Abstract
Subaqueous dredging is a management activity undertaken globally to improve navigation, remove contaminants, mitigate flood risk and/or generate aggregate. Water Injection Dredging (WID) is a hydrodynamic technique involving the turbation and downstream displacement of fine sediments using vessel-mounted water jets. Despite the technique being widely applied internationally, the environmental and ecological effects of WID are poorly understood. For the first time, this study used a Before-After-Control-Impact (BACI) experimental design to assess the effects of WID on water physicochemistry, and macroinvertebrate and fish communities within a 5.7 km-long reach of tidal river. WID targeted the central channel (thalweg) to avoid disturbance of the channel margins and banks. Mean but not peak turbidity levels were substantially elevated, and dissolved oxygen levels were reduced during periods of WID, although effects were relatively short-lived (≈3 h on average). Dredging resulted in significant reductions in benthic macroinvertebrate community abundance (particularly taxa that burrow into fine sediments), taxonomic richness and diversity. In contrast, minor changes were detected in marginal macroinvertebrate communities within and downstream of the dredged reach following WID. Reductions in fish taxonomic richness and diversity were recorded downstream of the dredged reach most likely due to behavioural avoidance of the sediment plume. No visibly stressed or dead fish were sampled during dredging. Results suggest that mobile organisms and marginal communities were largely unaffected by thalweg WID and that the technique represents a more ecologically sensitive alternative to traditional channel margin mechanical dredging techniques.
Highlights
Subaqueous dredging is an internationally ubiquitous engineering practice (Pledger et al, 2020) used to mitigate flood risk (Gob et al, 2005), remove contaminants (Bormans et al, 2016; Gustavson et al, 2008; Chen et al, 2018), generate aggregates and/or improve naviga tion (Van Maren et al, 2015; Wenger et al, 2017; Wu et al, 2018)
An in-situ experiment has quantified the effects of Water Injection Dredging (WID) on water physicochemistry, and macroinvertebrate and fish com munities within a tidal river
WID corresponded with significant effects for benthic communities in the dredged and downstream environments, and minor changes in marginal macroinvertebrate communities in the dredged reach
Summary
Subaqueous dredging is an internationally ubiquitous engineering practice (Pledger et al, 2020) used to mitigate flood risk (Gob et al, 2005), remove contaminants (Bormans et al, 2016; Gustavson et al, 2008; Chen et al, 2018), generate aggregates and/or improve naviga tion (Van Maren et al, 2015; Wenger et al, 2017; Wu et al, 2018). Several dredging technologies exist (mechanical, hydraulic and hydro dynamic), with each involving a sediment extraction/dispersal, trans port and/or disposal stage (see Manap and Voulvoulis, 2016). Removal of aquatic habitat structure, such as macrophytes, large wood and coarse sediments (e.g. cobbles and boul ders) during dredging, and the resulting homogenisation of instream habitats (Kanehl and Lyons, 1992; Kondolf, 1997; Gob et al, 2005), may result in degraded habitat quality and increased risk of organism entrainment (Drabble, 2012; Reine et al, 1998; Armstrong et al, 1982) and/or predation (Kanehl and Lyons, 1992). Through entrainment and/ or other mechanisms, fish (e.g. Freedman et al, 2013; Swales, 1982) and macroinvertebrate (e.g. Brooker, 1985; Szymelfenig et al, 2006; Meng et al, 2018) populations may be modified due to reductions in abun dance and/or species richness
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
