Vicenç Acuña

Drought and postdrought recovery cycles in an intermittent Mediterranean stream: structural and functional aspects

Abstract The effects of the intensity of seasonal droughts on stream ecosystems were studied in the Fuirosos, an intermittent forested Mediterranean stream. Macroinvertebrate community structure and stream ecosystem metabolism were measured during seasonal summer droughts in 2001, 2002, and 2003. Ecosystem metabolism was profoundly affected by stream intermittency. Organic matter that accumulated during the dry period enhanced ecosystem respiration during the postdrought recovery. Highest biotic diversity was found at low water levels as the stream dried and contracted. Macroinvertebrate community response to drying was stepped and apparently defined by thresholds of transition from drying to cessation of flow and from the dry phase to restoration of flow. Environmental conditions changed markedly with cessation of flow, causing large changes in community structure during 2001 and 2003 (dry years). Drying caused an increase in macroinvertebrate density that peaked in isolated pools soon after flow ceased, but then decreased rapidly because of the physicochemical changes associated with fragmentation of the watercourse. The macroinvertebrate community at the end of the summer dry phase (when flow resumed) differed from the community that had been present before drying began. Differences in community structure during the summer dry period were not as marked in 2002 (a wet year) as in 2001/2003. The influence of drought on the macroinvertebrate community differed across substrata. Drying led to significant changes in density on cobbles and leaves, but not on sand. Few taxa resisted drying, and resilience to drying was the dominant response to disturbance in the Fuirosos.

Why Should We Care About Temporary Waterways

Intermittently flowing streams and rivers should be recognized, afforded protection, and better managed. A proposed ruling by the U.S. Environmental Protection Agency (EPA), aimed at clarifying which bodies of water that flow intermittently are protected under law (1), has provoked conflict between developers and environmental advocates. Some argue that temporary streams and rivers, defined as waterways that cease to flow at some points in space and time along their course (see the figure, left) ( Fig. 1) (2), are essential to the integrity of entire river networks. Others argue that full protection will be too costly. Similar concerns extend far beyond the United States. Debate over how to treat temporary waterways in water-policy frameworks is ongoing (3), particularly because some large permanent rivers are shifting to temporary because of climate change and extraction of water (4). Even without human-induced changes, flow intermittency is part of the natural hydrology for streams and rivers globally.

Managing the effects of multiple stressors on aquatic ecosystems under water scarcity. The GLOBAQUA project

Water scarcity is a serious environmental problem in many European regions, and will likely increase in the near future as a consequence of increased abstraction and climate change. Water scarcity exacerbates the effects of multiple stressors, and thus results in decreased water quality. It impacts river ecosystems, threatens the services they provide, and it will force managers and policy-makers to change their current practices. The EU-FP7 project GLOBAQUA aims at identifying the prevalence, interaction and linkages between stressors, and to assess their effects on the chemical and ecological status of freshwater ecosystems in order to improve water management practice and policies. GLOBAQUA assembles a multidisciplinary team of 21 European plus 2 non-European scientific institutions, as well as water authorities and river basin managers. The project includes experts in hydrology, chemistry, biology, geomorphology, modelling, socio-economics, governance science, knowledge brokerage, and policy advocacy. GLOBAQUA studies six river basins (Ebro, Adige, Sava, Evrotas, Anglian and Souss Massa) affected by water scarcity, and aims to answer the following questions: how does water scarcity interact with other existing stressors in the study river basins? How will these interactions change according to the different scenarios of future global change? Which will be the foreseeable consequences for river ecosystems? How will these in turn affect the services the ecosystems provide? How should management and policies be adapted to minimise the ecological, economic and societal consequences? These questions will be approached by combining data-mining, field- and laboratory-based research, and modelling. Here, we outline the general structure of the project and the activities to be conducted within the fourteen work-packages of GLOBAQUA.

