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

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 thefield and (3) to develop a computer model of the phosphorus cycle. Thismodel will be used to test hypotheses concerning the functioning of thephosphorus cycle and to suggest future research.The cellular metabolism of phosphorus and its different forms and flowsin lakes are discussed to identify the important parameters needed tobuild a model. The method for measuring these parameters involves determiningchemically the size of the phosphorus pools and using the tracer32p to measure the fluxes. Bioassays and stoichiometric approximationsprovide further data.The concentrations of phosphorus in Castle fake from 14 August to 18September 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 sedimentsof 10. There was no measurable polyphosphate, but there was a detectableincrease in alkaline phosphatase activity with depth. The rate of32p uptake was constant over depth and time, with an increase underconditions of high photosynthesis. The rate of evolution of 32DOP wasquite variable, being the greatest under high photosynthesis and decreasingwith depth. Phosphorus was no limiting in bottle bioassaysand 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 ofphosphorus flux and pool size derived from stoichiometric calculationsof phytoplankton, bacteria and zooplankton carbon masses and fluxes andfunctions derived from the literature or experimentation. Model outputwas compared against the field-measured values and good agreementwas found. A steady-state model was modified to include the case of asudden addition of phosphorus fertilizer under different conditions. Thelessons learned from and the shortcomings of the model are discussed.The direction for future research into phosphorus dynamics is outlined.

Master files scanned at 600 ppi (256 Grayscale) using Capture Perfect 3.0 on a Canon DR-9080C in TIF format. PDF derivative scanned at 300 ppi (256 B&W), using Capture Perfect 3.0, on a Canon DR-9080C. CVista PdfCompressor 3.1 was used for pdf compression and textual OCR.