Driver: Residential, Commercial and Industrial Development

Perhaps the single greatest source of transformation in the Salish Sea terrestrial ecosystem is the conversion of lowland forests to a mosaic of residential, commercial and industrial lands created for human use. The state population, currently at over 6 million people, doubled over the last 40 years and is predicted to reach 8 million by 2030 (WOFM 2010). The highest population density is within the Puget Trough region (WOFM 2010). Changes in the landscape are driven by expanding human populations associated with growing businesses (e.g., Microsoft, Amazon.com, Boeing) and rich natural amenities (Alberti 2008), and changing family structure (single parent households associated with high divorce rates have greatly increased the demand for residential dwellings; Morrill 1992—see http://faculty.washington.edu/morrill/). Populations are expanding in the cities and exurban environments (Alberti et al. 2003; Alig et al. 2004; UNFPA 2007; WOFM 2007, 2010; Alberti 2008; Grimm et al. 2008). Increasing population growth results in more roads, more industry, more houses, more transportation, and more businesses. These changes mean positive changes to income, business growth, etc. However, we only focus in the current draft on the terrestrial ecological changes resulting from residential, commercial and industrial development rather than the benefits to human health and well-being; additionally, negative impacts of ecological changes on human health and well-being, such as impaired water quality and decreased resource availability, are currently omitted. Effects of development on nearshore ecosystems are discussed separately (see “Threat: Shoreline Modification”). We also treat agriculture separately due to the distinct set of pressures, states and impacts associated with this distinct type of development (see “Threat: Agricultural Practices (Placeholder)”).

Development-related land uses associated with residential, employment and commercial activities span a gradient of density and intensity from compact, highly developed urban, commercial and industrial centers to the more sparsely developed exurban and rural fringes (Alberti et al. 2004; Pickett et al. 2008). These drivers result in a diverse range of ecological effects (Alberti 2005). Development broadly encompasses low- to high-density housing as well as retail stores and businesses, industrial production and storage facilities, and transportation infrastructure. In the Driver-Pressure-State-Impacts-Response (DPSIR) model, these activities are represented in the “Drivers” (Figure 2).

Below, we review the Pressures associated with residential, commercial and industrial development, and the resultant State changes and system Impacts. Our primary focus in the current draft is on States and Impacts resulting from land use/land cover change as a Pressure in the Salish Sea ecosystem. Such effects manifest themselves at multiple levels, from ecosystems to species, and within both terrestrial and aquatic systems. States and Impacts associated with the Pressure of infrastructural demands will be addressed in future revisions. Increased chemical inputs, both naturally and anthropogenically derived, are a significant development associated Pressure (Figure 2). Chemical contaminants are reviewed more broadly and fully under “Threat: Pollution.” Additionally, Chapter 4, Effectiveness of Strategies to Protect and Restore the System, addresses the human Response to the problems associated with development, and will not be covered in this chapter.

Placeholder – positive and negative impacts of residential, commercial and industrial development on human health, socioeconomics and overall well-being

 

Figure 2

Figure 2. Driver-Pressure-State-Impacts-Response conceptual model for residential, commercial and industrial development in the Salish Sea ecosystem.

1. Pressure: Land Use/Land Cover Changes

Development is most visibly characterized by significant land use and land cover (LULC) transformations. In terrestrial systems of the Salish Sea region, forests, wetlands, prairies and agricultural lands are converted to residential, commercial and industrial uses. The rates of conversion have increased significantly in the late 20th century and are projected to continue to increase (Alig et al. 2004; Alberti 2005; Robinson et al. 2005; White et al. 2009). The region most heavily impacted by the human footprint in Puget Sound is in the central Sound: the amount of developed lands increased from 16% to 23% of the total area between 2002 and 2007 (Alberti et al. 2004; Hepinstall et al. 2008), an increase of approximately 1.4 percent per year. Continued development at this rate will result in developed lands extending well into the Cascade Mountain foothills by 2027 (Hepinstall et al. 2008).

