WSPC06762

• File Number: 8460.500
• Description: Platte River Basin - Endangered Species Issues - South Platte Recovery Program
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 1/1/1995
• Author: C M Tate J S Heiny
• Title: South Platte Agreement - The Ordination of Benthic Invertebrate Communities in the South Platte River Basin in Relation to Environmental Factors - From Freshwater Biology 33 - 439-454
• Water Supply Pro - Doc Type: Report/Study

onn? 41

452 CM, Tate and J,S, Heiny

Mountain ecoregion, Clear Creek at Golden had the
lowest Shannon diversity index value, number of
taxa and invertebrate density compared with other
mountain sites and was the only site affected by
mining. Differences in invertebrate communities
among forest, range, and built-up land use in the
mountain sites were not as distinct as compared with
different invertebrate communities found in plains
sites, In the Western High Plains ecoregion, geomor-
phology and land use affected invertebrate distribu-
tion as defined by DCA analyses, Land use was an
important factor affecting nutrient concentrations and
invertebrate communities, Sites in the plains/tributary
group were located in urban or a mixture of agricul-
ture/urban land use, These sites had higher nitrile,
ammonia, and total phosphorus concentrations than
sites in the plains/braided channel; higher nutrient
concentrations probably represent urban affects on
stream-water chemistry, The plains/braided channels
were wider and shallower than other plains sites and
land use primarily was agriculture or built-up, and
nutrient concentrations were lower than other plains
sites. Invertebrate density and total number of taxa
were greater and functional-feeding group composi-
tion was different in the plains/braided channel sites
compared with other plains sites. The land use at the
plains/ downstream from point-source sites was mixed
agriculrure/urban; however, these sites were below
the major municipal discharges into the South Platte
River Basin (Dennehy et ai" 1993) and nutrient concen-
trations were high, Organic pollution from point
sources, such as waste-water effluent, generally
decreases the number of insect species (Hynes, 1960)
as was shown in this srudy. In addition, community
composition was altered at these sites (Le. absence of
Trichoptera, greater proportion of non-insect taxa)
compared with plains/ tributary and plains/braided
channel sites, The plains/ downstream from point-
source sites were located in a rich algal zone (Table I)
where OIigochaeta dominated and oxygen concentra-
tions were high, This region is characterized by having
increased numbers of snails and an abundance of
Chironomidae (Wiederholm, 1984)_ The presence of
OIigochaeta, Physel/a sp" Simulium sp" and dominance
of Chironomidae genera and the absence of Trichop-
tera are characteristic of a stream reach effected by
organic pollution (Wiederholm, 1984), Similarly, Quinn
& Hickey (1990) reported that gross organic pollution
and runoff were important affects on community

composition at some sites in New Zealand streams.
Although spatial assemblages of invertebrate commu-
nities appear to be related to land-use patterns, specific
cause and effect relations cannot be addressed in the
present study,

Environmental factors affecting invertebrates

As noted in other large basin-scale studies, a combina-
tion of environmental factors affected the invertebrate
distribution and abundance within the South Platte
River Basin. Differences in invertebrate communities
occurred between mountains and plains and were
most highly correlated with differences in stream
slope, specific conductance, water temperature
(Table 3) and surface water organic nitrogen + ammo-
nia and total phosphorus concentrations and to a
lesser extent to factors such as drainage area, altirude,
sinuosity, stream order, mean substrate size, and
ammonia, nitrite, and nitrate + nitrate concentrations.
As previously discussed, differences in invertebrate
communities among sites within the plains region
varied according to geomorphology and land-use
affects on nutrient concentrations. With the exception
of nitrate + nitrite concentrations, nutrient concentra-
tions in the hyporheic waters were not related to
the invertebrate community, McMahon et at, (1994)
reported that groundwater effects on surface-water
nutrient concentrations were related to a combination
of factors such as redox conditions of groundwater,
land use and proximity of site to sources of nutrients
in the South Platte River Basin, In British streams,
different environmental factors were useful in describ-
ing invertebrate communities depending on the spatial
scale examined (Furse et ai" 1984; Wright et aI., 1984),
For instance, substrarum characteristics, alkalinity,
total oxidized nitrogen (Le, nitrate + nitrite) were use-
ful in distinguishing invertebrate communities among.
rivers in Great Britain, whereas discharge, distance
from source, width, and depth were useful in distin-
guishing within river sites and slope and altitude were
useful in distinguishing within and between sites in
rivers, Quinn & Hickey (1990) reported that silty and
sandy substrates and recent severe flooding caused
low biomass and taxonomic richness; whereas catch-
ment development and related environmental factors
(Le, increased periphyton, increased water temper-
ature) had the most widespread important effect on
community composition, Corkum (1989) determined

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@ 1995 Blackwell Science Ltd, Freshwater Biology, 33, 439--454