Sensitivity of DaisyGIS to LAI: Implications for land use based modelling of nitrate leaching

Geografisk Tidsskrift, Danish Journal of Geography 106(2): 75–85, 2006

Scaling is an important issue when measuring, modelling and understanding coupled socio-environmental terrestrial systems. Scaling may be enhanced through the incorporation of remotely sensed data. This paper assesses the sensitivity of DaisyGIS to changes in the Leaf Area Index (LAI) and discusses the implications for land use based modelling of nitrate leaching using remote sensing based LAI estimates. It is shown how DaisyGIS simulates nitrate leaching quite well over the period 2001 to 2004 except for one plot during a season with winter rape. It was found that the model is sensitive to changes in LAI with increases of up to 262% on nitrate leaching rates when reducing LAI by 15%. At the same time, the nitrate leaching rates at the field level vary considerably due to local changes in the water balance determined by soil profile characteristics. DaisyGIS is already an important tool for aiding decision makers and this study has shown how remote sensing based LAI estimates may be a valuable tool for model parameterisation and potentially for model validation.     

Evaluation of historical nitrate sources in groundwater and impact of current irrigation practices on groundwater quality

Abstract

Large-scale agricultural activities cause deterioration of groundwater resources throughout the world. This study focuses on the irrigated agricultural district of Jinghuiqu in Shaanxi, China. The objectives are to identify the main sources and processes that control nitrate transport, and to assess the impact of long-term irrigation practices on nitrate leaching. The hydrogeochemistry of major solute constituents and stable isotope ratios of NO₃ ^? in groundwater were used to identify historical sources of contamination and transformation processes occurring in the shallow groundwater of the Jinghuiqu irrigation district. The N-NO₃ ^? concentrations in groundwater ranged from 0.0 to more than 100 mg L^?1 in April 1990, and from 0.47 to 42.0 mg L^?1 in December 2009. Our measurements of N-NO₃ ^? show that the main reasons for this dramatic decline in N-NO₃ ^? concentrations from 1990 to 2009 are denitrification, which controls nitrogen types, together with the sharp decline of the groundwater table. The isotope ratios in collected samples showed that the source of nitrate was mainly manure, a result that corresponds with historical data showing that manure was the main nitrate source before the 1980s, and that fertilizers became dominant thereafter. A numerical model was then used to evaluate future impacts of current irrigation practices on groundwater sources. The HYDRUS-1D model was employed first to evaluate the water movement and the N-NO₃ ^? solute transport for a single irrigation pulse experiment carried out under field conditions, and then in evaluating the long-term impact of irrigation on N-NO₃ ^? leaching. Simulations showed that, after introducing irrigation, the downward drainage fluxes of N-NO₃ ^?, and the N-NO₃ ^? and N-tot concentrations increased at all depths within the 2-m soil profile. This indicates that N concentrations below 1-m depth and in the groundwater could become even more elevated with increased future irrigation.

Editor D. Koutsoyiannis

Citation Liu, X.-H., Sun, S.-J., Ji, P., and ?im?nek, J., 2013. Evaluation of historical nitrate sources in groundwater and impact of current irrigation practices on groundwater quality. Hydrological Sciences Journal, 58 (1), 1–15.     

富镁和贫镁坡缕石及其酸浸蚀产物的红外吸收光谱研究

本文对两个富镁和贫镁坡缕石的红外吸收光谱高频区的拟合结果表明,富镁坡缕石(p0)和贫镁坡缕石(g0)的八面体离子的配置有区别,前者除出现Mg3OH振动外,MgM2口OH振动的比例比AlM2口OH振动的大,后者则反之。经酸短时间浸蚀的和未经浸蚀的坡缕石红外吸收光谱相比,除部分吸收峰(如3560cm^-1)的峰形发生明显变化外,其余各吸收峰的峰形相似、强度稍有变化,且Siu-O-SiD的不对称振动吸收峰向低波数方向偏移、对称吸收峰向高波数方向偏移;坡缕石中790cm^-1左右的吸收峰的归属是不明确的,据实验确认它是由Siu-O-SiD的对称吸收所致;由985cm^-1、1030cm^-1、1080cm^-1和1200cm^-1左右4个吸收峰组成Si-O骨架振动吸收带的峰形、强度和峰位移反映了酸浸蚀过程中坡缕石的结构改变。两个坡缕石经360h盐酸浓度为1mol／L和3mol／L浸蚀后,所得产物的粉末X射线衍射谱虽仍具有坡缕石的衍射线,但它们的红外吸收光谱却只有与表面OH振动、物理吸附水相关的OH振动和几个SiO振动吸收峰,而无代表八面体振动、硅氧骨干中的大部分SiO振动和晶格中的结晶水的振动,说明酸对坡缕石浸蚀的最后产物是以硅氧为主。     

