Statistical Modeling of Phosphorus Dry Deposition Rates Measured in South Florida |
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| Authors: | Ahn Hosung James R Thomas |
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| Institution: | 1. MS #7120, South Florida Water Mamagement District, 3301 Gun Club Road, West Palm Beach, Florida, 33406, USA
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| Abstract: | Dry deposition may be a substantial source ofphosphorus (P) to the Florida Everglades. Drydeposition has been measured on a weekly basis in theregion since 1987, but a significant amount of thisdata is missing (about 34%) due to instrumentalfailures and sample contamination. This study developsa statistical model of the P dry depositiontime-series to estimate missing data. The model isbased on a multivariate stochastic time-series theory.Model parameters are calibrated using theexpectation-maximization algorithm which is efficientfor data sets with many gaps. The pooled mean andstandard deviation of the data before estimating themissing values was 88.4±85.7 μg P m-2d-1 and after estimating the missing values was87.8±82.4 μg P m-2 d-1. Modelverification demonstrates that the calibrated modelsprovide unbiased data estimates while preserving thestatistics of the raw data. For each sampling site themean and standard deviation before and after werequite similar. No trend with time was detected. The Pdeposition fluctuates seasonally (highest in Octoberand lowest in June), but this fluctuation does notfollow the seasonal pattern of Florida's rainfall. Random noise in the data, however, is significant andcauses long-term fluctuations of the data. The datawith gaps filled in are useful for computing theweekly P load distribution. |
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