Camino Fernández-Aláez

Loss of diversity and degradation of wetlands as a result of introducing exotic crayfish

The introduction of the alocthonous Louisiana red swamp crayfish (Procambarus clarkii) in Chozas (a small shallow lake situated in León (North-West Spain)) in 1996 switched the clear water conditions that harboured an abundant and a quite high richness of plants, invertebrates, amphibians and birds to a turbid one followed by strong losses in abundance and richness in the aforementioned groups. Crayfish exclusion experiments done in Chozas previous to this work confirmed the role of crayfish herbivorism on macrophyte destruction that had a trophic cascade effect on the wetland ecosystem. Direct and indirect effects of crayfish introduction on Chozas lake communities have been evaluated and compared with previous conditions before 1996 or with other related lakes in which crayfish were no present. Crayfish had a main role in submerged plant destruction and a potential effect on amphibia and macroinvertebrate population decrease. Plant destruction (99 % plant coverage reduction) was directly related to invertebrates (71 % losses in macroinvertebrate genera), amphibia (83 % reductions in species), and waterfowls (52 % reduction). Plant-eating birds were negatively affected (75 % losses in ducks species); nevertheless, fish and crayfish eating birds increased their presence since the introduction. Introduction of crayfish in shallow plant-dominated lakes in Spain is a main risk for richness maintenance in these endangered ecosystems.

Influence of water level fluctuation on the structure and composition of the macrophyte vegetation in two small temporary lakes in the northwest of Spain

The influence of water retention time and depth variation on the macrophyte community in two small shallow lakes in the northwest of Spain was studied. One lake is periodically flooded and the other deeper lake, which is usually inundated, dries up sporadically. The influence of water regime and the spatial heterogeneity of the abiotic environment on diversity values and their temporal evolution are shown. For each lake, a model of horizontal arrangement of species is established. A differential arrangement of optima for dominant species was observed along the depth gradient. This arrangement remained constant in time.

Nutrient content in macrophytes in Spanish shallow lakes

The concentrations of N, P and C in the above-ground biomass of 14 dominant macrophyte species in shallow lakes in N.W. Spain were measured. The plants included macroalgae, aquatic (submerged and floating leaved) and emergent angiosperms. Significant differences among the species and among the groups of macrophytes were observed for the three nutrients. The macroalgae showed the lowest P (0.053% dry weight) and C (35.24% dry weight) content, whilst an impoverishment in N (1.38% dry weight) was observed in the emergent species. Only the macroalgae showed a strong association between N and P (r = 0.743, p<0.0001), reflecting an important biochemical connection in these species. A negative relation was observed between N and C (r s = −0.711, p<0.0001) as a result of the change pattern exhibited by these nutrients in the tissues of aquatic and emergent angiosperms. The existence of N limitation of growth of both angiosperm groups, with a content below critical level, was deduced. P was established as the limiting factor of all the macrophyte groups (N:P = 35:1), especially macroalgae, in which it was below the critical minimum.

Among-habitat and Temporal Variability of Selected Macroinvertebrate Based Metrics in a Mediterranean Shallow Lake (NW Spain)

According to the European Water Framework Directive, waterbodies have to be classified on the basis of their ecological status using biological quality elements, such as macroinvertebrates. This needs to take into consideration the influence of natural variation (both spatial and temporal) of reference biological communities as this may obscure the effects caused by anthropogenic disturbance. We studied the influence of among-habitat and temporal (seasonal and interannual) changes on the macroinvertebrate communities of an Iberian shallow lake and the variability of 21 measures potentially useful for bioindication purposes. Two series of data were examined: (a) macroinvertebrate samples taken on four occasions over an annual cycle were used to assess the effects of seasonality and among-habitat variability; (b) macroinvertebrate samples collected in three consecutive summers were used to assess interannual variability. Coefficients of variation, expressed as percentage, were used to quantify the effect of among-habitat and temporal variability on the selected metrics. According to our results, % Insecta, Shannon–Wiener diversity index and the qualitative taxonomic metrics (measures based on number of taxa) were robust in terms of temporal (seasonal and interannual) and among-habitat variability. Abundance ratio and some metrics based on functional feeding groups were highly variable. Therefore, qualitative taxonomic metrics may be promising tools in biomonitoring programs of Mediterranean shallow lakes due to their comparatively low variability.

