This article was downloaded by: [176.9.124.142] On: 06 October 2014, At: 04:50 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK New Zealand Journal of Marine and Freshwater Research Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tnzm20 Performance of the Macroinvertebrate Community Index: Effects of sampling method, sample replication, water depth, current velocity, and substratum on index values John D. Stark a a Cawthron Institute , Private Bag 2, Nelson, New Zealand Published online: 21 Sep 2010. To cite this article: John D. Stark (1993) Performance of the Macroinvertebrate Community Index: Effects of sampling method, sample replication, water depth, current velocity, and substratum on index values, New Zealand Journal of Marine and Freshwater Research, 27:4, 463-478, DOI: 10.1080/00288330.1993.9516588 To link to this article: http://dx.doi.org/10.1080/00288330.1993.9516588 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. 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Terms Downloaded by [176.9.124.142] at 04:50 06 October 2014 & Conditions of access and use can be found at http://www.tandfonline.com/page/ terms-and-conditions New Zealand Journal of Marine and Freshwater Research, 1993: Vol. 27: 463-478 0028-8330/93/2703-0463 $2.50/0 © The Royal Society of New Zealand 1993 463 Performance of the Macroinvertebrate Community Index: effects of sampling method, sample replication, water depth, current velocity, and substratum on index values Downloaded by [176.9.124.142] at 04:50 06 October 2014 JOHN D. STARK Cawthron Institute Private Bag 2 Nelson, New Zealand Abstract The influences of sampling method, water depth, current velocity, and substratum on two macroinvertebrate-based biotic indices were investigated based upon 523 samples from 55 stony riffle sites on 23 New Zealand streams. A single hand-net sample estimated the site Macroinvertebrate Community Index (MCI) within ± 15% and four replicates yielded ± 10%. Between 8 and 10 replicate Surber samples produced ± 10% precision. Quantitative MCI (QMCI) values were more variable, with 10 or 11 replicate Surber samples required for ± 10% precision. Two procedures for detection of statistically significant differences between paired MCI or QMCI values are described. The detectable difference method (equal sample sizes) is preferred for statistical reasons but a f-test method can be used for unequal sample sizes. MCI and QMCI were relatively independent of depth, velocity, and substratum within the sampled ranges of these variables. This is a major advantage for the assessment of water pollution or enrichment using these indices. However, to avoid possible complications brought about by extreme values, sampling within the following ranges of these variables is suggested: depth 0.1-0.4 m, velocity 0.2-1.2 m s-1, and substrate 60-140 mm median diameter. Keywords benthic invertebrates; aquatic insects; sampling; substrate; current velocity; water depth; biotic indices; biological monitoring M93028 Received 11 May 1993; accepted 30 September 1993 INTRODUCTION Macroinvertebrates are normally abundant and important components of riverine ecosystems (Hilsenhoff 1977; Quinn & Hickey 1990), and they are easily the most commonly used group of freshwater organisms for the assessment of water quality (Rosenberg & Resh 1992). The individual species have different habitat preferences and, consequently, the community present in a given situation reflects its environment. Since the effect of stream pollution is to alter the aquatic environment, and its biological community, it is logical to detect pollution by monitoring the aquatic ecosystem (Hilsenhoff 1977). Usually, macroinvertebrate-based biomonitoring or pollution assessment is intended to monitor water quality through its influence on community composition. However, macroinvertebrate community structure is affected also by habitat characteristics such as current velocity, water depth, and substratum type. As Winterbourn (1981) noted, benthic invertebrates probably respond to a complex of smallscale environmental factors, and some species may respond to a hierarchical arrangement of such parameters. Whatever the case, temporal or betweensite differences in factors such as these will also be reflected in biotic index values and can complicate the assessment of water pollution. The Macroinvertebrate Community Index (MCI) and its quantitative variant (QMCI), proposed by Stark (1985) for use in stony riffles in New Zealand streams and rivers, are biotic indices. A preliminary version of the MCI was included in the Taranaki ringplain biological report (Taranaki Catchment Commission 1984). The MCI and QMCI were developed from the British Biological Monitoring Working Party Score System (BMWP1978; Armitage et al. 1983) and are similar to indices developed by Chutter (1972) in South Africa and Hilsenhoff (1977, 1987) in Wisconsin, USA. The MCI relies on prior allocation of scores (between 1 and 10) to taxa (usually genera) of 464 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 Downloaded by [176.9.124.142] at 04:50 06 October 2014 Table 1 Taxon scores for use in calculation of MCI and QMCI index values. INSECTA Ephemeroptera Ameletopsis Arachnocolus ktalophlebioid.es Austrodima Coloburiscus Deleatidium Ichthybotus Isothraulus Mauiulus Neozephlebia Nesameletus Oniscigaster Rallidens Siphlaenigma Zephlebia Plecoptera Acroperla Austroperla Cristaperla Halticoperla Megaleptoperla Spaniocerca Spaniocercoides Stenoperla Zelandobius Zelandoperla Megaloptera Archichauliodes Odonata Aeshna Antipodochlora Austrolestes Hemicordulia Xanthocnemis Procordulia Hemiptera Diaprepocoris Microvelia Sigara Coleoptera Antiporus Berosus Dytiscus Elmidae Hydraenidae Hydrophilidae Liodessus Ptilodactylidae Rhantus Scirtidae 10 8 9 9 9 8 8 8 5 7 9 10 9 9 7 5 9 8 8 9 8 8 10 5 10 7 5 6 6 5 5 6 5 5 5 5 5 5 6 8 5 5 8 5 8 Coleoptera (cont.) Staphylinidae Diptera Anthomyiidae Aphrophila Austrosimulium Calopsectra Ceratopogonidae Chironomus Cryptochironomus Culex Empididae Ephydridae Eriopterini Harrisius Hexatomini Limonia Lobodiamesa Maoridiamesa Microchorista Mischoderus Molophilus Neocurupira Orthocladiinae Parochlus Paradixa Paralimnophila Paucispinigera Peritheates Podonominae Polypedilum Psychodidae Sciomyzidae Stratiomyidae Syrphidae Tabanidae Tanypodinae Tanytarsini Tanytarsus Zelandoptipula Trichoptera Aoteapsyche Beraeoptera Confluens Conuxia Costachorema Ecnominidae Helicopsyche Hudsonema Hydrobiosella Hydrobiosis freshwater macroinvertebrates based upon their pollution tolerances. Taxa that are characteristic of pristine conditions score more highly than taxa that may be found predominantly in polluted conditions. Taxon scores are given