El Nino southern oscillation and seasonal drought drive riparian input dynamics in a Mediterranean stream

Inland waters substantially contribute to global carbon fluxes, and within them, low-order forested streams are important processors of allochthonous organic matter (OM) inputs. Leaf litter quantity and quality are expected to change in response to global change (e.g., climate change, land use change) but few long-term studies exist to better understand these shifts. The goal of this study was to assess the quantity and quality of OM sources to determine which global and local environmental factors control the dynamics of OM at the reach scale. The study was performed on a Mediterranean stream edged by a deciduous riparian forest over a 10-yr-time period. Riparian inputs, benthic and transported OM, and its carbon and nitrogen content were determined. The quantity of riparian inputs (912 +/- 56 g dry mass m(-2) yr(-1)) was comparable to temperate regions with deciduous riparian forests, but the Mediterranean climate determined the different dynamics of these inputs. El Nino Southern Oscillation was strongly related to the interannual variability in riparian inputs through changes in precipitation. The annual amount of inputs depended on previous cumulated nonflow periods, with successive nonflow periods causing a progressive decrease in riparian inputs. The distribution of inputs throughout the year followed either a unimodal or bimodal pattern according to the absence or presence of a nonflow period in summer. In addition, drought caused lower quality (higher carbon : nitrogen molar ratio) riparian inputs. Changes in the quantity and quality of OM were explained by both present and past local and global factors

Elemental ratios in sediments as indicators of ecological processes in Spanish reservoirs

Reservoir sediments are important archives of biogeochemical data, reflecting ecological processes that occur at the watershed system. In this paper, a preliminary study of the limnological significance of major element composition and element ratios in sediments of Spanish reservoirs is presented, by analysing two data-sets from different limnological regions. Reservoirs from Eastern and Western Spain present significant differences in the chemical composition of their sediments: higher average values for calcium and magnesium appear in the Eastern reservoirs, while, in Western Spain, higher mean values are found for alumino-silicate elements (i.e. silicon, aluminium, and potassium), iron and phosphorus. Meaningful ratios are Si/Al and Si/K, that are closely related to energy transport in sedimentary catchments, whereas in siliceous catchments Si/Al is an indicator of chemical weathering. Ca/Al ratio appears related to water mineralization, and, in the Eastern Region, the slope of the regression line between Ca/Al and conductivity reflects catchment mineralogy. In superficial sediments from both Eastern and Western regions, Fe/Al is linked to the authigenic precipitation of iron oxides and appears closely related to sedimentary phosphorus accumulation above background levels.El sedimento de los embalses constituye un importante registro de datos biogeoquímicos, ya que refleja los procesos ecológicos que tienen lugar en el conjunto de la cuenca hidrográfica. A partir del análisis de dos conjuntos de datos obtenidos en distintas regiones limnológicas, se presenta una aproximación preliminar al significado limnológico de la composición química y los cocientes elementales en el sedimento de los embalses españoles. Las regiones Este y Oeste de la Península muestran diferencias significativas en cuanto a composición química del sedimento: los mayores valores promedio en la región Este corresponden a la concentración de calcio y magnesio, mientras que en la región Oeste, los mayores valores medios corresponden a los elementos asociados a los alumino-silicatos (aluminio, silicio y potasio), hierro y fósforo. Los cocientes elementales con mayor significado son: Si/K y Si/Al estrechamente relacionados con la energía de transporte en la región calcárea, mientras que en la región silícica Si/Al es un indicador del proceso de meteorización química. Ca/Al se encuentra asociado a la mineralización del agua, y en la región Este la pendiente de la recta de regresión entre Ca/Al y la conductividad del agua refleja la mineralogía de la cuenca. En ambas regiones, el cociente Fe/Al en el sedimento superficial indica la precipitación endógena de óxidos de hierro y aparece estrechamente asociado a la acumulación de fósforo sedimentario por encima del nivel basal

