Sediment yield in the Patuxent River (Md.) undergoing urbanization, 1968–1969

Water discharge from the Patuxent River into its estuary was near-average (95%) during the water year 1968–1969 although precipitation was only 79% of the average. Suspended-sediment discharge into the estuary, however, was more then double the normal yield (344 metric tons/km² compared to 143 metric tons/km²). These increases in runoff and suspended-sediment yields, despite decreased precipitation, must be attributed to urbanization of the drainage basin.The maximum measured suspended-sediment concentrations in the rural Middle Patuxent basin (Piedmont Province) increased only 40-fold during an increase from “average” to high water runoff (15 mg/l to 600 mg/l). In the portion of the Little Patuxent River basin undergoing urbanization (Piedmont portion), stream concentrations increased by over two orders of magnitude (20 mg/l to 2400 mg/l) as a result of heavy rainfall. The area undergoing urbanization of the Little Patuxent yielded more than twice as much suspended sediment per unit area as the rural Middle Patuxent (620 metric tons/km² versus 290 metric tons/km²). This increase also is interpreted to be the direct result of erosion of soils denuded or disturbed during urban construction.Using the Middle Patuxent as a “standard” for normal erosion rates in rural areas, construction sites contributed about 82% of the suspended sediment discharged by the Patuxent River into its estuary even though such sites represented only 23% of the drainage basin.     

An extraction,analysis, and prioritization of Asna river sub-basins,based on geomorphometric parameters using geospatial tools

The Asna river basin is located in Hingoli and Nanded districts of Marathwada region of Maharashtra. A geomorphometric analysis is an important method for the investigation and management of natural resources of watershed. The geomorphometric analysis of Asna river basin classifies three sub-basins that have been delineated using GIS and remote sensing through measurements of linear, aerial, and relief aspects. The Asna river basin comprises an area of 1187 km² with seventh-order drainage pattern. As per Strahler classification, the upper part of the basin shows dendritic to sub-dendritic and the lower part exhibits parallel to sub-parallel drainage pattern. The total numbers of stream segments are 2422 and length of streams is 2187.92 km. The bifurcation value ranges from 1.26 to 5.58 indicating that there are no structural disturbances. The form factor value (0.49) indicates that the shape of the basin is moderately circular. The high values of drainage density, stream frequency, and low infiltration number indicate the high runoff due to impermeable lithology. The slope of the basin varies from 1 to 32.2%, terrain elevation ranges from 333 to 551 m, and overall relief of the basin is 218 m amsl. River sub-basin prioritization has an immense importance in natural resource management, especially in semi-arid regions. The present study is an attempt to prioritize the sub-basins of Asna river based on geomorphometric parameters. The weightage is assigned to different morphometric parameters of sub-basins based on erosion potential. The Asna river sub-basins have been classified into three categories as high, medium, and low on the basis of priorities for soil and water conservation. It is confirmed that sub-basin I is characterized as highly vulnerable to erosion and has high sedimentation load; sub-basin II has low priority, i.e., very low erodibility; and sub-basin III is of moderate type. The morphometric analysis and prioritization methods can be applied to hydrological studies in surface as well as subsurface water, climatic studies, rainwater harvesting, groundwater recharging sites, and watershed management.     

Chemistry of the heavily urbanized Bagmati River system in Kathmandu Valley, Nepal: export of organic matter, nutrients, major ions, silica, and metals

Water quality in less-developed countries is often subject to substantial degradation, but is rarely studied in a systematic way. The concentration and flux of major ions, carbon, nitrogen, silicon, and trace metals in the heavily urbanized Bagmati River within Kathmandu Valley, Nepal, are reported. The concentrations of all chemical species increased with distance downstream with the exceptions of protons and nitrate, and showed strong relationships with population density adjacent to the river. Total dissolved nitrogen (TDN), dominated by NH₄, was found in high concentrations along the Bagmati drainage system. The export of dissolved organic carbon (DOC) and TDN were 23 and 33 tons km^?2 year^?1, respectively, at the outlet point of the Kathmandu Valley, much higher than in relatively undeveloped watersheds. The cationic and silica fluxes were 106 and 18 tons km^?2 year^?1 at the outlet of the Bagmati within Kathmandu Valley, and 36 and 32 tons km^?2 year^?1 from the relatively pristine headwater area. The difference between headwaters and the urban site suggests that the apparent weathering flux is three times higher than the actual weathering rate in the heavily urbanized Bagmati basin. Fluxes of cations and silica are above the world average, as well as fluxes from densely populated North American and European watersheds. End-member composition of anthropogenic sources like sewage or agricultural runoff is needed to understand the drivers of this high rate of apparent weathering.     

