6. Nutrient Exchange at Water and Sediment Interface of the Largest Brackish Water Lagoon (Chilika), South Asia

The nutrient flux (NO₃⁻, NH₄⁺, PO₄³⁻ and SiO₄⁴⁻) at water and sediment interface studied for the Asia’s largest brackish water lagoon, Chilika. The benthic chamber (in situ) and diffusive flux techniques were employed for the estimation of nutrient flux. Measured nutrient flux by benthic chamber technique varied in between 3,000 and 14,000 µmol m⁻² d⁻¹ for NO₃⁻, 2,000 and 20,000 µmol m⁻² d⁻¹ for NH₄⁺, 120 and 2,400 µmol m⁻² d^–1 for PO₄³⁻, 3,000 and 20,000 µmol m⁻² d⁻¹ for SiO₄⁴⁻. Calculated nutrients flux by diffusive flux technique varied in between 1,200 and 7,500 µmol m⁻² d⁻¹ for NO₃⁻, 450 and 5,500 µmol m⁻² d⁻¹ for NH₄⁺, 15 and 280 µmol m⁻² d⁻¹ for PO₄³⁻, and 1,500 and 4,800 µmol m⁻² d⁻¹ for SiO₄⁴⁻. Sectoral variation for the flux enrichment (in situ flux: diffusive flux) were in between 1 × 8 and 5 × 9 in the central sector, between 2 × 5 and 18 in the outer channel, and between 1 × 5 to 6 × 1 in the northern sector. The higher flux enrichment in outer channel could be due to dominance of macrofaunal activities. In central sector, the benthic fluxes of PO ₄ ⁻³ and NH₄⁺ were 50 and 25% of the total nutrient flow of the Bhubaneswar municipal sewage treatment plant through river Daya and Bhargavi respectively. Pre-monsoon season, a noteworthy fractions of nutrients employed by primary producers in the water column, which is supplies by the benthic sediment regeneration in the central sector.