Mario Álvarez-Cabria

Modelling the spatial and seasonal variability of water quality for entire river networks: Relationships with natural and anthropogenic factors.

We model the spatial and seasonal variability of three key water quality variables (water temperature and concentration of nitrates and phosphates) for entire river networks in a large area in northern Spain. Models were developed with the Random Forest technique, using 12 (water temperature and nitrate concentration) and 15 (phosphate concentration) predictor variables as descriptors of several environmental attributes (climate, topography, land-uses, hydrology and anthropogenic pressures). The effect of the different predictors on the response variables was assessed with partial dependence plots and partial correlation analysis. Results indicated that land-uses were important predictors in defining the spatial and seasonal patterns of these three variables. Water temperature was positively related with air temperature and the upstream drainage area, whereas increases in forest cover decreased water temperature. Nitrate concentration was mainly related to the area covered by agricultural land-uses, increasing in winter, probably because of catchment run-off processes. On the other hand, phosphate concentration was highly related to the area covered by urban land-uses in the upstream catchment and to the proximity of the closest upstream effluent. Phosphate concentration increased notably during the low flow period (summer), probably due to the reduction of the dilution capacity. These results provide a large-scale continuous picture of water quality, which could help identify the main sources of change in water quality and assist in the prioritization of river reaches for restoration projects.

Microdistribution patterns of macroinvertebrate communities upstream and downstream of organic effluents

The present study analyses the distribution patterns of macroinvertebrate communities in four microhabitats (riffles, glides, leaf litter and bank roots) upstream and downstream of two waste water treatment plant (WWTP) effluents in northern Spain rivers. Macroinvertebrate communities were analysed in November 2006 by taking 5 samples from each of the microhabitats under unaffected (upstream WWTP) and affected (downstream WWTP) conditions, respectively. Water velocity, depth, substrate coarseness and hydraulic stress by means of the Froude number were also estimated at all sampling locations. Under unaffected conditions, the abundance and presence/absence of certain macroinvertebrate taxa were mainly determined by hydraulic characteristics (water velocity and Froude number) and feeding resource availability. However, neither macroinvertebrate richness nor abundance were neither significantly correlated with hydraulic stress nor substrate coarseness, although the number of macroinvertebrate taxa increased in microhabitats with high structural complexity. Macroinvertebrate abundance increased downstream of both WWTPs, while macroinvertebrate richness was not adversely affected by the organic enrichment of water. The structure and composition of macroinvertebrate communities occurring in riffles was similar under unaffected and affected conditions, while communities from leaf litter and submerged bank roots showed important changes above and below the WWTPs, indicating that they are probably the most appropriate communities for water quality assessment.

Macroinvertebrate community dynamics in a temperate European Atlantic river. Do they conform to general ecological theory

Spatial and temporal dynamics of macroinvertebrate communities have usually been linked to several environmental and anthropic factors. The aim of this study is to elucidate how important are these factors in structuring macroinvertebrate communities from temperate regions. Regarding the macroinvertebrate number of taxa, the Habitat Template Model, the Dynamic Equilibrium Hypothesis and the Intermediate Disturbance Hypothesis will be tested in order to know how important the diversity of instream elements and the hydrological disturbance frequency are in defining the macroinvertebrate taxonomic richness. Thus, the structure and composition of macroinvertebrate communities were analysed in nine sites of the Pas River basin, a temperate Atlantic basin in northern Spain, during winter, spring, summer and autumn 2005, together with water physicochemical and environmental characteristics. Macroinvertebrate abundance increased downstream and during summer, probably favoured by lower hydraulic stress and water organic enrichment. As predicts the Habitat Template Model, the macroinvertebrate number of taxa was related to habitat heterogeneity. However, no clear relationship amongst macroinvertebrate richness and water quality was found. The macroinvertebrate taxonomic richness did not correspond exactly with the Dynamic Equilibrium Hypothesis and the Intermediate Disturbance Hypothesis because it was relatively high in the absence of hydrological disturbances (summer). Thus, disturbance events may play a secondary role in determining the seasonal dynamic of the number of taxa. However, hydrological disturbances can be considered the most important factors explaining the seasonal pattern of macroinvertebrate abundance. On the other hand, spatial patterns of macroinvertebrate community structure and composition were mainly determined by resource availability, hydraulic conditions, habitat heterogeneity and human alterations, whilst hydrological predictability and resource availability might play a major role in determining seasonal dynamics.

