Collaborative multiple change detection methods for monitoring the spatio-temporal dynamics of mangroves in Beibu Gulf, China

Mangrove ecosystems are one of the most diverse and productive marine ecosystems around the world, although losses of global mangrove area have been occurring over the past decades. Therefore, tracking spatio-temporal changes and assessing the current state are essential for mangroves conservation. To solve the issues of inaccurate detection results of single algorithms and those limited to historical change detection, this study proposes the detect–monitor–predict (DMP) framework of mangroves for detecting time-series historical changes, monitoring abrupt near-real-time events, and predicting future trends in Beibu Gulf, China, through the synergetic use of multiple detection change algorithms. This study further developed a method for extracting mangroves using multi-source inter-annual time-series spectral indices images, and evaluated the performance of twenty-one spectral indices for capturing expansion events of mangroves. Finally, this study reveals the spatio-temporal dynamics of mangroves in Beibu Gulf from 1986 to 2021. In this study, we found that our method could extract mangrove growth regions from 1986 to 2021, and achieved 0.887 overall accuracy, which proved that this method is able to rapidly extract large-scale mangroves without field-based samples. We confirmed that the normalized difference vegetation index and tasseled cap angle outperform other spectral indexes in capturing mangrove expansion changes, while enhanced vegetation index and soil-adjusted vegetation index capture the change events with a time delay. This study revealed that mangrove changes displayed historical changes in the hierarchical gradient from land to sea with an average annual expansion of 239.822 ha in the Beibu Gulf during 1986–2021, detected slight improvements and deteriorations of some contemporary mangroves, and predicted 72.778% of mangroves with good growth conditions in the future

Tidal variation shaped microplastic enrichment patterns in mangrove blue carbon ecosystem of northern Beibu Gulf, China

Mangroves are considered to be a sink for microplastics (MPs) due to their unique characteristics. Previous studies mainly focused on the spatial distribution of MPs, but few researchers have addressed the influence of tidal variation on this distribution, especially since the MP total number in mangroves was unknown. In this study, surface sediment samples were collected in mangroves from the Beibu Gulf, South China Sea, and the abundance, composition, and number of MPs were investigated. The results showed that MPs were widely present in all mangrove sediment samples, with abundances ranging from 26.67 ± 9.43 to 239.94 ± 37.80 items/kg. The distribution of MPs was heterogeneous among different sampling sites, with the highest levels in the Shankou (SK) area. The MP abundance in the same mangrove forest gradually increased from the low tidal zone to the high tidal zone, with the enrichment factor ranging from 1.50 to 4.00. The MP abundance was significantly correlated with particulate organic carbon (POC) (n = 12, R = 0.664, p < 0.05). Results showed that mangroves had an interception effect on MPs and factors affecting MP distribution in mangrove sediments included not only tides but also human activities, such as aquaculture, agriculture, and residential life. Finally, this paper estimated the MP total number in mangroves at different sampling areas and tidal zones, and the middle tidal zone was considered to be more accurate for MP pollution assessment in mangroves

Evaluation of LAI Estimation of Mangrove Communities Using DLR and ELR Algorithms With UAV, Hyperspectral, and SAR Images

The high-precision estimation of mangrove leaf area index (LAI) using a deep learning regression algorithm (DLR) always requires a large amount of training sample data. However, it is difficult for LAI field measurements to collect a sufficient amount of sample data in mangrove wetlands. To tackle this challenge, this paper proposed an approach for expanding training samples and quantitatively evaluated the performance of estimating LAI for mangrove communities using Deep Neural Networks (DNN) and Transformer algorithms. This study also explored the effects of unmanned aerial vehicle (UAV) and Sentinel-2A multispectral, orbital hyper spectral (OHS), and GF-3 SAR images on LAI estimation of different mangrove communities. Finally, this paper evaluated the LAI estimation ability of mangrove communities using ensemble learning regression (ELR) and DLR algorithms. The results showed that: (1) the UAV images achieved the better LAI estimation of different mangrove communities (R2 = 0.5974–0.6186), and GF-3 SAR images were better for LAI estimation of Avicennia marina with high coverage (R2 = 0.567). The optimal spectral range for estimating LAI for mangroves in the optical images was between 650–680 nm. (2) The ELR model outperformed single base model, and produced the high-accuracy LAI estimation (R2 = 0.5266–0.713) for different mangrove communities. (3) The average accuracy (R2) of the ELR model was higher by 0.0019–0.149 than the DLR models, which demonstrated that the ELR model had a better capability (R2 = 0.5865–0.6416) in LAI estimation. The Transformer-based LAI estimation of A. marina (R2 = 0.6355) was better than the DNN model, while the DNN model produced higher accuracy for Kandelia candel (KC) (R2 = 0.5577). (4) With the increase in the expansion ratio of the training sample (10–50%), the LAI estimation accuracy (R2) of DNN and Transformer models for different mangrove communities increased by 0.1166–0.2037 and 0.1037–0.1644, respectively. Under the same estimation accuracy, the sample enhancement method in this paper could reduce the number of filed measurements by 20–40%

