Composition Of Aquatic Assemblages Research Articles

Triassic fish faunas from Miedary (Upper Silesia, Poland) and their implications for understanding paleosalinity

We describe two new fish-dominated faunas from the Middle Triassic (Ladinian) Miedary site, Upper Silesia, Poland, and present a comparative analysis of Middle-to-Late Triassic vertebrate assemblages from the Germanic Basin, in order to explore the influence of salinity on faunal composition. The composition of the assemblage from dolomite beds at Miedary is similar to those from the Muschalkalk facies, whereas the assemblage from glauconite beds appears to be the first brackish vertebrate assemblage of the Serrolepis lake-type recognized from the eastern Germanic Basin. Comparative analysis of all sites, using hierarchical clustering, nonmetric multidimensional scaling, and principal component approaches, revealed the existence of vertebrate taxa associated withfreshwater, brackish and marine conditions, as well as euryhaline taxa with wide salinity preferences. Moreover, it confirms the brackish nature of Serrolepis -bearing assemblages, and suggests that Serrolepis suevicus is a brackish specialist, indicative of oligohaline to miohaline paleosalinities. The Middle-Late Triassic vertebrate faunas appear dominated by stenohaline taxa, with a conspicuous separation of species living in the freshwater and marine conditions. The euryhaline taxa are rare, and comprise Acrodus lateralis , Eusauropterygia, Lissodus nodosus , and Saurichthyiformes. • Two new fish assemblages from the Middle Triassic of Europe are described. • Paleoenvironmental signature of Serrolepis-lake assemblages is confirmed. • There is noticeable relationship between aquatic assemblage composition and paleosalinity. • Preferred salinity ranges for various Mid-Late Triassic vertebrates are proposed. • Sufficient sampling and quantitative data are crucial for comparative studies on paleosalinity.

Modelling the response of floodplain aquatic assemblages across the lateral hydrological connectivity gradient

Hydrological connectivity is one of the main controlling factors of habitats and aquatic assemblages on river floodplains. Nevertheless, the lack of universal measures of river–floodplain connectivity (i.e. the lateral hydrological connectivity, LHC) limits the comparison of the response of aquatic assemblages to hydrological connectivity and impedes the understanding of floodplain functioning across different systems. To address these needs, we tested the ability of six different LHC surrogates to model changes in richness, abundance and composition of aquatic assemblages across a Mediterranean floodplain (Ebro River, NE Spain). As shown by generalised additive models, LHC surrogates explained 15% to 65% of the richness and abundance of aquatic assemblages. Zooplankton, macroinvertebrates and phytoplankton showed overlapping peaks of richness at flood duration rates of 5, 15 and 30 days year–1 respectively. Redundancy analyses showed that LHC surrogates explained 17% to 37% of aquatic assemblage composition. Distance to the river and flood duration were the most important determinants of macroinvertebrate composition, whereas flood magnitude and water-level variability best accounted for the variance in zooplankton and phytoplankton compositions. Models based on LHC surrogates such as those presented here can help in predicting the consequences of restoration measures and may be useful in setting restoration goals for aquatic assemblages.

Bioassessment of an Appalachian Headwater Stream Influenced by an Abandoned Arsenic Mine

Recent debate concerning the modification of safe drinking water standards for arsenic (As) has led to increased awareness of the risks As poses to both humans and the environment. However, few studies have examined the effects of As on the diversity and composition of aquatic assemblages in streams. Benthic macroinvertebrate surveys, chemical analysis of water column and sediment, and laboratory toxicity tests were conducted to assess effects of an abandoned As mine on a headwater stream, and to determine the primary component of toxicity. The average 48-hr LC50 value for Daphnia magna was 4316 microg As/L, and the average 96-hr LC50 value for Lepidostoma spp. was 2138 microg As/L. Reproduction was significantly reduced for D. magna at concentrations > or =312 microg As/L in water column laboratory bioassays, and for treatments in bioassays with sediments containing elevated As (> or =2630 mg/kg). These results support the findings of the in-stream benthic macroinvertebrate survey as the density and percent Ephemeroptera + Plecoptera, + Trichoptera (EPT) were substantially lower at sites downstream of the mine compared to upstream reference sites. Results of bioassays comparing the toxicity of As-contaminated site water and upstream reference water spiked with As salts suggest that As is the primary component of toxicity impacting the stream. Measured As concentrations at downstream sites were above the recommended Criterion Maximum Concentration of 340 microg As/L and Criterion Continuous Concentration of 150 microg As/L for protection of aquatic life published by the United States Environmental Protection Agency. At the study site, elevated As concentrations likely prevent recruitment of benthic macroinvertebrates and recovery of the perturbed headwater stream.