Selenium contamination in the Colorado River Basin, western USA: Remediation by leaching and nanofiltration membranes

Selenium (Se) is an essential micronutrient to biota, but can become a potent toxicant at elevated concentrations. The natural sources and chemical properties of Se species make the boundary between deficiency and toxicity narrow for some biota, with both…     

Arsenic Distribution Pattern in Different Sources of Drinking Water and their Geological Background in Guanzhong Basin,Shaanxi, China

To study arsenic(As) content and distribution patterns as well as the genesis of different kinds of water, especially the different sources of drinking water in Guanzhong Basin, Shaanxi province, China, 139 water samples were collected at 62 sampling points from wells of different depths, from hot springs, and rivers. The As content of these samples was measured by the intermittent flowhydride generation atomic fluorescence spectrometry method(HG-AFS). The As concentrations in the drinking water in Guanzhong Basin vary greatly(0.00–68.08 μg/L), and the As concentration of groundwater in southern Guanzhong Basin is different from that in the northern Guanzhong Basin. Even within the same location in southern Guanzhong Basin, the As concentrations at different depths vary greatly. As concentration of groundwater from the shallow wells(50 m deep, 0.56–3.87 μg/L) is much lower than from deep wells(110–360 m deep, 19.34–62.91 μg/L), whereas As concentration in water of any depth in northern Guanzhong Basin is 10 μg/L. Southern Guanzhong Basin is a newly discovered high-As groundwater area in China. The high-As groundwater is mainly distributed in areas between the Qinling Mountains and Weihe River; it has only been found at depths ranging from 110 to 360 m in confined aquifers, which store water in the Lishi and Wucheng Loess(Lower and Middle Pleistocene) in the southern Guanzhong Basin. As concentration of hot spring water is 6.47–11.94 μg/L; that of geothermal water between 1000 and 1500 m deep is 43.68–68.08 μg/L. The high-As well water at depths from 110 to 360 m in southern Guanzhong Basin has a very low fluorine(F) value, which is generally 0.10 mg/L. Otherwise, the hot springs of Lintong and Tangyu and the geothermal water in southern Guanzhong Basin have very high F values(8.07–14.96 mg/L). The results indicate that highAs groundwater in depths from 110 to 360 m is unlikely to have a direct relationship with the geothermal water in the same area. As concentration of all reservoirs and rivers(both contaminated and uncontaminated) in the Guanzhong Basin is 10 μg/L. This shows that pollution in the surface water is not the source of the high-As in the southern Guanzhong Basin. The partition boundaries of the high- and low-As groundwater area corresponds to the partition boundaries of the tectonic units in the Guanzhong Basin. This probably indicates that the high-As groundwater areas can be correlated to their geological underpinning and structural framework. In southern Guanzhong Basin, the main sources of drinking water for villages and small towns today are wells between 110–360 m deep. All of their As contents exceed the limit of the Chinese National Standard and the International Standard(10 μg/L) and so local residents should use other sources of clean water that are 50 m deep, instead of deep groundwater(110 to 360 m) for their drinking water supply.     

Exploitation of groundwater resources and protection of wetland in the Yuqia Basin

In Yuqia Basin, the climate is arid and the ecologic environment is fragile, and shortage of water resources has seriously restricted the sustainable development of local economy. In order to meet the needs of industrial and domestic water in the Yuqia Basin, numerical simulation was used to evaluate the groundwater resources and potential for exploitation. The results showed that the mathematical model and calculation parameters used were mainly in accordance with practical situation. The calculated value of the underground water level is consistent with measured value during the period of identification and validation. The total recharge of groundwater resources was 22.02×10~4 m~3/d, and the total drainage was 21.95×10~4 m~3/d at present. The Yuqia River leakage is the main supply source of groundwater. There is no significant effect on area of wetland when water source place exploited by 2.5×10~4 m~3/d at alluvial-diluvial fan of Yuqia River. After long-term exploitation, the spring flow reduces from 1.42×10~4 m~3/d to 1.01×10~4 m~3/d and wetland area reduces by 32.7% of original area. The calculation of water balance shows that it is safe to the Yuqia Basin, Da Qiadam Lake, the Mahai Basin at downstream of Yuqia River and wetland under the condition of water source place exploited by 2.5×10~4 m~3/d.     

