Changes of soil ecological stoichiometric ratios under different land uses in a small catchment of subtropical China

The role of soil elemental ecological stoichiometry in evaluation of nutrient cycling and limitation was not clear in local spatial scale. Thus, characteristic of soil C, N and P stoichiometric ratios and their relationships to land-use and soil properties were analyzed in a small catchment of subtropical China. Results showed that there were constrained soil C:N ratios in a small catchment. Soil C:P and N:P ratios were also constrained at the beginning; but they became variable after 10 years of different land uses. Soil C:N ratios in the small catchment were similar to those at national scale, but soil C:P and N:P ratios were remarkably lower at the local scale. Soil C:P ratios in paddy fields were 5.1–76.9% and 16.0–80.4% higher than those for other land uses in 2000 and 2010, respectively; the corresponding soil N:P ratios were also 3.8–66.7% and 19.1–75.0% higher. Over time, soil C:N ratios increased approximately 19.7–29.6% for all land uses after 10 years of utilization. Soil C:P and N:P ratios also increased for most land uses. Clay content was an important factor influencing soil C:P and N:P ratios. Except for paddy fields, N was still the limiting nutrient in most land uses, evaluating by elemental stoichiometry. Future work should focus on determining direct evidence of C and N limitations and their relationships to elemental stoichiometry in a small catchment.     

Trace elements and polycyclic aromatic hydrocarbons in road gully sediments from different land uses,Hong Kong

Purpose

This study investigated the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), and polycyclic aromatic hydrocarbons (PAHs) in sediments collected from gully pots for road drainage in Hong Kong. The presence and intensity of anthropogenic contamination of road gully sediments were assessed. Identifications of potential sources of trace elements and PAHs were performed to help understand the situation for future control of pollution to the land and aquatic environments.

Materials and methods

Gully sediment samples were collected from gully pots of 18 roads that are potentially exposed to different pollution sources in Hong Kong. The selection of roads considered different road features, adjacent land uses, and traffic volumes. Composite samples were collected for the analysis of trace elements (Cd, Cr, Cu, Pb, Ni, and Zn) and PAHs by an accredited environmental testing laboratory. Geo-accumulation index (I_geo), contamination factor (C_f), modified degree of contamination (mC_d), ecological risk factor (Er), and pollution load index (PLI) were used to assess the level of ecological risk of trace element contamination. Positive matrix factorization (PMF) and PAH diagnostic ratios were applied to identify the sources of trace elements and PAHs.

Results and discussion

Elevated trace element concentrations were commonly found in gully sediments. The concentrations of Zn (267–3700 mg kg^?1) were the highest compared to the other trace elements. Noticeable high concentrations of Cu (27–1020 mg kg^?1), Pb (21–332 mg kg^?1), and Cr (14–439 mg kg^?1) were found in all samples. The PAH contents were moderate to high (0.6 to 24.7 mg kg^?1). Commercial/industrial emissions and road features that cause frequent acceleration-deceleration and turning events showed important influences on the contaminant levels. Strong correlations between the concentrations of Cd, Cr, Pb, and Zn were identified, implying that these trace elements are likely from common sources. The contamination assessment indices reflect significant sediment pollution. The ecological risk ranges from the considerable/moderate-risk class to over the high-risk class.

Conclusions

The collected gully sediments are identified as highly contaminated and need to be isolated from the environment upon final disposal. Through the comprehensive analysis of the collected data, this study provides a detailed insight into the contaminant levels of road gully sediments and potential sources of contamination. Disposal of gully sediments and potential impacts due to release of contaminants into the downstream aquatic environment during rainstorm events should receive attention and need further investigation.

