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Groundwater is a critical resource in remote and isolated islands where rainfall hardly provides a continuous and even water supply. In this paper, in a very rare and uncommonly found artificial aquifer on Miyako Island, far away from the main continent of Japan, with limited experimental results of evaluations of crop water requirement, MODIS ET together with crop ETc estimated from Kc coefficient from the nearest island were compared to determine the reliability of the MODIS ET and FAO-56-based ETc value. The testified Kc approach for sugarcane ET was used to assess the risk of irrigation water shortages using historical metrological data and to predict the future risk of irrigation agriculture under different scenarios of GCM models. It was shown that FAO-56-based ETc and MOD16A2 were both applicable for crop evapotranspiration on the island. Then, the response of groundwater storage to gross irrigation water requirement was analyzed to clarify the effect of irrigation on groundwater storage and the risk of groundwater depletion under current and future climatic conditions. Results showed that the construction of the dam efficiently secured the irrigation of sugarcane. Using historical climatic data (1951–2021), the influence of estimated irrigation water requirements on groundwater showed that in 296 out of 852 months, irrigation was heavily required. Over a 71 year period, there was absolutely no water for irrigation four times, or nearly once every 18 years. Under the future projected climate from four bias-corrected GCM models with two emission scenarios (2022–2100), the risk of groundwater depletion both in terms of frequency and duration will increase. Therefore, there is a need for either improvement of irrigation water management or additional construction of artificial aquifers on the island. The study proved the value of ET derived from remote sensing in areas lacking the support of experimental results. The methodology developed in the study can be potentially used to evaluate long-term irrigation demand and groundwater management over dry periods for engineering design or dam construction globally.

A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00–0.20 ± 0.01 mg N l−1), whereas other factors did not vary significantly. NO3−-N and urea-N concentrations were higher than the NH4+-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO3−-N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p

Knowledge about the primary factor controlling stable isotope ratios of particulate nitrogen (δ15NPN) and total dissolved nitrogen (δ15NTDN) in a subtropical reservoir can improve the understanding of regional and global nitrogen cycles. Taking Lianhe Reservoir as a representative subtropical reservoir, we studied the spatial and temporal distributions of δ15NPN andδ15NTDN and their relationships with the surrounding physicochemical factors and phytoplankton. The results showed that variations in δ15NPN and δ15NTDN followed seasonal thermal cycles. The values of δ15NTDN were inversely proportional to those of δ15NPN. PCA showed that phytoplankton cell density and pH were the primary drivers of the variation of δ15NPN (45.2%). The primary factors influencing δ15NTDN were Chl a and phytoplankton cell density, which both indicated phytoplankton biomass. We also determined that the dominant species was Microcystis densa during the thermal stratification period and Staurodesmus aristiferus during the mixing period. Laboratory experiments showed that δ15NPN values in both M. densa (from 19.5 to 14.6‰) and S. aristiferus (from 19.4 to 16.0 ‰) media decreased significantly as the algal cells grew. Furthermore, the δ15NTDN values increased from 4.9 to 7.9‰ and from 4.7 to 6.9‰ in M. densa and S. aristiferus media, respectively, when the δ15NPN values decreased. These experimental results were consistent with field investigation results and indicated that variations in δ15NPN and δ15NTDN were mainly controlled by phytoplankton cell density, especially the cell density of the dominant species, in both the thermal stratification and mixing periods. The results also suggested that cell density, not phytoplankton species, was the key factor regulating the distribution of nitrogen stable isotopes. These results together indicated that phytoplankton cell density is the primary factor in the regulation of nitrogen stable isotope composition and that its influence is greater than that of other physical and chemical factors. This study provided detailed information supporting the primary role of phytoplankton in the nitrogen geochemical cycle and improved the understanding of biochemical processes in natural subtropical reservoirs.

