The Delta Stewardship Council’s Joint Brown Bag seminars convey the latest scientific research and information and are sponsored by the Council’s Science Program in conjunction with the Ecosystem Restoration Program and the Surface Water Ambient Monitoring Program.
The most recent three seminars focused on subsidence, native pondweed, and data integration.
California experiences two types of land subsidence—a gradual settling or sudden sinking of the earth’s surface owing to compression of subsurface materials. One is from the oxidation of peat soils in the Delta. The second type, and the single largest cause of subsidence in California, is the compaction of susceptible aquifer systems caused by excessive groundwater pumping. This second type was explored during an April 20 Delta Science Program Brown Bag Seminar.
“While more focus has been placed on the burden of infrastructure damage from subsidence, which can be repaired, compaction permanently decreases the capacity of the aquifer system to store water,” said Michelle Sneed from the U.S. Geological Survey. “Therefore subsidence occurring today can have a lasting effect on California’s water supply reliability.”
She explained that aquifer system compaction is concentrated in fine-grain units; silt and clays. The clay units are shaped like dinner plates and were originally deposited in random orientation “like after you’re done with dinner you toss your plates in the sink and they’re randomly oriented,” she said. There’s a lot of space between those grains (units)—that’s where water is stored. When groundwater levels are lowered, it increases stress on the geologic layers.
“If you go beyond a certain threshold, the clay units that are oriented in random orientations rearrange themselves more like a stack of plates you’d put in your cupboard,” Sneed explained. That results in a lot less space between the clay units, reducing its storage capacity.
Between one to 20 inches of subsidence had occurred in the San Joaquin Valley region during 2008-10, and it continues. Such ground subsidence adversely affects water conveyance systems, other infrastructure, and natural resources.
Water conveyance systems are particularly sensitive to subsidence. “To keep water flowing, we have to build up levees and we have to keep that water surface elevation (gradient) high to keep it flowing downhill”, she said.
In another recent seminar, Katharyn Boyer from San Francisco State University highlighted the current status and trends of native pondweed habitat in Suisun Bay and the western Delta.
Boyer’s April 27 presentation showed how native pondweeds respond to environmental conditions and how their presence could enhance native ecological communities in the San Francisco Estuary. Those pondweeds could support high abundances of invertebrates along the migratory path of fish species.
“Submerged aquatic vegetation has gotten a bad rap in this region of the San Francisco Estuary due to the negative effects of invasive Brazilian waterweeds,” she said.
In June 2011 Boyer and her research team started a mapping effort where they reviewed Google aerial images and digitized aquatic plant beds using Geographic Information Systems (GIS). They discovered that there are more than 1,200 acres of native pondweeds. They then looked at older images over the past two decades to see how the beds have changed over time. There was nearly a 20 percent increase in acreage of native pondweeds from 2002-2012.
“We believe [these beds] are expanding up the estuary in this period of drought,” Boyer said.
Boyer and her students measured distribution patterns of these aquatic plants and have been assessing the factors influencing their current and potential future distribution and abundance through field surveys and other experiments.
During a June 15 presentation, Amye Osti, the creator of the web-based open-source software OpenNRM, demonstrated www.baydeltalive.com to show how collaborative efforts to integrate data from separate sources are working in the Sacramento-San Joaquin Bay-Delta.
The website, www.baydeltalive.com, whose purpose is to make data management easier for the Delta, brings together separate datasets to better visualize real-time environmental conditions and incorporate environmental models capable of showing future conditions. It functions as a data central to the Delta and offers dashboards for extensive collections of physical, chemical, and biological monitoring data: relevant news, photos, and publications, a Delta community section, and modeling results.
“Baydeltalive and the other portals have an extensive document management system,” Osti said. “That’s because we believe you need more than a map if you’re going to be able to tell your spatial story. You have all this documentation, images, and data sets that you want to be able to attach to it [a specific location and map]. From this document library, you can add as many documents as you want.”