Study On The Total Water Pollutant Loads Allocation And Control In Jiaozhou Bay In Summer

In recent years, due to the rapid development of coastal society and economy, theincreasing serious water quality problems have widely caused the concerns for thehealth of ocean ecosystem. The total pollutant loads control was used as a valid tool toimprove coastal management.Jiaozhou Bay （JZB）, located at the southern coast of Shandong Peninsula, is atypical semi-enclosed bay with intensive influence of human activity. As a case, thetotal pollutant loads control and potential management scheme of JZB are discussed.A3-dimension physical-biological coupled model with the combined effect oftides （M2、S2、O1、K1）, wind, river flow and baroclinic gradient, is used to simulatewater quality response field of pollutants. With the response field and the linearoptimization model, the maximum pollutant loads of DIN, DIP and COD to the bayare calculated and optimally redistributed to eight pollutant sectors in JZB in summer.Scenarios are designed to discuss the management schemes. The major contents,significant results and useful conclusions have been achieved in the following:The major environment pressures are summarized from the historical data andliterature. To understand the state of JZB, a18-vessels synchronized biogeochemicalobservation was carried out from Aug28th to31st2010in JZB. The result shows thatthe average concentration of DIN, PO₄P, COD and SiO4-Si are31.41±17.07μmolL^-1,1.63±0.96μmol L^-1,1.36±0.15mg L^-1and9.01±3.88μmol L^-1, respectively insummer. The contribution of NH_-N, NO3-N and NO_-N to DIN are45.6%,47.2%and7.16%, respectively. The horizontal distribution of COD, DIN and DIP are similar,which shows a downward trend from two higher-concentration areas includingnortheast area and northwest estuary to low-concentration areas including the centerand mouth. In addition, the contribution of precipitation to nutrients increase, especially NO3-N, is qualitatively analyzed by compared to the historical data andmeteorological record. The evaluation of potential eutrophication index shows thatphosphorus limitation is common （general） in JZB, and PO4-P is the major limitingfactor. Rich eutrophication gradually transit to pool nutrient from north to south.According to the literature, the land-source pollutant loads of DIN, DIP and COD areestimated at eight Pollutant Discharge Sectors （PDSs）.To simulate the characteristic of residual current and distribution of water qualityparameters in JZB in summer, a3-D hydrodynamic model （POM）, including tidal flatthrough WAD （Wet And Dry） technology, with the tides （M2、S2、O1、K1）, wind, riverflow and baroclinic effect in consideration, coupling to biological model whichincludes ten biological state variables representing nutrients, phytoplankton andzooplankton, was developed. The model is calibrated and verified by co-tidal chart,water elevation observations at Dagang tide station and current at typical observedstation for hydrodynamic model, and by annual variations （annual scale）, distribution（monthly scale） and observed value （tidal scale） for water quality model. The featureof simulated residual current is compared with the result with only tidal process,which indicates that it is necessary to take tide, wind, and river flow and barocliniceffect into account.Based on the simulated response field, reference point of water quality and linearoptimization model, the marine environment capacities of DIN, DIP and COD areestimated. And the optimization model is known as the maximum total pollutant loadsto meet water quality standard. If functional standard of seawater quality is set as thetarget, the environment capacity is1848.1tons,182.0tons and35456.1tons in JZB insummer, respectively. The allocation results show that the Tuandao and Moshui RiverPDS allocation discharges are the largest and least percentage, respectively.Furthermore, considering efficiency and fairness among the PDSs, the economic,society and location index are introduced to optimize the maximum allowable loads.The results suggest that the allocated discharge in Tuandao PDS should be decreasedand that of Dagu River and Moshui River PDSs should be increased. In addition, if taking into account the impacts of stochastic pollutant dischargeand the fluctuation of water quality in a tide-dominated bay, the source loads obeyinglogarithmic normal distribution and constraint condition expressed in a probabilityform in tidal period are introduced to the above optimization procedure with GeneticAlgorithm to solve The results show that the outcomes are different from the previousresults because this model is more strict on water quality target in tide-dominated bay.Due to the complex nonlinear mechanism of transformation among various statevariables in marine ecosystems, the error is unavoidable with the hypothesis thatresponse field obeys the principle of linear superposition. The qualitative analysissuggests that the environment capacity and allowable discharge would beoverestimated when some element is limit, and vice versa.With the help of physical-biological coupled model, scenarios of managementare designed and estimated considering environment, economic and society benefit.The results show that scenario Ⅱ with moving excess pollutant loads to the sectorswhere there is residual environment capacity can be an alternative scheme, due to itsmaximum environment benefit and les economic and social benefit. Scenario Ⅴwith wetland construction is the best scheme due to the maximum environmental,economic and social benefit. Scenario Ⅳ with wastewater reuse is the secondscheme with the second highest score and conjunct with scenario Ⅴ for sewagetreatment plant and nonpoint sources, respectively. Scenario Ⅲ with deep seawastewater discharge and scenario Ⅵ with pollutant loads discharging at differenttidal phase are not recommended.At last, the author gives the suggestion for the pollutant loads control from theview of structural reduction, engineering reduction and management reduction andcalls on managers to strengthen management for water pollutant loads at differenttime scale.