Narcís Prat

Macroinvertebrate community structure and biological traits related to flow permanence in a Mediterranean river network

In Mediterranean climate areas, the great seasonal variability in temperature and rainfall is considered to be an evolutionary pressure that constrains plant and animal communities and their biological traits. Droughts alter habitat availability (changes of flow alter riffle-pool sequences), although habitat characteristics may also exacerbate drought to some extent. Using a simple quantitative index based on the proportion of conglomerate bedrock versus gravel and cobbles, pools versus riffles and winter versus summer flow, we show how habitat characteristics (in terms of substratum and flow) may influence the permanency of a stream site and how flow permanence constrains macroinvertebrate community structure and biological traits. Annual and seasonal macroinvertebrate richness, and the EPT (Ephemeroptera, Plecoptera and Trichoptera) and OCH (Odonata, Coleoptera and Hemiptera) metrics differed between permanent, intermittent and ephemeral sites, but not between permanent and intermittent sites. In contrast, distinct biological traits were observed in the three flow categories, although permanent sites presented few significant traits which was attributed to the stability of the habitat. Intermittent sites were dominated by taxa with pool-like strategies, while ephemeral sites were characterized by fauna with life-history adaptations to floods and droughts. In contrast to most traits (e.g., dissemination, reproduction, substrate relation), which were more constrained by local flow and substrate characteristics, life-cycle characteristics did not differ significantly among flow categories. This pattern can be explained by the features of the Mediterranean climate and particularly its high seasonal predictability, which serves as a large-scale filter of life-cycle traits, independently of local hydromorphological characteristics. Our findings indicate that drought is related to habitat characteristics and that local habitat variability favours organisms with certain traits, while other traits are independent of habitat variability on this scale and are probably affected by other large-scale habitat characteristics.

Salinisation of rivers: An urgent ecological issue

Secondary salinisation of rivers and streams is a global and growing threat that might be amplified by climate change. It can have many different causes, like irrigation, mining activity or the use of salts as de-icing agents for roads. Freshwater organisms only tolerate certain ranges of water salinity. Therefore secondary salinisation has an impact at the individual, population, community and ecosystem levels, which ultimately leads to a reduction in aquatic biodiversity and compromises the goods and services that rivers and streams provide. Management of secondary salinization should be directed towards integrated catchment strategies (e.g. benefiting from the dilution capacity of the rivers) and identifying threshold salt concentrations to preserve the ecosystem integrity. Future research on the interaction of salinity with other stressors and the impact of salinization on trophic interactions and ecosystem properties is needed and the implications of this issue for human society need to be seriously considered.

Benthic macroinvertebrate assemblages and macrohabitat connectivity in Mediterranean-climate streams of northern California

Abstract Drought leads to a loss of longitudinal and lateral hydrologic connectivity, which causes direct or indirect changes in stream ecosystem properties. Changes in macrohabitat availability from a riffle–pool sequence to isolated pools are among the most conspicuous consequences of connectivity loss. Macroinvertebrate assemblages were compared among 3 distinct stream macrohabitats (riffles [R], pools connected to riffles [Pc], disconnected pools [Pd]) of 19 Mediterranean-climate sites in northern California to examine the influence of loss of habitat resulting from drought disturbance. At the time of sampling, 10 sites were perennial and included R and Pc macrohabitats, whereas 9 sites were intermittent and included only Pd macrohabitats. Taxa richness was more variable in Pd, and taxa richness was significantly lower in Pd than in Pc but not R. These results suggested a decline in richness between Pc and Pd that might be associated with loss of connectivity. Lower Ephemeroptera, Plecoptera, and Trichoptera (EPT) richness relative to Odonata, Coleoptera, and Heteroptera (OCH) richness was observed for Pd than R and Pc macrohabitats. Family composition was more similar between R and Pc than between R or Pc and Pd macrohabitats. This similarity may be associated with greater connectivity between R and Pc macrohabitats. Correspondence analysis indicated that macroinvertebrate composition changed along a gradient from R to Pc and Pd that was related to a perennial–intermittent gradient across sites. High variability among macroinvertebrate assemblages in Pd could have been related to variability in the duration of intermittency. In cluster analysis, macroinvertebrate assemblages were grouped by macrohabitat first and then by site, suggesting that the macrohabitat filter had a greater influence on macroinvertebrate assemblages than did local site characteristics. Few taxa were found exclusively in Pc, and this macrohabitat shared numerous taxa with R and Pd, indicating that Pc may act as a bridge between R and Pd during drought. Drought is regarded as a ramp disturbance, but our results suggest that the response of macroinvertebrate assemblages to the loss of hydrological connectivity among macrohabitats is gradual, at least in Mediterranean-climate streams where drying is gradual. However, the changes may be more dramatic in arid and semiarid streams or in Mediterranean-climate streams if drying is rapid.