New Schizolepis Fossils from the Early Cretaceous in Inner Mongolia, China and its Phylogenetic Position

Three Schizolepis species collected from the Lower Cretaceous layer of the Huolinhe Basin,Inner Mongolia,China are described.These fossils are Schizolepis longipetiolus Xu XH et Sun BN sp.nov.,which is a new species,Schizolepis cf.heilongjiangensis Zheng et Zhang,and Schizolepis neimengensis Deng.The new species is a well-preserved female cone,slender and cylindrical in shape.The seed–scale complexes have long petioles and are arranged on the cone axis loosely and helically.The seed scales are divided into two lobes from the base.Each lobe is semicircular or elongate ligulate in shape,widest at the middle or the lower middle part,with an obtuse or bluntly pointed apex.The inner margin is almost straight and the outer margin is strongly arched.On the surface of the lobe,there are longitudinal and somewhat radial striations from the base to the margin.The seed is borne on the adaxial surface at the base or middle of each lobe.Schizolepis was established in 1847,and,although more than twenty species have been discovered and reported,its phylogenetic position is controversial because of the imperfection of fossils.Most authors have considered there to be a close evolutionary relationship between Schizolepis and extant Pinaceae.Here,we analyze characteristics and compare Schizolepis with Picea crassifolia Kom,which is morphologically most similar to Schizolepis.The results indicate that the genus probably has a distant evolutionary relationship with extant Pinaceae.A detailed statistical analysis of the global paleogeographic distribution of Schizolepis showed that all the fossils of this genus appeared in strata ranging from the Upper Triassic to the Lower Cretaceous in the North Hemisphere,being rare in the Upper Triassic and Lower Jurassic,but being very common from the Middle Jurassic to the Lower Cretaceous,and particularly abundant in the Lower Cretaceous.According to the statistical results,we speculate that the genus originated in Europe in the Late Triassic then spread from Europe to Asia between the Late Triassic and the Late Jurassic.In the Early Cretaceous most species existed in China’s three northeastern Provinces and the Inner Mongolia Autonomous Region and adjacent areas.Combining the paleogeographic distribution of the genus with ancient climatic factors,we deduced that Schizolepis began to decline and became extinct in the Early Cretaceous,and the reason for its extinction is closely related to the icehouse climate during the Early Cretaceous.     

http://www.sciencedirect.com/science/article/pii/S1674987112000667

The brackish-water bivalve Waagenopema Tokuyama,1959 is reported from the Lower Jurassic Badaowan Formation at four localities,along the southern margin and western margin of the Junggar Basin. Taphonomic features recorded in the field indicate that it occurs in autochthonous or parautochthonous assemblages.The autecology of Waagenopema therefore yields information on the palaeoenvironment of the area.The restriction of Waagenopema to marine and brackish-water settings suggests that the sea water once reached these areas during the Sinemurian.This paper discusses the palaeogeographic implications and suggests an ingression of the sea water from the west to the western and southern part of the Junggar Basin.Additionally,the two Waagenopema species collected from the Haojiagou section in the Junggar Basin are taxonomically documented.     

Foraminiferal Biostratigraphy of the Mobarak Formation (Lower Carboniferous) in Kiyasar Area,SE Sari,Northern Iran

The Mobarak Formation is near the town of Kiyasar in the south-east of Sari city, northern Iran. This formation conformably overlies the Geirud Formation (Upper Devonian). The lower part of the Mobarak Formation consisting of shales and thin- to medium-bedded limestone toward the top of these sequences changes into alternations of dark limestone and interbedded gray to black shales. Weathered yellow thick-bedded shales are observed at the top of the section. This formation is covered unconformably by sandstones attributed to the Dorud Formation (Lower Permian). The thickness of the formation in this region is 250 m. Four rock units have been recognized in this section. Foraminiferal biostratigraphy shows that the age of the Mobarak Formation in the Kiaysar region ranges from Lower Tournaisian to Early Middle Visean. The foraminifer Zones FAZ1 and FAZ2 are correlated with the Lower Tournaisian and Upper Tournaisian, whereas Zones FAZ3 and FAZ4 correlate with the Visean. Affinities exist between specimens recorded in the Kiyasar section with species known from other regions in eastern and Central Alborz, but there are important differences in their appearance.     

