Impervious Cover Research Articles

Balancing development and sustainability: Assessing risks and protecting aquatic biodiversity on US college and university campuses

AbstractExtensive urbanization impairs biological communities through landscape alteration and physiochemical changes to stream ecosystems. Analogous to urban development in cities, new building and facility expansion on university campuses can lead to dramatic changes in impervious cover and consequently, increased stormflow impacting downstream ecological communities. Here, we analyze the extent and relevance on a nationwide scale to determine campuses with the highest risk for ecological impairment. From the US‐wide analysis of 5761 college/university campuses, ~45% of campuses were within critical aquatic species watersheds, and >5% were identified as buffering critical habitat. The highest risk campus our study identified was selected to compare the impacts of planned, conventional development versus sustainable development on a sensitive aquatic species, the federally threatened Jollyville Plateau salamander (Eurycea tonkawae). Impervious cover, simulated increases in stormwater runoff, and total suspended solids (TSS) from the conventional expansion is estimated to lower salamander density. Conversely, an alternative campus expansion plan allowed for increased development but permitted provisions for reduced runoff and TSS, thereby maintaining current salamander densities. Our findings show that sustainable campus development plans have the potential to mitigate ecological disruption within watersheds, and that campus management and policies are critical for preserving biodiversity in the future.

Beyond Phosphorus: Salinization as a driver of eutrophication symptoms in North American lakes

The acceleration of global urbanization continues to fuel concerns surrounding water quality impairments in urban lakes, particularly eutrophication. Eutrophication of freshwater environments is generally assumed to be driven by increased anthropogenic phosphorus (P) supplies which can alleviate limitations on primary production. Salinization is also recognized as a stressor on urban freshwater quality, particularly in cold temperate climate regions where salts are applied to road surfaces as de-icing agents. While the ecological damages caused by P enrichment and salinization to freshwaters are both well established, thus far, their impacts on water quality have only been considered independently. Although improvements to the management of urban stormwater and wastewater have decreased P inputs to freshwater systems in recent decades, many lakes worldwide remain eutrophic, as indicated by declining dissolved oxygen (DO) concentrations and rising dissolved inorganic P (DIP) concentrations in the hypolimnion. Our previous study of an urban freshwater lake in Ontario, Canada, showed that persistent eutrophication symptoms are linked to salinization associated with impervious land cover expansion, rather than increased external P loading. In this research, we present a multiple decade of water chemistry data analyses for several other urban lakes in Ontario, Wisconsin, and Minnesota to determine how increased lake salinization rates intersect with water temperature and morphometry to alter water column stratification, thus, increasing eutrophication symptoms. Our trend analysis shows progressive salinization (observed through significant increases in chloride or electrical conductivity) of all the lakes investigated. Calculations of lakes mixing indices over time show that, on average, lake stratification is becoming more stable with increased salinity playing a crucial role in enhancing lake stratification. Overall, salinity is becoming a stronger regulator of water density than temperature in the cold temperate urban freshwater lakes of North America. The increasing salinity trends are accompanied by increasing hypolimnion hypoxia and increasing DIP to total P (TP) ratios in all lakes, thereby demonstrating the mechanistic link between salinization and internal P loading. Rising salinity intensifies water column stratification, in turn, reducing the oxygenation of the hypolimnion and enhancing internal P loading from the sediments. These results highlight that stricter management of de-icing salt application rates should be considered to control lake eutrophication symptoms in cold climate regions.

Historical racial redlining and contemporary patterns of income inequality negatively affect birds, their habitat, and people in Los Angeles, California

