Contributions of groundwater conditions to soil and water salinization

 Salinization is the process whereby the concentration of dissolved salts in water and soil is increased due to natural or human-induced processes. Water is lost through one or any combination of four main mechanisms: evaporation, evapotranspiration, hydrolysis, and leakage between aquifers. Salinity increases from catchment divides to the valley floors and in the direction of groundwater flow. Salinization is explained by two main chemical models developed by the authors: weathering and deposition. These models are in agreement with the weathering and depositional geological processes that have formed soils and overburden in the catchments. Five soil-change processes in arid and semi-arid climates are associated with waterlogging and water. In all represented cases, groundwater is the main geological agent for transmitting, accumulating, and discharging salt. At a small catchment scale in South and Western Australia, water is lost through evapotranspiration and hydrolysis. Saline groundwater flows along the beds of the streams and is accumulated in paleochannels, which act as a salt repository, and finally discharges in lakes, where most of the saline groundwater is concentrated. In the hummocky terrains of the Northern Great Plains Region, Canada and USA, the localized recharge and discharge scenarios cause salinization to occur mainly in depressions, in conjunction with the formation of saline soils and seepages. On a regional scale within closed basins, this process can create playas or saline lakes. In the continental aquifers of the rift basins of Sudan, salinity increases along the groundwater flow path and forms a saline zone at the distal end. The saline zone in each rift forms a closed ridge, which coincides with the closed trough of the groundwater-level map. The saline body or bodies were formed by evaporation coupled with alkaline-earth carbonate precipitation and dissolution of capillary salts. Received, May 1998 · Revised, July 1998 · Accepted, September 1998     

Soil salinization and critical shallow groundwater depth under saline irrigation condition in a Saharan irrigated land

In the arid irrigated lands, understanding the impact of shallow groundwater fluctuation on soil salinization has become crucial. Thus, investigation of the possible options for maintaining the groundwater depth for improving land productivity is of great importance. In this study, under saline irrigation condition, the effects of shallow groundwater depth on water and salt dynamics in the root-zone of date palms were analyzed through a particular field and modeling (SWAP) investigation in a Tunisian Saharan oasis (Dergine Oasis). The model was calibrated and validated against the measured soil water content through the date palm root-zone. The good agreement between measured and estimated soil water content demonstrated that the SWAP model is an effective tool to accurately simulate the water and salt dynamics in the root-zone of date palm. Multiple groundwater depth scenarios were performed, using the calibrated SWAP model, to achieve the optimal groundwater depth. The simulation results revealed that the shallow groundwater with a depth of ~80 cm coupled with frequent irrigation (20 days interval) during the summer season is the best practice to maintain the adequate soil water content (>0.035 (cm³ cm^?3) and safe salinity level (<4 dS m^?1) in the root-zone layer. The results of field investigation and numerical simulation in the present study can lead to a better management of lands with shallow water table in the Saharan irrigated areas.     

唐山曹妃甸浅层地下水水化学特征及咸化成因

为了查明曹妃甸浅层地下水水化学及咸化成因,采集研究区河水、地下淡水、微咸水、咸水、卤水、雨水和海水等不同类型水样,对其水化学组成、离子比、Piper三线图、吉布斯图、氢氧同位素组成及14C测年结果进行了分析。结果表明：(1)曹妃甸浅层地下水包括全新世沉积层潜水和晚更新世沉积层微承压水,且非原始封存在地层中而是形成于全新世中晚期。(2)地下潜水向海方向分布有淡水、微咸水、咸水水质类型,微承压水以咸水和卤水为主要水质类型;近冲洪积扇前缘水化学特征主要受岩石风化作用控制,围填海区及河口处水化学特征受海水混合作用控制,滨海平原区水化学特征主要受蒸发/结晶作用控制。(3)曹妃甸浅层地下水咸化过程主要是晚更新世以来海侵海退时期形成海洋蒸发盐经大气降水和河水多期溶滤所致,其盐分来源于海水蒸发盐,河口及围填海区地下潜水盐分主要来源于现代海水入侵。     

干旱区地下水咸化机制的区域氘盈余解析

定量研究干旱区地下水的咸化机制对于水资源管理具有重要意义。针对已有研究需要考虑补给源水δ18O和δ2H值的局限,提出了一种利用区域氘盈余计算初始水、蒸发和溶滤对地下水咸化贡献的方法,并以罗山地区第四系地下水为例进行了分析。结果表明:该方法计算误差较小,可以有效区分蒸发和溶滤的贡献。地下水先溶滤后蒸发的自然咸化过程决定了溶滤作用的主导地位,咸化规模主要取决于溶滤作用程度。     

