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UC Davis San Francisco Estuary and Watershed Science UC Davis San Francisco Estuary and Watershed Science Title Impounded Marshes on Subsided Islands: Simulated Vertical Accretion, Processes, and Effects, Sacramento-San Joaquin Delta, CA USA Permalink https://escholarship.org/uc/item/0qm0w92c Journal San Francisco Estuary and Watershed Science, 12(2) ISSN 1546-2366 Authors Deverel, Steven J. Ingrum, Timothy Lucero, Christina et al. Publication Date 2014 DOI https://doi.org/10.15447/sfews.2014v12iss2art5 Supplemental Material https://escholarship.org/uc/item/0qm0w92c#supplemental License https://creativecommons.org/licenses/by/4.0/ 4.0 Peer reviewed eScholarship.org Powered by the California Digital Library University of California JUNE 2014 Impounded Marshes on Subsided Islands: Simulated Vertical Accretion, Processes, and Effects, Sacramento–San Joaquin Delta, CA USA Steven J. Deverel1,*, Timothy Ingrum1, Christina Lucero1, and Judith Z. Drexler2 ABSTRACT From 4,700 to model-estimated 350 years BP, the simulated rate of vertical accretion at Franks Wetland There is substantial interest in stopping and revers- averaged about 0.12 cm yr-1, which is within the ing the effects of subsidence in the Sacramento–San range of rates in tidal wetlands worldwide. Our model Joaquin Delta (Delta) where organic soils predomi- results indicate that large sediment inputs during nate. Also, the passage of California Assembly Bill the last 150 to 200 years resulted in a higher accre- 32 in 2006 created the potential to trade credits for tion rate of 0.3 cm yr -1. On Twitchell Island, greater carbon sequestered in wetlands on subsided Delta organic inputs resulted in average vertical accretion islands. The primary purpose of the work described rates as high as 9.2 cm yr -1. Future simulations indi- here was to estimate future vertical accretion and cate that the managed impounded marsh will accrete understand processes that affect vertical accretion highly organic material at rates of about 3 cm yr -1. and carbon sequestration in impounded marshes on Model results coupled with GIS analysis indicate subsided Delta islands. Using a cohort-accounting that large areas of the periphery of the Delta, if model, we simulated vertical accretion from 4,700 impounded and converted to freshwater marsh, could calibrated years before present (BP) at a wetland be restored to tidal elevations within 50 to 100 years. area located within Franks Tract State Recreation Most of the central Delta would require 50 to 250 Area (lat 38.059, long −121.611, hereafter, “Franks years to be restored to projected mean sea level. A Wetland”)—a small, relatively undisturbed marsh large portion of the western Delta could be restored island—and at the Twitchell Island subsidence- to mean sea level within 50 to 150 years (large areas reversal demonstration project since 1997. We used on Sherman, Jersey, and Bethel islands, and small physical and chemical data collected during the study areas on Bradford, Twitchell, and Brannan islands, as well as literature values for model inputs. Model and Webb Tract). We estimated that long-term carbon results compared favorably with measured rates of sequestration rates for impounded marshes such as vertical accretion, mass of carbon sequestered, bulk the Twitchell Island demonstration ponds will range density and organic matter content. from 12 to 15 metric tons carbon ha-1 yr-1. Creation of impounded marshes on Delta islands can sub- 1 HydroFocus, Inc., Davis, CA USA stantially benefit levee stability as demonstrated by 2 U.S. Geological Survey, California Water Science Center cumulative force and hydraulic gradient calculations. Sacramento, CA USA * Corresponding author: [email protected] SAN FRANCISCO ESTUARY & WATERSHED SCIENCE INTRODUCTION Since the late 1980s, there has been substantial interest in stopping and reversing the effects of The 300,000-ha Sacramento–San Joaquin Delta is subsidence by creating impounded marshes. Under a critical natural resource, important agricultural the hypothesis that construction of permanently region and the hub for California’s water supply. flooded impounded marshes would stop subsidence Within an area of about 81,000 ha in the central and carbons loss, experiments were conducted in 3 Delta, an estimated 4.5 billion m of soils with a high 1,000-m2 enclosures on Twitchell Island beginning organic matter content (peat) accreted during the in 1993 under Steven Deverel's direction at the U.S. last 6,700 years as sea level rose (Shlemon and Begg Geological Survey (USGS), in cooperation with the 1975; Drexler et al. 2009a, 2009b; Mount and Twiss California Department of Water Resources. Deverel 2005). In tidal marshes, peat vertically accretes con- et al. (1998) reported a net carbon gain in perma- comitantly with sea level rise (Jelgersma et al. 1993; nently flooded