Assessing the potential environmental factors affecting cladoceran assemblage composition in arsenic-contaminated lakes near abandoned silver mines

Silver mining has a long history in Cobalt (Ontario, Canada), and it has left a complex environmental legacy where many lakes are contaminated with arsenic-rich mine tailings. In this exploratory survey, we examined subfossil Cladocera remains in the surface sediments of 22 lakes in the abandoned mining region to assess which environmental variables may be influencing the recent assemblage structure. Further, using a “top-bottom” paleolimnological approach, we compared the recent (top) and older (bottom) assemblages from a subset of 16 lakes to determine how cladoceran composition has changed in these lakes. Our regional survey suggests that the cladoceran assemblages in the Cobalt area are primarily structured by differences in lake depth, while site-specific limnological characteristics, including those related to past mining activities, may have limited roles in shaping the recent cladoceran compositions. The top-bottom paleolimnological analysis suggests that the cladoceran assemblages have changed in most lakes around Cobalt, however the magnitude and nature of changes varied across the study sites. As with most regional biological surveys, the responses to historical mining activities were not uniform across all sites, which further emphasizes the importance of considering site-specific limnological characteristics and multiple environmental stressors when assessing the impacts of mining pollution.

Cladocera remains and vegetation types to assess the state of oxbows

We assessed the usefulness of Cladocera remains for establishing the ecological status of oxbows and also tested the association of Cladocera species with various vegetation types. Cladocera remains were collected from the surface sediment of four habitat types (tangled vegetation, open water, reeds and tunnels) and 15 physical and chemical parameters of surface water were studied. In the surface sediment samples, we identified 32 Cladocera taxa. There was a significant difference in the number of species amongst habitat types as per ANOVA. The benthic and plant associated Cladocera communities of reeds, tangled vegetation, open water and tunnels were clearly separated from each other by NMDS ordination. CCA showed that habitat types had characteristic Cladocera species: Pleuroxus species were frequent in the tangled vegetation habitat, while Chydorus species were frequent in the open water. Remarkably, in reeds, Bosmina species were frequent, although these species are usually common in open water. Specimens of the Alona genus were found everywhere. Our findings suggest that the remains of Cladocera species may be useful indicators to assess and monitor the structure of freshwater lakes.

The usefulness of subfossil Cladocera remains in Younger Dryas climatic reconstructions in central Poland

Cladoceran-based paleotemperature estimates for the Younger Dryas for ten sections of paleo-oxbow lakes, valley mires, and lacustrine sediments from central Poland are presented, and their potential usefulness to climatostratigraphy is described. Most of the changes observed in the cladoceran assemblages are responses to climate changes. The cladoceran-based temperature reconstructions reflect cold conditions during the Younger Dryas (YD) and allow a division of this period into two phases: an older colder phase, between 12,800 and 12,000 cal yrs BP, and a younger, warmer phase, between ca. 12,000 and 11,500 cal yrs BP. The geomorphological features of the study sites and local environmental forces are also taken into consideration. The cladoceran-inferred summer temperature estimates from all of the study sites correspond closely with the available climate reconstruction for the YD in central Europe.

Exploring the world of micro sculptures - subfossil Cladocera remains under the SEM

<p>The scanning electron microscope (SEM) is widely used for the identification of microstructural characteristics and morphology of different microorganisms. Common procedures are based and developed for remains of living species. This paper presents an effective method for drying and preparing subfossil Cladocera remains for SEM observation, which has been recently adapted and tested on several samples originating from different American and European lakes. This method results to be fast and cheap, as it excludes the use of expensive and toxic reagents. Moreover, it allows to recognize the micro sculpture and other species specific characteristics present on the different body parts of the Cladocera remains. The present contribution provides 29 high quality pictures of 12 cladoceran species at magnification between 200x and 11,000x. SEM images reveal that the patterns observed on the shells under the light microscope actually are always three dimensional structures.</p>

Combining sediment Cladocera remains and geochemistry to reveal the role of a large catchment in driving changes in a small subalpine lake (Lake Ledro, N-Italy)

<p>Sediment Cladocera remains and geochemistry were analyzed at Lake Ledro, a small subalpine lake with a large catchment area located in northern Italy. The aim of the study was to investigate human, climate and hydrological impacts on the Cladocera community and on the geochemical components during the last few centuries. A sediment core was collected from the deepest point of Lake Ledro and radiometrically dated. Cladocera remains were analyzed to track the trophic lake evolution. The core bottom section revealed the dominance of Bosminidae in concomitance with nutrient pulses entering into the lake during major flood events. The abundance of species preferring cold water temperatures confirmed the deposition of this core section during the Little Ice Age. The flood event occurred in the first half of the 19^th century produced a drastic increase in littoral species, due to the development of new habitats. The decrease in Cladocera densities during the following lake stage was followed by a rapid increase in planktonic species during the nutrient enrichment after the 1960s. Statistical analyses revealed a clear response of Cladocera community to climate variability during oligotrophic periods, while no relation to temperature changes was recorded during high nutrient levels. A preliminary study on Bosminidae and Daphnidae body size and appendages length was carried out to reconstruct major changes in the lake food web. Only <em>Bosminia</em> spp. revealed clear body size changes: minor shifts were recorded before the 1930s in relation to the low nutrient concentrations, while the major changes occurred during the 1980s were interpreted as related to the appearance of Cladocera invertebrate predators. Geochemical components were studied using X-ray fluorescence spectroscopy (XRF) analysis in order to recognize the impact of the large catchment area and from the lake-level regulations on the lake hydrology. Moreover the Si:Al ratios profile confirmed the increase in lake productivity after the 1960s. Although both Cladocera and geochemical analysis indicate major changes since the 1960s, they also revealed diverse responses to common external and local forcing, thus confirming the value of a multi-proxy approach for disentangling the lake responses to different environmental stressors. Moreover, it outlined the importance of larger catchment areas on small lakes as they are to a larger extent influenced by the modifications occurring in the drainage basin.</p>