The influence of substratum type and nutrient supply on biofilm organic matter utilization in streams

We investigated the effect of benthic substratum type (sand and rocks) and nutrient supply (N and P) on biofilm structure and heterotrophic metabolism in a field experiment in a forested Mediterranean stream (Fuirosos). Rock and sand colonization and biofilm formation was intensively studied for 44 d at two stream reaches: control and experimental (continuous addition of phosphate, ammonia, and nitrate). Structural (C, N, and polysaccharide content and bacterial and chlorophyll density) and metabolic biofilm parameters (b-glucosidase, peptidase, and phosphatase enzyme activities) were analyzed throughout the colonization process. The epilithic biofilm (grown on rocks) had a higher peptidase activity at the impacted reach, together with a higher algal and bacterial biomass. The positive relationship between the peptidase activity per cell and the N content of the epilithic biofilm suggested that heterotrophic utilization of proteinaceous compounds from within the biofilm was occurring. In contrast, nutrient addition caused the epipsammic biofilm (grown on sand) to exhibit lowerb-glucosidase and phosphatase activities, without a significant increase in bacterial and algal biomass. The differential response to nutrient addition was related to different structural characteristics within each biofilm. The epipsammic biofilm had a constant and high C : N ratio (22.7) throughout the colonization. The epilithic biofilm had a higher C : N ratio at the beginning of the colonization (43.2) and evolved toward a more complex structure (high polysaccharide content and low C : N ratio) during later stages. The epipsammic biofilm was a site for the accumulation and degradation of organic matter: polysaccharides and organic phosphorus compounds had higher degradation activities.

Ecosystem services in Mediterranean river basin: Climate change impact on water provisioning and erosion control

The Mediterranean basin is considered one of the most vulnerable regions of the world to climate change and such changes impact the capacity of ecosystems to provide goods and services to human society. The predicted future scenarios for this region present an increased frequency of floods and extended droughts, especially at the Iberian Peninsula. This paper evaluates the impacts of climate change on the water provisioning and erosion control services in the densely populated Mediterranean Llobregat river basin of. The assessment of ecosystem services and their mapping at the basin scale identify the current pressures on the river basin including the source area in the Pyrenees Mountains. Drinking water provisioning is expected to decrease between 3 and 49%, while total hydropower production will decrease between 5 and 43%. Erosion control will be reduced by up to 23%, indicating that costs for dredging the reservoirs as well as for treating drinking water will also increase. Based on these data, the concept for an appropriate quantification and related spatial visualization of ecosystem service is elaborated and discussed.

Meteorological and riparian influences on organic matter dynamics in a forested Mediterranean stream

Abstract Organic matter inputs, transport, and storage, ecosystem metabolism, and organic C turnover length were measured in a forested Mediterranean 3rd-order stream (Fuirosos) over a period of 3 y. Meteorological patterns influenced the organic matter dynamics of Fuirosos through 2 pathways: summer weather and flood pulses. Summer rains affected the timing of litter fall and the extent of flow intermittency, which gave rise to accumulations of organic matter in the streambed in dry years. With the onset of flow, these organic matter accumulations were the energy sources for considerable ecosystem respiration (30 g O2 m−2 d−1). Interflood periods punctuated by flood pulses determined cycles of steady accumulation and abrupt removal of stored organic matter. During the interflood periods, the efficiency of organic matter processing increased continuously. The seasonal changes in the riparian forest influenced the ecological consequences of the flood pulses. Resilience of the ecosystem, measured in terms of gross primary production and ecosystem respiration, strongly depended on the supply of benthic organic matter and light availability, both of which were seasonally variable in the deciduous riparian forest.

Contraction, fragmentation and expansion dynamics determine nutrient availability in a Mediterranean forest stream

Temporary streams are a dominant surface water type in the Mediterranean region. As a consequence of their hydrologic regime, these ecosystems contract and fragment as they dry, and expand after rewetting. Global change leads to a rapid increase in the extent of temporary streams, and more and more permanent streams are turning temporary. Consequently, there is an urgent need to better understand the effects of flow intermittency on the biogeochemistry and ecology of stream ecosystems. Our aim was to investigate how stream nutrient availability varied in relation to ecosystem contraction, fragmentation and expansion due to hydrologic drying and rewetting. We quantified the temporal and spatial changes in dissolved nitrogen (N) and phosphorus (P) concentrations along a reach of a temporary Mediterranean forest stream during an entire contraction–fragmentation–expansion hydrologic cycle. We observed marked temporal changes in N and P concentrations, in the proportion of organic and inorganic forms as well as in stoichiometric ratios, reflecting shifts in the relative importance of in-stream nutrient processing and external nutrient sources. In addition, the spatial heterogeneity of N and P concentrations and their ratios increased substantially with ecosystem fragmentation, reflecting the high relevance of in-stream processes when advective transport was lost. Overall, changes were more pronounced for N than for P. This study emphasizes the significance of flow intermittency in regulating stream nutrient availability and its implications for temporary stream management. Moreover, our results point to potential biogeochemical responses of these ecosystems in more temperate regions under future water scarcity scenarios.