in Table 1. MCI values are 5 3 5 3 4 3 1 3 3 3 4 9 6 5 6 5 3 7 4 5 7 2 8 4 6 6 7 8 3 1 3 5 1 3 5 3 3 6 4 8 5 8 7 8 10 6 9 5 Trichoptera (cont.) Hydrochorema Kokiria Neurochorema Oeconesidae Olinga Orthopsyche Oxyethira Paroxyethira Philorheithrus Plectrocnemia Polyplectropus Psilochorema Pycnocentrella Pycnocentria Pycnocentrodes Rakiura Tiphobiosis Triplectides Zelolessica Lepidoptera Hygraula Collembola ACARINA CRUSTACEA Amphipoda Copepoda Cladocera Isopoda Ostracoda Paranephrops Paratya Tanaidacea MOLLUSCA Ferrissia Gyraulus Latia Lymnaea Melanopsis Physa Physastra Potamopyrgus Sphaeriidae OLIGOCHAETA HIRUDINEA PLATYHELMINTHES NEMATODA NEMATOMORPHA NEMERTEA COELENTERATA Hydra 9 9 6 9 9 9 2 2 8 8 8 8 9 7 5 10 6 5 10 4 6 5 5 5 5 5 3 5 5 4 3 3 3 3 3 3 5 4 3 1 3 3 3 3 3 3 calculated from macroinvertebrate presence-absence data using the following equation: site score MCI =• •x20 no. of scoring taxa Stark—Freshwater invertebrate biotic indices where the site score is the sum of individual taxon scores for all taxa present in a sample, and 20 is a scaling factor. In theory, MCI values can range between 200 (when all taxa present score 10 points each) and 0 (when no taxa are present), but in practice it is rare to find MCI values greater than 150. Only extremely polluted stony riffle sites score less than 50. At the other extreme, stony riffle sites with MCI > 120 may be regarded as pristine. The QMCI is calculated using the following equation: i=S Downloaded by [176.9.124.142] at 04:50 06 October 2014 QMCI = N where S = the total number of taxa in the sample, «,• is the number of individuals in the /-th scoring taxon, a, is the score for the i-th taxon, and N is the totail number of individuals collected in the sample. The QMCI uses quantitative macroinvertebrate data. In this paper, I draw upon an extensive unpublished macroinvertebrate community database (with associated current velocity, water depth, and substratum data), which has been collected as part of contract environmental consultant projects, supplemented by limited additional sampling (primarily to compare Surber and hand-net techniques). All sampling was concentrated in stony riffle habitats where macroinvertebrate diversity and density normally are greatest (Pridmore & Roper 1985). The specific aims of these investigations were to: 1. compare the efficiency of Surber and "foot-kick" hand-net sampling for MCI estimation; 2. assess the impact of sample size (or replication) on MCI and QMCI estimation; 3. define a statistical procedure for determining significant differences in MCI and QMCI values between two sets of samples; 4. assess the impact of current velocity, water depth, and substratum on MCI and QMCI values; and 465 5. provide practical guidance to improve the application of these indices for pollution surveillance and monitoring. METHODS Data collection Twelve matched-pair replicate samples were collected by Surber sampler (area 0.1 m2, 0.5 mm mesh) and "foot-kick" hand-net (0.5 mm mesh) from stony riffle habitat at four river sites near Nelson, New Zealand (Table 2). Hand-net samples were standardised by sampling within an area of about 0.5 m2 for about 10 s. Each sample was transferred to a white tray for inspection and then into a labelled 250 ml or 500 ml plastic jar where it was preserved with 70% alcohol / 4% formalin. At each Surber sample collection point, the following measurements were made: water depth, mean column current velocity (at 0.6 of the depth), and the median diameter of the six largest rocks within the quadrat (as an index of substratum). The median diameter is defined as the maximum width of the rock (where length > width > height). Although these measurements were not repeated, each handnet sample was collected near the equivalent numbered Surber sample (where depths, velocities, and substratum were similar). Macroinvertebrates were separated from debris in the laboratory by wet-sieving through a series of Endecott sieves (4 mm, 1 mm, 0.5 mm mesh). All animals in Surber samples were identified and counted. For hand-net samples, although only presence-absence data are required for MCI calculation, relative abundances of taxa were recorded on a Rare/Common/Abundant/Very Abundant scale. This additional information normally is worth collecting as it permits some discussion of community composition and often aids the interpretation of monitoring results. Table 2 Macroinvertebrate sampling site locations in the Maitai and Wakapuaka Rivers near Nelson. Sites on the Wakapuaka River are numbered from upstream (Wakl) to downstream (Wak3). Code Mai Wakl Wak2 Wak3 Maitai River Wakapuaka River at third picnic area Wakapuaka River below Teal River confluence luence Wakapuaka River opposite rifle range Grid reference NZMS 260 027 Date 369 923 440 976 433 977 438 000 8Nov91 20 Nov 91 22 Nov 91 20 Nov 91 466 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 Downloaded by [176.9.124.142] at 04:50 06 October 2014 Existing data were collated from Surber sampling in the Wanganui catchment (20 sites, 239 samples), Motueka catchment (25 sites, 145 samples), Waimea catchment (5 sites, 31 samples), and the Wairau River (1 site, 57 samples). Details of site locations, sampling dates and numbers of replicate samples collected are given in Appendix 1. All samples were collected from stony riffles. Water depths, mean water column current velocities, and median diameters of rocks present in sampler quadrats were measured for each sample collected (although rock dimensions were not measured for the Wairau data) (Stark 1988, 1989, 1990). Data analyses For all analyses, macroinvertebrate identifications were at the level required for MCI and QMCI calculation (see Table 1). The term "scoring taxa" refers to taxonomic richness at this (mostly generic) level. Changes in scoring taxa, densities, MCI, and QMCI with sample size The impact of sample size on MCI and QMCI values was investigated using four sets of 12-replicate handnet samples and 20 sets of 12-replicate Surber samples. Since numbers of scoring taxa and densities are also involved in index calculation, the influence of sample size was assessed for them too. For each taxa x 12-replicate data file the following procedure was followed. This procedure was required so that accurate minimum, mean, and maximum estimates of numbers of scoring taxa, densities, MCI, and QMCI could be calculated. For each sampling site, additional data files containing all possible combinations of 2, 3,...., 12 replicates were created from the original taxa by 12replicate data file. There are 66, 220, 495, 792, 924, 792,495,220,66,12, and 1 way(s) in which different combinations of 2 to 12 samples can be drawn from a series of 12 