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Efficient nutrient cycling and adequate sediment bioavailable nutrient supply are considered to be the two most important factors regulating the high productivity and subsequent carbon sequestration by mangrove ecosystems. We assessed spatial variability and the possible regulating factors of sediment bioavailable nutrients (nitrogen (N) and phosphorus (P)) and surface water-dissolved nutrients (N, P and silicate (Si)) in the five ecologically important mangrove ecosystems along the east and west coast of India during dry season. Higher bioavailable nitrogen concentrations in the sediments were recorded in Coringa mangroves (36.27 ± 14.7 μg g−1) and Bhitarkanika (18.54 ± 5.9 μg g−1) mangroves in the east coast followed by Karnataka (15.51 ± 8.26 μg g−1), Goa, (10.18 ± 9.96 μg g−1) and Kerala (6.36 ± 5.05 μg g−1) mangroves in the west coast. The dissolved inorganic nutrients in the mangrove waters ranged between 5.1 and 220.9 μmol l−1 for N and 0.07 and 3.9 μmol l−1 for P. These results indicated that terrestrial inputs, in situ remineralization and prevalent anoxic conditions regulated sediment nutrient content in these ecosystems, whereas the higher ammonium in the sediments was attributed to the greater nutrient adsorption by finer particles. The stoichiometry of the bioavailable nutrients (N, P) in the mangrove sediments deviated drastically from the Redfield ratio, and strong P limitation was recorded in most of the ecosystems. The results highlighted the potential role of sediment particle size and physiochemical (salinity and pH) properties in regulating bioavailable nutrient dynamics in mangrove sediments. [ABSTRACT FROM AUTHOR]

Seagrass meadows are among the most important coastal/ marine ecosystems for long-term carbon storage and conditioning of coastal waters. A combined air-water flux of CO2 and CH4 from the seagrass meadows was studied for the first time from Asia’s largest brackish–water lagoon, Chilika, India. Ecosystem-based comparisons were carried out during two hydrologically different conditions of dry and wet seasons in the seagrass dominated southern sector (SS); macrophyte-dominated northern sector (NS); the largely un-vegetated central sector (CS) and the tidally active outer channel (OC) of the lagoon. The mean fluxes of CO2 from SS, NS, CS and OC were 9.8, 146.6, 48.4 and 33.0mM m-2d-1, and that of CH4 were 0.12, 0.11, 0.05 and 0.07mM m-2d-1, respectively. The net emissions (in terms of CO2 equivalents), considering the global warming potential of CO2 (GWP: 1) and CH4 (GWP: 28) from seagrass meadows were over 14 times lower compared to the macrophyte-dominated sector of the lagoon. Contrasting emissivity characteristics of CO2 and CH4 were observed between macrophytes and seagrass, with the former being a persistent source of CO2. It is inferred that although seagrass meadows act as a weak source of CH4, they could be effective sinks of CO2 if land-based pollution sources are minimized. [ABSTRACT FROM AUTHOR]

Salt marshes are intertidal halophytic vegetations, distributed in mid to lower latitudes. They provide important ecosystem services, including transportation and remineralization of nutrients, habitat for coastal biota, coastal bioshield, biofilters and recreation and cultural benefits. In India, 15 salt marsh species so far have been reported, spread over 1600 km². Salt marshes are known to adapt themselves to the changing environmental conditions fairly quickly by maintaining a balance between the existing pressures and the prevailing state. Thus, they tend to retain a long-term ecosystem sustainability under changing environmental conditions. Recent studies have recognized them for their extraordinary capacity of carbon sequestration, which gives them edge amongst the coastal ecosystems, but the carbon stock is comparatively low due to their alarming decline in global areal extent. In the Indian context, salt marshes occupy a significant share of the coastline along with the other blue carbon ecosystems like mangroves and seagrasses. This provides India with a very promising alternative for achieving its Intended Nationally Determined Contribution towards climate change mitigation through enhancing additional carbon sinks (INDC goal # 5). But, despite its rich salt marsh diversity and distribution along the entire coastline, Indian salt marshes are one of the most overlooked coastal ecosystems. The documented studies on the Indian marshes are relatively scarce and studies addressing their carbon storage and climate change mitigation potential are totally non-existent. There is an urgent need for targeted scientific studies to be taken up on the Indian salt marsh ecosystems to develop a holistic and updated database, which can support resource management, decision-making and facilitate to estimate Blue carbon economy of India. [ABSTRACT FROM AUTHOR]