Intercalibration and comparison – major results and conclusions from the STAR project

The main results of the STAR project on the intercalibration of boundaries of European assessment systems and comparison between assessment methods are summarized here. The main findings are outlined in the context of the Water Framework Directive that requires reliable instructions to be set up on how to use and harmonise assessment systems and methods for European rivers. The main papers published on these subjects by STAR partners are reviewed, with focus on major questions addressed and approaches used for investigation. The need for broad coverage of geographic ranges and pressure gradients, together with the goal of providing outcomes appropriate to the effective application of the WFD are emphasized. Extensive datasets from a wide range of countries, stream types and sites and a large number of methods, metrics and approaches are compared and tested and various cross-cutting themes emerged. Among these, the value of the use of benchmarking systems for comparison and intercalibration is highlighted. Two ways of looking for comparability of assessment systems results were analyzed: a) by adopting identical sampling techniques across Europe and b) by harmonizing the classification results of the national assessment systems. In addition, the need, in the intercalibration process, for a proper definition of the criteria for reference conditions is underlined. This is because their imprecision now represents one of the major weaknesses of the whole intercalibration process. Direct and indirect approaches to intercalibration are considered and commented on for their potential use in distinct circumstances. Finally, the use common metrics for the intercalibration process, which make comparability across Europe valid, is tested and indeed encouraged.     

Aquatic plants as environmental indicators of ecological condition in New Zealand lakes

Submerged aquatic plants can act as measurable indicators of ecological conditions occurring within a lake, and they need only be monitored once a year or even less. Historically in New Zealand there has been a reliance on water quality sampling for monitoring the health of lakes and these methods can be complex and costly involving multiple site visits and chemical analysis of water samples. As a result, lake monitoring has been irregular, or not done at all. LakeSPI or ‘Lake Submerged Plant Indicators’ is a new management tool that uses aquatic plants to monitor and assess ecological condition in a wide range of lake types. The method generates three indices: a Native Condition Index (extent and diversity of native plants) and an Invasive Condition Index (extent and impact of alien weeds), which are generated from scores allocated to carefully selected vegetation features; and an integrated LakeSPI Index which is largely derived from components of the other two indices and provides an overall indication of lake ecological condition. The LakeSPI method can be used to assess the status of lakes and monitor trends occurring within them, and it is expected that the use of LakeSPI will facilitate regular monitoring and reporting on a much wider range of lakes than has been possible using traditional water quality methods. By utilizing submerged aquatic plants the method focuses on lake littoral margins where there is greatest public interaction and interest.     

Effects of artificial ultraviolet-B radiation on experimental aquatic microcosms

1. The effects of prolonged ultraviolet-B (UVB) radiation on freshwater communities were studied in indoor microcosms (600 L) with artificial light sources, simulating a clear, shallow, mesotrophic aquatic ecosystem. A range of six intensities (in duplicate) of UVB radiation, ranging from 0 (control) to 9.56 kJ m⁻² day⁻¹ at the water surface, was applied for 8 weeks. The UVB radiation levels, attenuation, shading and scattering were comparable to those in Dutch shallow freshwater systems. Physical, chemical and biological variables were monitored weekly.
2. The UVB treatment did not affect the abundance, species composition or biovolume of the phytoplankton or zooplankton communities, nor did it affect the periphyton or the macroinvertebrate community. A few species showed a significant response on some of the sampling dates, but there was no negative UVB effect at the community level. Overall, the ecosystems in the microcosms were not affected by the UVB treatment.
3. In a bio-assay, a laboratory clone of Daphnia pulex , not subjected to UVB radiation, was fed with seston from the microcosms. Daphnia pulex feeding on seston from the control microcosms grew faster, had better survival and better reproduction than D. pulex feeding on seston from the UVB treated microcosms. The phytoplankton–zooplankton interaction may have been influenced by the UVB treatment.
4. The dissolved oxygen content (DOC) concentrations in the microcosms were around 5 mg L^−1. The DOC levels in Dutch systems rarely fall below 10 mg L^−1. This might provide sufficient protection against the detrimental effects of increased UVB radiation.     

Synthesis and release of cyclic adenosine 3':5'-monophospliate by aquatic macrophytes

Tissues from the aquatic macrophyte species Scirpus subterminalis, Najas flexilis, Ceratophyllum demcrsum, Potamogeton zosteriformis, and Nuphar advena contain cAMP in quantities similar to those reported in algae. Scirpus, Najas , and Ceratophyllum released cAMP into the extracellular media in quantities which varied interspecifically and intraspecifically in differing media. Macrophytic release of cAMP may be an important source of dissolved cAMP in lakewater.     

A model on the competition between two macrophyte species in acidifying shallow soft-water lakes in the Netherlands

To predict changes in vegetation as a result of acidification in shallow Dutch lakes a mathematical model was formulated which describes the growth ofLittorella uniflora andJuncus bulbosus, species characteristic for non-acidified and acidified situations, respectively. The two species compete for light, CO₂ and nutrients. The model integrates current knowledge about the ecophysiology of the species. The results generated by the model are similair to field data concerning dominance of the species in different habitats.L. uniflora is able to grow well under environmental conditions associated with acidification, as long as it is not outcompeted byJ. bulbosus. The competitive advantage of morphological adaptions of the macrophyte species are discussed in relation to the model results.     