replicates. Numbers of scoring taxa, densities (for Surber samples), MCI, and QMCI (for Surber samples) were calculated for the original taxa by 12-replicate data file and for each of the 11 combination files. Taxonomic richness, densities, and biotic index values calculated for a site from all 12 replicates combined were termed the "total number of taxa caught", the "site mean density", the "site MCI" and the "site QMCI". Accretion curves for scoring taxa, densities, MCI, and QMCI were determined for hand-net (4 sites) and Surber (20 sites) samples, by expressing all values as percentages of the "site" values calculated from all 12 replicates combined. The mean, minimum, and maximum values for all combinations of sample size were calculated. All the above analyses were run using QuickBASIC 4.50 programmes written by the author. Influence of water depth, current velocity, and substratum on MCI and QMCI values Relationships between MCI and QMCI values and water depths, current velocities, and mean median rock diameters (as an index of substratum) were explored by X-Y plotting and calculating least-squares linear regressions for individual series of replicate Surber samples. The Bartlett %2 test was used to test whether any real correlations existed within the matrix of MCI, QMCI, depths, velocities, and substratum data. Bonferroni-adjusted probabilities were computed to provide protection for multiple tests (Wilkinson et al. 1992). The slope of each regression line was tested to determine whether it differed significantly from zero. These analyses were undertaken using SYSTAT. Similar plots with data from all Surber samples combined (n - 523, except substratum data which were available for only 454 samples), were unhelpful because mean index values differed between sites owing to factors other than water depth, current velocity, or substratum (primarily water quality). To overcome this difficulty, MCI and QMCI values were standardised within sites to average 100 for each series of replicates. Relationships between standardised index values (referred to hereafter as sMCI and sQMCI) and depths, velocities, and substratum were explored as explained above. Detection of statistically significant differences in MCI and QMCI between sites Narf et al. (1984) defined a procedure for obtaining a best estimate of Hilsenhoff s (1977) Biotic Index (HBI) standard deviation, and based upon this, described two statistical procedures to test for significant differences between paired HBI valuesthe detectable difference (DD) method for equal sample sizes (statistically preferred) and the Mest for unequal sample sizes. Narf et al. (1984) calculated mean HBI values and variances for 42 sites with six replicate samples per site. ANOVA was used to determine the withinsamples mean square {- variance), the square root of which is the best estimate of HBI standard deviation. Stark—Freshwater invertebrate biotic indices 467 Downloaded by [176.9.124.142] at 04:50 06 October 2014 Variances were homogeneous over the range of HBI values and mean HBI values and variances were not correlated. Similar procedures to those employed by Narf et al. (1984) were applied to Surber sample data from 91 sampling sites (Table 1, Appendix 1). These data comprised between 3 and 22 replicates per site. Relatively limited hand-net data series were available. Four sets of 12 replicates (from Maitai, Wakl, Wak2 and Wak3: Table 2) were supplemented by one series of 9 hand-net samples from the Patea River, King Edward Park, Stratford (24 September 1984), to repeat the ANOVA as described above to define detectable differences for MCI values based upon hand-net samples. RESULTS Additional taxa scores for MCI calculation Stark (1985) presented a table of taxon scores for use in MCI (and QMCI) calculation and noted that any use of the MCI or QMCI should cite such a published list of taxon scores and note any additional or amended scores. Since then, scores have been allocated to additional taxa, primarily by professional judgement. The expanded list of taxon scores is given in Table 1 so that calculation of the MCI/QMCI may continue to be standardised New Zealand-wide. Comparison of Surber and hand-net sampling A series of 12 replicate Surber samples contained between 35 (Maitai) and 52 (Wakapuaka 2) scoring taxa per site, whereas hand-net samples yielded between 41 (Maitai) and 54 (Wakapuaka 2) (Table 3). Hand-net samples generally yielded higher minimum, maximum, and mean numbers of scoring taxa per sample than Surber samples (although the reverse was true for Wakapuaka 1); most differences were not statistically significant (Mest, P > 0.05). Only at Wakapuaka 3 was the mean number of scoring taxa per sample greater in Surber samples (27.3 taxa) than hand-net samples (23.0 taxa) (f=3.55; P < 0.01). MCI Mean MCI values from four series of 12 replicate Surber samples ranged from 96.1 (Maitai) to 129.2 Table 3 Summary of numbers of scoring taxa and MCI values for 12 replicate Surber and hand-net samples collected from the Maitai and Wakapuaka Rivers (November 1991). SE = standard error of the mean, ^-values and probabilities are given for within-site comparisons between sampling methods for numbers of scoring taxa and MCI values. The only statistically significant difference was at Wakapuaka 3 where the mean number of scoring taxa per sample was greater in Surber samples than hand-net samples. Maitai Taxa Surber Hand-net Total Mean/sample Min/sample Max/sample SE Total Mean/sample Min/sample Max/sample SE t P MCI Surber Hand-net t P Mean Min Max SE Mean Min Max SE Waikapuaka 1 Wakapuaka 2 Wakapuaka 3 35 18.17 10 25 1.47 41 19.42 14 28 1.31 1.53 0.15 41 25.58 22 32 1.05 42 24.5 19 30 1.22 0.81 0.44 52 24.83 19 29 0.92 54 25.17 20 34 1.09 0.34 0.74 51 23.00 18 29 1.24 48 27.33 19 32 1.14 3.55 <0.01 96.10 85.33 110.67 2.16 97.03 88.89 109.29 1.76 0.34 0.74 129.21 122.61 133.65 0.93 127.15 117.27 137.69 1.53 1.34 0.21 123.10 113.79 129.47 1.38 125.58 118.82 133.91 1.29 1.31 0.22 115.42 106.32 128.89 1.81 116.35 110.34 123.75 1.32 0.34 0.74 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 468 CO 120 co e u 1 o c o X C0 Downloaded by [176.9.124.142] at 04:50 06 October 2014 9 O. E co « i CM Replicate hand-net samples Fig. 1 Macroinvertebrate taxonomic richness and MCI accretion curves. Means and ranges are derived from all possible combinations of sample order based upon series of 12 replicate hand-net samples from four sites (i.e., 48 samples). All values are expressed as a percentage of the cumulative total of the 12-replicate samples. (Wakapuaka 1), whereas MCI values from the handnet samples ranged from 97.0 (Maitai) to 127.2 (Wakapuaka 1) (Table 3). The rank order of sites based on MCI