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How Healthy is the San Francisco Estuary?

Kate Gazzo, M.S.

In September, Great Ecology staff attended the State of the Estuary Conference in Oakland which is focused on the current health of the Estuary. The San Francisco Estuary, the largest estuary along the Americas western coast, supports an abundance of life, including 18 million California residents. The Estuary is comprised of the San Francisco Bay and the Delta – a network of the Sacramento and San Joaquin Rivers and their tributaries. The 2015 State of the Estuary Report (a significant component of the conference) summarizes the most recent research and ecological trends for the Bay and Delta. According to the report, the condition of the San Francisco Bay and the condition of the Delta differ. The ecological status of the Delta is degraded and in a declining state as a result of water diversions and decreased freshwater inflows. The San Francisco Bay on the other hand has received years of restoration and attention and is much healthier; however, large areas, especially marsh, are jeopardized by sea-level rise.

 

Bay-Delta Overview

Overview of the Bay-Delta/Estuary system. Image courtesy of the U.S. Geological Survey

 

What factors have caused the Estuary to be in decline?

The Delta has been in a state of artificial drought for over fifty years (San Francisco Estuary Partnership 2015). Diversion of freshwater flows to the south for municipal and agricultural use have led to decreased freshwater entering the Bay and saltwater intrusion. Freshwater flows from the Sacramento and San Joaquin Rivers historically entered the delta, mixed with saltwater, and created abundant brackish water habitat; they also delivered sediment that created and sustained marsh habitat along the Bay-Delta. Over time, as less fresh water has entered the system, the salinity gradient, also known as the X2 gradient, has migrated further into the Delta and increased the salinity of these areas, altering habitat conditions for species such as Bay shrimp (San Francisco Estuary Partnership 2015). Additionally, little sediment is now imported under the low flow conditions across the Bay and Delta. In the face of climate change and sea-level rise, existing tidal marshes in the Bay Area are expected to flood and transition to open water habitat. Because the North and Central Bays are highly developed, there is little room upslope migration of marshes (San Francisco Estuary Partnership 2015).

Canal Water Transport

Canals built to transport water to south for human use have greatly dewatered the Estuary. Image Source: California Department of Water Resources

How is the drought affecting the Estuary?

The Bay-Delta/Estuary is facing a slew of problems including, projected sea-level rise between 2-5 ft., increasing water and air temperatures, salinity intrusion, and less water in spring and summer due to decreased snowpack (San Francisco Estuary Partnership 2015). However, the most pressing problem this year appeared to be a lack of water caused by continued water diversions coupled with extensive drought. The current drought is considered one of the worst on record due to the combination of minimal precipitation and historically unmatched high temperatures (MacDonald 2015). The combination of artificial human-induced drought and natural drought have led to a fraction of freshwater flows the Estuary typically receives under a normal water years, resulting in minimal water to be shared among fish, birds, farms, and municipalities.

Lake Oroville Reservoir

As of November, Lake Oroville, the state’s second largest reservoir was only at 28% of its capacity.
Image source: Paul Hames|California Department of Water Resources

 

How can we improve conditions in the Estuary?

With El Niño predicted to bring intense precipitation across California in 2016, some relief in the Estuary may be provided next year by increased river flows; nonetheless, flows will become increasingly inconsistent in forthcoming years as the frequency of floods and droughts becomes more variable. While many models indicate precipitation will increase across California, drought is also expected to be more frequent. Strategies to adapt to an uncertain climate future in the Estuary emerged at this year’s Conference. These strategies included:

SOE - RepairReferences

G. MacDonald. “Drought, Demography, and Conservation in 21st Century California”. State of the Estuary Conference. Oakland, CA. September 2, 2015.
San Francisco Estuary Partnership. 2015. State of the Estuary 2015. Oakland, CA.

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