Effects of dredging on the vegetation in a small lowland river

Abstract

BackgroundConventional river engineering operations have a substantial influence on the fluvial ecosystem. Regulation and channelization generally reduce the physical heterogeneity of river beds and banks and the heterogeneity of habitats. They determine the character, diversity and species richness of plant communities. The effect of river regulation on vegetation has been repeatedly investigated, but few studies have been conducted within reaches of previously regulated rivers. The aim of this work is to expand and current knowledge about the impact of dredging on the vegetation of a regulated section of a lowland river.Materials & MethodsThe study included pre-dredging (1 year before) and post-dredging surveys (results 1 and 2 years after dredging). The vegetation was analysed in terms of species composition, origin of species, life forms, distribution of Grime’s life strategies, and selected ecological factors. The Shannon–Wiener biodiversity index (H) and evenness were also analysed in each year of the study. The impact of dredging on the vascular flora was assessed by ‘before-after-control-impact’ (BACI) analysis.ResultsThe number of species and biodiversity as measured by the Shannon–Wiener index (H) increased in the analysed section of the river valley. However, enrichment of the flora was observed only on the floodplain, on the surface of the deposited dredging material, while the number of species in the river channel decreased, as dredging of the river bed and levelling of the banks had markedly reduced habitat diversity. Although species richness in the second year after the dredging approached the values recorded before the intervention, the absence of particularly species or phytocenoses associated with shallow river banks and sandbars was still observed. The change in habitat conditions and the destruction of the vegetation cover during the dredging enabled penetration by numerous previously unrecorded alien species of plants and apophytes. There was a perceptible increase in the role of therophytes in the flora. It is worth noting that the number of alien species and therophytes declined significantly in the second year after the dredging. Analysis of the proportions of species representing various life strategies showed that previously unrecorded species with the type R (ruderal) life strategy had appeared, representing by pioneer species occurring in frequently disturbed habitats. There was also a marked increase in the share of species representing the mixed C-R (competitive-ruderal) strategy, occurring in habitats with low levels of stress, whose competitive abilities are limited by repeated disturbances. By the second year after the dredging, however, these changes were largely no longer observed.ConclusionsThrough appropriate maintenance of the regulated river, it can be rapidly recolonized by vegetation after the procedure, but it may lead to the loss of some species and phytocoenoses.

Does lake eutrophication support biological invasions in rivers? A study on Dreissena polymorpha (Bivalvia) in lake–river ecotones

“…Firstly, it would inhibit the eutrophication processes, and secondly, it would reduce the colonization of outlets in high trophy lakes by alien and invasive dreissenids. Furthermore, the regulation and straightening of outlet beds increase the current velocity and decrease the ecological status (Bączyk et al., 2018 ; Stępień et al., 2019 ), which may also favor the colonization of outlets by the zebra mussel. In this case, the most optimal solution is to promote renaturalization of outlet beds and create meanders as well as riffle sequences that reduce or diversify current velocity (Palmer et al., 2010 ; Wohl et al., 2015 ).…”

Main macroinvertebrate community drivers and niche properties for characteristic species in urban/rural and lotic/lentic systems

“…A separate assessment of this factor during our study yielded data supporting the relationship between riparian habitat disturbance and the macroinvertebrate community in both types of aquatic ecosystems. Such changes in macroinvertebrate communities were registered in the Krąpiel River after hydrotechnical works, which resulted in changes in the vegetation cover (Szlauer-Łukaszewska and Zawal 2014;Stępień et al 2015Stępień et al , 2019Zawal et al 2015aZawal et al , b, 2016aBuczyński et al 2016;Dąbkowski et al 2016;Płaska et al 2016;Stryjecki et al 2016).…”

Effect of Canal Bank Engineering Disturbance on Plant Communities: Analysis of Taxonomic and Functional Beta Diversity

“…Post-disturbance release from competition and more underutilised resources may also result in more viable functional strategies for coexistence, increasing functional turnover [12,143]. For example, Stępie ń et al [144] recorded rapid post-dredging recovery to pre-disturbance levels (~2 years) for temperate riparian vegetation. Initial succession by ruderal therophytes and invasive species with distinct functional traits was followed by an increase in pre-disturbance species in the second year of succession [144].…”

“…For example, Stępie ń et al [144] recorded rapid post-dredging recovery to pre-disturbance levels (~2 years) for temperate riparian vegetation. Initial succession by ruderal therophytes and invasive species with distinct functional traits was followed by an increase in pre-disturbance species in the second year of succession [144]. Therefore, similarly to taxonomic-β, the high levels of functional-β in this study, driven primarily by turnover, might be primarily explained by stochastic biotic interactions driven by probabilistic initial community assemblages, with additional increases in viable functional strategies in disturbed sites.…”