Long-term variability in deposited fine sediment and macroinvertebrate communities across different land-use intensities in a regional set of New Zealand rivers

Macroinvertebrate communities in running waters are commonly used as bioindicators of fine sediment pollution, but few studies evaluate impacts across multiple years. We used a 5-year dataset from 46 rivers in Southland, New Zealand to investigate the consistency of the relationship between deposited fine sediment and stream macroinvertebrates across three categories of agricultural land-use intensity (low, medium, and high). We also compared the performance of four widely used invertebrate stream health metrics and their recently developed sediment-specific counterparts. Linear and non-linear regressions were fitted and effect sizes were interpreted to identify biologically meaningful relationships (<i>r</i>² ≥ 0.1). Sites within medium-intensity catchments showed the greatest number of such relationships (29 of 40 cases), compared to low- (8) or high-intensity catchments (23). Invertebrate metrics responded more frequently, and mostly negatively, to increasing sediment in medium- and high-intensity catchments. Overall, sediment-specific metrics performed better than their widely used counterparts. Our findings show that land-use intensity influences the multi-year dynamics of deposited fine sediment and the corresponding stream invertebrate responses. These temporal dynamics can be substantial and should be considered in future stream biomonitoring efforts.