Inventory and classification of wetlands in India

The Indian subcontinent has a large variety of freshwater, saline and marine wetlands. Whereas the mangroves are relatively well documented, very little is known about the other wetlands, with few exceptions. Only recently an inventory of these welands has been prepared but no effort has been made to classify them. A vast majority of the inland wetlands are temporary and/or man-made, and they have been traditionally used and managed by the local human populations. In this paper, first, we evaluate the classification schemes of the IUCN, US Fish and Wildlife Services and those of the Australian wetlands, for their applicability to Indian wetlands. Then, we propose a simple hierarchical classification of wetlands based on their location (coastal or inland), salinity (saline or freshwater), physiognomy (herbaceous or woody), duration of flooding (permanent or seasonal) and the growth forms of the dominant vegetation. We stress upon the hydrological factors which determine all the structural and functional characteristics of the wetlands. We consider that the various growth forms of wetland vegetation integrate the totality of hydrological variables and therefore, can be used as the indicators of different hydrological regimes.     

Ring width and vessel features of the mangrove Excoecaria agallocha L. depend on salinity in the Sundarbans,Bangladesh

The Bangladesh Sundarbans is the largest continuous mangrove in the world that providing crucial environmental services, particularly related to coastal protection and livelihoods of millions of people. However, anthropogenic disturbances, diseases infestation and environmental changes including sea level rise (SLR) and fresh-water flux into the delta are threatening the Sundarbans and other mangrove ecosystems worldwide. Protection of mangrove ecosystems requires knowledge on factors that mainly drive growth and vitality of tree species to evaluate which consequences can be expected from, mainly hydrology-related, environmental changes. In this study, we assessed the nature and periodicity of tree rings in Excoecaria agallocha, a wide spread mangrove species in the Bangladesh Sundarbans. We also analysed the influence of climatic factors, such as precipitation, temperature and vapor pressure deficit (VPD), and river discharge, as a proxy of salinity on ring width (RW) and vessel features, such as mean vessel area (MVA) and mean vessel density (MVD). E. agallocha forms distinct tree-ring boundary that characterized by a narrow (2–4 cells wide) band of radially flattened fibres. The RW as well as the MVA and MVD are crossdatable. The RW is mainly driven by salinity which is influenced by freshwater inputs through precipitation during monsoon along with river discharge January to April. The MVA and MVD responded to similar seasons and months as RW, but mostly with opposite signs in MVD. The results suggest that fresh water inputs through precipitation and river discharge positively influence the radial growth of E. agallocha in the Sundarbans. The RW and vessel features can be used as proxies to explore the growth dynamics of this species, especially in relation to global environmental changes.     

The performance and distribution of species along soil salinity gradients of mangrove swamps in southeastern Nigeria

Based on periodic soil salinity measurements direct gradient analysis procedures were used to relate the performance and distribution of mangrove swamp species to salinity gradients. Variations in soil salinity were due to distance from the coast, tidal incursions and freshwater inputs. All overstorey species showed statistically significant negative correlations with salinity while most groundlayer species were positively correlated with the same factor. Based on ecological group classification, no species was found to occur on the highest values of soil salinity. There were overlapping range of occurrences and ecological optima for most species along the gradients.     

Wetlands and global climate change: the role of wetland restoration in a changing world

Global climate change is recognized as a threat to species survival and the health of natural systems. Scientists worldwide are looking at the ecological and hydrological impacts resulting from climate change. Climate change will make future efforts to restore and manage wetlands more complex. Wetland systems are vulnerable to changes in quantity and quality of their water supply, and it is expected that climate change will have a pronounced effect on wetlands through alterations in hydrological regimes with great global variability. Wetland habitat responses to climate change and the implications for restoration will be realized differently on a regional and mega-watershed level, making it important to recognize that specific restoration and management plans will require examination by habitat. Floodplains, mangroves, seagrasses, saltmarshes, arctic wetlands, peatlands, freshwater marshes and forests are very diverse habitats, with different stressors and hence different management and restoration techniques are needed. The Sundarban (Bangladesh and India), Mekong river delta (Vietnam), and southern Ontario (Canada) are examples of major wetland complexes where the effects of climate change are evolving in different ways. Thus, successful long term restoration and management of these systems will hinge on how we choose to respond to the effects of climate change. How will we choose priorities for restoration and research? Will enough water be available to rehabilitate currently damaged, water-starved wetland ecosystems? This is a policy paper originally produced at the request of the Ramsar Convention on Wetlands and incorporates opinion, interpretation and scientific-based arguments.     

