Fish collection with a backpack electro-shocker	Measuring canopy cover	Measuring stream velocity	Collecting invertebrates

INTRODUCTION

To address the effects of urbanization on aquatic biological communities (invertebrates, fish, and algae), water chemistry, and physical habitat (collectively termed "BCP" for biological, chemical, and physical), the New England Coastal Basins (NECB) study team investigated the relations between varying intensities of watershed urbanization and stream ecology in the Boston Massachusetts metropolitan region. Sampling sites were chosen to represent a range of urbanization, while minimizing natural variability among drainage basins. The degree of urbanization for each drainage basin was characterized with a standardized urban index (0 – 100, lowest to highest) derived from land cover, infrastructure, and socioeconomic variables. This index is referred to as the urban land use gradient index (ULUGI). Two major objectives of this study were to:
1) determine if the BCP variables respond to urban intensity as defined by the ULUGI, and if so,
2) determine which BCP variables are useful indicators of urbanization.

METHODS

Deriving the Urban Landuse Gradient Index (ULUGI)

Fifty-three variables, including infrastructure, land-cover/land-use, socio-economic, and population statistics were evaluated for use in constructing the ULUGI. Of these 53 variables, 24 were included in the ULUGI by meeting the criteria specified in McMahon and Cuffney (2000). The ULUGI values assigned at each site represent the gradient of watershed urbanization from 0 (the site with the lowest amount of urbanization) to 100 (site with the highest amount of urbanization).

Site Selection

In selecting stream sampling sites, natural variability was controlled as much as possible so that ecological differences assessed by the study could be attributed to urbanization differences. To control for natural variability, only relatively small drainage basins (50 - 120 km²) within the USEPA Level III Ecoregion 59 (Northeastern Coastal Zone) were considered for selection. A further degree of watershed homogeneity was accomplished by using the Ecological Subsection Gulf of Maine Coastal Plain (U.S. Forest Service (USFS) Subsection 221Ai of Ecological Unit 221A, Southern New England Coastal Hills and Plain). [see figure 1 below].

Candidate sites that were third to fifth order streams were assessed during 1999 to meet specific criteria. These criteria included locating a sampling reach that was free-flowing for 150 meters, showed no sign of recent anthropogenic modification, contained riffles for sampling, and had well-defined banks with at least 50-percent mature-vegetation cover. The reason for selecting sites meeting these criteria was to increase confidence that the ecological differences in the sampling reaches were related to the degree of urbanization in the basin rather than to local disturbances within the reach. In all, 32 sites met the above criteria (see figure 2) and had watershed boundaries either in or adjacent to USFS Ecological Subsection 221Ai. However, two were later deleted from analysis because of major effects from water diversions or management.

Study Location Maps (click for full view)
Figure 1. ULUG sites and Ecoregions	Figure 2. ULUG sites and Land Use

Site Inventory (Excel file, 19kb)

Sample Collection

Biological communities were sampled from August 1 to September 1, 2000. Aquatic invertebrates were collected from five riffle areas in each sampling reach, combined for a composite quantitative sample, and designated as the invertebrate RTH (richest targeted habitat) sample. A qualitative invertebrate sample also was collected from various microhabitats along the length of the reach. This composite sample was designated as an invertebrate QMH (qualitative multi-habitat) sample. Periphyton algae were collected from five riffle areas for a composite quantitative sample, which was designated as the algae RTH sample. A second quantitative algal sample was collected from five deposition areas along the sampling reach, which was composited and designated the algae-DTH (depositional-targeted habitat) sample. Analogous to the invertebrate-QMH sample, a qualitative algal sample (algae-QMH) was collected and composited from various microhabitats along the sampling reach where periphyton growth was observed. Fish were collected from each reach by making two separate upstream passes with a backpack electro-shocker and were placed in live wells until they could be identified, measured for total length, checked for anomalies, then released back to the stream.

Water-chemistry samples were collected once in April and once in August 2000 to characterize water-quality conditions that were present before and during biological sampling. Water samples were analyzed for nutrients and pesticides. Concurrent with sampling, field measurements of specific conductance, water temperature, dissolved oxygen, pH, and alkalinity were taken. Physical habitat along the sampling reaches were typically measured within 1 day of collecting the invertebrate and algae samples. Habitat characteristics were measured at 11 equally spaced transects along the sampling reaches and included measurements of velocity, channel depth and width, aspect of flow, bed substrJanuary 9, 2013vegetation. Additionally, stream stage and water temperature were recorded at hourly intervals and monitored over a period of about a year, starting in late spring 2000. USGS NAWQA protocols were used for all sampling activities.

SUMMARY of RESULTS

The urban land-use gradient index (ULUGI) was shown to be an effective tool for defining urban intensity and for predicting the effects of urbanization on stream characteristics. Metrics that were most responsive to the urban index for each data set included Ephemeroptera, Plecoptera, and Trichoptera (EPT) taxa and non-insect taxa for invertebrates; cyprinid taxa for fish; diatom taxa for algae; alkalinity, conductivity, and nitrogen for chemistry; and water depth and temperature for physical habitat. The slope of the responses often was higher between urban index values from 0 to 35, indicating that aquatic health may deteriorate the most in watersheds with low to moderate levels of urbanization, and that there is comparatively little change in aquatic health at moderate to high levels of urbanization in a watershed.

Further details and conclusions from the study are published in the report The effects of urbanization on the biological, physical, and chemical characteristics of coastal New England streams (U.S. Geological Survey Professional Paper 1695, 47 p. by James Coles, Thomas Cuffney, Gerard McMahon, and Karen Beaulieu, 2004). The report is available in pdf format at: http://pubs.water.usgs.gov/pp1695

REFERENCE

McMahon, G. and Cuffney, T.F., 2000, Quantifying urban intensity in drainage basins for assessing stream ecological conditions. Journal of the American Water Resources Association. v. 36(6), p. 1247-1261. [Abstract (html)] [Paper (pdf file, 2.03 MB)]

RELATED STUDIES

National NAWQA's Effects of Urbanization on Stream Ecosystems, http://co.water.usgs.gov/nawqa/EUSE/