Abstract The Home Owners’ Loan Corporation (HOLC) was a U.S. government-sponsored program initiated in the 1930s to evaluate mortgage lending risk. The program resulted in hand-drawn “security risk” maps intended to grade sections of cities where investment should be focused (greenlined areas) or limited (redlined zones). The security maps have since been widely criticized as being inherently racist and have been associated with high levels of segregation and lower levels of green amenities in cities across the country. Our goal was to explore the potential legacy effects of the HOLC grading practice on birds, their habitat, and the people who may experience them throughout a metropolis where the security risk maps were widely applied, Greater Los Angeles, California (L.A.). We used ground-collected, remotely sensed, and census data and descriptive and predictive modeling approaches to address our goal. Patterns of bird habitat and avian communities strongly aligned with the luxury-effect phenomenon, where green amenities were more robust, and bird communities were more diverse and abundant in the wealthiest parts of L.A. Our analysis also revealed potential legacy effects from the HOLC grading practice. Associations between bird habitat features and avian communities in redlined and greenlined zones were generally stronger than in areas of L.A. that did not experience the HOLC grading, in part because redlined zones, which included some of the poorest locations of L.A., had the highest levels of dense urban conditions (e.g., impervious surface cover), whereas greenlined zones, which included some of the wealthiest areas of the city, had the highest levels of green amenities (e.g., tree canopy cover). The White population of L.A., which constitutes the highest percentage of a racial or ethnic group in greenlined areas, was aligned with a considerably greater abundance of birds affiliated with natural habitat features (e.g., trees and shrubs). Conversely, the Hispanic or Latino population, which is dominant in redlined zones, was positively related to a significantly greater abundance of synanthropic birds, which are species associated with dense urban conditions. Our results suggest that historical redlining and contemporary patterns of income inequality are associated with distinct avifaunal communities and their habitat, which potentially influence the human experience of these components of biodiversity throughout L.A. Redlined zones and low-income residential areas that were not graded by the HOLC can particularly benefit from deliberate urban greening and habitat enhancement projects, which would likely carry over to benefit birds and humans.

The economic impacts of green stormwater infrastructure: An evaluation of novel stormwater management policies in Washington, D.C.

Increases in urban stormwater infrastructure needs have led cities around the world to turn towards nature-based ‘green’ stormwater infrastructure (GI). While GI can be an effective tool for addressing many urban flooding and water quality problems, many policymakers remain skeptical of GI due to concerns about financial uncertainties and performance risks. Moreover, cost-benefit analyses of changes to urban infrastructure policies often fail to consider the economic impacts – jobs created and value added to the regional economy – of infrastructure (traditional or GI) construction. Compounding this, few studies have modeled the economic impacts of GI. In this paper, we analyze the economic impacts arising from novel development regulations requiring GI to offset impervious cover expansion in Washington, D.C (USA). Using data from a survey of GI construction firms, we determine annual, direct GI investment, and construct an input-output model to estimate indirect and induced economic impacts at the regional scale. We find that, from 2015 to 2020, GI construction supported over $91 million in average annual economic output, ∼$45 million in labor income, ∼$60 million in value added, and created (or supported) 437 jobs in the DC metropolitan region. Sensitivity analysis around regulatory stringency (higher or lower stormwater retention requirements) reveals asymmetric economic impacts that increase more given higher retention requirements than they decrease for lower retention requirements. Our analytical approach can serve as a model to help other regions produce a more comprehensive accounting of the economic feasibility of green infrastructure for urban stormwater management.

Evapotranspiration From Developed Land and Urban Watersheds in a Humid Subtropical Climate

AbstractUrbanization introduces new and alters the existing hydrological processes. Projecting the direction and magnitude of change of evapotranspiration (ET), often a large existing process, in humid subtropical climates is difficult due to the lack of land‐cover specific estimates of ET. This research aims to improve our fundamental understanding of ET in urban areas by focusing on ET specific to land‐cover classes of the National Land Cover Database (NLCD). Using multiple physically based models along with ET from reference watersheds, this study estimates ET—within the Atlanta, GA, USA region—for NLCD classes. ET also is estimated for urban watersheds—both in the Atlanta region and in areas with humid subtropical climate types—for which published ET estimates exist. There are major differences in land cover among the four developed classes: high‐intensity developed land is 92% impervious surfaces, while open‐space developed land—the least intensively developed land—is only 8% impervious surfaces. Consequently, open‐space developed land has an ET total that is over four times that of high‐intensity developed land. Due to a high percentage of impervious cover and substantial evaporation of water from impervious surfaces throughout the year, there is little intra‐annual variation in ET for the high‐intensity developed class. The land‐cover ET totals aggregate to reliable estimates for urban watersheds. The largest source of uncertainty for ET estimates in urban areas is likely the evaporation magnitude associated with impervious surfaces; therefore, more work is needed in determining those magnitudes for humid subtropical climates.

