Optimization of Shanghai Marine Environmental Monitoring Sites in the Identification of Boundaries of Different Water Quality Grades

Waterqualityiscriticaltoensurethatmarineresourcesandtheenvironmentareutilizedinasustainablemanner.TheobjectiveofthisstudyisthereforetoinvestigatetheoptimumplacementofmarineenvironmentalmonitoringsitestomonitorwaterqualityinShanghai,China.Toimprovethemappingorestimationaccuracyoftheareaswithdifferentwaterqualitygrades,themonitoringsiteswerefixedintransitionbandsbetweenareasofdifferentgradesratherthaninotherpositions.Followingbidirectionaloptimizationmethod,first,18candidatesiteswereselectedbyfilteringoutspecificsitecategories.Second,threeofthesewere,inturn,eliminatedbecauseoftheruledefinedbythechangesintheareasofwaterqualitygradesandbythestandarddeviationoftheinterpolationerrorsofdissolvedinorganicnitrogen（DIN）andphosphate（PO_4-P）.Furthermore,indicatorkrigingwasemployedtodepictthetransitionbandsbetweendifferentwaterqualitygradeswhenevernewsamplingsiteswereadded.Thefouroptimizationprojectsofthenewlyaddedsitesrevealthat,alloptimizedsitesweredistributedinthetransitionbandsofdifferentwatergrades,andatthesametimeintheareaswherethehistoricalsitesweresparselydistributed.Newsiteswerealsofoundintheoverlapregionofdifferenttransitionbands.Additionalsiteswereespeciallyrequiredintheseregionstodiscriminatetheboundariesofdifferentwaterqualitygrades.Usingthebidirectionaloptimizationmethodofthemonitoringsites,theboundariesofdifferentwaterqualitygradescouldbedeterminedwithahigherprecision.Asaresult,theinterpolationerrorsofDINandPO_4-Pcouldtheoreticallydecrease.