values was the same for both sampling methods (i.e., Wakapuaka 1 > Wakapuaka 2 > Wakapuaka 3 > Maitai). This site order is effectively from upstream to downstream. Hand-net samples generally yielded higher mean MCI values than Surber samples (although the reverse was true for Wakapuaka 1), but differences were small (usually much less than 2%) and statistically insignificant (Mest, P > 0.05). Since higher scoring taxa tend to be amongst the mayflies, stoneflies, and caddisflies, consistent noncollection of taxa in these groups could result in reduced MCI values. However, no consistent evidence of bias between sampling methods in the numbers of taxa collected was found within any of six major groups of invertebrates (Table 4), suggesting that MCI values calculated from either Surber or handnet samples would not be biased through noncollection of particular taxonomic groups. Changes in scoring taxa, densities, MCI, and QMCI with sample size Numbers of scoring taxa collected increased with sampling effort (Fig. 1 and 2). For both hand-net and Surber samples, the scoring taxa accretion curves had not reached asymptotes, indicating that 12 replicates were insufficient to collect all taxa present. Table 4 Numbers of macroinvertebrate taxa in six major groups recorded in 12 Surber (S) and handnet (H) samples from the M^aitai and Wakapuaka Rivers (November 1991). Major group Ephemeroptera (mayflies) Plecoptera (stoneflies) Coleoptera (beetles) Diptera (true flies) Trichoptera (caddisflies) Other taxa Total taxa Maitai S H 2 2 2 9 12 8 35 4 3 2 11 11 10 41 Wakapuaka 1 S H 6 3 3 10 13 6 41 5 3 3 13 12 6 42 Wakapuaka 2 S H 4 4 5 17 13 9 52 5 4 4 11 14 7 54 Wakapuaka 3 S H 6 4 5 13 14 9 51 7 3 3 13 14 8 48 Stark—Freshwater invertebrate biotic indices t? 469 150 150 o c o E o o 100 I o 110 a 90 a a 0 p E 50 X •= 10 Downloaded by [176.9.124.142] at 04:50 06 October 2014 • 100 CO i 50 IN 70 60 10 CO * - S? 120 (0 (0 u 10 10 400 400 CM ^? 300 | O IS o 200 a. E 100 -n> 0 •a 2 - 150 100 Q. (0 I E CM CO 10 15 50 50 15 Replicate Surber samples Fig. 2 Macroinvertebrate taxonomic richness, density, MCI, and QMCI accretion curves. Means and ranges are derived from all possible combinations of sample order based upon series of 12 replicate Surber samples from 20 sites (i.e., 240 samples). All values are expressed as a percentage of the cumulative total of the 12-replicate samples. Nevertheless a series of 12 replicate samples appears to capture a sufficiently high proportion of the true total number of taxa present in the stream reach for acceptable estimates to be gained of the true total taxonomic richness, mean densities, MCI, and QMCI values for the site. This is based upon the assumption that "true" site values are approached as sampling effort increases, tempered by the fact that it is rarely practical to collect as many as 12 replicates in monitoring situations. For example, only 4% of 46 studies surveyed by Resh & McElravy (1993) took more than 12 replicates, whereas 85% collected 5 or fewer. A single hand-net sample captured between 34.2% and 77.3% (mean 54.7%) of the total number of scoring taxa collected in 12 replicates (Fig. 1), whereas a single Surber sample captured between 15.2% and 78.1% (mean 45.8%) (Fig. 2). Once three samples had been collected an average of 77.1 % (range 51.295.5%) and 69.0% (range 36.4-96.3%) of the total number of scoring taxa collected in 12 replicates had been recorded (Fig. 1 and 2). These results indicate that numbers of taxa collected are very dependent upon the number of samples taken, and that considerable sample replication (perhaps 15-20 samples) is likely to be required if a primary objective is to compile a reasonably accurate inventory of the species present at a site. In this regard, approximately 20% fewer New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 470 scoring taxa, but also on accurate estimation of macroinvertebrate densities. As noted above, many Surber samples (7-11) are needed for estimation of macroinvertebrate densities with acceptable precision (say ± 20-50%). Ten or 11 Surber samples are required for estimation of QMCI values to within ± 10% of the combined 12-replicate value (Fig. 2). 200 150 - 100 - Downloaded by [176.9.124.142] at 04:50 06 October 2014 QMCI Fig. 3 Relationship between MCI and QMCI based upon data from 523 Surber samples. The linear regression line and 95% confidence limits are shown. hand-net samples than Surber samples would achieve similar results. Density Macroinvertebrate densities were available only for the quantitative Surber samples. Although the mean of all possible combinations of 12 replicates was constant, as expected, increasing sampling effort did improve the precision of density estimates (Fig. 2). Data from 20 sites indicated that a single Surber sample may yield a density between 17.3 and 317.7% of the 12-replicate value. Even triplicate samples fared little better (23.3-240.0%). MCI The mean MCI from 12 single hand-net samples was 101.3% of the combined 12-replicate value (range 86.8-115.6%). Thus, any single hand-net sample may yield an MCI value with an "error" of approximately ±15% (note that the upper and lower bounds are not symmetrical about the mean). Only four hand-net samples are required for + 10% precision in MCI estimation (Fig. 1). Between 8 and 10 replicate Surber samples were required to achieve MCI estimates within ±10% of the 12-replicate value (Fig. 2). QMCI QMCI values appear to be considerably more variable than MCI values as they rely not only on collection of Relationship between MCI and QMCI There was strong evidence of a positive linear relationship between MCI and QMCI values based upon data from 523 Surber samples (Fig. 3). MCI = 83.378 + 5.880 QMCI & = 0.477 (P = 0.0025) The strong rank correlation found between MCI and QMCI (Spearman's 7?s = 0.70) exceeded the Rs of 0.60 between MCI and QMCI noted by Quinn & Hickey (1990) for 88 New Zealand rivers. Influence of physical habitat on biotic index values Macroinvertebrate samples were collected from stony riffles encompassing a wide range of water depths (0.06-0.56 m, n = 523), current velocities (0.00-1.83 m s"1, n = 523) and substrata (median rock sizes 38300 mm, n = 454) (Fig. 4). No clear relationships occurred between index values and water depths, current velocities, and mean median rock diameters within the sampled ranges of these variables. For most replicate series, linear regression slopes did not differ significantly from zero. Within the sampled ranges of water depths, current velocities, and median rock sizes, no clear linear correlations were found with standardised biotic index values (sMCI and sQMCI) (Fig. 5). Absolute values of Pearson correlations