Effect of enhanced salinity on the chlorophyll-a concentration and partial pressure of CO₂ of a sewage-fed freshwater aquaculture pond: a microcosm experiment

ABSTRACT

Numerous fresh and saline-water tropical aquaculture ponds that often can be significant sources super-saturation of CO₂ towards the atmosphere are gradually increasing throughout the world. The role of salinity in regulating the chlorophyll-a and dissolved pCO₂ in a freshwater aquaculture pond, situated in East Kolkata Wetlands, Eastern India, was tested using a microcosm conducted during summer (April-May) and winter (December–January) months. The effects of enhanced salinity to microcosm sets of 5, 10 and 15 ppt were monitored for nine consecutive days. pH, dissolved oxygen (DO), pCO₂(water), chlorophyll-a, and gross primary productivity (GPP) were measured in-situ and every day during the entire microcosm. Enhanced salinity was hypothesised to alter the pCO₂(water) and chl-a dynamics of this system significantly. Increasing salinity to 5 ppt would enhance the photosynthetic potential of the existing primary producers and reduce the pCO₂(water) significantly, thus boosting the CO₂ sink strength. This enhanced CO₂ sink strength, accompanied with increased GPP and DO, was also observed in 10 ppt, only during summer; however, low temperature was found to abate the photosynthetic response during winter. Finally, in 15 ppt treatments, drastic chlorophyll-a reduction and extreme CO₂ super-saturation showed the existing phytoplankton community cannot cope with such high salinity.

KEYWORDS:

• Salinity
• microcosm
• aquaculture pond
• pCO₂
• chlorophyll-a
• gross primary productivity

Acknowledgements

The first author is indebted to the Council of Scientific and Industrial Research, India, for the CSIR-NET fellowship and Jadavpur University for providing lab facility. The authors are grateful to Sourav Samanta of School of Oceanographic Studies, Jadavpur University, for helping us to prepare the study area map. Moreover, the authors are indebted to Dr. Sourav Das of School of Oceanographic Studies, Jadavpur University and the anonymous reviewers for their valuable suggestions that have enriched the quality of the present work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Funding was supported by the National Remote Sensing Centre, Department of Space, Indian Space Research Organization, Hyderabad, India.