Towards a simple representation of chalk hydrology in land surface modelling

Abstract. Modelling and monitoring of hydrological processes in the unsaturated zone of chalk, a porous medium with fractures, is important to optimize water resource assessment and management practices in the United Kingdom (UK). However, incorporating the processes governing water movement through a chalk unsaturated zone in a numerical model is complicated mainly due to the fractured nature of chalk that creates high-velocity preferential flow paths in the subsurface. In general, flow through a chalk unsaturated zone is simulated using the dual-porosity concept, which often involves calibration of a relatively large number of model parameters, potentially undermining applications to large regions. In this study, a simplified parameterization, namely the Bulk Conductivity (BC) model, is proposed for simulating hydrology in a chalk unsaturated zone. This new parameterization introduces only two additional parameters (namely the macroporosity factor and the soil wetness threshold parameter for fracture flow activation) and uses the saturated hydraulic conductivity from the chalk matrix. The BC model is implemented in the Joint UK Land Environment Simulator (JULES) and applied to a study area encompassing the Kennet catchment in the southern UK. This parameterization is further calibrated at the point scale using soil moisture profile observations. The performance of the calibrated BC model in JULES is assessed and compared against the performance of both the default JULES parameterization and the uncalibrated version of the BC model implemented in JULES. Finally, the model performance at the catchment scale is evaluated against independent data sets (e.g. runoff and latent heat flux). The results demonstrate that the inclusion of the BC model in JULES improves simulated land surface mass and energy fluxes over the chalk-dominated Kennet catchment. Therefore, the simple approach described in this study may be used to incorporate the flow processes through a chalk unsaturated zone in large-scale land surface modelling applications. </jats:p

The effect of chalk representation in land surface modelling

Abstract. Modelling and monitoring of hydrological processes in the unsaturated zone of the chalk, which is a porous medium with fractures, is important to optimize water resources assessment and management practices in the United Kingdom (UK). However, efficient simulations of water movement through chalk unsaturated zone is difficult mainly due to the fractured nature of chalk, which creates high-velocity preferential flow paths in the subsurface. Complex hydrology in the chalk aquifers may also influence land surface mass and energy fluxes because processes in the hydrological cycle are connected via non-linear feedback mechanisms. In this study, it is hypothesized that explicit representation of chalk hydrology in a land surface model influences land surface processes by affecting water movement through the shallow subsurface. In order to substantiate this hypothesis, a macroporosity parameterization is implemented in the Joint UK Land Environment Simulator (JULES), which is applied on a study area encompassing the Kennet catchment in the Southern UK. The simulation results are evaluated using field measurements and satellite remote sensing observations of various fluxes and states in the hydrological cycle (e.g., soil moisture, runoff, latent heat flux) at two distinct spatial scales (i.e., point and catchment). The results reveal the influence of representing chalk hydrology on land surface mass and energy balance components such as surface runoff and latent heat flux via subsurface processes (i.e., soil moisture dynamics) in JULES, which corroborates the proposed hypothesis. </jats:p

Management impacts on soil organic matter of tropical soils.

Increased soil organic matter (SOM) improves the cation exchange capacity of tropical weathered soils, and liming is required to achieve high yields in these soils. Despite a decrease in SOM in the short term, liming may increase SOM with time by improving cation chemical bonds with soil colloids. Soil C may also be increased in high dry matter input cropping systems. We evaluated C changes in a Typic Rhodudalf as affected by four production systems with increasing residue inputs, with or without limestone or silicate. Soil use intensification by increasing the number of species in rotation as well as acidity remediation resulted in higher plant residue production. Introducing a green manure or a second crop in the system increased plant residue by 89% over fallow, but when a forage crop was used, plant residues more than doubled. Soil acidity amelioration increased plant residue deposition by 21% over the control. The introduction of a forage crop increased labile SOM and C contents in the particulate fraction, and lime or silicate application led to increases in the more stable SOM fraction. High amounts of plant residues (>70 Mg ha?1 in 5 yr) are effective in raising soil labile C, but the alleviation of soil acidity results in increased soil stable C irrespective of crop rotations in tropical weathered soils, and in this case plant residue deposition can be lower. Lime and silicate are equally effective in alleviating soil acidity and increasing soil C, probably due to the formation of cation bridges with soil colloids

Balanço de potássio no sistema plantio direto em razão da adubação potássica na sucessão milheto-soja.

Trabalho publicado também nos Resumos do CONGRESSO BRASILEIRO DE SOJA, 6., 2012, Cuiabá