Transformations of both land cover composition and configuration in the Puget Sound watershed, particularly in the central Sound region of Snohomish, King, Pierce and Kitsap Counties, have been extensive. In an analysis of LULC change in central Puget Sound, Alberti et al. (2004) measured a 6.7 percent increase in paved urban areas and a 7.8 percent increase in mixed urban areas from 1991 to 1999. Largely associated with increasing urbanization in the region, almost half of the land converted to urban land uses occurred in the Seattle metropolitan region, and included significant conversion of adjacent forests (Alberti et al. 2004). Similarly, Hepinstall et al. (2008) examined trends in LULC change in the central Puget Sound region from 1991-2002, and developed a model to forecast future trends of change. Between 1991-1995, observed annual rates of agriculture and coniferous forest loss were 8.0 and 2.3 percent per year, respectively. From 1995-1999, rates of agriculture loss slowed to 1.3 percent per year and coniferous forest began to show an increase of 1.0 percent per year (mostly as a result of regenerating forests in the uplands), but mixed deciduous-coniferous forest declined by 4.7 percent per year. By spatially extrapolating these trends into the future, Hepinstall et al. (2008) forecasted mature forest cover composition will decline from approximately 45% in 1999 to 27-30 percent of the total central Sound area by 2027. Significant native vegetation cover still remains in the Puget Basin: 53 percent of the central Puget Sound region was still composed of forested lands (down from 66 percent in 2002; Alberti 2009). However, the above trends suggest that land conversion, particularly of forests, has occurred and continues to occur at a considerable rate.

State: Vegetation Fragmentation and Loss

The most dramatic examples of LULC change result in the loss and fragmentation of plant cover. Fragmentation and loss describe two interrelated facets of landscape composition and pattern (Turner et al. 2001; Alberti and Marzluff 2004). Loss of native vegetation results from replacement by other land cover types, particularly those associated with residential development (e.g., buildings, roads, and planted landscapes). This loss affects land cover composition and changes ecosystem processes (Fahrig 1997; Alberti and Marzluff 2004; Wiegand et al. 2005; Donnelly and Marzluff 2006). Additionally, fragmentation can introduce sharp ecotones or edges that affect both material flows in ecosystems (Wickham et al. 2002; Walsh et al. 2005) and habitat conditions for species (deMaynadier and Hunter 2000; Hansen et al. 2005), particularly when there is a strong contrast between adjacent land cover types (e.g., impervious surface adjacent to forest). Since the vegetation loss and fragmentation are generally correlated and their interactions are difficult to untangle, we discuss their combined effects.

Impacts

Development-related LULC change leads to impacts across and between scales, from the landscape and ecosystem level down to the species level. Most readily apparent are changes in the spatial pattern and configuration of landscapes such as the fragmentation of forests. Landscape fragmentation impacts ecosystems at multiple scales and levels of organization: it affects the distribution and persistence of species (Wiegand et al. 2005; Donnelly and Marzluff 2006), as well as fluxes of nutrients and water (Baker et al. 2001b; Wickham et al. 2002; Walsh et al. 2005). Even regions of low-density development, in which a significant percent of the landscape is comprised of forest, can exhibit significant levels of fragmentation due to inclusions of roads, houses, and other structures (Hansen et al. 2005). Bisection of (forest) habitats by roads has significant population-level impacts on many species (deMaynadier and Hunter 2000; Steen and Gibbs 2004), particularly for those who are attracted to habitats near or that regularly cross roads and are struck by vehicles (Fahrig and Rytwinski 2009). Human-induced and -maintained land cover characteristics such as lawns and power transmission corridors modify biophysical structure and biogeochemical fluxes (e.g., Kaye et al. 2006) and negatively affect the persistence of native species assemblages (e.g., Alberti and Marzluff 2004; Hansen and Clevenger 2005). The specific spatial characteristics of fragmentation and its associated impacts are generally dependent on the intensity of development, which ranges from urban centers to rural fringes, (Alberti 2005; Alberti et al. 2007). Therefore, the threats to ecosystems not only result from the amount of vegetation conversion but also the resulting spatial pattern of the vegetation.

