The Soil Production Function: The Key Linkage Between Erosion Rates, Climate and Soil Thickness on Landscapes Developed on Bedrock

100多年来，人们一直认为基岩分解成可侵蚀土壤的速度取决于上覆土壤地幔的厚度。这一假设奠定了这样一种信念，即存在受天气限制和交通限制的景观。然而，建模真实景观而不是假设景观的新趋势，以及解决气候、地质、生物和人类活动耦合的复杂问题，要求对这一假设进行调查。土壤生产计划在控制土壤深度的空间变化和决定在什么条件下景观成为基岩主导方面发挥着重要作用。然而，目前尚无实地数据可以定量定义土壤生产函数的形状。建议将重点放在凸脊上发育的薄土壤（1m）上，其中侵蚀是由于扩散运输过程造成的，生产受到生物活动引起的机械破坏的强烈影响。我们发现土壤和部分风化的基岩之间的边界是突然的，这使得土壤厚度很容易确定。两种新的、独立的方法将被用来确定土壤生产函数。一种方法是从简单的油田关系中得到生产函数的估计。这种方法源于一个理论分析，该分析表明，在土壤产生与扩散（坡度依赖）过程的去除平衡的地方，扩散系数和曲率的乘积等于土壤产生速率。因此，如果产土速率取决于土壤厚度，则土壤厚度应随地形曲率而变化，如果扩散系数已知，则可以充分量化土壤的产土规律。另一种方法是通过分析在土壤柱底部发现的基岩中形成的宇宙核素来估计基岩到土壤的转化率。这种方法类似于以前使用宇宙核素对暴露的基岩进行的侵蚀速率估计，但这是一种新的应用，适用于目标岩石在地表以下的情况。虽然用这种方法估计基岩到土壤的转化率也假设土壤厚度处于稳定状态，但可以通过比较26Al和10Be浓度的比率来评估这一假设的长期变化。这种造型核素方法完全独立于第一种方法，可以提供长期降低速率和扩散率的估计。每种方法的初步研究结果表明，它们产生的结果与预期的产量随土壤深度的指数下降相一致。提出了一个为期三年的项目，通过应用这两种新方法来检验土壤生产中深度依赖的假设。6个地点，其中2个被灰岩覆盖，4个被花岗岩覆盖，已经被选中进行研究，这些研究是基于之前关于地貌过程、气候差异和长期侵蚀速率的巨大差异的工作。这两个灰狼遗址已经成为大量地貌学研究的主题，大型动物在运输和土壤生产中的扩散、气候历史和作用是众所周知的。在这里，我们将关注的问题是，该方法是否给出了合理的结果，并定义了一个明确的生产函数。花岗岩下的四个地点的长期侵蚀率相差1000倍，年降水量相差2倍，三个地点显示出大型动物活跃的证据，而澳大利亚的一个地点的土壤中没有大型动物。对所有六个地点的生产函数进行比较，应该能够揭示对生产函数的潜在控制，并使我们能够对具有广泛不同侵蚀率的景观如何具有土壤厚度形成解释。成功地确定土壤生产函数对于模拟景观演变具有重要价值，并且对于基岩下丘陵土地利用导致的加速土壤侵蚀的长期后果提供见解和指导。

Dietrich 9527006 For over 100 years it has been assumed that the rate of disintegration of bedrock into erodable soil depends on the thickness of the overlying soil mantle. This assumption underlies the belief that there are weathering-limited and transport-limited landscapes. The emerging trends toward modeling real landscapes rather than hypothetical ones and toward tackling complex problems coupling climate, geology, biology and human actions, however, requires that this assumption be investigated. Soil production plans an essential role in controlling the spatial variation in soil depth and in determining under what conditions landscapes become bedrock dominated. No field data currently exists, however, that permits quantitative definition of the shape of the soil production function. Propose to focus on the thin soils (1m) developed on convex ridges where erosion is due to diffusive transport processes and production is strongly influenced by mechanical disruption caused by biologic activity. Her we find the boundary between the soil and partially weathered bedrock to be abrupt, making the soil thickness easily defined. Two new, independent methods will be used to determine the soil production function. One method obtains an estimate of the production function from simple field relationships. This method arises from a theoretical analysis which shows that where soil production is in balance with removal by diffusive (slope dependent) processes, the product of the diffusion coefficient and curvature equals the soil production rate. Hence, if soil production rate depends on soil thickness, then soil thickness should vary with topographic curvature, and if the diffusion coefficient is known, the soil production law can be fully quantified. The other method estimates conversion rate of bedrock to soil from the analysis of cosmogenic nuclide build up in the bedrock found at the base of the soil column. The approach is analogous to erosion rate estimates previously done on expose d bedrock using cosmogenic nuclides, but this is a novel application to a case where the target rock is beneath the surface. Although estimates of bedrock to soil conversion rates by this method also assume steady state soil thickness, this assumption can be evaluated for long term variation by comparing the ratio of 26Al to 10Be concentrations. This cosmegenic nuclide method is entirely independent of the first, and can provide both estimates of long-term lowering rates as well as diffusivities. Preliminary findings for each method show that they yield comparable results consistent with an expected exponential decline in production rate with soil depth. A three-year project is proposed to test the assumption of depth dependency in soil production by applying these two new methods. Six sites, two underlain by greywacke and four by granite rocks have been selected for study based on previous work on geomorphic processes, on climatic differences, and by the very large differences in long-term erosion rates. The two greywacke sites have already been the subject of substantial geomorphic studies and the diffusivities, climatic history and role of macrofauna in transport and soil production are well-known. Here we will focus on the question of does the methodology give sensible results and define a clear production function. The four sites underlain by granitic rocks vary in long term erosion rates by as much as a factor of 1000, have annual precipitation that varies by a factor of 2 and three sites show clear evidence of active macrofauna burrowing while one, in Australia, has no macrofauna in the soil. Comparison of the production function for all six sites should shed light on the underlying controls on the production function and enable us to form an explanation for how landscapes with widely varying erosion rates could have the soil thickness. Successful determination of soil production functions will be of great value to modeling landscape evolution as well as to providing insight and guidelines about the long-term consequence of accelerated soil erosion due to land use in hilly lands underlain by bedrock.