Invasive weeds in urban riparian zones: the influence of catchment imperviousness and soil chemistry across an urbanization gradient

The riparian zones of urban waterways are frequently degraded by weed invasions. This study examined the effects of different levels of catchment imperviousness, as a surrogate for the extent and intensity of urbanisation, on invasive weeds and soil physical and chemical attributes. The study was conducted adjacent to waterways in the partly urbanised Georges River catchment in south western Sydney. Vegetation and soil sampling was undertaken in the riparian zone of 10 freshwater streams in non-urban (low imperviousness), peri-urban (moderate imperviousness) and urban (high imperviousness) sub-catchments. Soil samples were tested for a suite of physical and chemical properties (moisture, bulk density, organic matter, pH, salinity, phosphorus, potassium and calcium). Increased levels of sub-catchment imperviousness and urbanisation were associated with higher weed coverage and elevated soil geochemical attributes. One of the most interesting findings in this study was that urban soil calcium concentrations were over 2000 times greater than soils collected from non-urban catchments. The BIOENV procedure identified soil pH, salinity, calcium, organic matter, moisture and catchment imperviousness to be important environmental factors associated with variation in riparian vegetation. The single factor of soil pH was most highly correlated with variations in riparian vegetation. Soil pH was approximately 1.5 units higher in urban compared to non-urban riparian soils. We speculate that there is a link between urban concrete materials, urban soil and water contaminants and riparian weed invasion. We also recommend further study into the contribution of urban concrete materials on the geochemical contamination of riparian soils.     

The effects of urbanization on carnivores in the New York metropolitan area

Urban Ecosystems - The presence of human activity and development affects the distribution and behavior of carnivore species in various ways. It is necessary to examine the effects of urbanization...     

Spatial variation in soil inorganic nitrogen across an arid urban ecosystem

We explored variations in inorganic soil nitrogen (N) concentrations across metropolitan Phoenix, Arizona, and the surrounding desert using a probability-based synoptic survey. Data were examined using spatial statistics on the entire region, as well as for the desert and urban sites separately. Concentrations of both NO₃-N and NH₄-N were markedly higher and more heterogeneous amongst urban compared to desert soils. Regional variation in soil NO₃-N concentration was best explained by latitude, land use history, population density, along with percent cover of impervious surfaces and lawn, whereas soil NH₄-N concentrations were related to only latitude and population density. Within the urban area, patterns in both soil NO₃-N and NH₄-N were best predicted by elevation, population density and type of irrigation in the surrounding neighborhood. Spatial autocorrelation of soil NO₃-N concentrations explained 49% of variation among desert sites but was absent between urban sites. We suggest that inorganic soil N concentrations are controlled by a number of ‘local’ or ‘neighborhood’ human-related drivers in the city, rather than factors related to an urban-rural gradient.     

Direct and indirect effects of urbanization on soil and plant nutrients in desert ecosystems of the Phoenix metropolitan area,Arizona (USA)

Desert landscaping has become a dominant land cover type in arid US cities and often includes native plant species. Does replacement of native plant distribution in urban areas also reestablish ecological functioning characteristic of natural deserts? We compared ecological processes in three landscape types that are common to the metropolitan area of Phoenix, Arizona (USA): residential desert yards created from former lawns, Sonoran Desert preserves within the city, and Sonoran Desert preserves outside the city boundaries. Canopy cover, abundance of herbivorous insects, and soil properties (concentration of inorganic nitrogen (N), soil moisture and organic matter content, and water-holding capacity) were higher in residential desert yards than in native desert sites located both within and outside of the city. Furthermore, soil resources in desert yards were not organized around plant canopies, departing from the predictable resource island pattern that is characteristic of natural deserts. Intentional human manipulation and land use history accounts for these differences, while the urban environment contributes only subtly to soil N concentrations beneath plant canopies. While the use of desert landscaping may have important water conservation benefits, it does not help to mitigate the well-documented excess of reactive N within the Phoenix metropolitan area.     

