Burdon, FrankLea, Brooklyn2024-11-112024-11-112024https://hdl.handle.net/10289/17033Sedimentation is a significant stressor in streams and rivers globally. The natural sediment regime paradigm posits that human activities have greatly altered the natural transport of sediment in river networks and that land-uses leading to increased bank erosion and surface runoff have resulted in large quantities of fine sediment being deposited in streams and rivers. In New Zealand, land conversion from native forest to pastoral agriculture has dramatically increased riverine sediment loads, making deposited fine sediment (DFS) a major stressor that negatively impacts stream ecosystem health. Consequently, DFS is an important attribute managed under the National Policy Statement for Freshwater Management 2020. However, uncertainties remain in how best to monitor the effects of DFS, and what impacts different land-use types have on stream ecosystems in addition to the adverse influence of sedimentation. In my study, I surveyed 24 stream sites allocated evenly to three land-use types (native forest, pastoral agriculture, and horticulture, e.g. kiwifruit orchards) in the Tauranga Harbour basin. I measured habitat attributes, including DFS, and sampled stream macroinvertebrate communities at each site. Using macroinvertebrate data, I calculated and compared taxonomic and trait-based metrics as indicators of ecosystem health across land-use types. I used a variety of metrics, including the Macroinvertebrate Community Index (MCI) and its quantitative equivalent, the QMCI, the Average Score Per Metric (ASPM) index, and community-weighted mean trait abundances, including facets of functional diversity to assess impacts on stream health. I found that human land uses negatively influenced stream health, indicated by greatly reduced MCI, QMCI, and ASPM scores. Although DFS explained most of the negative influences on macroinvertebrate communities in pastoral and horticultural streams, there were differences between native forest and horticultural streams not accounted for by DFS that contributed to declines in ecosystem health. I also found that sediment-specific macroinvertebrate metrics (sediment ‘decreasers’) were the best indicators of DFS impacts on stream health. Contrary to my predictions, I did not find that functional diversity was strongly reduced by land use or DFS, although several key traits responded to these stressors. Notably, life history trait modalities involving the number of reproductive cycles per year and oviposition site responded strongly to DFS and land use, indicating potential mechanisms contributing towards the impacts of these stressors on macroinvertebrate communities. ii My study points to the need to continuously manage the deposition of fine sediment in streams to help mitigate the adverse effects of human land use. Future research should further explore the role that fine sediment and other stressors associated with human land uses play in the degradation of streams ecosystems in the Tauranga Harbour basin. Quantifying land use and land cover (LULC) attributes using geospatial tools will help further explore the relationship between catchment properties and macroinvertebrate responses. Additionally, issues regarding trait syndromes, trade-offs, and database inconsistencies must be addressed to better understand the mechanistic links between specific macroinvertebrate traits and fine sediment.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.freshwater ecologymacroinvertebratestauranga harboursedimentationstream ecologybay of plentyfunctional traitsmacroinvertebrate community indexanthropogenic stressorsThesis