ranged from 0.033 to 0.124, and Bonferroni adjusted probabilities were nonsignificant (0.081-1.000). The lack of any consistent relationships between index values and these three habitat descriptors at individual sites indicates that MCI and QMCI values are relatively independent of current velocity, water depth, and substratum in stony riffles within the sampled ranges of these variables. This is a major advantage for the application of these indices. Detection of statistically significant differences in MCI and QMCI between sites The variability of MCI and QMCI values must be known or estimated to permit detection of significant Stark—Freshwater invertebrate biotic indices 471 250 For hand-net samples, ANOVA yielded best estimates of MCI standard deviation Smh = 4.859 with 52 degrees of freedom. Single-sample hand-net MCI values ranged from 88.89 to 137.69. The following statistical techniques should be applied with caution to hand-net data because of the relatively limited database from which Smh was derived. 150 Detectable difference (DD) method The DD method requires that the same number of replicate samples be collected at each location. DD is the smallest difference (or change) that can be detected statistically for a given sample size. Based upon a = 0.1 (Type I error) and P = 0.2 (Type II error), Narf et al. (1984) derived the following equation: 0.0 0.2 0.4 0.6 0.8 1.0 Water depth (m) 0.25 0.20 (5 ° - 1 5 a 0.10(5°-15 •- 0.05 fl) a Downloaded by [176.9.124.142] at 04:50 06 October 2014 o a o —— 100 550 4= 0.0 0.4 0.8 1.2 1.6 2.0 o O Current velocity (m s"1) DD = u.o - - 0.4 200 150 0.3 100 0.2 —i 50 0.1 r~ 20 80 140 200 260 320 Median rock diameter (mm) Fig. 4 Frequency histograms of water depth (n = 523), current velocity (n = 523), and median rock diameter (n = 466) sampled at 55 stony riffle sites on 23 New Zealand streams. differences in water quality between streams, at different locations in the same stream, or for the same location sampled at different times. MCI values for single Surber samples ranged from 62.22 (Site WPipi) to 173.33 (Site Ml) with site means between 79.99 (WPipi) and 159.67 (Ml). QMCI values for single Surber samples ranged from 1.85 (Site Wml) to 9.18 (Site Ml) with site means between 2.49 (Rl) and 8.36 (Ml). For Surber samples, ANOVA yielded best estimates of MCI standard deviation Sm = 8.661 and QMCI standard deviation Sq = 0.625 with 431 degrees of freedom. Most MCI values were between 70 and 150 and QMCI values between 2 and 8. It is within these ranges that most reliance should be placed on these best estimates of index standard deviation (i.e., Sm and Sq). This restriction is not a serious limitation as, in practice, these ranges should cover all but the most polluted stony riffle sites. ZU4S where N is the sample size (i.e. number of replicates), S is the best estimate of biotic index standard deviation. DDs for MCI and QMCI were calculated by substituting N and Sm^, Sm or Sq in the equation above (Table 5). f-test method Narf et al. (1984) proposed a method based on the ttest to determine significant differences between biotic index values when there were unequal numbers of Table 5 MCI and QMCI detectable differences for between 1 and 12 replicate hand-net (MCI only) and Surber samples from stony riffles. Hand-net samples were standardised by sampling for 10 seconds and covering an area of approximately 0.5 m2. The difference in mean index values between two locations must be equal to or greater than the tabulated value below for the difference to be statistically significant. Number of replicates 1 2 3 4 5 6 7 8 9 10 11 12 Detectable difference Surber Hand-net MCI QMCI MCI 10.32 7.31 5.96 5.16 4.62 4.21 3.90 3.65 3.44 3.26 3.11 2.98 18.40 13.01 10.62 9.20 8.23 7.51 6.95 6.50 6.13 5.82 5.55 5.31 1.33 0.94 0.77 0.66 0.59 0.54 0.50 0.47 0.44 0.42 0.40 0.38 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 472 200 o o O •o 9 "i •o • ' • •••• i f i i • ' I ' ••• ••' ' • CO 150 9 .2 '•$ •Q CO a TJ 100 t» CO CO .0 0.1 0.2 0.3 0.4 0.5 0.6 (0 0.0 0.1 0.3 0.4 0.5 0.6 Downloaded by [176.9.124.142] at 04:50 06 October 2014 Water depth (m) a •a a 5> 1.0 1.5 2.0 J( O.O 0.5 1.0 1.5 2.0 200 300 400 1 Current velocity (m s' ) O •o 9 m ft •o (9 •* CO 100 200 300 400 0 100 Mean median rock diameter (mm) Fig. 5 Relationships between standardised MCI/QMCI values and water depth, current velocity, and an index of substratum size for all Surber sample data (Appendix 1). There are data from 91 site/times (523 samples) for depth and velocity and 88 site/times (466 samples) for substratum. Linear regression lines have been plotted within the range of xaxis values. Stark—Freshwater invertebrate biotic indices samples in each group. This equation (with the key to symbols adapted for the MCI and QMCI) was: test statistic = - x - x7 Downloaded by [176.9.124.142] at 04:50 06 October 2014 where: x, = sampled mean MCI or QMCI for location 1 x2 = sampled mean MCI or QMCI for location 2 «! = number of replicate samples for location 1 n2 - number of replicate samples for location 2 S = standard deviation Surber MCI (5m = 8.661) Surber QMCI (5q = 0.625) hand-net MCI ( S ^ = 4.859) The test statistic is compared with the table value of 1.645 (a = 0.1 and two-tailed test). If the test statistic is < 1.645, then the MCI (or QMCI) values do not differ significantly and do, therefore, denote similar pollution status or habitat quality. DISCUSSION The MCI (in particular) and QMCI have found widespread use throughout New Zealand by researchers, regional council, consultant, and university freshwater ecologists (e.g., Quinn & Hickey 1990; Quinn et al. 1992; Bay of Plenty Regional Council 1991, 1992; Stark 1993; F. M. Patrick, Royds Garden Ltd pers. comm.; D. Scott, University of Otago pers. coiran.). In some instances the indices probably have been calculated from a few replicate samples (often only one large hand-net sample), with accept-ance of the values generated rather than any appre-ciation of the statistical precision of index estimates. Biological monitoring often involves the collection of macroinvertebrate samples upstream and downstream of effluent discharge points or temporal comparisons of macroinvertebrate communities at sampling sites. This so-called BACI (Before-After, Control-Impact) design, first described by Green (1979), has since been extended by including spatial replication, to aid detection of many types of environmental impact that BACI designs would overlook (Underwood 1993). Sound sampling programme design is essential if the results of biomonitoring are to be interpretable. Interpretation almost always involves detecting significant changes in community composition and determining whether or not