Pollution: Levels and Trends

Our pollution statistics come directly from the National Park Service's "Monthly Public Use" (MPU) reports. We then performed "regressions" to analyze the "best fit" lines -- that is, to see if there is a trend over the years, as we did with recreation in Appendix C.

The NPS pollution data records pollution levels at monitors at various points along the Buffalo River and its tributaries. The NPS collects pollution data at each site weekly or so, so resulting in five or ten readings for each pollutant for each month. We averaged all of the readings for the different sites into one monthly average, which we interpret as the general pollution level for the river for that pollutant for that month. We collated by month for the period 1988 through 1992, and summarize the data in Appendix D-2. We collated the NPS pollution levels for acidity (pH), dissolved oxygen (DO), turbidity, and fecal coliform (FC). We have also collated the MPU data for temperature, but we do not analyze those statistics further.

The "fecal coliform" level indicates the amount of animal waste that is entering the BNR. We interpret fecal coliform levels as a measurement of livestock contamination of the river. Table 4.4 summarizes the fecal coliform levels graphically, and chapter 4.2 discusses the trends. Chapter 4.3 analyzes the correlation between the fecal coliform level and various recreational activities. We interpret "turbidity" as a measurement of soil runoff, and hence as a measurement of the effect of deforestation on the BNR. We interpret "dissolved oxygen" as a measure of nutrient overload (lower DO means too much nutrients and hence more algae and so on), and hence as a measurement of the effect of fertilizer runoff on the BNR. We interpret "pH" as a measure of general chemical contamination, and hence as a measurement of the effect that chemical use in the watershed has on the BNR. Note that, as with DO, lower pH means higher acidity, but evidently pH in the BNR is heavily "buffered," since it deviates very little. These data are also summarized in Table 4.4, discussed in chapter 4.2, and analyzed in chapter 4.3.

The fecal coliform levels are "episodic": extremely high levels occur soon after normal levels, and vice versa. This is presumably due to the source of fecal contamination -- usually during a severe rain event -- and due to the biological nature of the measurement -- it measures bacteria colonies, instead of chemical levels. Since we are interested in the trend and not in the extremes, we collated an additional set of data which re-summarizes the fecal coliform data at an arbitrary cutoff level of 500 units. Doing so is the equivalent of using a meter which only reads up to 500 units, instead of an unlimited high reading. This cutoff eliminates the extreme high values, which otherwise would skew the monthly average, and indeed are often high enough to affect the annual average. We summarize the cutoff fecal coliform data in Table 4.4, so that the trend is more apparent while ignoring extreme cases.

Dissolved Oxygen Trend, 1989 to 1992 Figure D-1

D.O. = 9.389 + (Year - 1988) x 0.194 R2 = 58%

(-0.38) (1.19) Conf.= 72%

Turbidity Trend, 1989 to 1992 Figure D-2

Turbidity = 2.469+ (Year - 1988) x 0.0281 R2 = 29%

(-0.0287) (0.092) Conf.= 7%

Fecal Coliform Trend, 1989 to 1992 Figure D-3

F.C. = -32.9+ (Year - 1988) x 37.0 R2 = 26%

(-1.4) (1.4) Conf.= 83%

Acidity Trend, 1989 to 1992 Figure D-4

pH = 8.0149 + (Year - 1988) x 0.0060 R2 = 23%

(2.7) (0.2) Conf.= 16%