Concordance of species richness patterns among multiple freshwater taxa: a regional perspective

Geographical gradients in species richness and the degree to which different taxa show congruent patterns remain unknown for many taxonomic groups. Here, I examined broad-scale species richness patterns in five groups of freshwater organisms; macrophytes, dragonflies, stoneflies, aquatic beetles and fishes. The analyses were based on provincial distribution records in Denmark, Norway, Sweden and Finland. In general, variation in species richness across provinces was concordant among the groups, but stoneflies showed weaker negative relationships with the other taxonomic groups. Species richness in most groups decreased with increasing latitude and altitude, and a considerable part of the variation was explained by mean July temperature. However, stoneflies showed a reversed pattern, with species richness correlating positively, albeit more weakly, with mean provincial altitude. Nevertheless, combined species richness of all five taxa showed a strong relationship with mean July temperature, accounting for 74% of variation in provincial species richness alone. Such temperature-controlled patterns suggest that regional freshwater biodiversity will strongly respond to climate change, with repercussions for local community organization in freshwater ecosystems in Fennoscandia.     

Fifty years of hydrobiological research in India

The paper provides an overview of the developments in hydrobiological studies in India during the past fifty years, and links them with a historical perspective of the pre-independence studies. Hydrobiological studies which were well developed in the beginning of this century, gained momentum soon after independence as all kinds of aquatic habitats were investigated for the assessment, conservation and optimum utilization of inland fishery resources of the country. However, the environmental issues which dominated since the 1972 Stockholm Conference, and growing realization of the problem of water pollution, resulted in a rapid proliferation of hydrobiological studies which tend to focus on correlation between the distribution of various organisms and degree of water pollution or the effects of various organic and inorganic pollutants. A sampling of published literature reveals that long-term, analytical and experimental studies of the whole ecosystems (natural or experimental), and studies of population interactions, biomanipulation, food chain dynamics, and energy flows are wholly lacking. The paper calls for the strengthening of field and laboratory facilities, and establishment of regional and national institutes of aquatic ecology which will be necessary for the management of both the water quality and aquatic biological resources for sustainable development.     

Macrophytes and groundwater drive extremely high organic carbon concentration of soda pans

1. Endorheic soda pans are among the highest dissolved organic carbon (DOC) content aquatic systems on the planet with concentrations up to 1 g/L. Considering the importance of inland waters in the global carbon cycle, understanding the drivers of such outstanding organic carbon pools is eminent. The soda pans of the Carpathian Basin present a wide variability of biotic and abiotic characteristics that provide an adequate system to assess the determinants of extreme high DOC concentrations. Here, we demonstrate through a multi-site comparison, a multi-year seasonal monitoring, and a laboratory experiment that the dissolved organic matter content of the highest DOC concentration soda pans is primarily of groundwater and emergent macrophyte origin.
2. More precisely, the multi-site comparison of 14 soda pans revealed that variation of coloured dissolved organic matter (CDOM) content of the surface water of soda pans is partially explained by the CDOM content (22% of variation) of local groundwater, indicating the significant role of allochthonous terrestrial DOC sources. Further 23% of CDOM variation could be accounted for by Bolboschoenus maritimus species-specific emergent macrophyte cover, while the contribution of Phragmites australis cover was only minor.
3. In line with the results of the multi-site comparison, our decomposition experiment demonstrated that both B. maritimus and P. australis have the potential to release substantial amount of organic matter into soda pans. However, the organic matter release of B. maritimus leads to twice as high DOC and 3.5-times higher CDOM concentrations than P. australis. Considering previous organic matter release studies, we concluded that P. australis is a relatively low organic matter releaser emergent macrophyte, and therefore the species composition of emergent macrophytes has to be carefully considered in autochthonous plant-derived DOM estimations.
4. Finally, the multi-year seasonal monitoring of two distinctive soda pans showed that the high organic matter concentrations depend not only on their intrinsic characteristics but also on interannual variability. More precisely, we demonstrated that the highest CDOM and DOC concentrations that occurred in a coloured (i.e. brown, low total suspended solids) soda pan with extensive (95%) macrophyte cover dominated by B. maritimus were measured in a period characterised by high pH and low water levels, which were presumably the consequence of increased evaporation due to decreased precipitation and above average temperature.
5. Our results indicate that considering climate change trends common for most endorheic regions (i.e. increased temperature and modified precipitation regimes), extremely high organic matter concentrations might become more frequent in the near future in local water bodies, particularly in those highly influenced by groundwater inflow. Furthermore, soda pans with vast specific macrophyte cover and substantial groundwater inflow might become organic carbon processing hotspots.

     

The Seasonal Succession of Epiphytic Communities within an Equisetum fluviatile L. Stand in Lake Pääjärvi,Southern Finland

The seasonal succession of epiphytic communities on Equisetum fluviatile was controlled both directly and indirectly by the macrophyte. Decaying macrophytic material supported rich algal growth and biomass accumulation in spring and early summer. Emergence of the macrophytes severely reduced underwater light availability, and the epiphytic algal biomass declined rapidly as a result of both lower photosynthetic activity of the epiphytic algae, and more intensive grazing by invertebrate herbivores. Epiphytic N: P ratios were lower than those in the water around suggesting that either the water was not the only source of phosphorus for the epiphytic algae or the algae took phosphorus up selectively from the water. Low epiphytic C: N ratios suggested a high potential nutritional value for herbivores.