Mangroves of Godavari – Analysis Through Remote Sensing Approach

The expansion of agriculture and aquaculture farms in the coastal areas has led to conversion of mangroves in the recent past. The extent of mangroves has also changed due to the erosion of mangroves along the coast and accretion near river mouths, leading to the formation of new mangrove areas. This study has been undertaken in the mangroves of the Godavari estuary, Andhra Pradesh, India to understand the changes in the extent of mangroves, namely accreted mangroves, erosion due to wave action and river water flow during floods, and changes due to forest restoration between 1986 and 2001, through remote sensing. The geomorphological changes due to river water flow in and around the mangroves have also been analysed. The changes in the vegetation due to forest restoration and natural regeneration are appreciable, while the changes in the area due to erosion and accretion are more or less equal. An analysis of the remote sensing images of 1986 and 2001 reveal that the mangroves outside the forest boundary have been converted to aquaculture. The sand spit of Hope Island has changed with time and has grown nearly 2.6 km between 1937 and 2001.     

Recognition of co-existence pattern of salt marshes and mangroves for littoral forest restoration

Climate-change driven sea level rise causes a increase in salinity in coastal wetlands accelerating the alteration of the species composition. It triggers the gradual extinction of species, particularly the mangrove population which is intolerant of excessive salinity. Thus despite being crucial to a wide range of ecosystem services, mangroves have been identified as a vulnerable coastal biome. Hence restoration strategy of mangroves is undergoing rigorous research and experiments in literature at an interdisciplinary level. From a data-driven perspective, analysis of mangrove occurrence data could be the key to comprehend and predict mangrove behavior along different environmental parameters, and it could be important in formulating management strategy for mangrove rehabilitation and restoration. As salt marshes are the natural salt-accumulating halophytes, mitigating excessive salinity could be achieved by incorporating salt-marshes in mangrove restoration activities. This study intends to find a novel restoration strategy by assessing the frequent co-existence status of salt marshes, with the mangroves, and mangrove associates in different zones of degraded mangrove patches for species-rich plantation. To achieve this, we primarily design a novel methodological framework for the practice of knowledge discovery concerning the coexistence pattern of salt marshes, mangroves, and mangrove associates along with environmental parameters using a data mining paradigm of association rule mining. The proposed approach has the capability to uncover underlying facts and forecast likely facts that could automate the study in the field of ecological research to comprehend the occurrence of inter-species relationships. Our findings are based on published data gathered on the Sundarban Mangrove Forest, one of the world’s most important littoral forests. The existing literature reinforces the findings that include all the sets of frequently co-occurring mangroves, their associates, and salt marshes along the salinity gradient of coastal Sundarbans. A detailed understanding of the occurrence patterns of all these, along with the environmental variables, would be able to promote decision-making strategy. This framework is effective for both academia and stakeholders, especially the foresters/ conservation planners, to regulate the spread of salt marshes and the restoration of mangroves as well.     

基于多源遥感的红树林监测

红树林是生长在热带以及亚热带海岸潮间带上的生态群落, 其生产力高, 固碳能力强, 对保持海岸带生物多样性具有十分重要的价值。本文介绍了利用多源遥感数据监测红树林的一些主要研究内容, 分为3个方面: (1)在时空模式研究方面, 利用高空间分辨率影像像素和对象结合的方法对红树林树种进行分类以及利用Landsat影像对红树林进行动态变化监测并分析其驱动因素; (2)在结构参数研究方面, 利用无人机多光谱数据及地面激光雷达数据对红树林叶面积指数进行反演; (3)在生理生化参数研究方面, 探讨了红树林叶绿素含量对淹没状况的响应、互花米草(Spartina alterniflora)入侵是否影响红树林光能利用率, 以及光化学反射指数(photochemical reflectance index, PRI)与光能利用率(light use efficiency, LUE)的关系。上述系列研究为提取红树林相关信息要素时如何选择合适的分析方法提供了有力的参考, 强调了遥感在研究红树林时空模式, 提取结构参数和生物生化参数监测的有效性, 从而更好地促进红树林生态系统的生物多样性保育工作。     

The interplay between mangroves and saltmarshes at the transition between temperate and subtropical climate in Florida

