San Dieguito River Park partnered with San Diego Coastkeeper to conduct water quality monitoring once a month at the San Dieguito Lagoon Urban Runoff Treatment Ponds from December 2010 through December 2017, and every other month in 2018, until funding for the program ended. The treatment ponds are a series of four ponds that are designed to naturally filter out contaminants, trash, and non-native seeds to make the water cleaner and healthier before entering the wetlands. Water is sampled and tested in two locations- Treatment Pond 1, where a storm drain dumps runoff from the neighboring homes, shopping centers, and streets, and Treatment Pond 4, before the water leaves the ponds and enters the wetlands. The water samples are tested onsite for pH, dissolved oxygen, conductivity, and temperature. A sample is filtered, and the filtered and an unfiltered sample is sent to the Coastkeeper lab for further testing of nitrates, phosphates, ammonia, bacteria levels, and more.
Visit the San Diego Coastkeeper website for a map of all the sampling sites in San Diego County and graphs showing the data collected. Also, check out this blog written by former San Diego Coastkeeper Water Quality Lab Manager, Travis Pritchard.
The following graphs were created by Travis using the first few month’s data from 2010-11. Some months do not have data from the second sampling site because not enough water was flowing through the ponds to reach Treatment Pond 4. The graphs provide an example of how the treatment ponds work to reduce the bacteria, nitrate, and ammonia levels and increase dissolved oxygen levels.
Notice in the two graphs above that the bacteria levels in Pond 4 were higher than Pond 1 on the first month of testing, and how much higher the levels were than subsequent months. This is possibly due to a rain event flushing the system for the first time in a few months. Dog waste is a huge contributor to bacteria polluting the water entering the Treatment Ponds. Please pick up after your dog and dispose of the bag in the trash.
A possible source of Nitrates and Ammonia is fertilizer. Part of a golf course and many private yards are within the watershed, and excess fertilizer can be washed down the storm drain. This can also explain why the cattails in Pond 1 grow so big and quickly. Park Rangers have to cut them down to clear the channel annually.
Dissolved Oxygen is what fish use to breathe. A minimum level to be considered healthy is 5mg/L. As water flows through the Treatment Ponds, it is aerated and also flows through vegetation that produces oxygen through photosynthesis. Some of this oxygen dissolves into the water. High levels of bacteria can deplete water of dissolved oxygen. Notice in the graphs for Pond 1 the upward trend in bacteria levels from March to May correlates with the downward trend in dissolved oxygen.
(Updated December 4, 2018 because the Water Quality Monitoring program has ended.)