Entire ecosystems and ecological communities are threatened by LULC changes and associated impacts. For example, western Washington’s native grasslands and oak woodlands have declined to less than 3% of the pre-European settlement areal extent (Crawford and Hall 1997). Factors contributing to their decline and degradation include urban and agricultural conversion, fire suppression, conifer tree invasion and invasion by non-native and invasive species (Giles 1970; Agee 1993; Clampitt 1993; Crawford and Hall 1997; Chappell et al. 2001). The prairies and oak woodlands of western Washington are composed of eight international vegetation classification plant associations that are now critically globally imperiled or globally imperiled (Washington Department of Natural Resources 2007; Natureserve 2008). As a result, many species of plants and animals associated with these ecosystems are also of conservation concern because of population declines, local extirpation, or close associations with declining plant communities including the golden paintbrush (Castilleja levisecta), Taylor’s checkerspot butterfly (Euphydryas editha taylori), streaked horned lark (Eremophila alpestris strigata), and mazama pocket gopher (Thomomys mazama) (Dunn and Ewing 1997; Stinson 2005; Camfield et al. 2010).

Placeholder – ecosystems that are most threatened or have been lost

The loss of extensive, contiguous mature forest ecosystems is one of the most significant consequences of LULC change associated with development. Changes in the composition and configuration of landscapes result in significant changes to biogeochemical and hydrologic cycling. Vegetation and soils within forested ecosystems mediate the cycling of nutrients and water. As vegetation composition and pattern changes with increasing development, these ecosystem functions are altered. However, because the changes in biogeochemistry and hydrology that result from development go beyond the impacts of vegetation fragmentation and loss, we discuss the specific impacts in greater detail below (see “State: Altered Biogeochemistry and Hydrology).

A number of studies demonstrate the impacts of vegetation fragmentation and loss on instream biotic conditions, highlighting the existing linkages between terrestrial and freshwater ecosystems. Expanding on a previous study of urban land use impacts on biotic integrity (Booth et al. 2004), Alberti et al. (2007) examined relationships between landscape composition (directly related to vegetation amount) and configuration (including levels of fragmentation and edge contrasts) in the central Puget Sound and benthic indices of biotic integrity. They found a strong negative relationships between benthic indices of biotic integrity and contiguity of urban land cover, a somewhat weaker negative relationship with overall imperviousness, and still weaker but significant negative relationships with road density and road crossings. They observed these relationships between benthic indices of biotic integrity and landscape pattern both at the level of drainage basins and within 100-300 m buffers around streams. Refined and expanded observations by Shandas and Alberti (2009), however, determined that within the immediate vicinity of streams, instream biota are affected by the percent vegetation cover, not the configuration of vegetation. Collectively, these measures of stream biotic integrity (Morley and Karr 2002) relate significantly to overall water quality conditions (see below for further discussion of such impacts) as a function of development-related landscape changes. Implications of these studies point to the potential effectiveness of increasing the amount of upland vegetation and connectivity for mitigating downstream flow rates and volumes, particularly as result of high imperviousness in urbanized landscapes.

Placeholder – impacts of vegetation fragmentation and loss on riparian and stream ecosystems

Some important/useful references and information to include in this subsection:

  • Key publications out of the River History Project and the various ages of the Water Center
    • Beechie, T., B. D. Collins, and G. Pess. 2001. Holocene and recent changes to fish habitats in two Puget Sound basins. In: J. M. Dorava, B. Palcsak, F. Fitzpatrick, and D. R. Montgomery, eds. Geomorphic Processes and Riverine Habitat. American Geophysical Union, Washington, D. C. pp. 37-54.
    • Collins, B. D., and D. R. Montgomery. 2002. Forest development, wood jams and restoration of floodplain rivers in the Puget Lowland. Restoration Ecology 10: 237-247.
    • Collins, B. D., D. R. Montgomery, and A. D. Haas. 2002. Historical changes in the distribution and functions of large wood in Puget Lowland rivers. Canadian Journal of Fisheries & Aquatic Sciences 59: 66-76.
    • Montgomery, D. R., B. D. Collins, J. M. Buffington, and T. B. Abbe. 2003. Geomorphic effects of wood in rivers. In: S. V. Gregory, K. L. Boyer, and A. M. Gurnell, eds., The Ecology and Management of Wood in World Rivers, American Fisheries Society Symposium 37. American Fisheries Society, Bethesda, MD. pp. 21-48.
  • fundamental shifts in vegetation from conifer dominated to alder and other deciduous and herbaceous vegetation along the shores of Lake Washington (Davis, M. B. 1973. Pollen evidence of changing land use around the shores of Lake Washington. Northwest Science 47:133–148)
  • effects of alder on instream nutrient levels (Volk, C. J., P. M. Kiffney, R. L. Edmonds. 2003. Role of riparian red alder (Alnus rubra) in the nutrient dynamics of coastal streams of the Olympic Peninsula, WA, U.S.A. American Fisheries Society Special Publication 34: 213-228.)
  • effects of urbanization and changing riparian vegetation on nutrient inputs to small streams (Roberts, M.L. and R.E. Bilby. 2009. Urbanization alters litterfall rates and nutrient inputs to small Puget Lowland streams. JNABS 28:941-954.)
  • Two volumes of JNABS focused on urbanization (v 24 and v 28):
  • Booth, D. B. 2005. Challenges and prospects for restoring urban streams: a perspective from the Pacific Northwest of North America. Journal of the North American Benthological Society 24:724-737.
  • Brown, L. R., T. F. Cuffney, J. F. Coles, F. Fitzpatrick, G. McMahon, J. Steuer, A. H. Bell, and J. T. May. 2009. Urban streams across the USA: lessons learned from studies in 9 metropolitan areas. Journal of the North American Benthological Society 28:1051-1069.
  • Carter, T., C. R. Jackson, A. Rosemond, C. Pringle, D. Radcliffe, W. Tollner, J. Maerz, D. Leigh, and A. Trice. 2009. Beyond the urban gradient: barriers and opportunities for timely studies of urbanization effects on aquatic ecosystems. Journal of the North American Benthological Society 28:1038-1050.
  • Feminella, J. W. and C. J. Walsh. 2005. Urbanization and stream ecology: an introduction to the series. Journal of the North American Benthological Society 24:585-587.
  • Grimm, N. B., R. W. Sheibley, C. L. Crenshaw, C. N. Dahm, W. J. Roach, and L. H. Zeglin. 2005. N retention and transformation in urban streams. Journal of the North American Benthological Society 24:626-642.
  • Meyer, J. L., M. J. Paul, and W. K. Taulbee. 2005. Stream ecosystem function in urbanizing landscapes. Journal of the North American Benthological Society 24:602-612.
  • Morgan, R. P. and S. E. Cushman. 2005. Urbanization effects on stream fish assemblages in Maryland, USA. Journal of the North American Benthological Society 24:643-655.
  • Roberts, M. L. and R. E. Bilby. 2009. Urbanization alters litterfall rates and nutrient inputs to small Puget Lowland streams. Journal of the North American Benthological Society 28:941-954.
  • Roy, A. H., M. C. Freeman, B. J. Freeman, S. J. Wenger, W. E. Ensign, and J. L. Meyer. 2005. Investigating hydrologic alteration as a mechanism of fish assemblage shifts in urbanizing streams. Journal of the North American Benthological Society 24:656-678.
  • Roy, A. H., A. H. Purcell, C. J. Walsh, and S. J. Wenger. 2009. Urbanization and stream ecology: five years later. Journal of the North American Benthological Society 28:908-910.
  • Smith, R. F., L. C. Alexander, and W. O. Lamp. 2009. Dispersal by terrestrial stages of stream insects in urban watersheds: a synthesis of current knowledge. Journal of the North American Benthological Society 28:1022-1037.
  • Steuer, J. J., J. D. Bales, and E. M. P. Giddings. 2009. Relationship of stream ecological conditions to simulated hydraulic metrics across a gradient of basin urbanization. Journal of the North American Benthological Society 28:955-976.
  • Walsh, C. J., T. D. Fletcher, and A. R. Ladson. 2005. Stream restoration in urban catchments through redesigning stormwater systems: looking to the catchment to save the stream. Journal of the North American Benthological Society 24:690-705.
  • Walsh, C. J. and J. Kunapo. 2009. The importance of upland flow paths in determining urban effects on stream ecosystems. Journal of the North American Benthological Society 28:977-990.
  • Wenger, S. J., A. H. Roy, C. R. Jackson, E. S. Bernhardt, T. L. Carter, S. Filoso, C. A. Gibson, W. C. Hession, S. S. Kaushal, E. Marti, J. L. Meyer, M. A. Palmer, M. J. Paul, A. H. Purcell, A. Ramirez, A. D. Rosemond, K. A. Schofield, E. B. Sudduth, and C. J. Walsh. 2009. Twenty-six key research questions in urban stream ecology: an assessment of the state of the science. Journal of the North American Benthological Society 28:1080-1098.