Weathering and Geochemical Processes Controlling Solute Acquisition in Ganga Headwater–Bhagirathi River, Garhwal Himalaya, India

Water and suspended sediment samples were collected along a longitudinal transect of the Bhagirathi – a headwater stream of the river Ganga, during the premonsoon and postmonsoon seasons, in order to assess the solute acquisition processes and sediment transfer in a high elevation river basin. Study results show that surface waters were dominated by HCO₃ and SO₄ in anionic abundance and Ca in cationic concentrations. A high concentration of sulphate in the source region indicates oxidative weathering of sulphide bearing minerals in the drainage basin. The combination of high concentrations of calcium, bicarbonate and sulphate in river water suggests that coupled reaction involving sulphide oxidation and carbonate dissolution are mainly controlling the solute acquisition processes in the drainage basin. The sediment transfer reveals that glacial weathering and erosion is the major influence on sediment production and transfer. The seasonal and spatial variation in ionic concentration, in general, is related to discharge and lithology. The sediment mineralogy and water mineral equilibrium indicate that water composition is in equilibrium with kaolinite. The river Bhagirathi annually delivers 0.74 M.tons of dissolved and 7.88 M.tons of suspended load to the river Ganga at Devprayag. The chemical and physical denudation rate of the Bhagirathi is 95 and 1010 tons/km²/yr, higher than the Indian and global average.     

Hydrological and geochemical characteristics of the Jamari and Jiparana river basins (Rondonia,Brazil)

The authors investigate the hydrological and geochemical characteristics of the Jamari (30430 km²) and Jiparana (60350 km²) river basins (Amazonia), during the period 1978–1984. A spectral analysis of Fourier is applied to time series of mean monthly river discharges, in order to assess the contribution (7 to 8%) of the surface runoff to the total river flow. The mean annual runoff coefficient calculated for the Jiparana river basin (36%), is higher than for the Jamari (32%), and this coefficient increases during the study period, only for the Jiparana. The total specific suspended sediment discharge calculated for both rivers shows the same value 13 t/km²/y, and the estimated suspended sediment concentration in the surface runoff is slightly superior for the Jiparana river (0.3 g/l) than for the Jamari one (0.2 g/l). The river suspended sediments are mainly composed of kaolinite, quartz and feldspar, but the Jiparana is more enriched in quartz. For both rivers, the dominant clay mineral is the kaolinite which is in agreement with the rock weathering type determined for both basins using the Tardy's weathering index: the monosiallitisation. The total chemical erosion rate calculated after correction for the atmospheric inputs (ions and CO₂), is higher for the Jiparana (10.11 t/km²/y) than for the Jamari river basin (7.75 t/km²/y). These values are lower than the mechanical denudation rate calculated previously for both river basins.     

Morphometric analysis of Suketi river basin,Himachal Himalaya,India

Suketi river basin is located in the Mandi district of Himachal Pradesh, India. It encompasses a central inter-montane valley and surrounding mountainous terrain in the Lower Himachal Himalaya. Morphometric analysis of the Suketi river basin was carried out to study its drainage characteristics and overall groundwater resource potential. The entire Suketi river basin has been divided into five sub-basins based on the catchment areas of Suketi trunk stream and its major tributaries. Quantitative assessment of each sub-basin was carried out for its linear, areal, and relief aspects. The analysis reveals that the drainage network of the entire Suketi river basin constitutes a 7th order basin. Out of five sub-basins, Kansa khad sub-basin (KKSB), Gangli khad sub-basin (GKSB) and Ratti khad sub-basin (RKSB) are 5th order sub-basins. The Dadour khad sub-basin (DKSB) is 6th order sub-basin, while Suketi trunk stream sub-basin (STSSB) is a 7th order sub-basin. The entire drainage basin area reflects late youth to early mature stage of development of the fluvial geomorphic cycle, which is dominated by rain and snow fed lower order streams. It has low stream frequency (Fs) and moderate drainage density (Dd) of 2.69 km/km ². Bifurcation ratios (Rb) of various stream orders indicate that streams up to 3rd order are surging through highly dissected mountainous terrain, which facilitates high overland flow and less recharge into the sub-surface resulting in low groundwater potential in the zones of 1st, 2nd, and 3rd order streams of the Suketi river basin. The circulatory ratio (Rc) of 0.65 and elongation ratio (Re) of 0.80 show elongated nature of the Suketi river basin, while infiltration number (If) of 10.66 indicates dominance of relief features and low groundwater potential in the high altitude mountainous terrain. The asymmetry factor (Af) of Suketi river basin indicates that the palaeo-tectonic tilting, at drainage basin scale, was towards the downstream right side of the drainage basin. The slope map of Suketi river basin has been classified into three main zones, which delineate the runoff zone in the mountains, recharge zone in the transition zone between mountains and valley plane, and discharge zone in the plane areas of Balh valley.     

