{"Bibliographic":{"Title":"Benthic invertebrates and sediment characteristics in subtidal habitat at Rice Island, Columbia River Estuary, December 1991 and March 1992","Authors":"","Publication date":"1992","Publisher":""},"Administrative":{"Date created":"08-16-2023","Language":"English","Rights":"CC 0","Size":"0000020446"},"Pages":["P\nBenthic Invertebrates\nand Sediment Characteristics\nin Subtidal Habitat at Rice Island,\nColumbia River Estuary,\nDecember 1991 and March 1992\nCenter\nLibrary\nService\nFisheries\nby\nSusan A. Hinton,\nNOAA,\nE.\nBoulevard,\nMontale\nRobert L. Emmett,\n2725\n98112\nWA\nSeattle,\nand George T. McCabe, Jr.\nOctober 1992\nZONE\nCOASTAI\nAND\nSTUDIES","BENTHIC INVERTEBRATES AND SEDIMENT CHARACTERISTICS\nIN SUBTIDAL HABITAT AT\nRICE ISLAND,\nCOLUMBIA RIVER ESTUARY,\nDECEMBER 1991 AND MARCH 1992\nby\nSusan A. Hinton\nRobert L. Emmett\nand\nGeorge T. McCabe, Jr.\nFinal Report\nFunded by\nU.S. Army Corps of Engineers\nPortland District\nP.O. Box 2946\nPortland, Oregon 97208\n(Contract E96920018)\nand\nCoastal Zone and Estuarine Studies Division\nNorthwest Fisheries Science Center\nNational Marine Fisheries Service\nNational Oceanic and Atmospheric Administration\n2725 Montlake Boulevard East\nSeattle, Washington 98112\nOctober 1992","CONTENTS\nPage\nINTRODUCTION\n1\nMETHODS\n2\nSampling\n2\nData Analyses\n5\nBenthic Invertebrates\n5\nSediments\n5\nRESULTS\n6\nBenthic Invertebrates\n6\nSediments\n8\nDISCUSSION\n8\nACKNOWLEDGMENTS\n12\nLITERATURE CITED\n14\nAPPENDIX\n15","INTRODUCTION\nThe U.S. Army Corps of Engineers (COE) Portland District is\nresponsible for annually dredging and disposing of more than\n2 million yd³ (1.5 million m³) of bottom sediments from the\nnavigation channel between River Miles (RM) 4.4 and 28.8 in the\nColumbia River estuary. Existing island and shoreline dredged-\nmaterial disposal sites are nearly filled to capacity, and\noptions for new disposal sites for such large volumes of dredged\nmaterial are extremely limited. One potential disposal site is\nthe area just north of Rice Island, an island created with\ndredged material. Proposals for expanding Rice Island with\ndredged material include creating a 10,000-ft (3,048-m) by 500-\nto 1,000-ft (152- to 305-m) spit to the north of the present\nisland. The south side of the proposed spit would be about 1,000\nft from the island, creating an island-spit configuration similar\nto that at Miller Sands, which is slightly upstream from Rice\nIsland.\nMajor concerns associated with new dredged-material disposal\nsites, especially when creating islands, are the effects of such\nactivities on aquatic communities. Therefore, in 1991, the COE\ncontracted the National Marine Fisheries Service (NMFS) to\nconduct surveys in July and September to assess the aquatic\ncommunities just north of Rice Island and at Miller Sands (Hinton\net al. 1992) . Subsequently, the COE contracted NMFS to conduct\ntwo additional but limited benthic surveys at Rice Island in\nDecember 1991 and March 1992. Data from the two limited surveys","2\nare presented in this report, which supplements the initial\nreport (Hinton et al. 1992) .\nMETHODS\nBenthic invertebrate and sediment samples were collected at\nsix previously established stations in the subtidal area north of\nRice Island in December 1991 and March 1992 (Fig. 1) . These\nstations were reoccupied using the Global Positioning System (see\nAppendix Table 1 for station locations) .