Early diagenesis of nurtrients （C, N, P and Si） stored in sediments of two reservoirs in southwestern China

Damming is a common anthropogenic intervention along the course of rivers, which is defined as ＂artificial-lake effect＂, both in China and across the world. Today as many as 48000 dams and/or reservoirs are in operation in the Changjiang River （Yangtze River） drainage area, and more are being constructed. While damming is well known to affect riverbome nutrient loads, and thus the riverine ecosystems owing to removal of carbon fixation, and removal of particles in reservoir sediments, there is limited information on the detailed early diagenesis of sediments in reservoirs including the regeneration processes of nutrients deposited in sediments and exchange flux across the sediment-water interface, which is important for mass balance of riverbome nutrients. In the present study, two large-size reservoirs, Wujiangdu Reservoir （WJDR） and Dongfeng Reservoir （DFR）, located on the main steam of the Wujiang River and with uniformity hydrography and discrepancy biogeochemical activity （e. g. primary production）, were selected for a comparative study on the detailed processes of nutrient regeneration. Water, pore water and sediment were sampled from these two reservoirs and dissolved organic carbon （DOC）, NH4^＋, NO3^-, PO4^3-, dissolved silica （DSi） in the overlying water and pore water, and total organic matter in sediments were determined. The results of correlation analysis suggested that in these two reservoirs, processes of nutrient regeneration near the sediment-water interface were significantly different. As a result of rapid decomposition of algae-derived ＂labile＂ organic matter in upper sediments, nutrient regeneration processes and upward fluxes in WJDR are dramatically stronger than those of DFR. NH4^＋ upward flux from sediment in WJDR was about 17 times higher than that in DFR. PO4^3- flux in WJDR is about 13 times above that in DFR. DOC flux in WJDR is larger that in DFR by 5 times, and DSi by 1 time.     

New Discovery of Oligocene Gastropod Opercula from the Yehucheng Formation in Northwestern China

Fourteen species of nonmarine gastropod opercula are found to be in high abundance in the Oligocene upper member of the Yehucheng Formation,Lanzhou Basin,northwest China.They are attributed to two families,namely Bithyniidae and Assimineidae,and four genera,namely Pseudemmericia,Bithynia,Mirolaminatus and Assiminea.Among them,three species are new,and they are Bithynia paramonolithic sp.nov.,B.obliquus sp.nov.,and B.disregularis sp.nov.Some of these species were first discovered in Paleogene strata of the vast Northwest China and can be compared with the opercula recovered from the Paleogene deposits in East and South China.It is inferred from the paleontology and sediment associations that the climate was slightly humid and the fauna probably inhabited the fresh or brackish water of a shallow lake in the Lanzhou Basin during the late early Oligocene period.     

A New Fossil Hangingfly (Mecoptera: Cimbrophlebiidae) from the Early Cretaceous of China

A new species, Cimbrophlebia rara sp. nov., in the family Cimbrophlebiidae（Mecoptera） is described and illustrated. This specimen was collected from the Early Cretaceous Yixian Formation at Liutiaogou in Inner Mongolia, China. This is the first record of a cimbrophlebiid from the Jehol biota. A key to all species of Cimbrophlebia is given. A preliminary review of published taxa data indicates that from the Middle Jurassic to the Early Cretaceous, Mecoptera became less diverse and less abundant in northeastern China at familiar level（from 11 to 6）, generic level（from 32 to 8） and specific level（from 44 to 14）.     

Stratigraphy of the Triassic?Jurassic Boundary Successions of the Southern Margin of the Junggar Basin, Northwestern China

