Spectral and growth characteristics of willows and maize in soil contaminated with a layer of crude or refined oil

Remote sensing holds great potential for detecting stress in vegetation caused by hydro-carbons, but we need to better understand the effects of hydrocarbons on plant growth and specific spectral expression. Willow (Salix viminalis var. Tora) cuttings and maize (Zea mays var. Lapriora) seedlings were grown in pots of loam soil containing a hydrocarbon-contaminated layer at the base of the pot (crude or refined oil) at concentrations of 0.5, 5, or 50 g·kg−1 . Chlorophyll concen-tration, biomass, and growth of plants were determined through destructive and nondestructive sampling, whilst reflectance measurements were made using portable hyperspectral spectrometers. All biophysical (chlorophyll concentration and growth) variables decreased in the presence of high concentrations of hydrocarbons, but at lower concentrations an increase in growth and chlorophyll were often observed with respect to nonpolluted plants, suggesting a biphasic response to hydrocarbon presence. Absorption features were identified that related strongly to pigment concentration and biomass. Variations in absorption feature characteristics (band depth, band area, and band width) were dependent upon the hydrocarbon concentration and type, and showed the same biphasic pattern noted in the biophysical measurements. This study demonstrates that the response of plants to hydrocarbon pollution varies according to hydrocarbon concentration and that remote sensing has the potential to both detect and monitor the variable impacts of pollution in the landscape.Atmospheric Remote Sensin

In situ root identification through blade penetrometer testing – Part 2:field testing

The spatial distribution, depths and diameters of roots in soil are difficult to quantify but important to know when reinforcement of a rooted slope or the stability of a plant is to be assessed. Previous work has shown that roots can be detected from the depth–resistance trace measured using a penetrometer with an adapted blade-shaped tip. Theoretical models exist to predict both forces and root displacements associated with root failure in either bending or tension. However, these studies were performed in dry sand under laboratory conditions, using acrylonitrile butadiene styrene root analogues rather than real roots. In this paper blade penetrometer field testing on two forested field sites, with Sitka spruce and pedunculate oak in sandy silt and clayey silt, respectively, is used to evaluate models under field conditions. Root breakages could be detected from blade penetrometer depth–resistance traces and using complementary acoustic measurements. Predictions of additional penetrometer resistance at root failure were more accurate than the displacement predictions. An analytical cable model, assuming roots are flexible and fail in tension, provided the best predictions for Sitka roots, whereas thick oak roots were better predicted assuming bending failure. These matched the modes of failure observed in three-point bending tests of the root material in each case. The presence of significant amounts of gravel made it sometimes difficult to distinguish between hitting a root or a stone. The root diameter could be predicted when root strength and stiffness, and soil penetrometer resistance were known and the right interpretative model was selected. Estimates based on peak force were more accurate than those based on root displacement. This measurement procedure is therefore a potentially valuable tool to quantify the spatial distribution of roots and their reinforcement potential in the field. </jats:p

In situ root identification through blade penetrometer testing – Part 1:interpretative models and laboratory testing

Root architecture and reinforcement are important parameters to measure the safety of vegetated slopes and stream banks against slope instability and erosion or to assess the stability of plants against environmental loading (e.g. windthrow of trees). However, these are difficult to measure without time-consuming sampling or counting procedures. Previous studies proposed using a penetrometer with an adapted geometry, and showed that individual root breakages could be detected as sudden drops in penetrometer resistance. However, there are no existing models to derive root properties from the measured traces. Here, several interpretative models are developed and their performance at identifying and characterising buried acrylonitrile butadiene styrene root analogues of varying diameter and architecture in sand are assessed. It was found that models, assuming the analogues broke in bending rather than tension, provided good predictions for the force–displacement behaviour. The simple analytical bending model developed here was shown to perform almost as well as more sophisticated numerical models. For all models, the predictions of additional penetrometer force required to break the root analogue were more accurate than predictions for lateral root displacement required to reach failure. The root analogue diameter and to a lesser extent the soil resistance and root angle were shown to affect the penetrometer resistance strongly. Root branching, root length and the distance between the point of load application and a root boundary (root tip or parent root) had a much smaller effect. When the root failure mechanism, root strength, root stiffness and soil resistance are known, an accurate prediction of the root diameter can be made based on the root peak resistance value identified from a blade penetration test. Penetrometer testing, a test which is easy to perform in the field, coupled with an accurate interpretative model might therefore be an effective method to rapidly quantify the spatial distribution, depths and diameters of roots. </jats:p