\nSampling\nEleven core samples were taken at each station with a\npolyvinyl chloride (PVC) coring device with an inside diameter of\n3.85 cm and a penetrating depth of 15 cm, and which collected a\n174.6-cm3 sample (Fig. 2) . Samples were collected by scuba\ndivers since all stations were subtidal. Ten core samples were\nplaced in labeled jars and preserved in a buffered formaldehyde\nsolution (>4%) containing rose bengal, a protein stain. In the\nlaboratory, samples were washed with water through a 0.5-mm\nscreen. All invertebrates were sorted from the preserved sample,\nidentified to the lowest practical taxonomic level (usually\nspecies), and counted. The specimens were then stored in labeled\nvials containing 70% ethyl alcohol. The eleventh core sample was\nsaved in a labeled plastic bag and refrigerated for analysis of\nsediment grain size and total volatile solids by the COE North\nPacific Division Materials Laboratory, Troutdale, Oregon.","Figure 1. . - - Sampling locations from benthic invertebrates and sediment at Rice Island,\n500\n1,500\n400\nkilometers\n4\n1,000\n15\n2\n35\n25\n55\n45\n300\nMeters\n0\nFeet\n200\n500\nOregon\n100\nMillion Sands\n0\n0\nRice Isian\nWashington\n14\n24\n34\n54\n44\nColumbia\nOcean\nPacific\nColumbia River estuary, 1991-1992. .\n23\n13\nRice Island\n33\n53\n43\nN\noccupied in Jul, Sep, and Dec 1991 and\nBenthic invertebrate and sediment site\nBenthic invertebrate and sediment site\n12\n22\n32\n52\n42\noccupied in Jul and Sep 1991\n21\n31\n11\n41\n51\nMar 1992","4\nVent\nTop cap\nClear plastic\nplate\nString\nPVC tubing\n15 cm\n3.85 cm\nBottom cap\nFigure 2. . -- PVC coring device used to collect benthic invertebrate\nand sediment samples in the Columbia River estuary.","5\nData Analyses\nBenthic Invertebrates\nThe 10 benthic invertebrate replicates from each station\nallowed calculation of a mean number/m2 and standard deviation\nfor each species, and total mean number/m² and standard deviation\nfor each station.\nTwo community structure indices, diversity and equitability,\nwere calculated for each sampling station. Diversity was\ncalculated using the Shannon-Wiener function (H) (Krebs 1978) .\ni=1\nwhere Pi = Xa/n (Xa is the number of individuals of a particular\nspecies in the sample, and n is the total number of all\nindividuals in the sample) and S = number of species.\nEquitability (E) , the second community structure index,\nmeasures the proportional abundances among the various species in\na sample (Krebs 1978). E ranges from 0.00 to 1.00, with 1.00\nindicating all species in the sample are numerically equal.\nE = H/log2s\nwhere H = Shannon-Wiener function and S = number of species.\nSediments\nMedian grain size (mm) , percent silt/clay, and percent\nvolatile solids were calculated for each station.","6\nRESULTS\nBenthic Invertebrates\nFor December 1991, 11 benthic invertebrate taxa were\nidentified at the six stations at Rice Island. Benthic\ninvertebrate densities at all stations exceeded 117,000\norganisms/m2 with the exception of Station 33 (3,866 organism/m²\n(Table 1, Appendix Table 2). The highest density was 199,458\norganisms/m at Station 51. Diversity ranged from 0.73\n(Station 51) to 1.60 (Station 33) . Equitability ranged from 0.26\n(Station 51) to 0.80 (Station 33) but was usually 0.40 or less.