these changes can be attributed to the effects of effluent discharge (for example). This second, usually more difficult question is not the key issue here. 473 Determination of significant differences requires sample replication (so that precision can be calculated) or a knowledge of the precision likely to be obtained if prescribed methods are followed. Since one of the primary aims of the MCI is to convey complex biological information to water managers in a costeffective manner, the number of samples required to be collected should, ideally, remain low. The number of samples collected in benthic macroinvertebrate surveys should be based upon the number of replicates required in order to estimate the value of a particular benthic measure (e.g., mean density of individuals or MCI) with a desired degree of precision and risk of error, or the number required to determine if a given degree of change has occurred (again with a certain risk of error). The size of the sampling unit, the magnitude of the mean of the particular benthic measure, the degree of aggregation, and the desired precision are all factors that influence the number of replicates that should be collected (Resh & McElravy 1993). Many authors have provided formulae for calculating precision (based upon sample variances) and methods for calculating sample size (i.e., the number of replicates) from pilot survey data (Elliott 1977; Resh & McElravy 1993). In practice, the number of replicates generally is "determined by experience or intuition and then modified by cost considerations" (Resh 1979). In view of the relatively high cost of sample processing (usually between 1 and 4 hours per Surber sample), as few samples as possible are desirable. Influence of sampling method on biotic index estimation My investigations have compared the efficiency of hand-net collections and Surber sampling for biotic index calculation. Both sampling methods are widely used: 107 of 122 studies surveyed by Winterbourn (1985) used these (or similar) sampling methods. The present study has confirmed the finding of Mackey et al. (1984) that qualitative hand-net samples collect more taxa than the same number of Surber samples. This is almost certainly because hand-net samples tend to be of larger volume and collect animals from a larger area of streambed than Surber samples. Since the list of scoring taxa is fundamental to the calculation of the MCI, it follows that hand-net samples are more efficient for estimating MCI values than Surber samples (e.g., Table 5). It appears that about 20% fewer hand-net samples than Surber samples achieve similar results. Furse et al. (1981) found that 50%, 68%, and 80% of species in a series of six replicate hand-net Downloaded by [176.9.124.142] at 04:50 06 October 2014 474 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 samples were caught in the first, second, and third sample and that this was in accord with other published information. In my study, I found that the first, second, and third samples collected 55%, 69%, and 77%, respectively, of the taxa that were captured by all 12 replicates. When my data were recalculated (using data from the first six replicates from each data series only) the percentages of taxa collected (i.e., 61%, 77% and 86%) were even greater than those noted by Furseet. al (1981). MCI values, however, are less influenced by sampling effort than species richness. Whereas a single hand-net sample may collect only 55% (on average) of the taxa collected by 12 replicates, the MCI is likely to be within 15% of the 12-replicate value. At least four replicate hand-net samples, which yield MCI estimates within ± 10%, are recommended, for studies where small differences in MCI between sites or times must be detected. If precise MCI estimates (i.e., within + 10%) are to be calculated from Surber samples, then 8 to 10 replicates should be collected. QMCI values are dependent on macroinvertebrate densities as well as numbers and kinds of taxa, and can only be determined from quantitative samples. Elliott (1977) suggested that density estimates within ± 20% of the mean may be acceptable in many stream surveys (unless the aims of the investigation dictate otherwise). My data indicate that 10 or 11 replicates would be required to achieve such precision in density estimates; 7 or 8 samples if ± 50% was acceptable. Similar numbers of replicates are required for estimation of QMCI values with the same precision. Quinn & Hickey (1990), in a survey of macroinvertebrate communities in 88 New Zealand rivers, found "moderately strong" correlations between both MCI and QMCI and indicators of enrichment (such as TKN, A270F, CHLa, PAFDW). They suggested that these indices were useful for monitoring water quality, and that the MCI, which requires less effort in sample processing, was slightly more sensitive than the QMCI as an index of water enrichment. However, although Quinn & Hickey (1990) collected seven Surber samples from each site, these were combined in the field so that the MCI and QMCI values they calculated were effectively based on single samples with no indication of how precise their estimates were. The present study indicates that MCI and QMCI values determined from seven replicate Surber samples were within approximately + 1 5 and ± 25 % of the 12-sample combined values, respectively (Fig. 1 and 2). The findings of this study call into question the scientific defensibility of the interpretation of longterm monitoring programme results where a relatively low level of effort is expended on each monitoring occasion, if temporal variation in index values is accepted at face value. For example, the biological monitoring programme for Petrochem's AmmoniaUrea Plant relies upon the collection of single handnet samples from a number of monitoring sites on four occasions per year. The programme has been ongoing since September 1981 (Stark 1993). Admittedly, the hand-net samples collected are approximately three times the volume of those collected as part of the present study so it is likely that estimates are within ± 10-12% of site MCI values. Such precision appears acceptable for monitoring of this type, particularly where trends in MCI over time are given greater weight in the interpretation than individual index values (Stark 1993). Influence of water depth, current velocity, and substratum It appears unnecessary to target particular depths or velocities for MCI or QMCI determination when sampling in stony riffles (at least within the ranges of these variables that I sampled). However, the influence of substratum on index values requires further investigation. This study has concentrated on stony riffles where the substratum comprised primarily