Status of arbuscular mycorrhizal fungi (AMF) in the Sundarbans of India in relation to tidal inundation and chemical properties of soil

The arbuscular mycorrhizal status of fifteen mangroves and one mangrove associate was investigated from 27 sites of three inundation types namely, diurnal, usual springtide and summer springtide. Roots and rhizospheric soil samples were analysed for spore density, frequency of mycorrhizal colonization and some chemical characteristics of soil. Relative abundance, frequency and spore richness of AMF were assessed at each inundation type. All the plant species except Avicennia alba exhibited mycorrhizal colonization. The study demonstrated that mycorrhizal colonization and spore density were more influenced by host plant species than tidal inundation. Forty four AMF species belonging to six genera, namely Acaulospora, Entrophospora, Gigaspora, Glomus, Sclerocystis and Scutellospora, were recorded. Glomus mosseae exhibited highest frequency at all the inundation types; Glomus fistulosum, Sclerocystis coremioides and Glomus mosseae showed highest relative abundance at sites inundated by usual springtides, summer springtides and diurnal tides, respectively. Spore richness of AMF was of the order usual springtide > diurnal > summer springtide inundated sites. The mean spore richness was 3.27. Diurnally inundated sites had the lowest concentrations of salinity, available phosphorus, exchangeable potassium, sodium and magnesium. Statistical analyses indicated that mycorrhizal frequency and AMF spore richness were significantly negatively correlated to soil salinity. Spore richness was also significantly negatively correlated to available phosphorus. The soil parameters of the usual springtide inundated sites appeared to be favourable for the existence of maximum number of AMF. Glomus mosseae was the predominant species in terms of frequency in the soils of the Sundarbans.     

Salinity effect on plant growth and leaf demography of the mangrove, Avicennia germinans L.

We assessed the effect of salinity on plant growth and leaf expansion rates, as well as the leaf life span and the dynamics of leaf production and mortality in seedlings of Avicennia germinans L. grown at 0, 170, 430, 680, and 940 mol m⁻³ NaCl. The relative growth rates (RGR) after 27 weeks reached a maximum (10.4 mg g⁻¹ d⁻¹) in 170 mol m⁻³ NaCl and decreased by 47 and 44% in plants grown at 680 and 940 mol m⁻³ NaCl. The relative leaf expansion rate (RLER) was maximal at 170 mol m⁻³ NaCl (120 cm m⁻² d⁻¹) and decreased by 57 and 52% in plants grown at 680 and 940 mol m⁻³ NaCl, respectively. In the same manner as RGR and RLER, the leaf production (P) and leaf death (D) decreased in 81 and 67% when salinity increased from 170 to 940 mol m⁻³ NaCl, respectively. Since the decrease in P with salinity was more pronounced than the decrease in D, the net accumulation of leaves per plant decreased with salinity. Additionally, an evident increase in annual mortality rates (λ) and death probability was observed with salinity. Leaf half-life (t _0.5) was 425 days in plants grown at 0 mol m⁻³ NaCl, and decreased to 75 days at 940 mol m⁻³ NaCl. Thus, increasing salinity caused an increase in mortality rate whereas production of new leaves and leaf longevity decreased and, finally, the leaf area was reduced.     

