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 catchment (Figure 5.2). There were insufficient data to assess the relationship between periphyton biomass and urban or exotic forest landcover. However, all four RSoE sites with a REC landcover class of ‘urban’ were classed as ‘poor’ based on compliance with MfE (2000) periphyton guidelines, while the single site representing exotic forest landcover was classed as ‘fair’. Number of sites 25 20 15 10 5 0 Excellent Good Fair Poor Indigenous forest Pasture Urban Exotic forest Figure 5.1: Periphyton classes assigned to each of 46 hard-bottomed RSoE sites, according to the degree of compliance with MfE (2000) guidelines for periphyton biomass and cover over the period July 2008 to June 2011. Sites are colourcoded according to their REC landcover class Mean periphyton biomass (mg chlorophyll a/m 2 ) 1000 100 10 1 0.1 REC landcover class Indigenous forest Exotic forest Pastoral Urban 0 10 20 30 40 50 60 70 80 90 100 % of upstream catchment in indigenous forest landcover 0.1 0 20 30 40 50 60 70 80 90 100 % of upstream catchment in pastoral landcover Figure 5.2: Scatter plots demonstrating the relationship between mean periphyton biomass (based on annual sampling in 2009, 2010 and 2011) and the proportion of indigenous forest (left) and pastoral landcover (right) in the catchment upstream of each RSoE site. Note that only sites classed as ’pastoral’ (n=17) are included in the pastoral landcover plot WGN_DOCS-#1100598-V3 PAGE 61 OF 160 Mean periphtyon biomass (mg chlorophyll a/m 2 ) 1000 100 10
River and stream water quality and ecology in the Wellington region: State and trends 5.1.5 Relationships between periphyton growth and environmental variables Spearman rank correlations between periphyton metrics and selected environmental variables showed that mean periphyton biomass tended to be more strongly correlated with environmental variables than periphyton cover. The environmental variables that demonstrated the strongest positive correlations with periphyton biomass were total nitrogen (TN), total Kjeldahl nitrogen (TKN), total phosphorus (TP) and water temperature (rs=0.67–0.76). In contrast, water clarity and habitat score exhibited strong negative correlations (rs=-0.69– -0.54) with periphyton biomass (Table 5.4, Figure 5.3). Mean filamentous periphyton cover showed stronger correlations with environmental variables than maximum filamentous cover; it was most strongly positively correlated with water temperature (rs=0.65), followed by TKN, TN and pH (rs=0.54–0.55) and most strongly negatively correlated with habitat score, water clarity and shade score (rs=-0.67– -0.54). Table 5.4: Spearman rank correlations between selected periphyton metrics and environmental variables at 46 RSoE sites. Correlations are listed from highest to lowest (both positive and negative) based on periphyton biomass results. Environmental variables used in the analysis are medians unless stated otherwise. Correlations in bold are statistically significant (p
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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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