Footprint Model Research Articles

Implementation of a Lagrangian Stochastic Particle Trajectory Model (LaStTraM) to Simulate Concentration and Flux Footprints Using the Microclimate Model ENVI-Met

The number of studies evaluating flux or concentration footprints has grown considerably in recent years. These footprints are vital to understand surface–atmosphere flux measurements, for example by eddy covariance. The newly developed backwards trajectory model LaStTraM (Lagrangian Stochastic Trajectory Model) is a post-processing tool, which uses simulation results of the holistic 3D microclimate model ENVI-met as input. The probability distribution of the particles is calculated using the Lagrangian Stochastic method. Combining LaStTraM with ENVI-met should allow us to simulate flux and concentration footprints in complex urban environments. Applications and evaluations were conducted through a comparison with the commonly used 2D models Kormann Meixner and Flux Footprint Predictions in two different meteorological cases (stable, unstable) and in three different detector heights. LaStTraM is capable of reproducing the results of the commonly used 2D models with high accuracy. In addition to the comparison with common footprint models, studies with a simple heterogeneous and a realistic, more complex model domain are presented. All examples show plausible results, thus demonstrating LaStTraM’s potential for the reliable calculation of footprints in homogeneous and heterogenous areas.

A product carbon footprint model for embodiment design based on macro-micro design features

Greenhouse gas emissions have become one of the most prominent global concerns of sustainable development. To reduce product life cycle carbon footprint, planning should begin at embodiment design phase. The accurate assessment of carbon footprint is the foundation of carbon footprint reduction. However, existing carbon footprint models cannot be applied to embodiment design phase due to incomplete and limited design information. With this in mind, this paper proposes a carbon footprint model for embodiment design based on macro-micro design features. First, a Function-Structure-Feature (FSF) model for embodiment design is established to convey the design information. The concept of design features is introduced (at both macro and micro levels). The macro design feature denotes the different operational states of the product and the constraint relationships between parts. The micro design feature denotes the specific properties of parts. Then, a model of product carbon footprint based on design features is presented through the analysis of the relationships between macro-micro design features and product carbon footprint. The feasibility of the proposed method is demonstrated through a gear hobbing machine. The product carbon footprint model allows quantitative evaluation of product carbon footprint during embodiment design phase, and the amount of carbon footprint from each type of design feature is predicted. Based on evaluation result, the design features can be improved to reduce product carbon footprint. Case study results show that the carbon footprint is decreased by 10.96% after improving design features.

Determining the Regional Carrying Capacity of the Wuhan City Circle Based on the Improved Ecological Footprint Method

AbstractThis study builds upon the traditional ecological footprint model by adding two new accounts of resource flows and using two new calculating method. This first account concerns water resources and accounts for water consumption in cities. The second account tracks basic types of pollutant accounts. Energy theory and net primary productivity were used to calculate the ecological footprint. Aiming at the problem of application in city, a city hectare spatial scale was used and a regional carrying capacity correction parameter was referenced. This framework provides insight into calculations of the bearing capacity of certain areas. The Wuhan City Circle was used as a case study with the objectives of calculating the ecological footprint and regional carrying capacity and analyzing its spatiotemporal evolution and capacity for sustainable development. The results indicated that from 2000 to 2015, the average annual rate of decline of the carrying capacity of the Wuhan City Circle was 9.18%, and from 2015 to 2017, the average annual rate of increase was 38.91%. The ecological footprints of fossil energy and build‐up land accounts increased over the years, exposing problems with land and energy utilization in the Wuhan City Circle. The continuous decline of the water resources carrying capacity reminds policy makers to pay attention to the protection of water areas. These results can help policy makers integrate historical data to adjust existing plans and make more specific future plans.

