Impact of long-term seaweed farming on water quality: a case study from Palk Bay, India

Commercial scale cultivation of Kappaphycus alvarezii, an introduced seaweed species has proved to be a profitable alternate livelihood in Palk Bay, Tamil Nadu, India since 2003. The current study was undertaken to evaluate the decadal changes in water quality during the period of large scale commercial cultivation of K. alvarezii. The hydrographic and water quality parameters were measured following standard procedures across three seasons (southwest monsoon, northeast monsoon and spring inter-monsoon). Consistently significant variations were not observed for the physico-chemical parameters between the culture and control sites in all the three culture locations during the three seasons. The observed variations were mostly site-specific. Statistical analyses revealed that there is no consistent variation of physico-chemical parameters in the study area in relation to the culture, control and reference sites. A comparison of the current study and previously reported aggregate data in this context indicated that the nutrient concentration was significantly higher during the current study than when compared to the pre-culture and initiation stages of culture, indicating no depletion in nutrient content due to seaweed culture. Moreover, long-term changes are insignificant in the Palk Bay region because of the influence of the Bay of Bengal waters seasonally enriched with inorganic nutrients from the major rivers draining into it during monsoon and the transport of nutrients across the coastal waters by the coastal and tidal currents. Therefore, the variations in the physico-chemical properties cannot be directly attributed as an impact of seaweed cultivation in Palk Bay. Rather, the changes were observed to be seasonal and found to be within the range already reported for this part of the coast.