The Effects of Meander Reconnection and Deflector Installation on the Physicochemical Water Quality

ABSTRACT River restoration efforts are gaining momentum in response to the pressing need for resilient river systems, in light of escalating climate change impacts. However, achieving predefined restoration goals remains challenging due to insufficient understanding of river system responses. Of particular complexity is assessing the success of restoration measures on water quality, a critical abiotic factor in freshwater ecosystems. This study examined the impact of meander reconnection and deflector placement on water quality. Two distinct meander sections and a degraded section were meticulously sampled both upstream and downstream to assess impacts. The meander sections were reconnected using different approaches: one fully reconnected, receiving all discharge, and the other partially reconnected, receiving part of the discharge while maintaining the channelized trench. The results showed promising potential of reconnected meanders for mitigating phosphorus and carbon levels. However, the effectiveness of these improvements was compromised by deflector placement, which led to increased erosion and release of phosphorus bound to organic soil particles. Conversely, dissolved nutrients (e.g. nitrate, orthophosphate, DOC) exhibited no significant alterations, likely attributed to the absence of macrophytes and the limited extent of restorative actions, which currently do not increase water residence time sufficiently. Temporal trends revealed progressive reductions in carbon, phosphorus, and nitrogen levels suggesting that time is a crucial factor in restoration success, possibly due to soil stabilization. Seasonal dynamics also played a significant role, with discernible effects observed primarily during summer. This study underscores the importance of long‐term, watershed‐scale investigations that account for seasonal variability to fully understand the impacts of river restoration.