\nThe lower diversity values resulted from fewer taxa or low\nequitability (i.e., unequal proportional abundances among the\ntaxa). The higher equitability value at Station 33 indicated the\ntaxa were more equally distributed.\nFor March 1992, 11 invertebrate taxa were identified at Rice\nIsland. Benthic invertebrate densities ranged from 2,319\norganisms/m2 (Station 33) to 182,879 organisms/m2 (Station 53) .\n.\nMost stations exceeded 130,000 organisms/m2 (Table 1, Appendix\nTable 2) Diversity ranged from 0.81 (Station 53) to 1.52\n(Station 55) and equitability ranged from 0.33 (Station 31) to\n0.66 (Station 55). Overall, diversity and equitability values in\nMarch were low, indicating few taxa and the unequal proportional\nabundances of these taxa.\nThe amphipod Corophium salmonis was the dominant benthic\ninvertebrate at Rice Island during the December 1991 and March\n1992 surveys, comprising 82 and 80% of the total number of","7\nTable 1. Summary of benthic invertebrates at Rice Island,\nColumbia River estuary, December 1991 and March 1992.\nDepths are corrected to mean lower low water.\nEquitability\nDiversity\nStandard\nNumber\nNumber\nStation\nDepth\n(E)\n/m2\ndeviation\n(H)\nof taxa\n(m)\nDECEMBER 1991\n0.40\n1.13\n28,685\n140,531\n0.4\n7\n31\n0.26\n0.73\n61,261\n199,458\n3.0\n7\n51\n0.80\n1.60\n3,394\n3,866\n3.5\n4\n33\n0.30\n0.79\n42,841\n117,682\n1.7\n6\n53\n0.36\n44,308\n1.08\n162,091\n3.3\n8\n35\n0.39\n0.90\n36,585\n177,639\n2.4\n5\n55\nMARCH 1992\n0.33\n22,124\n1.00\n130,996\n0.4\n8\n31\n0.38\n1.13\n24,780\n158,054\n8\n51\n3.0\n0.54\n1.26\n1,571\n2,319\n3.5\n5\n33\n0.35\n0.81\n26,989\n182,879\n1.7\n5\n53\n0.36\n1.07\n33,003\n181,934\n3.3\n8\n35\n0.66\n1.52\n2,657\n10,050\n2.4\n5\n55","8\norganisms per survey (Table 2) Other abundant taxa found in the\nstudy area were Turbellaria, Oligochaeta, the bivalve Corbicula\nfluminea, and Heleidae (Ceratopogonidae) larvae.\nSediments\nThe dominant median grain size in the Rice Island study area\nduring December 1991 and March 1992 was fine sand (0.125 to\n<0.25 mm in diameter) (Table 3) Very fine sand (0.0625 to\n<0.125 mm in diameter) occurred at Stations 31 and 51 in March\n1992. The amount of silt/clay for each station ranged from 0.0\n(Station 33) to 14.5% (Station 51) during the two surveys.\nPercent volatile solids per station for both surveys was never\ngreater than 1.7%, and usually 1.0% or less.\nDISCUSSION\nBenthic invertebrate densities at Stations 31, 51, 53, 35,\nand 55 in December 1991 and Stations 31, 51, 53, and 35 in March\n1992 at Rice Island were the highest ever reported in the\nestuary. Generally, benthic invertebrate densities in December\n1991 and March 1992 were much higher than densities at the same\nstations in July and September 1991 (Fig. 3; Hinton et al. 1992) .\nThe dramatic increase in abundance of Corophium salmonis numbers\nwas the cause of the incredibly high invertebrate densities in\nthe area. Peak densities of C. salmonis typically occur during\nDecember through March (Emmett et al. 1986) .\nIn three out of the four surveys, benthic invertebrate\ndensities were the lowest at Station 33 (Fig. 3) In addition,","9\nTable 2. --Abundance of major benthic invertebrate taxa at Rice\nIsland, Columbia River estuary, December 1991 and March\n1992. All values are mean numbers/m² data from six\nstations were combined for each survey.