| A dynamic model for dissolved inorganic nitrogen (DIN) and phosphate (PO4-P)cycles and budgets in Jiaozhou Bay was established according to the principles ofD-N-P-Z model. In the model, 6 state variables (DIN, PO4-P, phytoplankton,zooplankton, organic detritus, and dissolved organic nutrients) were included.Logically this model was divided into three modules - nutrients input, nutrients cyclein seawater, and output of both dissolved substances (e.g. DIN) and organic particles(e.g. phytoplankton and detritus). Processes of biological and chemical transfer andtransformation in seawater, as well as all main kinds of ways for nutrients input wereconsidered in detail. The results showed that this model could simulate the seasonalvariations of DIN, PO4-P, and phytoplankton biomass in Jiaozhou Bay properly. Notonly the logical structure but model parameters were feasible. Principles andvariations of biogeochemical cycles of DIN and PO4-P in Jiaozhou Bay could besimulated. Then it was used to estimate self-purification capacities, environmentalcapacities, surplus environmental capacities, budgets, and residence times of DIN andPO4-P in Jiaozhou Bay. New production and f ratio in Jiaozhou Bay were alsodiscussed by application of the model. The main conclusions were as follows:1. Calculation of environmental capacities of nutrients in Jiaozhou Bay: The largestvalues of self-purification capacities of DIN and PO4-P are in summer, and thesmallest are in winter and the similar intermediate values in spring and autumn.Surplus environmental capacities of DIN and PO4-P were positive and remainedconstantly, relative to 1st grade environmental capacities, from late 1970s to mid1980s, but it decreased sharply from mid 1980s to late 1990s. The value ofsurplus environmental capacity of DIN exceeded about 70 percent of the 1st grade environmental capacity in 1997. Since 1997, the impact of nutrients pollution has begun to mitigate because of the enhancing protection of marine ecology by local government. The variation of surplus environmental capacities of DIN and PO4-P in Jiaozhou Bay implicated that the discharge amounts of DIN and PO4-P to Jiaozhou Bay were bearable from late 1970s to mid 1980s. However, from mid 1980s to late 1990s, eutrophication in Jiaozhou Bay was more and more serious. From late 1990s, the efforts of ecological protection by local government began to emerge, and the seriousness of eutorphication in Jiaozhou Bay lightened.2. PO4-P budget in Jiaozhou Bay: Seawater-accommodated PO4-P in Jiaozhou Bay is attributable to discharge from the rivers around Jiaozhou Bay and input from seawater-bottom sediments exchanging, and output to Huanghai Sea by hydrodynamic process. Furthermore, the annual PCVP input amount is larger than the output amount in Jiaozhou Bay in 1998. The total input flux of PO4-P is about 1840 t in 1998, respectively accounted for 55% by rivers input, 29% by recycled PO4-P in Jiaozhou Bay, and 16% by seawater-bottom sediments exchanging. There were 5 specifications in phosphorus output, in which fluxes at phytoplankton phosphorus (PPT) and dissolved organic phosphorus (DOP) specifications, the largest 2 fluxes, are totally over 1000 t in 1998, respectively accounted for 46% by PPT, and 29% by DOP. Output flux at PO4-P specification only accounted for 24% of all phosphorus output in 1998.3. DIN budget in Jiaozhou Bay: Seawater-accommodated DIN in Jiaozhou Bay is attributable to discharge from the rivers around Jiaozhou Bay, input from seawater-bottom sediments exchanging, atmospheric deposition, and output to Huanghai Sea by hydrodynamic process. The annual DIN input amount is equal to the output amount in Jiaozhou Bay in 1998. The total input flux of DIN is about 30900 t in 1998, respectively accounted for 48% by rivers input, 25% by seawater-bottom sediments exchanging, 26% by recycled DIN in Jiaozhou Bay, and 1% by atmospheric deposition. There are 5 specifications in nitrogen o...
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