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Khung Kraben Lagoon (KKL) is a coastal lagoon situated in the eastern part of Thailand. There are two major species of seagrasses in KKL, Enhalus acoroides (Ea) and Halodule pinifolia (Hp), which have a combined total areal coverage of 335 ha. These two species can be found either separately or mixed in three zones: Ea zone, Hp zone, and Mixed zone (both species). This study aims to investigate the productivity and carbon sequestration of these species. Surveys indicated that H. pinifolia (42.97 %) had higher carbon sequestration than E. acoroides (35.23 %). A high percentage of nitrogen is in aboveground parts of these plants (Hp: 2.29 % and Ea: 2.02 %). E. acoroides in the Ea zone had the highest mean organic carbon production of 0.0886 Mg Cha-1. The monsoon period has direct effect on total organic carbon (TOC) production. The Southwest monsoon (SWM) period reduces production of seagrass while the Northeast monsoon (NEM) period promotes higher seagrass production. TOC production was significantly highest in April (0.2092 Mg Cha-1) during the monsoon transition (between NEM and SWM) in the Hp zone, as revealed by cluster analysis. In terms of litter decomposition, E. acoroides has a half-life of 4.31 weeks and a turnover period of 6.21 weeks, while H. pinifolia has a half-life of 7.37 weeks and a turnover period of 10.64 weeks. KKL is a net exporter of organic carbon to the outer sea (0.3042 Gg Cyear-1). These findings provide useful information for planning sustainable management to conserve seagrass meadows like the one in KKL. [ABSTRACT FROM AUTHOR]

Ao Kung Krabaen Lagoon (AKBL) is a small and shallow coastal lagoon situated in the eastern part of Thailand. It is an important "Blue Carbon" ecosystem of this region. However, water quality of the lagoon has drastically deteriorated in recent years. To counteract the problem, a comprehensive understanding of water circulation within the lagoon and exchange with the outer sea is needed. In this study, seasonal field observations were made and then applied in three-dimensional hydrodynamic simulations using Delft3D-FLOW. Results indicate that water properties, water circulation and water exchange differ notably by season. During the southwest (SW) monsoon (July-September), circulation is at its strongest, and there are strong double-gyre circulations. This results in enhancing exchange with the sea, hence significantly reducing flushing time. The flushing time during the SW monsoon is approximately three days. During the transition period (April-May) between the northeast monsoon and the SW monsoon, sluggish circulation dominates the lagoon. The flushing time increases to around 10 days, which is the annual maximum. Water circulation within the lagoon is mostly in two-dimensional patterns owing to its shallowness, even though water exchange occurs in three dimensions. This study also demonstrates that the tropical coastal lagoons scattered around the world should be considered three-dimensionally and with attention to varying water density both inside and outside the lagoon to properly model their hydrodynamics and exchange with the outer sea. [ABSTRACT FROM AUTHOR]

We present bulk organic carbon isotopic composition (δ13C), total organic carbon (TOC) content, and total organic carbon to total nitrogen (C/N) ratio along with major and trace element geochemistry of an AMS radiocarbon-dated Holocene sediment core collected from Chilika Lagoon, India. The data are used to understand changes in the organic matter (OM) sources and the strength of the Indian summer monsoon (ISM). Our results indicate that during early to middle Holocene (10.4–4.9 ka), terrestrial (23–65%) and macrophyte (24–32%) sources were significant contributors to the sediment OM; marine component contributed ≤23%. An abrupt shift in the OM sources was observed at ~4.0 ka, marked by a significant decrease in OM contributions from the terrestrial (5%) and macrophyte (14%) end-members, and an increase in the marine end-member source (70%) into the lagoon. The period from ~4.0 to 2.1 ka recorded the lowest and highest contribution from the terrestrial (5–11%) and marine (50–70%) sources, respectively. This was followed by a gradual increase in the terrestrial and decrease in the marine contribution to 21% and 25% till the present, respectively. During this period, phytoplankton became the major source (31–40%) of OM to the lagoon. This period also experienced increasing anthropogenic activities in the catchment. In this study, proxy records show a strong ISM during early Holocene (10.4–9.0 ka), which was followed by a gradual weakening until 4.9 ka. At ~4.0 ka, an abrupt and pronounced weakening of ISM occurred that was followed by an amelioration of ISM precipitation towards 1.1 ka. Later, the ISM gradually weakened to the present-day condition. Overall, Chilika Lagoon core records exhibit that changes in the Northern Hemisphere summer insolation regulate the long-term trend of ISM during the Holocene. [ABSTRACT FROM AUTHOR]

