Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—In this paper, we provide an introduction to water quality benefit estimation for noneconomists. Net water quality benefits are typically measured using the concept of consumer surplus, which is estimated using a number of economic valuation methodologies. These are divided into direct and indirect methods. Direct methods involve questioning survey respondents to determine their consumer surplus. Indirect methods use data from consumer market behavior to estimate economic values. When limited time or funding preclude costly data collection and the development of new consumer surplus estimates, the method of benefit transfer is used to tailor preexisting consumer surplus estimates to fit new policy situations. We provide an example of benefit transfer by estimating the value of water quality improvements for the Cape Fear River in North Carolina. Benefit transfer methods are used with three valuation approaches to estimate the benefits of water quality improvement.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—We examined fish assemblage responses to urban intensity gradients in two contrasting metropolitan areas: Birmingham, Alabama (BIR) and Boston, Massachusetts (BOS). Urbanization was quantified by using an urban intensity index (UII) that included multiple stream buffers and basin land uses, human population density, and road density variables. We evaluated fish assemblage responses by using species richness metrics and detrended correspondence analyses (DCA). Fish species richness metrics included total fish species richness, and percentages of endemic species richness, alien species, and fluvial specialist species. Fish species richness decreased significantly with increasing urbanization in BIR (<em>r </em>= –0.82, <EM>P </EM>= 0.001) and BOS (<em>r </em>= –0.48, <EM>P </EM>= 0.008). Percentages of endemic species richness decreased significantly with increasing urbanization only in BIR (<em>r </em>= – 0.71, <EM>P </EM>= 0.001), whereas percentages of fluvial specialist species decreased significantly with increasing urbanization only in BOS (<em>r </em>= –0.56, <EM>P </EM>= 0.002). Our DCA results for BIR indicate that highly urbanized fish assemblages are composed primarily of largescale stoneroller <em>Campostoma oligolepis</em>, largemouth bass <em>Micropterus salmoides</em>, and creek chub <em>Semotilus atromaculatus</em>, whereas the highly urbanized fish assemblages in BOS are dominated by yellow perch <em>Perca flavescens</em>, bluegill <em>Lepomis macrochirus</em>, yellow bullhead <em>Ameiurus natalis</em>, largemouth bass, pumpkinseed <em>L. gibbosus</em>, brown bullhead <em>A. nebulosus</em>, and redfin pickerel <em>Esox americanus</em>. Differences in fish assemblage responses to urbanization between the two areas appear to be related to differences in nutrient enrichment, habitat alterations, and invasive species. Because species richness can increase or decrease with increasing urbanization, a general response model is not applicable. Instead, response models based on species’ life histories, behavior, and autecologies offer greater potential for understanding fish assemblage responses to urbanization.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—Responses of invertebrate assemblages along gradients of urban intensity were examined in three metropolitan areas with contrasting climates and topography (Boston, Massachusetts; Birmingham, Alabama; Salt Lake City, Utah). Urban gradients were defined using an urban intensity index (UII) derived from basin-scale population, infrastructure, land-use, land-cover, and socioeconomic characteristics. Responses based on assemblage metrics, indices of biotic integrity (B-IBI), and ordinations were readily detected in all three urban areas and many responses could be accurately predicted simply using regional UIIs. Responses to UII were linear and did not indicate any initial resistance to urbanization. Richness metrics were better indicators of urbanization than were density metrics. Metrics that were good indicators were specific to each study except for a richnessbased tolerance metric (TOLr) and one B-IBI. Tolerances to urbanization were derived for 205 taxa. These tolerances differed among studies and with published tolerance values, but provided similar characterizations of site conditions. Basin-scale land-use changes were the most important variables for explaining invertebrate responses to urbanization. Some chemical and instream physical habitat variables were important in individual studies, but not among studies. Optimizing the study design to detect basin-scale effects may have reduced the ability to detect local-scale effects.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—In Brazil, most urban sewage is discharged without treatment into rivers. This is the situation for the Rio das Velhas, which receives in its upper course the sewage of the state capital of Minas Gerais, Belo Horizonte, with more than 2.4 million inhabitants. Our study focuses on the effects of basin urbanization on aquatic biodiversity and water quality in the Rio das Velhas. We use the assemblage structure and taxonomic composition of fishes and benthic macroinvertebrates as biological indicators of water quality. Effects of Belo Horizonte’s discharge included changes in water quality and declines in fish and benthos richness and diversity. However, the absence of dams in the Rio das Velhas main course, associated with connectivity with the Rio São Francisco system and tributaries in excellent condition, increase its rehabilitation potential.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—We evaluated several approaches for measuring natural and anthropogenic habitat characteristics to predict benthic macroinvertebrate assemblages over a range of urban intensity at 85 stream sites in the Santa Clara Valley, California. Land cover was summarized as percentage urban land cover and impervious area within upstream buffers and the upstream subwatersheds. Field measurements characterized water chemistry, channel slope, sediment, and riparian canopy. In addition to applying the visual-based habitat assessment in U.S. Environmental Protection Agency’s rapid bioassessment protocol, we developed a simplified urban habitat assessment index based on turbidity, fine sediment deposition, riparian condition, and channel modification. Natural and anthropogenic habitat variables covaried along longitudinal stream gradients and were highly correlated with elevation. At the scale of the entire watershed, benthic macroinvertebrate measures were equally correlated with variables expressing natural gradients and urbanization effects. When natural gradients were reduced by partitioning sites into ecoregion subsection groupings, habitat variables most highly correlated with macroinvertebrate measures differed between upland and valley floor site groups. Among the valley floor sites, channel slope and physical modification of channel and riparian habitats appeared more important than upstream land cover or water quality in determining macroinvertebrate richness and ordination scores. Among upland sites, effects of upstream reservoir releases on habitat quality appeared important. Rapid habitat evaluation methods appeared to be an effective method for describing habitat features important to benthic macroinvertebrates when adapted for the region and the disturbance of interest.