The interplay between mangroves and saltmarshes at the temperate to subtropical transition in Florida results in dramatic changes to the appearance of the coastal landscape. In the 1980s, freezes killed entire mangrove forests dominated by black mangroves, Avicennia germinans (L.). Following the freezes, saltmarshes dominated by smooth cordgrass, Spartina alterniflora Loisel, revegetated the intertidal zone. After a decade of mild winters, however, mangroves are beginning to reclaim the area. The rate of mangrove expansion was determined by comparing aerial photography (change from 1995 to 1999), and from monitoring transects (over a 3 year period) on three of the Cedar Keys, Florida (Lat. 29°08′). The rate of mangrove expansion varied among islands, and the mechanism of expansion ranged from propagule-trapping by saltmarshes along the edges of mangrove clumps to widespread dispersal and growth of existing or newly imported propagules. A freeze occurred during the study, which may have set back mangrove expansion by defoliating mangrove trees and resetting mangrove reproduction. Mangrove expansion was projected to take 20–30 years for complete seedling cover. Given the possibility of global climate change and its potential influence on the distribution of coastal vegetation, the timeframes and implications to coastal wetland ecosystems involved in this regular interplay will provide valuable baseline information for future studies.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Processes of organic carbon in mangrove ecosystems

In addition to carbon accumulation in plants, processes of organic carbon in mangrove ecosystems include origins of sediment organic carbon, carbon fluxes between mangroves and their adjacent systems (coastal waters and atmosphere), and cycling processes. Sediment organic carbon originates from suspending solids in coastal waters, mangrove plants and benthic algae. In mangroves with low organic carbon content in sediments, tidal seawater is the main origin of sediment organic carbon, while in mangroves with high sediment organic carbon contents, sediment organic carbon mainly originates from mangrove plants. Due to tidal flush, there is large material exchange between mangrove ecosystems and their adjacent coastal waters. In China, exports of organic carbon in litter falls and dissolved organic carbon from mangroves to their adjacent coastal waters have not been documented. Processes of mangrove litter falls, including production, decomposition, export and animal consumption, determine linkages among organic carbon among mangrove plants, secondary production and coastal ocean. Consumers especially benthic animals may influence organic carbon in mangrove ecosystems, because (1) their consumption rates are high, and their selective feeding on some food sources will change the relative quantities of export, bury and mineralization of organic carbon from different origins; (2) their consumption is much more than assimilation, resulting in the changes in sizes, forms and qualities of non-assimilated organic matters, and then the changes in availability of export, consumption or mineralization of organic carbon. Respiration and sulfate reduction are important mineralization processes of organic carbon in mangrove sediments. Mineralization rates of organic carbon in mangrove sediments are influenced by quantities, activities and particle sizes of organic matters, and other factors such as forest ages, root activities and animal burrowing activities. Researches on processes of mangrove organic carbon should be based on open systems, and ecological processes of organic carbon should be coupled with vegetation restoration.     

Applying remote sensing techniques to monitor shifting wetland vegetation: A case study of Danshui River estuary mangrove communities,Taiwan

The purpose of this study is to apply different remote sensing techniques to monitor shifting mangrove vegetation in the Danshui River estuary in Taipei, Taiwan, in order to evaluate a long-term wetland conservation strategy compromising between comprehensive wetland ecosystem management and urban development. In the Danshui estuary, mangrove dominated by Kandelia candel is the major vegetation, and a large area of marsh with freshwater grasses has been protected in three reserves along the river shore. This study applied satellite imagery from different remote sensors of various resolutions for spectral analysis in order to compare shifting wetland vegetation communities at different times. A two-stage analytical process was used for extracting vegetation area and types. In the first-stage, a normalized difference vegetation index (NDVI) was adopted to analyze SPOT, Landsat, and QuickBird imagery to obtain the spatial distribution of vegetation covers. In the second stage, a maximum likelihood classification (MLC) program was used to classify mangrove and non-mangrove areas. The results indicated that the spatial distribution of mangroves expanded 15.18 and 40 ha in two monitoring sites in 10 years, demonstrating the success of establishing reserves for protecting mangrove habitats. The analytical results also indicated that satellite imagery can easily discern the difference in characteristics between imagery of mangrove and other vegetation types, and that the logistical disadvantages of monitoring long-term vegetation community changes as well as evaluating an inaccessible area may be overcome by applying remote sensing techniques.     

1995-2019年广西山口红树林国家级自然保护区互花米草和红树林面积变化

互花米草根系发达,适应环境的能力强,在与其他植物争夺空间和养分的过程中容易占据优势.其作为外来入侵物种已对我国海岸带生态系统造成危害.为了探讨互花米草的入侵对我国红树林生长和扩张所造成的影响,本研究以广西山口红树林国家级自然保护区的红树林为例,通过对1995-2019年8景Land-sat多光谱遥感影像的解译,分析互花...     

