ABSTRACT
Cycling of chloroorganic substances from a pulp mill effluent has been studied with a model in the estuary serving as recipient for the discharge. The model is calibrated against emission of adsorbable organic halogens from the mill and the cycling of extractable organic chlorine. Outflow of tri- and tetrachlorinated substances from the recipient to the sea, related to emissions prior to reconstruction of the mill in 1986, was larger than the input to the recipient, due to mobilization of these substances from the sediment by resuspension. 6-Chlorovanillin and dichlorinated substances, considered to represent emissions of today, are exported directly to the open sea to a higher degree than the tri- and tetrachlorinated substances without being trapped within the recipient. There is a temporal variation in the retention, depending on seasonal variation in the hydraulic regime, with high export of tri- and tetrachlorinated substances during the spring and fall circulation. The export of 6-chlorovanillin and dichlorinated substances decreases during circulation due to increased sedimentation. The morphology of the basin and weather variations are shown to be the two most important factors controlling the cycling of chloroorganic substances in Gårdsfjärden.
