Short-Term Variability of Physico-Chemical Properties and pCO2 fluxes off Dhamra estuary from north-eastern India

Abstract

Short-term variability in physico-chemical properties of Dhamra estuarine system located in north-eastern India was investigated to understand the inter-seasonal variability. The oxygen data show 89–92% saturation in winter months compared to 60–70% during summer. Overall, the nitrate ranged between < 1.0 and 22.0 µmol l−1; however, phosphate concentrations never exceeded 1 µmol l−1 during the whole study period. In general, the lowest nutrient values were recorded during March and December irrespective of the year sampled. Pearson correlation matrix shows poor relationships between inorganic nitrate and phosphate suggesting decoupling in the Dhamra estuary. However, relationship between surface chlorophyll and nitrate was significant highlighting modest control on phytoplankton population. Interestingly, pCO2(air) exhibited considerable monthly variability during the sampling period, thereby accentuating the sea–air CO2 gradient. The pCO2(air) varied between 370 and 421 µatm, whereas pCO2(water) ranged between 146 and 751 µatm. The ΔpCO2 therefore showed monthly fluctuation and acted as a weak to moderate source to the immediate atmosphere. Our observation from Dhamra estuary suggests large inter-annual variability which therefore necessitates the need for near real-time measurements which is now a possibility with emerging coastal biogeochemical buoys.