     

密云水库上游地区不同土地利用方式面源污染试验

为了更合理地利用土地、减少面源污染,利用密云水库上游石匣坡地径流场不同土地利用试验小区的5年观测数据,分析不同土地利用方式对面源污染的影响。研究表明:不同土地利用方式多年平均次径流系数差异明显,依次为清耕休闲地>坡耕地玉米>荒草坡>鱼鳞坑刺槐>水平条山楂,多年平均土壤侵蚀量与径流中TP、TN和CODMn流失量随径流系数的增大而增加,流失量与径流系数呈显著的正相关关系;径流中养分含量与径流系数之间没有显著相关关系。因此,通过增加植被覆盖或改变土地利用方式可大大减轻水土流失及其造成的面源污染。     

Association of soil organic carbon with physically separated soil fractions in different land uses of Costa Rica

Abstract

Yams (Dioscorea spp.) are known to be very demanding in terms of soil fertility. The influence of deleterious soil fertility on the growth of yams, however, has not yet been studied. A field study was carried out in Côte d'Ivoire, in a fertile forest site and in a low fertility savanna site, submitted to identical climatic conditions, to determine how soil fertility affects Leaf Area Index, Leaf Area Ratio, Crop Growth Rate, Tuber Bulking Rate, Radiation Interception, Radiation Use Efficiency and final tuber yields in D. alata and D. rotundata, grown in the presence of adequate fertilizers. While germination and establishment of both species were not affected by the site, growth parameters of D. alata were superior to those of D. rotundata. This resulted in higher yields of D. alata, when compared to D. rotundata. Only the radiation use efficiency was higher in D. rotundata than in D. alata. Both species reached higher Crop growth rate and Tuber bulking rate and produced higher fresh tuber yields at the forest site than at the savanna site, reflecting the known demand of yams for high fertility soil. Correlation analyses showed significant relationships between the mean Leaf Area Index measured over the entire growth period, Tuber Growth Rate calculated between tuber initiation and harvest, and fresh tuber yields, suggesting that the development of leaf area is determining the growth rate of the tuber which itself determines the fresh tuber yield. The decrease in D. alata tuber yields at the savanna site was explained by a decrease in Leaf Area Index, while the decrease in D. rotundata tuber yields at this site was explained by a decrease in Radiation Use Efficiency. Both effects might have been the consequence of a suboptimal nitrogen and potassium nutrition at the savanna site.     

Phosphorus fractions and their availability in the sediments of eight tropical semiarid reservoirs

Journal of Soils and Sediments - We quantified the phosphorus (P) fractions and oxide content in the sediment of eight tropical semiarid reservoirs to assess how water-level decreases affect the...     

黄土高原小流域不同坡地利用方式的水土流失特征

坡地是黄土高原水土流失的主要来源,坡地利用方式与水土流失的关系研究是黄土高原水土流失综合治理与植被恢复中的重要基础科学问题。在陕北神木县六道沟小流域内,选择谷子地、黑豆地、退耕撂荒地、荒草地和柠条地等5种利用方式修建标准径流小区,观测了产流产沙状况,分析比较其水土流失特征。结果表明：观测期内谷子、黑豆、退耕撂荒、荒草和柠条等5个小区的产流量分别为2.1、2.2 、1.5、1.2和0.9 m3,径流系数分别为4.1%、4.6%、2.9%、2.4%和1.9%,产流量大小顺序为黑豆＞谷子＞退耕撂荒＞荒草＞柠条,最大产流量为最小值的2.4倍。谷子、黑豆、退耕撂荒、荒草和柠条等5个小区的侵蚀产沙量分别为196.6、228.6、27.2、23.3和10.4 kg,其大小顺序为黑豆＞谷子＞退耕荒草＞天然荒草＞柠条,最大土壤流失量为最小值的22.0倍,表明草灌木等植被类型在保持水土的作用方面要明显高于坡耕地,为评价流域植被恢复的水土环境效应和水土流失治理模式选择提供了基础数据参考。     