A review on the present status and management of mangrove wetland habitat resources in Bangladesh with emphasis on mangrove fisheries and aquaculture

The mangrove forest of Bangladesh, the largest continuous mangrove bulk, is one of the most important features of the coastal area of the country. The existence of the mangrove has increased the values of other coastal and marine resources such as the coastal and marine fisheries by increasing productivity and supporting a wide biological diversity. The deltaic mangrove of Bangladesh is ecologically different from the other, mostly nondeltaic mangroves of the world and is unique also in its floral and faunal assemblage; therefore, a number of endangered plants and animals that are extinct from other parts of the world, are existing in Bangladesh mangrove. However, the mangrove has been under intensive pressure of exploitation for the last few decades which, in addition to direct clearance and conversion have placed the mangrove under extreme threat. Shrimp farming is the most destructive form of resource use the mangrove has been converted to, which contributed significantly to mangrove destruction with a corresponding loss of biological resources. Concerns have been raised among the ecologists, biologists, managers and policy makers since the early 1990s; deliberate destruction of mangrove and unplanned development of coastal aquaculture particularly shrimp aquaculture have been put under extreme criticism and the sustainability has been questioned. The present status of the mangrove resources including mangrove fisheries and aquaculture and management practices have been reviewed in this paper; impacts of different forms of human interventions and resource use have also been discussed. It is suggested that the management options and the policy aspects should be critically reviewed and amended accordingly; beneficiaries and stakeholders at all levels of resource exploitation must take part and contribute to conservation and management. An immediate need for mangrove conservation has been identified.     

1960-2010年广西红树林空间分布演变机制

为全面摸清1960—2010年广西红树林空间分布及其演变机制,采用多源遥感数据提取不同年度的红树林空间分布信息,分析了广西红树林空间分布动态特点,采用基于斑块的红树林空间演变机理分析方法,研究了1960/1976—2010年广西红树林空间演变机制。结果表明:1960/1976年、1990s年、2001年、2007年和2010年广西红树林斑块数量分别为1020、829、1094、1718个和1712个,面积分别为9062.5、7430.1、7015.4、6743.2、7054.3 hm2,近50年间红树林面积减少了22.16%,年均减少0.53%,斑块数量增加了67.8%;斑块平均面积由1960/1976年的8.9 hm2减小至2010年的4.1 hm2,大斑块数量显著减少,斑块破碎化严重;不同时期、不同区域和海湾,红树林面积和斑块数量的变化量、变化速率均不同;1960/1976年的斑块中,只有24个斑块至2010年时尚保持稳定,占2.4%,绝大部分斑块都发生了某种程度的变化。进一步分析结果表明:1960/1976—2010年,斑块消失(46.1%)、碎化(40.4%)、萎缩(13.5%)是面积减少的主要途径,新增(70.0%)和碎化(29.9%)是斑块数量增加的主要途径,但在不同时期,斑块数量和面积在各个途径上发生的变化量不尽相同;养殖塘和盐田建设(80.0%)、工程建设(10.9%)和围垦(9.1%)是面积净减少的驱动因子,自然过程(92.6%)和人工造林(7.4%)是斑块数量净增加的驱动因子,不同驱动因子在不同时期对斑块数量和面积变化的影响程度不同;斑块数量变化主要由自然过程作用下通过新增(39.6%)、消失(-9.1%)两个途径,以及养殖塘和盐田作用下通过消失(-15.3%)、碎化(14.5%)两个途径发生,斑块面积变化主要由自然过程影响下通过新增(17.5%)、扩张(12.6%)、消失(-6.1%),以及养殖塘和盐田建设驱动下通过斑块消失(-14.8%)、碎化(-13.9%)、萎缩(-6.6%)3个途径发生。     

Effect of an integrated mangrove-aquaculture system on aquacultural health

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degrada-tion and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obo-vata, and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different toler-abilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia. It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aqua-culture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.     

Practical techniques for mapping small patches of mangroves

Practical mapping methods employing GPS field surveys and manual image analyses with affordable software were used to assess two mangrove sites in Aklan Province, NE Panay Island, central Philippines. The Jawili mangroves, absent from current maps, actually included 21.5 ha with 24 true mangrove species. On the other hand, the Batan Estuary mangroves, shown to be 4244 ha in available topographic maps, revealed only 406 ha of scattered patches. Actual mangrove data on specific areas worldwide is limited, especially in the Philippines where available maps show discrepancies from actual mangrove distribution. Remote sensing (RS) techniques provide promising results but require expensive setup, particularly for small areas. Therefore, financially limited users need affordable and rapid mapping alternatives. The practical techniques presented here can be immediately implemented at minimal cost and can produce useful estimates of actual mangrove area, fundamental for coastal management. Basic principles used here also have potential applications in other systems and locations. When resources are available though, additional confirmation and precise mapping are also further recommended.     