An exergy-based minimum carbon footprint model for optimum equipment oversizing and temperature peaking in low-temperature district heating systems

Total decarbonization strategies are facing technical and environmental challenges according to the 2nd Law of Thermodynamics, such as equipment oversizing versus temperature peaking by heat pumps to accommodate low-temperature renewable and waste energy sources. As a method of this paper, the Rational Exergy Management Model (REMM) derived fourteen metrics, aiming to minimize the CO2 emissions responsibility. Two case studies are presented. One of them is a fifth-generation district energy system concept with a 250 MW design heating load of 20,000 residence-equivalent apartments at a supply temperature of 35 °C. Results showed that two heat pumps in a cascade achieved a 23% higher exergy utilization rate with an optimum temperature peaking to 45 °C and 25% radiator oversizing. The second case study is concerned with the strategy of the Chinese government to substitute the domestic use of coal and wood with local wind turbines for electric heating to combat global warming. Five alternatives were considered; 1-Wind electricity to resistance heating, 2-Wind electricity to heat pumps, 3-Wind electricity to mini hydrogen fuel cells, 4-Wind electricity to hydrogen and micro-cogeneration, and 5-Hydrogen district systems with biogas, geothermal, and solar energy. Results showed that Case 1 has the maximum carbon footprint, whereas a custom-designed hydrogen house has the least footprint leading to about 90% CO2 emissions responsibility emanating from exergy destructions. The paper concludes that low-temperature heating either in district energy systems, in private buildings, or prosumers is both environmentally, economically, and technically feasible.

Ecological Footprint Model of Soekarno-Hatta International Airport from the Perspective of the Local Community

Soekarno-Hatta International Airport is prone to various environmental problems. The problem of population growth has an impact on increasing economic activity which directly impacts the environment. In every production activity from the environmental side, it will bring up the carrying capacity of the environment and the carrying capacity of the environment or ecological footprint. The problem will be difficult if it turns out that the ecological footprint that occurs exceeds the capacity of the existing environmental carrying capacity, also for airport problems. This will result in the airport being unsustainable. This article will discuss the model of the airport environmental footprint that is currently occurring at Soekarno-Hatta International Airport by utilizing the opinions of respondents who live and have activities around the airport. The factor analysis method is used to process the respondent’s data to obtain the factors that influence the environmental footprint and then through these findings a model can be developed which is expected to be able to abstract the current conditions. The research results show that the dominant environmental footprint at Soekarno-Hatta airport is overload airport activities impact, operational slot time optimization, and renewable of airport energy, which can then be built as an instrument to evaluate, build and develop airport control policies that are environmentally friendly and sustainable.

Water Footprint Evaluation of Steel Production in China

The shortage of water has become a serious problem in the development of the steel industry in China. Therefore,it is important for research to be done in environment management, estimating the potential improvement of steel industry. This study propose an improved water footprint model of steel production based on the water footprint network methodology and the life cycle assessment framework. The result shows that the water footprint of steel production is 41.09m3/t, which requires larger amounts of direct blue water. The case of China highlights the relevance of clean production, energy efficiency measures, and grading utilization on reducing the water footprint of steel production.

Spatially heterogeneity response of ecosystem services supply and demand to urbanization in China

A deep understanding of the impact of urbanization on ecosystem service (ES) supply and demand is crucial to regional ecological management and sustainable development. The existing studies mainly focused on the various impacts of urbanization on ES supply, however, there is still a lack of comprehensive research on the spatial heterogeneity response of ES supply, demand and supply-demand ratio (i.e., surplus or deficit) to urbanization, especially at the national scale. To fill this gap, we measured the spatiotemporal changes of ES supply, demand and supply-demand ratios in China utilizing the ecological footprint model at the county scale of resolution. Additionally, the Geographical Weighted Regression (GWR) model was used to explore the spatial heterogeneity response of ES supply, demand and supply-demand ratios to different types of urbanization (i.e., population, economic and land). The results showed that areas with larger total ES demand was mainly concentrated in the Northeast Plain, Liaodong Peninsula, North China Plain, Pearl River Delta, Southeast coastal areas, and Sichuan Basin, while the northwest, northeast and north of China had the greater total ES supply. The counties with strong ES deficit were found in southeastern China, while, most counties in northwestern China were in ES surplus. Additionally, there was significant spatial heterogeneity influence of different types of urbanization on ES in China. Population urbanization in the southeast and south of China had a strong positive impact on the supply-demand ratio in 2000 and 2015, while economic urbanization in the northwest and south regions exerted a more remarkable positive influence. The greater positive impact of land urbanization on the supply-demand ratios was mostly concentrated in northwest China in 2000, and this effect also appeared in southeast China in 2015. Moreover, land urbanization presented a more direct and dominant impact on the ES supply, demand and supply-demand ratios than population and economic urbanization. The findings highlighted that we should focus on the impact of urban expansion on the ecosystem, formulating rational land use planning and optimizing urban spatial configurations, can be used to offset the ES deficit and realize regional sustainable development.