An analysis of the stable isotopes and the major ions in the surface water and groundwater in the Leizhou Peninsula was performed to identify the sources and recharge mechanisms of the groundwater. In this study, 70 water samples were collected from rivers, a lake, and pumping wells. The surface water was considered to have a lower salinity than the groundwater in the region of study. The regression equations for δD and δ18O for the surface water and the groundwater are similar to those for precipitation, indicating meteoric origins. The δD and δ18O levels in the groundwater ranged from −60‰; to −25‰; and −8.6‰; to −2.5‰, respectively, and were lower than the stable isotope levels from the winter and spring precipitation. The groundwater in the southern area was classified as the Ca2+-Mg2+-HCO3--type, whereas the groundwater in the northern area included three types (Na+-Cl−-type, Ca2+-Mg2+-HCO3--type, and Ca2+-Mg2+-Cl−-type), indicating rapid and frequent water-rock exchange in the region. A reasonable conclusion is that the groundwater chemistry is dominated by rock weathering and rainwater of local origin, which are influenced by seawater carried by the Asian monsoon.

Microcystis blooms occur frequently in subtropical lakes and reservoirs and cause serious ecological and economic losses. A novel Microcystis bloom caused by Microcystis densa has broken out in many reservoirs in South China. In order to control M. densa bloom, it is important to predict the growth of M. densa, which is influenced by the synergistic uptake and assimilation of nitrogen and phosphorus. Therefore, it is necessary to develop a model of the response of Microcystis growth to nitrogen and phosphorus concentrations. Our study focused on both nitrogen and phosphorus, and studied their synergetic effect on M. densa growth. The growth kinetics, including the maximum specific growth rates and the half-saturation constant of M. densa for both nitrogen and phosphorus, were also determined. A modified model with Monod kinetics was developed to explain the synergistic effects of nitrogen and phosphorus on M. densa growth. The specific growth rate of M. densa can be predicted by nitrogen and phosphorus concentrations. This modified model was verified by the actual measures of the Lianhe Reservoir and Liuxihe Reservoir. It could relatively accurately predict the growth level of M. densa and helped for the daily monitoring of reservoir management for M. densa growth. [ABSTRACT FROM AUTHOR]

The study provides the major ion chemistry, chemical weathering rates and temporary and net CO2 sinks in the Beijiang River, which was characterized as hyperactive region with high chemical weathering rates, carbonate and silicate mixing lithology and abundant sulfuric acid chemical weathering agent with acid deposition and AMD origins. The total chemical weathering rate of 85.46 t km-2 a-1 was comparable to other rivers in the hyperactive zones between the latitude 0-30°. Carbonate weathering rates of 61.15 t km-2 a-1 contributed to about 70 % of the total. The lithology, runoff and geomorphology had significant influence on the chemical weathering rate. The proportion of carbonate outcrops had significant positive correlation with the chemical weathering rate. Due to the interaction between dilution and compensation effect, significant positive linear relationship was detected between runoff and total, carbonate and silicate weathering rates. The geomorphology factors such as catchment area, average slope and hypsometric integral value (HI) had non-linear correlation on chemical weathering rate and showed significant scale effect, which revealed the complexity in chemical weathering processes. DIC-apportionment showed that CCW (Carbonate weathering by CO2) was the dominant origin of DIC (35 %-87 %) and that SCW (Carbonate weathering by H2SO4) (3 %-15 %) and CSW (Silicate weathering by CO2) (7 %-59 %) were non-negligible processes. The temporary CO2 sink was 823.41 10³ mol km-2 a-1. Compared with the "temporary" sink, the net sink of CO2 for the Beijiang River was approximately 23.18 x 10³ mol km-2 a-1 of CO2 and was about 2.82 % of the "temporary" CO2 sink. Human activities (sulfur acid deposition and AMD) dramatically decreased the CO2 net sink and even make chemical weathering a CO2 source to the atmosphere. [ABSTRACT FROM AUTHOR]