Placeholder – impacts of vegetation fragmentation and loss on downstream estuarine/marine ecosystems

Vegetation fragmentation and loss also impact the biodiversity and species composition of the region. A series of studies (Donnelly and Marzluff 2004, 2006; Blewett and Marzluff 2005; Marzluff 2005; Hepinstall et al. 2008, 2009) examined avian species richness and abundance along the urban-to-rural gradient in the Seattle metropolitan region. Overall diversity was highest at 40-60 percent forest cover, with the abundance and richness of native forest bird species decreasing with decreasing forest cover, and with synanthropic species (i.e., those that thrive in human-dominated environments) and, to a lesser degree, early successional species increasing at higher levels of development. Intermediate levels of forest cover (and greatest levels of fragmentation), characteristic of low density residential development and rural fringes, provide sufficient habitat for native forest species along with edge habitats and resource supplements favorable to early successional and synanthropic species (Donnelly and Marzluff 2004, 2006; Blewett and Marzluff 2005; Hansen et al. 2005; Marzluff 2005; Withey and Marzluff 2009). Overall declines in biodiversity occur at high levels of urbanization and forest loss (Donnelly and Marzluff 2004, 2006; Hepinstall et al. 2008, 2009; Whittaker and Marzluff 2009). It is important to note in this system, as in many ecological systems, diversity is increased by fragmentation of uniform land covers so that many distinct types of habitats are found in close proximity. When either forest or intensively built urban land dominates an area, diversity decreases. In addition, as the distance to neighboring forest reserves increases and/or the extent of such reserves decreases with increasing development, urban and suburban bird populations are likely to decline dramatically (Marzluff et al. 2007). Projecting such trends into the future, Hepinstall et al. (2008, 2009) forecast reduced species diversity with the spread of development in the Puget trough, with sharper declines in forest and early successional species when forest cover is reduced below approximately 40 percent, and as developed areas become older and more established (hence losing their successional characteristics).

Enhanced food and habitat choices for early successional and synanthropic species, associated with lower development densities, result in community level changes. Withey and Marzluff (2009) examined the relationships between American crow (Corvus brachyrhynchos) abundance and activity levels and land cover composition and configuration at three spatial scales in King County. Crow abundance at site (up to 200 ha) and within-site (approximately 18 ha) scales was strongly associated with mixed LULC characteristics: developed lands provide access to plentiful anthropogenic food resources while adjacent urban forest/maintained vegetation patches that provide access to insects and songbird nestlings and suitable nesting sites. At more localized scales of 400 m2, crows use the range of cover types relatively evenly. While, increased heterogeneity and edge habitats often result in increased nest predation by corvids, raptors, squirrels and raccoons, such effects have not been documented in the Salish Sea ecosystem (Marzluff et al. 2007). In fact, reduced predation in some urban settings has been shown to positively impact populations of urban birds which, in turn, resulted in top-down trophic effects on insect herbivory (Faeth et al. 2005).

Analogous shifts in predator-prey dynamics and trophic relationships occur with urban coyote (Canis latrans) populations. Landscape heterogeneity combined with supplemental anthropogenic food resources – including house cats – in urban ecosystems provide favorable habitat conditions for coyotes in the Puget Sound region (Quinn 1997a,b) and other urban settings (Crooks and Soulé 1999; Crooks 2002; Patten and Bolger 2003; Gehrt and Prange 2007). Observations do not yield uniform conclusions regarding these trophic interactions (Gehrt and Prange 2007) and illustrate the important role of specific species-habitat relationships (Patten and Bolger 2003) in determining such interactions. Nonetheless, coyotes feed on mesopredators such as cats and raccoons (Quinn 1997a), which can have indirect positive impacts on urban songbird productivity (Crooks and Soulé 1999; Crooks 2002).