The Triassic?Jurassic (Tr?J) boundary marks a major extinction event, which (~200 Ma) resulted in global extinctions of fauna and flora both in the marine and terrestrial realms. There prevail great challenges in determining the exact location of the terrestrial Tr?J boundary, because of endemism of taxa and the scarcity of fossils in terrestrial settings leading to difficulties in linking marine and terrestrial sedimentary successions. Investigation based on palynology and bivalves has been carried out over a 1113 m thick section, which is subdivided into 132 beds, along the Haojiagou valley on the southern margin of the Junggar Basin of the northern Xinjiang, northwestern China. The terrestrial Lower Jurassic is conformably resting on the Upper Triassic strata. The Upper Triassic covers the Huangshanjie Formation overlaid by the Haojiagou Formation, while the Lower Jurassic comprises the Badaowan Formation followed by the Sangonghe Formation. Fifty six pollen and spore taxa and one algal taxon were identified from the sediments. Based on the key-species and abundance of spores and pollen, three zones were erected: the Late Triassic (Rhaetian) Aratrisporites?Alisporites Assemblage, the Early Jurassic (Hettangian) Perinopollenites?Pinuspollenites Assemblage, and the Sinemurian Perinopollenites?Cycadopites Assemblage. The Tr?J boundary is placed between bed 44 and 45 coincident with the boundary between the Haojiagou and Badaowan formations. Beds with Ferganoconcha (?), Unio?Ferganoconcha and Waagenoperna?Yananoconcha bivalve assemblages are recognized. The Ferganoconcha (?) bed is limited to the upper Haojiagou Formation, Unio?Ferganoconcha and Waagenoperna?Yananoconcha assemblages are present in the middle and upper members of the Badaowan Formation. The sedimentary succession is interpreted as terrestrial with two mainly lake deposit intervals within Haojiagou and Badaowan formations, yielding fresh water algae and bivalves. However, the presence of brackish water algae Tasmanites and the marine?littoral facies bivalve Waagenoperna from the Badaowan Formation indicate that the Junggar Basin was influenced by sea water caused by transgressions from the northern Tethys, during the Sinemurian.     

A New Species of Amsassia from the Ordovician of Korea and South China: Paleobiological and Paleogeographical Significance

A new species of the probable calcareous alga Amsassia, A. koreanensis, is recognized from the Duwibong Formation (Middle Ordovician, Darriwilian) of the Taebaeksan Basin in mid-eastern Korea. This is the first report of the genus from the Korean Peninsula, expanding its geographical range to the eastern Sino-Korean Block. The new species also occurs in the Xiazhen Formation (Upper Ordovician, Katian) at Zhuzhai in the South China Block. Amsassia koreanensis is the smallest species of this modular genus, having a maximum module diameter of 0.28 mm. Module increase is by bipartite, tripartite and quadripartite types of longitudinal axial fission, but unlike other species of the genus, quadripartite fission is common. The types of fission are comparable to those in some Tetradiida (now Prismostylales, florideophycean rhodophyte algae), although the processes of fission are different. The distribution of A. koreanensis further strengthens the biogeographical connection between the Sino-Korean and South China blocks, suggesting that these two paleocontinents were located closer together during the Middle to Late Ordovician than previously speculated.     

Organochlorine pesticides characteristics in water column of strategic drinking water sources in the Yangtze estuary

Biandansha, Qingcaosha and Meimaosha sands located respectively in the upper, middle and lower reaches of the Yangtze （Changjiang River） estuary are regarded as strategic drinking water sources of Shanghai City. In the coming decade, the Qingcaosha Reservoir will first be built and gradually take the place of present water sources in the Huangpu River. However, there is little report on the occurrence of persistent organic pollutants （POPs） such as organochlorine pesticides （OCPs） in those strategic water sources. Water samples collected from those strategic water sources were filtered in-situ by Whatman GF/F filters in April 20-23, 2006. Pesticides in the filtrates were enriched on ENVI-18 solid phase extraction （SPE） tubes. OCPs eluted from SPE tubes were determined by GC-μECD method with a mixed standard solution of 20 OCPs compounds. Pentachloronitrobenzene was added as internal standard. Total concentrations of OCPs varied between 15.1 and 83.1 ng/L in water samples from Shanghai strategic water sources. A half of twenty objective OCPs compounds including DDTs were not detected. In Qingcaosha waters, there were six compounds such as a-HCH, dieldrin, endrin, endrin ketone, β-endosulfan and endosulfan sulfate. Total concentrations of these OCPs ranged from 15.1 to 31.6 ng/L and averaged 19.9 ng/L. OCPs had higher concentrations at low water tide than at high water tide, and in bottom water than in surface water. In Biandansha and Meimaosha waters, lindane （T-HCH） of 9.0 ng/L and γ-chlordane of 8.8 ng/L were found, respectively. There was no significant difference between total OCPs concentrations in surface water from Biandansha and Qingcaosha, which are much lower than those in the downstream Meimaosha waters.     