\nDec 91\nMar 92\nTaxon\n11,654\n7,101\nTurbellaria\n7,817\n10,938\nOligochaeta\nPolychaeta\n115\n158\nNeanthes limnicola\nBivalvia\n2,849\nCorbicula fluminea\n1,847\n29\n200\nOstracoda\nAmphipoda\nCorophium salmonis\n109,793\n88,533\nCorophium spinicorne\n72\n86\nInsecta\n14\n29\nChironomidae larvae\n2,176\n1,117\nHeleidae larvae\n14\n14\nMiscellaneous\n14\n14\nOthers\n111,039\nTotal\n133,544","10\nTable 3. Sediment characteristics at Rice Island, Columbia River\nestuary, December 1991 and March 1992. Depths are\ncorrected to mean lower low water.\nStation\nDepth\nMedian grain\nPercent\nPercent\n(m)\nsize (mm)\nsilt/clay\nvolatile solids\nDECEMBER 1991\n31\n0.4\n0.1340\n1.3\n1.0\n51\n3.0\n0.1340\n5.8\n1.0\n33\n3.5\n0.2500\n0.0\n0.5\n53\n1.7\n0.1768\n1.6\n0.5\n35\n3.3\n0.2176\n1.5\n0.7\n55\n2.4\n0.2176\n1.6\n0.8\nMARCH 1992\n31\n0.4\n0.1088\n7.3\n1.0\n51\n3.0\n0.0769\n14.5\n1.7\n33\n3.5\n0.2500\n0.2\n0.5\n53\n1.7\n0.1539\n10.3\n0.7\n35\n3.3\n0.1436\n9.5\n0.9\n55\n2.4\n0.2333\n0.3\n0.5","11\n200\n180\n160\n140\n120\n100\n80\n60\n40\n20\n0\n31\n51\n33\n53\n35\n55\nStation\n200\n180\n160\n140\n120\n100\n80\n60\n40\n20\n0\n31\n51\n33\n53\n35\n55\nStation\nJuly 1991\nSeptember 1991\nDecember 1991\nMarch 1992\nMean number of benthic invertebrates/m2 and mean number of\nFigure 3.\nCorophium salmonis m² for six stations sampled at Rice Island,\nColumbia River estuary, 1991-1992.","12\nmedian grain size was the highest at Station 33 in these three\nsurveys (Fig. 4)\nMedian grain size and percent volatile solids remained\nfairly consistent when comparing the six stations occupied in\nJuly, September, and December 1991 and March 1992. Percent\nsilt/clay varied more than median grain size or percent volatile\nsolids, but was never exceedingly high (Fig. 4)\nThis report does not constitute NMFS's formal comments under\nthe Fish and Wildlife Coordination Act or the National\nEnvironmental Policy Act.\nACKNOWLEDGMENTS\nWe thank Loretta Clifford for her assistance in analyzing\nthe biological samples. The COE Portland District conducted the\nsediment analysis.","13\n0.3\n0.25\n0.2\n0.15\n0.1\n0.05\n0\n31\n51\n33\n53\n35\n55\nStation\n16\n14\n12\n10\n8\n6\n4\n2\n0\n31\n51\n33\n53\n35\n55\nStation\n1.8\n1.6\n1.4\n1.2\n1\n0.8\n0.6\n0.4\n0.2\n0\n31\n51\n33\n53\n35\n55\nStation\nMarch 1992\nJuly 1991\nSeptember 1991\nDecember 1991\n- Sediment characteristics for six stations sampled at\nFigure 4.\nRice Island, Columbia River estuary, 1991-1992.","14\nLITERATURE CITED\nEmmett, R. L. , G. T. McCabe, Jr., T. C. Coley, R. J. McConnell,\nand W. D. Muir.\n1986. Benthic sampling in Cathlamet Bay, Dregon--1984.\nReport to U.S. Army Corps of Engineers, Contract\nDACW57-84-F-0348, 11 p. plus appendices. (Available from\nNorthwest Fisheries Science Center, 2725 Montlake Blvd. E.\nSeattle, WA 98112-2097.)\nHinton, S. A., R. L. Emmett, and G. T. McCabe, Jr.\n1992. Fishes, shrimp, benthic invertebrates, and sediment\ncharacteristics in intertidal and subtidal habitats at Rice\nIsland and Miller Sands, Columbia River estuary. Report to\nU.S. Army Corps of Engineers, Contract E96910025, 53 p.\n(Available from Northwest Fisheries Science Center, 2725\nMontlake Blvd. E., Seattle, WA 98112-2097.)\nKrebs, C. J.\n1978. Ecology: the experimental analysis of distribution\nand abundance. Harper and Row. New York, NY. 678 p.","15\nAPPENDIX","16\nAppendix Table 1. --Station locations at Rice Island, Columbia\nRiver estuary, 1991-1992.