The nitrogen aspects of hydrological processes must be determined to identify nitrogen sources and relevant mechanisms. Landfills are the dominant disposal approach to deal with solid waste in urban areas in China. Landfills require adequate land and pose a potential threat to aquifer contamination, particularly in the humid zone, such as Guangzhou. The unlined Likeng landfill in Guangzhou was investigated in three campaigns during the period 2001-2007: water was sampled and analyzed for major ions, heavy metals, and stable isotopes of 18O and ²H in water, and 18O and 15N in nitrate. Contamination sources, water components, and groundwater flow were examined, revealing a mixture of various sources from landfill effluent, septic tank leakage, fertilizer, and manure following complex processes of recharge, mixing, and denitrification. The effluent from the landfill was rich in Na+, Ca2+, K+, HCO3-, and Cl- ions. A similar process of high NH4+ in effluent resulting in episodic increases in NO3- because of NH4+ oxidation was found in Likeng landfill when compared with landfills in Denmark and the USA. Twenty-five percent of the precipitation was lost to evaporation before recharging the aquifer, indicating a possible maximum recharge rate of 75% and the potential for a large amount of water penetration to the landfill if not well constructed. Apparent groundwater flow velocity of 3.7 x 10-7 m s-1 (11.67 m/a) was found for the front of the effluent under the landfill by considering the vertical and horizontal flow. These findings provide background to delineate the plume from Likeng landfill and to conceptualize the natural attenuation processes of other toxic compounds, which are imperative for any remediation strategy. [ABSTRACT FROM AUTHOR]

In this study, an approach is put forward to study the relationship between changing land use and groundwater nitrate contamination in the Sanjiang Plain. This approach emphasizes the importance of groundwater residence time when relating the nitrates to the changing land use. The principles underlying the approach involve the assessment of groundwater residence time by CFCs and the Vogel age model and the reconstruction of the land use at the groundwater recharge time by interpolation. Nitrate trend analysis shows that nitrates have begun to leach into the aquifers since agricultural activities boomed after the 1950s. Hydrochemical analysis implies that the possible process relating to the nitrate reduction in the groundwater is the oxidation of Fe(II)-silicates. However, the chemical kinetics of the oxidation of Fe(II)-silicates is slow, so this denitrification process contributes little to the nitrate variations. Stepwise regression shows that the nitrate concentrations of samples had no direct relationship with the land use at the groundwater sampling time, but had a relatively strong relationship with the land use at the groundwater recharge time. Dry land is recognized as the dominant factor contributing to the elevated concentration of nitrates. The nitrogen isotope for nitrate (δ15N-NO3) gives a more direct result of the identification of nitrate sources: the use of manure in agricultural activities. Principle component (PC) regression shows that the process of the dry land exploitation is the major process that controls the nitrate contamination in the Sanjiang Plain. [ABSTRACT FROM AUTHOR]

In order to understand the distribution and behavior of selected endocrine-disrupting chemicals (EDCs) in the Pearl River Delta, China, the concentrations of EDCs in water and suspended solid of rivers were quantified in agricultural, urban, and industrial zones of Dongguan watershed by GCIMS. In the last two zones, the concentration of EDCs in river ranged from 177 to 796 ng/L, from 17291to 90808 ng/L and from 10 to 56322 ngfL for octylphenol (OP), nonylphenol (NP) and bisphenol A (BPA), respectively. It was found the NP/OP ratio in waters was above 20. BPA/OP in water was less than 1 in industrial zone, above 1 in urban zone and more than 30 in the Pearl River, respectively. Also, the NP/OP ratio in suspended solid varied from 6 to 90 with a few changes for BPA/OP ratio. Finally, the risk assessment of EDCs in rivers demonstrated that almost all river reaches in the watershed could produce 50% level effect on the freshwater fish. [ABSTRACT FROM AUTHOR]