Fairness analysis and compensation strategy in the Triangle of Central China driven by water-carbon-ecological footprints.

This study proposes water-carbon-ecological footprints to form footprint family indicators for identifying the ecological compensation and regional development equilibrium in the Triangle of Central China (TOCC). The occupation of natural capital stock and flow consumption can be illustrated using a three-dimensional ecological footprint model, and Gini coefficient is integrated into the evaluation framework for fairness measurement from various aspects. Quantificational ecological compensation standards can be given with considering indicators associated with ecological resource conversion efficiency and willingness to pay. Results reveal that ecological and carbon footprints in the TOCC demonstrate rising trends from 2000 to 2015, while its water footprint presents a fluctuating trend. The majority of average Gini coefficients exceed the threshold value of 0.4 under different footprints, thereby indicating poor overall fairness of regional development. Water footprint in Jingmen, Xiangtan, and Yichun show relatively higher compensation expenses, while Yichang, Zhuzhou, and Fuzhou exhibit higher received compensation values compared with other cities. Carbon footprint in Wuhan, Loudi, and Xinyu indicate high compensation expenses due to their overuse of biological resources. Maximum amounts of compensation expense appear in Nanchang and Wuhan from the perspective of ecological footprint. This study can provide a theoretical reference for sustainable development in the TOCC by performing a comparative analysis with Beijing-Tianjin-Hebei urban agglomeration and developed countries.

AI-Assisted approach for building energy and carbon footprint modeling

This paper proposes an energy and carbon footprint modelling using artificial intelligence technique to assess the impact of occupant density for various types of office building. We use EnergyPlus to simulate energy consumption, and then estimate the related CO₂ emissions based on three years (2016–2018) of Actual Meteorological Year (AMY) weather data. Various occupant densities were used to evaluate the annual energy consumption and CO₂ emission. In this work, a robust deep learning technique of long short-term memory (LSTM) model was established to predict the time-series energy consumption and CO₂ emissions. A power exponential curve was suggested to correlate the behaviour of annual energy and CO₂ emission for occupant densities range from 10 to 100 m²/person for each office building type. The results of LSTM model show high prediction performance and small variations within the three types of office building data, which can be applied to the similar building model to predict and optimise energy consumption and CO₂ emission.

Water environment carrying capacity assessment of Yangtze River Economic Belt using grey water footprint model

Abstract Based on grey water footprint theory and the characteristics of the water resources system, this paper constructs the evaluation index of the water environment carrying capacity of the Yangtze River Economic Belt, and calculates the point-source grey water footprint, non point-source grey water footprint, and water environment carrying capacity of the study area from 2012 to 2017. The results show that the non point-source grey water footprint is much larger than the point-source grey water footprint. The non point-source grey water footprint decreased from 1,089.75 billion m3 in 2014 to 1,038.7 billion m3 in 2017, indicating that the pollutants discharged into the water were decreasing in those four years. In addition, the water environment carrying capacity of the western and middle sections of the Yangtze River Economic Belt are in a good state, but the eastern section is overloaded.

Evaluation on sustainability of water resource in karst area based on the emergy ecological footprint model and analysis of its driving factors: a case study of Guiyang city, China.

Water resources are indispensable resources that human society depends on for survival and development, and it is of great significance to maintain the sustainability and promote the sustainable development of water resources. In this study, the emergy ecological footprint model was adopted to evaluate the sustainability of water resources in Guiyang city from 2009 to 2018. Results showed that water resources in Guiyang during the study period were in an ecological surplus, were relatively secure, and had weakly sustainable status. The emergy ecological carrying capacity of water resources had fluctuated greatly with the annual average rainfall. Both the emergy ecological footprint of water resources and the emergy ecological footprint of water resources per 10,000 yuan GDP had declined. Both the ecological tension index and the sustainable utilization index of water resources had shown a rising trend since 2012, indicating that the socio-economic pressure on water resources has been increasing. And the sustainability of water resources in Guiyang may not be maintained in the future. The sustainability of water resources in Guiyang was affected by an ecological environmental mechanism based on its physical geography conditions and special hydrogeological structures, and a society mechanism based on its feature of growth of population, land utilization, and urbanization. Therefore, suggestions like transforming the traditional economy development model, optimizing the current allocation of water resources, and protecting the ecological environment are conducive to promoting the sustainable development of water resources in Guiyang.

