Determination of erosion characteristics is of great significance to assess the stability of geotechnical infrastructures that are subjected to seepage. Hole erosion tests (HETs) are the popular and simple laboratory measurements that have been used to determine erosion characteristics. These tests are indicative of the quantity of soil loss in term of internal erosion that can occur during seepage. It is noted that there are not many studies that focus on the development of theoretical model describing the erosion process (i.e. sediment detachment and transport) in HETs. The aim of this study is to propose a theoretical model based on Bernoulli’s principle to interpret the erosion measurements from HETs and employ the results for estimating erosion characteristics of soils. An analytical equation was deduced from a physically based model incorporating Bernoulli’s principle and erosion constitutive law for internal erosion within a soil pipe driven by pressure gradient. The analytical equation could be applied to determine the temporal development of eroded soil loss, radial erosion propagation, erosion rate, hydraulic shear stress, and pressure drop. The utility of proposed analytical solution was validated using a series of HETs performed in this study. Based on the novel analytical solution, erosion characteristics could be derived from the known realistic propagation of radial erosion.
Aims The impact of nutrient increase on nutrient resorption from senescent leaves is an important topic, which is not completely understood. Mangrove species are characterized by nutrient conservation mechanisms as a consequence of adaptation to nutrient-poor environments. The understanding of the response of the traits related to nutrient conservation strategies to nutrient availability is limited. This study aims to address whether nutrient resorption of mangrove species is responsive to long-term nutrient enrichment. Methods A field-based study was carried out in a Kandelia obovata dominated mangrove stand where a nutrient gradient was generated by the long-term discharge of aquaculture wastewater. Seasonal variations of nutrient resorption and nutrient availability were assessed. Important findings The data from summer and winter showed the same results: 1) resorption proficiency or the nutrient concentrations (N and P) in senescent leaves did not varied with nutrient increases except the plot that the N availability was extremely high; 2) the resorption efficiency of both N and P was positively correlated with nutrient availability, and N resorption efficiency was also positively correlated to leaf N: P ratio; 3) N resorption was complete while the resorption of P was incomplete. These results indicate that resorption proficiency of K. obovata is less sensitive than resorption efficiency to nutrient availability, and the positive response of N resorption efficiency is related to the imbalance of nutrient availability, while the positive response of P resorption efficiency is unrelated to plant nutrient status. We suggest that caution should be taken in using resorption efficiency of mangrove species to predict plant nutrient status.