Chemical pollution in inland shallow lakes in the Mediterranean region (NW Spain): PAHs, insecticides and herbicides in water and sediments.

The possible effect of land uses and human-related geographic patterns (presence of roads and urban settlements) on chemical pollution was evaluated in the waters and sediments of fifty-three Mediterranean shallow lakes. The presence of fifty-nine pollutants (belonging to PAHs, insecticides and herbicides groups) was analysed in these lakes by GC-MS. The studied lakes had similar pollutant concentrations to other lakes worldwide. The distribution of the compounds between water and sediment compartments was strongly influenced by log K(ow) values (an average of 3.61 for compounds found in water and of 4.69 for compounds found in sediments). A multivariate analysis suggested that the concentration of PAHs in water could be related to agricultural activities and not related to local road traffic. When assessing nutrient levels in the lakes, it was observed that eutrophicated lakes [>300 μg L(-1) total phosphorus (TP)] appeared in areas affected by urban or industrial use (at least 2% urban use in a 1-km radius around the lake), whilst lakes with lower TP concentrations were placed in forest areas (60% of forest use in a 1-km radius); in addition, the aqueous concentrations of Σ(PAH) were lower in lakes with higher TP concentrations (>150 μg L(-1) TP), which could be related to the adsorption capacity of PAHs onto suspended matter which is present in mesotrophic and eutrophic lakes, thus being removed from the aqueous phase.

The relative importance of natural and anthropogenic effects on community composition of aquatic macrophytes in Mediterranean ponds

To detect when changes in response to stressors are occurring, biomonitoring programs require an understanding of shifts in biota that occur in response to anthropogenic and natural effects. Aquatic plants are expected to reflect the environmental conditions of ponds and, according to the European Water Framework Directive, macrophytes should be considered in ecological status assessments of inland surface waters. We assessed the relative importance of natural and anthropogenic impacts on submerged, emergent and floating-leaved macrophytes in 44 ponds in Duero river basin (North Iberian Plateau). Constrained canonical ordinations included 15 taxa of submerged macrophytes and 24 species of emergent and floating-leaved macrophytes. Although the proportion of variation explained by all selected variables was relatively low (37%), we found that submerged community composition reflected the influence of natural (habitat and biotic variables) and anthropogenic effects. However, emergent and floating-leaved macrophytes were not influenced by biotic variables. Variance partitioning showed that degradation category was the best predictor of both submerged macrophytes and emergent and floating-leaved macrophyte composition. However, submerged macrophytes were more affected by chemical variables, whereas emergent and floating-leaved macrophyte composition was best explained by land-use variables. The results of this study support the use of macrophyte communities as effective indicators of the ecological status of Mediterranean ponds.

Spatial structure of the caddisfly (Insecta, Trichoptera) communities in a river basin in NW Spain affected by coal mining

The changes in caddisfly community structure and composition in the Sil River basin (NW Spain), associated with a gradient in natural conditions and a succession of alterations induced by human activity (mainly urban wastes and coal mining), were studied. Twenty-nine Trichoptera taxa belonging to 11 families were collected. The community diversity analysis showed important spatial differences from source to mouth. Towns and, above all, coal mines produced an increase in sulphate and chloride concentrations and conductivity, which adversely affected the trichopteran assemblages. A stepwise regression model, which introduced sulphate and chloride as variables, explained the changes in diversity produced in the basin (r=0.837, p< 0.01). The lowest diversity and richness values were recorded in the rivers suffering the greatest impact from coal mining or urban wastes. The heterogeneity values of the communities for the main rivers were clearly different. The greatest community heterogeneity corresponded to the main axis of the basin and was explained by spatial variability in water chemical composition. No relation was detected between structural changes at spatial level and geographical distance, such that pollution processes basically controlled the dynamics of the Trichoptera communities. Partial-CCA using distance from the source as a covariable revealed alkalinity and urban and mining-derived pollution as the main factors influencing caddisfly distribution. However, an ordination of sites in relation to the corresponding vectors did not fully agree with the chemical characteristics of the water. The species composition of the Trichoptera communities, therefore, did not seem to be good indicators of the chemical features of the rivers. The structure of the community (as expressed by richness and the Shannon index) appeared to be the better indicator of pollution.