This study combined bacterial incubation and hydrogeochemical methods to investigate denitrification in the surface water, top soil (0-20 cm), and shallow groundwater of the Ochi wetland in Japan. Surface water was rich in nitrate (40 mg/l) and denitrifying bacteria (700 per ml). Three functional zones in the wetland were identified in the top soil and shallow groundwater. In the upstream portion of the wetland (Zone I), the counts of denitrifying bacteria in top soil increased from 5200 to 14 970 per ml and nitrate decreased from 25∙4 to 1∙8 mg/l. Organic carbon concentrations decreased as sulfate increased from 4∙0 to 9∙6 mg/l in this zone. In the middle-stream of the wetland (Zone II), all concentrations of major anions, iron, organic carbon, and total nitrogen content in top soil were relatively constant, but the counts of denitrifying bacteria increased up to 70 200 per ml. In the downstream portion of the wetland (Zone III), complete removal of nitrate resulted in sharp reduction of counts of denitrifying bacteria. Correspondingly, dissolved oxygen (DO), organic carbon, and total nitrogen increased in this zone. Counts of denitrifying bacteria were lower in shallow groundwater than in top soil; nitrate concentrations in shallow groundwater were also very low in this zone. DO and the oxidation/reduction potential data suggest that groundwater flows to the surface along an extended flow path, thus providing nitrate for the denitrifying community. [ABSTRACT FROM AUTHOR]

The article discusses the importance of understanding hydrogeochemistry to study the water quality of karst water in southwest China. It notes that the groundwater is the significant water source for irrigation and drinking purposes in the region. In this regard, a study is conducted in surface water and groundwater to determine the geochemical processes that affect the quality of water in Gaoping karst basin in the country.

Precipitation has been recognized as one of the most important sources of groundwater recharge in the piedmont region of Taihang Mountain, North China Plain. However, a number of recent studies suggest the possibility of precipitation recharge in this region. This is because evapotranspiration from the intensive irrigated farming is several orders of magnitude of the annual precipitation. To reappraise potential precipitation recharge in the region, observed changes in seasonal groundwater storage and soil moisture of three soil core samples (each exceeding 10m deep) from a large soil-probe machine were analysed. Our analysis showed that groundwater storage in the winter/dry season (in the piedmont region) is influenced mainly by lateral recharge and the amount of precipitation in the preceding year. In the summer/rainy seasons, groundwater storage differs with precipitation year. With the exception of extraordinary rainstorm years (e.g. 1996 after the storm with 30 year return period), precipitation recharge is not apparent. Soil field capacity analysis also revealed a possibility of precipitation recharge, with a wide margin between actual soil moisture and soil moisture content at field capacity. Precipitation recharge is only feasible when a single or successive precipitation is in excess of the minima (170 mm), a very rare condition in the piedmont region, where precipitation is easily depleted by the water-scavenging field crops, which cover two-thirds of the total land area. [ABSTRACT FROM AUTHOR]

Abstract  The groundwater flow system and the flow velocity in the alluvial fan plain of the Hutuo River, China, have been studied, with an emphasis on relating geochemical characteristics and isotopes factors. Seven stretches of one river, six springs and 31 wells, with depths ranging from 0 m (river waters) to 150 m, were surveyed. The groundwater has a vertical two-layer structure with a boundary at about 80–100 m depth, yielding an upper and a lower groundwater layer. The δ18O and δD values range from −10.56 to −7.05‰ and −81.83 to −59‰, respectively. The groundwater has been recharged by precipitation, and has not been subjected to significant evaporation during infiltration into the aquifer in the upper layer. Using a tritium model, the groundwater flow in the alluvial fan plain showed horizontal flow velocity to be greater than vertical velocity. Groundwater in the upper layer is characterized by Ca–HCO3 type. From the spatial distribution characteristics of the stable isotope and chemical composition of the groundwater, agricultural irrigation was considered to have an influence on the aquifer by causing excessive groundwater abstraction and irrigation return. [ABSTRACT FROM AUTHOR]