Fossil Liverworts from the Lower Cretaceous Huolinhe Formation in Inner Mongolia, China

A new genus and species, Rebouliothallus huolinhensis sp. nov., and two uncertain species, Ricciopsis sp. and Hepaticites sp., are described. The fossils were collected from the Lower Cretaceous Huolinhe Formation of Huolinhe Basin, northeastern China. The new genus Rebouliothallus was established in the Aytoniaceae family of Marchantiales. Rebouliothallus huolinhensis appears to be quite similar to species of the extant genus Reboulia Raddi. The species is characterized by the relatively large ventral scales. Ventral scales are large, imbricate and arranged in two rows on the ventral surface. Rhizoids are either pegged or smooth. Ricciopsis sp. is characterized by the rosette-forming thallus. Hepaticites sp. shows some similarities to liverworts. Of the forty-nine Early Cretaceous floras of China, only two floras, one from the Huolinhe basin, Inner Mongolia and the other from the Jixi Basin, Heilongjiang Province, contain fossil liverworts. The rare fossil liverwort records in the Early Cretaceous floras of China may be the result of taphonomic bias.     

Effects of climate change on relationship between water and salts of waters ecosystems in arid zone, China

The process of salinization has increased dramatically over the past several decades in the northwest arid zone of China. Soil salinization has been recognized as a major environmental problem for many years in the Tarim River Basin. It is the key issue of solving the soil salinization problem to study interaction between water and salt in arid zone, which will provide useful principle and methodology to its solution. Taking Tarim River and Bosten Lake for example, by systematically collecting the basic data of hydrogeology, meteorology, and social economy, we analyzed the interaction of water and salt of Tarim River and Bostan Lake in natural and artificial conditions in aspects of basins, oases, lakes and marshes. The results showed that： （1） Temperature and precipitation are both increasing gradually in the whole Tarim River Basin, the climate tends to be come warmer and wetter, but the water quality condition is not optimistic; （2） At the end of the 1950s, mineralization degree was less than 1.0 g/L from the upper reaches to the lower reaches of the Tarim River. At present, it is more than 3.0 g/L in Alaer Lake （the upper reaches of the Tarim River） except in July, August and October, during which it is less than 1.0 g/L. In Qiala （the lower reaches）, it is more than 1.0 g/L except in March, moreover, it is about 5.0 g/L in July and December. The eco-water conveyance project implementation has still not improved Tarim River＇s water quality condition; （3） Bostan Lake was a tiny salt-water lake in the late 1950s, but the water-soil development of the oasis has aggravated the salinization in recent thirty years. Since the West Pumping Station was brought into operation in 1982, the Bostan Lake which accumulated salt has begun to be desalted. We consider that climate may not be the key factor for salinization in this area. Instead, socio-economic factors relevant to human activities should be mainly responsible for such changes, as is confirmed by our further analysis. In order to improve present situation of water-soil salinization, water resources utilization and management should be strengthened, highly efficient and water-saving irrigating technology should be spread,     

Did marine transgression happen in Late Cretaceous period in the southeast of Songliao Basin ？——Discussion from evidence of water chemistry

Cretaceous sediment is considered to be the important oil reservoir in the Songliao Basin, which is dominated by continental fluvial and lacustrine strata. In the past decades, research on whether the marine transgression happened in the Late Cretaceous period in the southeast of the Songliao Basin is always a hotspot in China. Previous studies analyzed the marine biology and geochemistry of sediments to argue if the marine transgression had occurred. However, the geochemistry of formation water which could indicate the paleo-environment has not attracted attention. In this paper, the geochemical variations of formation water between the Chaoyanggou anticline, Changchun anticline and Binxian depression in the southeast of the Songliao Basin are analyzed, then the results by comparisons with chemical properties of sea water indicated： （1） the extensive range of pH values from 6 to 10 concerning the formation water. The ranges of TDS of the formation water are from 1 g/L to 20 g/L, which is less than the value in the seatwater; （2） the level of the element Br, which is an important trace element to indicate the marine sedimentary environment, is lower than that from the sea water. The concentrations of the trace element B fluctuate intensively, probably due to the enhancement of water-rock interaction and the enrichment of organic matter; and （3） ionic ratio of Na/Cl and Br＊ 1000/Cl in the formation water are higher than the value of 0.8575 and lower than 1.5363 in the sea water, respectively, which might be attributed to halite dissolution.     