Evidence for Regional Stream Aggradation in the Central Oregon Coast Range during the Pleistocene-Holocene Transition

Low, nearly continuous terraces of similar age are present along streams in drainage basins that range in size from Drift Creek (190 km²) to the Umpqua River (11,800 km²) in the Oregon Coast Range. Radiocarbon ages from near the bose of fluvial sediments underlying these terraces are clustered at about 9000-11,000 ¹⁴C yr B.P. Beveled bedrock surfaces (straths) that underlie the fluvial sediments are 1-8 m above summer stream levels and are present along most of the nontidal reaches of the rivers that we studied. Where exposed, the bedrock straths are overlain by 2-11 m of fluvial sediment that consists of a bottom-stratum (channel) facies of sandy pebble-cobble gravel and a top-stratum (overbank) facies of sandy silt or silt. Eight radiocarbon ages from the fluvial sediments allow correlation of the lowest continuous terrace over a wide area and thus indicate that a regional aggradation episode occurred in Coast Range drainage basins during the Pleistocene-Holocene transition. The cause of such widespread aggradation is unknown but may be related to climate-induced changes in the frequency of evacuation of colluvium from hollows, which are common in all drainage basins in the region.     

Geo-diversity and its hydrological response in relation to landslide susceptibility in the Himalaya: a GIS-based case study

Assessment and inventory of landslide susceptibility are essential for the formulation of successful disaster mitigation plans. The objective of this study was to assess landslide susceptibility in relation to geo-diversity and its hydrological response in the Lesser Himalaya with a case study using Geographic Information System (GIS) technology. The Dabka watershed, which constitutes a part of the Kosi Basin in the Lesser Himalaya, India, in the district of Nainital, has been selected for the case illustration. The study constitutes three GIS modules: geo-diversity informatics, hydro informatics and landslide informatics. Through the integration and superimposing of spatial data and attribute data of all three GIS modules, Landslide Susceptibility Index (LSI) has been prepared to identify the level of susceptibility for landslide hazards. This resonance study, carried out over a period of five years (2007–2011), found that areas of most stressed geo-diversity (comprising very steep slopes above 30°, geology of Lower Krol and Lariakanta formation, geomorphology of moist areas and debris sites, land use of barren land with a very high drainage frequency and spring density) have a high landslide susceptibility because of high rate of average runoff (33 l/s/km²), flood magnitude (307.28 l/s/km²), erosion (398 tons/km²) and landslide density (5–10 landslides/km²). The areas of least stressed geo-diversity (comprising gentle slopes below 10°, geology of Kailakhan and Siwalik formation, geomorphology of depositional terraces, land use of dense forest with low drainage frequency and spring density) have the lowest landslide susceptibility because of the low rate of average runoff (6.27 l/s/km²), flood magnitude (20.49 l/s/km²), erosion (65.80 tons/km²) and landslide density (1–2 landslides/km²).     

塔里木河水质盐化及改善途径

塔里木河在1958年前是一条淡水河,河水的矿化度在各段及不同季节均未超过1.0g/L,现全河段各月平均矿化度除8月洪水季节<1.0g/L,其余各月都在1.0g/L以上。上游阿拉尔水文站平均每年有5个月为1～3g/L,4个月为3～5g/L,2个月超过5g/L,最高5月份达到6.3g/L.阿拉尔的淡水所占比例不足年平均径流量的35%.下游卡拉全部为微咸水。造成塔里木河水矿化度升高的原因,除气候干旱、蒸发强烈、土壤含盐量高等自然因素外,主要是灌溉、排水不合理,上游三条主要支流灌溉引水增加,使补给干流的淡水资源量由1960年前的50.0亿m3减少到1990年后的42.0亿m3;与此同时大量农田排水泄入塔里木河,每年带入盐量达467.4万t.要改善塔里木河水质,必须减少农田排水泄入,实行咸、淡分流,退耕还林;并在源流区适度开发地下水,使三源流向塔里木河输水量每年不少于46.0亿m3。     