Many cities around the world are developed at alluvial fans. With economic and industrial development and increase in population, quality and quantity of groundwater are often damaged by over-exploitation in these areas. In order to realistically assess these groundwater resources and their sustainability, it is vital to understand the recharge sources and hydrogeochemical evolution of groundwater in alluvial fans. In March 2006, groundwater and surface water were sampled for major element analysis and stable isotope (oxygen-18 and deuterium) compositions in Xinxiang, which is located at a complex alluvial fan system composed of a mountainous area, Taihang Mt. alluvial fan and Yellow River alluvial fan. In the Taihang mountainous area, the groundwater was recharged by precipitation and was characterized by Ca–HCO3 type water with depleted δ18O and δD (mean value of −8.8‰ δ18O). Along the flow path from the mountainous area to Taihang Mt. alluvial fan, the groundwater became geochemically complex (Ca–Na–Mg–HCO3–Cl–SO4 type), and heavier δ18O and δD were observed (around −8‰ δ18O). Before the surface water with mean δ18O of −8.7‰ recharged to groundwater, it underwent isotopic enrichment in Taihang Mt. alluvial fan. Chemical mixture and ion exchange are expected to be responsible for the chemical evolution of groundwater in Yellow River alluvial fan. Transferred water from the Yellow River is the main source of the groundwater in the Yellow River alluvial fan in the south of the study area, and stable isotopic compositions of the groundwater (mean value of −8.8‰ δ18O) were similar to those of transferred water (−8.9‰), increasing from the southern boundary of the study area to the distal end of the fan. The groundwater underwent chemical evolution from Ca–HCO3, Na–HCO3, to Na–SO4. A conceptual model, integrating stiff diagrams, is used to describe the spatial variation of recharge sources, chemical evolution, and groundwater flow paths in the complex alluvial fan aquifer system. [ABSTRACT FROM AUTHOR]

This article discusses the pollution of drinking water by the contamination of groundwater from leaking septic tanks in the Pearl River Delta of China. The authors used isotopic and geochemical characteristics of groundwater in Fengcun, China to show the anthropogenic impacts of urbanization in the region. They concluded that the nitrates were from septic tank point sources rather than regional nitrification and ammonification. They recommend that in the Pearl River Delta groundwater protection should be strengthened in rural areas.

Resumen Contaminacon de nitratos a causa de prcticas agrcolas en diferentes zonas hidrogeolgicas del sistema de flujo regional de aguas subterrneas en la planice del norte de China. Un estudio de la calidad del agua subterrnea en una zona amplia de la planice del norte de China se llev a cabo entre 1998 y el ao 2000. Este estudio indica que la contaminacin de nitratos es un problema grave que afecta el agua potable de una vasta poblacin. El uso de fertilizantes a base de nitratos en la agricultura ha aumentado considerablemente durante los ltimos 20aos para satisfacer las necesidades alimentices de la creciente poblacin. Durante el estudio, se tomaron 295 muestras de pozos de agua y manantiales para determinar la qumica de las aguas y el grado de contaminacin por nitratos. Altas concentraciones de nitratos, especialmente en una zona de recarga a lo largo del lado oeste, as como en la cercana a Pekn y en zonas locales en otras partes de la planicie, presentan un problema serio al sumunistro de agua potable. En ciertos lugares, la concentracion de nitratos excede el nivel mximo de seguridad para el agua potable 45mg NO3/L. El intenso uso de fertilizantes de nitratos y el abundante uso de agua subterrnea sin tratamiento para la irrigacin de cultivos contribuyen sustancialmente al problema. Sin embargo, sin lugar a dudas, la descarga de deshechos industriales y municipales en arroyos y en el acufero tambin contribuyen al problema. La falta de datos impide la evalucin de dichas fuentes. En la zona de recarga se encuentran nitratos hasta los 50m de profundidad. Cerca a Pekn, concentraciones relativamente altas de nitrato ocurren hasta los 80m de profunidad. En las zonas de descarga afectadas por el Ro Amarillo las concentraciones altas de nitrato se encuentran solamente a menos de 8m de profundidad. [ABSTRACT FROM AUTHOR]

