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

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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: WGN_DOCS-#1100598-V3 PAGE 135 OF 160
River and stream water quality and ecology in the Wellington region: State and trends MCI i S i 1 x 20 where S = the total number of taxa in the sample, and ai is the tolerance score for the ith taxon. MCI scores range from 0 (when no taxa are present) to 200 (when all taxa score 10 points each) although scores < 40 or > 150 are rare. The QMCI is calculated from fixed count data as follows: QMCI PAGE 136 OF 160 WGN_DOCS-#1100598-V3 S a i S i1 i N ( ni ai) where S = the total number of taxa in the sample, ni is the abundance for the ith scoring taxon, ai is the score for the i th taxon and N is the total fixed count for the sample. QMCI scores range from 0 to 10. The percentage of pollution sensitive Ephemeroptera (mayfly), Plecoptera (stonefly) and Trichoptera (caddisfly) (%EPT) taxa is calculated by dividing the number of EPT taxa by the total number of taxa identified in the sample. Similarly, the percentage of EPT individuals is calculated by dividing the number of EPT individuals by the total macroinvertebrate count for the sample. Both %EPT taxa and %EPT individuals calculations exclude the caddisfly taxa Oxyethira and Paroxyethira as they are known to be relatively insensitive to pollution. Habitat assessments In 2008, qualitative habitat assessments following methods outlined in Rowe et al. (2006) were undertaken at the same time as macroinvertebrate sampling at all RSoE sites. This assessment involved allocating a score to various instream and riparian habitat characteristics, including aquatic habitat abundance and diversity, hydrologic heterogeneity, channel shade, and the integrity of the riparian margin. These scores are summed to provide an overall habitat score and can range from 0 (lowest) to 140 (highest). Streambed substrate size assessments and index River and streambed substrate size is assessed annually (during macroinvertebrate sampling), at all RSoE sites using the Wentworth Scale which assigns substrate to the following categories: bedrock, boulder, cobble, pebble, gravel, sand and silt (see Harding et al. (2009) for further details on the size of each substrate type). For each site, a substrate index is calculated using the equation outlined in Harding et al. (2009).
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River and stream water quality and
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DISCLAIMER This report has been pre
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observed trends were unclear. The p
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5. Periphyton - state and trends 57
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Figure 2.1: RSoE monitoring sites a
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2.4.2 Biological variables River an
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4.2 Temporal trends River and strea
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TN (mg/L) Temperature ( 0 c) Shade
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Chlorophyll a (mg/m 2 ) 90 80 70 60
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25th percentile summer time flow m
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RS06 Shade RS11 Habitat RS35 RS49 R
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