Streambank Soil and Phosphorus Losses Under Different Riparian Land‐Uses in Iowa1

Abstract: Phosphorus and sediment are major nonpoint source pollutants that degrade water quality. Streambank erosion can contribute a significant percentage of the phosphorus and sediment load in streams. Riparian land‐uses can heavily influence streambank erosion. The objective of this study was to compare streambank erosion along reaches of row‐cropped fields, continuous, rotational and intensive rotational grazed pastures, pastures where cattle were fenced out of the stream, grass filters and riparian forest buffers, in three physiographic regions of Iowa. Streambank erosion was measured by surveying the extent of severely eroding banks within each riparian land‐use reach and randomly establishing pin plots on subsets of those eroding banks. Based on these measurements, streambank erosion rate, erosion activity, maximum pin plot erosion rate, percentage of streambank length with severely eroding banks, and soil and phosphorus losses per unit length of stream reach were compared among the riparian land‐uses. Riparian forest buffers had the lowest streambank erosion rate (15‐46 mm/year) and contributed the least soil (5‐18 tonne/km/year) and phosphorus (2‐6 kg/km/year) to stream channels. Riparian forest buffers were followed by grass filters (erosion rates 41‐106 mm/year, soil losses 22‐47 tonne/km/year, phosphorus losses 9‐14 kg/km/year) and pastures where cattle were fenced out of the stream (erosion rates 22‐58 mm/year, soil losses 6‐61 tonne/km/year, phosphorus losses 3‐34 kg/km/year). The streambank erosion rates for the continuous, rotational, and intensive rotational pastures were 101‐171, 104‐122, and 94‐170 mm/year, respectively. The soil losses for the continuous, rotational, and intensive rotational pastures were 197‐264, 94‐266, and 124‐153 tonne/km/year, respectively, while the phosphorus losses were 71‐123, 37‐122, and 66 kg/km/year, respectively. The only significant differences for these pasture practices were found among the percentage of severely eroding bank lengths with intensive rotational grazed pastures having the least compared to the continuous and rotational grazed pastures. Row‐cropped fields had the highest streambank erosion rates (239 mm/year) and soil losses (304 tonne/km/year) and very high phosphorus losses (108 kg/km/year).     

减氮覆膜下旱地麦田土壤团聚体中各物理组分的变化

分析覆膜条件下晋南旱塬土壤团聚体中各物理组分的变化,对于协同提高该区域土壤肥力及作物产能意义重大. 依托山西省洪洞县长期定位试验基地,采集7 a的0~20 cm土层原状土壤样品,分析农户施肥（FP）、测控施肥（MF）、测控施肥+垄膜沟播（RF）和测控施肥+平膜穴播（FH）这4个处理对小麦籽粒年均产量、土壤有机碳（SOC）含量和团聚体中各物理组分[未受保护的大团聚体中粗颗粒有机碳（M-cPOC）及细颗粒有机碳（M-fPOC）、受物理保护的大团聚体中微团聚体内颗粒有机碳（M-iPOC）、受（生物）化学保护的大团聚体中矿质结合态有机碳（M-MOC）、未受保护的微团聚体中细颗粒有机碳（m-fPOC）、受物理保护的微团聚体中颗粒有机碳（m-iPOC）、受（生物）化学保护的微团聚体中矿质结合态有机碳（m-MOC）]分布比例及其有机碳含量的影响. 结果表明,同FP处理相比,MF处理虽然显著降低了SOC含量,但是还能维持小麦籽粒产量,RF和FH处理协同提升了土壤肥力和作物产能,且以FH处理效果更佳,SOC含量和小麦籽粒产量分别提高了8.44%和48.86%. MF处理显著降低了M-cPOC含量,RF处理显著提高了M-iPOC含量,FH处理显著提高了M-fPOC、M-iPOC、M-MOC和m-iPOC含量,增幅分别为64.00%、98.39%、6.16%和17.48%. 此外,结合冗余分析发现M-iPOC组分对提高SOC含量和小麦籽粒产量起主要作用,贡献率高达61.5%. 因此,晋南旱塬区大团聚体对土壤肥力和作物产能的贡献高于微团聚体,平膜穴播通过提高M-iPOC含量,进而协同增加了土壤有机碳固存和小麦籽粒产量,可以在该区域乃至全国农作旱区推广该项栽培技术.     