Impervious Land Expansion as a Control Parameter for Climate-Resilient Planning on the Mediterranean Coast: Evidence from Greece

Impervious land expansion is linked to ecosystem fragmentation and degradation, posing threats to nature conservation and multiplying climate change impacts. This is particularly true on the Mediterranean coast, where persistent urbanization is coupled with tourism development, further intensifying coastal erosion, flood risk, heat stress and biodiversity loss, while decreasing carbon sequestration. In this research, high-resolution imperviousness data were analyzed through a geospatial methodology to detect patterns and processes in a heavily burdened Mediterranean coastal area, namely Greece. The methodology was structured on a set of GIS tools, analyzing the distribution of new impervious cover between 2006 and 2018, to evaluate pressures exerted on coastal territories and on the environmental protection network. The results revealed relatively slow rates of impervious land expansion at a nationwide scale, mostly attributed to the economic recession period in Greece. However, certain locations exhibited continuing artificialization of land even within Natura 2000 areas, while future pressures on coastal territories are expected to increase due to the restarting of construction activity and the continuing dynamic of the mass tourism sector. The conclusions imply that controlling for imperviousness is important in order to develop spatial planning policies for climate resilience, which should be decisively enforced in the Mediterranean to prevent a business-as-usual scenario.

Rise and fall of an avian oasis: Tracking the impacts of land use change in a key coastal wetland in the world's largest megalopolis

Tropical estuaries support wetlands with high biodiversity value and provide essential ecosystem services. Many of these systems, however, are global hotspots for urbanization, particularly in Asia, where this process has resulted in rapid conversion, fragmentation, and degradation of 80 % of the wetlands along the East Asian-Australasian Flyway (EAAF) for migratory birds. However, the impact of such landscape scale changes on migratory birds at a key stopover site along the EAAF has not been evaluated. Here, we used long-term data (> 40 years) from Deep Bay (Hong Kong), a shallow embayment in the Pearl River estuary (PRE) in south China, to investigate the impact of urbanization on (1) catchment land use and water quality, and (2) its impact on the capacity of the wetland to support populations of migratory waterbirds. Deep Bay supports the largest remnants of mangrove forests and tidal mudflats in the PRE and is an important refueling ground along the EAAF. It is also part of the Greater Bay Area (GBA, population 86 million), the world's largest megalopolis. The principal component analysis highlighted the nutrient loading and cleansing effect from seasonal flushing as characterizing variation in water quality in Deep Bay over four decades. Major shifts in water quality during the study period were accompanied by contemporaneous changes in wintering waterbirds numbers. Prior to 2003, the main drivers of water quality were organic nutrients from animal husbandry. Following large-scale reclamation and increases in impervious surface cover post-2003, primarily due to the development of the megacity of Shenzhen (population 17.7 million), the hydrodynamics of Deep Bay have changed, with knock-on effects of sedimentation, input of pollutants, and changes in the macrobenthos. The wintering waterbirds community responded to these changes both in total numbers and the relative importance of feeding guilds. Where total bird counts are positively influenced by benthic biomass, and the benthic biomass is positively correlated to the water quality that is driven by the cleansing effect of tidal flushing. These anthropogenic drivers have negatively impacted migratory birds that use Deep Bay as a refueling station. This study highlights the need for policymakers to control these drivers and limit the level to which sensitive coastlines are urbanized.

London Plane Bark Exfoliation and Tree-Ring Growth in Urban Environments

AbstractBackgroundBark exfoliation is a common feature of London planes (Platanus×acerifolia) that reportedly increases during periods of drought-induced stem shrinkage. Here, we explore the spatial patterns and potential drivers of plane bark exfoliation in Mainz, a central European city of 220,000 inhabitants, following the exceptional summer drought of 2018.MethodsWe estimate the degree of bark exfoliation of 349 urban plane trees across the city and use stem microcores to analyze their tree-ring widths from 2006 to 2019. Further to impervious cover, settlement structure and vegetation cover in the vicinity of each tree, we investigate the relationships between bark exfoliation and tree, site, and climate factors.ResultsResults indicate that plane bark exfoliation correlates significantly with tree size and inner bark width (bothp< 0.001) but is independent of impervious cover and local site conditions. Similarly, stem growth does not change within the city underlining the resilience of London planes to cope with highly diverse urban site conditions. Plane tree-ring widths were only weakly associated with exfoliation estimates (p< 0.05) but strongly controlled by cold season temperatures (p< 0.001).ConclusionAs tree growth was also not affected by summer drought, potential detrimental effects by limited infiltration, increased runoff and altered evaporation are of less concern for the plane trees in Mainz. Projected winter warming is likely to enhance urban plane growth in upcoming decades.