Tick infestation of birds across a gradient of urbanization intensity in the United States Great Plains

Urban Ecosystems - Migratory birds play an important role in large-scale movements of ticks and tick-borne pathogens, yet little is known about tick infestation of resident birds (e.g.,...     

Contrasting soil nitrogen dynamics across a montane meadow and urban lawn in a semi-arid watershed

Urbanization substantially increases nitrogen (N) inputs and hydrologic losses relative to wildland ecosystems, although the fate of N additions to lawns and remnant grasslands remains contested. In montane semi-arid ecosystems, N cycling is often closely coupled to snowmelt (the dominant period of infiltration) and snow cover, which impact soil temperature and moisture. Here, we compared soil N dynamics between a fertilized and irrigated urban lawn and nearby riparian meadow in Salt Lake City, Utah during a snow manipulation experiment. Snow removal increased freeze/thaw events but did not affect N pools, microbial biomass, denitrification potential, or soil oxygen (O₂). Mineral N was similar between sites despite lawn fertilization, but dissolved organic N (DON) was four-fold greater (2.1 ± 0.1 mg N l^?1) in lawn soil water. Infiltration was lower in the lawn subsoil, and leaching losses (modeled with Hydrus) were small at both sites (< 2 kg N ha^?1 y^?1) despite substantial lawn fertilization. Lawn soil O₂ fluctuated between 20.9 and 1.6 % following snowmelt and irrigation, but remained near 20 % in the meadow; the lawn had more reducing microsites as indicated by iron speciation. Post-snowmelt potential denitrification was six-fold greater in the lawn than the meadow. Lawns can potentially provide hotspots of denitrification in a semi-arid landscape that exceed some natural riparian ecosystems, whereas DON may represent an increasingly important form of N loss from lawns.     

Changes in chemical and physical propertiesof stream water across an urban-rural gradient in western Georgia

The Middle Chattahoochee River Watershed in western Georgia is undergoing rapid urban development. Consequently, Georgia’s water quality is threatened by extensive development as well as other land uses such as grazing. Maintenance of stream water quality, as land development occurs, is critical for the protection of drinking water, biotic integrity, and stream morphology. A two-phase, watershed-scale study was established to develop relationships among land use and water quality within western Georgia. During phase 1 (year one), physio-chemical, biological and morphological measurements were taken within 16 sub-watersheds, ranging in size from 500–2500 ha. Nutrient and fecal coliform concentrations within watersheds with impervious surface > 5% often exceeded those in other watersheds during both baseflow and storm flow. Also, fecal coliform bacteria in more urbanized areas often exceeded the US EPA’s standard for recreational waters. During the second phase of the study, models will be tested and calibrated based on newly chosen watersheds.     

Relation of urbanization to stream fish assemblages and species traits in nine metropolitan areas of the United States

We examined associations of fish assemblages and fish traits with urbanization and selected environmental variables in nine major United States metropolitan areas. The strongest relations between fishes and urbanization occurred in the metropolitan areas of Atlanta, Georgia; Birmingham, Alabama; Boston, Massachusetts; and Portland, Oregon. In these areas, environmental variables with strong associations (r_s ≥ 0.70) with fish assemblages and fish traits tended to have strong associations with urbanization. Relations of urbanization with fish assemblages and fish traits were weaker in Denver, Colorado; Dallas-Fort Worth, Texas; Milwaukee-Green Bay, Wisconsin; and Raleigh, North Carolina. Environmental variables associated with fishes varied among the metropolitan areas. The metropolitan areas with poor relations may have had a limited range of possible response because of previous landscape disturbances. Given the complexities of urban landscapes in different metropolitan areas, our results indicate that caution is warranted when generalizing about biological responses to urbanization.     