Latvia Lake provides one of the few high‐resolution palaeoenvironmental records from southeastern Primor'ye. It traces basin, vegetation and climate histories over the past c. 8.6 ka. The Latvia basin experienced four phases, two of which involved frequent shifts amongst lake, lagoon and bay settings (c. 8.6–7.0 cal. ka BP and c. 2.1 cal. ka BP–present). A sandbar was present between c. 7.0 and 6.9 cal. ka BP. The longest interval of Latvia basin stability was from c. 6.9–2.1 cal. ka BP when the basin was a lagoon of varying salinities. Quercus‐broadleaf forests characterized the regional vegetation throughout the past c. 8.6 ka. Variations in thermophilous species (e.g. Juglans,Carpinus,Ulmus,Tilia,Syringa) and Pinus koraiensis reflect shifts in temperature and moisture during the Middle Holocene. A period of warmest climate occurred c. 8.6–5.1 cal. ka BP with wettest conditions from c. 7.5–4.3 cal. ka BP, although all changes in temperature and precipitation were gradual. The Latvia Lake results indicate that changes in Middle to Late Holocene climates were linked more closely to shifts in the East Asian Summer Monsoon and less so to sea level oscillations. This investigation demonstrates that lakes of coastal Primor'ye can provide reliable palaeovegetation and palaeoclimate records despite their changing depositional environments. [ABSTRACT FROM AUTHOR]

Background: The chemically-rich seaweed Galaxaura is not only highly competitive with corals, but also provides substrate for other macroalgae. Its ecology and associated epiphytes remain largely unexplored. To fill this knowledge gap, we undertook an ecological assessment to explore the spatial variation, temporal dynamics, and diversity of epiphytic macroalgae of Galaxaura divaricata on patch reefs in the lagoon of Dongsha Atoll, a shallow coral reef ecosystem in the northern South China Sea that has been repeatedly impacted by mass coral bleaching events. Methods: Twelve spatially independent patch reefs in the Dongsha lagoon were first surveyed to assess benthic composition in April 2016, and then revisited to determine G. divaricata cover in September 2017, with one additional Galaxaura-dominated reef (site 9). Four surveys over a period of 17 months were then carried out on a degraded patch reef site to assess the temporal variation in G. divaricata cover. Epiphytic macroalgae associated with G. divaricata were quantified and identified through the aid of DNA barcoding at this degraded site. Results: Patch reefs in the Dongsha lagoon were degraded, exhibiting relatively low coral cover (5–43%), but high proportions of macroalgae (13–58%) and other substrate (rubble and dead corals; 23–69%). The distribution of G. divaricata was heterogeneous across the lagoon, with highest abundance (16–41%) in the southeast area. Temporal surveys showed consistently high covers (mean ± SD = 16.9 ± 1.21%) of G. divaricata for 17 months. Additional photographic evidence suggested that overgrowth of G. divaricata can persist for 3.5 years. Yet, G. divaricata provides substrate to other macroalgae (e.g., Lobophora sp.) that also limit the growth of corals. Conclusions: Our study demonstrates that an allelopathic seaweed, such as G. divaricata, can overgrow degraded coral reefs for extended periods of time. By providing habitat for other harmful macroalgae, a prolonged Galaxaura overgrowth could further enhance the spread of macroalgae, and strengthen negative feedback loops, decreasing the recovery potential of degraded reefs. [ABSTRACT FROM AUTHOR]

Temperature change scenarios over the Chilika Lagoon of India for 200 years (1901-2100) were quantified by the observational data sets of the Climate Research Units (CRU) of UK as well as 39 numbers of GCMs simulations from the Couple Model Inter-comparison Project Phase 5 (CMIP5) through Mann Kendall trends analysis. Long-term trend during 1901-2005 over Chilka Lake indicates the highest warming in the pre-monsoon season (1.79°C) and lowest warming (1.09°C) was shown in both the winter and post-monsoon seasons while opposite warming trends i.e., the lowest warming was observed in pre-monsoon season and highest warming was shown in the winter season for recent four decades (1969-2009) data. The performance of the CMIP5 GCMs was evaluated over a target point of Chilika Lake. Twelve numbers of models were considered as a group of "better performing GCMs" on the basis of their ability to simulate the long-term trends as well as the mean seasonal correlation with observation. Quantile mapping technique is used for adjusting the bias for the selected GCMs. Improvement in the multi-model ensemble (MME) of bias corrected better performing models compared to MME of 39 GCMs was judged with the help of Taylor plot as well as using four different conventional statistical indices viz. correlation (r), index of agreement (d index), Nash-Sutcliffe efficiency (NSE) and root mean square error (RMSE). All the ensemble members commonly available in the four Representative Concentrations Pathways (RCPs) from the better performing selected models show a temperature change of 0.27-3.61°C, 0.38-3.98°C, 0.28-3.72°C, 0.33-3.41°C and 0.22-2.50°C in annual, winter, pre-monsoon, monsoon and post-monsoon seasons respectively at the end of 21st century over Chilika Lagoon. [ABSTRACT FROM AUTHOR]

