uptake of ammonium, nitrate and phosphate and compared it between two streams draining catchments with contrasting land use. The selected streams were La Tordera and Gurri (NE Spain), draining a forest- and an agriculture-dominated catchment, respectively. In each stream, we compared nutrient uptake metrics, estimated from nutrient additions, between two reaches located upstream and downstream of a WWTP input. Measurements were done on 8-9 dates during 2002-2003. In La Tordera, the point-source increased concentrations of all studied nutrients; whereas in Gurri, this effect was less evident. Point-source effects on nutrient uptake differed between the two streams, and among solutes. In La Tordera, uptake lengths (S(w)) of ammonium and phosphate averaged hundreds of meters above the point-source, and increased (i.e., decreased uptake efficiency) 4 and 5 times, respectively, below the point-source. S(w) of nitrate was ≥2km regardless of reach location. In Gurri, S(w) of all studied nutrients was within the km range in the two reaches. In this stream, diffuse nutrient inputs from adjacent fields may overwhelm the local effect of the point-source input. Uptake velocities (v(f)) of the studied nutrients ranged between 10EXP(-6) and 10EXP(-4)m/s in the two streams, and were similar between the two reaches in each stream. However, phosphate v(f) decreased under increasing concentrations following a power function. This trend remained significant when combining our results with those compiled from literature, suggesting the efficiency loss response may be a general trend for phosphate across streams. The relative increases in uptake rates (U) below the point-source were proportional to the relative point-source contribution to downstream nutrient loads, especially for ammonium and nitrate. However, the increases in U were not enough to compensate for the increases in nutrient loads downstream of the WWTP input.

Net changes in nutrient concentrations below a point source input in two streams draining catchments with contrasting land uses.

We examined net changes in ammonium-Nitrogen (NH(4)(+)-N), nitrate-Nitrogen (NO(3)(-)-N), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), and dissolved organic carbon (DOC) chloride-corrected ambient concentrations along a reach located below a wastewater treatment plant (WWTP) input in a non-agricultural (12 dates) and an agricultural (6 dates) stream. Based on those net changes, we estimated processing length (Snet) and mass transfer coefficient (Vf) of the cited nutrients. In the agricultural stream, results suggest that diffuse nutrient inputs from adjacent agricultural fields had a greater effect on water chemistry than the WWTP input, and probably overwhelmed the stream capacity to retain and transform nutrients. In the non-agricultural stream we observed consistent longitudinal trends below the WWTP input only for NH(4)(+)-N and NO(3)(-)-N. The tight coupling between longitudinal NH(4)(+)-N decreases and NO(3)(-)-N increases in the non-agricultural stream, and lack of longitudinal trends of DIN on most dates suggest that NH(4)(+)-N from the WWTP input was being nitrified along the reach. These results suggest that WWTP inputs favor conditions to support hot spots for chemoautotrophic activity.