cobbles between 50 mm and 150 mm in median diameter (range: 40-300 mm, mean 94 mm). Within this range, MCI and QMCI values showed no obvious dependence on substratum. Extrapolation to other habitats (e.g., pools, backwaters, deep runs) and beyond the surveyed ranges of water depths, current velocities, and substratum would be unwise. For example, since muddy habitats support quite different macro-invertebrate communities than do stony riffles (comprising, on average, lower-scoring taxa), lower index values may be anticipated. In summary, the MCI and QMCI are useful indices of water quality and for the assessment of enrichment in stony streams (Quinn & Hickey 1990; Stark 1993). For cost-effectiveness, the MCI is recommended over the QMCI as it is more reliably estimated from fewer samples. Hand-net samples are preferred over Surber samples, with a single hand-net sample yielding MCI estimates with error of ± 10.32 MCI units (detectable difference method) or within ± 15% of the value obtained from 12 replicate samples combined. Knowledge of the precision achieved enhances the performance and scientific defensibility of biomonitoring programmes and synoptic biological surveys. Stark—Freshwater invertebrate biotic indices Downloaded by [176.9.124.142] at 04:50 06 October 2014 Water depths, current velocities, and substratum commonly encountered in stony riffle habitats appear to have little impact on index values and my results indicate that there is no need to sample specific microhabitats within riffles. Nevertheless, it may still remain prudent to minimise between-site (or time) variation in these parameters, and to limit sampling to water depths of 0.1-0.4 m, current velocities to 0.2-1.2 m s"1; and substratum median rock diameters to 60-140 mm. These suggested limits, which are within the ranges of these variables sampled during my investigations, are unlikely to impose any practical difficulties with sampling point selection. Further research into the influence of substratum type on biotic index values is desirable, with particular emphasis on extending the application of these useful tools to habitats other than stony riffles (e.g. pools, runs, sandy or muddy areas, and macrophyte beds). ACKNOWLEDGMENTS I thank the following for assistance with field work: Susan Bamfield and Jane MacGibbon (Bioresearches Ltd)— Wanganui catchment; Mace Ward (Nelson Marlborough Fish and Game Council) and Graeme Body (Water Resources Survey)—Motueka River; Yvonne Stark and Rod Asher (Cawthron Institute)—all other rivers; and the Nelson-Marlborough Regional Council for the loan of a Gurley Pygmy current meter. Some preliminary macroinvertebrate sample processing was undertaken by Susan Bamfield and Jane MacGibbon (Bioresearches Ltd), but most macroinvertebrate samples were processed by Yvonne Stark, Rod Asher, Krystyna Ponikla, Sue Cleaver, and John Kapa (Cawthron Institute). This research, which was supported by a grant from the Foundation for Science Research and Technology, owes much to the extensive macroinvertebrate database that I have been able to compile while undertaking freshwater biological consultancies. In particular, I am grateful to the following for permission to use macroinvertebrate data sets collected under contract: Dr Ian Johnstone (North Island Hydro Group Manager, Electricorp Production)—Wanganui catchment; Mr Bill Allen (Technical Services Manager, Marlborough Electric)—Wairau River; and Mr Andrew Fenemor (Water Resources Manager, Nelson Marlborough Regional Council (now Tasman District Council))—Motueka, Riwaka and Waimea catchments. I thank Dr Paul Gillespie (Cawthron Institute), Dr Mike Winterbourn (Department of Zoology, University of Canterbury) and one anonymous referee for their helpful comments on the manuscript. REFERENCES Armitage, P. D.; Moss, D.; Wright, J. F.; Furse, M. T. 1983: The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running water sites. Water research 17: 333-347. 475 Bay of Plenty Regional Council 1991: Bay of Plenty Regional Council regional monitoring network 1991. Bay of Plenty Regional Council technical report 8: 44 p. Bay of Plenty Regional Council 1992: Bay of Plenty Regional Council natural environment regional monitoring network: freshwater ecology programme riverine component 1992. Bay of Plenty Regional Council technical report 29: 87 p. Biological Monitoring Working Party 1978: Final report: assessment and presentation of the biological quality of rivers in Great Britain. Unpublished report, Department of the Environment. 37 p. Chutter, F. M. 1972: An empirical biotic index of the water quality in South African streams and rivers. Water research 6: 19-30. Elliott, J. M. 1977: Some methods for the statistical analysis of samples of benthic invertebrates. Second edition. Freshwater Biological Association scientific publication 25. 159 p. Furse, M. T.; Wright, J. F.; Armitage, P. D.; Moss, D. 1981: An appraisal of pond-net samples for biological monitoring of lotic macro-invertebrates. Water research 15: 679-689. Green, R. H. 1979: Sampling design and statistical methods for environmental biologists. John Wiley & Sons, New York. 257 p. Hilsenhoff, W. L. 1977: Use of arthropods to evaluate water quality of streams. Department of Natural Resources, Madison, technical bulletin 100. 15 p. Hilsenhoff, W. L. 1987: An improved biotic index of organic stream pollution. The Great Lakes entomologist 20: 31-39. Mackey. A. P.; Cooling, D. D.; Berrie, A. D. 1984: An evaluation of sampling strategies for qualitative surveys of macroinvertebrates in rivers, using pond nets. Journal of applied ecology 27: 515-534. Narf, R. P.; Lange, E. L.; Wildman, R. C. 1984: Statistical procedures for applying Hilsenhoff s Biotic Index. Journal of freshwater ecology 2: 441-448. Pridmore, R. D.; Roper, D. S. 1985: Comparison of the macroinvertebrate faunas of runs and riffles in three New Zealand streams. New Zealand journal of marine and freshwater research 19: 283-291. Quinn J. M.; Hickey, C. W. 1990: Characterisation and classification of benthic invertebrate communities in 88 New Zealand rivers in relation to environmental factors. New Zealand journal of marine and freshwater research 24: 387-409. Quinn, J. M.; Williamson, R. B.; Smith, R. K.; Vickers, M. L. 1992: Effects of riparian grazing and channelisation on streams in Southland, New Zealand. 