Effects of human-driven water stress on river ecosystems: a meta-analysis

Human appropriation of water resources may induce water stress in freshwater ecosystems when ecosystem needs are not met. Intensive abstraction and regulation cause river ecosystems to shift towards non-natural flow regimes, which might have implications for their water quality, biological structure and functioning. We performed a meta-analysis of published studies to assess the potential effects of water stress on nutrients, microcontaminants, biological communities (bacteria, algae, invertebrates and fish), and ecosystem functions (organic matter breakdown, gross primary production and respiration). Despite the different nature of the flow regime changes, our meta-analysis showed significant effects of human-driven water stress, such as significant increases in algal biomass and metabolism and reduced invertebrate richness, abundance and density and organic matter decomposition. Water stress also significantly decreased phosphate concentration and increased the concentration of pharmaceutical compounds. The magnitude of significant effects was dependent on climate, rainfall regime, period of the year, river size and type of water stress. Among the different causes of water stress, flow regulation by dams produced the strongest effects, followed by water abstraction and channelization

Drivers of phytoplankton responses to summer wind events in a stratified lake: A modeling study

Extreme wind events affect lake phytoplankton by deepening the mixed layer and increasing internal nutrient loading. Both increases and decreases in phytoplankton concentration after strong wind events have been observed, but the precise mechanisms driving these responses remain poorly understood or quantified. We coupled a one-dimensional physical model to a biogeochemical model to investigate the factors regulating short-term phytoplankton responses to summer wind events, now and under expected warmer future conditions. We simulated physical, chemical, and biological dynamics in Lake Erken, Sweden, and found that strong wind could increase or decrease the phytoplankton concentration in the euphotic zone 1 week after the event, depending on antecedent lake physical and chemical conditions. Wind had little effect on phytoplankton concentration if the mixed layer was deep prior to wind exposure. Higher incoming shortwave radiation and hypolimnetic nutrient concentration boosted phytoplankton concentration, whereas higher surface water temperatures decreased concentrations after wind events. Medium-intensity wind events resulted in more phytoplankton than high-intensity wind. Simulations under a future climate scenario did not show marked differences in the way wind events affect phytoplankton concentration. These findings help to better understand how wind impacts vary as a function of local environmental conditions and how climate warming and changing extreme weather dynamics will affect lake ecosystems

A Conceptual Framework for Understanding the Biogeochemistry of Dry Riverbeds Through the Lens of Soil Science

Intermittent rivers and ephemeral streams (IRES) encompass fluvial ecosystems that eventually stop flowing and run dry at some point in space and time. During the dry phase, channels of IRES consist mainly of dry riverbeds (DRBs), prevalent yet widely unexplored ecotones between dry and wet phases that can strongly influence the biogeochemistry of fluvial networks. DRBs are often overlooked because they do not strictly belong to either domain of soil or freshwater science. Due to this dual character of DRBs, we suggest that concepts and knowledge from soil science can be used to expand the understanding of IRES biogeochemistry. Based on this idea, we propose that DRBs can be conceptually understood as early stage soils exhibiting many similarities with soils through two main forces: i) time since last sediment transport event, and ii) the development status of stabilizing structures (e.g. soil crusts and/or vascular plants). Our analysis suggests that while DRBs and soils may differ in master physical attributes (e.g. soil horizons vs fluvial sedimentary facies), they become rapidly comparable in terms of microbial communities and biogeochemical processes. We further propose that drivers of DRBs biogeochemistry are similar to those of soils and, hence, concepts and methods used in soil science are transferable to DRBs research. Finally, our paper presents future research directions to advance the knowledge of DRBs and to understand their role in the biogeochemistry of intermittent fluvial networks

A framework for ensemble modelling of climate change impacts on lakes worldwide : the ISIMIP Lake Sector

