Assessing the Potential Impacts of Environmental and Climate Change on Wetlands in the Mekong Delta, Vietnam Using Remote Sensing and Modelling Approaches

Abstract

<p>Wetlands, which are considered as one of the most critical and valuable ecosystems on Earth, provide a wide range of critical ecosystem services to ecology and the human community. The Mekong Delta (MD) in Vietnam, a huge tropical wetland, is dominated by three key wetland types: mangroves in coastal zones, inland and coastal <i>Melaleuca</i> wetlands and important human-made wetlands (i.e., paddy ecosystems). The wetlands in the MD significantly contribute to ecosystem services and livelihoods of local communities. For example, forest wetlands regulate water balance, provide forest commodities, and conserve biodiversity. Meanwhile, paddy fields play important roles in food security and ecosystem protection and conservation. Moreover, the wetlands greatly contribute to socio-economic development and alleviation of poverty and hunger by offering resources, including food, medicine, other non-timber products, and eco-tourism resources.</p> <p>However, the wetland ecosystems are under threat from regional anthropogenic, global climate change, and the associated sea level rise (SLR). Particularly, the coastal wetlands (mangroves and coastal <i>Melaleuca</i> wetlands) are susceptible under SLR and changes in local climates including altered water balance, higher temperatures, and extreme events such as floods and droughts. For the case of paddy ecosystems, climate change with greater intensity and frequency of floods and droughts in combination with salinity intrusion due to SLR in recent years have already challenged rice crop production in the MD, subsequently threatening food security. </p> <p>Understanding the long-term changes in wetlands and exploring their driving factors are important for protecting and conserving wetland ecosystems and their critical services. Additionally, identifying potential impacts of changes in climate variables and SLR on wetlands is fundamental for the development of management, mitigation and adaptation strategies, which can be used to minimize the impacts of climate change and to protect and conserve the wetlands. Even though several studies have been undertaken concerning wetland ecosystems in the MD, the dynamics and drivers of these important wetland areas, and the potential impacts of changes in climate and SLR on the important wetlands are not yet well documented or researched. Therefore, this study aimed to investigate the long-term changes to wetlands under climate and environment impacts and to project future climate change and its impact on wetland ecosystems in the MD, Vietnam using remote sensing, GIS, ecological niche models, and climate models.</p> <p>The wetland ecosystems in the south-west coast of the MD have experienced critical changes over the period 1995/2020. The substantial increase in aquaculture ponds is at the expense of mangroves, forested wetlands, and rice fields, while shoreline erosion significantly affected coastal lands, especially mangrove forests. The interaction of a set of environmental and socio-economic factors were responsible for the dynamics. In particular, SLR was identified as one of the main underlying drivers" however, the rapid changes were directly driven by policies on land-use for economic development in the region. The trends of wetland changes and SLR implicate their significant effects on environment, natural resources, food security, and likelihood of communities in the region sustaining for the long-term.</p> <p>The study used GIS-based fire danger modelling approach and remote sensing techniques to evaluate the fire danger and its potential impacts on land-cover and wetlands in the MD. The change in climate with prolonged drought and high temperature is likely to cause serious fire danger. Importantly, forests, especially <i>Melaleuca</i> forests in U Minh wetlands, and agricultural land were under severe fire danger. Hence, measures such as proper management of forests and agricultural activities for mitigating forest fires and integrated fire and water strategies for either fire danger mitigation or biodiversity conservation are necessary for sustainable management of the MD wetland.</p> <p>This study also examined the potential impacts of climate change and SLR on the three dominant species of these wetland types, <i>Avicennia alba (A. alba)</i> and <i>Rhizophora apiculata (R. apiculata)</i> in mangrove wetlands and <i>Melaleuca cajuputi (M. cajuputi)</i> in <i>Melaleuca</i> wetlands, utilizing an species distribution model (SDM) approach. The projected reduction in habitat suitability of <i>A. alba, R. apiculata</i>, and <i>M. cajuputi</i> by mean values of 27.9%, 28.7% and 30.0%, respectively by the year 2070 indicates the vulnerability of the wetland species to climate change impacts. Increases in temperature, and in seasonal variation in precipitation and temperature, and SLR were key driving factors responsible for the losses of suitable habitat. </p> <p>Potential changes in mangrove distribution in response to future SLR scenarios in the coastal area in the south of the MD were investigated using the Sea Level Affecting Marshes Model (SLAMM). Simulation results show that the average annual mangrove losses are likely to be 0.54% and 0.22% for subsidence and stable scenarios, respectively. The findings demonstrate the considerable impacts of SLR on MD mangrove ecosystems, and the strong influence of subsidence processes. The findings from the present study are useful sources for development of proper strategies for minimizing the impacts of SLR on mangrove ecosystems and their vital associated-services, to protect and conserve the mangrove ecosystems in the region. </p> <p>The current work also identified changes in habitat suitability for a coastal <i>Melaleuca</i> wetland species in response to different future climate change and SLR scenarios, in the West Sea of the MD, with the aid of an ensemble SDM and the SLAMM. Simulated results suggested mean losses in suitable habitat of 29.8% and 58.7% for stable and subsidence scenarios, respectively, for the year 2070 in comparison to the baseline scenario. Relative SLR with considerable subsidence rate was suggested as one of the main drivers responsible for the habitat suitability loss.</p> <p>The use of ensemble SDM approach to examine the potential impacts of climate change and SLR on paddy ecosystems also demonstrates the vulnerability of the ecosystems under future climate and SLR scenarios. In particular, the mean loss of suitable land and mean gain of unsuitable land were 31.4% and 64.6%, respectively, for the year 2050 compared to the present. Salinity intrusion, increases in precipitation during rainy season and decreases in precipitation during dry season were key factors driving the loss of suitable habitat. The findings of this study critically support policy makers and planners in developing appropriate strategies for adaptation and mitigation in response to climate change for sustainable rice cultivation.</p> <p>Generally, the obtained findings provide valuable information on how climate and environment variability affect wetland ecosystems. Moreover, the outcomes of this study will provide statistical and spatial data on the current and future changes of wetland habitat suitability in the MD. The valuable knowledge and critical data will support the government, planners, policy makers and private investors in developing appropriate management, adaptation and mitigation strategies for protection and conservation of the wetland ecosystems in the region under future climate.</p>