中国北方-蒙古干旱半干旱区土壤铵态氮的分布及其环境控制因素

土壤铵态氮是植物所能直接吸收利用的矿化氮中的重要组成部分,其含量的变化涉及到氮循环中众多生物过程,是氮生物地球化学过程中的中间环节。影响土壤中铵态氮含量的因素众多,但究竟何种因素是其变化的主因,一直没有定论。中东亚地区的植被、土壤、气候梯度性变化明显,为研究土壤铵态氮含量与环境因子之间的关系提供了理想的研究场所。对一条穿越多个植被、土壤、气候带样带的表土分析结果表明,表土中铵态氮与该地区5-9月平均温度具有显著的线性关系,但与降水量关系不大;同时表土铵态氮含量与土壤pH值也具有显著的线性关系。说明该地区温度和土壤pH值的变化是影响表土铵态氮变化的重要因素,而降水量对土壤铵态氮含量具有短促的、脉冲式的影响。     

GIS-based evaluation of groundwater quality and estimation of soil salinization and land degradation risks in an arid Mediterranean site (SW Tunisia)

Arabian Journal of Geosciences - The present work is concerned with the valorization of clay minerals of the Aleg formation (Coniacian-middle Campanian) in the clinker manufacturing. The studied...     

黄河三角洲浅层地下水盐分来源及咸化过程研究

黄河三角洲地下水咸化已成为区域最突出的生态环境问题之一。识别地下水补给及盐分来源是有效控制和改善地下水咸化问题的关键。本研究采集了研究区浅层地下水、地表水和海水等不同类型水样,利用离子比、Piper三线图、吉布斯图等方法对八大离子浓度、δD和δ¹⁸O 组成、Br和Sr 浓度等进行地下水补给研究与盐分来源辨析。结果表明:(1)黄河三角洲浅层地下水以总溶解性固体(TDS)为338 g/L的咸水为主,地下水水化学类型较为单一,主要为Cl-Na型。(2)三角洲区域地下水以大气降水补给为主,并且在补给过程中经历了不同程度的蒸发作用的影响,黄河现行流路区域地下水主要来源于河水侧渗补给,但浅层地下水含水层水平渗透性较差限制了黄河侧渗补给范围。(3)海洋是黄河三角洲浅层地下水盐分的主要来源,黄河现行流路区域及近岸地下水盐分来源于海水混合,三角洲北部刁口河等古河道区域地下水盐分主要来源于海相蒸发盐淋滤溶解。     

Combined gamma and M-test-based ANN and ARIMA models for groundwater fluctuation forecasting in semiarid regions

The shortage of surface water in arid and semiarid regions has led to the more use of the groundwater resources. In these areas, the groundwater is essential for activities such as water supply and irrigation. One of the most important stages in sustainable yield of groundwater resources is awareness of groundwater level. In this study, we have applied artificial neural networks (ANN) and autoregressive integrated moving average (ARIMA) models for groundwater level forecasting to 4 months ahead in Shiraz basin, southwestern Iran. Time series analysis was conducted according to the Box–Jenkins method. Meanwhile, gamma and M-test were considered for determining the optimal input combination and length of training and testing data in the ANN model. The results indicated that performance of multilayer perceptron neural network (4, 14, 1) and ARIMA (2, 1, 2) is satisfactory in the groundwater level forecasting for one month ahead. The performance comparison shows that the ARIMA model performs appreciably better than the ANN.     

Contribution of geophysical surveys to groundwater modelling of a porous aquifer in semiarid Niger: An overview

Subsurface geophysical surveys were carried out using a large range of methods in an unconfined sandstone aquifer in semiarid south-western Niger for improving both the conceptual model of water flow through the unsaturated zone and the parameterization of numerical a groundwater model of the aquifer. Methods included: electromagnetic mapping, electrical resistivity tomography (ERT), resistivity logging, time domain electromagnetic sounding (TDEM), and magnetic resonance sounding (MRS). Analyses of electrical conductivities, complemented by geochemical measurements, allowed us to identify preferential pathways for infiltration and drainage beneath gullies and alluvial fans. The mean water content estimated by MRS (13%) was used for computing the regional groundwater recharge from long-term change in the water table. The ranges in permeability and water content obtained with MRS allowed a reduction of the degree of freedom of aquifer parameters used in groundwater modelling.     

A catchment water balance model for estimating groundwater recharge in arid and semiarid regions of south-east Iran

This paper presents a new model of the rainfall-runoff-groundwater flow processes applicable to semiarid and arid catchments in south-east Iran. The main purpose of the model is to assess the groundwater recharge to aquifers in these catchments. The model takes into account main recharge mechanisms in the region, including subsurface flow in the valley alluvium in mountainous areas and recharge from the bed of ephemeral rivers. It deals with the effects of spatial variation in the hydrological processes by dividing the catchment into regions of broad hydrologic similarity named as highland, intermediate and aquifer areas. The model is based on the concept of routing precipitation within and through the catchment. The model has been applied to the Zahedan catchment and the results indicate that the groundwater level estimated by the recharge model generally is in agreement with the behaviour of groundwater levels in observation wells. The sensitivity analysis indicates that when the rainfall in the aquifer area is used to replace the values recorded in the intermediate area and the highland area, the recharge estimates are reduced by 42-87%. This result supports the division of the catchment into different zones of hydrological similarity to account for spatial variability of hydrological processes. Electronic Publication     

An approach to the ecological characterization of arid and semiarid basins

A morphometric study of 61 sub-basins of the River Segura basin (SE Spain) enables us to attribute ecological processes in streams of these arid and semiarid watersheds to altered patterns of discharge resulting from human activity. Methods used are compared to other, commonly used limnological indexes.     

