Xavier D. Quintana

State of the art in the functioning of shallow Mediterranean lakes: workshop conclusions

Studies on shallow lakes from the north temperate zone show that they alternate between clear and turbid water states in response to control factors. However, the ecology of semiarid to arid shallow Mediterranean lakes is less explored. Hydrological effects (e.g. water level fluctuations, water residence time) on major ions and nutrient dynamics and processes, and ecology of submerged macrophytes appear to have a crucial role for food webs in shallow Mediterranean lakes. Nutrient control may be of greater priority in eutrophicated warm shallow lakes than in similar lakes at higher latitudes. This will be relevant for the implementation of the European Water Framework Directive, and conservation and management of these ecosystems. Strong trophic cascading effects of fish resulting from dominance of omnivorous and benthivorous fish species, whose diversity is usually high, together with frequent spawning and absence of efficient piscivores, seem to be the reason for the lack of large-bodied grazers that could control phytoplankton. However, such effects may vary within the region depending on fish distribution and community. These factors need elaboration in order to allow shallow lake ecologists and managers to develop better restoration strategies for eutrophicated shallow Mediterranean lakes. Consequently, modifications for the implementation of the European Water Framework Directive for determining ecological status in shallow Mediterranean lakes appear to be necessary. Furthermore, the implications of climate warming may be even more challenging than in high latitude lakes since shallow lakes in the Mediterranean region are among the most sensitive to extreme climate changes. There is an urgent need for data on the ecology of shallow lakes in the region. An appeal is made for international cooperation, development of large-scale research and information exchange to facilitate this and a web-based discussion list has been implemented.

Succession of the animal community in a Mediterranean temporary pond

Abstract Successional changes in the animal community of a temporary pond on the Iberian Peninsula were analyzed based on taxon abundance and the biomass–size spectrum. Changes in the community were studied over 6 hydroperiods during 1996 and 1997. Community dynamics were analyzed using multivariate analysis and a new statistical approach based on the Pareto probability distribution. Three successional phases could be distinguished on the basis of changes in taxon abundance. This pattern is consistent with the 3-phase model reported in other temporary ponds in temperate latitudes. The 1st and 3rd phases corresponded to changes in hydrological factors (pond drying, water turnover) and to seasonality, whereas the 2nd phase corresponded to more stable hydrological conditions. Five successional phases could be distinguished on the basis of biomass–size spectra with similar structure. These phases were consistent with variations over time of parameter c of Pareto Model I. The 3 middle phases (II, III, and IV) identified using the size-spectrum approach corresponded to the single middle phase identified using the taxonomic approach. Thus, community changes during the middle phase were better resolved by analysis of the biomass–size spectrum than by analysis of taxon abundance.

Patterns of composition and species richness of crustaceans and aquatic insects along environmental gradients in Mediterranean water bodies

Differences in the dynamics of ecological processes between Mediterranean and colder temperate aquatic systems could imply different patterns in faunal communities in terms of composition and biodiversity (i.e. species richness and rarity). In order to identify some of these patterns the crustacean and aquatic insect composition and biodiversity of four water body types, classified according to their salinity and water permanence, were compared. Moreover, the relationships between species richness and water, pond and landscape variables were analysed. A total number of 91 water bodies located throughout Catalunya (NE Iberian Peninsula) were sampled. Three species assemblages were observed: one for permanent freshwaters, another for temporary freshwaters, and a third one for saline waters (SW), since permanent and temporary saline water bodies had similar composition. Differences in salinity were associated with proportion of crustaceans versus insects and with singularity. Thus, saline ponds had a higher proportion of crustaceans, and lower values of singularity. Conductivity was significantly related to total (crustaceans plus insects) richness, and also related to insect richness. The main difference between the models obtained for crustacean species richness and insect species richness is the significance of landscape variables in the latter, and this fact could be related to the different dispersion types of these two faunal groups: active for insects versus passive for crustaceans.

Zooplankton structure and dynamics in permanent and temporary Mediterranean salt marshes : taxon- based and size-based approaches

Differences between zooplankton structure (species abundance and size distribution) and dynamics of permanent and temporary basins of a Mediterranean salt marsh (Emporda Wetlands, NE Spain) were analysed by means of taxon-based and size-based approaches. These basins are shallow bodies of water which are occasionally connected. They were isolated after water retreat from a broadly flooded, low-lying area close to the open sea. Although temporary and permanent basins show no differences in the most abundant zooplankton species, they differ in their zooplankton diversity, temporal pattern and size structure. The zooplankton assemblages of temporary basins exhibit a temporal pattern with six phases, which are conditioned to the hydrological cycle, each one dominated by one species, whereas in the permanent basin this temporal pattern shows only two phases. Zooplankton size distribution of the temporary basins is dominated by large sizes (copepodites and copepods) while the permanent basin is dominated mainly by small sizes (rotifera and nauplii of copepods). In the temporary basins, the shape of the biomass size spectrum changes according to the hydrological cycle and reflects the dynamics of the ecological interactions among zooplankton species. Differences in the zooplankton composition and dynamics of the permanent basin are not a consequence of water permanence but of the ecological interactions among species involved. The presence of a stable fish population in the permanent waters may explain the high values of zooplankton diversity and the low densities of large zooplankton.