Carbon and nutrient exchange of mangrove forests with the coastal ocean

Mangrove forests exchange materials with the coastal ocean through tidal inundation. In this study, we aim to provide an overview of the published data of carbon (C) and nutrient exchange of mangrove forests with the coastal ocean at different spatial scales to assess whether the exchange is correlated with environmental parameters. We collected data on C (dissolved and particulate organic C; DOC and POC) and nutrient exchange (dissolved and particulate nitrogen, N and phosphorus, P) and examined the role of latitude, temperature, precipitation, geomorphological setting, hydrology, dominant mangrove species and forest area in explaining the variability of the exchange. We identified that there are a range of methodologies used to determine material exchange of mangroves with the coastal zone, each methodology providing data on the exchange at different spatial scales. This variability of approaches has limited our understanding of the role of mangroves in the coastal zone. Regardless, we found that mangrove forests export C and nutrients to the coastal zone in the form of litter and POC. We found that precipitation is a major factor influencing the export of C in the form of litter; sites with low annual precipitation and high mean annual temperatures export more C as litter than sites with high precipitation and low temperature. Furthermore, export of POC is higher in zones with low mean annual minimum temperature. Identification of broad-scale trends in DOC and dissolved nutrients was more difficult, as the analysis was limited by scarcity of suitable studies and high variability in experimental approaches. However, tidal amplitude and the concentration of nutrients in the floodwater appears to be important in determining nutrient exchange. The strongest conclusion from our analysis is that mangrove forests are in general sources of C and nutrients in the form of litter and POC and that they are most likely to be exporting C subsidies in dry regions.     

红树林湿地在海岸生态系统维护中的功能*

综述了红树林湿地在海岸生态系统中所具有的维护生物多样性、防风消浪、促淤护岸、防灾减灾、净化海水、调节大气和美化海岸带景观等方面的功能。探讨了广东及华南沿海红树林的分布状况和存在问题,指出了华南沿海现存的红树林湿地正在遭受严重的威胁和破坏。华南沿海现存红树林湿地面积仅有1.5×10⁵hm²,比历史最大面积减少了70%;广东省的红树林湿地由10年前的1.47×10⁴hm²减少到现在的9100hm²,减少了38%。提出了建立和完善红树林自然保护网络系统、积极实施红树林湿地生态修复工程、注重红树林的引种和种苗培育技术研究、充分评估红树林湿地的巨大生态效价等对策与建议。     

The mangrove-based coastal and nearshore fisheries of Bangladesh: ecology,exploitation and management

The mangrove forest of Bangladesh, the largest continuous mangrove forest of the world, is one of the most important coastal features of the country. The existence of the mangrove has increased the values of other coastal and marine resources such as the coastal and marine fisheries by increasing productivity and supporting a wide biological diversity. The artisanal fishery, which is highly influenced by mangroves, has been contributing 85–95% of the total coastal and marine catch of Bangladesh. The mangrove also supports offshore and deep sea fisheries by playing a significant role as nursery ground for many deep sea fishes and shrimps including the giant tiger shrimp (Penaeus monodon) which is the major species of the industrial bottom trawl fishery of Bangladesh. The mangrove also contributes significantly in shrimp farming which has been the most significant export-oriented industry since the 1970s. However, the mangrove fisheries have been under intensive pressure from deleterious fishing activities and deliberate aquaculture development by destructing mangrove habitats. The impacts of mangrove have been reflected in the contribution of artisanal fishery catch that has been in a continuous decline since the 1980s. Shrimp farming has been the most destructive contributor to mangrove destruction with a corresponding loss of biological resources particularly the wild shrimp fishery. This paper reviews different aspects of the mangrove fisheries of Bangladesh and discusses the impacts of different fisheries. The paper identifies the importance of reviewing, amending and/or replacing the traditional management approaches by the new management techniques such as habitat restoration and stock enhancement in the natural environment; the paper also identifies the need for research findings in formulating and implementing new management approaches.     

