Biodiversity-friendly designs for gravel pit lakes along the Drina River floodplain (the Middle Danube Basin, Serbia)

Abstract

Massive gravel excavation is one of the most destructive forces affecting riverine habitats in Europe. However, gravel pit lakes are also recognized as valuable wildlife refuge areas. Different hydromorphological characteristics of gravel pits may influence aquatic biota differently. Optimal selection of gravel excavation procedures may create favorable conditions for ecosystem diversity. The aim of this study was to correlate hydromorphological variables against macrophyte composition and metrics in gravel pit lakes along the lower course of the Drina River. Field research was carried out at 18 gravel pit lakes (60 survey sectors) and four fluvial lakes (13 survey sectors), during the summer months of 2015, 2016 and 2018. The role of hydromorphological variables in structuring macrophyte assemblages was tested using the partial Canonical Correspondence Analysis, while the Generalized Linear Model was performed to test the ability of selected hydromorphological attributes to predict macrophyte quantitative metrics. The results demonstrated high habitat quality and conservation value of the gravel pit lakes compared to natural sites. Hydromorphological predictors for different macrophyte assemblages were defined. General recommendation is that two pit types should be excavated within a single extraction field, with the minimal impact to the riparian and shore zones. The first type should be located up to 100m from river main channel, having area lt 1000m(2) and a relative depth ratio gt 5%. The second type should be optimally located 300m form river main channel, with maximum depth of 3-4m, surface area of 10,000-20,000m(2), and a relative depth ratio lt 5%.