J . LETITIA GRENIER LEAD SCIENTIST
The State of the Estuary Report is the most comprehensive health report ever completed for the San Francisco Bay-Delta Estuary . It uses the best available science and most recent data contributed by over 30 scientists to assess the status of various parts of the ecosystem . The purpose is to identify problems with estuarine health, so that conservation and restoration efforts can focus on solutions. This 2015 report expands on the scope of its predecessor in 2011, including Delta indicators for the first time, various new indicators for San Francisco Bay, and new sections linking the Estuary to the Gulf of the Farallones . The results show that the Upper Estuary (Suisun Bay and the Delta) is in critical condition . San Francisco Bay is in better health but jeopardized by climate change. Immediate action, significant investment, and bold changes to status quo management will be needed if we choose to recover and maintain a healthy estuary.
HOW HEALTHY IS THE ESTUARY?
The Upper Estuary (Suisun Bay and the Delta) is in fair to poor condition and getting worse, while the Lower Estuary (San Francisco Bay) is healthier . The status of half of the Delta indicators (most of which include Suisun Bay) is fair and the other half is poor. These indicators suggest that many Delta ecosystem components are either deteriorating over time, or have mixed trends across subregions. In contrast, the status of most Bay indicators is fair, with trends either improving or mixed across subregions.
WHY ARE THE DELTA AND SUISUN BAY IN CRITICAL CONDITION? WHY IS SAN FRANCISCO BAY IN BETTER CONDITION?
The Delta and Suisun Bay ecosystems are in poor health because human activities have had more profound impacts on the Upper Estuary than on San Francisco Bay . Also, restoration efforts are further along in the Bay, and the results show. Throughout the Estuary, the same three intertwined aspects of ecosystem degradation, described below, stand out as critical areas to address through management action.
First, we have severely altered the physical processes that create and maintain habitats. Freshwater inflows and beneficial floods now exert such a small fraction of their former influence that they no longer build and maintain the physical structure of habitats in the Estuary, nor support critical ecological functions . Indeed, diversions for human use have so reduced inflows that the Bay is in a state of chronic, artificial drought. This great loss means that low salinity habitat occurs over too small a space, too short a time, and too far upstream to support dependent food webs and wildlife . In the Lower Estuary, similar changes to the hydrology of Bay watersheds and the diking of tidal areas have deprived estuarine wetlands of the sediment they need to build up their elevation in relation to sea-level rise, something the Estuary’s unfettered physical processes once accomplished. In the absence of more sediment, many Bay marshes will likely be lost to the advancing Bay in the decades to come.
Second, this impairment of critical physical processes is intertwined with habitat loss, degradation and fragmentation, which are generally more severe in the Upper Estuary . Tidal marsh now covers just 2% of its former extent in the Delta and most of the remaining patches are too small to support thriving populations of marsh-dependent wildlife. By contrast, the amount of current marsh and newly restored tidal areas in San Francisco Bay and Suisun Bay recently reached 50,000 acres – a landmark threshold halfway to the regional goal set just 16 years ago . In other habitats, low-salinity open waters in the Upper Estuary and woody riparian areas in the Delta have steeply declined . Eelgrass is in poor condition in the Bay but making a comeback due to restoration efforts.
Third, these losses of physical processes and habitats have reverberated through biological systems, contributing to unproductive food webs, small and declining native wildlife populations, and the dominance of invasive species . Indicator status consistently shows problems with burgeoning invasions (aquatic vegetation, invertebrates, and fish) and anemic food webs in the Upper Estuary . Food webs seem to be in somewhat better condition in the lower Estuary . The health of native fish communities strongly declines going upstream, with Bay fish in good condition and Upper Estuary fish in poor to very poor condition . Birds and mammals are generally in fair condition across the Estuary, although declines in the endangered Ridgway’s rail in the South Bay and diving ducks in North and Central Bays are cause for concern .
Read the entire State of the Estuary report HERE