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A mathematical and experimental model of the phosphorus cycle in Castle Lake, California

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  • A study of the phosphorus dynamics in castle Lake, California, is presented. The approach is (1) to identify the important phosphorus parameters, (2) to develop and apply methods measuring the parameters in the field and (3) to develop a computer model of the phosphorus cycle. This model will be used to test hypotheses concerning the functioning of the phosphorus cycle and to suggest future research. The cellular metabolism of phosphorus and its different forms and flows in lakes are discussed to identify the important parameters needed to build a model. The method for measuring these parameters involves determining chemically the size of the phosphorus pools and using the tracer 32p to measure the fluxes. Bioassays and stoichiometric approximations provide further data. The concentrations of phosphorus in Castle fake from 14 August to 18 September 1972 were extremely low: in µg l⁻¹, dissolved inorganic 0.1, total dissolved 1-3, and total 1-4, with a maximum 0.5 m off the sediments of 10. There was no measurable polyphosphate, but there was a detectable increase in alkaline phosphatase activity with depth. The rate of 32p uptake was constant over depth and time, with an increase under conditions of high photosynthesis. The rate of evolution of 32DOP was quite variable, being the greatest under high photosynthesis and decreasing with depth. Phosphorus was no limiting in bottle bioassays and was even inhibitory on occasion at additions as low as 1 µg l⁻¹. The model of the phosphorus cycle was derived from expected rates of phosphorus flux and pool size derived from stoichiometric calculations of phytoplankton, bacteria and zooplankton carbon masses and fluxes and functions derived from the literature or experimentation. Model output was compared against the field-measured values and good agreement was found. A steady-state model was modified to include the case of a sudden addition of phosphorus fertilizer under different conditions. The lessons learned from and the shortcomings of the model are discussed. The direction for future research into phosphorus dynamics is outlined.
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file details Internal_Report_145.pdf 2017-07-18 Público Baixar