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 Figure 5.4: RSoE sites Whareroa Stream at Waterfall Road (left) and Awhea River at Tora Road (right) Most of the RSoE sites assigned to the ‘poor’ periphyton class recorded very high median concentrations of TN (>1 mg/L) and/or TP (>0.04 mg/L). Awhea River at Tora Road (Figure 5.4) and Huangarua River at Ponatahi Bridge were two exceptions, recording only low or moderate median nutrient concentrations. However, these two sites are characterised by both high water temperatures (median values >14 o C) and long accrual periods (mean annual maximum accrual period is estimated to be 105 days at both), a reflection of their location in the eastern Wairarapa which typically experiences dry summers. Both sites also have minimal shade. The other exception in the ‘poor’ class was Mangaroa River at Te Marua. This site recorded only moderate concentrations of TN and TP and a low median water temperature. The reason for high periphyton growth at this site is unclear but could be related to the relatively long accrual periods this site can experience (average annual maximum accrual period of 89 days). 5.1.6 Macrophytes Nine RSoE sites have substrate dominated by soft sediment (eg, silt and sand) which makes them more suitable for growth of macrophytes than periphyton. Although monitoring of macrophyte cover was not undertaken during the July 2008 to June 2011 reporting period (monitoring only commenced in July 2011), general observations made at the time of routine monthly water quality sampling suggest that extensive macrophyte cover is frequently present at four soft-bottomed RSoE sites: Mangapouri Stream at Bennetts Road (Figure 5.5), Mangaone Stream at Sims Road Bridge, Whangaehu River 250 m from confluence and Whareama River at Gauge. Extensive macrophyte growth has also been observed at some hard-bottomed RSoE sites, many of which have substrate at the lower size limit of that suitable for periphyton growth and/or experience long accrual periods. These sites include Pauatahanui Stream at Elmwood Bridge, Makara Stream at Kennels, Wainuiomata River upstream of White Bridge, Parkvale Stream at Weir and Taueru River at Gladstone Bridge. Most of these sites are located near the bottom of low lying catchments dominated by pastoral land use. WGN_DOCS-#1100598-V3 PAGE 65 OF 160
River and stream water quality and ecology in the Wellington region: State and trends Figure 5.5: Extensive growth of Lagarosiphon major just downstream of the RSoE sampling site on the Mangapouri Stream at Bennetts Road (March 2009) 5.2 Temporal trends 5.2.1 Approach to analysis Temporal trends in periphyton growth were assessed at each of 46 hard substrate RSoE sites using two data sets: monthly observations of percent periphyton streambed cover from September 2003 to June 2011 and periphyton biomass (chlorophyll a concentration) data from annual sampling between summer/autumn 2004 and 2011 (n=8) 19 . The 2003/04 to 2010/11 period was the longest available for trend assessment since major changes were made to the RSoE site network in 2003 (refer Section 2.1). Trends in periphyton cover were assessed using annual mean and maximum cover data – a similar approach to that used by Quinn and Raaphorst (2009). In order to be consistent with the methods used in Quinn and Raaphorst (2009), annual mean cover results were calculated based on the number of periphyton cover assessments made at a site (ie, this is in contrast to the approach used in Section 5.1 where cover data were calculated based on the total number of visits to each site). Annual mean and maximum cover values were calculated for the period July to June for all years (except for 2003/04 which was limited to September to June because observations of mat and filamentous streambed cover only commenced in September 2003) 20 . Non-parametric Spearman Rank correlations were used to determine whether or not statistically significant temporal trends were present in periphyton cover 19 n=7 for periphyton biomass at the three Hutt River sites (the 2011 biomass results were excluded due to the influence of a fresh). 20 The absence of July and August data for the 2003/04 year is unlikely to significantly affect the results of trend analysis at many RSoE sites because periphyton cover is not regularly recorded during these months. PAGE 66 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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Appendix 1: Monitoring site details
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