Assessment of the water supply:demand ratios in a Mediterranean basin under different global change scenarios and mitigation alternatives.

Spatial differences in the supply and demand of ecosystem services such as water provisioning often imply that the demand for ecosystem services cannot be fulfilled at the local scale, but it can be fulfilled at larger scales (regional, continental). Differences in the supply:demand (S:D) ratio for a given service result in different values, and these differences might be assessed with monetary or non-monetary metrics. Water scarcity occurs where and when water resources are not enough to meet all the demands, and this affects equally the service of water provisioning and the ecosystem needs. In this study we assess the value of water in a Mediterranean basin under different global change (i.e. both climate and anthropogenic changes) and mitigation scenarios, with a non-monetary metric: the S:D ratio. We computed water balances across the Ebro basin (North-East Spain) with the spatially explicit InVEST model. We highlight the spatial and temporal mismatches existing across a single hydrological basin regarding water provisioning and its consumption, considering or not, the environmental demand (environmental flow). The study shows that water scarcity is commonly a local issue (sub-basin to region), but that all demands are met at the largest considered spatial scale (basin). This was not the case in the worst-case scenario (increasing demands and decreasing supply), as the S:D ratio at the basin scale was near 1, indicating that serious problems of water scarcity might occur in the near future even at the basin scale. The analysis of possible mitigation scenarios reveals that the impact of global change may be counteracted by the decrease of irrigated areas. Furthermore, the comparison between a non-monetary (S:D ratio) and a monetary (water price) valuation metrics reveals that the S:D ratio provides similar values and might be therefore used as a spatially explicit metric to valuate the ecosystem service water provisioning.

Occurrence and in-stream attenuation of wastewater-derived pharmaceuticals in Iberian rivers

A multitude of pharmaceuticals enter surface waters via discharges of wastewater treatment plants (WWTPs), and many raise environmental and health concerns. Chemical fate models predict their concentrations using estimates of mass loading, dilution and in-stream attenuation. However, current comprehension of the attenuation rates remains a limiting factor for predictive models. We assessed in-stream attenuation of 75 pharmaceuticals in 4 river segments, aiming to characterize in-stream attenuation variability among different pharmaceutical compounds, as well as among river segments differing in environmental conditions. Our study revealed that in-stream attenuation was highly variable among pharmaceuticals and river segments and that none of the considered pharmaceutical physicochemical and molecular properties proved to be relevant in determining the mean attenuation rates. Instead, the octanol-water partition coefficient (Kow) influenced the variability of rates among river segments, likely due to its effect on sorption to sediments and suspended particles, and therefore influencing the balance between the different attenuation mechanisms (biotransformation, photolysis, sorption, and volatilization). The magnitude of the measured attenuation rates urges scientists to consider them as important as dilution when aiming to predict concentrations in freshwater ecosystems.

Does it make economic sense to restore rivers for their ecosystem services

Temperate forests managed to maximize sustainable yield of wood products can reduce the availability of dead wood on the forest floor and in adjacent streams, which in turn can impair ecological processes such as retention and transformation of organic matter. Lack of tools to link ecological processes with their effects on human well-being leads forest managers to ignore the cost on other services from terrestrial and aquatic ecosystems. We examine how adding dead wood to restore stream channel complexity affects the provision and value of selected ecosystem services, mainly related to the retention and transformation of matter and cycling of nutrients, as well as to the effects on aquatic biota. Specifically, we evaluated the cost-effectiveness of stream restoration through a comparative analysis of four reach-scale projects in streams flowing through temperate forest and into a drinking water reservoir and two scenarios of active and passive restoration at the basin scale. Results indicate that the lack of dead wood in streams has an important economic cost because of the effects on fish provisioning, opportunities for recreation and tourism, water purification and erosion control. Active reach-scale restoration resulted in a 10- to 100-fold increase in the monetary benefits provided by streams, accounting as much as 1·8 € per metre of restored river length each year. Results of the reach-scale cost-benefit analyses estimated that the time required to recover the active restoration investment ranged from 15 to 20 years in low- to middle-order streams. Synthesis and applications. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services. Our study showed that restoration of natural wood loading in streams greatly increases the ecosystem services they provide. The benefits in terms of the analysed services surpass the costs of active restoration over realistic timeframes, whereas this was not the case for passive restoration. Inclusion of other ecosystem services such as conservation of biodiversity might make restoration more economically profitable. Overall, our study provides a decision framework for managing temperate riparian forests in the context of ecological services