Abstract
The two-stage ditch is a river restoration technique that aims at improving the sediment regime and lateral channel connectivity by recreating a small floodplain alongside a stream reach. This study aimed to analyze the efficiency of a two-stage ditch in improving the stream sediment structure and functions under different hydrological conditions (baseflow, post-bankfull, post-flood). Stream sediments were collected in channel sections adjacent to the two-stage ditch, adjacent to a natural floodplain along channelized reaches without inundation areas. Grain sizes, organic matter content and phosphorous (P) fractions were analyzed along with functional parameters (benthic respiration rate and P adsorption capacity, EPC0). The reach at the two-stage ditch showed no changes in sediment texture and stocks, while the floodplain reach showed higher fines and organic matter content under all hydrological conditions. The sediments in degraded reaches were more likely to be P sources, while they were more in equilibrium with the water column next to the natural floodplains and the two-stage ditch. Only functional parameters allowed for assessing the restoration effects on improving the sediment stability and functionality. Due to its sensitivity, the use of P adsorption capacity is recommended in future studies aiming at evaluating the response of river sediments to restoration measures under different hydrological conditions.
Highlights
River restoration is a widespread strategy to mitigate the negative impacts of human alterations on freshwater ecosystems [1,2] by improving disrupted hydrologic, geomorphic, and ecological processes in degraded reaches [3,4,5]
We measured the potential of a two-stage ditch in improving the sediment conditions employing both functional and structural parameters under different hydrologic conditions
The phosphorus adsorption capacity was affected by the presence of a floodplain, whether artificial or natural
Summary
River restoration is a widespread strategy to mitigate the negative impacts of human alterations on freshwater ecosystems [1,2] by improving disrupted hydrologic, geomorphic, and ecological processes in degraded reaches [3,4,5]. A common approach to assess restoration effectiveness is to measure the spatiotemporal variation of physico-chemical, hydromorphological, and biological parameters [6,7]. Such structural parameters provide insights into the structure of the studied ecosystem [8] but do not inform on the recovery of ecosystem functions and processes [9], showing a poor alignment with the overall aims of river restorations. Functional indicators facilitate better insight into aquatic ecosystems’ viability and functionality than structural indicators [13], being good candidates for informing on post-restoration ecosystem changes [5]
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