No abstract

No abstract

Large wood is a key structural and functional component of rivers, and it is reintroduced to provide physical habitat, encourage channel stability, and influence in‐channel hydraulic conditions at a range of scales. Typically, studies assessing the influence of reintroduced wood on in‐channel hydraulic character have been undertaken at relatively small scales—at a site. Relatively little is known about how reintroduced wood influences in‐channel hydraulic character at larger reach scales and over different discharges. In this study, the hydraulic character or hydraulic landscape of multiple reference (wooded), control (unwooded), and managed (wood reintroduced) reaches (average length = 430 m) at 10 different discharges in the Barwon‐Darling River, Australia, were analysed. Landscape scale hydraulic character was compared using spatial metrics describing the size, shape, and relative location of hydraulic patches in each reach. It was hypothesised that reintroducing wood would significantly influence hydraulic landscapes within the managed reaches, with those reaches becoming more similar to reference reaches. The reintroduction of wood into the Barwon‐Darling River did not significantly influence the hydraulic landscapes of the managed reaches; instead, they remained more similar to control reaches across discharges. Discharge did significantly influence the hydraulic landscape, with stepwise changes in the character of the hydraulic landscape in response to increasing discharge. The limited influence of reintroduced wood on the hydraulic landscapes is hypothesised to be because reintroduced wood did not match naturally occurring wood in terms of the character of individual pieces or their spatial distribution within the reach.

Benefits of reintroduced large wood in river channels are largely based on studies at site scales in high-energy systems. By comparison, relatively little is known of the benefit of reintroduced large wood in low-energy systems at larger, reach scales. The present study assessed the effects of reintroducing large wood on fish assemblages along the Barwon–Darling River, Australia. Fish were sampled in replicated reaches subject to three treatments: six reference (wooded), six control (unwooded) and six managed (wood reintroduced) reaches. Sampling was conducted before and several months after wood addition, and then during a period following several large floods. Results demonstrate that reintroducing large wood had limited effects on fish. There were significant differences between treatments in fish length, but not in total abundance or species composition between treatments. Significant differences were detected in total abundance, species composition and fish length over time. There was an interaction recorded between treatments and time for fish length, but not total abundance or species composition. It is suggested that the lack of response by fish was because the physical character and position of the reintroduced wood pieces did not replicate ‘natural’ reference conditions. However, high variability in fish assemblages through time, likely in response to hydrological variation, reduced the power of the study to detect differences between fish over the shorter time period of the study (<5 years).

No abstract