双酚S在两种典型地带性土壤中的吸附/解吸行为研究

采用批平衡实验方法研究了双酚S（BPS）在两种典型地带性土壤中的吸附/解吸行为.结果表明,吸附动力学曲线符合拟二级动力学方程.吸附等温线呈非线性,且同时符合Freundlich和Langmuir方程.相比而言,BPS更易吸附在高有机质含量的黑土中,298 K反应温度下BPS在黑土和红壤上的最大吸附容量分别为497.8和156.6 mg·kg^-1.吸附到两种土壤中的BPS存在解吸滞后现象,这可能是由于BPS以化学吸附和微孔扩散的形式存在于土壤中的缘故.溶液pH与BPS在土壤中的吸附容量呈负相关关系,即中性形态的BPS比阴离子形态的BPS具有更高的吸附容量.与结构类似物双酚A（BPA）的吸附相比,BPS在土壤中的吸附量更低,因此具有更高的迁移能力,可能会引起更高的环境健康风险.本研究结果为了解BPS在土壤中的迁移规律提供了数据支持.     

2,4-D Mineralization in soil profiles of a cultivated hummocky landscape in Manitoba,Canada

The objective of this study was to quantify 2,4-D (2,4-dichlorophenoxyacetic acid) mineralization in soil profiles characteristic of hummocky, calcareous-soil landscapes in western Canada. Twenty-five soil cores (8 cm inner diameter, 50 to 125 cm length) were collected along a 360 m transect running west to east in an agricultural field and then segmented by soil-landscape position (upper slopes, mid slopes, lower slopes and depressions) and soil horizon (A, B, and C horizons). In the A horizon, 2,4-D mineralization commenced instantaneously and the mineralization rate followed first-order kinetics. In both the B and C horizons, 2,4-D mineralization only commenced after a lag period of typically 5 to 7 days and the mineralization rate was biphasic. In the A horizon, 2,4-D mineralization parameters including the first-order mineralization rate constant (k ₁), the growth-linked mineralization rate constant (k ₂) and total 2,4-D mineralization at the end of the experiment at 56 days, were most strongly correlated to parameters describing 2,4-D sorption by soil, but were also adequately correlated to soil organic carbon content, soil pH, and carbonate content. In both B and C horizons, there was no significant correlation between 2,4-D mineralization and 2,4-D sorption parameters, and the correlation between soil properties and 2,4-D mineralization parameters was very poor. The k ₁ significantly decreased in sequence of A horizon (0.113% day^?1) > B horizon (0.024% day^?1) = C horizon (0.026% day^?1) and in each soil horizon was greater than k ₂. Total 2,4-D mineralization at 56 days also significantly decreased in sequence of A horizon (42%) > B horizon (31%) = C horizon (27%). In the A horizon, slope position had little influence on k ₁ or k ₂, except that k ₁ was significantly greater in upper slopes (0.170% day^?1) than in lower slopes (0.080% day^?1). Neither k ₁ nor k ₂ was significantly influenced by slope position in the B or C horizons. Total 2,4-D mineralization at 56 days was not influenced by slope positions in any horizon. Our results suggest that, when predicting 2,4-D transport at the field scale, pesticide fate models should consider the strong differences in 2,4-D mineralization between surface and subsurface horizons. This suggests that 2,4-D mineralization is best predicted using a model that has the ability to describe a range of non-linear mineralization curves. We also conclude that the horizontal variations in 2,4-D mineralization at the field scale will be difficult to consider in predictions of 2,4-D transport at the field scale because, within each horizon, 2,4-D mineralization was highly variable across the twenty-five soil cores, and this variability was poorly correlated to soil properties or soil-landscape position.     

降雨条件下冰碛土滑坡模型试验研究

实践指出降雨是引发边坡破坏的重要外部因素之一。为研究降雨作用下冰碛土滑坡规律和导致滑坡的内在因素,本次研究制作了 3 种坡度的冰碛土边坡模型,进行了 3 种降雨强度下的共 9 组降雨作用下的冰碛土滑坡试验, 通过试验观测边坡土含水率、土压力变化及边坡变形数据,从而揭示降雨条件下冰碛土边坡破坏的机制。通过对冰碛土边坡降雨试验过程的观测发现,边坡模型坡脚位置的含水率最先稳定,各观测点的土压力没有观测到明显变化规律。实验过程中降雨入渗导致的滑坡变形大致可以划分为 4 个阶段,首先为局部性土颗粒滑落,其次为边坡表面形成冲蚀沟,然后小范围的冲沟逐渐扩展为中部和上部连片滑动,最后冰碛土边坡浅层形成贯通性滑动体,滑动的泥水混合物流动一段距离后在坡脚处形成堆积体。3 种暴雨工况下各坡度边坡主要特征表现为边坡表层土体产生小范围坡面径流,径流逐渐增强形成冲蚀沟,其后发生滑坡破坏。3 种大雨工况下坡度超过 45°的边坡发生了滑坡破坏。3 种中雨工况下仅 60°边坡产生了滑坡破坏。结果表明降雨强度和边坡坡度是影响冰碛土滑坡发生的主要因素。     

