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 About 0.284 m moles l-1 is withdrawn from the reservoir for primary production each day and returned back through respiration and decomposition.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.
ABSTRACT
A influência do fenômeno da friagem nas variáveis meteorológicas e nos fluxos de energia e CO2 , foi realizada numa área de floresta próxima à região de Ji-Paraná, Rondônia, durante o mês de junho de 2001. A friagem ocasionou uma diminuição de 35 por cento no valor da temperatura do ar. Notou-se uma redução de 75 W.m-2, na radiação solar incidente, associada à nebulosidade presente em decorrência da penetração da massa de ar fria. Conseqüentemente, tanto o fluxo de calor sensível (H) quanto o de calor latente (LE), apresentaram uma diminuição no seu valor médio diário, apresentando uma diferença em relação aos dias normais de 8 e 34 por cento, respectivamente. A concentração de CO2 permaneceu constante, sem apresentar o aumento comum durante a noite, devido à condição de vento forte típica da friagem. Em situação normal o fluxo médio durante o dia de CO2 (-2,44 mmol m-2 s-1) foi menor que durante os dias de friagem (-5,78 mmol m-2 s-1); enquanto que os fluxos médios noturnos foram +1,77mmol m-2 s-1 e +2,83mmol m-2 s-1 durante situações de dias normais e de friagem, respectivamente.
Observations of the influence of a Cold Spell phenomena on meteorological variables and on energy and CO2 fluxes were made in a forest site near Ji-Paraná, Rondonia, during June 2001. Friagem caused a diminution of 35 percent at air temperature. A reduction of 75 W.m-2 from normal days (200 W.m-2) to cold days (125 W.m-2) in the mean incoming solar radiation was also observed. During the Cold Spell days, both sensible heat (H) and latent heat fluxes (LE) showed a decrease in their mean daily value, showing a difference from normal days of 8 e 34 percent, respectively. The CO2 concentration remained constant, without increase during the night, due to the windy condition of cold days. During normal days the mean diurnal CO2 flux (-2,44 mmol m-2 s-1) was lesser than that one at phenomena days (-5,78 mmol m-2 s-1), while the mean nocturnal fluxes were +1,77mmol m-2 s-1 e +2,83mmol m-2 s-1 during normal and cold days, respectively.