Diurnal variation in physical-chemical properties and primary production in the interconnected marine, mangrove and freshwater biotopes of Kakinada coast, Andhra Pradesh, India

Abstract

Diurnal variation in hydrological variables and dissolved inorganic nutrients such as PO ^sup3−_inf4 -P, N O ^sup−_inf2 -N, NO ^sup−_inf3 -N and NH ^sup+_inf4 -N were studied in three interconnected biotopes including freshwater, marine and mangrove brackish water of the Kakinada coastal zone, Andhra Pradesh. Samples were collected at intervals of 3 hours, for a period of 24 hours. In the marine environment salinity varied from 26‰ to 32‰ whereas in the mangrove waters it fluctuated from 12‰ to 20‰ and in both biotopes salinity showed bimodal type of oscillation. Dissolved oxygen content was high in the mangrove waters during day time but decreased rapidly during the night hours. In the marine environment PO_f4 ^p3−-P concentration varied from 0.345 to 1.195 μg at l⁻¹, NO ^sup−_inf3 -N from 1.03 to 6.62 μg at l⁻¹ and NO ^sup−_inf2 -N from 0.086 to 0.506 μg at l⁻¹. The highest and the lowest concentrations of PO ^sup3−_inf4 -P, NO ^sup−_inf3 -N, NO ^sup−_inf2 -N recorded in the mangrove waters were 0.790 and 0.325 μg at l⁻¹, 7.10 and 1.60 μg at l⁻¹ and 0.278 and 0.060 μg at l⁻¹, respectively. The concentration of PO ^sup3−_inf4 -P, NO ^sup−_inf3 -N and NO ^sup−_inf2 -N were high in the freshwater canal, the maximum and minimum values being 1.110 and 0.730 μg at l⁻¹, 26.40 and 9.98 μg at l⁻¹ and 0.520 and 0.252 μg at l⁻¹ respectively. The concentration of ammonia was relatively high in the mangrove water. Gross and net primary production in the mangrove water was 4 times higher than in the marine biotope. There was no ‘export’ of dissolved nutrients from the mangrove environment to the adjacent marine waters.