地下水浅埋区土壤水分运动参数田间测定方法探讨

研究ＧＳＰＡＣ系统的水分运移机理和建立统一的水系统模型需要确定土壤水分运动参数,本文根据田间土壤排水试验的观测数据,初步探讨了地下水浅埋区土壤水分运动参数的确定方法。该方法将多维问题最优化技术与土壤水运动方程数值求解技术相结合,寻求田间条件下最优的土壤水分运动参数,克服了室内试验方法的不足。田间土壤排水试验无须特殊的试验设备和试验条件,具有较强的可操作性。     

电磁感应方法在土壤盐渍化评价中的应用研究

本文应用电磁感应方法(大地电导率探测仪EM38),对新疆焉耆盆地的土壤电导率进行了测量,分析了电磁感应方法所得结果和土样分析结果之间的相关关系,证实了电磁感应方法的有效性.基于电磁感应方法测量的结果,对新疆焉耆盆地土壤盐渍化进行了定性评价.结果表明,在开都河上游,土壤盐渍化程度普遍较轻;在中游地带,灌区内的土壤盐渍化改良取得了一定的成效,土壤中的含盐量较低,但是在远离河谷的非灌区,土壤含盐量依然很高;在下游及靠近博斯腾湖的地区,土壤含盐量普遍较高,并有随深度增加而增加的趋势.     

ASTER遥感影像数据在土壤盐渍化评价中的应用

本文通过运用ASTER遥感影像数据,对不同地物进行光谱分析,根据不同地物在不同波段的光谱特征曲线,分别提取植被和水体信息,然后进行非监督分类.并结合物探试验和土样分析结果,进行聚类分析,定性和定量的评价了焉耆盆地内土壤盐渍化程度分布状况.评价结果为:在焉耆盆地的平原区内,非盐渍化土壤,457.65km2;轻度盐渍化土壤,335.61 km2;中度～重度盐渍化土壤,580.93 km2;盐土,41.11 km2.根据野外实际调查,评价结果的精度达到了85%以上.     

Simulation of temporal variation for reference evapotranspiration under arid climate

Interpretation of 2500 km of newly processed 2D seismic and regional potential field data has led to the identification of two new Miocene–Oligocene sedimentary basins in the northern part of offshore Egypt. The western part of the basin is deeper and has thick sedimentary cover. The upper part of the Miocene section is tested in its southern part through two wells, where the eastern subbasin is still virgin and is located at the intersection between Temsah basins and southeastern end of the Levantine basin. The main sedimentary unit of the basin is the Miocene–Oligocene sedimentary section, which was proven by the exploration and production activities in Nile Delta to be one of the hydrocarbon-generating facies. This fact is supported by 1D basin analysis using the average parameter values, which shows a hydrocarbon window, extending from lower Miocene to upper Miocene. The basin dimensions are more than 2000 km² area and more than 4000 m of thickness, with variable petroleum system parameters’ potentialities, starting from Tortonian–Serravallian to lower Oligocene section.

     

Modelling the response of shallow groundwater levels to combined climate and water-diversion scenarios in Beijing-Tianjin-Hebei Plain,China

A three-dimensional groundwater flow model was implemented to quantify the temporal variation of shallow groundwater levels in response to combined climate and water-diversion scenarios over the next 40 years (2011–2050) in Beijing-Tianjin-Hebei (Jing-Jin-Ji) Plain, China. Groundwater plays a key role in the water supply, but the Jing-Jin-Ji Plain is facing a water crisis. Groundwater levels have declined continuously over the last five decades (1961–2010) due to extensive pumping and climate change, which has resulted in decreased recharge. The implementation of the South-to-North Water Diversion Project (SNWDP) will provide an opportunity to restore the groundwater resources. The response of groundwater levels to combined climate and water-diversion scenarios has been quantified using a groundwater flow model. The impacts of climate change were based on the World Climate Research Programme’s (WCRP’s) Coupled Model Intercomparison Project phase 3 (CMIP3) multi-model dataset for future high (A2), medium (A1B), and low (B1) greenhouse gas scenarios; precipitation data from CMIP3 were applied in the model. The results show that climate change will slow the rate of decrease of the shallow groundwater levels under three climate-change scenarios over the next 40 years compared to the baseline scenario; however, the shallow groundwater levels will rise significantly (maximum of 6.71 m) when considering scenarios that combine climate change and restrictions on groundwater exploitation. Restrictions on groundwater exploitation for water resource management are imperative to control the decline of levels in the Jing-Jin-Ji area.