Analysis of COD Transport in Qinhuangdao Coastal Waters

摘要

The transport of pollutant is an important topic for self-purificationcapability and environment evaluation of ocean. Chemical oxygendemand (COD, determined by potassium permanganate) is selected as akey parameter to indicate the water pollution degree. This studyemploys field measurements and numerical model of water quality toresearch the characteristic of COD transport in Qinhuangdao coastalwaters. To investigate the seasonal distributions of COD, the fieldmonitoring of water quality at 46 sampling points was implemented inthe dry season (April) and the flood season (August) in 2013. Thecoastal waters were with a relative higher average COD concentrationof 1.43 mg/L in the flood season for the large amount of terrestrialCOD inputs, compared with the average COD concentration of 1.08mg/L in the dry season. The simulation of COD transport inQinhuangdao coastal waters in the flood season demonstrates that CODtransport is jointly controlled by the reverse tidal current in SW-NEdirections and the discharges of rivers. For the estuary with smallerriver discharge, COD transport in the coastal waters is drivendominantly by tidal current. The comparison of COD transport scope inthe spring and neap tides indicates that the river input COD wastransported farther due to low mixing in neap tide period. The newlybuiltartificial island near the coastal line hinders the nearshore waterexchange, resulting in the deterioration of water quality in the estuaryand around the island. For the estuary with large river discharge, CODtransport in the estuarine water is greatly influenced by river discharge,for example, there was little change of COD distribution at the estuaryof Luanhe River during the spring and neap tides in the same riverdischarge.