A wetland is an important part of the headwater in the discharge area of a basin. It controls not only groundwater discharge such as seepage or springs, but also the migration of chemical matter from the basin. In order to make clear how and where natural attenuation processes happen in wetlands, a typical headwater in Chiba, Japan, was chosen for an investigation of the behaviour of nitrate in groundwater. From the viewpoint of hydro-geomorphology, the wetland in the study site can be divided into three zones: the shallow water-table zone, the seepage zone, and the spring zone along the downstream direction. There were six piezometer groups; each group contained four piezometers, individually set at depths of 1, 2, 3 and 4 m. Major ions and d15N of groundwater from piezometers, wells and springs were analysed. It was found that nitrate in groundwater mainly came from the fertilizers used in the upstream recharge area of the study site. When the groundwater moved up across the wetland, nitrate concentration in the groundwater decreased rapidly in the shallow water-table zone due to denitrification. Nitrate-free water can be found at the seepage zone. However, the behaviour of nitrate in the spring water was different from that in the seepage zone, since both dilution and denitrification processes were involved in the decrease of nitrate concentration in groundwater. In particular, the dilution process mainly controlled the decline of nitrate at the location where the nitrate-free groundwater flowing horizontally from the seepage zone mixed with the high-nitrate groundwater flowing upward before emerging as a spring. It was also found that denitrification only occurs suddenly in a narrow zone or a thin layer of the order of a few metres. Copyright 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The North China Plain (NCP) is an important agricultural area in China and has a high population density. Serious water shortages have occurred in this region over the last 20 years. Water transfer from the Yangtze River (the east route) was initiated in the year 2002 to provide water for the major cities of the NCP. This study was carried out before the implementation of the water transfer project, focusing on the spatial integration of the groundwater flow system and geochemical characteristics, which are mainly controlled by tectonics, geomorphology, and lithology. The field survey and the geochemical analyses of the groundwater samples indicated that the groundwater in the NCP has a two-layer structure, with a boundary at a depth of about 100150 m. The two layers differ in pH, concentrations of SiO2 and major ions, and isotopes (18O, deuterium and tritium (T)). Chemical components in the upper layer showed a wider range and higher variability than those in the lower layer, indicating the impact of human activity. The flow direction of the groundwater in the upper layer was examined in detail in two profiles, showing that the upper layer flows east towards the CangzhouDaming fault, while the groundwater in the lower layer flows northeast towards Tianjin. Three hydrogeological zones are identified: recharge (Zone I), intermediate (Zone II), and discharge (Zone III). The recharge zone was found to be low in chloride (Cl-) but high in T. The discharge zone was found to be high in Cl- and low in T. This may be due to the difference in groundwater age. The discharge zone was subdivided into two sub-zones, Zone III1 and Zone III2, by considering the effects of human activities. Zone III2 was strongly affected by water diversions from the Yellow River. As groundwater flows from the recharge zone to the intermediate and discharge zones, chemical patterns evolve in the order: Ca-HCO3 > Mg-HCO3 > Na-Cl + SO4. Copyright 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The energy balance components were measured above the surface of an irrigated wheat and maize field over three successive years using the Bowen ratio technique. The experiments were carried out at Luancheng Experimental Station of Agro?ecosystem (LESA), Heibei, China, from December 1999 through to September 2001. The seasonal course of energy balance over an irrigated field, the diurnal Bowen ratio patterns in different seasons, and the effect of leaf?area index (LAI) and soil moisture on the energy balance are discussed. Over 3 years, the net radiation Rn varied from 31·6 to 668 · 1 W m?2, and the soil heat flux G varied from ?12 · 7 to 170 · 9 W m?2. The latent heat flux LE also shows apparent correspondence with the development of phenology, e.g. LAI. The diurnal course of the Bowen ratio in different seasons can be categorized into three typical patterns: (1) a ‘wheat pattern’, characterized by a steep morning peak followed by a decrease with the daytime mean value of around 0·30; (2) a ‘maize pattern’, which is a relatively flat course with a daytime mean ? of around 0·20–0·25; and (3) a ‘winter pattern’, with a near?noon high peak with a daytime mean ? of more than 10 times that those for wheat or maize. There are linear correlations between evaporative fraction (EF) and LAI for both wheat and maize before senescence seasons. The correspondence of EF appears more dependent on LAI for maize than for wheat. The EF does not appear correlated to soil water status, whereas the Bowen ratio is affected by extractable soil water content for wheat to some extent. No correlation for maize is found. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Surface energy fluxes above the canopies of well?irrigated winter wheat and maize in the North China Plain were measured by the Bowen?ratio energy balance technique in 1999–2000. Seasonal variation of the ratio of latent heat flux ?E to available energy Rn ? G showed that the ratio of ?E to Rn ? G exceeded 83% when leaf area index (LAI) varied from 2·0 to 6·0. The seasonal trend of evaporative fraction (EF) for winter wheat was similar to that of LAI before senescence stage, which is a critical factor controlling EF, which itself reflects the partitioning of available energy into ?E. The Priestley–Taylor parameter ? over the wheat and maize canopies changed greatly over the course of a growing season, and the seasonal average ? of winter wheat was 1·17 and 1·26, and that of maize was 1·06 and 1·09 in the two consecutive years. ? for winter wheat was exponentially correlated to 0–20 cm surface soil moisture, but not for maize and with the increase of soil depths, the correlation between ? and soil moisture was weak. Under different soil moisture conditions, a linear correlation between extractable soil water and leaf water potential ? for winter wheat was found. Copyright © 2004 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Knowledge of the mechanisms of water infiltration in sand dunes and wadis is a key to understanding the hydrological conditions in arid and semiarid regions. To trace infiltration processes in sand dunes, an artificial rainfall infiltration experiment was conducted in a typical sand dune in Al Ain, United Arab Emirates. Thermal sensors and tensiometers were set at two sites, a rainfall test site and a natural site, at depths of 10, 30, 60, 120, and 200 cm, respectively. For a start, the variations in temperature between the sites were compared with tension as well as soil water at the same depths. Field observations showed that the temperature of the sand dunes at the rain experimental site was affected more strongly by air temperature than that at the natural site, which means that temperature distribution in the sand dune has a very close relation with the water content. Then, the scheme combined with temperature difference and moving average was tested in tracing the temperature variation with movement of the infiltration front. It was found that the vertical temperature correlated well with the water movement in the sand dune, from which the average velocity of infiltration was estimated at 3 cm/h. [ABSTRACT FROM AUTHOR]

