The seasonal distribution and pollution potential of dissolved heavy metals and nutrients in subterranean estuaries in southern India.

In order to better understand the distribution pattern, pollution degree and the submarine groundwater discharge (SGD) of dissolved heavy metals, 15 subterranean estuaries (STEs) along southwest Indian coast were sampled over three contrasting seasons. The average concentration of metals were ranked as, pre-monsoon > monsoon > post-monsoon with 3 to 12-fold higher groundwater metal concentrations than the adjacent seawater. Average SGD derived essential metal fluxes were five times higher than the toxic metal fluxes of which Fe and Zn together contributed >90 %. Using the Single Factor Contamination Index, the majority of sites were minimally contaminated with only two sites indicating moderate ecological risk due to As. Higher fluxes of Fe, Cu and Zn were likely a result of rising anthropogenic activities. The SGD derived nutrient fluxes were an important source of DIP for primary production in coastal waters and represented 30 % and 44 % of the DIN and DIP inputs respectively.

Increasing carbon, nutrient and trace metal accumulation driven by development in a mangrove estuary in south Asia.

Mangrove forests sequester organic carbon, nutrients and toxic metals sorbed to fine sediment, and thus restrict the mobility of pollutants through estuarine environments. However, mangrove removal and environmental degradation caused by industrial activity and urban growth can impact the ability of mangrove communities to provide these critical ecosystem services. Here, we use sediment profiles from an impacted tropical estuary in southwest India to provide a c. 70-year record of carbon, nutrient and trace metal burial in the context of rapid urban development and the systemic removal of mangrove communities. Our results show that carbon and nutrient accumulation rates increase sharply during the 1990's in accordance with the high rates of deforestation. Nitrogen and phosphorus accumulation rates increased fourfold and twofold, respectively, during the same period. Organic carbon accumulation was fivefold higher than the global average during this period, reflecting intense deforestation during the last three decades. The enrichment of Hg, Zn, Pb, Mo, Ni, Cu and Mn demonstrate clear anthropogenic impact starting in the 1950's and peaking in 1990. Mercury, the trace metal with the highest enrichment factor, increased sevenfold in the most recent sediments due to increased fossil fuel emissions, untreated water and incineration of medical waste and/or fertilizers used in aquaculture. Organic carbon isotope (δ13C) and C:N molar ratios indicate shifts to more terrestrial-derived source of organic matter in the most recent sediments reflecting growing deforestation of which may be prevalent in southeast Asia due to increasing development. This study emphasizes the critical role played by mangrove ecosystems in attenuating anthropogenically-derived pollutants, including carbon sequestration, and reveals the long-term consequences of mangrove deforestation in the context of rapidly developing economies.

Salinity and temperature profiling for the submarine groundwater discharge simulations: Quantification through heat and solute transport model.

Developed coastal regions are the hotspots for contaminated groundwater discharge, affecting sensitive marine ecosystems. The present study aims to identify submarine groundwater discharge (SGD) locations and quantify the contaminant load reaching to the western coast of India (Gujarat coast) using stable isotopes, seepage meter, heat and solute transport model. The coastal aquifers are highly enriched in trace metals due to various active natural processes and anthropogenic activities across the coast. Terrestrial and recirculated SGD was a significant contributor to flow and metal load, which ranged from 1.04 to 181.1 m3.year-1 and 0-77.41 kg.year-1, respectively. The highest estimated SGD in the Gujarat coast was relatively less than the SGD reported in the Bay of Bengal and comparable to the South Chennai coast. The order of metal flux found in the study was Zn > Fe > Cr > Pb > Ni > Cu > Mn, whereas the highest flux of Zn (77.41 kg. year-1) was reported at Fansa beach, which was 7x Fe-flux and 45 x Cr-flux, respectively. Higher micronutrients (Fe and Zn) load in the southern coast leads to increased vulnerability of eutrophication, algal blooms and biotic ligand formation in aquatic species. This enrichment of micronutrients in the coastal ecosystem was evident by the growth of seaweeds on the seabed at SGD identified locations.

Measurement of submarine groundwater discharge (SGD) into Tiruchendur coast at southeast India using 222Rn as a naturally occurring tracer.

Application of natural tracers such as radon isotope mass balance has been useful in estimating the submarine groundwater discharge (SGD). This study used 222Rn and evaluated the magnitude of SGD at Tiruchendur coast of southeast India in the Gulf of Mannar (Indian Ocean). Higher magnitudes of 222Rn in the porewater and seawater in comparison with the groundwater suggest simultaneous SGD with fluxes of 0.1-0.25 m3 m-2 d-1 at offshore and 0.4-0.20 m3 m-2 d-1 at the near shore. These baseline data would contribute to the management and protection of the Gulf of Mannar region in near future.

Evaluation, effect and utilization of submarine groundwater discharge for coastal population and ecosystem: A special emphasis on Indian coastline.

Submarine groundwater discharge (SGD) is an important process driven by marine and terrestrial forces. Low tide affects SGD the most, therefore the ideal time to detect SGD is the low tide, especially during spring tide. Techniques to detect and quantify SGD along with the understanding of the related aquifer characteristics is discussed in this study. Scientific community across the world is realizing the importance of studying and mapping SGD because in the scenario of climate change, this part of the global hydrological cycle is an important process and is known to have a significant effect on the marine ecosystem due to nutrient and metal inputs around the region of discharge. Therefore, understanding the processes governing SGD becomes very important. In this review, various components and processes related to SGD (e.g. Submarine Groundwater Recharge, Deep Porewater Upwelling, Recirculated Saline Groundwater Discharge), along with detailed discussion on impacts of SGD for marine ecosystem is presented. Also, it highlights the future research direction and emphasis is put on more research to be done keeping in mind the changing climate and its impacts on SGD.