Inhibitory effect of zinc on the remineralisation of dissolved organic matter in the coastal environment

Abstract

To understand the role of zinc (Zn) in the biogeochemical cycle in coastal environments, we examined the bacterial remineralisation of dissolved organic matter (DOM) with 2 composite experiments using microcosms supplemented with Zn. In Expt 1, using samples collected from 2 stations in the Seto Inland Sea, Japan, we found that a decrease in DOM due to bacterial remineralisation during a 14 d experimental period had negative responses to Zn at both sites, but we found an inhibitory effect on bacterial abundance only at a station in the western part of the Seto Inland Sea. In Expt 2, comparison of the response of the remineralisation process to Zn among 3 kinds of organic substrate showed that Zn has little effect on 2 authentic standards (laminarin and bovine serum albumin) and that remineralisation of DOM originating from natural seawater was significantly suppressed by the addition of Zn. Based on the regression curves, we estimated the potential impact of Zn on the remineralisation of DOM. At a water quality standard of Zn concentration (86 ug Zn 1- 1 ), DOM concentrations at the end of the experimental period (Day 14) increased 2.4 to 6.9 %, and turnover time prolonged with a timescale of weeks to months. These potential shifts induced by Zn suggest that the allochthonous input of Zn into the coastal environment leads to suppression of energy flow in the microbial loop and enhances transport of DOM from coastal to offshore areas.