Changes in the hydrology and sediment transport produced by large dams on the lower Ebro river and its estuary

The mean annual flow of the lower Ebro river has reduced by 29% during this century (592 to 426 m3 s−1). The main causes are increased water use and evaporation from reservoirs in the river basin. The losses due to irrigation explain 74% of the decrease, whereas losses by evaporation in the reservoirs explain another 22%. Decreased flow in the lower Ebro river caused an increase in the salt wedge in the estuary. During the study period, the permanent low river flows from July 1988 to April 1990 caused the continuous presence of the salt wedge for 18 months. Historical data for sediment transport in the Ebro river are scarce and incomplete. Limited data before the construction of reservoirs in the Ebro basin allow only an estimate of the order of magnitude of annual suspended sediment transport (3·0 × 107 Mt yr−1). Before the construction of large reservoirs in the lower Ebro at the end of the 1960s, the sediment transport was estimated to be around 1·0 × 107 Mt yr−1. This amount was reduced to around 0·3 × 106 Mt yr−1 after construction of the dam. Currently, this amount ranges from 0·1 to 0·2 × 106 Mt yr−1, which represents a reduction of more than 99% in sediment transport. On a seasonal scale, the effects of the dams have been the standardization of the river flow and the virtual suppression of peaks in sediment transport. In the estuary, the salt wedge dynamics changed and its presence increased. River regulation and hydropower generation also changed the hydrology of the river on a daily scale. The effect of local storms on the river flow and the sediment transport has been suppressed. At present, these changes are related to hydropower generation.

Water use and quality and stream flow in a Mediterranean stream

Abstract We examine how the use and management of water resources and waste-water inputs affect the stream flow and its biological quality in a Mediterranean stream, the Congost (NE Spain). Agricultural, farming, urban and industrial activities take place from its headwaters to its lower section, and there are many weirs and wells along the stream. The effects of four sewage plants, built in the basin in the last 5 years, on river flow and water quality are analysed. Today most of the river flow comes from the sewage plants and few or any dilution from natural stream exist. In the upper part of the basin two biological plants are located, due to the lack of dilution, the biological recovery of the freshwater community is poor, although coarse fish communities may be found at the end of this section. In the middle and lower parts of the stream, water is treated in two physicochemical plants, and as a result, the stream in this section has no fish or macrofauna at all. It is concluded that in Mediterranean streams, end-pipe measures, even using biological plants, may be insufficient for the recovery of stream communities due to the lack of natural flow related to the climate and the high demand of the water resources.

Ecological and historical filters constraining spatial caddisfly distribution in Mediterranean rivers