陶瓷杯与蒸渗仪测定硝态氮和氨态氮淋溶的比较

土壤硝态氮（NO₃^--N）和氨态氮（NH4+-N）淋溶量测定方法因草本植物和土壤类型不同而异。试验采用陶瓷杯（ceramic suction cups）和蒸渗仪（lysimeters）分别测定草地土壤NO₃^--N和NH4+-N淋溶量。蒸渗仪直径为50 cm和深度为70 cm,土壤类型分别为新西兰Gorge silt loam、Mataura sandy loam和Lismore stony silt loam,重复4次。陶瓷杯水平插入蒸渗仪不锈钢筒,陶瓷杯插孔中心离不锈钢筒底部距离分别为35 cm（上陶瓷杯）和60 cm（下陶瓷杯）。在试验前,喷灌72 h冲洗蒸渗仪土壤溶液,使淋溶液NO₃^--N浓度接近0 mg·L^-1,然后1次性施加250 kg N·hm^-2尿素溶解液,用喷灌系统喷灌蒸渗仪,每周喷灌1次,喷灌系统误差使Gorge、Mataura和Lismore土壤喷灌强度分别为15.0、19.0和18.7 mm·h^-1,1次喷灌持续时间为3 h。在Gorge和Lismore土壤,陶瓷杯和蒸渗仪测定NO₃^--N淋溶量差异显著。在Gorge土壤,上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为64、68和54 kg N·hm^-2,测定NH₄⁺-N淋溶累计量分别为0.43、0.49和0.43 kg N·hm^-2;在Mataura土壤,上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为57、68和62 kg N·hm^-2,测定NH₄⁺-N淋溶累计量分别为0.51、0.37和0.23 kg N·hm^-2;在Lismore土壤,上陶瓷杯、下陶瓷杯和蒸渗仪测定NO₃^--N淋溶累计量分别为61、103和99 kg N·hm^-2,测定NH₄⁺-N淋溶累计量分别为1.70、2.24和2.04 kg N·hm^-2。在结构发育良好的Gorge和Lismore土壤,陶瓷杯不适合测定NO₃^--N淋溶量,但适合应用于砂土质地和发育不完善Mataura土壤。NH₄⁺-N淋溶累计量占NO₃^--N淋溶累计量的0.37%～2.93%,在测定和计算氮淋溶时,NH₄⁺-N淋溶可以忽略不计。     

The influence of biotope on invertebrate assemblages in lentic environments: A study of two perennial alkaline wetlands in the Western Cape,South Africa

As a step towards the biological assessment of wetlands in South Africa, this study investigates the influence of biotope characteristics on the spatial distribution of aquatic invertebrates. The aim was to assess whether different wetland biotopes support significantly different invertebrate assemblages in terms of the composition and abundance of microcrustaceans and macroinvertebrate taxa. During October 2006, three different biotopes were sampled within Verlorenvlei and Wave's Edge wetlands (Western Cape, South Africa) using a long-handled sweep net. Composition and abundance of invertebrate assemblages were compared between and within sites for each of the wetlands. Assemblage composition generally differed among biotopes within each wetland, as revealed by cluster analysis and MDS plots. At Verlorenvlei, biotopes formed distinctive clusters with low site-specific variability. Assemblage composition at Wave's Edge revealed coarser groupings with clusters distinguishing between vegetated and non-vegetated biotopes only. Biotopes within each wetland differed significantly in terms of taxon richness, Shannon diversity and mean total invertebrate biomass (g m⁻³), whilst mean total density (ind m⁻³) differed only between biotopes in Verlorenvlei. Considerable shifts in invertebrate assemblage structure corresponded to differences in electrical conductivity among sites at Verlorenvlei. For large physico-chemically heterogeneous wetlands such as Verlorenvlei, it is suggested that smaller physico-chemically homogenous zones should be identified a priori and within these areas vegetated biotopes should be sampled over the broadest possible spatial scale, whilst open-water biotopes can be sampled more narrowly. For small, reasonably homogenous wetlands such as Wave's Edge, we suggest a less broad spatial representation of biotopes and instead one should concentrate on increasing the number of sample repetitions per site.     