长江三角洲地区竹林经营中的氮磷流失负荷概算

通过分析长江三角洲地区竹林集约经营面积、竹林施肥情况及氮(N)、磷(P)流失率,对该区竹林经营中因施肥产生的N、P流失量进行了概算.结果表明,长江三角洲地区竹林中每年N、P流失量分别为3795～6067t、828～1104t.其中,浙江省竹林地的N、P流失量分别为3573～5713 t、779～1039 t,均占总流失量的94%.从单位面积上的流失量来看,浙江省竹林地N流失负荷(9.8～15.6kg/hm2)显著低于该省农田N流失负荷(57.4 kg,hm2),而P流失负荷(2.1～2.8 kg/hm2)稍高于农田(1.7 kg/hm2) .在部分高度集约经营地区,竹林地每年的N、P流失更高.这些竹林地主要位于水源上游或河湖两岸,流失的N、P进入水体后,将对水体造成污染,降低水质,加速下游水体的富营养化.     

土地利用变化对长江上游生态系统服务价值的影响

该文以典型生态脆弱带——长江上游地区1980、1990和2000年的土地利用动态数据为基础,参照中国陆地生态系统单位面积服务价值表,结合敏感度分析,探讨了土地利用变化及其对生态系统服务价值的影响。结果表明,1980－1990年研究区林地、草地和湿地面积都有不同程度增长,生态系统服务价值呈增加趋势;但在1990－2000年间,建设用地、耕地和未利用地面积大幅度增加,且大多来源于林地和草地等地类的转化或退化,使得整个研究期间内各项生态系统服务功能都出现不同程度的衰退。生态系统服务价值也从1980年的11 119.16亿元减少到2000年的11 077.85亿元,净减少值为41.31亿元。该区域快速城市化和以经济利益为目的的发展模式给生态系统服务功能和可持续发展带来巨大压力,这种生态环境急剧退化的趋势必须引起高度重视并进行有效控制。     

Assessing the potential effect of different land cover management practices on sediment yield from an abandoned farmland catchment in the Spanish Pyrenees

Purpose  

Sediment delivery from headwater catchments to reservoirs is a serious threat to reservoir sustainability and is a critical issue in Mediterranean environments where water resources are scarce. In this study we assessed the consequences of two landscape management scenarios (natural vegetation recovery and scrub clearance) on soil erosion and sediment yield. The results were analyzed in relation to predicted and measured rates of soil erosion and sediment yield, with the aim of promoting better management practices.     

长江上游地区土地利用/覆被和景观格局变化分析

利用1980年、1990年和2000年3个时期土地利用数据,将GIS和景观生态学的数量分析方法相结合,运用Arc Info和Arc View以及Fragstats(栅格版),分析了长江上游地区1980~2000年间的土地利用/覆被和景观格局的变化。结果表明：研究期间,林地和耕地大幅度减少,草地和建设用地面积显著增加,水域和未利用地相对变化幅度不大。研究区土地利用类型转移的主要方向是林地转化为草地和耕地、耕地转化为建设用地和草地、草地转化为未利用地。通过对该区斑块类型级别指标的分析,得出水域、建设用地和未利用地分离度和破碎度较大,而耕地、林地和草地在宏观政策和人类活动强烈干扰下,分离度和破碎度呈现先降低后升高的趋势。通过对景观级别指标的分析,得出整个区域景观结构日趋破碎,景观异质性也逐渐提高,土地向着多样化和均匀化发展。长江上游地区脆弱的生态体系对土地利用变化响应强烈,造成水土流失和沙漠化程度加剧,自然灾害频发等景观生态效应。可通过调整景观尺度上的土地利用方式,使长江上游地区生态建设及水土资源实现可持续发展。     

Phosphorus fractions and phosphorus delivery potential of a luvisol derived from loess amended with organic materials