Spatial Expansion and Soil Organic Carbon Storage Changes of Croplands in the Sanjiang Plain, China

Soil is the largest pool of terrestrial organic carbon in the biosphere and interacts strongly with the atmosphere, climate and land cover. Remote sensing (RS) and geographic information systems (GIS) were used to study the spatio-temporal dynamics of croplands and soil organic carbon density (SOCD) in the Sanjiang Plain, to estimate soil organic carbon (SOC) storage. Results show that croplands increased with 10,600.68 km2 from 1992 to 2012 in the Sanjiang Plain. Area of 13,959.43 km2 of dry farmlands were converted into paddy fields. Cropland SOC storage is estimated to be 1.29 ± 0.27 Pg C (1 Pg = 103 Tg = 1015 g) in 2012. Although the mean value of SOCD for croplands decreased from 1992 to 2012, the SOC storage of croplands in the top 1 m in the Sanjiang Plain increased by 70 Tg C (1220 to 1290). This is attributed to the area increases of cropland. The SOCD of paddy fields was higher and decreased more slowly than that of dry farmlands from 1992 to 2012. Conversion between dry farmlands and paddy fields and the agricultural reclamation from natural land-use types significantly affect the spatio-temporal patterns of cropland SOCD in the Sanjiang Plain. Regions with higher and lower SOCD values move northeast and westward, respectively, which is almost consistent with the movement direction of centroids for paddy fields and dry farmlands in the study area. Therefore, these results were verified. SOC storages in dry farmlands decreased by 17.5 Tg·year−1 from 1992 to 2012, whilst paddy fields increased by 21.0 Tg·C·year−1

Investigating the decline of ecosystem services in a production mangrove forest using Landsat and object-based image analysis

The Matang Mangrove Forest Reserve is widely recognised as a sustainably managed mangrove forest. However, recently evidence of multiple ecosystem services decline has emerged. The primary objective of this study was to apply remote sensing techniques to assess the impact of the silviculture in the mangrove forest reserve on the provision of ecosystem services. It applied an object-based approach to classify multi-temporal Landsat imagery. The classified images enabled the study to characterise and analyse the spatiotemporal changes in the distribution of stand age composition and structure over a 35 year period. Links were established between the classified images and the ecosystem services assessment based on the assumption that the classification results provided a reliable proxy for an indirect analysis on the temporal and spatial distribution of aboveground biomass of the mangrove forest reserve. The relationship between the potential impacts of the observed changes derived from the classified images with the data obtained from the ecosystem services assessment were analysed. The analysis showed that the fluctuation in greenwood yield was affected by varying rates of regeneration, exposure to excessive thinning and delays in harvesting. The production of blood cockles around the mudflats of the mangrove forest reserve was determined to be influenced by both timber extraction and natural coastal erosion. An undetected ecological change in the late eighties and anthropogenic disturbances were possible key factors behind the decline in the population of the Milky Stork and migratory shorebirds. The study highlights the importance of understanding and managing the trade-offs between wood production and ecosystem services in a managed mangrove forest and provides an important reference for the future management of the Matang Forest Reserve and other multiple-use wetland forests

Applications of Remote Sensing Data in Mapping of Forest Growing Stock and Biomass

This Special Issue (SI), entitled "Applications of Remote Sensing Data in Mapping of Forest Growing Stock and Biomass”, resulted from 13 peer-reviewed papers dedicated to Forestry and Biomass mapping, characterization and accounting. The papers' authors presented improvements in Remote Sensing processing techniques on satellite images, drone-acquired images and LiDAR images, both aerial and terrestrial. Regarding the images’ classification models, all authors presented supervised methods, such as Random Forest, complemented by GIS routines and biophysical variables measured on the field, which were properly georeferenced. The achieved results enable the statement that remote imagery could be successfully used as a data source for regression analysis and formulation and, in this way, used in forestry actions such as canopy structure analysis and mapping, or to estimate biomass. This collection of papers, presented in the form of a book, brings together 13 articles covering various forest issues and issues in forest biomass calculation, constituting an important work manual for those who use mixed GIS and RS techniques

Ecosystem Service and Land-Use Changes in Asia

This book highlights the role of research in Ecosystem Services and Land Use Changes in Asia. The contributions include case studies that explore the impacts of direct and indirect drivers affecting provision of ecosystem services in Asian countries, including China, India, Mongolia, Sri Lanka, and Vietnam. Findings from these empirical studies contribute to developing sustainability in Asia at both local and regional scales

Celebrating 25 Years of World Wetlands Day

The purpose of this Special Issue is to celebrate 25 years of “World Wetlands Day”. There is no other ecosystem that has its very own Ramsar Convention or such a challenge impacting ecosystem sustainability. Papers for this Special Issue provide an overview of wetland status and function within different regions of the world. The papers in this Special Issue of Land consist of three review papers, ten research articles and one perspective paper. Edward Maltby’s review paper provides us with an overview of the paradigm shift of how we value and assess wetlands over time. Ballut-Dajud et al. provide us with a worldwide perspective on factors affecting wetland loss. Finally, Jan Vymazal provides us with a historical overview of the development of water quality treatment wetlands in Europe and North America. The research papers can be grouped into four groups: 1) use of remote sensing to analyze stability and dynamic factors affecting wetlands; 2) factors affecting the wetlands’ ability to store carbon; 3) assessment of wetlands effect on water quality; and 4) understanding historical use and value of wetlands, farmer’s attitudes about wetland management, and how we can value wetland ecosystem services. Finally, Bryzek et al. remind us that, as wetland researchers and managers, we should minimize damage to wetlands even through field monitoring work

