Manuel Toro

Defining criteria to select reference sites in Mediterranean streams

The European Water Framework Directive establishes the need to define stream type-specific reference conditions to identify “high ecological status”. Methods for selecting reference sites using a priori criteria have been proposed by many authors. A review of these criteria revealed that the most relevant criteria for streams and rivers were those related to riparian vegetation, diffuse and point sources of pollution, river morphology and hydrological conditions and regulation. In this work, we propose 20 criteria that reflect the characteristics of Mediterranean streams and their most frequent disturbances for the selection of reference sites in Mediterranean streams in Spain. We studied 162 sites located in 33 Mediterranean basins belonging to five stream types. Of the locations, 57% were selected as a priori reference sites by having applied the proposed criteria. Reference sites were identified for all stream types except for “large watercourses” which includes the lower reaches of some rivers in this study area. This a priori selection of reference sites was subjected to validation using the macroinvertebrate community by applying of an IBMWP threshold, which is considered to be an indicator of undisturbed sites in Mediterranean streams. This approach determined that whole of this selection (100%) could be considered valid reference sites. Furthermore, we identified differences in the reference conditions for each stream type on the basis of macroinvertebrate assemblage composition.

The MEDiterranean Prediction And Classification System (MEDPACS): an implementation of the RIVPACS/AUSRIVAS predictive approach for assessing Mediterranean aquatic macroinvertebrate communities

In Spain, a national project known as GUADALMED, focusing on Mediterranean streams, has been carried out from 1998 to 2005 to implement the European water framework directive (WFD) requirements. One of the main objectives of the second phase of the project (2002–2005) was to develop a predictive system for the Spanish Mediterranean aquatic macroinvertebrate communities. A combined-season (spring, summer, and autumn) predictive model was developed by using the latest improvements on the selection of best predictor variables. Overall model performance measures were used to select the best discriminant function (DF) models, and also to evaluate their biases and precision. The final predictive model was based on the best five DF models. Each one of these models involved eight environmental variables. Final observed (O), expected (E), and O/E values for the number of macroinvertebrate families (NFAM) and two biotic indices (IBMWP and IASPT) were calculated by averaging their values, previously weighted by the quality of each DF model. Regression analyses among the final O and E values for the calibration dataset showed a high proximity to the ideal theoretical model, where the final E values explained 73–84% of the variation present in the macroinvertebrate communities of the Spanish Mediterranean watercourses. The ANOVA performed among the reference (calibration and validation) and test datasets showed clear differences for the O/E values. Finally, the assessments carried out by the predictive model were sensitive to anthropogenic pressure present in the study area and allowed the definition of five ecological status classes according to the WFD requirements.

Chronostratigraphy of the sedimentary record of Limnopolar Lake, Byers Peninsula, Livingston Island, Antarctica

Abstract The chronostratigraphy of the sedimentary record of Limnopolar Lake, located on Byers Peninsula (Livingston Island, South Shetland Islands, Maritime Antarctica), is described based on radionuclides and radiocarbon age dating. The oldest moss macrofossil age was 6700±50 yr bp (7510±80 cal yr bp) from which the age/depth model estimates a basal age for the sedimentary record of c. 8300 cal yr bp, suggesting an earlier deglaciation of Byers Peninsula than reported in previous studies. Lithological units and other stratigraphic zones are described throughout the sediment core, showing different mineralogical composition and a fine alternation of clays and silty clays and moss layers of Drepanocladus longifolius. Based on magnetic susceptibility analyses, a number of probable primary and reworked tephra layers were identified, seven of them confirmed by SEM observations, and most of them in agreement with the regional tephrachronology stratigraphy for the north-west Antarctic Peninsula. Sedimentation rates showed no significant changes during the last 5000 years with the exception of an abrupt event that took place around 5400 cal yr bp, which implied the sedimentation of c. 30 cm of clays in a very short time, probably related to a period of glacial re-advance that caused abrupt changes in geomorphological processes in the catchment.

