Opuatia Peat Bog Management Plan - Waikato Regional Council

5.4 Nutrient enrichment
Wetlands are very sensitive to nutrient enrichment, and it is second only to
hydrological disturbance as a cause of loss of natural character (Sorrell 2010). While
often the most difficult aspect to manage, if not addressed it usually leads to excessive
growth of weeds, rapid vegetation succession and poor habitat for aquatic fauna.
Levels of nutrients have been analysed for Opuatia Wetland by Browne and Campbell
(2005) and are summarised and compared with other New Zealand wetlands in
Table 3. While none of the sampling sites were within the WRC peat bog, several
sites were within 200 m of the southern boundary.
Table 3: A comparison of mean and range (in brackets) of soil parameters for
wetlands sampled in New Zealand and Opuatia Wetland. From Browne
and Campbell (2005).
NZ bogs NZ swamps Opuatia bogs and Opuatia swamps
(6 sites)
(17 sites) fens (n=22)
(n=6)
Soil pH 4.0 (3.7-4.4) 5.2 (4.1-5.9) 4.99 (4.31-5.36) 5.05 (4.81-5.39)
Total Carbon* 92.7 (24.1-239.8) 39.8 (5.2-100.6) 33.3 (24.2-43.3) 39.8 (29.8-47.4)
Total Nitrogen* 0.82 (0.02-1.83) 2.12 (1.15-3.24) 1.35 (0.69-1.98) 2.39 (1.72-2.78)
Total Phosphorus* 0.08 (0.01-0.20) 0.28 (0.15-0.59) 0.08 (0.03-0.13) 0.26 (0.18-0.33)
C:N 48.5 (35.9-79.7) 18.0 (14.2-30.6) 26.4 (17-49) 16.7 (14-19)
C:P 1904 (533-4221) 163 (45-435) 507.1 (236.9-1041.8) 161.35 (116.3-
212.7)
N:P 39.0 (20.6-81.6) 9.1 (4.0-20.6) 18.79 (13.7-27.3) 9.54 (8.34-11.72)
* units of mg cm -3
The above table shows that the soil pH for bogs and fens in Opuatia Wetland were
much higher than for other New Zealand bog sites. As discussed in Section 5.1, this
is probably a result of occasional flood events that cover the entire Opuatia Wetland.
Total nitrogen is generally higher than the averages for other New Zealand bogs and
swamps although within the overall range. These results indicate that nutrient
enrichment is occurring within the Opuatia Wetland.
6. RESTORATION AND IMPLEMENTATION PLAN
6.1 Hydrology
Two options are presented for addressing management of the hydrology at the WRC
peat bog.
Option 1 - Further Investigation
Further investigation into the hydrology of the WRC peat bog could be undertaken to
clarify issues discussed in Section 5.1. It is likely that the causeway is having some
effect on water levels in the adjacent vegetation communities, but it is not known to
what extent water levels are affected and how far these effects penetrate into the
wetland. Piezometers were set up in 2006/07 in Opuatia Wetland as part of a PhD
© 2011
18
Contract Report No. 2621