Community data from 36 watersheds were used to evaluate the response of fish, invertebrate, and algal assemblages in New Jersey streams to environmental characteristics along a gradient of urban land use that ranged from 3 to 96 percent. Aquatic assemblages were sampled at 36 sites during 1996-98, and more than 400 environmental attributes at multiple spatial scales were summarized. Data matrices were reduced to 43, 170, and 103 species of fish, invertebrates, and algae, respectively, by means of a predetermined joint frequency and relative abundance approach. White sucker (Catostomus commersoni) and Tessellated darter (Etheostoma olmstedi) were the most abundant fishes, accounting for more than 20 and 17 percent, respectively, of the mean abundance. Net-spinning caddisflies (Hydropsychidae) were the most commonly occurring benthic invertebrates and were found at all but one of the 36 sampling sites. Blue-green (for example, Calothrix sp. and Oscillatoria sp.) and green (for example, Protoderma viride) algae were the most widely distrib-uted algae; however, more than 81 percent of the algal taxa collected were diatoms.
Principal-component and correlation analyses were used to reduce the dimensionality
of the environmental data. Multiple linear regression analysis of extracted
ordination axes then was used to develop models that expressed effects of increasing
urban land use on the structure of aquatic assemblages. Significant environmental
variables identified by using multiple linear regression analysis then were
included in a direct gradient analysis. Partial canonical correspondence analysis
of relativized abundance data was used to restrict further the effects of residual
natural variability, and to identify relations among the environmental variables
and the structure of fish, invertebrate, and algal assemblages along an urban
land-use gradient. Results of this approach, combined with the results of the
multiple linear regression analyses, were used to identify human population
density (311-37,594 persons/km2), amount and type of impervious surface
cover (0.12-1,350 km2), nutrient concentrations (for example, 0.01-0.29
mg/L of phosphorus), hydrologic instability (for example, 100-8,955 ft3/s
for 2-year peak flow), the amount of forest and wetlands in a basin (0.01-6.25
km2), and substrate quality (0-87 percent cobble substrate) as variables
that are highly correlated with aquatic-assemblage structure. Species distributions
in ordination space clearly indicate that tolerant species are more abundant
in the streams impaired by urbanization and sensitive taxa are more closely
associated with the least impaired basins. The distinct differences in aquatic
assemblages along the urban land-use gradient demonstrate the deleterious effects
of urbanization on assemblage structure and indicate that conserving landscape
attributes that mitigate anthropogenic influences (for example, stormwater-management
practices emphasizing infiltration and preservation of existing forests, wetlands,
and riparian corridors) will help to maintain the relative abundance of sensitive
taxa. Complementary multiple linear regression models indicate that aquatic
community indices were correlated with many of the anthropogenic factors that
were found to be significant along the urban land-use gradient. These indices
appear to be effective in differentiating the moderately and severely impaired
streams from the minimally impaired streams. Evaluation of disturbance thresholds
for aquatic assemblages indicates that moderate to severe impairment is detectable
in New Jersey streams when impervious surface cover in the drainage basin reaches
approximately 18 percent.
Glossary
Abstract
Introduction
Purpose and Scope
Study area
Acknowledgments
Approach
Design of land-use gradient
Aggregation of anthropogenic factors used in assessment
Data collection
Stream Characteristics
Habitat
Ichthyofauna
Macroinvertebrates
Attached algae (periphyton)
Water quality
Volatile organic compounds (VOCs)
Pesticides
Trace elements and organochlorine compounds in bed sediment
Watershed characteristics
Interpretation of digital data
Derivation of the index of impervious area
Flow-path length and topography
Analytical methods
Spatial and temporal assessment
Univariate and multivariate approaches
Principal components analysis
Detrended correspondence analysis
Multiple linear regression
Indices of aquatic community impairment
Partial canonical correspondence analysis
Analysis of benchmark communities
Resolution of taxonomic ambiguities and data censoring
Variability of aquatic communities
Species abundance
Spatial and temporal variability in aquatic assemblages
Distinctions among benchmark community groups
Identification of important environmental variables
Indirect gradient assessment of aquatic assemblages
Significant environmental factors
Environmental associations across multiple pCCA axes
Relation of environmental characteristics to aquatic assemblages
Impervious surfaces
Hydrologic instability
Effects of runoff quality
Erosion, sedimentation, and stream-channel modification
Trace elements
Riparian conditions and stream buffers
Forest and wetlands
Relation of land-use changes to assemblage structure of long-lived species
Community indices
Indicator taxa
Complementary analytical techniques
Summary and conclusions
References cited
For additional information write to:
NAWQA Project Chief
U.S. Geological Survey
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