Impacts of Fin-Fish Farming on the Organic Carbon Mineralization and Resultant Phosphorus Dynamics in Sediments of Hadong, Southern Coast of Korea

Abstract

We investigated the environmental impacts of fin-fish farming on organic carbon mineralization (CorgM) by sulfate reduction (SR) and iron reduction (FeR), and resultant phosphorus (P) dynamics and benthic nutrient flux in coastal sediments. CorgM rates (CorgMR) and SR rates (SRRs) at the farm site were 1.7- and 15.3-fold, respectively, greater than those measured at the control site. In the farm site, the SR dominated CorgMR, comprising up to 105% of CorgMR, whereas FeR was relatively dominant, accounting for 62.5% of CorgMR, in the control sediments. At the farm site, biogenic P (Bio-P) and authigenic P (Aut-P) accounted for 20.6% and 39.4% of total P, respectively, higher than at the control site (Bio-P: undetected; Aut-P: 26.4%). The difference reflected the fish feed inputs, mainly composed of loosely sorbed P (Lsor-P, 36.3%), Bio-P (31.0%), and Aut-P (20.3%). Elevated bioavailable P (Lsor-P + Fe-bound P + Bio-P) and accelerated SR stimulated P regeneration resulting from P desorption during FeOOH reduction, coupled with H2S oxidation, was responsible for Aut-P precipitation at the farm site. Benthic dissolved inorganic N and P fluxes at farm sites were 2.1- and 3.0-fold higher than at the control site. The lower N:P flux ratio (4.43) at the farm site than at the control site (6.23) was also consistent with enhanced P regeneration under sulfidic conditions. Overall results suggested that fish feed input from aquaculture activities amplified SR-dominated mineralization, altering sedimentary P speciation and increasing P release, which may alter the ecosystem community structures.