Influence of a parking area on soils and vegetation in an urban nature reserve

We studied the influence of a car park on soil and vegetation within Richmond Park, UK, before and after imposition of fenced boundaries restricted public access. Soil and vegetation samples were taken before (once) and after (twice) access restrictions were enforced. The over-riding trend in all the data was for soil adjacent to the car park to be less acidic and more fertile than pristine local soils, accompanied by a more eutrophic grassland community (Lolium perenne/Trifolium repens, compared with Agrostis/Festuca grassland away from the car park). The chemical influence of the car park extended at least 50 m from its boundary. A common acidophilic collembole Folsomia quadrioculata was replaced by Cryptopygus thermophilus adjacent to the car park. There was little evidence from the vegetation data that car park closure benefitted the ecosystem, but chemical data showed signs of progressive recovery in the 2 years following restrictions. Possible explanations for the car park's influence on the local landscape are suggested to include calcareous chippings and canine faecal deposits.     

The effect of artificial light on bat richness and nocturnal soundscapes along an urbanization gradient in an arid landscape of central Peru

Urbanization usually reduces bat richness; however, the presence of green areas within cities and peripheral rural areas in arid ecosystems may provide microhabitats for some species. Light pollution is a major feature of urbanization, but its impact on bat behavior appears to be species-specific and previous studies have documented contrasting responses. Moreover, the effect of urbanization on bat species has been poorly studied in arid regions. We assessed the effect of artificial night light intensity (as a proxy of urbanization) on both bat occupancy and the acoustic space used (ASU) in an urbanization gradient in Peruvian central coast, based on passive acoustic recorders. We collected 26,169 recordings from 19 sites which resulted in 579 independent detections of 15 bat species. Variation in both ASU and species richness was best explained by artificial night light intensity. Species-specific effects of the artificial night light intensity based on a multi-species occupancy modeling showed that this covariate had a negative effect on occupancy for most of the bat species (12 species). ASU and both observed and posterior bat species richness were positively correlated, suggesting that ASU can be used as a proxy of bat richness. This study provides evidence that both bat richness and occupancy decrease with artificial light intensity; nevertheless, eight species used urban areas, similar to results found in other cities around the world.

     

Litter decomposition and nitrogen mineralization in oak stands along an urban-rural land use gradient

We investigated litter mass loss and soil nitrogen (N)-transformation rates in oak stands along a 130-km, urban-rural transect originating in New York City to examine the relationship between changes in these parameters and previously documented differences in soil temperature, heavy metal and total salt concentrations, and soil biota. Reference litter from a rural site was placed in litterbags, and rates of mass loss and changes in N concentration in litter residues were measured over a 6-month period. Net N-mineralization and nitrification rates were measured in A horizon soils using laboratory incubations under constant moisture and temperature. Both mass loss (76%) and N release (65%) from litterbags reached their maximum in urban stands, whereas net N-mineralization rates were 2.3-fold higher than in rural A horizon soils. Litter fragmentation by earthworms and higher soil temperatures are potential causes of the higher mass loss rates observed in urban stands. The higher releases of N measured in the urban litterbags could be a result of their faster mass loss rates, exogenous inputs of N from atmospheric deposition, a relatively low heterotrophic demand for N, or a combination of these factors. The results of this study suggest that in comparison with rural stands, urban forests are characterized by comparatively high rates of litter decomposition, and may also be characterized by comparatively high rates of N mineralization. Additional studies are needed to test whether these effects are common to urban environments in general.     

