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

River and stream water quality and ecology in the Wellington region: State and trends
Periphyton
Formal periphyton assessments are limited to the 46 RSoE sites with hard substrates.
Monthly assessment of visible streambed cover
Periphyton cover is determined by estimating the percentage of visible mats (>0.3 cm
thick) and filaments (>2 cm long) present on the stream or river bed within a 20 cm
diameter metal ring. Ten observations are made across the width of the stream or river,
along a transect. If the stream or river is not wide enough for 10 observations, five
observations are made across the width of the waterway in two locations at the site.
Two transects of five observations (usually to 0.6 m depth) are also used where it is not
possible to wade across more than half of the river's width.
Visible streambed assessments are typically carried out in a run, as opposed to riffle or
pool-type habitats.
Annual assessment of biomass
Periphyton samples for quantitative biomass assessments (chlorophyll a and Ash Free
Dry Matter) are collected over late summer/early months at the time of
macroinvertebrate sample collection. Sampling protocols follow a modified version of
quantitative method 1a (QM-1a), as outlined by Biggs and Kilroy (2000) that involves
pooling periphyton samples from 10 rocks into a single composite sample for analysis.
Biomass assessments are carried out on periphyton samples collected in riffle-type
habitats in close proximity to macroinvertebrate sampling sites.
Macroinvertebrates
Macroinvertebrate samples (3 replicate samples in years 2004 to 2009 and one thereafter)
are collected at or adjacent to each RSoE water sampling site over late summer/early
autumn months. The timing of sampling is determined at random, although
macroinvertebrate sampling is, where practicable, avoided within two weeks of any flood
event (flood events are defined as flows greater than three times the median river flow).
Samples are collected with the use of a kick-net (0.5 mm mesh size) following Protocol C1
of the national macroinvertebrate sampling protocols (Stark et al. 2001) for the 46 RSoE
sites with hard substrate (in riffle habitat) and Protocol C2 for the nine RSoE sites with a
soft substrate. All samples are processed in accordance with protocol P2 (Stark et al.
2001).
Calculation of Biotic Indices: MCI, QMCI, %EPT taxa and %EPT individuals
Macroinvertebrate Community Index (MCI) values were developed by Stark (1985) for
assessing organic enrichment of stony or hard-bottomed streams based on sampling
macroinvertebrates from riffle (preferably) or run habitats. The MCI relies on prior
allocation of scores (between 1 and 10) to macroinvertebrate taxa (usually genera) based
on their tolerance of organic enrichment (the most recent tolerance scores can be found
in Stark and Maxted 2007). Taxa that are characteristic of unenriched conditions score
more highly than taxa found in polluted conditions. The MCI is calculated as follows:
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