Impervious Area Research Articles

Changing pattern and driving factors of ecosystem service value of the lakes in Northern China since 1990

Lakes in Northern China are widely distributed with large surface areas, and play a crucial role in maintaining ecological security in the northern regions of China. In this study, based on the relationship between ecosystem services (ES) value and lake key indicators, including lake area, potential evapotranspiration, comprehensive trophic level index (TLI), precipitation, and lake volume, the lake ecoservice production functions (LEPFs) were constructed to evaluate lake ecosystem service value (LESV) in Northern China. Subsequently, the driving factors influencing LESV were identified at the lake-basin scale. The results showed that the total LESV in Northern China increased from 5,088.7 billion yuan in 1990 to 5,112.9 billion yuan in 2020, by increasing 0.47%. The total LESV of Xinjiang (XJ) and Tibetan Plateau (TP) lake regions showed an increasing trend, with rates of 5.39% and 2.32%, respectively. However, those of Inner Mongolia Plateau (IMP), Northeast Plain and Mountains (NPM), and Eastern Plain (EP) lake regions showed a decrease, with rates of 19.83%, 6.29%, and 1.72%, respectively. The changing rate in LESV varied significantly among different lake regions. Approximately 30% and 40% of the lakes in XJ and TP lake regions had a growth rate exceeding 0.3 billion yuan, while 86% and 14% of lakes in NPM and IMP lake regions experienced a decline exceeding 0.3 billion yuan, respectively. 40% of the lakes in EP lake region had a growth rate of less than 0.05 billion yuan, and 60% of the lakes had a decline rate of less than 0.05 billion yuan. The average temperature, precipitation, impervious area, and water area within the lake-basins had a significant impact on LESV. Among them, the effect of climate change on LESV was higher than that of the anthropogenic factors. These findings can provide helpful references for the assessing methods of the LESV at a large regional scale and developing lake conservation policies.

Urbanization effects on the spatial patterns of spring vegetation phenology depend on the climatic background

Cities have been considered ideal surrogates for evaluating ecological responses to climate warming. Although research has revealed that the urban heat island effect is not the only determinant that drives the rural-urban difference in spring phenology, limited attempts further explore the effect of complex interactions between urbanization and climates on the start of the season (SOS). Here, we employed the percentage of impervious surface area as an indicator of urbanization levels, incorporating the urban heat island (UHI) effect and climates to decipher the multiple effects on the temporal shift in SOS. Our results suggest that urbanization, the UHI effect, and climates jointly drive the phenological timing in cities. The SOS is highly linearly correlated with urbanization levels and UHI effects (p<0.001) in the zones with warm and humid climates, whereas relatively warmer, cooler, or arid climates break down the linearity. Geographically, the SOS is north-south symmetrical for the rural-urban ecosystem at the national scale, which initiates at the mid-latitudes (around 30 °N, 67.58 DOY ± 2.23 days) first and then towards the low (around 20 °N, 105.25 DOY ± 1.31 days) and high-latitudes (45 °N, 123.01 DOY ± 1.45 days). Chilling accumulation and spring temperature jointly contribute to this phenomenon. As the UHI effect is similar to the projected global warming in the future, understanding the phenological responses to urbanization in various climates is insightful for evaluating the impact of future warming on plants' phenological behavior in the global ecosystem.

Stormwater reuse for water-sensitive city - Integrated analysis of urban hydrology for efficient alternatives of Amaravati city, India.

In the present study, Amaravati, a proposed city of Andhra Pradesh, India, is identified for stormwater reuse analysis and for various efficient options for reuse. Peak runoff from the entire catchment is determined for the management of stormwater using different models such as soil and water assessment tool (SWAT), stormwater management model, and intensity-duration-frequency curves by the log Pearson Type III method. Further, the bio-retention cell low-impact development option with 60% impervious area, 60% zero depression impervious area, bio-retention cell for 40% area for each sub-catchment, and the underground stormwater network system, for part of peak runoff reduction, remaining peak runoff is considered for reuse. The remaining peak runoff is proposed to be reused for irrigation purposes (option 1), and storage retention ponds as extended detention ponds (option 2). Also, in situ storage/percolation is recommended for unaccounted stormwater within or around each premise. The findings can help to propose, implement, and maintain various stormwater reuse measures and/or practices for any city.

