Quantitative Assessment of Soil Genesis Using a Controlled Decade-Scale Experiment

9316378格雷厄姆利用土壤进行详细的地貌和环境解释是有限的，因为缺乏作为各种环境因素作用的成土率和趋势的准确知识。这项研究将通过分析50年前在南加州圣迪马斯实验森林开始的一项独特的正在进行的实验，来量化十年尺度的土壤发生过程。大的(5.3米x 5.3米x 2.1米深)土墙坑里填满了均质的土壤材料，种植了构成四种本地植物(香茅、天麻、灌木橡树和库尔特松树)的强制生物序列。土壤形成的初始阶段的时间顺序记录是由每7.5厘米原始填充材料层的存档样本和1958、1975和1987年在每种植被下的递增深度采集的土壤样本提供的。这项研究的目的是量化生物、大气和土壤成因对初始均匀填充材料的影响，作为每个土壤-植被系统的时间函数。质量平衡方法将被用来量化12、29和41年后在四个不同植物物种下发育的土壤中成分的得、失和再分配。待分析的成分包括主要成岩元素、粘土、粉砂、成壤铁氧化物、可交换阳离子、C、N和重金属。计算将以存档的原始母质样品为基础，对应于随后几年开发和采样的土层。生物质的数量和组成将被测量并计入质量平衡。该站点有大气干湿降雨量的长期测量，也将包括在内。放射性同位素将用于区分不同土壤成分的来源和处置。土壤和树木年轮中独特的锶、钕和铅同位素比例将作为示踪剂，指示大气和矿物风化元素的来源。物质平衡和放射性同位素示踪方法的结合将产生对土壤-植被系统中的添加、损失、转移和转变负责的过程的详细核算。精确的量化和解释是有必要的，因为圣迪马斯土壤-植被地块可能是现有的最严格限制和最有文件证明的土壤发生实验。它们填补了运行数年的实验研究和处理102至106年时间尺度的传统土壤年代序列研究之间的关键空白。这项研究的结果将比目前存在的对土壤演化的初始阶段有更准确的理解。这一知识可用于改进对土壤断层运动历史的解释，并在与人类对大气化学的影响相称的时间尺度上预测元素的源和汇，包括重金属污染物和植物营养物质。

9316378 Graham The use of soils for detailed geomorphic and environmental interpretations is limited by lack of precise knowledge of pedogenic rates and trends as a function of various environmental factors. This research will quantify decade-scale soil genesis processes by analyzing a unique on-going experiment started =50 years ago at the San Dimas Experimental Forest in Southern California. Large (5.3m x 5.3m x 2.1m deep) earthen-walled pits were filled with homogenized soil material and planted with monocultures constituting an imposed biosequence of four native plant species (chamise, ceanothus, scrub oak, and Coulter pine). A chronosequential record of the initial stages of soil formation is provided by archived samples from each 7.5 cm layer of original fill material and soil samples taken at incremental depths in 1958, 1975, and 1987 under each type of vegetation. The objective of this research is to quantify the biotic, atmospheric, and pedogenic influences on the initial homogeneous fill material as a function of time for each of the soil-vegetation systems. A mass balance approach will be used to quantify gains, losses, and redistributions of constituents in the soils developed after 12, 29, and 41 years under the four different plant species. Constituents to be analyzed include major rock-forming elements, clay, silt, pedogenic Fe oxides, exchangeable cations, C, N, and heavy metals. Calculations will be based on the archived original parent material samples corresponding to soil horizons that developed and were sampled in subsequent years. Biomass quantity and composition will be measured and included in the mass balance. Long-term measurements of atmospheric wet- and dry-fall exist for the site and will also be included. Radiogenic isotopes will be used to distinguish the origin and disposition of various soil constituents. Distinctive Sr, Nd, and Pb isotopic rations in soils and tree rings will serve as tracers to indicate atmospheri c and mineral weathering sources of elements. The combination of mass balance and radiogenic isotope tracer methods will yield a detailed accounting of processes responsible for additions, losses, transfers, and transformations in the soil-vegetation systems. Precise quantification and interpretation is warranted because the San Dimas soil-vegetation plots are likely the most closely constrained and well documented soil genesis experiments in existence. They fill a critical gap between experimental studies that operate over several years and traditional soil chronosequence studies that address time scales of 102 to 106 years. Results of this research will yield a much more precise understanding of the initial stages of soil evolution than currently exists. This knowledge can be used to improve interpretations of fault movement histories from soils and to predict sources and sinks of elements, including heavy metal contaminants and plant nutrients, on a time scale commensurate with human-induced effects on atmospheric chemistry.