Organic matter Protection through low Redox, Aggregation and Sorption (OPRAS)
OPRAS predicts the formation and loss of organic matter and pores in soils. It is used by researchers to predict changes in soil carbon and water-holding capacity in response to climate, nutrient inputs, and notably to soil drainage and re-wetting.
OPRAS is a dynamic process model that predicts the formation and loss of soil organic matter, pores and water-holding capacity in soils across the mineral - organomineral - peat continuum. It integrates soil biogeochemistry and hydrology processes to predict changes in soil carbon and porosity on the basis of the fundamental mechanisms that protect soil organic matter (SOM): Sorption, Occlusion and Hypoxia. OPRAS links to TopModel to predict the effects of land-management on catchment-scale streamflow. For the NERC-AHRC project "PARAGUAS" (PÁRamos para AGUA y Sociedád), OPRAS was linked to a physically based catchment hydrology model (TopModel) to predict the effects of land-management on catchment-scale streamflow. TopModel is a well-established and openly available model: https://cran.r-project.org/web/packages/topmodel/index.html.
Note that OPRAS is not part of the UKCEH N14CP family of models; it is based on different principles.
OPRAS was first developed under the the NERC Macronutrient Cycling programme and published as an equilibrium version in 2019. A dynamic version was developed in 2020-22 for catchment-scale applications. OPRAS now links to TopModel to predict the effects of land-management on catchment-scale streamflow. Investment to date approx 1 person-year.
OPRAS is a highly innovative model of soil carbon and nutrient biogeochemistry, with novel capabilities compared to other models: (1) OPRAS integrates soil biogeochemistry and hydrology is based on actual physicochemical protection mechanisms for soil organic matter; (2) OPRAS predicts transitions among major soil groups (mineral <-> organomineral <-> peat); (3) the linked OPRAS-TopModel considers soil thickness and hydraulic properties to be dynamic rather than static (allowing pore volume to vary with compaction, etc) whilst maintaining a simple budget for soil stocks of mineral and organic matter.
OPRAS was developed by UKCEH. Imperial College London (Wouter Buytaert) is a partner for implementing linked OPRAS-TopModel.
OPRAS is open access: available to use at no cost by request to the model owner.
Development of OPRAS was funded by UKRI strategic research programmes: NERC Macronutrient Cycles; NERC-AHRC Colombia-Bio.