Implications of ocean acidification on micronutrient elements-iron, copper and zinc, and their primary biological impacts: A review.

This review has been undertaken to understand the effectiveness of ocean acidification on oceanic micronutrient metal cycles (iron, copper and zinc) and its potential impacts on marine biota. Ocean acidification will slow down the oxidation of Fe(II) thereby retarding Fe(III) formation and subsequent hydrolysis/precipitation leading to an increase in iron bioavailability. Further, the increased primary production sustains enzymatic bacteria assisted Fe(III) reduction and subsequently the binding of weaker ligands favours the dissociation of free Fe(II) ions, thus increasing the bioavailability. The increasing pCO2 condition increases the bioavailability of copper ions by decreasing the availability of free CO32- ligand concentration. The strong complexation by dissolved organic matter may decrease the bioavailable iron and zinc ion concentration. Since ocean acidification affects the bioavailability of essential metals, studies on the uptake rates of these elements by phytoplankton should be carried out to reveal the future scenario and its effect on natural environment.

Spatial variations in dissolved inorganic nutrients in the groundwaters along the Indian coast and their export to adjacent coastal waters.

Submarine Groundwater Discharge (SGD) is one of the main external nutrient sources to the coastal waters. The concentrations of nutrients in groundwaters are a few folds higher than that of adjacent coastal waters; therefore, SGD enhances nutrients levels in the coastal waters and influences coastal biota. In order to examine the spatial and seasonal variability in nutrient concentrations and exchange to the coastal waters, groundwater samples were collected at ~ 90 locations along the Indian coast during the wet and dry seasons. This study revealed that dissolved inorganic nitrogen (DIN) and dissolved inorganic phosphates (DIP) and urea were found to be high during the dry than wet period. Higher concentrations of DIN and DIP were observed during both wet and dry periods in the groundwater along the east than the west coast of India. The State-wise mean amount of fertilizer used during Kharif (wet) and Rabi (dry) period in each Indian State showed significant correlation with mean concentrations of DIN and urea. The observed linear relationship of DIN with bacterial respiration and inverse relationship with DO saturation and ammonium in groundwater suggested that decomposition of organic matter and nitrification contributed to the DIN pool in the groundwater. The mean rate of SGD fluxes varied between 1.6 × 104 m3/day and 1.75 × 1011 m3/day in the Indian coastal region. The annual mean SGD flux of DIN and DIP was estimated to be 0.103 ± 0.02 and 0.021 ± 0.01 Tg (1 Tg = 1012 g) to the western coastal Bay of Bengal (east coast of India) and 0.06 ± 0.03 and 0.015 ± 0.01 Tg/y to the eastern coastal Arabian Sea (west coast of India) respectively. The estimated SGD flux of DIN and DIP to the Indian coastal waters amounted to 0.163 ± 0.04 and 0.036 ± 0.02 Tg/y respectively, and it is almost close to that of nutrients discharged by rivers (0.22 ± 0.05 and 0.11 ± 0.03 Tg/y respectively). Among the external sources of nitrogen and phosphorus, such as river discharge, atmospheric deposition, the contribution by SGD is highly significant in the Bay of Bengal (30 and 17% respectively) than in the case of Arabian Sea (24 and 25% respectively).