Manel Leira

Effects of water-level fluctuations on lakes: an annotated bibliography

Water-level fluctuations (WLF) in lakes and rivers, especially their extent, frequency and duration, are dominant forces controlling the functioning of these ecosystems. In particular, WLF play an important role in the lake’s littoral and aquatic–terrestrial interface processes. WLF may take place on different spatial and temporal scales under natural conditions but water levels have been artificially modified in regulated lakes, and their impacts are expected to be enhanced within the actual global change scenarios with forthcoming management problems. This article presents an overview on the literature published on this important topic since 1991 by using journals indexed in the ISI Web of Knowledge. The overall objective was to examine temporal and spatial trends in publications on WLF, the specific aspect of WLF concerned and their main effects. Throughout the article we have used case studies to illustrate different effects of WLF on the variety of lake habitats and indicators that have been studied. Overall, the number of papers published on the subject since the 1990s has risen steadily, when less than ten papers were published each year; until 2006 and peaking in 2005. The greatest number of papers on WLF has been carried out in Europe and North America (c. 73%). These data also showed that the effects of WLF have not been studied equally for different groups of organisms. There is a greater interest on macrophytes, which are the most studied group of organisms (18.4% of the papers). Nearly 7% of the papers deal with algae, and zooplankton and invertebrates account for a 7% followed by fish. WLF effects on ecosystems are very complex, and the biological effects in lakes are greatest in shallow water and littoral areas, where even small changes in water levels can result in the conversion of large areas of a standing-water environment in air exposed habitats. Finally, these data might serve to highlight knowledge gaps still existing on this topic and, in particular, some of the approaches that can potentially contribute to solve several of these lacunae are explored.

Recent histories of six productive lakes in the Irish Ecoregion based on multiproxy palaeolimnological evidence

Palaeolimnological data from six mesotrophic, eutrophic and hypertrophic lakes in the Irish Ecoregion, in the form of microfossil (cladocera, diatoms and pollen) and sediment chemistry data from radiometrically dated sediment cores, were used to reconstruct past variations in lake water quality and catchment conditions. Basal sediments from sediment cores from the six sites ranged in age from the late 18th century to the early 20th century. A weighted averaging partial least squares regression model was developed to reconstruct past epilimnetic total phosphorus concentrations. The results indicate that all but one of the study sites currently are in a far more productive state compared with the beginning of the sediment core record and that those same five lakes have experienced accelerated enrichment post c. 1980. Two of the sites demonstrated long-term enrichment, in one case beginning in the late 19th century, while both eutrophication and oligotrophication have occurred at three sites. The results highlight the difficulties in applying a general temporal end-point for reference conditions and demonstrate that productive lakes in the Irish Ecoregion have complex, locally specific and often long histories of enrichment. These may not be responsive to reduced external loadings of phosphorus and, as a result, restoration could prove particularly challenging. The results also provide evidence of the ways in which palaeolimnological techniques can assist implementation of the EU Water Framework Directive.

Use of multivariate analyses to investigate the contribution of metal pollution to diatom species composition: search for the most appropriate cases and explanatory variables

The aim of this study was to elucidate how the spatial scale and the set of variables included influence our ability to detect the effects of different types of pollution on the biota. Using variance partitioning analysis, we assessed the individual importance of a set of environmental factors (eutrophication and organic pollution) versus metal level pollution on the community structure of diatom assemblages at different spatial scales. At regional scale, environmental factors did not explain more of the variance compared to the watershed study. The results of the watershed scale field survey indicate that diatom community composition was influenced by low metal concentrations, but this pattern was only observed by the inclusion of biofilm metal concentration data. We recommend the analysis of metal traces in the water phase and the biota (fluvial biofilms) as well as the use of the Diffusive Gradient in Thin films (DGT) technique to characterize low metal level pollution in freshwater systems.