Effects of Urbanization and Forest Fragmentation on Atmospheric Nitrogen Inputs and Ambient Nitrogen Oxide and Ozone Concentrations in Mixed Temperate Forests

AbstractUrban ecosystems around the globe experience greater atmospheric nitrogen (N) deposition compared to rural areas and are particularly vulnerable to fragmentation due to land use change. However, while the influences of urbanization and forest fragmentation on atmospheric inputs to temperate forests have been determined separately, the combined effects of the two changes on temperate forest ecosystems have yet to be assessed. To investigate these combined effects, we deployed throughfall collectors to measure atmospheric N inputs and passive samplers to measure nitrogen oxides (NOx) and ozone (O3) throughout the 2018 and 2019 growing seasons in seven temperate forest sites along an urbanization gradient from Boston to central Massachusetts. We found a positive relationship between the amount of impervious surface area (% ISA) surrounding each site and throughfall nitrate () inputs at the forest edge, with urban edge inputs nearly double the rate at rural edge sites. There were higher rates of inputs in the rural forest interior than edge sites, while urban sites experienced significantly higher concentrations of NOx and O3 both in the interior and at the edge compared to rural sites. Atmospheric N inputs were significantly elevated in the early (May–July) compared to the late (August–November) growing season and concentrations of NOx and O3 were also elevated in the midgrowing season (June–September). Our results demonstrate that together, urbanization and forest fragmentation lead to greater rates of atmospheric N inputs and ambient pollutant concentrations of NOx and O3 in temperate forests of the northeastern U.S.

Landscape Composition and Its Effect on the Urban Thermal Environment in Kendari City

The rapid urbanization activities in Kendari City over the last decade have changed its natural landscape, including demands for infrastructure development such as residential areas, which is currently one of the most massive activities. The purpose of this study was to analyse the effect of landscape composition on the urban thermal environment in the Kendari City area in relation to LST and UHI parameters based on UTFVI thresholds. Landsat 8 time series data for 2019 – 2023 is used to observe urban thermal environmental conditions in the study area. The results showed that during the last four years LST in Kendari City tends to increase every year with R 2 > 0.09. As a result of this increasing trend the UHI area in Kendari City also experienced an increase. More than 25% of the Kendari City area is indicated to experience the UHI phenomenon with SUHI ranging from 24 °C to the highest temperature and the concentration increases linearly with the density of the impervious surface area. However, this does not happen in areas with a landscape composition that is categorized as green space. As for the UTFVI results, more than 28% of the areas experiencing the UHI phenomenon are within the UTFVI threshold > 0.020 and more than 60% of the area in Kendari City is denoted as an area with relatively excellent conditions within the range ecological evaluation indices then the rest is in good and normal condition.

Adequacy Analysis Using UAV of Heavy Rainfall Disaster Reduction Facilities According to Urban Development in Republic of Korea

Urban development is a project that enhances human life, but its hydrological impact increases runoff by expanding impervious areas. Furthermore, localized and intense rainfall resulting from the effects of climate change is exacerbating damage to urban areas. The Republic of Korea has established detention ponds as reduction facilities for heavy rainfall disasters, and the law stipulates that the impact of disasters that increase due to the development projects will remain unchanged from before. However, ensuring precision in millimeter or centimeter units during the design of reduction facilities is challenging. In this study, our aim is to assess the suitability of using unmanned aerial vehicles (UAVs) for the detention pond, a facility that reduces runoff resulting from urban development. The target area is a detention pond located in Innovation City, Ulsan Metropolitan City, Republic of Korea. We compared and analyzed design drawings and topographical data. The increased runoff due to the development project was 0.59 m3/s, and the effectiveness of disaster reduction was evaluated by the installation of a detention pond. The detention pond’s reduction effect was analyzed to be 1.16 m3/s for the design drawing and 1.57 m3/s for the topographical analysis. The detention pond currently in place in the target area was found to provide additional disaster reduction benefits compared to the original design plan. The findings of this study can be utilized in relevant laws and guidelines as a method to evaluate the suitability of future reduction facilities.

Mapping impervious surface area increase and urban pluvial flooding using Sentinel Application Platform (SNAP) and remote sensing data.

