In developing a water quality monitoring program, the sampling frequency chosen should be able to reliably detect changes in water quality trends. Three datasets are evaluated for Minimal Detectable Change in surface water quality to examine the loss of trend detectability as sampling frequency decreases for sites within the National Park Service's Sonoran Desert Network by re-sampling the records as quarterly and annual datasets and by superimposing step and linear trends over the natural data to estimate the time it takes the Seasonal Kendall Test to detect trends of a specific threshold. Wilcoxon Rank Sum analyses found that monthly and quarterly sampling consistently draw from the same distribution of trend detection times; however, annual sampling can take significantly longer. Therefore, even with a loss in power from reduced sampling, quarterly sampling of Park waters adequately detects trends (70%) compared to monthly whereas annual sampling is insufficient in trend detection (30%).

Water quality data and land use information were analyzed within the Alafia River watershed in Florida to determine spatial and temporal trends in these variables over a 16 year time period from 1991-2006. Monthly water quality data (for dissolved oxygen, turbidity, fecal coliform, total phosphorus, and total nitrogen) were statistically analyzed using the modified seasonal Kendall nonparametric test for trends that accounts for serial correlation. The statistical trend analysis was conducted for the entire study period, but monthly, seasonal, and land use trends were also examined. Land use information was examined using Geographic Information Systems to determine the percent change in land use proportion from 1990 to 1999, 1999 to 2006, and 1990 to 2006. The proportions of each land use and their percent change were then related to the trends in water quality. The results of this analysis showed that water quality for the parameters turbidity and total phosphorus have been shown to be improving with statistically significant decreasing trends for turbidity at stations 74, 111, 116, and 139 and for total phosphorus at stations 74, 114, and 115. A statistically significant decreasing trend in dissolved oxygen was determined for stations 116 and an increasing trend in total nitrogen for stations 114, 115, and 151 implying water quality for these parameters is degrading. Other noted trends were high fecal coliform and total nitrogen at station 111, which has higher proportions of agricultural land use and an increasing proportion of urban and built-up land use. Also, low dissolved oxygen was noted at station 74. The proportions of land use for the entire study area have changed from predominantly wetlands to now urban and built-up land use. While agricultural, rangeland, and wetlands land use have shown a reduction in the proportion of coverage in the contributing zone of almost every station, urban and built-up land use has increased in proportion at every station.