In a long-term field experiment, started in 1962, the fate of P applied with different organic materials [farmyard manure (FYM), compost and sewage sludge] in comparison to mineral fertilizer was investigated. Soil samples were collected after 38 years' continuous addition of these amendments to a luvisol derived from loess and cultivated to a cereal-root crop sequence. The total P (P_t) content of all treatments increased compared with the original soil; NaOH-inorganic P (NaOH-P_i) representing Fe- and Al-bound P was the dominant inorganic fraction. At the beginning of the experiment the various P pools could be quantitatively ranked in the following order: NaOH-P_i>residual P~NaHCO₃-P_i>H₂O-P>HCl-P. The order changed as follows: NaOH-P_i>NaHCO₃-P_i>residual P~H₂O-P>HCl-P, with transformations of non-labile residual P to the labile NaHCO₃-P_i pool with continued P fertilization and cropping. In addition, the content of organic P (P_o) forms (NaOH-P_o and NaHCO₃-P_o) increased. P_t delivery potential (desorbable P pool) increased between 35% and 185% compared to the P delivery potential in 1962. Compared to mineral fertilizer application, the application of organics resulted in a significantly higher, and FYM in a lower, P adsorption capacity of soils. The calcium lactate-extractable P (plant-available P) increased from 43.1 mg kg^-1 soil in 1962 to 175.9 mg kg^-1 soil in the treatment with 49 t compost ha^-1. The increase in the citrate-dithionate Fe-O ranged between 44% and 154% in the different treatments compared to the Fe-O content in 1962. In a pot experiment with soil from the field experiment, P removal by ryegrass was in the following sequence: FYM>compost=sewage sludge>mineral fertilizer.     

Characterization of organic matter fractions in the top layer of soils under different land uses in Central‐Eastern Europe

The objective of this study was to investigate differences in organic matter fractions, such as dissolved organic carbon and humic substances, in soils under different land uses. Soil samples were collected from the upper layer of arable lands and grasslands. Humic substances (HS) were chemically fractionated into fulvic acids (FA), humic acids (HA) and humins (HUM), and based on the separated fractions, the humification index (HI) and the degree of HS transformation (DT) were calculated. Dissolved organic carbon (DOC) was determined by cold (CWE) and hot water (HWE) extractions. Regardless of land use, the results indicated significant differences in soil organic carbon (SOC) and HS composition, with HA and HUM as the dominant fractions. Total SOC was higher in grassland (median = 17.51 g kg^?1) than arable soils (median = 9.98 g kg^?1); the HI and DT indices did not differ significantly between land uses (HI = 0.3–10.3 and DT = 0.2–6.2 for grasslands, p > 0.05; HI = 0.3–3.9 and DT = 0.2–20.1 for arable lands, p > 0.05). This indicates the relatively high stability of organic carbon and efficient humification processes in both land uses. Additionally, in arable soils lower CWE‐C (0.75 g kg^?1) and higher HWE‐C (2.59 g kg^?1) than in grasslands (CWE‐C = 1.13 g kg^?1, HWE‐C = 1.60 g kg^?1) can be related to farming practice and application of soil amendments. The results showed that both labile and humified organic matter are better protected in grassland soils and are consequently less vulnerable to mineralization.     

Spatial and temporal dynamics of land degradation and fluvial erosion in the middle and upper Yangtze River Basin,China

Land degradation in the middle and upper Yangtze has caused loss of cultivable land, sediment deposition in reservoirs and changes in the runoff: sediment yield relationships of major tributaries. The Jialin River and the Dukou-Pingshan sector of the Jingsha River together contribute over 75 per cent of all the sediment carried by the Yangtze at Yichang. As the Jialin catchment has the highest rates of erosion per unit area, high sediment discharges from that river exert a major influence on peak summer sediment discharges on the Yangtze. Even though land degradation is increasing in severity, there is no clear overall pattern or trend in variations in sediment yield since 1950. Some tributaries are affected by major reservoir construction and soil conservation works, others are not.     