The effects of the NAO on the ice phenology of Spanish alpine lakes

Three Spanish alpine lakes located in the Central Range (Peñalara Lake and Cimera Lake) and the Pyrenees (Redon Lake) are selected to understand the effects of the North Atlantic Oscillation (NAO) on ice phenology. A conceptual lake model is formulated based on Pearson’s correlation coefficients obtained between season-scale time series of the NAO index, climatic data (i.e., precipitation, air temperature and snow data) and limnological variables (ice phenology records). The results suggest that the effects of the NAO are only reflected in the thawing process via the air temperature and the insulating effect of snow accumulation on the ice cover. An altitude component is evident in our survey because the effects of the NAO on Peñalara Lake (the lowest altitude studied lake) are restricted to winter, whereas for Redon Lake (the highest altitude studied lake), the effects extend into spring. A latitudinal component is also clear when comparing our data with northern European lakes. Snow accumulation primarily depends on the air temperature at high latitudes, and both precipitation and the air temperature control snow accumulation at lower latitudes. Consequently, in northern Europe, the NAO signal is primarily reflected in lake ice phenology via the air temperature, whereas our results confirm that in southern Europe, the strong dependence of precipitation on the NAO determines the importance of the NAO for lake ice cover.

Specific composition and ecology of chrysophyte flagellates in Lake Sanabria (NW Spain)

Lake Sanabria is a glacial lake located at 1000 m a.s.l. in NW Spain. Its water is characterised by a low content of mineral salts, rather low pH, and oligotrophic status, which are all currently viewed as being favorable for Chrysophyte growth and proliferation. The study of the phytoplankton at different depths of the water column for three years showed that Chrysophytes were one of the groups of algae less well-represented in the phytoplankton (1% and 8%, respectively, for numbers of cells and biovolume).Ochromonas, Pseudopedinella, Mallomonas and Dinobryon were the more representative chrysophyte genera. D. cylindricum, D. divergens and D. crenulatum were some of the Dinobryon species observed. M. akrokomos, M. crassisquama and M. costata were among the most frequent Mallomonas species. Observations on the Chrysophyte cysts from samples of the lake sediment suggest that variability of representation is higher than in planktonic samples.The maximum values of Chrysophyte biovolume were found in the nutrient-exhausted epilimnion of summer and autumn which could be related to the mixotrophic capabilities of several species.

Structure of planktonic microbial communities along a trophic gradient in lakes of Byers Peninsula, South Shetland Islands

Abstract A systematic limnological survey of water bodies of Byers Peninsula (Livingston Island, South Shetland Islands) was carried out during the summer of 2001/02. Abundances of microbial plankton were determined which allowed a delineation of the pelagic food web structure. We also report the nutrient status of these lakes. We demonstrate the occurrence of a trophic gradient that extended from upland lakes (oligotrophic) to the coastal ones (eutrophic). The study shows that a lakes morphology regulates the relative importance of the pelagic and benthic habitats, whereas nutrient loads mainly determine its trophic status. Yet, some of the variability observed could be also a legacy of the landscape. Photosynthetic pigments analyses by high-performance liquid chromatography of the lake waters revealed a major occurrence of chlorophytes, chrysophytes and diatoms. The chlorophyll a concentrations in lakes in the central plateau were consistently lower (< 2.5 μg l-1) than coastal sites, which were one order of magnitude higher. Numbers of both bacterioplankton and autotrophic picoplankton also increased from inland to coastal sites. However, the relative role of autotrophic picoplankton in the total phytoplankton assemblage decreased with the increase in nutrients loads. Our results show that the trophic status clearly plays a significant role in structuring the pelagic communities of these lakes despite climatic constraints.

