CENTRE a program fo r the con trol of all do m estic and industri al point pollutio n sources and t he development of water ma nagement plan for the reductio n of nutrients and o ther po llutio n loading coming to the Lake. These two o ptions bracket the range of potential water quality c hanges short of sea ling off th e Lake from all m arin e influ ence. T he first optio n - m aintaining th e prese nt na viga tio n chann el configuration in combination w ith poll utio n source co ntro l m easures - has a locall y positive water quality impact and serves to provide a base lin e fo r oth er analyses as well as answe1ing policy-related q uestions. The option of re turning to the pred redging bathymetry, in co mbi nation with the im pl e m entation of a watershed m anagement program and poll u tion so urce control m easures produces the g reatest positive c hanges in water quality . T he assessm ent of the relative contribution of th e closure of the navigation chann el and a watershed m anagem ent program to wate r qual ity cha nges in the Lake is still in progress.
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At the time of w riting, modeling evaluation co ntin u es. P re li mina ry res u lts indicate that control of direct point source d isc harges by itself wi ll not have a major e ffec t on the eutroph icatio n of the Lake. P o int so urce control is th o ug h essenti al for improving water qual ity lo ca lly and fo r protecting publi c health. M ore significant improvem ents can come in fro m the implem entation of a lo ng-term watershed managemen t plan, aim ed at redu cin g th e nutri en t and pollu tant loadings from the ri ve rs d isc h a rgin g into t he Lake . Considering that the system see ms to be in a state of d yn am ic eq u ilibrium, m aintain ing the navigation chann el will not lead to increased degradation of water quality. Closing the navigatio n chann e l will even tua lly return the sal inity of t he Lake to its historic levels prio r to the dredging of th e chann el, of about 1.2 ppt. , and wi ll signifi ca ntly redu ce the sa lin ity stratifi ca tion. Weaker de nsity stratification wi ll continue to exist seasonally due
to th e variability of water temperatures. Th e reduction of salinity stratification will increase dissolved oxygen levels in the Lake , however t he therm al stratifi catio n may still provide eno ugh de nsity gradients during part of t he yea r to prevent the oxyge nation o f th e hypolimnion. T he extent of the impact of the elimination of salinity stratification o n anoxic conditions in th e hypolimnio n is still unde r evaluatio n . An essential e lement of the solutio n to th e proble m o f anoxic conditions in the hypolimnion is the reduc tion of the o rga nic matter in t he Lake, w h ic h re qu i res redu c tion of t h e p ri m ary productio n (ph ytoplankton , i.e. algae). T his in tu rn requ ires reduction of the nutrie nts com ing into the Lake, w hich can be achieved primarily th ro ugh control and management of different activi ties in th e watershed and seco ndarily thro u g h trea tm e nt of all wastewater direc tly discharged in the Lake.
Coa sta l & Estu ar ine Data Collection Lake, River & Wetland Monitoring Hydrologic / Hydrographic Services Stormwater & Wastewater Studies Radio Telemetry Systems Flood Warning System s Climate Monitoring
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WWW,9(00VlSf'O.Vl,COt'Yl,O.U WATER MARCH 20 01
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