Monitoring Tidal-Marsh Change

November 13, 2015

It was pre-dawn, and the gate to the Oro Loma marsh in Hayward, California, was locked. Draped on the gatepost was a necklace of about ten U-locks, allowing multiple organizations to access the marsh. As Sierra to the Sea interns with Point Blue Conservation Science, Anna Kennedy and I had the key to one of them. We went to Oro Loma that morning to collect data on birds in the restored wetlands beyond the gate − to add to the understanding of changing marshes and the estuary as a whole.

The 365-acre marsh in South San Francisco Bay was ecologically restored in November 1997 and is now part of the Hayward Regional Shoreline, a complex managed by East Bay Regional Park District. The levee holding back the bay was breached in two places, allowing tidal waters to once again flow over the landscape. Now, in place of the former industrial salt production ponds, tidal marsh habitat is nourished by the ebb and flow of water and nutrients of the San Francisco Estuary.

Point Blue ecologists have surveyed wetlands surrounding San Francisco Bay for decades, documenting the effects of environmental change and also resource management practices. One biologist I talked to recalls Oro Loma in 1997 as an empty expanse of muddy ground. Now it is a tidal marsh with increasing biological diversity.

To learn more about Oro Loma, I logged into Point Blue’s data portal, the California Avian Data Center (CADC) and reviewed data that Point Blue collected nine years ago at the same locations where Anna and I conducted our surveys. The ability to make comparisons over time gave me a clear sense of the power of information.

I zeroed in on Song Sparrow numbers. Year-round residents of the Bay’s tidal marshes, the three endemic subspecies of Song Sparrows are important indicators of habitat quality. On two surveys in 2007, biologists recorded 10 and 11 Song Sparrows at Oro Loma. During my survey in 2015, I recorded 33!

This sizable increase is one of the clear signals that restoration is succeeding. The so-called “tidal marsh Song Sparrow” depends on a diverse mix of marsh vegetation, often including shrubs lining the channels where the salty water of the bay inundates the marsh plain. Thick plantlife provides the sparrows with shelter from predators especially during high tides when they are most vulnerable to exposure and permits their populations, even small ones, to survive and grow.

A different story appeared to be the case for another songbird at Oro Loma, the Marsh Wren. It was completely absent during our surveys this year, whereas 17 and 8 had been recorded during the two survey efforts in 2007, ten years after the levee was breached.

I asked Point Blue ecologists about this and learned that this marsh has been undergoing treatment for invasive Spartina (cordgrass), as part of a recent bay-wide effort. While removal of the non-native plant is good for the marsh, it has caused a temporary loss of Marsh Wren habitat. When native Spartina and other native vegetation return, so will the wrens. This is another instance of ecosystem resilience linked to management practices by people.

By measuring changes like these on much larger time and geographic scales, scientists can detect trends among marsh-reliant species and assess restoration success.

The new Sierra to the Sea internship at Point Blue has a focus on climate-smart restoration, the growing practice of using science to help design ecological restoration that anticipates climate change. After surveying several marshes around the Bay, Anna and I went on to examine the impact of future sea-level rise on the same sites. We used an amazing online tool from Point Blue, called Future San Francisco Bay Tidal Marshes. This publicly available tool is a great example of a new focus on helping resource managers and other key stakeholders make smart decisions in preparation for the effects of climate change.

At Oro Loma marsh, for example, we were able to view projections of where wetlands might keep pace with rising water in the bay (but only if enough sediment, or mud, washes into the system) – and buffer parts of Hayward and San Leandro from flooding.

Oro Loma is interesting in the context of climate-smart conservation for yet another reason. Directly adjacent is a wastewater treatment facility where managers are constructing a “horizontal levee” – using a man-made structure to expand functioning tidal marsh. The goal is to help protect urban infrastructure, increase coastal resiliency to storm surge and sea-level rise, and improve the bay’s water quality. Using this kind of “green infrastructure” to augment nature’s services is now a growing priority in the San Francisco Bay area and beyond.

After our last survey that morning at Oro Loma marsh, Anna and I walked back towards the entrance gate. The tide had changed; the activity of birds had shifted; and the noise of human activity beyond the marsh was increasing. As the city woke up in full force, the marsh seemed even more important for the balance of the natural and man-made—and for the future health of this bayshore ecosystem.

Megan Elrod, Claire Peaslee, and Lishka Arata contributed to this story.