Stability and endemicity of benthic diatom assemblages from different substrates in a maritime stream on Byers Peninsula, Livingston Island, Antarctica: the role of climate variability

Abstract Diatom assemblages from four different substrates from a stream on Byers Peninsula were analysed during the summer. The substrate type was the main factor explaining the variability in the diatom assemblages. Sandy biofilms showed a higher diversity and a greater number of endemic species. Two main hydrological regimes were observed: 1) a hydrologically unstable period with high variability in stream flow and successive freezing and thawing periods, 2) a late summer hydrologically stable period, characterized by low stream velocity and variability. The structure of the diatom communities was different between the two hydrological periods, although the substrate modulated the difference. The diatom assemblages showed low similarity among the substrates and high dominance of endemic species during early summer. The late summer community showed high dominance of motile cosmopolitan species on all substrate types. As the length of both hydrological regimes would ultimately be driven by climatic variability, the predicted climate warming could reduce overall stream diversity. Hence, subtle changes could alter the length of both hydrological periods. The relationship between diatom species association with different substrates and hydrological regimes could be relevant for tracking past climate variability using diatom palaeorecords.

Community structure and photosynthetic activity of benthic biofilms from a waterfall in the maritime Antarctica

Abstract High-energy flowing water habitats such as waterfalls are uncommon in Antarctica, though they may become more regular as temperature increase. Both high spatial and temporal environmental variability is expected on them. The extent of their biological colonization will depend on the amount of ecological strategies displayed by the surrounding biota. We report here a study on phototrophic microbenthic communities inhabiting such environment in a stream on the Byers Peninsula of Livingston Island. Five different biofilms were distinguished by colour, and were located in specific microhabitat types in the waterfall, which flowed down a steep canyon. Photosynthetic pigment content and microscopic observations demonstrated a different assemblage of chlorophytes, cyanobacteria and diatoms among them. Biofilms were not randomly distributed in the stream channel, which may be related to water flow, nutrient availability and moisture. The exopolymeric substances content, stoichiometry and pigment composition varied among biofilms, likely reflecting differences in the water and nutrients availability. The photosynthetic rates were in the range of the observed in previous studies in the site and varied according to the habitat within the stream. Communities dominated by chlorophytes were restricted to the central channel, suggesting adaptation to faster flow regime. However, cyanobacterial biofilms appeared in a great range of environmental conditions. They were rare in the central channel where water flow was greatest, but achieved large biomass stocks on submerged and even exposed sites in the splash zone at the edge of the flowing water. This study shows how Antarctic biofilms can have a large variability in community structure and biomass over short length scales, reflecting the range of microhabitats in this Antarctic waterfall ecosystem, and the potential occurrence of different strategies to overcome fluctuating conditions.

Maritime Antarctic Lakes As Sentinels Of Climate Change

Remote lakes, such as lakes from the Maritime Antarctica, can be used as sentinels of climate change, because they are mostly free of direct anthropogenic pressures, and they experience climate change as a main stressor capable of modifying the ecosystem structure and function. In this paper, the content of a lecture that has been presented at the First Conference of Lake Sustainability, which has been centred in our studies on lakes from Byers Peninsula (Maritime Antarctica), are summarized. These included physical, chemical and biological studies of these lakes and other freshwater ecosystems, which highlighted the relevance of biotic interactions for these ecosystems and its sensibility to temperature variations and to biological invasions, which is of relevance given the acute regional warming occurring during the last decades in the area, concomitant with the enhancement of dispersion of alien species linked to the increased presence of humans.

Robust optima and tolerance ranges of biological indicators: a new method to identify sentinels of global warming

This study aims to introduce the robust optimum (RO) method as an alternative to the classical weighted averaging (WA) method for estimating the ecological optimum as well as the optimum and tolerance ranges of a taxon with respect to an environmental variable in limnological studies. The RO method is based on robust location and scale estimates rather than on the mean and the standard deviation used by the WA method. The results of our study support the well-known fact that the presence of outliers and the asymmetry of the distribution of the environmental variable might cause a significant effect on the WA-calculated ecological optimum as well as on tolerance ranges. We compared both methods through the identification of potential biological indicators of global warming. Biological data included several benthic, oligostenotherm macroinvertebrate families inhabiting the Júcar River Basin (JRB, eastern Spain). The results of this comparison suggest that the RO method is more appropriate for estimating the distribution of taxa and, consequently, that it provides more realistic information for identifying potential sentinels of global warming in running aquatic systems. Currently, the identification of such sentinels is a goal for several environmental protection laws, such as the European Union Water Framework Directive.