The WAVES model was used to simulate the effect of global warming on soil moisture on the semi-arid Taihang Mountain in China. Parameters of the WAVES model were first adjusted according to soil moisture data from a field global warming experiment. Then, the reliability of WAVES in predicting soil moisture changes induced by climatic change was confirmed by comparing the simulated and observed soil moisture values under different climatic conditions and plant growth rates of another field treatment. Next, 10 climate change scenarios incorporating increases in temperature and changes in precipitation were designed. When a simulation was conducted using the leaf area index (LAI) growth pattern from a field experiment under the present climatic conditions, the results suggested that the combination of temperature increase and precipitation decrease would greatly decrease soil water content throughout the entire simulation period. On the other hand, only when precipitation increased by 20% and temperature increased by 2 °C, the effect of precipitation increase on soil moisture was obviously positive. Although soil moisture conditions in the T2P1 (temperature increase by 2 °C and precipitation increase by 10%) and T4P2 (temperature increase by 4 °C and precipitation increase by 20%) scenarios were slightly better during the rainy season and not much changed before the rainy season, the positive effect of 10% precipitation increase on soil moisture was totally offset by moisture decrease caused by a 4 °C temperature increase in the T4P1 scenario. At the same time, the trends of soil-moisture change were highly coincident with predicted changes in productivity. Finally, the predicted LAI values from other studies were combined with the climatic change scenarios and used in the simulation. The results showed that changes in LAI alleviated, at least to some extent, the effects of temperature and precipitation changes on soil moisture. [ABSTRACT FROM AUTHOR]

Reports that daily evapotranspiration from a winter wheat field on the North China Plain measured by large-scale weighing lysimeter was linearly related to that measured by the Bowen ratio energy balance (BREB) technique. Average of soil evaporation from the post-winter dormancy revival stage to the grain ripening stage; Amount of the net radiation flux Rn was used to warm soil on clear days during winter dormancy; During the revival stage, conductive heat flux G that also used most of the incoming Rn, but the ratio of latent heat flux uE to Rn that increased; Percentage of uE of Rn during the stem-extension stage; Increase of uE/Rn; Percentage of G;. Percentage of uE during the ripening stage; Evaporative fraction (EF) that can be expressed as a function of plant status and atmospheric boundary layer conditions; Relationship between EF and available energy under moderate air temperature and vapor pressure deficit conditions that was examined for five combinations of aerodynamic and canopy conductance; Theoretical relationship that indicates that EF should be highly correlated to soil water content; Correlation that has been difficult to identify under field conditions; Observation that there exists a threshold value of Rn m G, above which EF is less than 1?0, and that the threshold value is lower under soil-water deficit conditions than under abundant soil-water conditions.

