Abstract
Author(s): Cloern, James E.; Robinson, April; Richey, Amy; Grenier, Letitia; Grossinger, Robin; Boyer, Katharyn E.; Burau, Jon; Canuel, Elizabeth A.; DeGeorge, John F.; Drexler, Judith Z.; Enright, Chris; Howe, Emily R.; Kneib, Ronald; Mueller–Solger, Anke; Naiman, Robert J.; Pinckney, James L.; Safran, Samuel M.; Schoellhamer, David; Simenstad, Charles | Abstract: To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function. Primary production is a crucial ecosystem process, which directly limits the quality and quantity of food available for secondary consumers such as invertebrates and fish. The Delta has a low rate of primary production, but it is unclear whether this was always the case. Recent analyses from the Historical Ecology Team and Delta Landscapes Project provide quantitative comparisons of the areal extent of 14 habitat types in the modern Delta versus the historical Delta (pre-1850). Here we describe an approach for using these metrics of land use change to: (1) produce the first quantitative estimates of how Delta primary production and the relative contributions from five different producer groups have been altered by large-scale drainage and conversion to agriculture; (2) convert these production estimates into a common currency so the contributions of each producer group reflect their food quality and efficiency of transfer to consumers; and (3) use simple models to discover how tidal exchange between marshes and open water influences primary production and its consumption. Application of this approach could inform Delta management in two ways. First, it would provide a quantitative estimate of how large-scale conversion to agriculture has altered the Delta's capacity to produce food for native biota. Second, it would provide restoration practitioners with a new approach—based on ecosystem function—to evaluate the success of restoration projects and gauge the trajectory of ecological recovery in the Delta region.
Highlights
The Sacramento–San Joaquin Delta is a highly disturbed ecosystem bearing little resemblance to the habitat mosaic, hydrological system, and biological communities that existed in the mid-19th century
We outline here a science-based approach to measure the effects of one human disturbance—landuse change—on the ecosystem process of primary production
Is low productivity an inherent attribute of the Delta, or is it largely a consequence of human disturbances such as land-use change? How much has primary production changed over time, and how much would it be enhanced through different restoration actions? What are the rates and food value of production by non-native aquatic plants in today’s Delta?
Summary
The Sacramento–San Joaquin Delta is a highly disturbed ecosystem bearing little resemblance to the habitat mosaic, hydrological system, and biological communities that existed in the mid-19th century. Continuing losses of native plants, mammals, resident and migratory birds, fish, and their invertebrate prey motivated California’s Delta Reform Act that established a goal of protecting, restoring, and enhancing the Delta ecosystem This goal is challenging because of the magnitude and diversity of human disturbances that have reduced the Delta's capacity to support native plant and animal communities. The Historical Ecology Team (Whipple et al 2012) and Delta Landscapes Project (Grossinger et al 2014) have recently produced spatially explicit comparisons of the Delta’s historical and contemporary habitat mosaics These provide, for the first time, opportunities to (1) quantify the effects of land-use change on Delta primary production, and (2) compare anticipated increases of primary production from planned habitat restoration actions against a baseline of historic primary production in the Delta
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