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Discharge reduction, as caused by water diversion for hydropower, and fine sediments deposition, are prevalent stressors that may affect multiple ecosystem functions in streams. Periphytic biofilms play a key role in stream ecosystem functioning and are potentially affected by these stressors and their interaction. We experimentally assessed the interactive effects of discharge and fine sediments on biofilm metabolism in artificial indoor channels using a factorial split-plot design with two explanatory variables: water discharge (20, 39, 62, 141 and 174 cm3 s-1) and fine sediments (no sediment or 1100 mg L-1 of sediments). We incubated artificial tiles for 25 days in an unpolluted stream to allow biofilm colonization, and then placed them into the indoor channels for acclimation for 18 days. Subsequently, we manipulated water discharge and fine sediments and, after 17 days, we measured biofilm chlorophyll-a concentration and metabolism. Water velocity (range, 0.5 to 3.0 cm s-1) and sediment deposition (range, 6.1 to 16.6 mg cm-2) increased with discharge, the latter showing that the effect of increased inputs prevailed over sloughing. In the no-sediment treatments, discharge did not affect biofilm metabolism, but reduced chlorophyll-a. Sediments, probably as a consequence of nutrients released, promoted metabolism of biofilm and chlorophyll-a, which became independent of water discharge. Our results indicate that pulses of fine sediments can promote biofilm algal biomass and metabolism, but show interactive effects with discharge. Although discharge reduction can affect the abundance of basal resources for food webs, its complex interactions with fine sediments make it difficult to forecast the extent and direction of the changes. [ABSTRACT FROM AUTHOR]

Human activities have altered the environmental controls on river metabolism, i.e., gross primary production (GPP) and ecosystem respiration (ER). These coupled processes affect water quality, CO2 emissions, and biodiversity. Efforts to mitigate these impacts often lack long‐term, high‐resolution data needed to assess their success. Here, we estimated a 20‐yr time series of daily metabolism from dissolved oxygen (DO) data following pollution abatement (sewage treatment) in the Oria River, Spain. Ammonium concentration declined immediately after sewage abatement, whereas dissolved organic matter absorbance (proxy for concentration) declined slowly. Summer GPP declined with ammonium concentration. ER declined more strongly but more gradually than GPP and was driven by lower rates of autotrophic respiration (AR) and heterotrophic respiration following sewage treatment. Reduced AR reflected a decrease in the fraction of daily GPP being respired by algae themselves. Decline in ER caused net ecosystem production to increase from highly negative to approximately zero. Diel DO swings also declined and episodes of hypoxia nearly disappeared following reduced metabolic rates, and were paralleled by lower benthic chlorophyll a, increased macroinvertebrate indices, and a recovery of fish assemblages. Overall, wastewater treatment plants installation constrained river metabolism, greatly improved water quality, and enabled invertebrates and fish to recolonize the river. However, most variables responded gradually and these changes would not have been evident with short‐term DO data. These gradual responses revealed the need of long‐term, high‐resolution data to gain insight into long‐temporal scale responses superimposed on short‐temporal scale metabolic variation, especially in the current context of climate and land‐use change. [ABSTRACT FROM AUTHOR]

Water abstraction is rapidly increasing worldwide in order to respond to escalating demands for water, food and energy. Abstraction can alter the hydrological regime of streams and rivers, reduce in-stream habitats, change water quality and affect fluvial communities. It can also impair ecosystem functioning, although this aspect has been seldom assessed., We experimentally tested the effect of water abstraction on stream functioning in a headwater mountain stream using a before and after control-impact (BACI) design. We quantified changes in water physicochemical properties, biofilm biomass and activity (exo-enzymes and metabolism), and ecosystem processes (nutrient cycling, organic matter retention and breakdown)., Water abstraction did not affect water physicochemical properties, but reduced the biomass and the alkaline phosphatase activity of biofilm per surface unit, the areal uptake of nutrients, and the travel distance of organic matter. It did not affect the biofilm metabolism and breakdown of submerged leaf litter, but decreased the total breakdown., The impacts were larger when analysed per unit of channel length. All variables, except benthic chlorophyll- a, were significantly reduced by abstraction, due to the contraction of the wetted channel., The decrease in the biomass and activity of biofilm, as well as in nutrient uptake and total organic matter breakdown observed in this study could increase nutrient concentration in downstream reaches and reduce the energy transfer to higher trophic levels. Ecosystem services of permanent headwater streams are likely to be compromised with the reduction of wetted-channel width. [ABSTRACT FROM AUTHOR]

The effluents of wastewater treatment plants ( WWTPs) include a complex mixture of nutrients and pollutants. Nutrients can subsidise autotrophic and heterotrophic organisms, while toxic pollutants can act as stressors, depending, for instance, on their concentration and interactions in the environment. Hence, it is difficult to predict the overall effect of WWTP effluents on river ecosystem functioning., We assessed the effects of WWTP effluents on river biofilms and ecosystem metabolism in one river segment upstream from a WWTP and three segments downstream from the WWTP and following a pollution gradient., The photosynthetic capacity and enzymatic activity of biofilms showed no change, with the exception of leucine aminopeptidase, which followed the pollution gradient most likely driven by changes in organic matter availability. The effluent produced mixed effects on ecosystem-scale metabolism. It promoted respiration (subsidy effect), probably as a consequence of enhanced availability of organic matter. On the other hand, and despite enhanced nutrient concentrations, photosynthesis-irradiance relationships showed that the effluent partly decoupled primary production from light availability, thus suggesting a stress effect., Overall, WWTP effluents can alter the balance between autotrophic and heterotrophic processes and produce spatial discontinuities in ecosystem functioning along rivers as a consequence of the mixed contribution of stressors and subsidisers. [ABSTRACT FROM AUTHOR]

Abstract: There is increasing awareness of the need to include ecosystem function into river assessment protocols. Metabolism, one of the most integrative ecosystem functions, is relevant across all sizes and types of rivers, and highly sensitive to many stressors. Continuous monitoring allows using Odum''s classic method, but the mathematical analysis of long data series is arduous. Here we present RIVERMET©, a flexible, user-friendly software to assist in these calculations, that can be freely downloaded from the Internet. It consists in an Access database plus an Excel file to help import and store data, and in an Excel file with macros to make calculations. RIVERMET© can calculate the reaeration coefficient directly from night-time oxygen concentration, indirectly from empirical formulae, or can accept values obtained with any other method. It corrects the reaeration coefficient values so obtained for diel changes in temperature, and can automatically analyze the relationship between reaeration and discharge. All results can be graphed, outliers easily purged and results recalculated. Continuous monitoring of river discharge, temperature and oxygen concentration, combined with RIVERMET© allows to easily measure river metabolism, to monitor the function of river ecosystems, to assess the effect of natural or human disturbances, and to analyze post-disturbance recovery trajectories. [Copyright &y& Elsevier]