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—We evaluated a comprehensive set of natural and land-use attributes that represent the major facets of urban development at fish monitoring sites in the rapidly growing Raleigh-Durham, North Carolina metropolitan area. We used principal component and correlation analysis to obtain a nonredundant subset of variables that extracted most variation in the complete set. With this subset of variables, we assessed the effect of urban growth on fish assemblage structure. We evaluated variation in fish assemblage structure with nonmetric multidimensional scaling (NMDS). We used correlation analysis to identify the most important environmental and landscape variables associated with significant NMDS axes. The second NMDS axis is related to many indices of land-use/landcover change and habitat. Significant correlations with proportion of largest forest patch to total patch size (<em>r </em>= –0.460, <EM>P </EM>< 0.01), diversity of patch types (<em>r </em>= 0.554, <EM>P </EM>< 0.001), and population density (<em>r </em>= 0.385, <EM>P </EM>< 0.05) helped identify NMDS axis 2 as a disturbance gradient. Positive and negative correlations between the abundance of redbreast sunfish <em>Lepomis auritus </em>and bluehead chub <em>Nocomis leptocephalus</em>, respectively, and NMDS axis 2 also were evident. The North Carolina index of biotic integrity and many of its component metrics were highly correlated with urbanization. These results indicate that aquatic ecosystem integrity would be optimized by a comprehensive integrated management strategy that includes the preservation of landscape function by maximizing the conservation of contiguous tracts of forested lands and vegetative cover in watersheds.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—Parcel by parcel, urban/suburban development is one of the most active converters of land in the Hudson River Valley in New York State. We are taking an integrative approach to understanding the drivers of and responses to urbanization, by studying how economy drives land use change and how that, in turn, affects downstream indicators of ecosystem state. The ultimate goal of the project is to provide a tool for policymakers, illustrating consequences of different development strategies. In this paper, we discuss synoptic ecological assessments of two major Hudson River tributaries in Dutchess County, the Wappinger Creek and Fishkill Creek watersheds. Physical, chemical, geographic, and biotic indices are compiled, creating a multivariate data set. These data, when set into a geographic information database, provide a spatial response to land use. Application of a regionally calibrated index of biotic integrity showed little relationship to urbanization, although some component metrics indicated a response. Chemical or biogeochemical indicators were more reflective of urbanization gradients. A hierarchy of responses, beginning with physicochemical and moving up to fish assemblages, reflected decreasing responses to urbanization. However, fish densities and the stable isotopic ratios of nitrogen determined in a sentinel species (eastern blacknose dace <em>Rhinichthys atratulus</em>) were significantly affected by urbanization. Longitudinal gradients of elevation were identified as strong drivers of development, potentially confounding relationships of land-use attributes and ecological responses.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—Patterns of stream benthic algal assemblages along urbanization gradients were investigated in three metropolitan areas—Boston (BOS), Massachusetts; Birmingham (BIR), Alabama; and Salt Lake City (SLC), Utah. An index of urban intensity derived from socioeconomic, infrastructure, and land-use characteristics was used as a measure of urbanization. Of the various attributes of the algal assemblages, species composition changed along gradients of urban intensity in a more consistent manner than biomass or diversity. In urban streams, the relative abundance of pollutiontolerant species was often higher than in less affected streams. Shifts in assemblage composition were associated primarily with increased levels of conductivity, nutrients, and alterations in physical habitat. Water mineralization and nutrients were the most important determinants of assemblage composition in the BOS and SLC study areas; flow regime and grazers were key factors in the BIR study area. Species composition of algal assemblages differed significantly among geographic regions, and no particular algal taxa were found to be universal indicators of urbanization. Patterns in algal biomass and diversity along urban gradients varied among study areas, depending on local environmental conditions and habitat alteration. Biomass and diversity increased with urbanization in the BOS area, apparently because of increased nutrients, light, and flow stability in urban streams, which often are regulated by dams. Biomass and diversity decreased with urbanization in the BIR study area because of intensive fish grazing and less stable flow regime. In the SLC study area, correlations between algal biomass, diversity, and urban intensity were positive but weak. Thus, algal responses to urbanization differed considerably among the three study areas. We concluded that the wide range of responses of benthic algae to urbanization implied that tools for stream bioassessment must be region specific.

Effects of Urbanization on Stream Ecosystems

<em>Abstract.</em>—Data collected as part of two studies to examine the influences of landscape modification on the ecology of three coastal Southern California river systems—the Calleguas Creek, Malibu Creek, and Santa Clara River watersheds—provided the opportunity to examine relations between urbanization and fish assemblages in Southern California coastal streams. Fish were collected at 63 sites from 1999 to 2001. Watershed land use was determined and classified into three land use types: agriculture, developed, and open space. Seven fish assemblage metrics were examined, including species richness, number of native and alien species, total fish abundance, percent abundance of native and alien species, and percent abundance of arroyo chub <em>Gila orcuttii</em>. Ten fish species were collected, and arroyo chub was the only species collected in all three watersheds. Native species included arroyo chub, threespine stickleback <em>Gasterosteus aculeatus</em>, steelhead <em>Oncorhynchus mykiss</em>, and Pacific staghorn sculpin <em>Leptocottus armatus</em>. There were no significant differences in fish assemblage metrics among the three land-use types. Both wetted stream width and depth were significantly related to native fish abundance. Results from this study suggest that the relatively species poor fish assemblages of Southern California may not be sensitive to watershed land use disturbance, but may be sensitive to local hydrologic conditions.