Hillslope Site Research Articles

Boron retention within a catena of rhyolitic soils and Its effect on radiata pine growth and nutrition

Boron deficiency in Pinus radiata (D. Don) plantations in N.S.W. has been particularly evident on soils derived from acid igneous parent materials. A slope sequence (catena) of soils on a rhyolitic parent material was selected to study the amount of boron retention and its relationship to soil development. The soils at three positions, a hillcrest, mid-slope and lower slope, were described and various soil chemical and physical properties were determined for each horizon. Tree height, deformity, survival and foliar chemistry of 6 year old P. radiata were measured in plots adjacent to the three soil profiles studied. Boron adsorption isotherms varied within individual soil profiles by horizon and also between the different soil profiles in the catena. Boron adsorption was highest in the hillcrest soil B horizons and lowest in the bleached A2 horizons of the lower slope soil. The Freundlich isotherm constant k was found to be significantly correlated with clay content (r = 0.88), exchangeable aluminium (r = 0.79, exchangeable potassium (r = 0.68), and dithionite-citrate extractable iron (r = 0.66). Leaching and illuviation of iron oxides and clay has been accentuated in the two soil profiles on the hillslope sites of the catena. As clay, aluminium and iron oxides have been removed from the surface horizons of the lower slope soil, the ability of these horizons to adsorb and therefore retain boron has been greatly diminished. Position on the catena also affected P. radiata growth survival and foliar chemistry. Tree height decreased while the incidence of deformity increased down the slope. It is suggested that the progressive deterioration in tree growth down the slope is mainly caused by the trees being increasingly affected by boron stress as a result of decreasing capacity of the soils to retain boron by adsorption against leaching towards the lower slope.

Stabilization of boulders at a hillslope site in Hong Kong : Grigg, P V; Wong K M Q J Engng GeolV20, N1, 1987, P5–14

Stabilization of boulders at a hillslope site in Hong Kong : Grigg, P V; Wong K M Q J Engng GeolV20, N1, 1987, P5–14

Stabilization of boulders at a hillslope site in Hong Kong

Summary In Hong Kong, there is a high incidence of surface boulders on hillside slopes. Recently attention has been focused on the neutralization of these boulders where they may affect downslope developments. A study to assess and stabilize a boulder field adjacent to one site is described and discussed. The study considered the mode of development of the boulder field, development of a boulder stabilization philosophy, undertaking of a ground survey, and design of the various stabilization measures.

Hillslope Solute Sources and Solutional Denudation on a Magnesian Limestone Hillslope

A wooded hillslope site underlain by Magnesian Limestone was monitored for a one-year study period to identify any spatial variation in solute sources, solute uptake and solutional denudation. The empirical results were compared with an existing theoretical model of such a soil/water/bedrock weathering system. The theoretical model had a hydrological system (throughflow) and a hydrochemical basis (equilibrium chemical kinetics) which were found to be inappropriate for the study site. Both the model predictions and the empirical results suggested that relative denudation rates increased upslope, which would ultimately produce slope decline. This was related to spatial variation in soil chemistry, in particularly soil pH, produced by pedogenesis and deposition rather than any variation in water flow rates or flow routes over the hillslope. More appropriate models for the hydrological and weathering processes operating on Magnesian Limestone are developed.

Modelling Hillslope Soil Water Status during Drainage

Modelling Hillslope Soil Water Status during Drainage

Calibration program of the Canadian Meteorological Service

An existing model of the transmission of solar irradiance through a leafless deciduous forest, which was derived for horizontal canopies, was extended to account for the effects of variable slope inclination and orientation. The extended model assumes that slopes are planar and that reflection from surrounding slopes is negligible. The model was calibrated and tested using data collected during the winter and spring at two hillslope sites in southern Quebec, Canada. Root mean square errors based on the entire verification data sets were 13 and 18% of the average below-canopy irradiances for the two sites for 20-min averages. These r.m.s. errors decreased to 8.8 and 15% of the mean irradiances for hourly averages, and 2.5 and 6.8% of the means for daily averages. The main difficulty in applying the model lies in specifying the crown-space absorption coefficient, which must be empirically determined.

Calibration of solar radiation equipment at the U.S. Weather Bureau

An existing model of the transmission of solar irradiance through a leafless deciduous forest, which was derived for horizontal canopies, was extended to account for the effects of variable slope inclination and orientation. The extended model assumes that slopes are planar and that reflection from surrounding slopes is negligible. The model was calibrated and tested using data collected during the winter and spring at two hillslope sites in southern Quebec, Canada. Root mean square errors based on the entire verification data sets were 13 and 18% of the average below-canopy irradiances for the two sites for 20-min averages. These r.m.s. errors decreased to 8.8 and 15% of the mean irradiances for hourly averages, and 2.5 and 6.8% of the means for daily averages. The main difficulty in applying the model lies in specifying the crown-space absorption coefficient, which must be empirically determined.