Micropollutants but high risks: Human multiple stressors increase risks of freshwater ecosystems at the megacity-scale

Micropollutants in water environments have attracted widespread attention, but how human and natural stressors influence the risks of micropollutants has not been comprehensively revealed. A megacity-scale study of the ecological risks of micropollutants in the surface water of Beijing, China is presented to illustrate the magnitudes of the influences of multiple anthropogenic and natural stressors. A total of 133 micropollutants representing typical land use patterns in Beijing, were quantified with the mean concentration range of ND (not detected) to 272 ng·L−1. The micropollutant concentrations in the south were obviously higher than those detected in the northern areas, and neonicotinoid pesticides showed the highest mean concentration of 311 ng·L−1. The chronic and acute risks of micropollutants to algae, invertebrates, and fishes were determined, and herbicides, organophosphorus esters, and insecticides account for the primary risks to algae, invertebrates, and fishes, respectively. The cropland and impervious cover cause the differences in the pollution and risks of micropollutants. The land use in riparian zones greater than 2 km shows a great influence on the chronic chemical risks (CCRs) for the three groups of species, indicating that too local scale does not explain the local pollution status. Climate conditions and human land use are important drivers explaining the CCRs to which various trophic levels of species are exposed. Results demonstrate that multiple categories of micropollutants pose adverse risks to freshwater in the megacity of Beijing, while climate conditions, pollution discharge, and human land use induce the chemical risk of micropollutants to aquatic organisms, and the land use in different riparian zones show different effects on the risks.

High summer land surface temperatures in a temperate city are mitigated by tree canopy cover

As climate warms, the impact of existing urban heat islands on the health of residents in towns and cities will worsen. A reduction in impervious in cities may help to reduce temperatures, but the relationship between tree canopy coverage and land surface temperature (LST) is not well characterised. Here, we quantified the summer LST of the temperate city of Leeds, UK using Landsat 8 TIRS remote sensing image and explored the spatial relationships between LST and impervious land cover, greenspace coverage, type of greenspace and canopy cover. We found a strong relationship between LST and canopy coverage across the built-up region of Leeds and use this relationship to project the impact of future canopy cover expansion. We found that of the nine main types of greenspaces in Leeds, private gardens occupied the greatest fraction of the total greenspace area and offered most potential for canopy cover expansion. Results suggest that a doubling of canopy coverage across the city, could reduce the mean LST by around 2.5 °C during the warmest summer months. Such a temperature reduction adds further weight to efforts by cities and countries globally to increase tree cover to both mitigate for and adapt to climate change.

Urban stream restorations increase floodplain soil carbon and nutrient retention along a chronosequence

Stream restoration is a common management practice to meet regulatory or voluntary efforts to improve water quality via nutrient and carbon (C) retention, including in the Chesapeake Bay watershed. However, most restoration projects have few quantifiable measures of project success, no standard metrics, and rarely collect pre-restoration data. Storage of nutrients, such as phosphorus (P) and nitrogen (N), in floodplain soils of restored streams can act as an easily quantifiable indicator of restoration success, particularly when the project goals include improved water quality. To determine how floodplains of restored streams change in their P and C storage as time since restoration increases, floodplain surficial soil samples (10 cm depth) were collected from 18 streams in the urbanized Piedmont region of northern Virginia, representing a chronosequence of time (1–10+ yrs.) since restoration as well as unrestored streams with high impervious surface cover (ISC) and unrestored streams with low ISC. The samples were analyzed for total carbon (TC), total nitrogen (TN) and total phosphorus (TP) storage, whereas C turnover rate and equilibrium phosphorus concentration (EPC0) were measured as metrics of C and P loss. These metrics were compared to time since restoration and potential environmental drivers, including soil moisture, pH, median particle size (D50), organic matter content (OM), and bioavailable P, iron (Fe), and aluminum (Al). These stream restorations demonstrated increasing nutrient storage for TC, TN, and TP along the chronosequence to values greater than both unrestored or reference streams, as well as decreasing C turnover and no significant changes in EPC0. Soil wetness and OM, key drivers in nutrient retention, also increased as restoration projects aged increasing C, N, and P storage. Overall, stream restoration did improve soil C, N, and P retention in floodplains as compared to unrestored sites and exceeded those of low ISC ‘reference’ sites.