Placeholder – impacts on amphibian species

Placeholder – impacts on fish species

Placeholder – impacts on marine mammals

Placeholder – impacts on breeding versus non-breeding and resident versus migratory populations

State: Increased Imperviousness

Changes in LULC associated with residential, commercial and industrial development result in changes to hydrologic and material fluxes, volumes and pathways. At the more extreme level is the replacement of native vegetation with impervious surfaces: roadways, building structures, and artificial drainage pathways. Levels of imperviousness in urban landscapes result in modified surface- and groundwater pathways, water filtration and flow rates, which disrupts the balance between ground and surface water flows. Consequently, flows are linearized, more directly transported into streams and water bodies and result in more abrupt, extreme peaks in stream flow rates and volumes after storm events (Tague and Band 2001; Booth et al. 2002; Kaye et al. 2006). These modified pathways take both direct forms (e.g., culverts and stormwater drainage systems), and indirect forms (e.g., roads, building roofs, parking lots, and other built structures) that divert and focus water flow.

One of the significant characteristics of impervious surfaces is their relative permanence. Once constructed, residential, commercial and industrial structures tend to remain in place or are replaced by new impervious structures (Alberti et al. 2004; Alberti 2008). Alberti et al. (2004) noted that 86 percent of the central Puget Sound region consisting of paved land cover in 1991 was in the same state 8 years later. For mixed urban classes, which comprise between 15-75 percent impervious surfaces, persistence from 1991 to 1999 was approximately 96 percent (Alberti et al. 2004).

Impacts

As a result of increasing imperviousness associated with development, water, nutrients, bacteria, toxics and pollutants that would be absorbed, filtered and channeled by soils and vegetation in forested watersheds are more likely to be transported directly, more acutely, and in larger volumes, to streams, rivers, lakes, and ultimately the Salish Sea. By definition, impervious surface cover also impairs or prohibits the infiltration of water and nutrients into soils by creating an impermeable barrier over soils and by compacting remnant soil layers (Ragab et al. 2003a,b; Gregory et al. 2006; Kaye et al. 2006). Managed lawns also act as semi-pervious, if not impervious, surfaces, despite their vegetative nature: they have shallow, densely packed rootmats that result in compacted soils that reduce permeability relative to native forest communities (Schueler 1995; May et al. 1997).

Placeholder – expanded discussion of impervious surface impacts on hydrology and soils needed; e.g., C. P. Konrad, D. B. Booth, and S. J. Burges, 2005, Effects of urban development in the Puget Lowland, Washington, on interannual streamflow patterns: Consequences for channel form and streambed disturbance: Water Resources Research, v. 41(7), W07009, doi:10.1029/2005WR004097. See also other Water Center studies.

Placeholder – expanded discussion of altered soil conditions such as compaction and reduced absorption

Increased runoff from impermeable surfaces results in rapid and significant discharge of water, often highly contaminated into the Salish Sea. In the more extensively developed watersheds of central Puget Sound, stream gauge data indicate extensive fluctuations around annual mean daily flow volumes, and frequent occurrences of volumes above such levels . Krahn et al. (2007) attribute levels of persistent organic pollutants (POPs) occurring in resident Puget Sound marine mammals to direct transport of contaminants to water bodies, a consequence of imperviousness (Booth et al. 2002). A significant proportion of waterbodies in Washington listed as impaired for one or more pollutants under Section 303(d) of the Clean Water Act fall within the most developed regions that also have the highest impervious cover in the Puget Sound lowlands (Alberti et al. 2004).

Increased water and contaminant runoff from impervious surfaces have significant implications for biotic conditions in the Sound/Basin ecosystem (see Pollution threat below). For example, Bilby and Mollot (2008) observed significant relationships between changes in land cover and coho salmon (Oncorhynchus kisutch) abundance. Urbanizing watersheds in the central and northern Sound, which in the late 1980’s provided habitat for approximately 20 percent of the total number of spawning fish, were occupied by less than 5 percent of total fish numbers by around 2000. They attribute these shifts to heightened runoff resulting from increased imperviousness, leading to both higher water flow rates and volumes and increased mobilization of contaminants relative to levels observed in watersheds dominated by rural residential and forested areas (Bilby and Mollot 2008). Benthic indices of biotic integrity (Morley and Karr 2002; Booth et al. 2004; Alberti et al. 2007; Shandas and Alberti 2009) and fish (Matzen and Berge 2008) have declined as a consequence of the percent imperviousness within watersheds.

