The EPA has listed the Ventura River as an "impaired water body" for a variety of problems, including trash, bacteria, water diversion and pumping, and pesticides (DDT/PCBs). The Clean Water Act requires that government take action to solve the problems to ensure the river is fishable and swimable. The regulatory mechanism for this is "Total Maximum Daily Load," or TMDL.
The primary concern is that algae growth may be fueled by excess nutrients (nitrate and phosphate), which in turn creates large daily swings in dissolved oxygen (DO.) If DO drops below 4 mg/l, aquatic life can become stressed and fish kills may occur. (This is also called 'eutrophication') The presence of endangered species makes this issue even more critical.
Stream Team volunteer data has been used along with scientific analysis at UCSB to monitor and study algae over the past year. This graph is actual data from 24 hours of sampling on the Ventura River. It illustrates how photosynthesizing algae releases O2 during daylight hours, generating peak DO measurements in the early afternoon. However, overnight DO levels drop dramatically, with a minimum in the pre-dawn hours.
Traditionally, nutrients are seen as the driver for excess algae growth. Nutrients may originate from broad land uses such as agriculture, livestock, septic tanks, treated wastewater, as well as atmospheric deposition. It turns out that algae is widespread throughout the Ventura River watershed, and is highly variable with season and annual climate (wet or dry year.) Algae is also dependent on river flows, water temperature, sedimentation, and a host of other variables. Because of these complex relationships, algae may be seen as a symptom of ecological stress, rather than a problem in itself. This raises a complex question when it comes to regulating algae as a pollutant: the TMDL process was originally developed to control point-source pollution.
It is clear that in this watershed with shallow, over-drafted aquifers and strong surface water/groundwater interactions, a meaningful algae TMDL will require a watershed approach that takes into account ecosystem processes. Integrated watershed management will be necessary to address excess algae in the Ventura River.
Paul Jenkin is the Environmental Director of the Ventura County Chapter of the Surfrider Foundation, and founder of the Matilija Coalition. The Surfrider Foundation is an international environmental organization dedicated to the protection and enhancement of the world’s waves and beaches through conservation, activism, research, and education (CARE).
Since 1994, Paul has worked to restore the coast and watershed where he lives, in Ventura, California.