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

River and stream water quality and ecology in the Wellington region: State and trends
the various guidelines across the 55 RSoE sites is summarised in Table 4.3.
Overall, median values for each water quality variable met their corresponding
guideline values at around two-thirds or more of sites. Visual clarity and
dissolved reactive phosphorus (DRP) were the two exceptions; median values
only met guidelines at 44% and 55% of sites, respectively.
Table 4.3: Summary of compliance with selected water quality guidelines/TVs,
based on median values for data collected monthly from 55 RSoE sites over July
2008 to June 2011
Variable Guideline/TV
Number (and percentage) of sites
complying with guideline values
Water temperature (ºC) ≤19 55 (100%)
Dissolved oxygen (% saturation) ≥80 49 (89.1%)
pH 6.5–9.0 54 (98.2%)
Visual clarity (m) ≥1.6 24 (43.6%)
Turbidity (NTU) ≤5.6 44 (80.0%)
Nitrite-nitrate nitrogen (mg/L) ≤0.444 39 (70.9%)
Ammoniacal nitrogen (mg/L) ≤0.021 49 (89.1%)
Nitrate nitrogen – toxicity (mg/L) ≤1.7 52 (94.5%)
Total nitrogen (mg/L) ≤0.614 36 (65.5%)
Dissolved reactive phosphorus (mg/L) ≤0.010 30 (54.5%)
Total phosphorus (mg/L) ≤0.033 37 (67.3%)
E. coli (cfu/100mL)
≤100
≤550
35 (63.6%)
51 (92.7%)
4.1.3 Water temperature
None of the 55 RSoE sites recorded a median water temperature value greater
than the 19 o C guideline. However, 30 sites exceeded this guideline on at least
one sampling occasion and 17 sites exceeded it on more than 10% of sampling
occasions (Table 4.2). Awhea River at Tora Road and Totara Stream at
Stronvar exceeded the guideline on 33% and 27% of sampling occasions,
respectively.
The highest maximum water temperature recorded was 25 o C at Waipoua River
at Colombo Road, just on Greater Wellington’s RFP critical threshold. The
next highest maximum temperatures were recorded at Awhea River at Tora
Road and Totara Stream at Stronvar (24.3 o C and 24.1 o C, respectively).
RSoE sites located on the lower reaches of the region’s larger rivers
(eg, Ruamahanga River at Pukio), sites associated with the eastern Wairarapa
hill country (eg, Awhea River at Tora Road), and sites on rivers and streams
that experience long periods of low flows (eg, Waipoua River at Colombo
Road) generally recorded the highest median water temperatures. Rivers and
streams with limited streamside vegetation and shading (eg, Parkvale Stream at
Weir) also tended to have higher median water temperatures (Figure 4.1). In
contrast, sites located in catchments dominated by indigenous forest with hill
elevation source of flows typically recorded the lowest median water
temperatures over the reporting period (Figure 4.1).
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