Occurrence of fluid mud (mud banks) in the southwest coast of India is an enigma for the scientific community. Over the years, several multi-disciplinary studies were conducted and various hypotheses were postulated on the occurrence and sustenance of fluid mud. Nevertheless, none of them could be proved or disproved with field data. In the present study, an attempt was made to assess the validity of some of the prevailing hypothesis on its occurrence such as subterranean conduit flow of mud/water from a coastal lagoon, submarine groundwater discharge, river flows etc. by integrating field surveys, refining the hydrogeological understanding of the area and application of environmental isotopes ( 222 Rn, δ 18 O, δ 2 H and 3 H) in the ‘Alappuzha mud bank’ region, Kerala, during its formation in the southwest monsoon period. In-situ 222 Rn monitoring survey in the coastal waters of Pallana showed that 222 Rn activities in the fluid mud region were negligible compared to the suspected continental end members such as Pamba River, Vembanad Lagoon, shallow and deep groundwater indicating that there was no freshwater inputs from these sources. Comparison of the characteristic stable isotopic signatures of δ 18 O and δ 2 H in the samples from the fluid mud region and the suspected continental end members implied that there was no mixing of these water sources with the seawater. 3 H results indicated that the shallow groundwater is modern and recharged annually from precipitation while deep groundwater in the Warkali aquifer within the study area is old (>50 years). It also indicated that there is no vertical interconnection between the Vembanad Lagoon and the deep Warkali aquifers. Hence, from the study, it appears that river flows, submarine groundwater discharge or subterranean (conduit flow) flow from the Vembanad Lagoon may not be responsible for the occurrence and sustenance of fluid mud in Pallana coast, Alappuzha. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Holocene experienced five major phases of climate variations. • The Indian summer monsoon was stronger during the Early and Late Holocene. • There was a prolonged phase of weak monsoon during the Mid-Holocene. • Spectral analysis of χ lf data suggests solar influence on ISM rainfall. Core sediments from the Chilika Lagoon in the eastern part of the Core Monsoon Zone (CMZ) of India have provided a record of local environmental changes and catchment processes during the past 7800 cal. years B.P. Variations in the rock magnetic parameters (χ lf , χ hf , χ ARM and IRM's at varying field strengths) of sediment samples reflect climate-induced changes in the Chilika Lagoon catchment. The down-core variations in the concentration-dependent magnetic parameters indicate an intensified summer monsoon and enhanced terrigenous input to the lagoon during the Early to Mid-Holocene (∼7.8 ka to ∼ 5.5 ka B.P.). In contrast, the Mid- to Late Holocene period witnessed a weaker Indian Summer Monsoon Rainfall (ISMR) and less terrigenous input to the lagoon, with an intermediate phase of strengthened monsoon around 2 to 1 ka B.P. Spectral analysis of sedimentary magnetic susceptibility (χ lf) data show significant periodicities (at 95 % significance level) of 2523, 573, 147, 93, 59, and 55 years, which are in agreement with the periodicities shown by other paleoclimatic proxies from the region. [ABSTRACT FROM AUTHOR]

Abundance of macrobenthos in the outer channel area of Chilika lagoon in the east coast of India was studied during Monsoon season of 2007 & 2008. In total 27 species of macrobenthic organisms were collected during the study period season. Crustacea was emerged as the most dominate group representing 9 species followed by polychaetes with 8 species while 5 species belonged to bivalvia and 3 species to gastropoda. The others group in the study area included nematodes and echiurids. The mean density of macrobenthos was 378 organism m-2 and 392 organism m-2 in 2007 & 2008.The biomass was measured as and biomass 0.525 g m-2 and 0.575 g m-2 during 2008 &2007. Mean values of diversity indices like Margalef's richness index was 2.7 in 2007 and 3.0 in 2008. While Shannon's H' was 1.7 of 2008 and 1.8 in 2007. The Evenness J was calculated as 0.76 in 2008 and 0.94 in 2007. The result of the study shows that hydrographical parameters like Temperature (°C), pH and Salinity (psu) parameters had modest relationship with population density and biomass. The preference of macrobenthic organism to any specific parameter couldn't be established clearly and this would be due to the presence of more opportunistic filters feeders than the deposit feeders. The opening of a new outlet connecting with the sea had good influence on species richness and population density. [ABSTRACT FROM AUTHOR]

