River and stream water quality and ecology - Greater Wellington ...

observed trends were unclear. The presence of improving nutrient concentrations across
a wide spectrum of sites, including several reference (pristine) sites, suggests that the
improvements are more likely related to natural factors such as climate variability than
changes in land use or land management practices. Similarly, variation in river and
stream flow probably influenced many of the trends identified in periphyton and
macroinvertebrate metrics.
Overall, while the absence of wide scale deteriorating trends in water quality and
ecological health is positive, many of the RSoE sites are considered ‘degraded’, with
some very degraded when considered in the national context. For example, most urban
sites and several lowland pastoral sites recorded nutrient concentrations well above their
respective national median values for similar urban and rural streams. The RSoE sites
in poorest condition – in particular those with small catchments dominated by urban or
intensive agricultural land uses – share in common one or more of the following
‘stressors’: nutrient enrichment, poor water clarity, nitrate or heavy metal toxicity,
microbiological contamination and instream habitat degradation. Management of these
stressors requires a whole of catchment approach that addresses municipal wastewater
discharges to water (in the Wairarapa Valley in particular), nutrient loss (from both
overland runoff and leaching via shallow groundwater) in intensively farmed rural
catchments, sediment runoff associated with erosion-prone farmland, exotic forestry and
urban development, sewer infrastructure leaks/faults, urban stormwater discharges,
water abstraction, and direct stock access to streams and riparian margins.