Author(s): Joseph Sebastian Paimpillil; Thresiamma Joseph; Balachandran
Linked Author(s):
Keywords: Mud banks; Nutrient injection; Coastal fertilization
Abstract: The west coast of India is environmentally more sensitive than the east coast as it is bordering one of the most sensitive ecosystems, the Arabian Sea. As far as the chemical features are concerned, the general picture so far emerged out is that except during the monsoon periods, the southwest coastal waters remained oligotrophic. Recent studies contradict these findings and had shown that even after the monsoon period, fresh injection of nutrients by hitherto unknown processes fertilizes the coastal waters that are either permanent or quasi-permanent in nature. Increased human population along the coastal belt has also resulted in concomitant increases in widespread use of septic tanks and nutrient inputs to coastal waters, particularly from regions occupying limestone beds. The input of these nutrients supported high primary production up to 14 mg/m3 of chlorophyll a (peak column production of 1529 mgCm-2d-1), approximately 3 times greater than the peak values reported so far from these waters. During the post monsoon season, the regions in the vicinity of the narrow coastal strip had nutrient enrichment with nitrite (0. 5 – 2. 0 uM), phosphate (0. 4 – 2. 8 uM), ammonia (1 – 7 uM) and nitrate (1 – 6 uM). A band of N/P > 15 funneling out from southern region was indicative of an ‘external source’ of nitrogenous compounds into the coastal waters. With the injection of nutrients in non-monsoon months when mud banks were passive, a new influence of Vembanad Lake on the coastal waters is very clear. The causative factors discussed are indicative of existence of a subterranean flow connecting Vembanad Lake to the adjacent coastal waters through the submerged porous lime shell beds. Forcing of nutrient rich ground water occurs when the water level difference between sea and lake attains a critical value to overcome the frictional resistance. Such conditions prevail during heavy fresh water discharges and on the sea level remaining at its annual low. The possibility of heavy rains and flash floods linked with cyclones are high with climate variability, the critical conditions for ground water flow can prevail in other seasons and also at similar coastal locations.
Year: 2005