Reports that the characteristics of evapotranspiration and canopy surface conductance of winter wheat have been measured and analysed by using the Bowen ratio?energy balance (BREB) method. Daily and seasonal variations of leaf stomatal resistance under different soil water conditions that have been monitored and analysed; Available energy (Rn m G) of the wheat field that is partitioned into latent heat during the growing seasons after turning to green. Bowen ratio (H/LE) for winter wheat; Seasonal trend of LE/Rn that shows a parabola curve; Ratio of LE/Rn varies; G/Rn that shows a declining logarithmic trend during the observation period; Daily mean evapotranspiration rate; Daily average value for canopy conductance gc; Seasonal trend of leaf stomatal resistance that shows that the stomatal resistance in blooming and milking are lower than that in other growing stages; Stomatal conductance that is strongly dependent on soil water status in natural conditions; Slope of the gst?ESW line that varies through the growing stages, with the largest slope occurring in the milking stage; Construction of a simple but realistic model of stomatal conductance?soil moisture relations.

Focuses on studies conducted to illustrate the spatial distribution of recharge for groundwater in the arid regions of United Arab Emirates (UAE) from 1996 to 1997 using chemical and isotopic method. Review of chemical and isotopic techniques in evaluating recharge in an arid environment; Hydrological setting and classification; Results of the study.

To understand the distribution and behavior of phenolic endocrine-disrupting chemicals (EDCs) in surface water and suspended particulate matter (SPM), the Xiaohe River in the North China Plain (NCP) was investigated. The river concentrations (means; ng/L) of EDCs varied from 21.1-83.4 (54.1) for octylphenol (OP), from 38.7-1819.3 (569.7) for nonylphenol (NP), and from 49.2-774.5 (391.0) for bisphenol A (BPA). Particulate concentrations (means; ng/L) for OP, NP and BPA were in the range of 11.9-19.7 (23.4), 14.4-1196.5 (785.1), and 18.2-31.9 (22.5), respectively. SPM accounted for 22.6-54.2%, on average, of the total phenolic EDC pollution in surface water. The averaged particulate OP, NP and BPA proportions were 24.0, 60.5 and 11.2%, respectively, of their total concentration in water columns. A mass balance equation based on chloride was used to evaluate the mixing effect on the behavior of EDCs along the river. The good model fitting results showed that mixing process was the predominant factor to determine EDC concentrations in the Xiaohe River. Based on the combined effect models, potential environmental risks were assessed showing that most surface waters contaminated by EDCs have a medium effect on aquatic organisms in the Xiaohe River basin. [ABSTRACT FROM AUTHOR]

Phosphorus (P) forms, with respect to sediment characteristics, and an in-stream sluice were studied in the river-lake system, Huai River catchment area, China. The mean of total P in sediments in the mainstream of the Huai River was higher than that in the Hongze Lake. It was found that P fractions varied in the sediments throughout the river and lake. Detrital-P was the dominant P fraction in the mainstream and organic P and detrital-P were the dominant P fractions in the lake, which could indicate: biologically available and non-biologically available forms. Useful information for the interpretation of P fractions could also be obtained from major sediment characteristics. Whether the relations between P fractions and grain size characteristics were significant or weak, 0.125 mm was a threshold grain size for P fraction distribution in sediment. In addition, the Bengbu Sluice, one of the most important in-stream facilities in the Huai River catchment area, regulated not only the transport of P in sediments upstream and downstream of the sluice, but also the distribution of P fractions in the river-lake system. Therefore, it was confirmed that nutrient loadings could be prevented from reaching the watershed, as well as improved ecological diversity by integrating sluice operation.