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<br />Table 3 Environmental variables having a significant
<br />regression with detrended correspondence analyses (OCA)
<br />axis 1 and 2 scores
<br />
<br />00073S
<br />
<br />Invertebrates of the South Ptatte River 447
<br />
<br />than plains/tributary and plains/downstream from
<br />point-source sites (Duncan's multiple range test,
<br />P < 0,05),
<br />The taxonomic composition of invertebrates differed
<br />among site groups (Table 2), Only six taxa occurred in
<br />all four site groups, which included two mayflies (Baetis
<br />tricaudatus and Tricorythodes minutus), one blackfly
<br />(Simulium sp,), and three chironomid taxa (Cricotopus
<br />trifascia, Orthodadius sp, and Polypeditum sp,) (Table 2),
<br />Two families of mayflies (Leptophlebiidae and
<br />Ephemerellidae), five families of Plecoptera (Pteronar-
<br />cyidae, Nemouridae, Capniidae, Perlidae, and Perlodi-
<br />dae), seven families of Trichoptera (Philopotamidae,
<br />Psychomyiidae, Rhyacophilidae, Glossosomatidae,
<br />Brachycentridae, Lepidostomatidae and Helicopsychi-
<br />dae), two families of Diptera (Deuterophlebiidae and
<br />Tipulidae), one subfamily of Chironomidae (Diamesi-
<br />nae), and Lepidoptera were collected only in the moun-
<br />tains, Planaria (Turbellaria), Oligochaeta, leeches
<br />(Hirudinea), snails (Physetla sp,), Isopoda, Amphipoda,
<br />Caenidae (Ephemeroptera), and Psychodidae (Diptera)
<br />were collected only in the plains region (Table 2), In
<br />the order Trichoptera, Arctopsyche grandis was collected
<br />only in mountain sites, and Cheumatopsyche sp. was
<br />collected only in the plains region,
<br />Relative abundance of invertebrate orders and non-
<br />insects varied among site groups (Fig, 5), Diptera and
<br />Ephemeroptera composed 69% or more of relative
<br />abundance at all site groups (Fig, 5) and Trichoptera
<br />was the third most abundant group at all site groups
<br />except for the plains/downstream from point-source
<br />sites_ Plecoptera and Coleoptera composed 2% of the
<br />relative abundance in mountain sites but were rare
<br />(< 0,2%) or absent in plains sites (Fig, 5, Table 2), In
<br />contrast, non-insects composed 2% or more (2% for
<br />plains/tributary, 3% for plains/braided channel, 30%
<br />for plains/ downstream from point-source) of the relat-
<br />ive abundance in plains sites but were rare (< 0.2%) in
<br />mountain sites. Relative abundance of Ephemeroptera
<br />increased in plains/braided channel and plains/tribu-
<br />tary sites, Plecoptera and Trichoptera were not collected
<br />at the plains/ downstream from point-source sites.
<br />Composition of functional feeding groups also
<br />varied among site groups (Fig, 6), Collector- gatherers
<br />were the dominant functional feeding-group in all site
<br />groups (Fig, 6), Functional feeding group composition
<br />for mountain and plains/braided channel sites were
<br />similar; collector-gatherers, collector-filterers, and
<br />shredders composed 93.5-94,6% of the total, and
<br />
<br />Environmental variable
<br />
<br />r"
<br />
<br />p
<br />
<br />DCA axis 1
<br />PhYSical characteristics
<br />Drainage area""
<br />Altitude*
<br />Sinuosity
<br />Slope""
<br />Stream order
<br />Mean substrate size""
<br />Water temperature
<br />
<br />Surface~water chemistry
<br />Specific conductance
<br />Nitrate + nitrite concentrationst
<br />Nitrite concentrationst
<br />Organic N + ammonia
<br />concentrationst
<br />Ammonia concentrationst
<br />Total phosphorus concentrationst
<br />
<br />Hyporheic-water chemistry
<br />Nitrate + nitrite concentrationst
<br />
<br />DCA axis 2
<br />Physical characterstics
<br />Channel width
<br />Mean phi
<br />
<br />Surface~water chemistry
<br />Nitrate + nitrite concentrationst
<br />Nitrite concentrationst
<br />Ammonia concentrationst
<br />Total phosphorus concentrationst
<br />
<br />0,29 0,0073
<br />0,28 0,0082
<br />0.20 0.0237
<br />0.59 0,0001
<br />0,28 0,0132
<br />0.16 0,0426
<br />0.50 0,0002
<br />0,68 0,0001
<br />0.30 0.0054
<br />0.25 0,0122
<br />0.48 0,0003
<br />0.18 0,0333
<br />0.52 0.0001
<br />0,27 0,0094
<br />0.32 0,0047
<br />0.15 0,0458
<br />0,36 0.0022
<br />0,27 0,0086
<br />0,25 0.0123
<br />0,23 0,0163
<br />
<br />"" Natural log transformation used for analysis.
<br />t Square-root transformation used for analysis.
<br />
<br />sites. Invertebrate density was not different among
<br />mountain, plains/tributary, and plains/ downstream
<br />from point-source sites or between mountain and
<br />plains/braided channel .sites; however, invertebrate
<br />density at plains/braided channel sites was greater
<br />than plains/tributary and plains/downstream from
<br />point-source sites (Duncan's multiple range test,
<br />P < 0,05),
<br />Mean number of taxa/ site was twenty-five (range =
<br />10-36) for mountains, eighteen (range ~ 13-26) for
<br />plains/braided channel, thirteen (range = 11--15) for
<br />plains/ tributary and eleven (range = 6-14) for plains/
<br />downstream from point-source sites. The mean num-
<br />ber of invertebrate taxa also was significantly different
<br />among site groups (ANOVA, P = 0,0049)_ There was
<br />no significant difference among plains sites or between
<br />mountain sites and plains/braided channel sites;
<br />mountain sites, however, had a greater number of taxa
<br />
<br />@ 1995 Blackwell Science Ltd, Freshwater Biology, 33, 439-454
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