Placeholder – impacts on other fish species, zooplankton, and broader food web structure and function

State: Altered Biogeochemistry and Hydrology

Changes in the vegetation structure within watersheds alter or remove the water and nutrient retentive capacity associated with intact forests (Tague and Band 2001; Wickham et al. 2002; Groffman et al. 2004, 2006; Kaye et al. 2006). Ecological functions performed by remnant urban forest patches are diminished relative to their more connected, structurally and biologically complex exurban counterparts. Urban forests, for instance, exhibit higher potentials for nitrogen saturation (Wickham et al. 2002; Groffman et al. 2004; Zhu and Carreiro 2004). Water absorption into soils is also diminished or locally eliminated, particularly with higher levels of imperviousness. Changes in geomorphology and biota within urban riparian soils have been shown to lower denitrification potentials and thereby increase fluxes of nitrates into streams (Groffman et al. 2002, 2003, 2005). With losses of forest vegetation due to urban development, carbon sequestration will decline, with significant broader-scale implications for climate change (Churkina et al. 2010; Hutyra et al., in press). It should be noted, however, that recent research on forests along an urban-to-rural gradient in Seattle has pointed to significant carbon storage capacity within even urbanizing landscapes (Hutyra et al., in press).

LULC changes result in additional sources and inputs of nutrients. Fertilization of residential and recreational lawns contributes to increased soil nitrogen concentrations and runoff levels (King and Balogh 2001; Valiela and Bowen 2002; Law et al. 2004; Hope et al. 2005; Toran and Grandstaff 2007). Pet waste has also been suggested to be a significant component in urban nitrogen budgets (Baker et al. 2001a). Atmospheric deposition of nitrogen is typically higher in urban areas as a result of transportation- and industry-related combustion activities (Vitousek et al. 1997; Valiela and Bowen 2002; Kaye et al. 2006).

Impacts

Collectively, the above changes in material fluxes and concentrations contribute to increased pollution and sedimentation in streams. Brett et al. (2005) examined LULC-dependent contributions of nutrients and sediments to stream concentration levels along an urban-to-rural gradient in the central Puget Sound. They examined relationships between biophysical characteristics, such as land cover, topography and soils, and nutrient and sediment concentrations within 17 subbasins of the Cedar/Sammamish Water Resource Inventory Area. Compared with more completely forested basins, urban streams exhibited roughly 40% higher nitrogen levels and approximately 110% higher phosphorus levels. They note that though these nutrient discharge levels are lower than what might be observed within agricultural regions (e.g., Wickham et al. 2002; Weller et al. 2003), the levels have significant non-point source pollution implications.

Development-related LULC changes also alter hydrologic flow rates and volumes, particularly through the introduction of impervious surfaces (see above). Booth et al. (2002) examined impacts of development-related modifications to hydrology in King County, WA, particularly in the context of stormwater runoff. They found that, as a consequence of altered hydrologic conditions, hydrographs for urban streams exhibited peak discharge rates that are as much as twice as high as under pre-development conditions. Beyond the immediate, direct impacts of imperviousness on urban hydrology, Booth et al. (2002) noted that upstream rural development can also have a significant impact on downstream water quality and quantity and stream channel stability, through land clearing and removal of riparian vegetation. Their results emphasize the importance of limiting imperviousness within hydrologically sensitive segments of drainage basins, but also the relatively more significant contribution that can be made by maintaining significant upland forest cover (e.g., through clustered development) and riparian vegetation (see also Baker et al. 2001b).

Cuo et al. (2009) compared hydrologic effects associated with lowland urban development to upland forest harvesting using a version of the Distributed Hydrology-Soil-Vegetation Model (DHSVM; see also Cuo et al. 2008) along with historic and current land cover and meteorological data. The hydrology of upland basins subject to forest harvest remained largely intact but with decreased evapotranspiration and faster snowmelt rates. Earlier snowmelt trends in the early 21st century, a function of shifting temperatures, have also led to decreased summer flows in upland regions. In lowland watersheds LULC change increased flows due to changes in infiltration and surface flows associated with urban development. Relative increases in flow rates and volumes in the lowland sites depended on the level of development within specific basins.

