Implications for Greenhouse Gas Emission Reductions and Economics of a Changing Agricultural Mosaic in the Sacramento–San Joaquin Delta

Abstract

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 CO 2 -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 CO 2 -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 CO 2 -e yr -1 (44% reduction). When rice was cultivated on 38% of the island, profit increased 12% and emissions were 22,000 t CO 2 -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.

Hot moments drive extreme nitrous oxide and methane emissions from agricultural peatlands

“…We calculated a mean annual GWP of 1.86 Tg CO 2 e y −1 (range: 1.58-2.21 Tg CO 2 e y −1 ) for agricultural peatlands in the region, with N 2 O emissions representing 0.48 Tg CO 2 e y −1 (range: 0.28-0.77 Tg CO e y −1 ). Assuming the field estimates measured here are representative of local management practices, N 2 O fluxes alone could represent 26% (annual range: 18%-33%) of agricultural maize peatland CO 2 e emissions in this region, a significantly higher percentage than previous estimates (Deverel et al, 2017;Hemes et al, 2019). Soil types with similar organic matter content represent over 40,000 ha of agricultural peatlands in the Sacramento-San Joaquin Delta region (Deverel et al, 2016;Soil Survey Staff, 2020) and these soils are dominated by maize production.…”

Simulation of Subsidence Mitigation Effects on Island Drain Flow, Seepage, and Organic Carbon Loads on Subsided Islands Sacramento–San Joaquin Delta

“…With the recent development of the carbon methodology for Delta wetlands (Deverel et al 2017a), income is also available for demonstrated greenhouse gas emissions reductions in managed, permanently flooded wetlands and rice. Assessment of implementation of a mosaic of traditional crops (on low organic matter soils) and wetlands and rice (on high organic matter soils) on Staten Island demonstrated substantial greenhouse gas reduction benefit and profitability comparable with the status quo (Deverel et al 2017b). Such a mosaic could be applicable on other Delta islands.…”

A Biogeochemical Compromise: The High Methane Cost of Sequestering Carbon in Restored Wetlands

“…Wetland drainage and subsidence is not unique to the Delta (Moomaw et al, 2018); many economically and ecologically important river deltas around the world are sinking at rates faster than sea levels are rising (Syvitski et al, 2009). The net climate benefit associated with restoration, however, is highly uncertain (Deverel et al, 2017;Hoper et al, 2008;Neubauer, 2014). The net climate benefit associated with restoration, however, is highly uncertain (Deverel et al, 2017;Hoper et al, 2008;Neubauer, 2014).…”

“…In order to avoid the large CO 2 emissions that result from oxidizing drained peat soils (Knox et al, 2015), subsided delta peatlands are currently being reflooded to harness a multitude of environmental benefits, including nutrient retention, habitat preservation, and storm protection, in addition to soil accretion through C sequestration (Himes-Cornell et al, 2018;Paustian et al, 2016). The net climate benefit associated with restoration, however, is highly uncertain (Deverel et al, 2017;Hoper et al, 2008;Neubauer, 2014).…”