Impacts of low-head hydropower plants on cyprinid-dominated fish assemblages in Lithuanian rivers

Abstract

The meso-scale habitat simulation model MesoHABSIM was applied in three Lithuanian lowland rivers to study the effect of low-head hydropower plants (HPPs) on the fish habitats. Stream flow time series on a daily scale for the period 1970–2015 were used to describe flow regime downstream of HPPs for periods before and after their installation. Conditional habitat suitability criteria were developed for 4 species of cyprinid fish, schneider (Alburnoides bipunctatus), dace (Leuciscus leuciscus), roach (Rutilus rutilus) and vimba (Vimba vimba) to simulate their available habitat at different water discharges. Modelling results showed that HPPs have a significant impact on habitat availability in the low flow period in dry years below HPPs due to insufficient released flow. The environmental flow, as prescribed by the Lithuanian national law, is estimated between 80 and 95% exceedance probability of the mean minimum discharge of 30 days. This flow leads to a significant reduction in frequency and duration of available suitable habitats for vimba and schneider during low flow period. The roach habitat is the least affected. The results of habitat modelling are in line with the actual data on the occurrence and relative abundance of considered fish species in the studied river stretches. A general comparison of the relative abundance of modelled fish species in 42 natural river stretches and 20 stretches below the HPPs also showed that the relative abundance of roach is significantly higher, and that of schneider is significantly lower in river sections below the HPPs than the abundance in natural river sections. All results indicate that the current environmental flow does not secure survival of certain fish species. The applicability of the average low flow release during summer could be a plausible alternative to the current environmental flow in order to maintain ecosystem health and services.

Analysis of Hydrologic Regime Changes Caused by Small Hydropower Plants in Lowland Rivers

“…However, no clear trends in the changes of minimum flows were identified. Virbickas et al [16] analyzed the impact of three HPPs (Skuodas, Kuodžiai, and Dvariūkai, i.e., the same as in the present study) on fish habitats in downstream river stretches in the warm period. The analysis revealed that at the extremely low flows, the studied stretches became unsuitable or only partly suitable for studied fish species.…”

The Combined Impact of Hydropower Plants and Climate Change on River Runoff and Fish Habitats in Lowland Watersheds

“…Two additional WGSs of Dubysa-Lyduv ėnai (for the Širvinta and Šešup ė rivers) and Minija-Kartena (for the Bartuva River) were selected for the restoration of natural conditions of river discharge at selected river stretch. The selection of a river analog was based on a similar catchment area, similarity in physico-geographical and hydrometeorological characteristics, and absence of anthropogenic structures, which could interrupt the continuity of the river, e.g., dams [39]. The regression equations between analyzed rivers and river-analog were created using daily discharge data before the date of HPPs construction (Table 1).…”

“…Conditional habitat suitability criteria (CHSC) have previously been developed for 4 fish species: roach, dace, schneider, and vimba [39]. For the remaining species, within the current study, new CHSC were developed (Appendix A, Table A1) and validated using the same method [39].…”

“…The changes in flow characteristics in Lithuanian lowland rivers due to hydropower generation [38] and the impact of altered flow on some fish species at different annual runoff [39] have already been studied. The impact of climate change on future river runoff [40,41], its extremes [42], and the structure of fish assemblages [43] were also assessed.…”

Quantitative assessment of ecological operation effects based on flood pulses and ecology-economic coupling model: a case study of Three Gorges Reservoir, China

“…To maintain river functions (biological habitats, material exchanges, natural landscapes, etc. ), governments generally require reservoir managers to control the discharge based on the recommended environmental flow (Turgeon et al 2021), which is often determined by hydrology methods, hydraulics methods, habitat simulation methods and holistic methods (Goguen et al 2020). However, these methods ignore the importance of runoff flood pulses, because the recommended environmental flow are determined from the base flow (the minimum flow that meets the basic ecological function of the river) and the fixed value (Lobera et al 2021).…”