珠江三角洲小流域地下水化学特征及演化规律

珠江三角洲地下水环境日益恶化,已成为制约经济社会发展的重要因素。以珠海市具有典型特征的闭合小流域作为研究对象,分旱、雨两季采集地下水分析主要离子及D、18O同位素,全面系统地研究了地下水水化学的时空变异特征与演变规律。结果表明：研究区内地下水主要受大气降水及附近地表水体渗透补给,以蒸发及地下水径流排泄,季节变化对区域内水化学空间变异性影响较小。沿地下水流方向（补给区-径流区-排泄区）,地下水化学类型主要从Ca-Na（Mg）-HCO3型向Na-Cl和Na-K-HCO3-CO3型演化,风化-溶滤、离子交换、海陆交互作用是控制当地地下水质演变的主要水文化学过程。     

鲁中山区小流域不同土地利用类型的土壤分形及水分入渗特征

为探讨坡耕地土壤入渗性能退化特征与分形机制,对鲁中山区选择典型小流域,运用土壤分形和水文学原理与方法,通过测定坡耕地、弃耕地、生态林地和经济林地4种土地利用类型的土壤分形特征与入渗性能,探讨土壤人渗速率与土壤颗粒分维及孔隙分维的定量关系。结果表明：1）不同土地利用类型土壤稳渗速率表现为坡耕地〉弃耕地〉生态林地〉经济林地,土壤颗粒分维数与孔隙分维数表现为生态林地〉经济林地〉弃耕地〉坡耕地;2）研究区土壤颗粒分维与孔隙分维数之间显著正相关,二者与土壤黏粒及粉粒体积分数显著正相关、与土壤入渗速率显著负相关;3）霍顿入渗模型和幂函数模型比较适用于拟合研究区土壤入渗过程与入渗速率,而菲利浦模型的适用性较差。因此,研究区土壤具有粗骨性砂土的物理特性,坡耕地耕作会加剧土壤中粉粒和黏粒等细粒物质流失,降低土壤颗粒分布与孔隙分布的均匀性及其分维数,导致土壤入渗性能增强但水肥保蓄性能降低。     

退耕背景下北洛河上游水沙变化分析

为探明黄土丘陵沟壑区退耕还林（草）政策的水沙响应问题,以1980--2009年期间植被重建规模较大的北洛河上游为研究区域,采用双累积曲线法和Pettit突变检验法,探讨径流输沙的变化趋势和跃变时间,同时结合气候和水土保持措施的资料,对不同时段的水沙过程进行对比分析。结果表明：1）径流量和输沙量变化可以分为2段（1980--2002年和2003--2009年）,年时间尺度上,后段较前段径流量减少0．32亿m^3、输沙量减少0．29亿t,并且后段波动较前段小;2）在月时间尺度上,2个时段的月降水量与月均流量过程基本相同,月均流量和输沙率关系基本呈现8字形,但是变幅及变率不同;3）相对于1980--2002年,2003--2009年年均降雨量、降雨侵蚀力分别减少10．06％和10．28％,降水具有减少径流和输沙的潜在条件。剔除降雨的影响,林草措施的减水和减沙效应分别为41％和81％。     

Effects of different land use types on infiltration capacity in a catchment in the highlands of Ethiopia

Infiltration capacity is an important variable for understanding and predicting a range of soil processes. This study investigated for different slope positions the effects of forest conversion to cultivation and grazing on soil infiltration capacity. Infiltration capacity was measured in the field in each land use type using a double‐ring infiltrometer. A total of 108 soil samples (3 slope positions × 3 land use types × 4 soil profiles × 3 soil depths) were collected to determine the variables that affect infiltration capacity viz. particle size distribution, organic carbon content, dry bulk density and soil moisture content. The results showed that in the cultivated and grazed land compared with forest, infiltration capacity and soil moisture content were 70 and 45% smaller respectively, and dry bulk density was 13–20% larger. Changes in soil structure caused by surface soil compaction because of tillage and animal trampling coupled with a smaller soil organic carbon content, are likely to be the principal factors causing the decline in infiltration capacity and soil moisture content after conversion of forest to cultivation and grazing.     