Modeling urban evapotranspiration using remote sensing, flux footprints, and artificial intelligence

As climate change progresses, urban areas are increasingly affected by water scarcity and the urban heat island effect. Evapotranspiration (ET) is a crucial component of urban greening initiatives of cities worldwide aimed at mitigating these issues. However, ET estimation methods in urban areas have so far been limited. An expanding number of flux towers in urban environments provide the opportunity to directly measure ET by the eddy covariance method. In this study, we present a novel approach to model urban ET by combining flux footprint modeling, remote sensing and geographic information system (GIS) data, and deep learning and machine learning techniques. This approach facilitates spatio-temporal extrapolation of ET at a half-hourly resolution; we tested this approach with a two-year dataset from two flux towers in Berlin, Germany. The benefit of integrating remote sensing and GIS data into models was investigated by testing four predictor scenarios. Two algorithms (1D convolutional neural networks (CNNs) and random forest (RF)) were compared. The best-performing models were then used to model ET values for the year 2019. The inclusion of GIS data extracted using flux footprints enhanced the predictive accuracy of models, particularly when meteorological data was more limited. The best-performing scenario (meteorological and GIS data) showed an RMSE of 0.0239 mm/h and R2 of 0.840 with RF and an RMSE of 0.0250 mm/h and a R2 of 0.824 with 1D CNN for the more vegetated site. The 2019 ET sum was substantially higher at the site surrounded by more urban greenery (366 mm) than at the inner-city site (223 mm), demonstrating the substantial influence of vegetation on the urban water cycle. The proposed method is highly promising for modeling ET in a heterogeneous urban environment and can support climate change mitigation initiatives of urban areas worldwide.

Estimation of tourism carbon footprint and carbon capacity

Abstract The calculation of tourism carbon footprint is of great significance to low-carbon tourism. This study estimates the tourism carbon footprint in Heilongjiang Province from 2009 to 2018 by using tourism carbon footprint and tourism carbon capacity models. The results show that the total tourism carbon footprint of Heilongjiang Province increased fast to 2.97 times from 5.926million tons in 2009 to 21.13million tons in 2018, while its per capita tourism carbon footprint increased from 53.9 kg to 116.0 kg. During the same period, tourism carbon capacity continued to grow steadily from 15.18billion tons to 21.96billion tons, and the growth rate was 50% of the growth rate of tourism carbon footprint. Tourism carbon emissions can be absorbed by environmental capacity, and the risk of carbon deficit is relatively small.

Ecological compensation of grain trade within urban, rural areas and provinces in China: a prospect of a carbon transfer mechanism

In order to solve regional ecological inequity in carbon emissions, building a balanced ecological compensation mechanism is paramountly important. With the help of the carbon transfer mechanism, the study is designed to evaluate the ecological compensation of grain trade within urban, rural areas, and provinces in China. This current study applied the carbon footprint model of grain crops in various provinces and measures d the inter-provincial and urban–rural carbon transfer through a multi-objective optimization model. Obtained results show that the carbon footprint of crops for per-unit production of corn, wheat, and rice is higher in the southwest and northeast region than that of the northwest and southeast region, but across the regions, a net carbon sink trend was observed. The carbon footprint of wheat production in Inner Mongolia and rice in Shandong showed a net carbon emission effect and had negative externalities toward environmental protection. Carbon balance can be attained with a balance carbon payment system, but a proper carbon payment mechanism is not developed in China. Hence, concerning establishing a scientific and reasonable time-worthy carbon ecological compensation policy is urged by this current study.