2. Benthic invertebrates. New Zealand journal of marine and freshwater research 26: 259-273. Downloaded by [176.9.124.142] at 04:50 06 October 2014 476 New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 Resh, V. H. 1979: Sampling variability and life history features: basic considerations in the design of aquatic insect studies. Journal of the Fisheries Research Board of Canada 36: 290-311. Resh, V. H.; McElravy, E. P. 1993: Contemporary quantitative approaches to biomonitoring using benthic macroinvertebrates. In: Rosenberg, D. M.; Resh, V. H. ed. Freshwater biomonitoring and benthic macroinvertebrates, pp. 159-194. Chapman & Hall, New York, London. Rosenberg, D. M.; Resh V. H. 1992: Introduction to freshwater biomonitoring and benthic macroinvertebrates. In: Rosenberg, D. M ; Resh, V. H. ed. Freshwater biomonitoring and benthic macroinvertebrates, pp. 1-9. Chapman & Hall, New York, London. Stark, J. D. 1993: Ammonia-Urea Plant biomonitoring-Is it defensible? In: Boyce, W.; Ericksen, N.; Hingley, N. ed. Proceedings of the Regional Resource Futures Conference, Hamilton (27-29 August 1991). Centre for Environmental and Resource Studies, University of Waikato, New Zealand, pp. 343-350. Stark, J. D. 1985: A macroinvertebrate community index of water quality for stony streams. Water & Soil miscellaneous publication 87: 53 p. Stark, J. D. 1988: Macroinvertebrate communities in the Branch and Wairau Rivers (July-November 1987). Unpublished Cawthron Institute report prepared for Marlborough Electric Power Board. 31 p. + Appendices. Stark, J. D. 1989: Macroinvertebrate communities in the Wanganui catchment. Unpublished Cawthron Institute report prepared for the Electricity Corporation of New Zealand. 27 p. + Appendices. Stark, J. D. 1990: Macroinvertebrate communities in the Motueka and Riwaka catchments. Unpublished Cawthron Institute report prepared for NelsonMarlborough Regional Council. 40 p. + 14 Appendices. Wilkinson, L.; Hill, M.; Welna, J. P; Birkenbeuel, G. K. 1992: SYSTAT for Windows: Statistics, Version 5 Edition. Evanston, IL: SYSTAT Inc. Taranaki Catchment Commission 1984: Freshwater biology: Taranaki Ring Plain water resources survey. Taranaki Catchment Commission, Stratford. 196 p. + Appendices. Underwood, A. J. 1993: The mechanics of spatially replicated sampling programmes to detect environmental impacts in a variable world. Australian journal of zoology 18: 99-116. Winterbourn, M. J. 1981: The use of aquatic invertebrates in studies of stream water quality. In: A review of some biological methods for the assessment of water quality with special reference to New Zealand-Part 2. Water & Soil technical publication 22: 5-16. Winterbourn, M. J. 1985: Sampling stream invertebrates. In: Pridmore, R. D.; Cooper, A. B. ed. Biological monitoring in freshwaters: proceedings of a seminar. Ministry of Works and Development for the National Water and Soil Conservation Authority. Water & Soil miscellaneous publication 83. 477 Stark—Freshwater invertebrate biotic indices Downloaded by [176.9.124.142] at 04:50 06 October 2014 APPENDIX 1 Macroinvertebrate Surber sampling site locations, dates, and numbers of replicates collected in the Wanganui, Wairau, Motueka, and Waimea River catchments. Site code Grid Reference NZMS 260 Wanganui River catchment Whpti Whakapapaiti Stream at SH47 Whpni Whakapapanui Stream at SH47 Whlnus Whakapapa River upstream of intake S19 236 255 S19 269 256 S19 234 288 Whlnds WhFb Whakapapa River downstream of intake Whakapapa River at Footbridge recorder S19 233 288 S19 225 292 WhOioF WhOio WhOwh Whakapapa River at Oio Farms Whakapapa River at Oio Whakapapa River at Owhango S19 195 327 S19 172 370 S19 170 415 WhKak Whakapapa River at Kakahi S19 188 488 WSH47 WWanRd WWhpki WPiri WChGr WTeMa WPipi WJeru Puke Manus Mang Wanganui River at SH47 Wanganui River at Wanganui Road Wanganui River at Whangapeki Bridge Wanganui River at Piriaka Wanganui River at Cherry Grove Wanganui River at Te Maire Wanganui River at Pipiriki Wanganui River at Jerusalem Pukehinau Stream at old mill site Mangatepopo Stream upstream of intake Manganuiateao River east of Raetahi Wairau River catchment (Marlborough) Wu Wairau River downstream of Woolshed Strm confluence Date Number of replicates T19 337 354 S19 297 408 S19 212 476 S18 130513 S18 058 545 S19 997 491 R21 859 897 R21 890 809 S19 263 364 T19 312 361 S20 966 044 21 Dec 88 21 Dec 88 20 Dec 88 22 Mar 89 20 Dec 88 21 Dec 88 22 Mar 89 22 Mar 89 20 Dec 88 19 Dec 88 23 Mar 89 19 Dec 88 21 Mar 89 20 Mar 89 15 Mar 89 21 Mar 89 21 Mar 89 25 May 89 23 May 89 24 May 89 24 May 89 20 Mar 89 20 Mar 89 24 May 89 12 12 12 12 8 12 12 12 12 12 12 12 12 9 12 12 9 6 6 6 6 9 6 6 N29 037 272 08 Jul 87 15 Motueka catchment (Nelson) Br Brooklyn at DSIR BG1 Blue Glen Creek at road culvert B1 Baton River at Baton Flats B2 Baton River at Loveridge's Ford Dl Donald Creek in beech forest D2 Donald Creek at Tui E Ellis River 800m above Baton River confluence G Graham River at main road bridge Ml Motueka River at Blue Glen N26 079 122 N28 016 532 M 2 7 869874 N27 936 923 M28 881 592 M28 872 628 M 2 7 852 898 N27 961 994 N28 028 528 M2 Motueka River at Golden Downs N28 992 647 M3 Motueka River above Tadmor River confluence N27 933 827 28 Sep 87 24 Nov 87 22 20 27 Feb 89 20 Feb 89 21 Feb 89 28 Feb 89 27 Feb 89 27 Feb 89 28 Feb 89 28 Feb 89 31 May 88 23 Aug 88 17 Nov 88 17 Feb 89 05 Jul 92 31 May 88 23 Aug 88 17 Nov 88 17 Feb 89 31 May 88 25 Aug 88 17 Nov 88 10 Feb 89 05 Jul 92 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 (Continued overleaf) New Zealand Journal of Marine and Freshwater Research, 1993, Vol. 27 478 Appendix 1 (Continued) Grid Reference NZMS 260 Downloaded by [176.9.124.142] at 04:50 06 October 2014 Site code M4 Motueka River at Woodstock N27 951944 M5 Motueka River at Woodman's Corner N27 067 095 Mp l Mp2 P Rl Motupiko River above Korere Motupiko River at Quinney's Bush Pearse River at picnic area Riwaka River below Moss Bush N28 918 599 N28 947 719 N27 923 969 N26 041175 R2 Ra St Tl T2 Wl W2 W3 Riwaka River at Little's Rainy River at ford Stanley Brook at Barker's Tadmor River at Tui Road bridge Tadmor River at Rakau footbridge Wangapeka River above Rolling River confluence Wangapeka River below Nettleton's Wangapeka River at Walter Peak N26 028 183 N29 938 484 N27 949879 M28 869 632 N28 930 781 M28 749 738 M28 837 785 N27 901 850 Waimea River catchment (Nelson) Wml Waimea River 200m downstream of Appleby Bridge N27 209 887 Wm2 Waimea River at Challies Island N27 204 868 Wrl Wairoa River off Clover Road West N27 194 828 Wr2 Wairoa River at Gorge N28 210 791 Wi Wai-iti River off Livingston Road N27 188 831 Date 01 Jun 88 17 Nov 88 16 Feb 89 05 Jul 92 01Jun 88 25 Aug 88 17 Nov 88 10 Feb 89 07 Jul 92 20 Feb 89 20 Feb 89 28 Feb 89 01Jun 88 24 Aug 88 17 Nov 88 10 Feb 89 07 Jul 92 27 Feb 89 20 Feb 89 28 Feb 89 27 Feb 89 21 Feb 89 21 Feb 89 21 Feb 89 21 Feb 89 05 Jul 92 26 Apr 88 30 Apr 92 12 May 92 26 Apr 88 30 Apr 92 26 Apr 88 30 Apr 92 26 Apr 88 30 Apr 92 26 Apr 88 30 Apr 92 Number of replicates
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