The First Stegosaur （Dinosauria, Ornithischia） from the Upper Jurassic Shishugou Formation of Xinjiang, China

A new stegosaur species, Jiangjunosaurus junggarensis, gen. et sp. nov., is erected based on a specimen collected from the Upper Jurassic upper section of the Shishugou Formation in the Junggar Basin, Xinjiang, China. It represents the first stegosaur from the Jurassic of Xinjiang and increases the diversity of the dinosaur fauna in the Shishugou Formation. The new genus is characterized by symmetrical and proportionally wide tooth crowns, a sub-rectangular axial neural spine seen in lateral view, and large openings on the lateral surfaces of the cervical centra. A preliminary character analysis suggests that this new taxon is more derived than the Middle Jurassic stegosaur Huayangosaurus but more primitive than most other known stegosaur species.     

Study on rain-runoff process in the peripheral mountainous area of the Sichuan Basin

Studies on rain-runoff process in the peripheral mountainous area of the Sichuan Basin, which is regarded as a key ecological shelter, will contribute to flood control and environmental protection for the Upper Yangtze River Basin. In two typical catchments--the Fujiang River Catchment and the Wujiang River Catchment, rainfall simulations have been conducted to study the rain-runoff processes of yellow soil and limestone soil in three types of land use--forestland, farmland and grassland. Results showed that （1） within the same rainfall process, overland flow occurs first on farmland, then on grassland, and finally on forestland; （2） soil surface coverage has a great impact on the occurrence and amount of overland flow. The runoff amount can increase 2-4 times after the coverage is removed; （3） the infiltration before the occurrence of overland flow will decrease because of higher gravel contents of soil, but it takes no effect on infiltration once overland flow becomes stable; （4） the runoff coefficient of the limestone soil forestland is greater than that of the yellow soil forest land, but less than that of the farmland; （5） three empirical infiltration models, including Horton＇ model, Kostiakov＇ model, and modified Kostiakov＇ model, were compared by using the observed results under rainfall simulation. The results showed that the Kostiakov＇ model performed better than both the Horton＇ model and modified Kostiakov model. According to the results of this research, the Kostiakov＇s model can be used to simulate rainfall infiltration when water erosion is modeled in the peripheral mountainous area of the Sichuan Basin.     

Distribution,characteristics, and research status of microplastics in the trunk stream and main lakes of the Yangtze River: A review

Microplastic pollution has become an environmental issue of great concern owing to the persistence of microplastics and their potential adverse effects on biota.The Yangtze River is the longest river in China and the third-longest river in the world,and the microplastics in this river will affect the health of a large population living along with it.To ensure the survival safety of people,it is essential to plan ahead and investigate in advance in order to understand the microplastic pollution in the river and work out countermeasures.This paper reviews the literature concerning the microplastic pollution in the Yangtze River basin and analyzes the abundance,shapes,colors,and composition of microplastics in the water bodies and sediments in the trunk stream and main lakes of the Yangtze River.The results are as follows.Compared to other river basins in China and abroad,the microplastics in the Yangtze River basin have a moderate abundance and high spatial heterogeneity.Owing to the barrier effect of the Three Gorges Dam on microplastics,the abundance of microplastics in the Three Gorges Reservoir is generally an order of magnitude higher than that in other sections of the river.Most microplastics in the water bodies and sediments are less than 1 mm in size and are transparent and colorful.In terms of shapes,they are dominated by fibers,followed by fragments and films.In terms of composition,the microplastics in the source region of the Yangtze River are mainly composed of nylon and polyethylene,while the microplastics in the surface water from the lower reaches of the Jinsha River to the Yangtze River estuary are dominated by polypropylene and polyethylene.The microplastics are primarily derived from the secondary microplastics in the environment,and relatively intensive human activities increase the abundance of microplastics.These results serve as bases for understanding and preventing microplastic pollution in the Yangtze River.     

