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

Abstract

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 (r 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.