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The study provides a review and analysis of historical water-quality data in BCNP, ENP, and LNWR (Phase 1) and nearby coastal waters of south Florida (Phase 2). This information will help establish water-quality standards and baseline conditions in the parks, and will help evaluate the potential effects of CERP on water quality.
10500 University Center Drive, Suite 215
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McPherson, Benjamin F.; Sobczak, Robert; Clark, Christine
Carlson, J. E.; Meeder, J. F.; Duever, L. C.; Gunderson, L. H.; Riopelle, L. A.; Alexander, T. R.; Myers, R. F.; Spangler, D. P.
Torres, A. E.
Miller, R. L.; Sobczak, R.; Clark, C.
Schneider, W. J.; McPherson, B. F.; Buchanan, T. J.
Armbruster, J. T.; McPherson, B. F.; Freiberger, H. J.
Higer, A. L.
Higer, A.; Morris, M.
Alexander, R. B.; Ohe, D. J.
Lorenz, D. L. and others
web page only
Baseline historic water-quality data in LNWR was assembled, evaluated and made available on SOFIA. An interpretative report that summarizes the historic water-quality data and trends in LNWR is being prepared and will be published in 2005.
2. Assemble and make available metadata and data for flow and water quality that have been collected in tidal rivers of ENP. Include methods of collection and QA for water-quality data, including comparisons of grab samples and auto-samples with cross section and depth data.
The major task is to compile and summarize data on flows and water-quality that have been collected in tidal rivers of ENP by different agencies and universities. Metadata and selected data collected by different agencies and universities over the last 50 years will be summarized and posted into the USGS South Florida Information Access (SOFIA) web site.
We used loess (locally weighted scatter-plot smoothing) plots (Slack and others, 2003) to evaluate long-term data and to show the generalized direction of change in concentration with time.Loess smoothing was used for adjusting concentrations for flow or stage changes in order to reduce the normal seasonal changes in concentration due to variations in flow or stage. Without these adjustments, cyclical variations in concentrations due to seasonal or drought-related changes in flow or stage make it difficult to determine if there are real long-term trends in concentration due to other changes within the drainage basin. Loess smoothing is accomplished by fitting a linear regression for many small parts of the x-axis (horizontal axis) and piecing together a line. The loess regression weights the close (local) data points more than more distant data points, and is similar to a moving average. When viewing plots of data and loess smooth lines, the reader may perceive a trend in concentration that is not statistically significant especially when the statistical programs adjust for severe wet and dry periods.
The uncensored seasonal Kendall test and Tobit regression procedures, provided with the S-ESTREND program, were used to analyze water-quality data for trends. A 95-percent confidence level (p = 0.05) was used for all of the statistical tests. The uncensored seasonal Kendall test requires that a minimum of 5 years of data be available, that censored (less than) data be no more than about 5 percent of the data set, and that there is only one censoring level. In addition, there are requirements for a minimum abundance of data in the first and last fifth of the time span being tested. This test allows water-quality data to be flow or stage adjusted. The uncensored seasonal Kendall test was used to test for trends in specific conductance, chloride, and TN. The uncensored seasonal Kendall test is considered robust; that is, it is not sensitive to outliers in the data (Schertz and others, 1991). The uncensored seasonal Kendall test permits the user to compare only data from the same seasons over the period of record, which reduces the effect of seasonal water-quality changes and improves one's ability to determine long-term trends. Three seasons were used in most cases. Comparisons were made between concentrations in the same seasons in the first year and each following year to count the number of increases and decreases. Then, comparisons were made between concentrations in the same seasons in the second year and each following year, and so on. For each season, a single value was selected for use in the seasonal Kendall test. For seasons with multiple values, the most central value with respect to time, that is also paired with discharge or stage, was selected to represent the season (Schertz and others, 1991). Because of this selection process, some of the data that are visible on a graph and that influence the shape of the loess smooth plots, may not be used by the seasonal Kendall test procedure. Consequently, graphs showing all of the data points over time may appear to show a trend that is not found to be statistically significant using this procedure.
The Tobit regression analysis was used to test for trends in sulfate and TP concentrations. This was necessary because the percentage of censored data was often more than the 5-percent limit suggested for the uncensored seasonal Kendall test, and because the sulfate and TP data sets usually contained more than one censoring level, making the data set unsuitable for the uncensored seasonal Kendall test.
Data requirements for using the S-ESTREND program sometimes prevented the use of the full period of record for statistical analysis. In addition, the S-ESTREND program assumes a monotonic trend (tends to increase, decrease, or have no trend, but not change from an increase to a decrease or vice versa) in concentration, which is not the case for sites where an increase in concentration was followed by a decrease. Consequently, we used loess smooth plots to decide where to break the data sets into shorter periods for trend analysis. Common linear regressions were used to look for trends in stage over time.
Any use of trade, product, or firm names is for descriptive purposes only and does not constitute endorsement by the U.S. Government
1. Assemble historical water-quality and nutrient data (1995-2003) at two index sites, Shark River and Trout Creek, and evaluate how well these data represent total channel flows (by measuring water quality across the section and at different depths compared with grab samples and auto samples and assigning error bars). Post on SOFIA
2. Prepare and publish a 4-page USGS Fact Sheet that summarizes work that has been done and work that is underway on nutrient loading to coastal waters of ENP.
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