Measuring nocturnal near-surface urban heat island intensity in the small, mid-latitude city of Inverness, Scotland

ABSTRACT Few publications have considered the urban heat island (UHI) effect in small settlements. This paper, therefore, presents the findings of a UHI study conducted in the small, mid-latitude city of Inverness, Scotland (population: 63,220). The study aimed to provide an initial appraisal of the scale of UHI phenomena in Inverness and to understand the factors associated with its presence. Mobile vehicular traverses of a study transect were conducted on 30 dates during June, July & August 2019. Measurements of near-surface air temperature were recorded at 19 local climate zone observation points between 20:00 and 23:00 BST. Daily mean UHI intensity (UHII) during the study ranged from 0.7 to 3.5°C, with an overall mean UHII of 1.6°C. Land use characteristics impacted the UHII, with areas with higher fractions of impervious surface cover returning significantly higher air temperatures. UHII increased with the onset of sunset, and the highest UHII occurred on dates with up to 1–2 oktas of cloud cover, low relative humidity, and high cloud base height. The results align with previous studies and comparisons are drawn between Inverness and other settlements globally. Further research in Inverness is recommended to better understand UHI effects and influence national planning policy.

Hydrochemical Delineation of Spring Recharge in an Urbanized Karst Basin, Central Kentucky

ABSTRACT Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit relatively rapid hydraulic, chemical, and thermal responses to storms. In urbanized karst basins, impervious cover, stream channelization, and utility infrastructure can alter infiltration, provide alternate pathways for subsurface flow, and affect ambient water quality. We combined continuous logging of electrical conductivity (EC) and water temperature with analyses of stable isotopes (deuterium and oxygen-18) to differentiate focused and diffuse recharge in a karst basin in Lexington, Kentucky, during 2018. Logging occurred at the McConnell Springs Blue Hole and a sinkhole that drains to it; isotopes, specific conductance, and temperature were manually monitored at those sites and along two losing stream reaches. Water temperature at McConnell Springs and stable isotope abundances showed seasonal variability. The Blue Hole responded within hours to stormwater infiltration at the sinkhole (∼2.1 km upgradient), with recharge events marked by colder stormwater in winter and warmer stormwater in spring to early autumn. Stable isotopes indicated that sinkhole infiltration was minimally affected by evaporation during periods of ponding (up to 9 days). Spring discharge appeared to represent a mixture of focused and diffuse, partly evaporated recharge, consistent with a simple hydrologic model of rainfall, runoff, and infiltration in the basin. EC spikes at the spring during January–March were consistent with pulses of road salt or brine in runoff or snowmelt. Despite limited monitoring data, results suggest that restoration of the sinkhole and its inlet stream were effective in stormwater management during an un usually wet year.

An Event-Based Resilience Index to Assess the Impacts of Land Imperviousness and Climate Changes on Flooding Risks in Urban Drainage Systems

Assessing the resilience of urban drainage systems requires the consideration of future disturbances that will disrupt the system’s performance and trigger urban flooding failures. However, most existing resilience assessments of urban drainage systems rarely consider the uncertain threats from future urban redevelopment and climate change, which leads to the underestimation of future disturbances toward system performance. This paper fills in the gap of assessing the combined and relative impacts of future impervious land cover and rainfall changes on flooding resilience in the context of a densely infilled urban catchment served by an urban drainage system in Salt Lake City, Utah, USA. An event-based resilience index is proposed to measure climate change and urbanization impacts on urban floods. Compared with the traditional resilience metric, the event-based resilience index can consider climatic and urbanized impacts on each urban flooding event; the new resilience index assist engineers in harvesting high-resolution infrastructure adaptation strategies at vulnerable spots from the system level to the junction level. Impact comparison for the case study shows that impervious urban surface changes induce greater effects on the system performance curves by magnifying the maximum failure level, lengthening the recovery duration, and aggravating the flooding severity than rainfall intensity changes. A nonlinear logarithmic resilience correlation is found; this finding shows that flooding resilience is more sensitive to the land imperviousness change due to urban redevelopment than rainfall intensity changes in the case study. This research work predicts the system response to the disturbances induced by climate change and urban redevelopment, improving the understanding of impact analysis, and contributes to the advancement of resilient urban drainage systems in changing environments.

