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

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River and stream water quality and ecology in the Wellington region: State and trends 9. Conclusions Analysis of water quality, periphyton and macroinvertebrate data collected at 55 RSoE sites over the period July 2008 to June 2011 has found clear linkages between river and stream health and catchment land use. Sites classified as having ‘good’ or ‘excellent’ water quality (27 sites) and ecosystem health (27 and 36 sites for periphyton and macroinvertebrate indicators, respectively) tend to be located on the upper reaches of rivers and streams that drain the forested Tararua, Rimutaka and Aorangi ranges. As the proportion of pastoral and/or urban landcover increases within a site’s upstream catchment, water quality and macroinvertebrate health tend to decline while nuisance periphyton and macrophyte growth increases. Of the 15 sites graded ‘poor’ for water quality, five are located in urban areas and ten drain predominantly pastoral catchments – of which most support at least some intensive agriculture. Similar patterns were observed with periphyton growth and macroinvertebrate health, although geological and climatic factors in part account for some sites (particularly those in the eastern Wairarapa hill country) being assigned to ‘fair’ or ‘poor’ classes for these indicators. Analysis of New Zealand Freshwater Fish Database records also showed that a significant relationship exists between fish community condition and upstream catchment landcover in the Wellington region. Fish community condition is significantly higher at sites located on rivers and streams draining predominantly indigenous forest catchments than at those draining pastoral or urban catchments. Based on limited monitoring, fish community condition at some RSoE sites contrasts significantly with the water quality, periphyton and macroinvertebrate indicators measured at these sites. The majority of RSoE sites exhibited relatively stable water quality and ecological health over the time periods examined (2006 to 2011 and 2004 to 2011, respectively). Generally speaking, the majority of statistically significant trends tended to be indicative of improving water quality (predominantly declining nutrient concentrations) but deteriorating ecological condition (increasing periphyton cover/biomass and declining macroinvertebrate community health). In most cases the reasons for the observed trends were unclear. The presence of improving nutrient concentrations across a wide spectrum of sites, including several reference 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 WGN_DOCS-#1100598-V3 PAGE 117 OF 160
River and stream water quality and ecology in the Wellington region: State and trends 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. 9.1 Recommendations 1. Review Greater Wellington’s existing River SoE monitoring programme, giving priority consideration to: Standardising the timeframe of water sample collection to within ±1 hour where possible; Revisiting existing QA/QC practices in place for both field sampling and analytical laboratory components of the programme; Implementing a formal regional fish monitoring programme; Introducing regular assessments of instream sedimentation and habitat quality; and Establishing greater linkages with SoE hydrological, groundwater quality and downstream (estuary and lake) monitoring networks. 2. Continue work to establish estimates of flow at all RSoE monitoring sites, and improve existing estimates at sites where direct flow measurements are not regularly taken. 3. Consider, in the next assessment of state and trends in RSoE monitoring results: Further exploration of the use of indices, such as the Canadian Water Quality Index (CCME 2001), to summarise river and stream health, including the potential for a single index that integrates water quality, ecological indicators (periphyton, macroinvertebrates and fish) and habitat quality; Identifying, and reporting against, selected indicators of river and stream health applicable to different management purposes (eg, aquatic ecosystem health and trout habitat/angling), using thresholds that take into account the natural diversity of river and stream types in the Wellington region; Analysing temporal trends in physico-chemical water quality over both five and ten-year timeframes; and Exploring alternative methods to assess the ecological significance of trends in periphyton and macroinvertebrate indicators. PAGE 118 OF 160 WGN_DOCS-#1100598-V3
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River and stream water quality and
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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5. Periphyton - state and trends 57
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Figure 2.1: RSoE monitoring sites a
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2.4.2 Biological variables River an
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4.2 Temporal trends River and strea
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TN (mg/L) Temperature ( 0 c) Shade
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Page 76 and 77: River and stream water quality and
Page 80 and 81: Chlorophyll a (mg/m 2 ) 90 80 70 60
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