A palaeoenvironmental reconstruction to aid in the restoration of floodplain and wetland habitat on an upper deltaic plain, California, USA

Abstract

While tens of millions of dollars have been spent on land acquisition and planning for current and future floodplain and wetland restoration in the Sacramento-San Joaquin Delta, knowledge of the historical processes and landscape heterogeneity that are helpful in guiding the environmental restoration are often scarce. This study used palaeoenvironmental reconstruction to increase the historical perspective, with the aim of improving environmental management. Twelve sediment cores collected from the McCormack-Williamson Tract (MWT) leveed farmland and the juxtaposed Delta Meadows (DM) tidal wetland were sampled for a suite of environmental proxies. MWT was a non-tidal flood plain during much of the late-Holocene, with a mosaic of other habitats including dry uplands, riparian forests, and freshwater wetlands persisting nearby. Comparison with the regional sea-level history suggests that the upper delta gradually came under tidal influence 3000–800 calendar years before present (cal BP). Despite this, floodplain landforms and habitats prevailed at DM from 3650–330 cal BP, after which wetlands expanded, suggesting that a flood-based disturbance regime typified the upper delta for most of the late-Holocene. Recently, the upper deltaic plain has been profoundly disturbed by agriculture and other activities, rendering significant loss of habitat. It is believed that a flood-based disturbance regime will recur at MWT if the levees surrounding the tract are intentionally breached as planned for restoration, culminating in a variety of habitats similar to pre-agricultural conditions. Concentrations of Hg, Pb, As, and P pollutants elevated several-fold in surficial sediments are of particular concern, potentially becoming problematic after restoration.

Recent (1975–2004) Vegetation Change in the San Francisco Estuary, California, Tidal Marshes

“…Stratigraphic analyses of sediment cores collected from San Francisco Bay and Delta wetlands have provided detailed records of decadal-to millennial-scale, wetland vegetation, salinity, and geomorphic changes (Brown and Pasternack, 2005;Byrne et al, 2001), in addition to evidence for episodic events (Goman and Wells, 2000) and variations in accretion dynamics (Drexler, de Fontaine, and Brown, 2009;Watson, 2004). Specifically, studies of stratigraphic shifts in the abundance of microfossils and macrofossils have provided evidence for the findings presented here.…”

A Paleoecological Perspective on Wetland Restoration

“…In contrast to the aforementioned sources of paleoecological information, the study of palynomorphs (pollen and spores) has been more broadly applied to provide context for restoration and conservation projects, although at slightly lower spatial resolution than the macrofossil assemblages provide (Brown and Pasternack 2005;Burney and Burney 2007;van Leeuwen et al 2008;Jackson and Hobbs 2009;Brown 2010). The broad appeal of using fossil pollen and spores to gain insight into pre-disturbance conditions corresponds to their high degree of decay resistance, which leads to good preservation potential in late Quaternary sedimentary and wetland deposits (Fig.…”

Spatial Relationships of Levees and Wetland Systems within Floodplains of the Wabash Basin, USA

“…Our work illustrates the complex spatial links between levees and wetlands at a watershed scale and can be used to inform restoration work near levees. For instance, Brown and Pasternack () endorsed levee breaches in the Sacramento‐San Joaquin Delta area to mimic fluvial disturbance regimes necessary for wetland restoration. A watershed‐scale view of spatial relationships between constructed levee and floodplain wetlands will be useful for identifying possible restoration areas.…”