Effect of salinity on fungal diversity in the rhizosphere of the halophyte Avicennia germinans from a semi-arid mangrove

This study aimed to inventory fungal populations associated with the rhizosphere of Avicennia germinans in different salinity levels in a semi-arid mangrove in the Colombian tropics. Targeting the ITS1 and ITS2 regions provided complementary information, allowing a better approach to inventorying the fungal biodiversity. Amorosia and Aspergillus were the most abundant ascomycete genera, while Cystobasidium was the most abundant basidiomycete genus. Only five genera showed significant differences in abundance among the three salinity levels. Nevertheless, 65.4% of the genera were classified as exclusive for a specific salt content. Saprotrophs were the most abundant functional group and symbiotrophs were detected as mycorrhizas, fungi with biocontrol activity and entomopathogenic activity. These ecological groups play an important role in the cycling of organic matter and the availability of nutrients for mangrove plants and their tolerance to environmental and biotic stresses. This study highlights soil salinity as a determining factor in the composition of the fungal community in mangroves.     

短时间和长时间盐度对木榄幼苗生长及叶片膜脂过氧化作用的研究

对短时间和长时间盐胁迫下红树植物木榄 (Bruguieragymnorrhiza(L .)Lamk )幼苗的生长、叶片膜脂过氧化作用、叶绿素含量、电解质渗漏率、叶片肉质化程度等与盐胁迫强度之间的关系进行了对比研究。不同的盐胁迫时间下 ,随盐胁迫强度的提高 ,木榄幼苗的生长、叶片超氧化物歧化酶 (SOD)活性、丙二醛 (MDA)含量、肉质化程度S及叶绿素含量等变化趋势相似 ,表明不同盐胁迫时间下红树植物木榄的耐盐机制并没有发生根本改变。但随着盐胁迫时间的延长 ,木榄幼苗发生了一系列适应盐胁迫的变化 ,如木榄幼苗的最适生长盐度由 10g/L提高到 2 0g/L ,叶片电解质渗漏率下降 ,表明在本研究的实验条件下 ,长时间盐胁迫下木榄幼苗表现出对盐胁迫更大的适应性。膜脂过氧化不是盐胁迫下木榄叶片膜损伤的主要原因     

Protocol for in vitro propagation of Excoecaria agallocha L., a medicinally important mangrove species

An in vitro propagation protocol has been developed for Excoecaria agallocha L. (Euphorbiaceae), a mangrove species. Nodal segments were used for axillary shoot proliferation. One shoot from each node of binodal explants was observed 3 weeks after inoculation. The best axillary sprouting was seen on a newly formulated medium containing BA, Zeatin and IBA in concentrations of 13.3 μM, 4.65 μM and 1.23 μM, respectively. The new medium, first used in this study, has a specific composition of major nutrients, MS micronutrients and iron compounds. Nodal segments from rooted cuttings and seedlings responded better than those of mature tree explants. Multiple shoot induction was complemented with efficient shoot elongation, and repeated subculture of binodal segments from axillary shoots resulted in 10–12 shoots per explant in 3 months. Rooting was achieved by growing shoots in the new medium with 0.23 μM IBA. Regenerated plants were successfully acclimatized to the natural environment, and about 85% of plantlets survived under ex vitro conditions. This is the first report of micropropagation in the genus Excoecaria and also in mangrove tree species. Received: 11 August 1997 / Revision received: 10 February 1998 / Accepted: 2 March 1998     

Mapping ecosystem functions to the valuation of ecosystem services: implications of species–habitat associations for coastal land-use decisions

Habitats and the ecosystem services they provide are part of the world’s portfolio of natural capital assets. Like many components of this portfolio, it is difficult to assess the full economic value of these services, which tends to over-emphasize the value of extractive activities such as coastal development. Building on recent ecological studies of species–habitat linkages, we use a bioeconomic model to value multiple types of habitats as natural capital, using mangroves, sea grass, and coral reefs as our model system. We show how key ecological variables and processes, including obligate and facultative behaviors map into habitat values and how the valuation of these ecological processes can inform decisions regarding coastal development (habitat clearing). Our stylized modeling framework also provides a clear and concise road map for researchers interested in understanding how to make the link between ecosystem function, ecosystem service, and conservation policy decisions. Our findings also highlight the importance of additional ecological research into how species utilize habitats and that this research is not just important for ecological science, but it can and will influence ecosystem service values that, in turn, will impact coastal land-use decisions. While refining valuation methods is not necessarily going to lead to more rational coastal land-use decisions, it will improve our understanding on the ecological–economic mechanisms that contribute to the value of our natural capital assets. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.