Environmental classification of springs of the Italian Alps and its consistency across multiple taxonomic groups

Abstract.  The traditional and widely used ecomorphological spring classification—pool springs (limnocrenes), seepages (helocrenes), and flowing springs (rheocrenes)—is based mainly on the flow regime at the spring mouth. This clear distinction is based purely on environmental conditions, but how and to what extent these spring typologies are reflected by biological assemblages consisting of different taxonomic groups remains largely untested. Classification of habitats typically is based on one or few taxonomic groups. However, groups are likely to differ in their response to the environment, so different, equally valid classifications might result with different groups. We evaluated the responses and their congruence of a wide range of taxonomic groups to different spring types. Eighty-six springs in the Italian Alps were first classified based on environmental factors only. The consistency of this classification was tested using diatoms, bryophytes, vascular plants, nematodes, mollusks, oligochaetes, water mites, copepods, ostracods, chironomids, stoneflies, and caddisflies. When only environmental variables were used, 7 spring types were distinguished: limnocrenes and helocrenes, low- and high-altitude rheocrenes on carbonate rocks, rheocrenes on siliceous rocks, rheocrenes with high discharge, and hygropetric rheocrenes. This classification was reflected by most taxonomic groups, and many species were characteristic for ≥1 spring type. However, the predictive power of the environment for determining species distribution was generally low, a result suggesting that other factors may play an important role in structuring spring assemblages. Concordance among taxonomic groups was found for 2 macrogroups of organisms: autotrophs (diatoms, bryophytes, and vascular plants) and heterotrophs. This result shows that achieving a general classification of springs relevant across all taxonomic groups would be difficult.

Discharge and the response of biofilms to metal exposure in Mediterranean rivers

The expected response of fluvial biofilms to the environment and metal pollution prevailing under different discharge conditions was investigated. The relationship between inter-annual hydrological variability and metal concentration in water and sediments was explored in Mediterranean rivers (Catalonia, NE Spain) affected by low but chronic metal pollution, using monitoring data provided by the Catalan Water Agency (ACA). During the period investigated (2000–2006), metal pollution was characterized by low water concentrations and high concentrations in sediments. The most consistent pattern was observed for sediment cadmium (Cd) concentrations, showing a positive relationship with annual discharge, reaching values of environmental concern (above ecotoxicological benchmarks). A different pattern was observed for Cu, Zn, and As increasing with flow in some sites and decreasing in others. While Cd seems to proceed from diffuse sources being washed by surface runoff, Zn, Pb, and As may proceed from either diffuse or point-sources in the different river sites investigated. The relevance of diffuse metal pollution in the area of study indicates that polluted landfills runoff might be an important source of metals causing repetitive pulses of high metal concentration in the receiving water courses. The experimental results presented demonstrate that metal effects in fluvial biofilms may be accumulative, increasing the toxicity after repetitive pulse exposures. Since draughts and extreme rain events are expected to increase at higher latitudes due to global change, the sources of metal pollution, its final concentration and potential effects on the fluvial ecosystem may also change following the patterns expected for human-impacted Mediterranean rivers.

210Pb-dating of a lake sediment core from Lough Carra (Co. Mayo, western Ireland): use of paleolimnological data for chronology validation below the 210Pb dating horizon

The chronologies and sediment accumulation rates for a lake sediment sequence from Lough Carra (Co. Mayo, western Ireland) were established by applying the constant initial concentration (CIC) and constant rate of supply (CRS) hypotheses to the measured (210)Pb(excess) profile. The resulting chronologies were validated using the artificial fallout radionuclides (137)Cs and (241)Am, which provide independent chronostratigraphic markers for the second half of the 20th century. The validity of extrapolating the derived CIC and CRS dates below the (210)Pb dating horizon using average sedimentation rates was investigated using supplementary paleolimnological information and historical data. Our data confirm that such an extrapolation is well justified at sites characterised by relatively stable sedimentation conditions.

Metal Ecotoxicology in Fluvial Biofilms: Potential Influence of Water Scarcity

Human activity is responsible for the entrance of toxic substances into aquatic ecosystems. These substances entail a risk for the components of the ecosystem (toxicological stress). As a result of global change, aquatic ecosystems are under strong environmental stress due to changes in water flow or nutrient concentration among others. This chapter presents a review of experimental and field studies addressing metal effects on fluvial biofilms and their implications for understanding the potential influence of water scarcity on the fate and effects of metals in fluvial systems. Water scarcity might increase metal exposure (due to low dilution), uptake (due to higher retention under low flow), toxicity and/or accumulation (depending on the dose and time of exposure) but may also cause opposite effects depending on the source of pollution. In addition, the influence that water scarcity might have on nutrient loads will also modulate the fate and effects of metals. Future studies addressing the role of environmental stress on the effects of toxicants at a community scale will be fundamental to predict the impact of toxicants in the aquatic ecosystems.

