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 Whakatomotomo Road) to ‘very good’ (Whareroa Stream at Queen Elizabeth Park). Comparisons between fish community condition and other commonly reported measures of stream health (eg, water quality, periphyton growth and macroinvertebrate community composition) indicate that, at least at some RSoE sites, there can be significant discrepancies in the condition or ‘health’ reported for a site. These discrepancies most likely arise, at least in part, due to the fact that diadromous fish communities respond to whole catchment scale influences (eg, both upstream and downstream landcover/land use influences as well as local habitat), whereas other measures primarily respond to only local and upstream catchment influences (David et al. 2010). Regardless of the causes, it is clear that monitoring of fish communities is required to provide a more complete picture of ecosystem health. Similar to landcover relationships reported for the whole of New Zealand (Joy 2009), analysis of IBI scores calculated from NZFFD data for the Wellington region has demonstrated that fish community condition is typically highest in rivers and streams located in catchments dominated by indigenous forest and poorer in catchments dominated by pastoral or urban landcover. Fish condition in urban streams appears to be poorest overall, although the difference between urban and pastoral landcover types was not statistically significant. However, this analysis has indicated that some reaches of urban and/or pastoral rivers and streams can still retain high freshwater fish values. For example, based on interpretation of water quality and macroinvertebrate community health, Whareroa Stream at Queen Elizabeth Park is ranked 52 nd and 50 th of the 55 RSoE sites, respectively. However based on its IBI score, this site is ranked in the top 10% of all NZFFD records for the Wellington region. Analysis of IBI scores generated from NZFDD data indicated that there has been a decline in fish community condition in the Wellington region since the 1990s; this decline was statistically significant for rivers and streams under pastoral landcover. Similar declining trends in rivers and streams draining pastoral and urban landcover have been reported in a nationwide assessment of IBI scores (Joy 2009). Allibone et al. (2010) also reported a decline across New Zealand in populations of a number of diadromous species that occur in the Wellington region (inanga, koaro, shortjaw kokopu, torrentfish and redfin and bluegill bullies); the loss of shortjaw kokopu populations from the Wellington region was specifically mentioned. WGN_DOCS-#1100598-V3 PAGE 99 OF 160
River and stream water quality and ecology in the Wellington region: State and trends 8. Discussion This section revisits the main findings from Sections 4 through 7. A regional overview of state and trends in river and stream health is presented first, with this information then considered in a national context. The principal issues affecting the region’s rivers and streams are discussed and key management issues identified, with brief consideration also given to downstream receiving environments. Lastly, monitoring limitations and knowledge gaps are outlined. 8.1 Regional overview 8.1.1 State Analysis of RSoE water quality, periphyton and macroinvertebrate data collected at 55 sites (46 in the case of periphyton) over the period July 2008 to June 2011 found that: 27 (49%) sites were assigned ‘good’ or ‘excellent’ water quality grades, indicating that median values for at least five of the six key indicator variables in Greater Wellington’s Water Quality Index (WQI) met guideline values; 27 (59%) sites were classed as ‘good’ or ‘excellent’ in terms of compliance with MfE (2000) periphyton cover/biomass guidelines, indicating infrequent or nil occurrence of nuisance periphyton growth; and 36 (65%) sites were classed as having ‘good’ or ‘excellent’ macroinvertebrate community health, based on a comparison of mean MCI scores against the thresholds in national guidance provided by Stark and Maxted (2007). The remaining sites (35–51% depending on the indicator) were classed as having ‘fair’ or ‘poor’ water quality or ecosystem health. While this report has not attempted to assess the suitability of rivers and streams for other, values 28 such as recreational use and trout fishery/spawning, these values are also likely to be impaired at some RSoE sites. For example, the two Ruamahanga River sites with a WQI grade of ‘fair’ (Gladstone and Pukio) are in close proximity to recreational water quality monitoring sites with Suitability for Recreation Grades of ‘poor’ (see Greenfield et al. 2012). Similarly, sites on a number of river and stream reaches listed in Greater Wellington’s existing Regional Freshwater Plan (WRC 1999) as supporting trout habitat (eg, Taueru River at Gladstone, Kopuaranga River at Stewarts, Mangatarere Stream at SH 2 and Huangarua River at Ponatahi Bridge), frequently exceeded MfE (2000) periphyton guidelines for protection of trout habitat and angling values. Water quality, periphyton cover/biomass and macroinvertebrate health all showed clear linkages with upstream catchment landcover (Figure 8.1). Sites classified as having ‘good’ or ‘excellent’ water quality and ecosystem health tend to be located on the upper reaches of rivers and streams that drain the 28 The specific values that rivers and streams in the Wellington region are to be managed for are currently being considered as part of the review of Greater Wellington’s existing Regional Freshwater Plan. PAGE 100 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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