DDT及其主要降解产物污染土壤的植物修复

用植草方法研究了受DDT及其主要降解产物污染土壤的植物修复试验, 比较了10种草在不同污染浓度下对 5种土壤的修复能力.研究表明, 同一品种的草在不同土壤中对污染物的清除能力是不同的, 不同品种的草在同一土壤中对污染物的清除能力也是不同的.在植物修复的过程中, 通过草对有机污染物吸收的途径而去除土壤中污染物所作的贡献很小, 植草3个月后, 草对DDT及其主要降解产物的吸收与富集仅占原施药总量的 0.13%—3.0%, 而7.10%—71.94%的DDT及其主要降解产物从土壤中消失.     

一株降解邻苯二甲酸酯真菌的筛选及其降解特性研究

采用富集培养法,从PAEs污染的农田土壤中筛选出1株邻苯二甲酸酯类化合物(PAEs)降解真菌F9,经形态学特征及18S rDNA序列分析,初步鉴定为爪哇正青霉(Eupenicillum javanicun).通过正交试验研究,得出菌株F9的最优降解条件是:C:N为20:1、pH为7.0、最佳PAEs初始浓度为50 mg·L^-1.菌株F9对土壤中复合PAEs(DMP、DEP和DOP)有良好的降解效果.在30 d培养期内,可将灭菌土壤中300 mg·kg^-1的PAEs降解65.2%,且培养第一阶段(0~15 d)的降解率远高于第二阶段(16~30 d).     

黄河三角洲新生湿地土壤碳氮磷分布及其生态化学计量学意义

河口湿地是连接陆地生态系统和海洋生态系统的纽带。土壤碳(C)、氮(N)、磷(P)元素是湿地生态系统营养水平的重要指示物,显著影响湿地生态系统的生产力。本文研究了黄河三角洲新生湿地不同植被下土壤C、N、P的分布特征和生态化学计量特征。结果表明,1)黄河三角洲新生湿地C、N、P含量分别为1.2~8.4、0.2~0.8、0.4~0.6g/kg,平均值分别为3.5、0.4、0.5g/kg;土壤表层的C、N、P含量显著高于亚表层。2)黄河三角洲新生湿地C/N、C/P、N/P比值分别为4.62~12.67、2.02~16.39、0.22~1.53,平均值分别为8.77、6.81、0.77。土壤C/N、C/P、N/P比值随土壤剖面深度向下递减,不同植被土壤之间的C/N、C/P、N/P比值有所不同。土壤生态化学计量比值显示黄河三角洲新生湿地土壤有机质分解快,氮的矿化度高。因此,提高该地区土壤有机质的归还,同时适当增加氮肥使用成为湿地生态恢复的优先选项。     

贵州荔波喀斯特与非喀斯特地区土壤水运移的对比研究

以我国西南地区典型的喀斯特与非喀斯特样地为研究对象,采集大气降水和土壤水,根据其δD值、δ18O值和水量特征探讨土面生境非植物主根区土壤水的运移特征。结果表明:喀斯特样地土壤基质流的混合作用较弱,非喀斯特样地表层(0～20 cm)土壤基质流的混合作用也较弱,但随深度增加基质流的混合作用增强;喀斯特与非喀斯特样地土壤基质流都可能存在活塞流运移机制,尤其是喀斯特样地,活塞流很可能是基质流的一种重要运移机制;喀斯特样地土壤介质中存在优先流,优先流空间异质性较大;蒸发作用对非喀斯特样地表层土壤基质孔隙水影响较大,而对喀斯特样地土壤水的影响较小。这为喀斯特区水资源的管理和合理利用,以及区域植物水分利用和营养元素循环利用等研究奠定基础。     

Outlier identification and visualization for Pb concentrations in urban soils and its implications for identification of potential contaminated land

Outliers in urban soil geochemical databases may imply potential contaminated land. Different methodologies which can be easily implemented for the identification of global and spatial outliers were applied for Pb concentrations in urban soils of Galway City in Ireland. Due to its strongly skewed probability feature, a Box–Cox transformation was performed prior to further analyses. The graphic methods of histogram and box-and-whisker plot were effective in identification of global outliers at the original scale of the dataset. Spatial outliers could be identified by a local indicator of spatial association of local Moran's I, cross-validation of kriging, and a geographically weighted regression. The spatial locations of outliers were visualised using a geographical information system. Different methods showed generally consistent results, but differences existed. It is suggested that outliers identified by statistical methods should be confirmed and justified using scientific knowledge before they are properly dealt with.