Understanding changes in mangrove forests and the implications to community livelihood and resource management in Kenya

Mangrove forests support the livelihoods of many coastal communities in developing countries. Mangrove forests around the world are being lost due to a combination of human and natural pressures. There is an intricate relationship between resource use and degradation and resource-dependent communities. Dependency on resources can lead to an ecosystem's degradation if management disregards local people's needs. Degraded mangroves are more vulnerable to environmental changes and may be less able to provide the ecosystem services and goods that are crucial to the livelihood of local people. The key outcome of sustainable resource management is to identify ways to improve both environmental quality and the living conditions of the local communities. Therefore, the sustainable management of mangrove forests requires an understanding of: (a) how mangroves are used by local communities; (b) the local perceptions of changes happening in the mangrove areas and (c) how changes in mangroves are affecting local livelihoods including adaptation options. Focussing on coastal Kenya and using Lamu as a case study, this multi-method research used systematic literature review, household surveys, participatory consultation workshops, land use land cover change analysis, and ecosystem services modelling to understand local mangrove uses, perceptions of change in mangroves and the implications to uses and users, including adaptation options. The thesis first provides an overview of mangrove ecosystem services and the global utilization of mangrove resources. The contribution of mangroves to fisheries is the most researched ecosystem service followed by habitat use and carbon sequestration and storage. The review indicates that wood used for construction and fuel is the mangrove resource most often mentioned in the literature, and it is often associated with the loss of mangrove forests. A survey conducted in 592 households in five locations in Lamu county noted high levels of dependency on mangrove forests and varying perceptions about changes in mangrove areas and drivers of change. The variation is noted across gender, occupation, and location of respondents. Most of the respondents indicated a perceived increase in mangrove cover in the last decade. In contrast, an analysis of land cover data shows a decrease in mangrove cover in Lamu county and Kenya at a very slow rate (0.01% annual average between 2010-2019), with areas closer to settlements exhibiting higher deforestation rates. Mangrove loss also increases the exposure of local areas to coastal hazards. Analysis using the InVEST coastal vulnerability model indicates that 16% of the country’s coastline is currently at a relatively higher risk of exposure to coastal hazards. This may increase to 25% with the loss of mangroves and to 41% if coral reefs are also lost. Although coral reefs contribute the most to reducing the proportion of the country’s coastline to exposure, mangroves contribute the most in Lamu and Tana River counties. Stakeholders’ consultations conducted in Lamu, Kwale and Kilifi counties identified differences between communities regarding perceived key threats and the adaptation options being employed. The threats identified during these consultations were dominantly related to human use and climate change was a lower concern. Although overharvesting of wood resources was identified as a common threat, coping strategies for this threat differ along the coast. While some counties are using an alternative source of wood, others are switching to alternative methods of construction (bricks, cement) and fuel (LPG gas). Subsidies for communities to use alternatives to mangrove products and seasonal or rotational closure of mangrove areas are some of the proposed interventions for mangrove resource sustainability. In addition, while the ban on mangrove harvesting was noted to be beneficial in Kwale county as it supported conservation efforts in place, it was observed to be detrimental in Lamu county due to traditionally depending on mangrove harvesting and use. To be effective and sustainable, the management needs to take into account local perceptions and needs and recognize differences across neighbouring communities. A framework that provides key steps that can be taken to assess adaptation needs and alternatives was developed in this study. The study also identified the need for long-term alternatives for the livelihoods of those depending on mangroves. These alternatives can only be realized if the management of mangrove areas includes opportunities to build local skills and capacity while recognising that needs vary across locations

Use of geographic information systems for aquaculture and recommendations for development of spatial tools

There are many spatial issues associated with aquaculture which must be understood in order to support sustainable development and mitigate other potential issues. Geographic Information Systems (GIS) are used for investigation, analysis and modelling of aquaculture and there have been a considerable number of studies since the late 1980’s. However, despite the range of applications, GIS is still often underutilised and stakeholders have requested more GIS-based tools to support management and regulation of the sector. Consequently, there is a need to establish a knowledge base of existing applications and identify the challenges and opportunities to encourage development of tools that address user needs. This study presents a quantitative analysis of primary scientific literature, focusing on over 200 studies, to enable a comprehensive overview of the application of GIS and the trends associated with its use for aquaculture. Furthermore, there is a detailed assessment of the considerations when developing GIS-based tools for aquaculture which culminates in five key recommendations regarding 1) Usability of the tool, 2) Data requirements, 3) Accessibility to end user, 4) Capabilities and training requirements, and 5) Longevity of the tool. These recommendations can guide future development and application of tools to support aquaculture planning and management and assess spatial issues relevant for the sector