Summary 1. Contemporary species distributions are determined by a mixture of ecological and historical filters acting on several spatial and temporal scales. Mediterranean climate areas are one of the worlds biodiversity hotspots with a high level of endemicity, which is linked to complex ecological and historical factors. 2. This paper explores the ecological and historical factors constraining the distribution of caddisfly species on a large regional scale. A total of 69 taxa were collected from 140 sampling sites in 10 Iberian Mediterranean river basins. Approximately 74% of taxa can be considered rare, with the southern basins (the Baetic–Riffian region) having greater endemicity. The greatest richness, involving a mixture of northern and southern species, was found in the transitional area between the Baetic–Riffian region and the Hesperic Massif. 3. The historical processes occurring during the Tertiary (i.e. the junction of the Eurasian and African plates) explained 3.1% of species distribution, whereas ecological factors accounted for 20.7%. Only 0.3% was explained by the interaction of history and ecology. A set of multi‐scale ecological variables (i.e. basin, reach and bedform characteristics) defined five river types with specific caddisfly assemblages. The commonest caddisfly species accounted for the regional distribution pattern, while rare taxa contributed to the explanation of subtle patterns not shown by common species. 4. Despite the importance of historical factors for biogeography and the large scale used in our study, ecological variables better explained caddisfly distribution. This may be explained by the length of time since the historical process we are considering, the high dispersion and colonisation capacity of many caddisfly species, and the strong environmental gradient in the area. Because of the historical and environmental complexity of Mediterranean areas, rare taxa should be included in ecological studies so that the singularity of these ecosystems is not missed.

Use of macroinvertebrate-based multimetric indices for water quality evaluation in Spanish Mediterranean rivers: an intercalibration approach with the IBMWP index

For the European Parliament and Commission to implement the Water Framework Directive (WFD), the water-quality indices that are currently used in Europe need to be compared and calibrated. This will facilitate the comparative assessment of ecological status throughout the European Union. According to the WFD, biologic indices should respond consistently to human impacts, using multimetric approaches and water-quality classification boundaries adjusted to a common set of normative definitions. The European Commission has started an intercalibration exercise to review biologic indices and harmonize class boundaries. We used data from rivers in Spain to compare the IBMWP (Iberian Biological Monitoring Working Party) index, which is commonly used by water authorities in Spain and by several research centers, with the Intercalibration Common Multimetric Index (ICM-Star), which was used as a standard in the intercalibration exercise. We also used data from Spanish rivers to compare the multimetric indices ICM-7 (based on quantitative data) and ICM-9 (based on qualitative data) with the IBMWP. ICM-7 and ICM-9 were proposed by the Mediterranean Geographical Intercalibration Group (Med-GIG). Additionally, we evaluated two new multimetric indices, developed specifically for macroinvertebrate communities inhabiting Mediterranean river systems. One of these is based on quantitative data (ICM-10), while the other is based on qualitative data (ICM-11a). The results show that the IBMWP index responds well to the stressor gradient present in our data, and correlates well with ICM-Star. Moreover, the IBMWP quality class boundaries were consistent with the intercalibration requirements of the WFD. However, multimetric indices showed a more linear relation with the stressor gradient in our data, and less variation in reference values. In addition, they may provide more statistical power for detecting potential environmental impacts. Multimetric indices produced similar results for quantitative and qualitative data. Thus, ICM-10 (also named IMMi-T) and ICM-11a (also named IMMi-L) indices could be used to meet European Commission requirements for assessing the water quality in Spanish Mediterranean rivers.

Assessing the ecological status in the context of the European Water Framework Directive: Where do we go now?

The Water Framework Directive (WFD) is now well established as the key management imperative in river basins across Europe. However, there remain significant concerns with the way WFD is implemented and there is now a need for water managers and scientists to communicate better in order to find solutions to these concerns. To address this, a Science-Policy Interface (SPI) activity was launched in 2010 led by Directorate-General for Research and Innovation and Onema (the French national agency for water and aquatic ecosystems), which provided an interactive forum to connect scientists and WFD end-users. One major aim of the SPI activity was to establish a list of the most crucial research and development needs for enhancing WFD implementation. This paper synthesises the recommendations from this event highlighting 10 priority issues relating to ecological status. For lakes, temporary streams and transitional and coastal waters, WFD implementation still suffers from a lack of WFD-compliant bioassessment methods. For rivers, special attention is required to assess the ecological impacts of hydromorphological alterations on biological communities, notably those affecting river continuity and riparian covering. Spatial extrapolation tools are needed in order to evaluate ecological status for water bodies for which no data are available. The need for more functional bioassessment tools as complements to usual WFD-compliant tools, and to connect clearly good ecological state, biodiversity and ecosystem services when implementing WFD were also identified as crucial issues.

