This research project focuses on the waterways of Mt. Grand, a South Island High Country sheep station. The station is 2136 ha of mostly mountainous terrain, running fine wool merino sheep and a small herd of beef cattle. Nearby, flatter land has undergone agricultural intensification, and several higher altitude areas of the station have been converted to public conservation land through Tenure Review. Situated between these conversions, Mt. Grand Station faces intensified agronomic pressures to remain economically viable, which may affect the ecological quality of its waterways. The aim of this research was to monitor sedimentation levels and phosphate concentrations (variables closely associated with land-use intensification) in three different catchments containing contrasting land-use, and to investigate how these variables affect benthic macroinvertebrate habitat. Three streams in differing catchments were sampled at different altitudes for physicochemical parameters including phosphate concentrations, visual clarity and total suspended solids. Macroinvertebrate communities were also sampled, to investigate the ecological health of each sample site. The headwaters of each stream are in steep, high altitude areas of the station, transitioning to flatter terrain at lower altitudes as they flow out to the adjacent Hawea Flat. The steep slopes of Mt. Grand face soil erosion issues, and are a ready source of sedimentation to be mobilised to the waterways. Stock have unrestricted access to all of the streams. On three occasions during the year, stream waters were sampled for analysis of Total Phosphorus, Total Dissolved Phosphorus, cDGT and total suspended solids concentrations, as well as other associated physicochemical parameters. Total Phosphorus concentrations in riparian soils, and deposited stream sediment at each sample site were also sampled. The benthic macroinvertebrate communities were sampled to ascertain macroinvertebrate community index scores, and Ephemeroptera Plecoptera Trichoptera taxa richness percentages.
Overall, the ecological quality of stream water quality was good, but the results have shown a reduction in quality at the bottom of one catchment. Phosphate and total suspended solids concentrations were highest in a catchment containing no significant native vegetation, and increased agricultural land-use. Thick layers of deposited sediment were observed at lower altitudes of this catchment on all research trips. At the lowest altitude sample site within the catchment, Total Phosphorus concentrations in multiple samples exceeded the trigger value set for upland New Zealand streams and rivers. The Total Dissolved Phosphorus results from this sample site also indicate that a management response may be required to ensure Mt. Grand Station meets its statutory responsibilities in regards to water quality under the relevant regional plan. The sample site at the bottom of this catchment also recorded the lowest macroinvertebrate community index scores, and the lowest percentages of observed pollution intolerant taxa. The combined results from all three catchments show a negative relationship between the observed percentages of sensitive macroinvertebrate taxa, and phosphate enrichment. The findings of this research will assist station management to make better-informed decisions as to where any management responses may be best implemented, helping them to meet their statutory responsibilities in regards to maintaining the ecological quality of the regions freshwater resources. This research project paid particular focus to Mt. Grand Station because it is managed by Lincoln University.
