Abstract
doi: https://doi.org/10.15447/sfews.2017v15iss3art2 We quantified the greenhouse-gas (GHG) emission and economic implications of alternative crop and wetland mosaics on a Sacramento–San Joaquin Delta island: Staten Island. Using existing GHG fluxes measurements for the Delta and biogeochemical models, we estimated GHG emissions for a range of scenarios, including the status quo, modified groundwater management, and incorporating rice and managed wetlands. For current land uses, emissions were predicted to vary greatly (48,000 to 105,000 t CO2-e yr− 1) with varying groundwater depth. GHG emissions were highest when water depth was 120 cm, the typical depth for a Delta island, and lowest if water table depth was shallowest (60 cm). In the alternate land-use scenarios, we simulated wetlands and rice cultivation in areas of highest organic-matter soils, greatest subsidence, and GHG emissions. For each scenario, we analyzed economic implications for the land-owner by determining profit changes relative to the status quo. We spatially assigned areas for rice and wetlands, and then allowed the Delta Agricultural Production (DAP) model to optimize the allocation of other crops to maximize profit. The scenario that included wetlands decreased profits 79% relative to the status quo but reduced GHG emissions by 43,000 t CO2-e yr− 1 (57% reduction). When mixtures of rice and wetlands were introduced, farm profits decreased 16%, and the GHG emission reduction was 33,000 t CO2-e yr− 1 (44% reduction). When rice was cultivated on 38% of the island, profit increased 12% and emissions were 22,000 t CO2-e yr− 1 lower than baseline emissions (30% reduction). Conversion to a mosaic of wetlands and crops including rice could substantially reduce overall GHG emissions of cultivated lands in the Delta without greatly affecting profitability.
Highlights
Many deltas worldwide are sinking because of reduced aggradation, compaction and soil loss caused by fluid withdrawal, soil drainage, and oxidation of organic matter (Syvitski et al 2009)
To estimate greenhouse gas (GHG) emissions reductions, we determined the net emission that resulted from the difference between baseline and reduced depth to groundwater and alternative land-use emissions
A similar approach could potentially be adapted for these islands on which traditional crops could be grown on the lower organic-matter soils, and rice and wetlands could be grown and created, respectively, on higher organic-matter soils, such that overall income for the island is not substantially different from the baseline condition. Though management practices such as maintaining shallower groundwater through drainage management can substantially reduce GHG emissions, alternative land uses are required for substantial GHG removals for typical Delta islands such as Staten
Summary
Many deltas worldwide are sinking because of reduced aggradation, compaction and soil loss caused by fluid withdrawal, soil drainage, and oxidation of organic matter (Syvitski et al 2009). Deltas are epicenters of urban and agricultural development (World Bank c2009). Changes have come at a SAN FRANCISCO ESTUARY & WATERSHED SCIENCE significant cost. Many of the natural processes, and the species dependent on the natural processes and habitats, are in decline. Changes in landscape structure and process have caused increasing flood risk, exacerbated by ongoing subsidence and sea level rise (Syvitski et al 2009; Kirwan and Megonigal 2013). Cultivation of peat soils, contributes significantly to greenhouse gas (GHG) emissions from these landscapes (e.g., Knox et al 2015)
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