Modelling macroinvertebrate and fish biotic indices: From reaches to entire river networks

We modelled three macroinvertebrate (IASPT, EPT number of families and LIFE) and one fish (percentage of salmonid biomass) biotic indices to river networks draining a large region (110,000km2) placed in Northern and Eastern Spain. Models were developed using Random Forest and 26 predictor variables (19 predictors to model macroinvertebrate indices and 22 predictors to model the fish index). Predictor variables were related with different environmental characteristics (water quality, physical habitat characteristics, hydrology, topography, geology and human pressures). The importance and effect of predictors on the 4 biotic indices was evaluated with the IncNodePurity index and partial dependence plots, respectively. Results indicated that the spatial variability of macroinvertebrate and fish indices were mostly dependent on the same environmental variables. They decreased in river reaches affected by high mean annual nitrate concentration (>4mg/l) and temperature (>12°C), with low flow water velocity (<0.4m/s) and aquatic plant communities being dominated by macrophytes. These indices were higher in the Atlantic region than in the Mediterranean. This study provides a continuous image of river biological communities used as indicators, which turns very useful to identify the main sources of change in the ecological status of water bodies and assist both, the integrated catchment management and the identification of river reaches for recovery.

Effects of sewage effluents and seasonal changes on the metabolism of three Atlantic rivers

Sewage inputs on fluvial ecosystems affect benthic communities and alter trophic networks resulting in changes on river functioning. Functional indicators (e.g. river metabolism) have been proposed as a valuable tool to evaluate ecosystem impairment. In the present study we monitored river metabolism in spring (few days after a major flood) and in summer (after 35days of low flow conditions) using both single-station and two-stations methods over a 24h period up and downstream of wastewater treatment plant (WWTP) effluents on three Atlantic river reaches located in northern Spain (Europe). Concurrently with river metabolism, we characterized environmental characteristics (flow, velocity, depth, pH, water temperature, nutrients, etc.), benthic macroinvertebrate communities and biofilm (algae and epilithic biomass). Ecosystem Respiration (ER24) was similar at the different periods and locations, but Gross Primary Productivity (GPP) tended to decrease in impacted reaches (downstream WWTPs) and in summer (except in the Saja River). However, the balance of the metabolic processes showed a trend towards autotrophy in the largest river, while WWTP effluents increased its autotrophy. Chlorophyll a concentration was >4 times larger in spring than in summer in all river reaches, while epilithic biomass followed a similar but less obvious pattern. Increase of invertebrate scraper densities (mainly, Potamopyrgus antipodarum) seems to be a plausible explanation for biofilm biomass temporal patterns in all sites (higher in spring than in summer), altering GPP and ER24 patterns. Thus, metabolism rates show different responses to WWTP effluents depending on season and on the relationships among functional and structural components, with special focus on the composition and structure of macroinvertebrate communities. Increasing our understanding of cause-effect relationships on the impairment of aquatic ecosystems needs to account for both structural and functional components and their interactions.

Local environment rather than past climate determines community composition of mountain stream macroinvertebrates across Europe

Community assembly is determined by a combination of historical events and contemporary processes that are difficult to disentangle, but eco‐evolutionary mechanisms may be uncovered by the joint analysis of species and genetic diversity across multiple sites. Mountain streams across Europe harbour highly diverse macroinvertebrate communities whose composition and turnover (replacement of taxa) among sites and regions remain poorly known. We studied whole‐community biodiversity within and among six mountain regions along a latitudinal transect from Morocco to Scandinavia at three levels of taxonomic hierarchy: genus, species and haplotypes. Using DNA barcoding of four insect families (>3100 individuals, 118 species) across 62 streams, we found that measures of local and regional diversity and intraregional turnover generally declined slightly towards northern latitudes. However, at all hierarchical levels we found complete (haplotype) or high (species, genus) turnover among regions (and even among sites within regions), which counters the expectations of Pleistocene postglacial northward expansion from southern refugia. Species distributions were mostly correlated with environmental conditions, suggesting a strong role of lineage‐ or species‐specific traits in determining local and latitudinal community composition, lineage diversification and phylogenetic community structure (e.g., loss of Coleoptera, but not Ephemeroptera, at northern sites). High intraspecific genetic structure within regions, even in northernmost sites, reflects species‐specific dispersal and demographic histories and indicates postglacial migration from geographically scattered refugia, rather than from only southern areas. Overall, patterns were not strongly concordant across hierarchical levels, but consistent with the overriding influence of environmental factors determining community composition at the species and genus levels.