The Hardening of the American Landscape

Problem, research strategy, and findings Patterns of change in urban surfaces have implications for equity, health, and environmental quality in future cities and for their adaptability to climate change. Relatively little detailed research has been done on the role of land use policies—particularly the recent generation of infill and climate adaptation policies—in shaping urban surfaces and related environmental systems. I used a novel approach integrating three methods—land use change models, urban form assessments, and policy-based scenarios—to evaluate patterns of change. I applied these methods to a case study simulation of future development in Denver (CO) and used a stormwater management example to evaluate the capacity of the local management system to treat expansion of the city’s hardscape. I found that the proportion of impervious cover in the city is projected to increase substantially, possibly to levels discussed in the literature as severely affected. A major social commitment to adaptation policies such as green infrastructure would be necessary to mitigate projected hardscape increases. Dispersed development strategies generate substantially more hardscape than geographically targeted development, which suggests that there is also untapped potential for climate adaptation in general land use policy. I share common limitations of scenario-based methods. Takeaway for practice Changes in the composition of urban surfaces in the next 2 decades could have significant environmental effects. In this research, I developed and tested methods that bridge infrastructure and land use planning practices—the public works and community planning silos in local governments—to evaluate these processes and effects. These methods should be useful in many cities.

Hydrochemical Delineation of Spring Recharge in an Urbanized Karst Basin, Central Kentucky

ABSTRACT Because of well-integrated surface and subsurface drainage in karst terrains, springs can exhibit relatively rapid hydraulic, chemical, and thermal responses to storms. In urbanized karst basins, impervious cover, stream channelization, and utility infrastructure can alter infiltration, provide alternate pathways for subsurface flow, and affect ambient water quality. We combined continuous logging of electrical conductivity (EC) and water temperature with analyses of stable isotopes (deuterium and oxygen-18) to differentiate focused and diffuse recharge in a karst basin in Lexington, Kentucky, during 2018. Logging occurred at the McConnell Springs Blue Hole and a sinkhole that drains to it; isotopes, specific conductance, and temperature were manually monitored at those sites and along two losing stream reaches. Water temperature at McConnell Springs and stable isotope abundances showed seasonal variability. The Blue Hole responded within hours to stormwater infiltration at the sinkhole (∼2.1 km upgradient), with recharge events marked by colder stormwater in winter and warmer stormwater in spring to early autumn. Stable isotopes indicated that sinkhole infiltration was minimally affected by evaporation during periods of ponding (up to 9 days). Spring discharge appeared to represent a mixture of focused and diffuse, partly evaporated recharge, consistent with a simple hydrologic model of rainfall, runoff, and infiltration in the basin. EC spikes at the spring during January–March were consistent with pulses of road salt or brine in runoff or snowmelt. Despite limited monitoring data, results suggest that restoration of the sinkhole and its inlet stream were effective in stormwater management during an unusually wet year.

Urbanization reduces soil microbial network complexity and stability in the megacity of Shanghai

Urbanization is altering the co-occurrence networks of ecological communities that are critical to maintaining ecosystem functions and services. Soil microbial communities play key roles in various ecosystem processes, but how soil microbial co-occurrence networks respond to urbanization is unclear. Here we analyzed co-occurrence networks in soil archaeal, bacterial, and fungal communities from 258 soil sampling sites across the megacity of Shanghai along large urbanization gradients. We found that topological features of microbial co-occurrence networks were strongly altered by urbanization. In particular, microbial communities in more urbanized land-use and highly impervious land cover had less connected and more isolated network structures. These structural variations were accompanied by the dominance of connectors and module hubs affiliated with the Ascomycota in fungi and Chloroflexi in bacteria, and there were greater losses in efficiency and connectivity in urbanized than in remnant land-use in simulated disturbances. Furthermore, even though soil properties (especially soil pH and organic carbon) were major factors shaping topological features of the microbial networks, urbanization still uniquely explained a proportion of the variability, particularly those describing network connections. These results demonstrate that urbanization has clear direct and indirect effects on microbial networks and provide novel insights into how urbanization alters soil microbial communities.

