Emission trading is one of the most effectivealternatives to controlling water pollution.Water environmentalfunctional zone(WEFZ)is used to determine thewater quality standard and identify the zone boundary foreach river or reach.In this study,a new emission tradingscheme was addressed based on WEFZ,accounting forboth the temporal dimension and water quality control.Atemporal factor of emission trading was proposed based onvariations in the environmental capacity within a year bydividing the year into three periods,including high,normal,and low periods of environmental capacity.Duringeach period,emission trading was implemented exclusively.A water quality-control scheme was suggestedbased on the water quality requirement in the waterfunctional zone,in which the water quality at thedownstream boundary of the zone was required to meetthe water standard following auto-purification in thestream.Two methods of calculating water quality controlare addressed for point-source pollution and non-pointsourcepollution.The calculated temporal dimension andwater quality control were located in Dongxi River of theDaning Watershed in the Three Gorges Watershed.Thehigh period was during June,July,and August,the normalperiod was during April,May,September,and October,and the low period was during January,February,March,November,and December.The results from the waterquality calculation demonstrated that the discharge ofpoint-source and non-point-source pollutions led to anexcess of common contaminants at the downstreamboundary of WEFZ.The temporal and spatial factorsabove should be incorporated into the emission tradingscheme based on WEFZ.