impounded marshes in the enclosures Mitsch and Gosselink 2000) and when organic mat- and, thus, demonstrated their ability to stop and ter accumulates at a faster rate than it decomposes reverse the effects of subsidence. In contrast, they (Boelter and Verry 1977; Mitsch and Gosselink 2000). reported a net carbon loss for seasonally flooded Climate, plant community dynamics, tectonics, and wetlands drained from early fall through winter and hydrologic processes influence long-term peat accu- drained during spring and summer thus indicating mulation (Siegel 1983; Jelgersma et al. 1993; Mitsch that this wetland water management regime will and Gosselink 2000). Using physical and chemical result in continued subsidence. These results and data for cores collected throughout the Delta, Drexler those of Miller et al. (2000) led to the conversion of et al. (2009a, 2009b) provided insight into verti- 6 ha of agricultural land to the impounded marsh cal accretion of peat and demonstrated fundamen- demonstration project on Twitchell Island (Miller tal differences among islands where mineral input et al. 2008) in 1997 by personnel of the California was more dominant (e.g., Browns Island) because Department of Water Resources, HydroFocus, Inc., of sediment input from the Sacramento River and Reclamation District 1601, and U.S. Geological those where organic accretion predominated (e.g., Survey California Water Science Center (USGS– at a wetland area located within Franks Tract State CWSC). The 6-ha plot was split into two similarly Recreation Area [lat 38.059, long −121.611], here- sized areas, the East Pond and the West Pond, and after, “Franks Wetland”) near the San Joaquin River the ponds were flooded to depths of 25 cm and (Figure 1). 55 cm, respectively in the fall of 1997. Vertical Subsidence of peat began during the late1800s and accretion in the Twitchell Island marsh areavaried early 1900s when Delta islands were levied and spatially, and depended on water depth, plant com- drained for agriculture (Thompson 1958). The primary munity composition and colonization, degree of cause is microbial oxidation of peat (Deverel and marsh maturity, and water residence time (Miller et Rojstaczer 1996) and present-day rates range from al. 2008). From 1997 to 2008, wetland-surface eleva- -1 less than 5 to over 30 mm yr -1 (Deverel and Leighton tions increased by an average of about 3 cm yr , -1 2010). Consequences include increased seepage and but rates varied spatially from -0.5 to + 9.2 cm yr hydraulic forces on levees, decreased levee stabil- (Miller et al. 2008; Miller and Fujii, 2010). The largest ity, increased subsurface drainage loads of dissolved rates occurred within dense stands of Schoenoplectus organic carbon, methyl mercury and salinity, and acutus (hardstem bulrush) and Typha (cattail) species. higher drainage costs due to increasing pumping lifts. Since the passage of California Assembly Bill 32 in Also, farming is becoming more difficult and some 2006 with its requirements to reduce greenhouse gas subsided islands contain areas that are no longer emissions, interest has increased in carbon dioxide arable because of excessive wetness. 2 JUNE 2014 A d n la Is t it r Netherlands r e M d Pierson n a l District s I r e t t u S Dead Horse Island Ryer Island New Hope Tract Grand Island Canal Ranch Tyler Island Brack Tract Brannan-Andrus Twitchell Island Staten Island Demonstration Project Island Terminous Tract Twitchell Island Bouldin Southern Under ee Island nk hi ct S ra Seepage Calculation T d r d V Rio Blanco o Webb e n n f ic a e d l Tract Is Empire King a s la I n S r herman d Tract Island Island B Bishop Tract M a d n M n d la e s e df I v Is o Q i l r y ll a d e u e n rs Bethel I d Shima e s im Is Rindge J l Tract Island a b la Tract n y n d d McDonald Wright- Browns Island Hotchkiss Holland Island Eastern Under Elmwood Tract Tract Tract Seepage Calculation Bacon Island Roberts Islan Veale d Tract Ro Lower Jones R u Palm ea gh Tract dy a Tract I nd sl Franks Wetland an W d Orwood o od Upper Jones Tract Is w la ar nd d Tract Victoria Island Byron Tract Coney I Island Union Island 0 2.5 5 10 Kilometers Figure 1 Location of Franks Wetland, Twitchell Island, and Browns Island 3 SAN FRANCISCO ESTUARY & WATERSHED SCIENCE sequestration in impounded marshes on Delta islands. Much of the previous modeling of marsh accretion Twitchell Island results indicate the potential for processes in wetlands in the San Francisco Estuary large carbon sequestration rates (Deverel et al. 1998; focused primarily on inorganic processes (Krone Miller et al. 2000, 2008) and there is a large accom- 1985) and used a constant rate of organic accretion modation space below sea level on Delta subsided (Orr et al. 2003; French 1993). In contrast, Callaway islands of over 2.3 billion m3 (Deverel and Leighton et al.
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