\nBenthic/sediment\nLatitude\nLongitude\nstation\n31\n46°15.245\n123°43.032\n51\n15.401\n43.150\n33\n46°15.442\n123°42.108\n53\n15.600\n42.194\n35\n46°15.464\n123°41.434\n55\n15.591\n41.550","17\nAppendix Table 2. --Summary of benthic invertebrate surveys (by\nstation) during December 1991 and March 1992\nat Rice Island, Columbia River estuary.\nSample size: 10\nDate: 19 Dec 91\nStation: 31\nStandard\nTotal\nFrequency of\nMean\nTaxon\nnumber\ndeviation\nnumber\noccurrence\n/m2\n/m2\n(%)\n6,920\n187\n100\n16,063\nTurbellaria\n515\n601\n6\n50\nNeanthes limnicola\n13,658\n4,967\n159\n100\nOligochaeta\n2,361\n30\n100\n2,577\nCorbicula fluminea\n86\n272\n1\n10\nOstracoda\n23,656\n1,252\n100\n107,546\nCorophium salmonis\n86\n272\n1\n10\nCorophium spinicorne\nNumber of taxa:\n7\nStandard deviation/sample:\n33\nMean number/sample:\n164\nStandard deviation: 28,685\nMean number/m²: 140,531\nH = 1.13\nE = 0.40\nSample size:\n10\nDate: 19 Dec 91\nStation: 51\nStandard\nFrequency of\nMean\nTotal\nTaxon\ndeviation\nnumber\nnumber\noccurrence\n/m2\n/m2\n(%)\n9,964\n10,837\n116\n100\nTurbellaria\n362\n2\n20\n172\nNeanthes limnicola\n4,973\n14,431\n168\n100\nOligochaeta\n887\n12\n80\n1,031\nCorbicula fluminea\n52,409\n173,516\n2,020\n100\nCorophium salmonis\n415\n3\n30\n258\nCorophium spinicorne\n86\n272\n1\n10\nEphemeroptera\nNumber of taxa:\n7\nStandard deviation/sample:\n71\nMean number/sample:\n232\nStandard deviation: 61,261\nMean number/m²: 199,458\nE = 0.26\nH = 0.73","18\nStation: 33\nDate: 19 Dec 91\nSample size:\n10\nTaxon\nTotal\nFrequency of\nMean\nStandard\nnumber\nnumber\ndeviation\noccurrence\n/m²\n(%)\n/m²\nTurbellaria\n4\n20\n344\n724\nOligochaeta\n10\n60\n859\n992\nCorophium salmonis\n5\n40\n430\n607\nHeleidae larvae\n26\n70\n2,233\n2,298\nNumber of taxa:\n4\nMean number/sample:\n5\nStandard deviation/sample:\n4\nMean number/m²:\n3,866\nStandard deviation: 3,394\nH = 1.60\nE = 0.80\nStation: 53\nDate: 19 Dec 91\nSample size:\n10\nFrequency of\nTaxon\nTotal\nMean\nStandard\nnumber\nnumber\ndeviation\noccurrence\n(%)\n/m2\n/m2\nTurbellaria\n39\n90\n3,350\n2,638\nOligochaeta\n114\n100\n9,793\n4,691\nCorbicula fluminea\n28\n90\n2,405\n2,173\nCorophium salmonis\n1,182\n100\n101,533\n40,045\nCollembolla\n1\n10\n86\n272\nHeleidae larvae\n6\n50\n515\n601\nNumber of taxa:\n6\nStandard deviation/sample:\nMean number/sample:\n137\n50\nMean number/m2: 117,682\nStandard deviation: 42,841\nH = 0.79 E = 0.30","19\nStation: 35\nDate: 19 Dec 91\nSample size:\n10\nFrequency of\nTaxon\nTotal\nMean\nStandard\nnumber\nnumber\ndeviation\noccurrence\n/m2\n/m2\n(%)\nTurbellaria\n206\n100\n17,695\n5,496\nOligochaeta\n70\n100\n6,013\n3,265\nCorbicula fluminea\n34\n90\n2,921\n2,150\nOstracoda\n1\n10\n86\n272\nCorophium salmonis\n1,507\n100\n129,450\n40,974\nCorophium spinicorne\n1\n10\n86\n272\nHeleidae larvae\n67\n100\n5,755\n2,397\nChironomidae larvae\n1\n10\n86\n272\nNumber of taxa:\n8\nMean number/sample:\nStandard deviation/sample:\n189\n52\nMean number/m²: 162,091\nStandard deviation: 44,308\nH = 1.08\nE = 0.36\nSample size: 10\nStation: 55\nDate: 19 Dec 91\nTotal\nFrequency of\nMean\nStandard\nTaxon\nnumber\nnumber\ndeviation\noccurrence\n/m2\n/m²\n(%)\n262\n100\n22,506\n13,749\nTurbellaria\nOligochaeta\n25\n80\n2,148\n1,777\n2,148\n1,682\nCorbicula fluminea\n25\n90\nCorophium salmonis\n1,703\n100\n146,286\n31,193\n3,316\nHeleidae larvae\n53\n80\n4,553\nNumber of