Loss of wetland habitat in the Delta has reduced net primary productivity by 94%, but achieving current restoration goals could restore 12% of this loss. – Estuary News Magazine

In a new study published in the September 2021 issue of Science of The Total Environment, researchers modeled net primary production of the Delta under historical and contemporary conditions in order to project the potential benefits of restoration. The loss of net primary productivity—the amount of energy available to pass up the food chain—associated with human modification of the Delta since the early 19th century has reduced the energy available to support biodiversity and ecosystem services. Using the San Francisco Estuary Institute’s Historical Ecology Project, which modeled the early Delta based on archival photos, maps, and texts from the early 1800s, researchers estimated the total area for five specific habitat types: open water, tidal marsh, non-tidal marsh, riparian forest/scrub, and seasonal floodplains. The 94% loss of net primary productivity is even greater than the estimated 77% loss of total wetland extent (defined as hydrologically connected habitat), as the Delta lost high-productivity marsh habitat and gained lower-productivity open water habitat.“Not only have we reduced the magnitude of net primary production, but we’ve also transformed the marsh fuel ecosystem into one fueled more by aquatic plants, many of which are non-native, and phytoplankton,” says James Cloern, one of the study’s lead authors, when presenting results at the 2021 Bay-Delta Science Conference. Although habitat restoration could potentially restore an estimated 12% of lost primary production, factors such as invasive species, water management, and climate change mean that these efforts are unlikely to return Delta ecosystem function to its historical state. However, Cloern says the study’s methods could be used to help inform more rigorous wetland restoration programs around the world.

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PANPP refers to potential aquatic net primary production, an estimate of what primary production would be in today's environment but in the historical Delta landscape.

Loss of wetland habitat in the Delta has reduced net primary productivity by 94%, but achieving current restoration goals could restore 12% of this loss.

In a new study published in the September 2021 issue of Science of The Total Environment, researchers modeled net primary production of the Delta under historical and contemporary conditions in order to project the potential benefits of restoration. The loss of net primary productivity—the amount of energy available to pass up the food chain—associated with human modification of the Delta since the early 19th century has reduced the energy available to support biodiversity and ecosystem services. Using the San Francisco Estuary Institute’s Historical Ecology Project, which modeled the early Delta based on archival photos, maps, and texts from the early 1800s, researchers estimated the total area for five specific habitat types: open water, tidal marsh, non-tidal marsh, riparian forest/scrub, and seasonal floodplains. The 94% loss of net primary productivity is even greater than the estimated 77% loss of total wetland extent (defined as hydrologically connected habitat), as the Delta lost high-productivity marsh habitat and gained lower-productivity open water habitat.“Not only have we reduced the magnitude of net primary production, but we’ve also transformed the marsh fuel ecosystem into one fueled more by aquatic plants, many of which are non-native, and phytoplankton,” says James Cloern, one of the study’s lead authors, when presenting results at the 2021 Bay-Delta Science Conference. Although habitat restoration could potentially restore an estimated 12% of lost primary production, factors such as invasive species, water management, and climate change mean that these efforts are unlikely to return Delta ecosystem function to its historical state. However, Cloern says the study’s methods could be used to help inform more rigorous wetland restoration programs around the world.

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About the author

Elyse DeFranco

Elyse writes about wildlife ecology and environmental science for Estuary. Her background as a wildlife biologist often leads her to stories about the joys of scientific discovery and the ways that people interact with, and about, the environment. She currently writes from a floating abode in the San Francisco Bay, where the neighbors occasionally nest on her roof. Some of her writing and photography can be found here.