A hydrodynamic field study of the Segara Anakan lagoon combined with a reconstruction of the recorded data using a three-dimensional numerical model provides insights into the processes driving the hydrodynamics of the lagoon. This includes bathymetry, quantification of water volume fluxes with ADCP measurements, sea level recordings, salinity measurements, water budget and numerical model results for the periods of the field studies. Salinity measurements at the Klaces village show a complete flushing of the western lagoon during neap tide in the rainy season, which is assumed to increase the sedimentation. Mean salinities of the western part are in the order of 10 and 21 g/kg, while the eastern part has a larger mean salinity of 27 and 32 g/kg for the rainy and dry season, respectively. A numerical sensitivity study shows a relationship between the Citanduy discharge and the nett water volume transport between the eastern and western part of Segara Anakan. A nett transport to the west, which differs from neap to spring tides, turns to zero when Citanduy discharges are between 300 and 400 m3/s. The flushing time of the lagoon depends on the monsoon season and is about 1–3 days at the western outlet and increases to 12 days in the central parts. [ABSTRACT FROM AUTHOR]

Chilika Lagoon (19°28′-19°54′N, 85°06′-85°36′E), on the Orissa coast, India, is one of the world's unique ecospheres. It is the largest brackish water lagoon with estuarine character. Because of its rich biodiversity and socioeconomic importance, it was designated as a "Ramsar site"--a wetland of international importance--in 1981. Interest in detailed analysis of the circulation, biotic, and abiotic factors affecting the lagoon and its limnology is a result of the opening of the new mouth on 23 September 2000 to resolve the threat to its environment from various factors--eutrophication, weed proliferation, siltation, industrial pollution, and depletion of bioresources. This paper describes the development of a two-dimensional depth-averaged hydrodynamic model for Chilika Lagoon and the resulting simulation of currents and salinity corresponding to (i) the Southwest and Northeast monsoon seasons and (ii) pre- and post-mouth-opening conditions. Numerical experiments are performed to understand the different factors--wind, tides and freshwater influx--and their independent and collective roles. Comparison of results obtained with one or both of the openings is made to quantify and validate the changing salinity pattern, which has improved the productivity of the lagoon. Our study shows the salinity levels to be much lower during the southwest monsoon compared to the northeast monsoon, which is validated by observations. The decrease in salinity is attributed to more freshwater influx during the southwest monsoon. There is a significant increase (14%-66%, depending on the sector) in salinity after opening of the new mouth, the maximum change being observed in the channel that connects the lagoon to the sea. The constriction in the lagoon that blocks the tidal effects entering the lagoon is found to be responsible for maintaining the main body of the lagoon with low salinity. The dynamic model will be an important input for our on going work in seasonal study of the ecology of Chilika Lagoon. [ABSTRACT FROM AUTHOR]

A three-dimensional, high-resolution numerical model with tide-generating and wind forces was used to simulate a passive tracer to study the water mass flushing rate in a coastal lagoon— Tapeng Bay. Model results show that north–northwesterly monsoons in winter can suppress ebb tidal currents flowing northwestward and concurrently suppress lagoon water exchanges with open shelf water, leading to a poor flushing rate. By contrast, both the westerly and southeasterly prevailing wind conditions in summer allowed lagoon water to mix, producing long-distance motion in the form of tidal residual currents from the southeast toward the northwest of the bay. This wind stress disturbance induced a horizontal mixing of the longitudinal lagoon water and led to greater water mass exchanges between Tapeng Bay and the open shelf. Therefore, tide-generating forces and suitable monsoons crucially influence the residence time of water mass in coastal lagoons. • For more accurately assess water exchange in Tapeng Bay, a high-resolution numerical model is used to simulate the water residence time under different Asian monsoon conditions; it is verified. • The observations, including CTD and ADCPs sampling, usefully help the study. • The model results suggest that it is not appropriate to use a box model to estimate residence times for coastal lagoons worldwide, particularly where the lagoons are not well-mixed water. [ABSTRACT FROM AUTHOR]

Cantharus tranquebaricus (Gmelin, 1791) is reported for the first time in Pondicherry mangroves, southeast coast of India. Three adult specimens have been found in the Thengaithittu lagoon during post monsoon season of 2009. It is a characteristic species of molluscan fauna of the Bay of Bengal and the descriptions of the shell are provided. [ABSTRACT FROM AUTHOR]