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

River and stream water quality and ecology in the Wellington region: State and trends
Annual mean and maximum
mat periphyton streambed cover (%)
100
90
80
70
60
50
40
30
20
10
RS21 annual maximum
RS21 annual mean
RS22 annual maximum
RS22 annual mean
0
2004 2005 2006 2007 2008 2009 2010 2011
Figure 5.7: Annual mean and maximum mat periphyton streambed cover at Hutt
River opposite Manor Park Golf Club (RS21) and Hutt River at Boulcott (RS22),
based on monthly assessments undertaken over 2003/04 to 2010/11 (based on a
July to June year). The horizontal red line indicates the MfE (2000) streambed cover
guidelines for mat periphyton (60%)
Clear trends were evident in periphyton biomass at four sites (Table 5.7): a
decreasing trend at Waitohu Stream at Forest Park and increasing trends at
Mangaroa River at Te Marua, Wainuiomata River upstream of White Bridge
and Ruamahanga River at Gladstone (Figure 5.8). The three increasing trends
ranged in magnitude from 9 to 18 mg/m 2 /yr, representing an increase of more
than 20% per year relative to the mean periphyton biomass values.
Exceedance of the MfE (2000) guideline for protection of aquatic biodiversity
at all three sites and a corresponding decreasing trend in macroinvertebrate
health at one site (Ruamahanga River at Gladstone, see Section 6.2.2) suggests
that these increases in periphyton biomass may be ecologically significant. In
contrast, the small magnitude of the decreasing trend at Waitohu Stream at
Forest Park, a site with already low periphyton biomass, is unlikely to be
ecologically significant.
Table 5.7: Summary of ‘probable’ (p