以體積含水比估計蚯蚓移動路徑

Abstract

本文目的為研究土壤含水量對於蚯蚓移動行為之影響，其中包括三項，其一，乾燥地表蚯蚓移動之情形，其二，降雨蚯蚓之移動情形，其三，健康狀況不佳蚯蚓下雨移動情形。文中假設蚯蚓活動之土壤俱有均質性，並假設蚯蚓居住在生長曲線較高之土壤較為舒適，並往其方向移動，本文主要提出蚯蚓含水量控制方程式來描述蚯蚓鑽土行為，方程式中使用之參數皆為實驗室可得量測的參數，包括水力傳導係數與蚯蚓鑽地表的速度，其方程可求得蚯蚓於地表下之移動速度，積分後可得蚯蚓在土壤中的位置與時間之關係。由於紫外線易造成蚯蚓麻痺，故其方程式計算終止於蚯蚓爬出至地表。本研究以一維蚯蚓含水量控制方程式模擬，模擬結果包括，其一，在乾燥地表情況下，蚯蚓會往地底下移動；其二，降雨量越大，蚯蚓越容易爬至地表；其三，健康狀況不佳之蚯蚓下雨時越有可能爬出至地表，並與前人的研究有相同的趨勢。

The purpose of this study is to discuss the influences of the soil water content on earthworm movements. Three situations including earthworm movement in the soil with dry surface, and the movement of either healthy or sick earthworms in the soil during rainfall via numerical simulations were studied. This study was based upon two assumptions. First, the earthworms inhabit in the homogenous soil. Second, The earthworms go towards the soil with higher growth curve. Here, an 1-D earthworm movement-water content governing equation (EWE) was proposed to describe the relationship between earthworm movement and soil water content. The relationship between displacement of the earthworms and time, thus, was derived by integrating EWE with time. The simulation of the earthworm movement required with some experimental parameters, such as hydraulic conductivities, the theory maximum drilling velocity (TMDV) of the earthworm, etc. The simulation of earthworm movement was terminated once the earthworms reached the ground surface, since ultraviolet radiation can cause earthworms paralysis based upon the previous studies. The numerical simulation results match with the previous studies and show that (1) earthworms manage to move downwards to the soil as ground surface is drying, (2) earthworms tend to move to the surface under greater rainfall intensity, and (3) earthworms are more likely to move to the surface at rainfall while they are sick. All of the three conclusion match with the with former observations.