Distribution and Forming Model of Fluvial Terrace in the Huangshui Catchment and its Tectonic Indication

<正>The Huang Shui River,a main tributary of the Yellow River,crosses a series of tectonically subsided and uplifted areas that show different patterns of terrace formation.The distribution of fluvial terrace of the Huang Shui River is studied through topographic and sedimentologic terrace mapping.Three terraces in the Haiyan Basin,four terraces in the Huangyuan Basin,19 terraces in the Xi'ning Basin(the four high terraces may belong to another river),nine terraces in the Ping'an Basin, five terraces in the Ledu Basin and 12 terraces in the Minhe Basin are recognized.Sedimentology research shows that the geomorphologic and sedimentological pattern of the Huang Shui River,which is located at the margin of Tibet,are different from that of the rivers at other regions.The formation process of the terrace is more complicated at the Huang Shui catchment:both accumulation terrace and erosion terrace were formed in each basin and accumulation terraces were developed in some basins when erosion terraces were formed in other basins,indicating fluvial aggradation may occur in some basins simultaneously with river incision in other basins.A conceptual model of the formation process of these two kinds of fluvial terraces at Huang Shui catchment is brought forward in this paper.First,the equilibrium state of the river is broken because of climatic change and/or tectonic movement,and the river incises in all basins in the whole catchment until reaching a new equilibrium state.Then,the downstream basin subsides quickly and the equilibrium state is broken again,and the river incises at upstream basins while the river accumulates at the subsidence basin quickly until approaching a new equilibrium state again.Finally,the river incises in the whole catchment because of climatic change and/or tectonic movement and the accumulation terrace is formed at the subsidence basin while the erosion terrace is formed at other basins.The existence of the accumulation terrace implied the tectonic subsidence in the sub-basins in Huang Shui catchment.These tectonic subsidence movements gradually developed from the downstream Minhe Basin to the upstream Huangyuan Basin.Dating the terrace sequence has potential to uncover the relationship between the subsidence in the catchment and the regional tectonic at the northeastern Tibetan Plateau.     

Aquatic ecological risk assessment of OCPs in Huaihe River, Jiangsu section

The Huaihe River Basin, located between the Yellow River and the Yangtze River, is one of the most populated areas in the eastern part of China. The Huaihe River is probably the most heavily polluted one among the three largest rivers in China. The Jiangsu section is the downstream reaches of the Huaihe River, where organochlorine pesticides （OCPs） may come from local discharge due to flourishing industry and agriculture, and also from inflows from upstream. OCPs are usually hazardous organic pollutants, and may endanger the aquatic ecosystem of the Huaihe River, Jiangsu section. Surface water of the Huaihe River, Jiangsu section in both high-flow period and low-flow period was sampled and OCPs were determined using GC-ECD. 15 OCPs were detected, including 2,4＇-DDT, 4,4＇-DDT, 4,4＇-DDD, α-HCH, β-HCH, γ-HCH, aldrin, endrin, dieldrin, methoxychlor, heptachlor, hexachlorobenzene（HCB）, α-endosulfan, α-Endosulfan and heptachlorepoxide. The span of total OCPs concentration is between 26.27-124.39 ng/L. Among the 15 OCPs detected, aquatic ecological risk assessment was performed for 12 ones except for α-endosulfan, α-endosulfan and heptachlorepoxide due to lack of the relevant toxicity data of the three compounds. The acute toxicities of 12 OCPs to multi aquatic species were collected from AQUIRE database and other sources. Environmental Concentration Distribution （ECD） and Species Sensitivity Distribution （SSD） were achieved after Kolmogorov-Smirnov test. The risk quotient distributions were acquired using Monte Carlo simulation. The aquatic ecological risks caused by single OCPs were analyzed. It is shown that endrin and 2,4＇-DDT have the highest risk while HCB and HCHs have the lowest risk. Then the joint ecological risk caused by all 12 OCPs was calculated based on the concept of equivalent concentration and it proves to be significantly higher than risk caused by any single OCP. Furthermore, the probability of aquatic ecological risk was calculated according to different ecological risk criteria （ERC）. The comparative analysis shows that ERC is very important to the result of ecological risk assessment.