The spatiotemporal evolution of ecological security in China based on the ecological footprint model with localization of parameters

With the outbreak of the current global eco-environmental crisis, ensuring global and local ecological security (ES) has become a priority for many countries in the world. In the past few decades, social and economic development in China has induced many ecological and environmental problems, which have negatively impacted ES of China and the world. In recent years, with the increasing awareness of China’s ecological and environmental protection, the Chinese government has actively participated in global ecological and environmental governance and raised ES to the height of national security. A systematic and comprehensive assessment of ES is the basis of ES assurance, which can enable governments to accurately grasp the ES status of different regions and adopt targeted management measures. The ecological footprint (EF) model is a mature model that has been widely used for ES assessment. Thus, this study used an EF model with localized parameters analyzing the spatiotemporal changes in China’s ES from 2006 to 2016 on a provincial scale. Then, from an “occupation-carrying” perspective, this study explored the main aspect that induced changes in regional ES and identified the main type of ecological land that threatened regional ES. Results showed that a) during the study period, China’s ES status showed a deteriorating trend and the current ES is not optimistic. However, the ecological carrying capacity of most provinces in China has increased, indicating that China’s ecological and environmental protection has achieved initial results; b) currently, the provinces whose ES status are moderate unsafe and quite unsafe are mainly distributed in the eastern coastal region and the region near the boundary between the second and third ladders; c) the high-intensity occupation of the ecological environment and biological resources attributed to the rapid development of the social economy is the main cause for the negative changes in ES in most areas; d) for most provinces in China, cropland occupation and fossil energy consumption pose great threats to the regional ES status. China should jointly consider ES, energy security, and food security in its future development plans.

Assessing local impacts of water use on human health: evaluation of water footprint models in the Province Punjab, Pakistan

PurposeThe water footprint (WF) method is widely applied to quantify water use along the life cycle of products and organizations and to evaluate the resulting impacts on human health. This study analyzes the cause-effect chains for the human health damage related to the water use on a local scale in the Province Punjab of Pakistan, evaluates their consistency with existing WF models, and provides recommendations for future model development.MethodLocally occurring cause-effect chains are analyzed based on site observations in Punjab and a literature review. Then, existing WF models are compared to the findings in the study area including their comprehensiveness (covered cause-effect chains), relevance (contribution of the modeled cause-effect chain to the total health damage), and representativeness (correspondence with the local cause-effect chain). Finally, recommendations for the development of new characterization models describing the local cause-effect chains are provided.Results and discussionThe cause-effect chains for the agricultural water deprivation include malnutrition due to reduced food availability and income loss as well as diseases resulting from the use of wastewater for irrigation, out of which only the first one is addressed by existing WF models. The cause-effect chain for the infectious diseases due to domestic water deprivation is associated primarily with the absence of water supply systems, while the linkage to the water consumption of a product system was not identified. The cause-effect chains related to the water pollution include the exposure via agricultural products, fish, and drinking water, all of which are reflected in existing impact assessment models. Including the groundwater compartment may increase the relevance of the model for the study area.ConclusionsMost cause-effect chains identified on the local scale are consistent with existing WF models. Modeling currently missing cause-effect chains for the impacts related to the income loss and wastewater usage for irrigation can enhance the assessment of the human health damage in water footprinting.

The Agricultural Planting Structure Adjustment based on Water Footprint and Multi-objective optimisation models in China

Aimed at solving the practical problems of the water resource shortage and the unreasonable agricultural planting structure in north China, this research looked at adjusting agricultural planting structure to save water. The agricultural structure of Zhangjiakou was optimised in terms of saving agricultural water, reducing pollution and increasing economic output. Taking “reduction of irrigated land + effective utilisation coefficient of irrigation water + planting structure adjustment” as the optimal path, the optimal agricultural planting structures were determined for water-saving scenarios of 15%, 20% and 30%. (1) Vegetables have the largest economic contribution, reaching 58.94%. Potato has the second-highest economic contribution and the largest water footprint, reaching 2461.41 × 106 m3. (2) Potato, vegetables and corn, with the larger TN pollutant accounting for 36.44%, 18.20% and 17.18%, were the main crops whose planting scales that needed to be reduced, while oil plant, fruit, naked oat and bean were the main crops whose planting scale could be increased. (3) From a comprehensive comparison of the amount of water saved and the benefits to the environment, the 15% water-saving plan was the best, and the cumulative reduction of pollution was 766.40 t. It is essential to adopt a combined approach of reducing irrigated land reduction, controlling crop scale and using water-saving irrigation methods to develop green and efficient water-saving practices and along with the implementation of precision agriculture techniques.

