ABSTRACT
The species diversity of a cultural eutrophic lake at Ranchi was studied in relation to external variables (forcing functions) and internal or state variables. The lake receives daily detergent inputs in the form of washings of a variety of objects. A model was constructed for the estimation of detergent inputs from the increase in the phosphate concentration, and from changes in the concentration of inorganic carbon. Nutrients such as inorganic carbon, nitrates, phosphates, sulphates were found to be high in contrast to natural unpolluted systems. The DOM, COD and BOD were also found to be high suggesting organic pollution of the system with an organic carbon load of 5.4 m moles l-1. The growth and development of the plankton constituents was studied in this regime. The natural planktonic rhythm was found to be modified by the polluted condition existing in the lake. The phytoplankton exhibited four peaks in March, May, August, and November while, the zooplankton showed three peaks in February, July and October. The abundance of zooplankton during the annual cycle oscillated with that of the phytoplankton. There was much more evenness in the zooplankton population in comparison to the phytoplankton. Analysis of both, the zooplankton as well as the phytoplankton population was done using the Bray-Curtis dissimilarity index, importance value index and Shannon-Weaver diversity index. The importance value index was found to provide a better evaluation of the plankton community than the diversity index. The phytoplankton population showed no correlation with nutrient availability as indicated by the correlation-regression analysis and the planktonic rhythm was not in tune with normal unpolluted conditions. The lake was classified as meso-polysaprobic using biological and chemical indices (Pantle and Buck index:3.5, BOD:60; DOM:9.3 and COD:130).
ABSTRACT
Mathematical modeling of ecosystems requires a considerable amount of knowledge about the subsystems functioning within the broad framework and the various rate processes and transfer coefficients that control the dynamic aspects. A detailed analysis of the transfer rates and budget of inorganic carbon and nutrients in a simulated pond was conducted for assessment and comparison with aquatic bodies that undergo cultural eutrophication. In these systems the processes are complicated by a variety of inputs. Such inputs interfere with the assessment of lake background conditions and water quality. We used the compartmental model of biogeochemical cycling to calculate transfer rate of inorganic carbon and nutrients through various processes. The major external variables or forcing functions considered were light and temperature, while the state variables included the biotic and the abiotic compartments. The major processes studied were: photosynthesis, respiration and decomposition that play an important part in balancing the nutrient content of the system and maintain a dynamic equilibrium. The study illustrates how computational modeling studies are useful for analysis and management of systems for control and optimization of processes. The system shows a perfect cycling of carbon and the rate of withdrawal is equal to the return keeping the system in balance. About 0.284 m moles l-1 is withdrawn from the reservoir for primary production each day and returned back through respiration and decomposition. The concentration of nitrates and phosphates resonate in tune with the utilization of carbon and productivity.