Combined use of Daphnia magna in situ bioassays, biomarkers and biological indices to diagnose and identify environmental pressures on invertebrate communities in two Mediterranean urbanized and industrialized rivers (NE Spain)

Environmental factors affecting aquatic invertebrate communities were assessed using Daphnia magna in situ bioassays and biological indices based on community assemblages of benthic macroinvertebrates. Investigations were carried out in two heavily industrialized and urbanized river basins from the NE of Spain (Llobregat and Besós). Measures of energy consumption (i.e. algal grazing), and of specific biochemical responses (biomarkers) were conducted on individuals transplanted upstream and downstream from effluent discharges of sewage treatment plants. In both rivers there was a clear deterioration of the ecological water quality parameters and benthic communities towards downstream reaches. In all but one of the 19 locations studied, transplanted organisms were affected in at least one of the five measured responses. In three of them, significant effects were detected in most of the traits considered. Principal Component and Partial Least Square Projections to Latent Structures regression analyses indicated that the measured responses in D. magna in situ bioassays and those of macroinvertebrate assemblages were affected by distinct environmental factors. From up to 20 environmental variables considered, seven of them including habitat degradation, suspended solids, nitrogenous and conductivity related parameters affected macroinvertebrate assemblages. On the other hand, levels of organophosphorus compounds and polycyclic aromatic hydrocarbons were high enough to trigger the responses of D. magna in situ bioassays. These results emphasize the importance of combining biological indices with biomarkers and more generalized and ecologically relevant (grazing) in situ responses to identify ecological effects of effluent discharges from sewage treatment plants in surface waters.

Effect of dumping and cleaning activities on the aquatic ecosystems of the Guadiamar River following a toxic flood

The main aim of the study was to document the recovery of the aquatic ecosystem after the release of toxic mining waste in the Guadiamar River Basin (Sevilla, SW Spain) in April 1998. Samples of water, plankton, periphyton and macroinvertebrates were taken once a month at nine sampling stations (six affected by the toxic release and three for control). Water hardness and pH recovered in a few weeks and did not change significantly thereafter in the river or in the marsh stations. Only the Agrio River (the tributary that received the initial waste dump) had a low pH (3-5) throughout the study period. High ammonia contents (up to 300 microM) were measured at two sampling stations due to sewage and oil mill pollution. Eutrophication was also common at most of the stations, including one reference site. The planktonic community did not differ substantially between reference and affected stations. On all occasions the small phytoplankton and zooplankton (rotifers) were dominant. Compared with the reference station, chlorophyll a in the riverine area increased, especially in the sewage-affected stations, while in the marsh area, no significant differences were found between affected and reference stations. After 6 months of cleaning operations, in November 1998 the macroinvertebrate community of the river was composed mainly of species of short life cycles typical of ponds (Heteroptera, Coleoptera and Odonata), while typical riverine species found at the upstream control station had not recolonized the river due to the transformation of the river into a series of artificial ponds constructed as sediment traps. An analysis of variance showed significantly higher values (P < 0.05) for all heavy metals analysed (Zn, Cu, Pb, As, Cd, Sb, Tl) in plankton and macroinvertebrate communities from impacted sites. Values found in invertebrates were highly variable, with a mean concentration of the most abundant metals, Zn and Cu, between two and three times those found in unpolluted areas. Values for As were up to five times higher while Pb, Sb and Tl showed up to 10-fold increases. At the affected stations, the metal concentrations found in biofilms, plankton and particulate material were more than five times greater than those in invertebrates. The slow recovery of the aquatic ecosystem clearly reflected the impact of the metal discharge and the subsequent cleaning activities following the mine spill, as well as the sewage inputs at two of the stations studied.