Empirical evidence demonstrates that lakes and reservoirs are warming across the globe. Consequently, there is an increased need to project future changes in lake thermal structure and resulting changes in lake biogeochemistry in order to plan for the likely impacts. Previous studies of the impacts of climate change on lakes have often relied on a single model forced with limited scenario-driven projections of future climate for a relatively small number of lakes. As a result, our understanding of the effects of climate change on lakes is fragmentary, based on scattered studies using different data sources and modelling protocols, and mainly focused on individual lakes or lake regions. This has precluded identification of the main impacts of climate change on lakes at global and regional scales and has likely contributed to the lack of lake water quality considerations in policy-relevant documents, such as the Assessment Reports of the Intergovernmental Panel on Climate Change (IPCC). Here, we describe a simulation protocol developed by the Lake Sector of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) for simulating climate change impacts on lakes using an ensemble of lake models and climate change scenarios for ISIMIP phases 2 and 3. The protocol prescribes lake simulations driven by climate forcing from gridded observations and different Earth system models under various representative greenhouse gas concentration pathways (RCPs), all consistently bias-corrected on a 0.5 degrees x 0.5 degrees global grid. In ISIMIP phase 2, 11 lake models were forced with these data to project the thermal structure of 62 well-studied lakes where data were available for calibration under historical conditions, and using uncalibrated models for 17 500 lakes defined for all global grid cells containing lakes. In ISIMIP phase 3, this approach was expanded to consider more lakes, more models, and more processes. The ISIMIP Lake Sector is the largest international effort to project future water temperature, thermal structure, and ice phenology of lakes at local and global scales and paves the way for future simulations of the impacts of climate change on water quality and biogeochemistry in lakes.Peer reviewe

GLOBAL-FATE (version 1.0.0): A geographical information system (GIS)-based model for assessing contaminants fate in the global river network

Contains fulltext : 214387.pdf (publisher's version ) (Open Access

River pollution by priority chemical substances under the Water Framework Directive: a provisional pan-European assessment

In this paper, we build a preliminary inventory of dissolved phase water emissions of 36 of the 45 chemical priority substances under the European Union's Water Framework Directive. For point sources, we consider the European Pollutant Release and Transfer Register (E-PRTR) containing reported emissions from major industrial facilities.We consider all other sources as diffuse, and we estimate European average chemical emission factors from available measurements of dissolved phase concentrations, assuming simple emission patterns such as population and agricultural land. The emission inventory enables modelling concentrations, which have been compared with independent measurements. Due to the way they are estimated, they cannot withstand a point-by-point comparison. However, predicted concentrations exhibit a frequency distribution and order of magnitude compatible with observations, and match a fair proportion of independently reported exceedances of environmental quality standards for many of the substances studied. While apparently a preliminary picture based on crude simplifications, our representation suggests that simple drivers such as population and agriculture are useful to describe chemical pollution at European scale. From our preliminary inventory, E-PRTR industrial point emissions seem to account for a relatively small share of total emissions. Consequently, apart from specific measures such as upgrades to urban wastewater treatment plants in certain high impact areas, the management of priority substances may require a more strategic approach to emission control, addressing chemical use across sectors and the management of out-phased, legacy chemicals. At the same time, we advocate that improving emission inventories requires monitoring data reflecting the variability of emission patterns across Europe, as presently available monitoring data do not enable a catchment-specific estimation of emissions.JRC.D.2-Water and Marine Resource

Effect of small water retention structures on diffusive CO2 and CH4 emissions along a highly impounded river

The impoundment of running waters through the construction of large dams is recognised as one of the most important factors determining the transport, transformation, and outgassing of carbon (C) in fluvial networks. However, the effects of small and very small water retention structures (SWRS) on the magnitude and spatiotemporal patterns of C emissions are still unknown, even though SWRS are the most common type of water retention structure causing river fragmentation worldwide. Here we evaluated and compared diffusive carbon dioxide (CO2) and methane (CH4) emissions from river sections impounded by SWRS and from their adjacent free-flowing sections along a highly impounded river. Emissions from impounded river sections (mean [SE] = 17.7 [2.8] and 0.67 [0.14] mmol m(-2)d(-1), for CO2 and CH4, respectively) never exceeded those from their adjacent free-flowing river sections (230.6 [49.7] and 2.14 [0.54] mmol m(-2)d(-1)). We attribute this finding to the reduced turbulence in impounded river sections induced by SWRS compared to free-flowing river sections (i.e., physical driver). Likewise, the presence of SWRS favoured an increase of the concentration of CH4 in impounded waters, but this increase was not sufficient to cause a significant influence in the CH4 efflux from the downstream free-flowing river sections. By contrast, this influenced the larger-scale longitudinal patterns of dissolved CH4, which exhibited a dear shifting pattern along the study stretch, modulated by variables associated with the presence of SWRS, such as higher water residence times, higher sedimentation rates, and higher temperatures. Overall, our results show that the presence of SWRS can modify the concentrations of C gases in highly impounded rivers but exerts a minor influence on diffusive C emissions