Environmental drivers in mangrove establishment and early development: A review

Mangroves have a global distribution within coastal tropical and subtropical climates, and have even expanded to some temperate locales. Where they do occur, mangroves provide a plethora of goods and services, ranging from coastal protection from storms and erosion to direct income for human societies. The mangrove literature has become rather voluminous, prompting many subdisciplines within a field that earlier in the 20th century received little focus. Much of this research has become diffuse by sheer numbers, requiring detailed syntheses to make research results widely available to resource managers. In this review, we take an inclusive approach in focusing on eco-physiological and growth constraints to the establishment and early development of mangrove seedlings in the intertidal zone. This is a critical life stage for mangroves, i.e., the period between dispersal and recruitment to the sapling stage. We begin with some of the research that has set the precedent for seedling-level eco-physiological research in mangroves, and then we focus on recent advances (circa. 1995 to present) in our understanding of temperature, carbon dioxide, salinity, light, nutrient, flooding, and specific biotic influences on seedling survival and growth. As such, we take a new approach in describing seedling response to global factors (e.g., temperature) along with site-specific factors (e.g., salinity). All variables will strongly influence the future of seedling dynamics in ways perhaps not yet documented in mature forests. Furthermore, understanding how different mangrove species can respond to global factors and regional influences is useful for diagnosing observed mortality within mangrove wetlands, managed or natural. This review provides an updated eco-physiological knowledge base for future research and reforestation activity, and for understanding important links among climate change, local physico-chemical condition, and establishment and early growth of mangrove seedlings.     

Effect of an integrated mangrove-aquaculture system on aquacultural health

Mangroves are unique intertidal halophyte formations growing in sheltered tropical and subtropical coastal areas. Due to the increasing population and economic development, mangroves have faced degradation and loss, which has been mainly caused by land conversion into aquaculture ponds in Asia. In the past several decades, the rapid growth of aquaculture has induced water pollution. Using mangroves for effluent treatment from coastal aquaculture ponds could be a suitable approach for wastewater treatment and healthy aquaculture development. An Integrated Mangrove-Aquaculture System (IMAS) was established to test whether the idea of a mangrove in situ treatment for aquaculture wastewater is feasible. The monocultures of three mangroves, Sonneratia caseolaris, Kandelia obovata, and Aegiceras corniculatum were established with area proportions of 45%, 30%, or 15%, respectively. One control pond without mangroves was also set up. The results indicated that the mangroves had different tolerabilities to long-term inundation. The aquaculture ponds had different fishery yields, considering the mangrove species and area proportions. The water quality of most of the experimental ponds was better than the control pond, except for the planted Sonneratia. It is concluded that mangroves can reduce the concentration of dissolved inorganic nitrogen and phosphate, buffer the pH value and increase the concertration of dissolved oxygen in aquaculture water bodies effectively. It is suggested to use 15% of the Aegiceras corniculatum area to conduct in situ purification of aquaculture wastewater and to enhance aquaculture production.     

The assessment of mangrove biomass and carbon in West Africa: a spatially explicit analytical framework

Mangrove forests are highly productive and have large carbon sinks while also providing numerous goods and ecosystem services. However, effective management and conservation of the mangrove forests are often dependent on spatially explicit assessments of the resource. Given the remote and highly dispersed nature of mangroves, estimation of biomass and carbon in mangroves through routine field-based inventories represents a challenging task which is impractical for large-scale planning and assessment. Alternative approaches based on geospatial technologies are needed to support this estimation in large areas. However, spatial data processing and analysis approaches used in this estimation of mangrove biomass and carbon have not been adequately investigated. In this study, we present a spatially explicit analytical framework that integrate remotely sensed data and spatial analyses approaches to support the estimation of mangrove biomass and carbon stock and their spatial patterns in West Africa. Forest canopy height derived from SRTM and ICESat/GLAS data was used to estimate mangrove biomass and carbon in nine West African countries. We developed a geospatial software toolkit that implemented the proposed framework. The spatial analysis framework and software toolkit provide solid support for the estimation and relative comparisons of mangrove-related metrics. While the mean canopy height of mangroves in our study area is 10.2 m, the total biomass and carbon were estimated as 272.56 and 136.28 Tg. Nigeria has the highest total mangrove biomass and carbon in the nine countries, but Cameroon is the country with the largest mean biomass and carbon density. The resulting spatially explicit distributions of mangrove biomass and carbon hold great potential in guiding the strategic planning of large-scale field-based assessment of mangrove forests. This study demonstrates the utility of online geospatial data and spatial analysis as a feasible solution for estimating the distribution of mangrove biomass and carbon at larger or smaller scales.