Climate change and the future of freshwater biodiversity in Europe: a primer for policy-makers.

Abstract Earths climate is changing, and by the end of the 21st century in Europe, average temperatures are likely to have risen by at least 2 °C, and more likely 4 °C with associated effects on patterns of precipitation and the frequency of extreme weather events. Attention among policy-makers is divided about how to minimise the change, how to mitigate its effects, how to maintain the natural resources on which societies depend and how to adapt human societies to the changes. Natural systems are still seen, through a long tradition of conservation management that is largely species-based, as amenable to adaptive management, and biodiversity, mostly perceived as the richness of plant and vertebrate communities, often forms a focus for planning. We argue that prediction of particular species changes will be possible only in a minority of cases but that prediction of trends in general structure and operation of four generic freshwater ecosystems (erosive rivers, depositional floodplain rivers, shallow lakes and deep lakes) in three broad zones of Europe (Mediterranean, Central and Arctic-Boreal) is practicable. Maintenance and rehabilitation of ecological structures and operations will inevitably and incidentally embrace restoration of appropriate levels of species biodiversity. Using expert judgement, based on an extensive literature, we have outlined, primarily for lay policy makers, the pristine features of these systems, their states under current human impacts, how these states are likely to alter with a warming of 2 °C to 4 °C and what might be done to mitigate this. We have avoided technical terms in the interests of communication, and although we have included full referencing as in academic papers, we have eliminated degrees of detail that could confuse broad policy-making.

Comparison of nutrient and contaminant fluxes in two areas with different hydrological regimes (Empordà Wetlands, NE Spain)

Nutrient (N and P), heavy metal (Ni, Cd, Cr, Cu and Pb) and pesticide (DDT, DDD, DDE, lindane, aldrin, endrin, dieldrin, permethrin, atrazine and simazine) concentrations in water and sediment were analysed in the Empordà Wetlands, a Mediterranean wetland area in NE Spain. Mean nutrient and contaminant concentrations and input and output loads via tributaries were compared in two marshes with different water turnover: a freshwater marsh (FWM), with a high water turnover rate due to continuous surface water inputs and outputs, and a brackish water marsh (BWM), with lower turnover and no continuous surface output, where water remains confined during dry periods. Mean concentrations of most heavy metals exceeded the maximum permissible concentration (MPC) in BWM, whilst only some pesticides reached MPC in FWM. The confined waters of BWM showed higher sensitivity to contaminant input loadings than FWM due to the lack of continuous water outputs. Non-point source pollution inputs during runoff (mainly in FWM) and concentration during confinement (mainly in BWM) showed as the main environmental problems related to nutrients and contaminants in these ecosystems. Thus, the importance of confinement and its effect on pollutant concentrations must be borne in mind to achieve correct management of Mediterranean wetlands.

Spatial and temporal patterns of pioneer macrofauna in recently created ponds: taxonomic and functional approaches

Man-made ponds are often created to compensate for the loss and degradation of wetlands, but little is known about the processes taking place in these artificial environments, especially at a community level. The macrofaunal assemblage and water chemistry of newly created ponds in three nearby areas in the NE Iberian Peninsula were studied during the first year of life of these ponds in order to (i) detect if any invertebrate assemblage structure change was taking place, (ii) evaluate the effect of local factors on the invertebrate assemblage in each site, and (iii) compare the information obtained by taxonomic and functional approaches. Although invertebrate colonization was rapid, no relevant changes in assemblage parameters were related to time, implying that more time may be needed to detect successional changes in invertebrate assemblages. Local factors—especially those related to hydrological stability—produced notable differences both in the assemblage parameters and in the taxonomic and functional compositions of the invertebrate fauna. Finally, information provided by the functional approach was redundant with respect to that obtained by the classical taxonomic approach: in these newly created systems, the high dominance of a small number of taxa makes the functional approach a simple biological traits analysis of the few dominant species.

