Modelling of Dissolved Oxygen Changes in Water of Lakes

In a paper a numerical eutrophication model was presented to show the dissolved oxygen concentration prognosis in four lakes situated in North-Eastern Poland. According to administrative division, lakes Necko, Rospuda Augustowska, Biale Augustowskie, and Studzieniczne are localized in Podlasie region, Augustow district, in a direct neighborhood of over 30 000-habitant Augustow town. The total catchment of lakes system covers a major part of river Rospuda-Netta catchment the largest water flow within catchment area. Other tributaries are: river Zalewianka lake Necko tributary and Augustowski Canal - lake Studzieniczne tributary. Simulations of water quality changes in studied lakes were carried out for the single year: since May 1, 2006 till April 30, 2007 at the second level of eutrophization process complexity in a module EUTRO, i.e. intermediate eutrophication kinetics, considered as four interacting systems: phytoplankton kinetics, the phosphorus cycle, the nitrogen cycle, and the dissolved oxygen balance. That level makes possible to predict the ammonia, nitrates, organic nitrogen, orthophosphates, organic phosphorus, dissolved oxygen, carbon biochemical oxygen demand, and chlorophyll a concentrations. Determinations of lake and tributaries water were performed that same period. Modeled aqueous environment of four lakes was divided into two segment types: surface (epilimnion) and subsurface (hypolimnion). Due to the exclusion of modeling the processes occurring in bottom sediments and descriptions of sediments influence on water quality in a form of time functions (e.g. functions of ammonia release from the bottom in mg NH4/m(2)day and orthophosphates in mg PO4/m(2)day as well as utilization of oxygen for sediments mineralization mg O-2/m(2)day), no segments of benthic-type were isolated. Achieved results from model's calculations (since May 1, 2006 till April 30, 2007 in daily increment) were plotted on Fig 5. - 12. and compared with empirical studies made once a month in each segment. Analysis of data presented in figures revealed that there is possible to create a model, which in case of DO indicator, remains in statistically significant dependencies on empirical results from determinations of lake water. Assuming that values predicted in the model are consistent with real data, such model gives an opportunity to obtain information on water quality both in time between results from monitoring, and makes possible to predict changes of that quality taking into account the same factors affecting the water quality and changes during simulations of these quantities variations in time and different parts of modeled environment.