Present-day oxidative subsidence of organic soils and mitigation in the Sacramento-San Joaquin Delta, California, USA | Affaissement actuel de sols organiques par oxydation et atténuation dans le Delta Sacramento-San Joaquin, Californie, Etats-Unis d’Amérique La subsidencia actual de los suelos orgánicos y la mitigación en el Delta de Sacramento-San Joaquin, California, EE.UU 美国加利佛尼亚州沙加缅度河—圣华金河三角洲有机土壤目前的氧化性下沉及减缓措施 Atual subsidência de solos orgânicos por oxidação e sua mitigação no Delta de Sacramento-San Joaquin, Califórnia, EUA
2016
Deverel, Steven J. | Ingrum, Timothy | Leighton, David
Subsidence of organic soils in the Sacramento-San Joaquin Delta threatens sustainability of the California (USA) water supply system and agriculture. Land-surface elevation data were collected to assess present-day subsidence rates and evaluate rice as a land use for subsidence mitigation. To depict Delta-wide present-day rates of subsidence, the previously developed SUBCALC model was refined and calibrated using recent data for CO₂ emissions and land-surface elevation changes measured at extensometers. Land-surface elevation change data were evaluated relative to indirect estimates of subsidence and accretion using carbon and nitrogen flux data for rice cultivation. Extensometer and leveling data demonstrate seasonal variations in land-surface elevations associated with groundwater-level fluctuations and inelastic subsidence rates of 0.5–0.8 cm yr–¹. Calibration of the SUBCALC model indicated accuracy of ±0.10 cm yr–¹ where depth to groundwater, soil organic matter content and temperature are known. Regional estimates of subsidence range from <0.3 to >1.8 cm yr–¹. The primary uncertainty is the distribution of soil organic matter content which results in spatial averaging in the mapping of subsidence rates. Analysis of leveling and extensometer data in rice fields resulted in an estimated accretion rate of 0.02–0.8 cm yr–¹. These values generally agreed with indirect estimates based on carbon fluxes and nitrogen mineralization, thus preliminarily demonstrating that rice will stop or greatly reduce subsidence. Areas below elevations of –2 m are candidate areas for implementation of mitigation measures such as rice because there is active subsidence occurring at rates greater than 0.4 cm yr–¹.
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