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<br /> OGJ735
<br />446 eM. Tate and J,5, Heiny
<br />Table 2 Continued
<br /> Plains
<br /> Down-stream
<br /> Braided from point
<br />Taxonomic group Mountain channel Tributary source
<br />Chironominae
<br /> Chironomini *Chironomus sp +
<br /> *Cryptochironomus sp. + +
<br /> *Dicrotendipes sp. + +
<br /> *Microtendipes sp. +
<br /> "Parachironomus sp. +
<br /> *Polypedilum sp. + + + +
<br /> Tanytarsini *Cladotanytarsus sp + + +
<br /> *Micropsectra sp. +
<br /> "Paratanytarsus sp. + I
<br /> "Sublettea sp. +
<br /> *Tanytarsus sp. + + + ,
<br /> ,
<br />Athericidae Atherix pachypus (Bigot) + t
<br /> I
<br />Empididae *Chelifera sp. + <
<br /> *Hemerodromia sp. + +
<br />Ephydridae +
<br />""Muscidae +
<br />Total number of taxa = 74 35 28 22
<br />
<br />Reservoir near Hartsel (SPll, Fig, 2) was the only
<br />high-altitude (> 1590 m) site that grouped with the
<br />plains/braided channel sites, This site had a lower
<br />stream slope (2,1 m km-1) and wider channel (channel
<br />width = 33.2 m) compared with other mountain sites
<br />(Table 4), Also, Physella sp, and Gammarus sp" which
<br />are characteristic of plains streams, were collected at
<br />this site (Table 2), This site was not included in the
<br />physical, nutrient, and invertebrate community-data
<br />analyses (except Shannon diversity) described below
<br />because it was not located in the Western High Plains
<br />ecoregion.
<br />Stream slope and substrate size decrease, whereas
<br />water temperature, specific conductance (Table 4), sur-
<br />face-water-nutrient concentrations (nitrate + nitrite,
<br />organic + ammonia, nitrite, ammonia and total phos-
<br />phorus; Fig_ 3) and hyporheic water nitrate concentra-
<br />tions increase as streams flow from the mountains
<br />to the plains, Within the plains, the plains/braided
<br />channel sites had wide braided channels (Table 4) and
<br />lower concentrations of surface water nitrate + nitrite
<br />and total phosphorus (Fig, 3) compared with plains/
<br />tributary and plains/downstream from point-source
<br />sites. Specific conductance and surface-water-nutrient
<br />concentrations (Table 4, Fig, 3) were similar for plains/
<br />tributary and plains/downstream from point-source
<br />sites. Plains/ downstream from point-source sites had
<br />the highest mean nitrate + nitrite concentrations in
<br />
<br />hyporheic water compared with all sites (Fig, 3), and
<br />algae also were abundant at these sites (Table 1),
<br />Comparison of Shannon diversity indices at sites
<br />plotted across the DCA ordination diagram show the
<br />general pattern of greatest diversity in the mountains
<br />(Fig, 4), Diversity values averaged 2,86 (range = 2.15-
<br />3,04) for mountains, 2_67 (range = 2.51-2,95) for
<br />plains/braided channel, 2.36 (range = 1.78-2,67) for
<br />plains/ tributary and 1.92 (range = 1.76--2,22) for
<br />plains/downstream from point-source sites. Diversity
<br />was significantly different among groups (ANOYA,
<br />P = 0,0005), Mountain sites had greater diversity than
<br />plains/tributary and plains/downstream from point-
<br />source sites but was not different from plains/braided
<br />channel; diversity in plains/braided channel and
<br />plain/ tributary sites was not different but both had
<br />greater diversity than plains/downstream from point-
<br />source sites (Duncan's multiple range test, P < 0,05),
<br />The total number of invertebrate taxa was greatest
<br />in the mountains, and the plains/downstream from
<br />point-source sites had the least number of taxa
<br />(Table 2), Invertebrate density was significantly differ-
<br />ent among DCA site groups (ANOYA, P = 0,0254)_
<br />Mean invertebrate density was 9700 m -2 (range =
<br />1980--18100) for mountains, 13 400 m-2 (range = 3700--
<br />20300) for plains/braided channel, 2380 m -2 (range =
<br />100--5160) for plains/tributary and 3630 m-2 (range =
<br />2650--4950) for plains/ downstream from point-source
<br />
<br />.
<br />
<br />@ 1995 Blackwell Science Ltd, Freshwater Biology, 33, 439-454
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