Improvement and application of the three-dimensional ecological footprint model

The ecological footprint (EF) is an important tool for assessing ecological resource occupancy. The three-dimensional (3D) EF changes the EF from a plane to a column, and the bottom (EFsize) represents the human appropriation of the annual natural resource flow provided by the earth, while the height (EFdepth) represents the number of years required to regenerate the resources consumed within 1 year. According to the difference in the human demands for the productive functions of land, this paper improves the 3D EF model based on three sub-items, namely, the basic land footprint (including the footprint of cropland, grazing land and fishing grounds), which captures the demands of the physical part of food and clothing; forest land footprint, which captures wood and carbon absorption demands; and the built-up land footprint, which captures production and living space demands. The improved model is a 3D structure with three different heights. The bottom shows human appropriation of annual natural flows of the sub-items, and there is competition between the sub-items. The sub-heights are related to the overshoot of the sub-items. The forest land footprint depth is earlier and deeper than the 3D EF, and the footprint depth of the built-up land and basic land kept the natural depth. Therefore, humans perceive climate change, but their daily survival is not significantly affected. The flow occupancy ratio (orflow) and the accumulated ecological debt depth (EFdepthaccum) are introduced to analyse the closeness to the overshooting state and the years of using existing resources to eliminate historical ecological debt, respectively.

Upscaling Northern Peatland CO2 Fluxes Using Satellite Remote Sensing Data

Peatlands play an important role in the global carbon cycle as they contain a large soil carbon stock. However, current climate change could potentially shift peatlands from being carbon sinks to carbon sources. Remote sensing methods provide an opportunity to monitor carbon dioxide (CO2) exchange in peatland ecosystems at large scales under these changing conditions. In this study, we developed empirical models of the CO2 balance (net ecosystem exchange, NEE), gross primary production (GPP), and ecosystem respiration (ER) that could be used for upscaling CO2 fluxes with remotely sensed data. Two to three years of eddy covariance (EC) data from five peatlands in Sweden and Finland were compared to modelled NEE, GPP and ER based on vegetation indices from 10 m resolution Sentinel-2 MSI and land surface temperature from 1 km resolution MODIS data. To ensure a precise match between the EC data and the Sentinel-2 observations, a footprint model was applied to derive footprint-weighted daily means of the vegetation indices. Average model parameters for all sites were acquired with a leave-one-out-cross-validation procedure. Both the GPP and the ER models gave high agreement with the EC-derived fluxes (R2 = 0.70 and 0.56, NRMSE = 14% and 15%, respectively). The performance of the NEE model was weaker (average R2 = 0.36 and NRMSE = 13%). Our findings demonstrate that using optical and thermal satellite sensor data is a feasible method for upscaling the GPP and ER of northern boreal peatlands, although further studies are needed to investigate the sources of the unexplained spatial and temporal variation of the CO2 fluxes.

Investigation and assessment of ecological water resources in the salt marsh area of a salt lake: A case study of West Taijinar Lake in the Qaidam Basin, China

The water ecology of salt marshes plays a crucial role in climate regulation, industrial production, and flood control. Due to a poor understanding of water ecology and the extensive mining of salt resources, concerns are mounting about declining groundwater levels, shrinking salt marshes, and other problems associated with the simple yet extremely fragile water ecosystem of salt marshes in arid salt lake areas. This study assessed the ecological status of water resources in the downstream salt marsh area of West Taijinar Lake in the Qaidam Basin, China (2010-2018). Using data from a field investigation, the water ecosystem was divided into an ecological pressure subsystem, an environmental quality subsystem, and a socio-economic subsystem according to an analytic hierarchy process. Each subsystem was quantitatively assessed using the ecological footprint model, the single-factor index, and available data for the salt marsh area. The results showed that water resources were always in a surplus state during the study period, whose development and utilization had a safe status. Surface water had low plankton diversity with no evidence of eutrophication, but its Cl- and SO42- concentrations were too high for direct industrial water uses. Groundwater quality was classified into class V because of high salt concentrations, which could be considered for industrial use given the demand of industrial production. The socio-economic efficiency of water resources was high, as distinguished by decreased water consumption per 10,000 yuan GDP and excellent flood resistance. In conclusion, the ecological status of water resources was deemed good in the study area and this could help sustain regional development. However, since the water ecology in this area is mainly controlled by annual precipitation, it would be challenging to deal with the uneven distribution of precipitation and flood events and to make full use of them for groundwater recharge. This study provides insight into the impact of salt lake resource exploration on water ecology, and the results can be useful for the rational utilization of water resources in salt marshes in other arid areas.