Abstract
Ecosystem deterioration in small lowland agricultural rivers that results from river dredging entails a significant threat to the appropriate ecohydrological conditions of these water bodies, expressed as homogenization of habitats and loss of biodiversity. Our study was aimed at a comparison of abundance and taxonomic structure of bottom-dwelling macroinvertebrates in dredged and non-dredged stretches of small lowland rivers and tributaries of the middle Narew River, namely: Czaplinianka, Turośnianka, Dąb, and Ślina. The experimental setup was (1) to collect samples of the bottom material from the river stretches that either persisted in a non-modified state (dredging was not done there in the last few years) or had been subjected to river dredging in the year of sampling; and (2) to analyze the abundance and taxonomic structure of macroinvertebrates in the collected samples. The study revealed that at the high level of statistical significance (from p = 0.025 to p = 0.001), the total abundance of riverbed macroinvertebrates in the dredged stretches of the rivers analyzed was approximately 70% lower than in non-dredged areas. We state that the dredging of small rivers in agricultural landscapes seriously affects their ecological status by negatively influencing the concentrations and species richness of benthic macroinvertebrates.
Highlights
Modified water bodies in agricultural landscapes may potentially play an important role as refuges for freshwater biodiversity [1,2,3,4], inappropriate management of these ecosystems vastly decreases the aquatic ecosystems’ health [5,6,7]
The t-values for the comparison of the taxonomic composition of macroinvertebrates of dredged and natural river stretches reached 4.420; that gives a statistical significance at the level of p = 0.001
This study revealed that the species composition and abundance of macroinvertebrates is much lower in dredged stretches of the rivers analyzed than in the stretches where river dredging was not done, leaving the structure and thickness of bottom sediments untouched
Summary
Modified water bodies in agricultural landscapes may potentially play an important role as refuges for freshwater biodiversity [1,2,3,4], inappropriate management of these ecosystems vastly decreases the aquatic ecosystems’ health [5,6,7]. Mechanic dredging of the river bed degrades the structure and composition of riverbanks and bottoms and negatively affects macroinvertebrate communities [6,8,9,10,11,12]. Considering the scale of river dredging in Poland in recent years, reported as critically affecting ecohydrological features of small and medium lowland rivers [13,14], and wishing to follow the Water Framework Directive’s (WFD) call for European Union member states to conserve the status of their waters, we believed that technical measures applied in a country-wide manner for the “reduction of flood risk in agricultural areas” had to be revisited to assess their compliance with the requirements of environmental conservation and to protect rivers. As the first step towards revealing the responses of aquatic ecosystems to bottom dredging, we intended to undertake comparative research on the bottom macroinvertebrates of selected dredged and non-dredged stretches of small lowland rivers. Our research was performed in small lowland rivers located in northeastern
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