Water sources of urban trees in the Los Angeles metropolitan area

In semi-arid cities, urban trees are often irrigated, but may also utilize natural water sources such as groundwater. Consequently, the sources of water for urban tree transpiration may be uncertain, complicating efforts to efficiently manage water resources. We used a novel approach based on stable isotopes to determine tree water sources in the Los Angeles basin, where we hypothesized that trees would rely on irrigation water in the soil rather than develop deep roots to tap into groundwater. We evaluated the oxygen (δ¹⁸O) and hydrogen (δD) isotope ratios of xylem water, irrigation water, soil water, and groundwater in a study of temporal patterns in water sources at two urban sites, and a study of spatial patterns at nine urban sites and one “natural” riparian forest. Contrary to our hypothesis, we found that despite frequent irrigation, some trees tap into groundwater, although in most species this was a small water source. Some trees appeared to be using very shallow soil water at <30 cm depth, suggesting that these mature urban trees were quite shallowly rooted. In the natural site, trees appeared to be using urban runoff in addition to shallow soil water. We were able to identify tree uptake of precipitation at only 3 sites. The results show that some irrigated trees utilize groundwater and do not rely solely on irrigation water, which may make them able to withstand drought and/or water conservation measures. However, some irrigated trees may develop very shallow root systems, which may make them more susceptible.     

Comparison of decapod communities across an urban-forest land use gradient in Puerto Rican streams

Urbanization influences a range of factors related to stream health, including the hydrologic regime, water quality, and riparian conditions that lead to negative effects on terrestrial and aquatic ecosystems. However, impacts on freshwater decapods from urbanization of tropical streams have not been reported. We hypothesized that changes in decapod communities in watersheds with different levels of urbanization are related to changes in physical stream habitats caused by different land uses and their effects on water discharge. The impacts of land use on the physico-chemical characteristics of streams and freshwater decapod communities were evaluated in three watersheds characterized by low, moderate and high-intensities of urbanization in Puerto Rico. For the low and moderately developed urban watersheds, decapod species richness ranged from 10 to 11 species; the highly urbanized watershed only had 4 species. Macrobrachium faustinum and Xiphocaris elongata were the most ubiquitously species and were found in all watersheds. Multivariable analysis of physical characteristics and densities of the decapod families resulted in one axis that explained 80 % of the total variation among the watersheds and was correlated with stream discharge. The effect of discharge is likely a result of frequent high flows that sustain habitats with high concentrations of dissolved oxygen and low concentrations of pollutants. An increase in physico-chemical parameters were observed from the LUW to the HUW. These results indicate that the decapod communities were most likely influenced by land use and environmental conditions that affected erosional aspects related to water discharge and water quality in the highly impacted watersheds.     

A comparison of three landscape classifications and investigation of the potential for using remotely sensed land cover data for landscape classification

Numerical landscape classifications group land units (e.g. 1-km grid squares) with similar characteristics into distinct landscape types (termed land classes). Landscape classifications have considerable potential as tools in rural land-use planning. To date, a plethora of numerical classifications have been developed, yet little attempt has been made to quantify differences between classifications which may arise through the use of different attribute data and classification techniques. The present paper quantifies differences between three hierarchical landscape classifications developed using closely related algorithms, but using contrasting attribute data. Two classifications were based on land cover; from field survey and remote sensing, respectively. The third was based primarily on abiotic environmental variables. Quantitative comparisons between the three classifications indicate that similar land classes are recognisable at different levels of environmental and ecological organisation. It is concluded that the use of remotely sensed land cover in the production of landscape classification has many advantages over previous approaches. Foremost among these benefits are the ease with which digital land cover data can be handled within Geographic Information Systems and the consequential ability to produce classifications rapidly at differing spatial resolutions. The potential roles of numerical landscape classifications in rural planning are reviewed.     

Managing urban growth and development in the Riyadh metropolitan area, Saudi Arabia

The paper examines public sector management of urban growth and development in the Riyadh Metropolitan Area, Saudi Arabia. The focus of the paper is on institutional capacity building and development intervention. The paper traces changes in public sector management structures and development activities over the history of the city with the aim of assessing development impact and identifying forces that have shaped the evolving state of urban management. The paper notes that urban management has significantly improved with time but the persistence of urban problems coupled with projections of future growth point to the need for further improvements. The paper, in conclusion, while acknowledging the utility of the metropolitan development strategy (MEDSTAR) being formulated for the city, points to the need for broader administrative reform to improve the ability to cope with long-term challenges of growth in the city. Some issues that reform could address are suggested.     