Expansion of urban impervious surface (UIA) and increased urban pluvial flooding (UPF) have an impact on urban dynamics, socioeconomic activities, and our environment. Therefore, monitoring the increase in UIS and its effect on UPF is essential. The notion of this research is based on the mapping of impervious surface area increase in three major cities of Pakistan. There were two key objectives: (i) Mapping impervious surface area growth using the global impervious surface area index (GISAI) on Google Earth Engine from 1992 to 2022 and (ii) mapping the pluvial flood extent in selected urban areas using Sentinel-1 Ground Range Detected (GRD) data. Thus, we have utilized the GISAI for mapping urban impervious surface area (UISA) using Landsat time-series data on GEE. Our research findings revealed that about 16.8%, 23.5%, and 16.4% of the impervious surface have been increased in Islamabad, Lahore, and Karachi, respectively. Also, Lahore city has the highest overall accuracy, aiming at the GISAI of 93%, followed by Karachi and Islamabad with an overall accuracy of 86% and 85%, respectively. The results indicated that urban flooding has occurred in those areas where the ISA has grown during the last three decades. It shows significant changes in the impervious surface area that cause enhanced urban pluvial flooding in major cities of Pakistan. Also, Sentinel-1 data and the SNAP tool significantly mapped flooded areas in the selected zones. So, providing cities and local governments with increased quick flood detection capabilities is essential. It can also provide feasible policy recommendations for Pakistan decision-makers in city management. Therefore, we suggest a modeling-based solution to identify high-risk locations in major cities for upcoming UPF events.

Abandoned cropland compensates the decrease in net ecosystem productivity of impervious surface expansion in China

Abandoned cropland and impervious surface expansion are generally considered to have positive and negative impacts on net ecosystem productivity (NEP), respectively. However, the comprehensive comparison of the impacts of these two land use changes on NEP remains lacking. We use multi-year land cover data, NEP data, and statistical data to track the interannual variability of abandoned cropland and impervious surface expansion in China, and subsequently estimate their impacts on NEP. From 2000 to 2019, 30.8 × 106 ha of cropland in China was abandoned, while the impervious surface area expanded by 8.97 × 106 ha over the period. The average annual abandonment rate and impervious surface expansion rate were 0.83% and 2.96%, respectively. The average annual NEP of abandoned cropland and impervious surface expansion were 39.9 g C/m2 and 16.2 g C/m2, respectively. Using the space-for-time method to estimate NEP changes, results showed that the carbon sink of 0.013 Tg C accumulated by abandoned cropland not only offset the carbon source of 0.01 Tg C from impervious surface expansion but sequestered additional 0.003 Tg C during the study period. Further analysis of the relationships between NEP and natural and anthropogenic factors revealed that temperature had the most significant positive impact on NEP (0.35, p < 0.01), while the urbanization rate had the most significant negative impact on NEP (−0.33, p < 0.01). This study provides a new insight for regulating the effects of land use changes on natural carbon sink/source, and highlights the importance of abandoned cropland to enhancing natural carbon sink.

Spatiotemporal patterns of urban forest carbon sequestration capacity: Implications for urban CO2 emission mitigation during China's rapid urbanization

Urban forests provide ecological functions and human well-being. However, spatiotemporal changes in urban forest carbon sequestration (CS) under rapid urbanization remain poorly understood. We established a model to predict the annual CS dynamics in urban forests based on plot-measured CS and Landsat images. Our results showed that the urban forest coverage in Changchun increased from 18.09 % to 24.01 % between 2000 and 2019, especially in the urban suburbs. However, urban forest patches became more fragmented and less connected, particularly in the urban center. The NDVI is better than other vegetation indices for mapping urban forest CS. We observed a gradual increase in urban forest CS capacity from 2000 to 2019, with higher CS capacity found in urban suburbs compared to urban centers. The class distribution of urban forest CS capacity was skewed toward low values (0–2 g·m−2·d−1), but this tendency diminished gradually. In 2000, the urban forest in Changchun offset approximately 2.11 % of carbon emissions but declined to 0.88 % by 2019 due to increased carbon emissions. Rapid urbanization was the main factor affecting CS, with impervious surface area accounting for 48.7 % of the variation. Urban landscape pattern indices also influenced the CS, with higher forest patch connectivity and lower patch density leading to greater CS capacity. Our study helps urban managers develop urban greening strategies for carbon neutrality and low-carbon city.