Light History Influences the Response of Fluvial Biofilms to Zn Exposure

Fluvial biofilms are subject to multistress situations in natural ecosystems, such as the co‐occurrence of light intensity changes and metal toxicity. However, studies simultaneously addressing both factors are rare. This study evaluated in microcosm conditions the relationship between short‐term light intensity changes and Zn toxicity on fluvial biofilms with long‐term photoacclimation to different light conditions. Biofilms that had long‐term photoacclimation to 25 μmol photons · m−2 · s−1 (low light [LL] biofilms), 100 μmol photons · m−2 · s−1 (medium light [ML] biofilms), and 500 μmol photons · m−2 · s−1 (high light [HL] biofilms) were characterized by different structural (Chlorophyll‐a [Chl‐a], total biomass‐AFDW, EPS, algal groups, and diatom taxonomy) and physiological attributes (ETR‐I curves and photosynthetic pigments). HL biofilms showed higher light saturation intensity and a higher production of xanthophylls than LL biofilms. In contrast, LL biofilms had many structural differences; a higher proportion of diatoms and lower AFDW and EPS contents than ML and HL biofilms. A clear effect of light intensity changes on Zn toxicity was also demonstrated. Zn toxicity was enhanced when a sudden increase in light intensity also occurred, mainly with LL biofilms, causing higher inhibition of both the Φ′PSII and the ΦPSII. A decoupling of NPQ from de‐epoxidation reaction (DR) processes was also observed, indicating substantial damage to photoprotective mechanisms functioning in biofilms (i.e., xanthophyll cycle of diatoms) due to Zn toxicity. This study highlights the need to take into account environmental stress (e.g., light intensity changes) to better assess the environmental risks of chemicals (e.g., metals).

Rapid ecosystem recovery from diffuse pollution after the Great Irish Famine

Remarkably little is known about the effectiveness or rates of recovery of aquatic ecosystems from reductions in human-associated pressures at landscape scales. The retention of anthropogenic contaminants within ecosystems can retard rates of recovery considerably, while the trajectories of recovery processes vary with the extent of disturbance and the resilience of biotic assemblages. The Great Irish Famine of 1845-1850 comprised one of the most significant human disasters of the 19th century, causing the death of approximately one million people and the emigration of a further two million from the country between 1845 and 1855. We found, through analysis of detailed historical census data combined with paleolimnological investigation of sedimentary nutrient concentrations, stable isotope ratios, and diatom assemblages, that the trophic level of Lough Carra, a largely shallow calcareous lake in the west of Ireland with no urban areas or point sources of any significance in its catchment, reduced considerably during and immediately after the Great Famine, shifting to new equilibria within just 2-10 years. Our results demonstrate that the reduction of human pressures from diffuse sources at landscape scales can result in the rapid and monotonic recovery of aquatic ecosystems. Moreover, the recovery of ecosystems from diffuse pollution need not necessarily take longer than recovery from pollution from point sources.

Is the biological classification of benthic diatom communities concordant with ecotypes

In this study a biological classification based on diatom communities (a posteriori classification) was used to search for the most appropriate a priori classification in reference conditions, on the basis of 31 reference sites encompassing eight watersheds in the NE Iberian Peninsula. We considered three different a priori systems for comparison: (i) a typological classification (ecotypes and subecotypes) based on geomorphology and water flow; (ii) the watershed as a unit, irrespective of its size; and (iii) a classification based on the geographical distance between sites under the assumption that biological characteristics are increasingly similar in geographically closer sites. Classification in ecotypes and subecotypes was the most robust with minor differences between them. The watershed (hydrological units) classification was significant though weaker than the typological classification and there was a larger environmental variation within watersheds than within ecotypes. Finally, results showed that geographically closer sites were not more biologically similar in terms of diatom community composition. We can conclude that the ecotypological environmental-based classifications developed by the local water agency did adequately describe the biological classification based on epilithic diatoms.