硫酸钾镁肥浮选尾矿热浸-冷结晶法提取七水硫酸镁工艺研究

以国投新疆罗布泊钾盐有限责任公司(简称国投罗钾)提供的硫酸钾镁肥浮选尾矿和氯化镁饱和卤水为原料,探索出了一条以硫酸钾镁肥浮选尾矿为原料,以氯化镁饱和溶液为浸取介质,通过中温溶浸、冷却结晶(包括盐田冷析)等工艺方法制取七水硫酸镁的工艺路线,给出了各工序的工艺技术条件及主要技术指标。     

Potassium leaching in undisturbed soil cores following surface applications of gypsum

Displacement studies on leaching of potassium (K⁺) were conducted under unsaturated steady state flow conditions in nine undisturbed soil columns (15.5 cm in diameter and 25 cm long). Pulses of K⁺ applied to columns of undisturbed soil were leached with distilled water or calcium chloride (CaCl₂) at a rate of 18 mm h⁻¹. The movement of K⁺ in gypsum treated soil leached with distilled water was at a similar rate to that of the untreated soil leached with 15 mM CaCl₂. The Ca²⁺ concentrations in the leachates were about 15 mM, the expected values for the dissolution of the gypsum. When applied K⁺ was displaced with the distilled water, K⁺ was retained in the top 10–12.5 cm depth of soil. In the undisturbed soil cores there is possibility of preferential flow and lack of K⁺ sorption. The application of gypsum and CaCl₂ in the reclamation of sodic soils would be expected to leach K⁺ from soils. It can also be concluded that the use of sources of water for irrigation which have a high Ca²⁺ concentration can also lead to leaching of K⁺ from soil. Average effluent concentration of K⁺ during leaching period was 30.2 and 28.6 mg l⁻¹ for the gypsum and CaCl₂ treated soils, respectively. These concentrations are greater than the recommended guideline of the World Health Organisation (12 mg K⁺ l⁻¹).     

云南广南某金矿浸出工艺试验研究

阐述云南广南某金矿矿石矿物成分、化学成分基础上,对该金矿矿石进行了全泥氰化试验和柱浸试验可行性研究。实验研究表明：A样柱浸尾渣金品位为0．06g／t,渣计金浸出率为91．9％,氰化钠耗量为255g／t;B样柱浸尾渣金品位为0.06g／t,渣计金浸出率为909％,氰化钠耗量为310g／t,试验结果证明该矿样为易浸矿石,试验为下步现场试验提供了技术依据.     

酸法地浸采铀中信息参数的判断及其应用

介绍了酸法地浸采铀工艺信息技术的显示,在长期生产和科研实践的基础上,总结归纳了酸法地浸采铀工艺的基本信息技术,以及如何利用这些信息对地浸开采实现有效的判断和调控,这些内容是地浸工作者必备和需要掌握的重要开采技术和手段。     

Rare earth element and strontium isotope geochemistry in Dujiali Lake,central Qinghai-Tibet Plateau,China: Implications for the origin of hydromagnesite deposits

Rare earth element (REE) and strontium isotope data (⁸⁷Sr/⁸⁶Sr) are presented for hydromagnesite and surface waters that were collected from Dujiali Lake in central Qinghai-Tibet Plateau (QTP), China. The goal of this study is to constrain the solute sources of hydromagnesite deposits in Dujiali Lake. All lake waters from the area exhibit a slight LREE enrichment (average [La/Sm]_PAAS = 1.36), clear Eu anomalies (average [Eu/Eu*]_PAAS = 1.31), and nearly no Ce anomalies. The recharge waters show a flat pattern (average [La/Sm]_PAAS = 1.007), clear Eu anomalies (average [Eu/Eu*] _PAAS = 1.83), and nearly no Ce anomalies (average [Ce/Ce*]_PAAS = 1.016). The REE+Y data of the surface waters indicate the dissolution of ultramafic rock at depth and change in the hydrogeochemical characteristics through fluid-rock interaction. These data also indicate a significant contribution of paleo-groundwater to the formation of hydromagnesite, which most likely acquired REE and Sr signatures from the interaction with ultramafic rocks. The ⁸⁷Sr/⁸⁶Sr data provide additional insight into the geochemical evolution of waters of the Dujiali Lake indicating that the source of Sr in the hydromagnesite does not directly derive from surface water and may have been influenced by both Mg-rich hydrothermal fluids and meteoric water. Additionally, speciation modeling predicts that carbonate complexes are the most abundant dissolved REE species in surface water. This study provides new insights into the origins of hydromagnesite deposits in Dujiali Lake, and contributes to the understanding of hydromagnesite formation in similar modern and ancient environments on Earth.