Placeholder – expand discussion of impacts on riparian and stream ecosystems; additional references and information for effects of urbanization on stream hydrology and geomorphology

Useful references:

  • D. B. Booth, 2005, Challenges and prospects for restoring urban streams: Journal of the North American Benthological Society, v. 24, pp. 724-737.
  • C. P. Konrad, D. B. Booth, and S. J. Burges, 2005, Effects of urban development in the Puget Lowland, Washington, on interannual streamflow patterns: Consequences for channel form and streambed disturbance: Water Resources Research, v. 41(7), W07009, doi:10.1029/2005WR004097.
  • M. McBride and D. B. Booth, 2005, Urban impacts on physical stream conditions: effects of spatial scale, connectivity, and longitudinal trends: Journal of the American Water Resources Association, Vol. 41, No. 3, pp. 565-580.

State and Impacts: Physical Disturbance

Placeholder – includes state changes of increased ambient light, noise and heat, and relative impacts on suitable conditions for species

Placeholder - State and Impacts: Altered Food Webs

2. Placeholder- Pressure: Infrastructural Demands

Placeholder- State and Impacts: Water Withdrawals

State and Impacts: Wastewater - Placeholder (link to Pollution threat)

Placeholder - State and Impacts: Stormwater

Placeholder - State and Impacts: Transportation Corridors

3. Uncertainties and Information Gaps

The review above highlights the myriad pressures, state changes and consequent impacts associated with residential, commercial and industrial development. The growing field of urban ecology (Alberti 2008) increasingly provides information and an understanding of the distinct community-, ecosystem- and landscape-level interactions that characterize developed lands, and the unique role of humans in such systems. Changes associated with development result in species composition shifts, and changes in ecological community structure and the flows of water and materials in the Salish Sea ecosystem (e.g., Hepinstall et al. 2008, 2009). As the region becomes increasingly developed, we can expect these resultant ecological shifts to expand in extent and intensity.

Despite all that is known regarding ecological changes associated with development, significant gaps remain in quantifying the extent and relative magnitude of such impacts. A growing body of literature exists on shifts in bird, fish, and to some degree amphibian assemblages along urban-to-rural gradients in Puget Sound. Much work remains, however, to systematically investigate changes in plant communities, for which some data are available but with few syntheses, and invertebrate communities, for which little data appears to be available. Interactions between taxa, such as competition, predation and trophic relationships associated with development, have also been explored for birds and in freshwater and marine systems, but remain to be examined for other significant taxonomic groups in the Sound. A more thorough investigation of federal, state and local government reports, as well as non-governmental organization documents, may in fact provide significant information to fill many of these gaps. Such an expanded compilation of information and syntheses is thus strongly recommended

Syntheses examining biogeochemical impacts of residential, commercial and industrial development in the Salish Sea appear to be limited, particularly in the peer-reviewed journal literature. Much of the existing research on shifts in nutrient fluxes in developed landscapes such as changes in absorption and discharge rates associated with vegetation loss and increased imperviousness have come from studies in Baltimore (e.g., Groffman et al. 2002, 2003, 2004, 2005; Law et al. 2004; Pickett et al. 2008) and Phoenix (e.g., Baker et al. 2001a; Hope et al. 2005), the two urban ecosystem sites in the National Science Foundation’s Long-Term Ecological Research network. Similar comprehensive investigations remain to be compiled for the Salish Sea ecosystem. Systematic exploration of nutrient, sediment and other material loadings as a function of LULC composition and configuration within various watersheds, particularly along urban-to-rural gradients, would greatly enhance our understanding and prediction of biogeochemical trends, and resultant ecological impacts. Significant data sources exist through sampling efforts of federal (e.g., US Geological Survey), state (e.g., Washington Department of Ecology) and local (e.g., King County Department of Natural Resources and Parks) agencies. Again, some of the needed syntheses may exist in, and hence be identified through an expanded survey of, the larger body of government agency reports. However, sampling in some watersheds is limited to a single station, which is insufficient to capture the heterogeneity of landscape conditions and biogeochemical sources. Beyond data limitations, there is also the need to comprehensively analyze existing data, in order to understand the interplay between the distinct landscape characteristics of developed versus undeveloped lands. Expanded efforts at adapting existing ecosystem process models or developing new ones for the region could help us understand and predict the effects of development on biogeochemical fluxes (see the section on ecosystem models below).

 

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