Why is the Delta starving?

The Sacramento-San Joaquin Delta is one of the most studied ecosystems in the world and one of the most degraded. We spoke to James Cloern, Associate Researcher and Scientist Emeritus at the PPIC Water Policy Center, about his new study, which estimates how primary production (the largely photosynthetic-driven process that forms the basis of the food chain) delta) was lost – and how the state could restore part of it. (Sign up here to hear him talk about the study in a virtual brownbag on August 24.)

Tell us a bit about your new study.

This project started seven years ago, when I heard a lecture at the San Francisco Estuary Institute (SFEI). SFEI had compiled information about the historic delta landscape, compared it with the modern landscape, and found that it had totally transformed. The interior delta system was once a vast complex of wetlands of over 2,000 square kilometers, most of which were marshes. The littoral marshes were flooded at high tide twice a day, and the non-littoral marshes were inundated during years and seasons of high flow. But 98% of the swamps have disappeared since the early 1800s.

We have these wonderful measures of land use change, but what do they mean ecologically? SFEI thought it was a good question to ask, and the study was born.

Wetlands are magical places where land and water meet. They are exceptional in biodiversity, supporting some 20,000 species of plants and animals around the world. Humans have transformed wetlands even more than forests and grasslands: our conversion of forests and grasslands has resulted in a 25% loss of global primary production for terrestrial species. We lost even more wetlands, but we knew nothing about the loss of primary production in the wetlands. This was the first study to examine this.

Our approach was really simple. We knew from SFEI studies how many hectares of connected wetland habitats had been lost (77%). We found that 94% of historical primary production was lost due to landscape transformation. OK, so how did a 77% loss of wetland habitat result in a 94% loss of primary production? The key is that we have lost virtually all high productivity marshes while increasing the area of ​​low productivity open water habitat.

The Delta Plan includes restoration goals: are they enough to reverse the losses?

When we started working on this project, I was only interested in the historical changes in the Delta. My colleagues said that we had to go beyond; it is an era of restoration and we have to think about the future. And of course, they were right. The state has specific goals to restore over 30,000 acres of coastal marshes; they have other targets for non-intertidal marshes and floodplain habitats. With a time horizon of 2050, our calculations suggest that if we are successful, we can recover around 12% of the primary production lost and double or triple the food supply of wetland dependent species in the delta.

What changes would you like to see and what gives you hope?

In 2013, Ellen Hanak and I published an essay titled “It’s Time for Bold New Approaches to Link Delta Science and Policy Making”. We have identified three reasons why it has been so difficult to stop the continued degradation of the Delta ecosystem. First, this is a complex scientific problem, and we need tools to understand the interplay of the many drivers of change. Second, there is a cultural divide between the scientific community and those who rely on science to make difficult management decisions. Third, we are faced with institutional fragmentation: there is no institutional structure to coordinate the production and application of scientific information.

Almost a decade later, these great challenges persist. We haven’t invested enough in synthetic science or integrative modeling. We continue to manage the delta from the perspective of a single stressor (e.g. flow only), without considering the cumulative effects of landscape change, nutrients, emergence of non-native species , unprecedented sea level rise and heat waves and multiple effects. -years of drought.

But here’s what gives me hope. We have taken steps towards a common approach to Delta science, in which all parties set the agenda and fund research. The scientific action program of the Delta Science program is one example. And the Delta Science Program rightly promotes investments in forward-looking science based on the cold reality that the Delta will keep changing. I am also encouraged by the investments in its scholarship program which has become an important training ground for early career researchers committed to making science that makes a difference.

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About Gail Mena

Gail Mena

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