Stormwater Treatment Using Natural and Engineered Options in an Urban Growth Area: A Case Study in the West of Melbourne

The expected increase in urbanization and population in coming years is going to increase the impervious land area, leading to substantial increases in stormwater runoff and hydrological challenges, and presents significant challenges for urban potable water supply. These are worldwide challenges that can potentially be ameliorated by harvesting stormwater for potable use or for other uses that can reduce the pressure on potable water supply. This study sought to assist the local water authority in planning for future potable water supply through a review of the scientific literature to determine the likely chemical and microbial characteristics of stormwater, the treatment train (TT) requirements, and the likely costs of treatment to achieve potable standards for the high-growth metropolitan region of Melbourne, Australia. Literature stormwater quality statistical data and treatment process performance data were used to model the expected product water microbial and chemical quality after treatment using a number of advanced TT options. The results of the modelling were compared with literature microbial log reduction targets (LRTs) for the potable use of stormwater and with the Australian Drinking Water Guidelines (ADWG). It was found that a reverse osmosis (RO)-based TT with microfiltration pre-treatment and post-RO advanced oxidation and chlorination in storage reservoirs is a conservative stormwater potable use treatment option. A less conservative and less expensive ozone-and-biologically active filtration (O3/BAF)-based TT option is also proposed if RO concentrate disposal is deemed to be too challenging. These results could be useful in climate change adaptation involving the evaluation of options for the mitigation of future population-growth- and climate-change-driven water supply challenges, as well as urbanization-driven stormwater hydrology and receiving water pollution challenges.

Changes in the surface urban heat island between 1986 and 2021 in the polycentric Górnośląsko-Zagłębiowska Metropolis, southern Poland

Progressing urbanization forces urban infrastructure development and leads to an increase in artificial impervious surfaces that directly contribute to changes in surface urban heat island (SUHI) in cities. This study discusses spatial and temporal changes in the SUHI extent and intensity in the biggest Metropoly in Southern Poland in summer between 1986 and 2021. The study is based on Landsat satellite images, demographic and land cover data from 1990 to 2018 from CORINE Land Cover (CLC) classifications. The comparison of satellite images recorded in different years, on similar dates and under similar meteorological conditions revealed an increase in the SUHI extent from 0.6 to 4.3 % between 1986 and 2021 due to increase in the share of impervious areas. Moreover, regardless of changes in spatial extent, the mean land surface temperature (LST) of all types of land cover increased, which may be related to recent warming. In the research period, permanent surface heat island covered 0.85 % of the GZM, and over 50 % of its area was located only within four cities. Although the mean LST for SUHI increased, the SUHI intensity decreased due to increased LST of the cold island. The SUHI extent was more related to the inhabitant number (correlation: 0.83 to 0.98) than population density (0.39–0.58). SUHI expansion in combination with recent warming of climate is a particularly negative effect where society is ageing, like in GZM.

Assessment and simulation of thermal environments in Taiyuan urban built-up area, China

The urban heat island (UHI) effect has intensified with increases in impervious surface areas and population densities due to urbanization, which affects the quality of urban life and ecological services. Here, the Moran’s I and hot spot analysis (Getis-Ord Gi*) are used to explore spatial autocorrelation of land surface temperature (LST) in Taiyuan built-up area. Then, the built-up area is divided to 41 sub-areas to accurately explore the urban LST differences caused by different LULC types. Moreover, geographically weighted regression (GWR) is used to analysis the spatial heterogeneity of LST. Finally, we simulate the LST changes using the CA-Markov model in the study area in the year 2030. Our results showed that 1) average LST was 22.76°C in Taiyuan built-up area in 2018. The Highest-temperature areas were distributed in heavy-industry intensive areas in the north, north central, and southeast, whereas the Lowest-temperature areas mainly corresponded to rivers, lakes, urban forests, and green spaces. 2) The Moran’s I gradually decreased from 0.8635 to 0.2097 with an increase in the spatial distance threshold. The optimal recognition effect was obtained at a 400 × 400-m scale. The Getis-Ord Gi* analysis indicated that the cold area was 1248.32 km2 (12.24% of the study area) and the hot area was 43.84 km2 (11.11% of the study area) in 2018. 3) The GWR analysis showed significant spatial non-stationarity in the influence of LULC types on LST. The GWR model was calculated with reference to the observation values of the adjacent areas, so as to better reveal the spatial relationship between artificial surface, woodland, water, grassland, and bare land and LST. 4) The UHI distribution was more concentrated in 2030 than in 2021. The statistics of the proportion and transfer matrix of LST indicated that the proportion of the Highest and Lowest-temperature areas in 2030 decreased and the UHI effect will further intensify. This study could be used to guide sustainable development in cities and provides theoretical support for adjusting the urban spatial structure.