“新区建设与大城市的发展”学术研讨会暨中国城市经济学会大城市专业委员会2009年会会议综述

2009年7月4日～6日、南中国城市经济学会大城市专业委员会主办、天津城市科学研究会和环渤海经济研究会协办的“新区建设与大城市的发展”学术研讨会．暨中国城市经济学会大城市专业委员会2009年会在天津滨海新区召开。出席会议的有中国城市经济学会大城市委员会的委员和有关专家、学者共56人。中国城市经济学会常务副会长龙永枢。中国城市经济学会副会长、天津市人大原副主任王德惠．天津市政协原副主席王家瑜．     

Relationships between urban parks and bird diversity in the Bangkok metropolitan area,Thailand

An analysis of the birds in Bangkok’s urban parks and landscapes provided guidance in designing healthy urban ecosystems. This research studied the relationships between bird diversity, park size, distance to the nearest main park, and habitat compositions in 10 urban parks in the Bangkok metropolitan area between January and August in 2013. Thirty sampling points per park were used to observe the number and species of birds in each urban park. A total of 50 bird species were found. Phutthamonthon, the largest urban park (400 ha), contained the greatest number of species (39 species), followed by Suan Luang Rama IX (80 ha and 34 species) and Wachirabenchatat (60 ha and 29 species). Moreover, the diversity index (H′) was highest in Phuttamonthon (1.17), followed by Thawiwanarom (1.08), and Wachirabenchatat (1.04). Larger urban parks and parks closer to the largest urban park had higher species richness than smaller parks and parks further from the largest urban park. The large parks contain higher habitat compositions than small parks. These findings can be applied to future urban ecosystem planning to combine the importance of park size (island size, and its proximity to a large park) and its arrangement, including features such as wetland, forest, buildings and grassland; and provide basic advice for future urban park design, as well as re-design of current urban parks.

     

Unfair treatment, neighborhood effects, and mental health in the Detroit metropolitan area

Why do racial differences in many indicators of mental and emotional well-being show inconsistent patterns? We propose that mental and emotional well-being are influenced by aspects of the social context, including experiences of unfair treatment and the concentration of households with incomes below the poverty level, and that differential exposure to these factors influences racial differences in mental well-being. We analyze the reporting of psychological distress and life satisfaction in a multistage area probability sample of 1,139 African American and white residents of the Detroit metropolitan area aged 18 and older. Both psychological distress and life satisfaction are significantly associated with exposure to unfair treatment and with the proportion of households in the census block group that were below the poverty level. Racial differences in psychological distress and life satisfaction were eliminated or reversed once differentials in the percent of households living below the poverty line and exposure to unfair treatment were accounted for. These findings contribute to a growing body of evidence that "race" effects operate through multiple pathways that include race-based residential segregation and its attendant economic disinvestment at the community level, and interpersonal experiences of unfair treatment.     

Class inequalities in access to social capital in the metropolitan area of Buenos Aires

this paper analyzes social class inequalities in access to social capital. Quantitative methodology was used with data from the PI-Clases “Reproduction and social mobility in family trajectories and life courses” survey, conducted in the Metropolitan Area of Buenos Aires in 2015 (n = 1065). Social capital measures where derived from the Position Generator (Lin, 2001) to identify the volume, status and range of the respondent’s networks. Results show that there are class inequalities in access to social capital in terms of the number of contacts, mean status of contacts, range of contact’s status and highest status of contacts. Also, the working class is more heterogeneous in its access to social capital, suggesting it has a sector that has network ties with people from the middle class and a sector with lower social capital. The observed trend is of gradational differences between class strata, with more marked inequalities between the service, intermediate and working class, but with fluid class boundaries without social segregation. Also, social capital is conditioned by intergenerational mobility trajectory, showing a trend of elasticity in the class composition of social relationships. The upwardly mobile can increase their access to social capital but don’t reach the same level as the intergenerationally stable, while the downwardly mobile retain some social capital from their class origins.