Water Quality and BOD

Pollution from fertilizer runoff increases levels of nutrients such as phosphate and nitrate in water, causing algae to bloom and increase the amount organic material in the water. Once decomposition of algae and other organics such as dead plants, sewage and food waste begins, large amounts of dissolved oxygen are used up in the process, creating "dead zones" in the water where lack of oxygen decreases potential for life of fish, plants and other water creatures. Dissolved Oxygen (DO) levels can be tested to determine the biological oxygen demand (BOD), which is a measure of the amount of oxygen that is consumed resulting from the decomposition of organic material in water. We tested BOD levels by comparing DO values of water in Tecolote Creek over a five day period.

Figure 1. Relation between BOD Level and Water Quality.

Figure 2. Map showing BOD Level at each tested site in Tecolote Canyon.

Figure 3. BOD levels related to percent organic content in sediment. 

Results displayed in Figure 1 show that about half of the sites in tested Tecolote Canyon lie in the category of "Very Good" water supply, another four are moderately clean, while sites near USD and Mt. Etna were measured to be poorly polluted on account of their BOD level. The correlation between BOD level and percent organic that would be expected can be observed for the most part in Figure 3 where a higher levels of organics in the sediment correspond with a high BOD, except for at sites SN1 and CH which show the opposite. 

Thankfully, for the most part Tecolote Creek did not exhibit measurable problems with dissolved oxygen. Many sites were actually found to contain clean water upon assessment. The site with the highest BOD was located near the creek outlet, which suggests that pollution was caused due to runoff from sites further upstream. Even with these hopeful results, we should not remain ignorant to the situation. We did prove that a higher organic content would increase the BOD and so measures must still be taken to limit the amount of organic waste that we allow to escape into our water.