IMPACT OF LAND USE ACTIVITIES ON THE HYDROLOGICAL REGIME IN THE JUNJUNG RIVER BASIN, PENANG ISLAND, MALAYSIA

Land use activities in the river basin have a very significant negative impact on the hydrological regime, especially surface runoff. The study of the impact of land use activities on the hydrological regime in the Junjung river basin aims to analyse changes in the rate of surface runoff due to current land use changes and land use planning in 2030. To achieve the goal of this study, curve number analysis was used as a determinant of hydrological parameters in the development of HEC HMS modelling in the study basin area. The results of the study found that the current land use in 2020 recorded an average curve number value of 85.77 and then increased to 86.36 in 2030 due to land use changes in 2030. The change in the value of the curve number has had an impact on the hydrological regime that is surface runoff because there is an increase in the percentage of impervious areas from 22.84 percent in 2020 to 31.14 percent by 2030. The rate of change in runoff is shown through the simulation of the peak flow rate that occurs according to the frequency of the event, which is between 0.7 to 4.9 percent. The results obtained from this study can be used as fundamental data for advanced studies of flood control and management for better sustainable flood risk management.

Spatiotemporal trends of urban-induced land use and land cover change and implications on catchment surface imperviousness

Urbanization, changes in land use and land cover (LULC), and an increase in population collectively have significant impacts on urban catchments. However, a vast majority of LULC studies have been conducted using readily available satellite imagery, which often presents limitations due to its coarse spatial resolution. Such imagery fails to accurately depict the surface characteristics and diverse spectrum of LULC classifications contained within a single pixel. This study focused on the highly urbanized Dry Creek catchment in Adelaide, South Australia and aimed to determine the impact of urbanization on spatiotemporal changes in LULC and its implications for the land surface condition of the catchment. Very high spatial resolution imagery was utilized to examine changes in LULC over the past four decades. Support Vector Machine-learning-based image classification was utilized to classify and identify the changes in LULC over the study area. The classification accuracy showed strong agreement, with a kappa value greater than 0.8. The findings of this analysis showed that extensive urban development, which expanded the built-up area by 34 km2, were responsible for the decline in grass cover by 43.1 km2 over the last 40 years (1979–2019). Moreover, built-up areas, plantation, and water features, in contrast to grass cover, have demonstrated an increasing trend during the study period. The overall urban expansion over the study period was 136.6%. Urbanization intensified impervious area coverage, increasing the runoff coefficient, equivalent impervious area, and curve number by 60.6%, 60.6%, and 7.9%, respectively, while decreasing the retention capacity by 38.6%. These modifications suggest a potential variability in catchment surface runoff, prompting the need for further research to understand the surface runoff changes brought by the changes in LULC resulting from urbanization. The findings of this study can be used for land use planning and flood management.

Urbanization related changes in lepidopteran community

Urbanization displaces natural habitats with impervious surfaces and managed ornamental green infrastructure. This study compared the structure of lepidopteran community in an office campus cleared from forest to that in the remaining forest. For the comparison, we trapped 2,233 lepidopteran specimens of 56 species from an office campus and adjacent forest. The species richness of lepidopteran assemblage in the office campus was half of that in the forest and consisted primarily of the same species found in the forest. The abundance and biomass of Lepidoptera in the office campus was a quarter of that in the forest. The biomass and abundance of Lepidoptera decreased along with the impervious area within 100-meter radius around the traps and approached zero when impervious surfaces covered the area entirely. The specimens in the trapped lepidopteran assembly from the office campus were on average larger, indicating elevated mobility, than those caught from the forest. Our results support earlier studies concluding that fragmented urban landscape selects for large mobile species, which can feed on ornamental plants or can disperse between high-quality habitats within urban landscape. Green infrastructure with native plants, high-quality native habitats and their connectivity can maintain species-rich lepidopteran communities in urban landscapes.

