Ditch Design and Ecological Outcomes: Investigating the Link Between Agricultural Drainage, Macroinvertebrates, and Water Quality in Sweden

Agricultural drainage systems are essential for managing water levels in farmland, yet they often prioritize conveyance efficiency over ecological function, contributing to biodiversity loss and water quality degradation. Remediation measures, such as two-stage ditches, re-meandering, and bank regrading, are typically aimed at reducing sediment and nutrient loads, but frequently neglect habitat complexity and biodiversity. This study investigates how these remediation practices influence macroinvertebrate communities in agricultural ditches across central and southern Sweden, highlighting novel insights on integrating ecological considerations into drainage system design. We evaluated ecological impacts across 18 paired sites, each consisting of an upstream conventional trapezoidal channel and a downstream remediated section. Water chemistry, sediments, and channel morphology were measured alongside macroinvertebrate sampling, while trait-based analyses were conducted to assess macroinvertebrates’ utility as bioindicators of water quality. Bayesian linear mixed-effects (BLM) models were used to determine the relative influence of climate, region, and remediation efforts on biodiversity outcomes. Results indicate that remediated sections generally supported slightly higher species richness than upstream controls, suggesting modest ecological benefits. However, Shannon and Simpson indices revealed no significant differences in community evenness, and macroinvertebrate composition varied substantially among sites, with no distinct patterns separating remediated and non-remediated sections. The BLM confirmed that remediation had a small but positive effect on species richness, though climatic and regional factors also emerged as key drivers of macroinvertebrate diversity. Our findings show that ditch remediation does not negatively affect aquatic biodiversity and may confer slight ecological gains. Future remediation efforts could further enhance biodiversity by emphasizing habitat complexity. Overall, this study underscores the value of integrating biodiversity considerations into agricultural water management and calls for additional research on structural complexity and natural geomorphological processes, thereby promoting multifunctionality in agricultural drainage systems.