Urbanisation of a growing tropical mega-city during the 21st century — Landscape transformation and vegetation dynamics

Fine scale spatial and temporal patterns in land-cover dynamics arising from rapid urbanisation of tropical regions are poorly understood. We quantify changes in landcover across the Bangkok region using high-resolution aerial imagery from ∼ 2004 to ∼ 2018 and address three questions: i) does urbanisation generate temporal shifts in the form of vegetation cover-urbanisation intensity relationships?, ii) do urban expansion and densification generate different vegetation dynamics?, iii) do net changes in vegetation cover and loss vary with urbanisation intensity? The form of vegetation cover-urbanisation intensity relationships exhibited negligible temporal variation, supporting the use of space-for-time substitution approaches for predicting future landcover dynamics. During our study period impervious surface cover increased by ∼ 474 km2and there were net losses of grassland (∼583 km2) and rice-fields (∼94 km2), and a net gain in treecover (∼137 km2). These changes have substantial implications for urban heat islands, flood risk and biodiversity. Urban expansion contributed more to vegetation dynamics than densification, partly because expansion impacted more land. Densification minimised loss of green-space, grasslands, and agriculture (rice-fields), but generated substantial local tree cover loss, which is critical to retain in highly urbanised areas. This contrasts with increasing tree cover elsewhere, including areas experiencing urban expansion. Trade-offs thus arise between impacts on different vegetation types when meeting the demand for tropical urban development through densification or expansion. Densification benefits most vegetation types but must be accompanied with tree protection and planting schemes to balance these trade-offs and minimise detrimental impacts of densification on people, ecosystem services and biodiversity.

Impact of land use land cover change on the land surface temperature: A case study of Shillong

Shillong has been experiencing changes in land use land cover over the past years especially in the town areas where a lot of built-ups are emerging. In response to this, there has been some impacts in the distribution of temperature. In this study, remote sensing techniques have been used. The maximum likelihood method has been used for supervised classification of land use land cover from false color composite images. Landsat 5 TM and Landsat 8 OLI/ TIRS has been used in this study. The study period is 30 years from 1992 - 2022 with an interval of 15 years. The emergence and increase of more built-up and impervious land cover type surfaces has made the land surface temperature to increase. The correlation between NDVI and LST shows a negative relationship while that of NDBI and LST shows a positive relationship. The temperature has been increasing with an average of 2° C each interval of study. The hotspot analysis has been used to demarcate the heat zones. The highest temperature is found in the crowded and high built-up areas while the lowest temperature is found in the vegetated lands which further cause heat island effect in these highly built-up areas. Key Words: Land use land cover, Land surface temperature, Change detection, Hotspot analysis, Correlation analysis, Heat-island effect.

An Assessment of Southeast United States Headwater Tidal Creek Sediment Contamination Over a Twenty-Year Period in Relation to Coastal Development.

Headwater tidal creeks are a primary link between estuarine and upland habitats, serving as conduits for runoff. They are sentinel habitats, providing early warning of potential harm, thus ideal systems to evaluate the effects of coastal suburban and urban development on environmental quality. Estuarine sediments have concentrations of metals, polycyclic aromatic hydrocarbons (PAHs), pesticides, polychlorinated biphenyls (PCBs), and polybrominated diphenyl ethers (PBDEs) that are associated with human activity. High concentrations of contaminants can impair faunal communities, habitat quality, and ecosystem function. Forty-three headwater creeks were sampled between 1994 and 2006 to assess contaminants, and 18 of these were sampled again in 2014/2015. Watersheds were classified as forested, forested to suburban, suburban, or urban land. These values are based on their percent impervious cover (IC) levels and change in IC from 1994-2014. Analyses of temporal data resulted in significant relationships between IC and select metals, PAHs, pesticides, PCBs, and PBDEs. In addition, 11 of the creeks sampled in 2014/2015 have paired data from 1994/1995, allowing for change analysis over the 20 years. Results indicated increasing chemical contamination occurring with increasing levels of development, although only PAHs and total dichloro-diphenyl-trichloroethane (DDT) exhibited a statistically significant increase over time; PAHs also exhibited significantly higher concentrations in developed creeks. Additionally, several metals were deemed enriched in developed creeks based on reference conditions. These results expand our knowledge of how these systems respond to urban development and can inform managers about how human population growth along coastlines may predict altered tidal creek health.