Balancing upland green infrastructure and stream restoration to recover urban stormwater and nitrate load retention

Urban watersheds have experienced ecosystem degradation due to land cover change from vegetation to impervious areas. This transformation results in increased stormwater runoff, stream channel erosion and sedimentation, and both increased inputs and reduced ecosystem retention of nutrients. Ecosystem restoration practices, including terrestrial and aquatic low impact development (LID), are becoming widely implemented in urban watersheds globally. A major question is how “green” and “grey” infrastructure can be optimally balanced to shift ecohydrological behavior towards pre-urbanization conditions. Traditional stormwater engineering typically controls runoff by temporary storage (detention) and release of stormwater, while LID designs are developed to reduce runoff by a combination of infiltrating precipitation and evapotranspiration, while promoting biogeochemical retention of nutrients. These practices are often combined with stream and riparian restoration that increases nutrient retention and reduces in-stream loads. In this study, we simulated the potential impact of three types of terrestrial LID and green infrastructure (GI) on watershed runoff and nitrate (NO3–) loading to local streams, independent of detention storage effects. The treatments included increased tree canopy, vegetated roadside bioswales, and permeable pavement. We then evaluated the individual and interactive impacts of these practices on the effectiveness of NO3– load reduction provided by stream restoration, which is affected by the altered runoff and nutrient loading caused by the LID and GI. Urban reforestation provided the highest effectiveness in terms of reducing stormflow and nutrient export, while bioswales and permeable pavement unexpectedly increased in-stream NO3– loads. Retrofit of the previously developed watershed by LID/GI alone may not provide sufficient mitigation in stormwater and nutrient loads, and should be balanced with additional grey infrastructure, such as detention ponds, rain cisterns, and sewer system upgrades.

Urbanization and greenspace effect on plant biodiversity variations in Beijing, China

It is of great significance to understand how urbanization and greenspace areas gradient affect urban plant biodiversity for urban renewal and planning toward urban biodiversity conservation. However, the factors affecting plant diversity under rapid urbanization remain unknown in many cities. To this end,702 vegetation sampling plots from 219 2 km × 2 km grids were selected to explore the urban plant biodiversity variation within two perpendicular 10 km width transects running across the urban center in north-south and east-west directions within the 6th ring road in Beijing, China. Impervious surface area (ISA) and Greenspace area (GSA) of each grid were interpreted from high resolution remote sensing images. ISA mainly includes road surface, asphalt, and buildings, and GSA includes tree, shrub and herb canopy. A total of 396 plant species were recorded, including 95 tree species, 87 shrub species, and 214 herb species. The 396 species belonged to 298 genus and 93 families. We found that woody plant diversity, tree size attributes (DBH, height, canopy breadth), and total plant taxa increased significantly with increased urbanization while herb plant diversity decreased significantly. However, the GSA has no significant impact on plant diversity and taxa. We further found the higher woody plant diversity and lower herb plant diversity in ISA’s with a percentage > 50%, and in the ISA percentage < 50% with larger ISA and GSA area (ISA+GSA percentages (i.e., >80%). ISA and GSA can thus be predictive factors for estimating urban plant diversity, which was related to urban planning and different greening decision-makers. The results of this study have important implications for further understanding how current urbanization factors affect plant diversity, which could implement better scientific urban planning to conserve and restore urban biodiversity in many cities around the world.

Toward a more socially equitable stormwater management fee: The case of Corpus Christi in Texas, USA

This study evaluates a popular approach to assessing stormwater utility fees in the context of social equity. Analyses are based on comparing single-family land parcels in different neighborhoods of Corpus Christi, a U.S. city in the state of Texas that recently introduced a stormwater fee program. The stormwater fees are based on the same stormwater runoff factor for all single-family residential land parcels. We instead derive stormwater runoff estimates from parcel-scale impervious area measurements through the application of a machine-learning model to high-resolution remote sensing data. The difference between the official runoff factor and our estimate tends to be larger among land parcels in census tracts with proportionally more low-income and Hispanic households. This finding at odds with the ability-to-pay principle is attributable to the association of different neighborhoods’ sociodemographic compositions with their housing development patterns. Our work not only contributes to the design of a stormwater fee program that better characterizes the generation of stormwater runoff but it also helps city officials alleviate social inequity for homeowners in economically disadvantaged communities.

