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

9316378格雷厄姆由于缺乏对各种环境因子的成土率和趋势的精确认识，土壤用于详细的地貌和环境解释受到限制。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形成过程。大的（5.3米× 5.3米× 2.1米深）土墙坑填入均匀的土壤材料，种植单一栽培，构成四种本地植物物种（羚羊、海芋、灌丛栎和库尔特松）的强制生物序列。每7.5 cm原始填充物层的存档样本和1958年、1975年和1987年在每种植被下的增量深度的土壤样本提供了土壤形成初始阶段的时间顺序记录。本研究的目的是量化每个土壤-植被系统对初始均匀填充材料的生物、大气和成壤影响，作为时间的函数。采用质量平衡方法对四种不同植物在12、29和41年后形成的土壤中成分的收益、损失和再分配进行量化。要分析的成分包括主要的造岩元素、粘土、淤泥、成土的铁氧化物、可交换阳离子、碳、氮和重金属。计算将以存档的原始母质样品为基础，这些样品与随后几年形成的土壤层相对应。将测量生物量的数量和组成，并将其包括在质量平衡中。该地点存在大气湿降和干降的长期测量，也将包括在内。放射性成因同位素将用于区分各种土壤成分的来源和分布。土壤和树木年轮中不同的Sr、Nd和Pb同位素比例将作为示踪剂，指示元素的大气和矿物风化来源。质量平衡和放射性同位素示踪方法的结合将产生对土壤-植被系统中增加、损失、转移和转化过程负责的详细核算。精确的量化和解释是有必要的，因为圣迪马斯土壤植被图可能是现存最严格限制和记录最充分的土壤发生实验。它们填补了持续数年的实验研究与传统土壤时间序列研究之间的一个关键空白，传统土壤时间序列研究的时间尺度为102至106年。这项研究的结果将使我们对土壤演化的初始阶段有比目前更精确的了解。这些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来源和汇，包括重金属污染物和植物养分。

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.