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

2.4.2 Biological variables
River and stream water quality and ecology in the Wellington region: State and trends
(a) Periphyton and macroinvertebrates
Ecosystem health is also assessed at each of the 55 RSoE sites through annual
biological monitoring, incorporating semi-quantitative assessments of
periphyton biomass and macroinvertebrate communities during stable/low
flows in summer/autumn. Periphyton assessments are only undertaken at sites
with hard substrates such as cobbles and large gravel (46 in total, see Appendix
1). Periphyton cover is also assessed monthly at these sites at the time of water
sample collection. Details of current biological monitoring field and analytical
methods are summarised in Appendix 3.
Biological assessment methods have remained largely unchanged since
September 2003, the exception being that since 2010, the number of
invertebrate samples collected from each site reduced from three to one.
(b) Macrophytes
Formal monitoring of aquatic macrophyte cover commenced at selected RSoE
sites in July 2011 using methods outlined in Collier et al. (2007). Prior to this
time, only general observations of the presence of nuisance macrophyte
growths were recorded during monthly water sampling.
(c) Fish
In the last few years, Greater Wellington has trialled recently developed
standardised fish sampling protocols (David et al. 2010) at several RSoE sites.
Overall, however, most fish surveys to date have been undertaken at other
locations in the region to gather further information on the spatial distribution
of freshwater fish and/or to assist with targeted investigations. The location of
many RSoE sites on large rivers and streams precludes them from being
assessed using currently available standardised methodologies.
2.4.3 Supporting variables
(a) Flow
Flow is a fundamental supporting variable for monitoring river and stream
health. Many water quality variables, notably turbidity, vary with flow and
measurements need to be flow-adjusted for temporal trend assessment purposes
(Davies-Colley et al. 2011). Flow measurements are also needed to calculate
nutrient and contaminant loads, and to determine accrual periods for the
interpretation of biological data.
Continuous flow recorders are located at, or very near to, 15 RSoE sites. For
the other 40 sites, flows are estimated using Greater Wellington’s extensive
network of continuous and spot flow measurement records, in combination
with flow records from NIWA’s site network (Thompson & Gordon 2010a).
The level of confidence in the accuracy of flow estimates varies across these
sites due to the proximity of each RSoE site to a flow recorder (eg, whether or
not the flow recorder is located in the same river catchment or another river
catchment) and also the number of ‘spot gaugings’ available at each site to
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