taxa:\n5\nStandard deviation/sample:\n43\nMean number/sample:\n207\nStandard deviation: 36,585\nMean number/m2:\n177,639\nH = 0.90\nE = 0.39","20\nStation: 31\nDate: 17 Mar 92\nSample size:\n10\nTaxon\nTotal\nFrequency of\nMean\nStandard\nnumber\noccurrence\nnumber\ndeviation\n(%)\n/m²\n/m²\nTurbellaria\n116\n100\n9,964\n5,436\nOligochaeta\n123\n100\n10,566\n4,706\nCorbicula fluminea\n41\n90\n3,522\n2,235\nOstracoda\n4\n40\n344\n444\nCorophium salmonis\n1,238\n100\n106,343\n20,371\nCorophium spinicorne\n1\n10\n86\n272\nHeleidae larvae\n1\n10\n86\n272\nChironomidae larvae\n1\n10\n86\n272\nNumber of taxa:\n8\nMean number/sample:\n153\nStandard deviation/sample:\n26\nMean number/m²: 130,996\nStandard deviation: 22,124\nH = 1.00\nE = 0.33\nStation: 51\nDate: 17 Mar 92\nSample size:\n10\nTaxon\nTotal\nFrequency of\nMean\nStandard\nnumber\nnumber\noccurrence\ndeviation\n(%)\n/m²\n/m²\nTurbellaria\n145\n100\n12,455\n5,284\nNeanthes limnicola\n7\n70\n601\n415\nOligochaeta\n262\n100\n22,506\n8,482\nCorbicula fluminea\n16\n80\n1,374\n1,160\nOstracoda\n10\n40\n859\n1,215\nCorophium salmonis\n1,398\n100\n120,087\n16,252\nCorophium spinicorne\n1\n10\n86\n272\nHeleidae larvae\n1\n10\n86\n272\nNumber of taxa:\n8\nMean number/sample:\n184\nStandard deviation/sample:\n29\nMean number/m²:\n158,054\nStandard deviation: 24,780\nH = 1.13\nE = 0.38","21\nStation: 33\nDate: 17 Mar 92\nSample size:\n10\nTaxon\nTotal\nFrequency of\nMean\nStandard\nnumber\nnumber\ndeviation\noccurrence\n(%)\n/m2\n/m²\nTurbellaria\n1\n10\n86\n272\nOligochaeta\n4\n40\n344\n444\nHeleidae larvae\n20\n90\n1,718\n1,145\nChironomidae larvae\n1\n10\n86\n272\nHydracarina\n1\n10\n86\n272\nNumber of taxa:\n5\nMean number/sample:\n3\nStandard deviation/sample:\n2\nMean number/m²:\n2,319\nStandard deviation: 1,571\nH = 1.26\nE = 0.54\nStation: 53\nDate: 17 Mar 92\nSample size:\n10\nTaxon\nTotal\nFrequency of\nMean\nStandard\nnumber\nnumber\ndeviation\noccurrence\n/m²\n(%)\n/m²\nTurbellaria\n77\n100\n6,614\n4,688\nOligochaeta\n137\n100\n11,768\n4,809\nCorbicula fluminea\n84\n100\n7,216\n3,781\nCorophium salmonis\n1,829\n100\n157,109\n22,940\nCorophium spinicorne\n2\n20\n172\n362\nNumber of taxa:\n5\nMean number/sample:\n213\nStandard deviation/sample:\n31\nMean number/m2: 182,879\nStandard deviation: 26,989\nH =\n0.81\nE = 0.35","22\nSample size:\n10\nDate: 17 Mar 92\nStation: 35\nTotal\nFrequency of\nStandard\nMean\nTaxon\nnumber\nnumber\ndeviation\noccurrence\n/m2\n/m²\n(%)\n13,314\n7,224\n155\n100\nTurbellaria\n30\n344\n601\nNeanthes limnicola\n4\n19,929\n5,637\n232\n100\nOligochaeta\n4,639\n3,245\n54\n100\nCorbicula fluminea\n32,440\n1,668\n100\n143,280\nCorophium salmonis\n2\n10\n172\n543\nCorophium spinicorne\n2\n20\n172\n362\nHeleidae larvae\n272\n1\n10\n86\nEphemeroptera\nNumber of taxa:\n8\nStandard deviation/sample:\n38\nMean number/sample:\n212\nStandard deviation: 33,003\nMean number/m²: 181,934\nH = 1.07\nE = 0.36\nSample size:\n10\nDate: 17 Mar 92\nStation: 55\nFrequency of\nStandard\nTotal\nMean\nTaxon\nnumber\nnumber\ndeviation\noccurrence\n/m2\n/m2\n(%)\n172\n362\n2\n20\nTurbellaria\n6\n40\n515\n724\nOligochaeta\n444\n4\n40\n344\nCorbicula fluminea\n4,381\n2,122\n51\n100\nCorophium salmonis\n54\n100\n4,639\n2,333\nHeleidae larvae\nNumber of taxa:\n5\nStandard deviation/sample:\n3\nMean number/sample:\n12\nStandard deviation:\n2,657\nMean number/m²:\n10,050\nE = 0.66\nH = 1.52"]}