THE COUPLING OF LAND TO COASTAL SEA BY NUTRIENT RICH GROUNDWATER FLUX: GREENING OF  ARABIAN SEA

Joseph Sebastian Paimpillil, Center for Earth Research & Environment Management, India
K.K Balachandrsn, National Institute of Oceanography, India

Abstract

The investigations in coastal waters had sufficient hints of ground water seepage to Arabian Sea across  the narrow strip of submerged porous lime shell beds running almost parallel to the coast. This supplies considerable quantities of primary nutrients to the coastal waters and precondition it for rich primary production. The present study revealed the highest value of 14 mg/m3 for chlorophyll a , approximately 3 times greater than the peak values reported so far from these waters. A band of N/P > 15 funneling out from coastal region during non-mud bank period had provided an indication of ‘external source’ of nitrogenous compounds into the coastal waters. The long-term (decadal) trend of chlorophyll showed a “greening” of the near-shore waters.  The human population along the coastal belt with more than 70 % of households without proper sanitation facilities has resulted in concomitant increases in widespread use of septic tanks and nutrient inputs to coastal waters, particularly from regions occupying limestone beds. The ground water quality of the region had shown nitrate in sediment extract up to 12 μM, ammonia (in water) 8μM, urea (in water) 14 μM, urea (sediment extract) 15 μM. The nutrient levels also had seasonal variations with the maximum values in post monsoon months with the minimum levels in monsoon months. The necessary forcing for the ground water flow is gained when the fresh water level in lake and the sea level had a critical difference. Such condition prevailed during the peak southwest monsoon months due to heavy river discharges to the lake. The possibility of heavy rains and flash floods linked with ongoing climate variability, such critical conditions can occur during other seasons and also at similar locations in the coastal region. Any noticeable change of the current oligothrophic nature of the coastal region can contribute to the removal of atmospheric carbon through photosynthesis and later by planktonic grazing and sinking. International initiatives undertaken by IUCN and based on environmental degradation and poverty, this area was identified as high priority area for detailed study, preparing for ICZM and also for pilot testing.

Keywords: nutrient fluxes, plankton blooms, ground water fluxes, Arabian sea