Water Quality Monitoring Study

One PHIG citizen science project is monitoring the water quality of Grayson Creek at the back of the school site, which has been ongoing since 2015. This continuing assessment of the creek health and changes in water quality is being shared with the Contra Costa Watershed Forum and the Walnut Creek Watershed Council. The data and findings are also useful to county agencies such as Fish and Wildlife, Flood Control, and Resource Conservation District to make better decisions on flood control, long term planning, and creek restoration projects.

Once a month volunteers test the creek water quality in two locations using test strips, reagents for testing phosphorus concentrations, and a professional grade YSI meter. One location is a pooled area with less rapid flow, where water quality is measured at both the surface and at one foot depth. This is helpful in understanding the environmental conditions at the surface where insects land and at the bottom of the creek where macroinvertebrates, tadpoles, crawdads, and fish live. The other location for comparison is an area with greater flow but it has input from a channel coming off of the sports fields at the back of the center.
DO chart

PHIG intern Lauren has drawn several conclusions from the data on the health of the creek. Lauren found that while the creek pH is usually in the tolerant range for aquatic life, it is often greater than ideal, which could be due to urban runoff or higher carbon dioxide levels. General hardness and carbonate have remained constantly in the desirable range.

Lauren noted that dissolved oxygen was lower than usual in 2020, even lower than a dip in 2018. High temperatures, stagnant water, and bacteria are some causes for low dissolved oxygen. She also noticed higher nitrite and nitrate levels in 2020-21, which could be caused by fertilizer runoff. Nitrite has often been above the desirable level, which could stress fish populations in the creek. Of new concern is pollution from phosphates noticed above tolerant ranges mostly at the same inlet into the creek.

Currently the creek seems healthy enough to support some smaller organisms. Minnows, tadpoles, crawdads, small fish, and a variety of birds, as documented also by Mt. Diablo Audubon Society, have found habitat in and around Grayson Creek.

creek study