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

River and stream water quality and ecology in the Wellington region: State and trends
influenced the deteriorating trends reported for many sites. The 2004 and 2005
summers at the start of the trend analysis period were characterised by high
river flows and frequent freshes, contributing to low periphyton biomass and
high macroinvertebrate scores.
Analysis of NZFFD records identified a statistically significant decline in
indigenous fish community condition in the Wellington region (particularly
evident at pastoral sites) between the earliest time period (1960–1990) and the
two more recent periods (1991–2000 and 2001–2010) examined. As will be
discussed next, this observation is also present in the national record.
8.2 National context
The strong relationship between river/stream health and landcover/land use in
this report is consistent with patterns observed in other regions (eg, Collier &
Hamer 2010; Neale 2010) and across New Zealand (eg, Quinn & Raaphorst
2009; Ballantine et al. 2010; Ballantine & Davies-Colley 2010); rivers and
streams located in catchments dominated by indigenous forest typically have
better water quality, healthier macroinvertebrate communities and less
periphyton growth than those located in pastoral and urban catchments. Fish
communities generally exhibit a similar pattern (Joy 2009).
8.2.1 Water quality
Making direct comparisons between the data presented in this reported with
similar data reported by other regional councils or nationally is problematic
given differences in monitoring site networks (eg, number and location of
sites), sampling frequency, and sampling and analytical methods between some
regions. However, the recent analysis of regional water quality data sets
undertaken as part of the Land and Water New Zealand (LAWNZ) 29 initiative
provides an indication of how water quality in the Wellington region currently
compares with the rest of New Zealand. According to this analysis
(summarised in Table 8.1), for the period January 2004 to December 2011:
RSoE sites classed as upland (>150 m altitude) forest were generally in a
similar or better condition than the national average (median), although
three of the seven RSoE sites in this class recorded median DRP
concentrations above the national median.
Regional median values for most variables in the lowland (