The patterns of soil nitrogen stocks and C : N stoichiometry under impervious surfaces in China

Abstract. Accurate assessment of soil nitrogen (N) storage and carbon (C) : N stoichiometry under impervious surface areas (ISAs) is key to understanding the impact of urbanization on soil health and the N cycle. Based on 888 soil profiles from 148 sampling sites in 41 cities across China, we estimated the country's N stock (100 cm depth) in the ISA soil to be 98.74±59.13 Tg N with a mean N density (NISA) of 0.59±0.35 kg m−2, which was significantly lower (at all depths) than the soil N density (NPSA=0.83±0.46 kg m−2) under the reference permeable surface areas (PSAs). The NISA was also only about 53 %–69 % of the reported national mean soil N density, indicating that ISA expansion caused soil N loss. The C:N ratio of ISA (10.33±2.62) was 26 %–34 % higher than that of natural ecosystems (forests, grasslands, etc.) but close to the C:N of PSA. Moreover, there was a significant C–N correlation in ISA soil, showing no signs of C–N decoupling as suggested by the previous studies. The ISA had smaller variances in the C:N ratio than did the PSA at regional scale, indicating convergence of soil C:N stoichiometry due to ISA conversion. The eastern subregion of China had the highest NISA, although its natural soil N density was among the lowest in the country. Unlike the vertical pattern in natural permeable soils, whose N density declined faster in the upper soil layers than in the lower layers, NISA decreased linearly with depth. Similarly to natural soil N, NISA was negatively correlated with temperature; but unlike natural soil C:N which was positively correlated with temperature, the C:NISA was negatively correlated with temperature. NISA was not correlated with net primary productivity, but was significantly correlated with the soil N density of adjacent PSA and the urbanization rate. These findings indicate the ISA soil had a unique N distribution pattern, possibly as the result of intensive disturbances during land conversion. The dataset “Observations of soil nitrogen and soil organic carbon to soil nitrogen stoichiometry under the impervious surfaces areas (ISA) of China” is available from the National Cryosphere Desert Data Center (https://doi.org/10.12072/ncdc.socn.db2851.2023) (Ding et al., 2023).

Monitoring of wetland cover changes in protected areas to trade-offs between ecological conservation and food security: A case study from the Dongting Lake, China

The United Nations' Sustainable Development Goals (SDGs) for 2030 underscore the urgency of “eradicating hunger and ensuring food security” (SDG 2: Zero Hunger) and the critical need to “cease and reverse land degradation and biodiversity decline” (SDG 15: Life on Land). The Dongting Lake area in China, serving as a significant wetland nature reserve and grain production zone, is increasingly confronted with complex, interdependent trade-offs between agricultural cultivation and the ecological and environmental preservation of wetlands (SDG 2 and 15). To analyze the trade-off between conservation and food security, it is crucial to rely on long-term, continuous monitoring of land cover changes in the lake area. However, the absence of reliable optical remote sensing has posed a significant challenge due to the prevalence of cloudy and rainy conditions. Our study begins by integrating long-term Landsat and MODIS data using the GF-SG fusion algorithm to generate 8-day NDVI data with a spatial resolution of 30 m. This analysis focuses on the areas outside the embankment of Dongting Lake (referred to as O-DTL) from 2003 to 2020. We then employ a pixel-connected sample migration method to facilitate automated sampling of land cover types and a random forest classification algorithm to analyze long-term dynamic changes. Finally, by combining meteorological and social data, we examine the temporal patterns of land cover changes in the study area and identify the underlying factors influencing them. The results indicate a trade-off between the fluctuation of cropland and forest area from 2003 to 2020. Water body areas have exhibited a significant decrease, while impervious surface areas have consistently increased annually. Impervious surface areas have experienced a substantial increase of approximately 70%, with almost 90% of this expansion resulting from the conversion of cropland. Under the premise of maintaining a stable area for food cultivation, the land consumed by urban expansion eventually encroached on the wetland water bodies of the reserve. The reduction in wetland water area in the O-DTL can be primarily attributed to agricultural cultivation, while urban expansion and urbanization have indirectly contributed to the decrease. This study provides a case in which prioritizing food security (SDG 2) takes precedence over ecological conservation (SDG 15), highlighting its significant implications for guiding subsequent development in the Dongting Lake area. This finding is crucial for minimizing unintended consequences and maximizing co-benefits between sustainable development goals.