亚高山林草交错带不同土地利用方式下的土壤氮库和氮转化速率

Soil nitrogen pools (NP), denitrification (DN), gross nitrification (GN), N2O and CO2 flux rates with their responses to temperature increases were determined under five different land uses and managements in a subalpine forest-grassland ecotone of the eastern Tibetan Plateau. Land uses consisted of 1) sparse woodland, 2) shrub-land, 3) natural pasture, 4) fenced pasture, and 5) tilled pasture mimicking a gradient degenerating ecosystem under grazing impacts. The NO3--N content was higher than the NH4+-N content. Comparing tilled pasture with fenced pasture showed that higher intensive management (tillage) led to a significant decrease of soil organic matter (SOM) (P < 0.05) in the soils, which was in contrast to the significant increases (P < 0.05) of DN, GN, N2O and CO2 flux rates. GN (excluding tilled pasture) and CO2 flux rates increased with a temperature rise, but DN and N2O flux rates normally reached their maximum values at 12--14 oC with tilled pasture (the highest management intensity) being very sensitive to temperature increases. There was a difference between net nitrification and GN, with GN being a better indicator of soil nitrification.     

Recent land-use and soil-erosion history within a small catchment in Connemara, western Ireland: evidence from lake sediments and documentary sources

Environmental magnetism, elemental chemistry, pollen, macrofossil, and radioisotopes were studied on top-metre cores from Ballydoo Lough, Connemara, western Ireland, to reconstruct the impact of changing farming practices on soil erosion in a lake catchment. Documentary evidence, including detailed agricultural statistics, gave an independent land-use history over the period represented in the sediment record, i.e. most of the last two centuries. Maximum soil erosion, which involved unweathered coarse material as well as topsoil, was associated with a rapidly rising rural population and increased arable activity during the early 19th century. The Great Famine (1845–1847) halved the population, but arable and especially pastoral farming quickly recovered and were maintained at a high level from the late 1850s until the late 1890s. During this time, the rate of soil erosion slowed down considerably and the contribution of coarse mineral material relative to topsoil declined. Erosion of peaty soils was less important as potato cultivation declined and the middle slopes of the catchment were no longer cultivated. From the end of the 18th century to the 1970s, sediment accumulation and erosion rates were less and progressive podzolisation occurred as pastoral and particularly arable farming declined. The uppermost sediments record a sharp increase in soil erosion, involving mainly organic-rich soils from the upper slopes. This increase is attributed to a sharp rise in livestock numbers, especially sheep. A feature of the pollen record is the high arboreal pollen representation (43%–66% of total terrestrial pollen), which consists mainly of secondary pollen. It indicates a substantial input of pollen-bearing organic detritus derived from peaty soils and peat cuttings in the catchment.     

福建闽江上游不同林地类型土壤水库“库容”的特性

 以裸露地为对照,研究木荷林地、杉木林地、封山育林地的土壤水库“库容”组成及其特性,以探讨森林土壤水库的蓄水调水机制。结果表明:木荷林地、杉木林地和封山育林地土壤水库总“库容”,分别为503.95、471.62和451.48mm,分别是裸露地的1.23、1.15、1.10倍;兴利库容分别为326.87、332.21和309.94mm,分别是裸露地的1.23、1.25、1.17倍;死库容分别为114.29、89.60和101.46mm,分别是裸露地的1.11、0.87、0.99倍;防洪库容分别为62.79、49.81和40.08mm,分别是裸露地的1.52、1.21、0.97倍。最大有效库容为389.66、382.02和350.02mm,分别是裸露地的1.27、1.25、1.14倍。不同林地类型土壤水库的“库容”组成,均表现为兴利库容>死库容>防洪库容。与裸露地相比,林地土壤水库“库容”的增加,与林木生长对林地土壤结构的改良作用和林地地表的良好覆盖有关。