Nutrient Removal Vis?à?Vis Change in Partial Pressure of CO_2 During Post?Monsoon Season in a Tropical Lentic and Lotic Aquatic Body: A Comparative Study

摘要

The rate of nutrient removal and changes in pCO_2 (water) were compared between a lentic aquaculture pond [East Kolkata Wetlands (EKW), India] and a lotic estuarine system [Diamond Harbor (DH) in Hugli Estuary, India] during the post‐monsoon season (experiencing a similar tropical climate) by means of ex situ microcosm experiment. Though the DH waters were found to be substantial source of CO_2 towards atmosphere and EKW waters to be sink for CO_2 (according to the initial concentration of CO_2), the eight consecutive days microcosm experiment revealed that the nutrient removal and pCO_2 reduction efficiency were significantly higher in DH (ΔpCO_2—90%) compared to EKW (ΔpCO_2—78%). Among the five nutrients studied [dissolved nitrate‐nitrogen (?NO3–N), dissolved ammonium nitrogen (?NH4–N), silicate, phosphate and iron], dissolved NO_3– N followed by NH_4– N was the most utilized in both EKW and DH. Except silicate, the other nutrients reduced to 78–91% in EKW and 84–99% in DH samples of their initial concentrations. Chlorophyll‐a concentration steadily depleted in EKW (~ 68–26 mg m~(?3)) during the experiment indicating intense zooplankton grazing, whereas in DH it increased rapidly (~ 3.4–23 mg m~(?3)) with decreasing pCO_2 (water). The present observations further indicated that regular flushing of EKW aquaculture ponds is required to avoid stagnation of water column which would enhance the zooplankton grazing and hamper the primary production of an otherwise sink of CO_2. In DH, controlled freshwater discharge from Farakka and reduction of untreated organic waste might allow the existing phytoplankton community to enhance their photosynthetic activity.