Congruence between functional and taxonomic patterns of benthic and planktonic assemblages in flatland ponds

Using data from 31 ponds, we investigated the importance of environmental (e.g. habitat complexity, nutrient content, pH) and biotic factors (i.e. fish predation) on the spatial patterns of planktonic (phytoplankton and zooplankton) and benthic (macroinvertebrates) assemblages. We also evaluated the degree of concordance among assemblages and between the functional and taxonomic composition of assemblages, and test the hypothesis that surrogates of biodiversity (e.g. taxonomic or functional groups) can be used in pond conservation and biomonitoring studies. We found that the spatial patterns of benthic and pelagic assemblages were determined by macrophyte coverage, water quality and, to a lesser extent, fish. However, shifts in the taxonomic and functional composition were not congruent. Moreover, local environmental variation was slightly more important for the taxonomic than the functional composition of assemblages, except for phytoplankton. The degree of concordance among assemblages was also weak, which may be partly due to the fact that species respond individualistically to environmental variation. These findings also suggest that the coupling between benthic and pelagic habitats in flatland ponds is weak, and that the use of surrogate measures or indicator groups in pond conservation studies may not be appropriate.

Assessment of eutrophication effects on charophytes in Mediterranean ponds (North-Western Spain)

The distribution of charophyte vegetation in 57 ponds located in the basin of the River Duero in North-Western Spain was studied in relation to eutrophication. A total of 11 charophyte taxa were recorded in 40 ponds. However, only Chara fragilis Desv., Chara connivens Salzm. ex A. Braun and Nitella translucens (Pers.) C. Agardh were found in more than 17% of the ponds where charophytes occurred. Significant differences between ponds with and without charophytes were found for the following parameters: volatile suspended solids (VSS), total suspended solids (TSS), turbidity, chlorophyll-a, nitrate and total phosphorus (TP). These variables were significantly lower in ponds where charophytes were present. Charophytes were found over a wide range of TP concentrations (20―6884 μg L ―1 ). However, taxa showed differing sensitivities to phosphorus concentrations. Thus, Chara connivens and Chara fragilis showed the highest optimum values for TP concentration (1875 and 551 μg L ―1 TP, respectively) while Nitella translucens registered the lowest optimum value for TP (69 μg L ―1 ). The charophyte cover showed a significant negative correlation with VSS and chlorophyll-a. As for charophyte taxa, Chara connivens cover was positive and significantly correlated with orthophosphate (SRP), while Nitella translucens cover showed a significant negative correlation with TP and TSS. The ordination of charophyte taxa showed a principal gradient of mineralization and ecological condition and a secondary gradient of eutrophication.

Environmental drivers of aquatic macrophyte assemblages in ponds along an altitudinal gradient

The aim of this study was to explore the environmental drivers of the aquatic macrophyte assemblage in a large, heterogeneous Spanish region covering a wide altitudinal range. We hypothesized that physicochemical variables affecting assemblages would differ depending on altitude. The study was conducted in 46 plateau ponds and 21 mountain ponds. Our results revealed a shift in hydrophyte assemblage composition and structure along an altitude and water chemistry gradient. However, altitude was not a good predictor of species richness. Conductivity and nutrient concentrations were higher in plateau ponds than in mountain ponds and binary logistic regression showed that conductivity was the best variable for differentiating between both pond types. Canonical correspondence analysis indicated that conductivity was the main factor responsible for the species distribution in both pond types. Generalized linear models showed that in plateau ponds, total phosphorus and mean depth were the strongest predictors of submerged macrophyte coverage, and no model could be created for richness. In the mountain ponds, conductivity and pond area explained coverage of submerged plants, while richness was related to pond area. Our results corroborated the hypothesis to be tested, and the conclusions obtained may be of relevance for making decisions on conservation and restoration.