Variability of benthic assemblages in relation to the hydrological pattern in Mediterranean salt marshes (Empordà wetlands, NE Iberian Peninsula)

The structure and composition of benthic assemblages (organisms > 100 μm) and the main factors which control them were studied in the coastal basins of the Emporda wetlands (NE Iberian Peninsula). Five coastal basins were sampled in three different conditions during one hydroperiod (1997-1998): (1) one month after the main autumnal inundation when the water level was high; (2) in the middle of the hydroperiod; and (3) when the basins were close to desiccation. Based on the hydrological pattern, three types of basins were distinguished: non-disturbed permanent waters (type 1), non-disturbed temporary waters (type 2), and disturbed temporary waters (type 3). These three types are in agreement with the classification result from the benthic assemblage composition. The type 1 basins, where more stable environmental conditions were found, had an assemblage characterised by a high density of individuals, total biomass and diversity. The assemblage of type 2 basins had lower richness and diversity values with little temporal variability. The high frequency of freshwater inputs in type 3 basins causes a high taxonomic singularity and high temporal variability of species richness and diversity. The main environmental parameters (salinity, sand percentage, total phosphorus from the sediment, and total organic carbon from the water) related to the structure of benthic assemblages, also discriminating three groups, were coincident with the three types derived from distinct hydrological patterns. Thus, water regime summarises the physical factors which ultimately determine benthic fauna.

Effects of Temperature, Salinity and Fish in Structuring the Macroinvertebrate Community in Shallow Lakes: Implications for Effects of Climate Change

Climate warming may lead to changes in the trophic structure and diversity of shallow lakes as a combined effect of increased temperature and salinity and likely increased strength of trophic interactions. We investigated the potential effects of temperature, salinity and fish on the plant-associated macroinvertebrate community by introducing artificial plants in eight comparable shallow brackish lakes located in two climatic regions of contrasting temperature: cold-temperate and Mediterranean. In both regions, lakes covered a salinity gradient from freshwater to oligohaline waters. We undertook day and night-time sampling of macroinvertebrates associated with the artificial plants and fish and free-swimming macroinvertebrate predators within artificial plants and in pelagic areas. Our results showed marked differences in the trophic structure between cold and warm shallow lakes. Plant-associated macroinvertebrates and free-swimming macroinvertebrate predators were more abundant and the communities richer in species in the cold compared to the warm climate, most probably as a result of differences in fish predation pressure. Submerged plants in warm brackish lakes did not seem to counteract the effect of fish predation on macroinvertebrates to the same extent as in temperate freshwater lakes, since small fish were abundant and tended to aggregate within the macrophytes. The richness and abundance of most plant-associated macroinvertebrate taxa decreased with salinity. Despite the lower densities of plant-associated macroinvertebrates in the Mediterranean lakes, periphyton biomass was lower than in cold temperate systems, a fact that was mainly attributed to grazing and disturbance by fish. Our results suggest that, if the current process of warming entails higher chances of shallow lakes becoming warmer and more saline, climatic change may result in a decrease in macroinvertebrate species richness and abundance in shallow lakes.

The Role of plant type and salinity in the selection for the denitrifying community structure in the rhizosphere of wetland vegetation

Coastal wetlands, as transient links from terrestrial to marine environments, are important for nitrogen removal by denitrification. Denitrification strongly depends on both the presence of emergent plants and the denitrifier communities selected by different plant species. In this study, the effects of vegetation and habitat heterogeneity on the community of denitrifying bacteria were investigated in nine coastal wetlands in two preserved areas of Spain. Sampling locations were selected to cover a range of salinity (0.81 to 31.3 mS/cm) and nitrate concentrations (0.1 to 303 μM NO3-), allowing the evaluation of environmental variables that select for denitrifier communities in the rhizosphere of Phragmites sp., Ruppia sp., and Paspalum sp. Potential nitrate reduction rates were found to be dependent on the sampling time and plant species and related to the denitrifier community structure, which was assessed by terminal restriction fragment length polymorphism analysis of the functional genes nirS, nirK and nosZ. The results showed that denitrifier community structure was also governed by plant species and salinity, with significant influences of other variables, such as sampling time and location. Ruppia sp. and Phragmites sp. selected for certain communities, whereas this was not the case for Paspalum sp. The plant species effect was strongest on nirK-type denitrifiers, whereas water carbon content was a significant factor defining the structure of the nosZ-harboring community. The differences recognized using the three functional gene markers indicated that different drivers act on denitrifying populations capable of complete denitrification, compared to the overall denitrifier community. This finding may have implications for emissions of the greenhouse gas nitrous oxide.