Highly humic lakes are typical for the boreal zone. These unique ecosystems are characterised as relatively undisturbed habitats with brown water, high acidity, low nutrient content and lack of macrophytes. Current lake assessment methods are not appropriate for ecological assessment of highly humic lakes because of their unique properties and differing human pressures acting on these ecosystems. This study proposes a new approach suitable for the ecological status assessment of highly humic lakes impacted by hydrological modifications. Altogether, 52 macroinvertebrate samples from 15 raised bog lakes were used to develop the method. The studied lakes are located in the raised bogs at the central and eastern parts of Latvia. Altered water level was found as the main threat to the humic lake habitats since no other pressures were established. A multimetric index based on macroinvertebrate abundance, littoral and profundal preferences, Coleoptera taxa richness and the Biological Monitoring Working Party (BMWP) Score is suggested as the most suitable tool to assess the ecological quality of the highly humic lakes.

This study analyses the impact of small hydropower plants (HPP) on fish in three Latvian transboundary river basin districts. The MesoHABSIM habitat simulation model was applied to seven Latvian lowland rivers regulated by HPP, four of which belong to the salmonid river type and three to the cyprinid type. Daily stream flow time series for 1961–2018 were used for flow regime calculations in reference (unimpacted) and altered (impacted by HPP operation) flow conditions. Conditional habitat suitability model/criteria for fish were used to assess a potentially available habitat at different flow conditions. Brown trout (Salmo trutta) for salmonid rivers and chub (Squalius cephalus) for cyprinid rivers were selected as case examples to show habitat suitability for different stream types. The authors found significant differences in habitat availability for salmonid and cyprinid rivers, indicating that ecological flows must be calculated separately for fast- and slow-flowing rivers. This study is the first attempt in Latvia to set ecological flow values not only using hydrological calculations but also biological data as an indicator of ecological changes.

Hydromorphological quality assessment is an important research topic, especially after the implementation of the EU Water Framework Directive. In this study the hydromorphological quality at 46 sites in 22 streams of the Venta River Basin District (RBD) in Latvia was investigated during the vegetation periods of 2011-2013. The UK River Habitat Survey method was used in the research. No significant differences in Habitat Quality Assessment (HQA) and Habitat Modification Scores (HMS) were found between stream types. We found that the most important factor affecting HQA scores in our research territory was instream vegetation, which coincides with results of other researchers. There was a significant negative correlation between HQA and HMS. Distance from the source had a negative correlation with HQA and a positive correlation with HMS. River type had a positive correlation with special features (beaver dams, fringing reed bank, wetlands, etc.).

Plastic particles impact on freshwater ecosystem -a mesocosms case study 12.00-12.