Choice of benthic macroinvertebrate-based metrics for assessing water quality in the littoral zone under anthropogenic disturbance in southern Lake Kivu (Central Africa)

Benthic macroinvertebrates are widely used to assess the ecological quality of fresh waters. This is because they are in direct contact with the aquatic environment and respond differently to pollutants and changes in the watershed, which are difficult to assess by toxicological or chemical monitoring alone. this study used benthic macroinvertebrate parameters to assess the quality of the nearshore waters of lake Kivu. Twenty-six metrics covering various aspects of the community were tested using whisker plots to compare their sensitivity in discriminating between reference and disturbed stations. Nine parameters (% EPT taxa, % Diptera taxa, % Chironomid taxa, % Insect taxa; % no Insects taxa, ratio EPT/Chironomid taxa, % moderate tolerant taxa, % very moderate tolerant taxa, Family Biotic Index) were found to be sensitive and were able to discriminate between reference and disturbed stations. All sensitive metrics, with the exception of the percentage of EPT taxa, were positively and/or negatively correlated with the physico-chemical parameters affected by the changes in the littoral zone. The combined values of the three calculated biotic indices (ASPT, BMWP and FBI) showed that the biological water quality varies from moderate to good in the reference stations and from average to poor in the disturbed stations. It is concluded that metrics based on benthic macroinvertebrates are effective for assessing water quality in the littoral zone of Lake Kivu in the context of the lack of historical water quality databases and specific tools for toxicological assessment. It is suggested to compare the performance of this approach with others currently used in bio-indication.

Multiple-Stressor Interactions in Tributaries Alter Downstream Ecosystems in Stream Mesocosm Networks

We studied how multiple-stresssors in tributaries affect function, diversity, and physical habitat of recipient downstream ecosystems. Using a mesocosm model of a stream network, we manipulated sediment and nutrients individually and in combination in tributaries of second-order channels, to test the effect of complex stressor interactions within tributaries on recipient channels. Sedimentation in second-order channels increased with the level of disturbance of the tributaries. Moreover, Ephemeroptera, Plecoptera, and Trichoptera (EPT) density and EPT richness were higher in second-order channels fed by tributaries where the stressors were applied separately, compared to those fed by tributaries where the stressors were applied simultaneously. Our observations suggest this result was due to the combination of the two stressors within the same tributary reducing EPT drift from the tributaries further than the addition of the stressors in separate tributaries. These results support the hypothesis that cumulative upstream disturbance can influence downstream recipient ecosystems in stream networks. However, contrary to our expectations, most observed effects were due to impacts on dispersal patterns of EPT taxa, rather than downstream accumulation of disturbances throughout the network. Our results underscore the importance of metacommunity frameworks to understand how tributary disturbance may influence population dynamics in downstream ecosystems.

Analyzing multiple stressor effects on EPT taxa in a mesocosm experiment with DNA metabarcoding

Multiple stressors diversely and often adversely affect stream ecosystems around the globe. Therefore, understanding multiple stressor effects on different organisms is essential for a better ecosystem understanding, an accurate water quality assessment and improved ecosystem management. However, while multiple stressor effects should be assessed at species level this taxonomic resolution is often not achieved e.g. for stream macroinvertebrates. Due to their high abundance and diversity, species-level identification is often not feasible with morphology‑based approaches. DNA metabarcoding represents an alternative approach for studying multiple stressor interactions at species level. In an outdoor experiment over 10,000 specimens from the insect orders Ephemeroptera, Plecoptera and Trichoptera (EPT), which are routinely used as bioindicators, and their responses to stressors were studied. In the experiment salinity, fine sediment deposition and flow velocity were manipulated in a full‑factorial design in 64 mesocosms with two microhabitats each (streambed and leaf litter), resulting in eight replicates per treatment. DNA metabarcoding revealed 122 EPT Operational Taxonomic Units (OTUs), from which the most abundant 27 alone showed 14 different response patterns to the applied stressors. The high taxonomic resolution achieved by DNA metabarcoding revealed species specific stressor responses that were hidden at a lower taxonomic resolution. As a prominent example, Rhithrogena semicolorata responded negatively to fine sediment deposition and flow velocity reduction, while Ecdyonurus torrentis (both Heptageniidae, Ephemeroptera) was insensitive to experimental manipulation, highlighting different stressor responses among species within the same family (Fig. 1, Beermann et al. 2020). Even for well-studied organisms such as EPT taxa, this study shows that DNA metabarcoding has the potential to depict response patterns at species or OTU level despite high specimen abundance. Consequently, DNA metabarcoding promises to be a rewarding method when investigating and assessing multiple stressor effects on stream water quality.

Ecology of Leuctra geniculata (Plecoptera: Leuctridae), an atlantomediterranean species on the north-eastern border of its area

The first records of Leuctra geniculata Stephens, 1836 in the north-eastern border of its area (the Czech Republic) are presented and an overview of references, synonyms and distribution of the species is given. The ecological preferences of the species, supported by chemical and hydromorphological parameters, are defined. Probable dissemination paths into the Czech Republic and the supposed life cycle of the species are discussed. Photographs of morphological characters, SEM photos of eggs, associated macroinvertebrate assemblages (EPT taxa) and maps of distribution are included.