青藏高原东部长江流域盆地陆地化学风化研究

长江河水主要离子由流域盆地碳酸盐岩的风化所控制,沱沱河和楚玛尔河受蒸发盐岩影响较为明显;河水溶质载荷Si,Si/TZ *,Si/(Na* K)等指标表明,长江流域盆地地表硅酸盐岩风化还是浅表层次的;金沙江地表化学剥蚀速率为1.74×103mol/yr.km2,雅砻江为1.69×103mol/yr.km2,大渡河为1.57×103mol/yr.km2,岷江为1.88×103mol/yr.km2,长江河源区楚玛尔河为2.32×103mol/yr.km2,沱沱河为1.37×103mol/yr.km2,流域地表化学剥蚀速率可与世界上其它造山带的河流进行对比。     

Hydrochemistry of the Amur River: Weathering in a Northern Temperate Basin

We report the dissolved major element, organic carbon, and δ¹³C_DOC, δ¹³C_POC, δD, δ¹⁸O, and ⁸⁷Sr/⁸⁶Sr composition of 19 summer samples from the Amur River. The Amur transported 2.6 Tg C/year of total organic carbon to the Sea of Okhotsk. The physical weathering rate (PWR) based on suspended particulate material was 13 (1.4–14) tons/(km² year), and the chemical weathering rate based on total dissolved solids was 7 (4.3–46) tons/(km² year). We further quantified the sources of the dissolved cations using an inverse model: rain accounted for 2 (0.6–5)%, evaporite 3 (0.7–7)%, carbonate 51 (29–74)%, and silicate 45 (25–64)%. The silicate weathering rate (SWR) in the Amur basin was 23 (15–98) × 10³ mol/(km² year) or 0.67 (0.40–2.81) tons/(km² year), comparable to those of the Siberian rivers and the Mackenzie at higher latitudes. The SWR of the Amur was negatively correlated with elevation and relief, and positively correlated with runoff.     

Organic carbon concentrations and transport in small mountain rivers,Panama

Tropical small mountainous rivers (SMRs) are increasingly recognized for their role in the global export of dissolved organic carbon (DOC) to the oceans. Here we utilize the Isthmus of Panama as an ideal place to provide first-order estimates of DOC yields across a wide assemblage of bedrock lithologies and land cover practices. Samples for dissolved organic carbon (DOC) analysis were collected across Panama along an E–W transect from the central Panama area to the Costa Rican border for 24 mainstem rivers, 3 large tributary rivers, and one headwater stream. Sampling occurred during both the wet and the dry seasons. DOC concentrations during the wet season are higher than during the dry season in all but three of the rivers. Concentrations vary greatly from river to river and from season to season, with values as low as 0.64 mg l⁻¹ to greater than >25 mg l⁻¹ with the highest concentrations observed for the rivers draining Tertiary marine sedimentary rocks in the Burica and Azuero peninsulas. DOC yields from Panamanian rivers (2.29–7.97 tons/km²/y) are similar to or slightly lower than those determined for other tropical SMR systems. Areas underlain by Tertiary aged sediments exhibited significantly higher mean DOC yields compared to their igneous counterparts, despite maintaining substantially lower aboveground carbon densities, suggesting the important influence of lithology. Finally, regression analyses between DOC yields and select watershed parameters revealed a negative and statistically significant relationship with maximum and mean gradient suggesting lower soil retention times may be linked to lower DOC yields.     

Evaluating natural and anthropogenic trace element inputs along an alpine to urban gradient in the Provo River,Utah, USA

Numerous natural and anthropogenic processes in a watershed produce the geochemical composition of a river, which can be altered over time by snowmelt and rainfall events and by built infrastructure (i.e., dams and diversions). Trace element concentrations coupled with isotopic ratios offer valuable insights to disentangle the effects of these processes on water quality. In this study, we measured a suite of 40+ trace and major elements (including As, Cd, Ce, Cr, Cs, Fe, La, Li, Mo, Pb, Rb, Sb, Se, Sr, Ti, Tl, U, and Zn), Sr isotopes (⁸⁷Sr/⁸⁶Sr), and stable isotopes of H and O (δD and δ¹⁸O) to investigate natural and anthropogenic processes impacting the Provo River in northern Utah, USA. The river starts as a pristine mountain stream and passes through agricultural and urban areas, with two major reservoirs and several major diversions to and from the river. We sampled the entire 120 km length of the Provo River at 13 locations from the Uinta Mountains to Utah Valley, as well as two important tributaries, across the range of hydrologic conditions from low flow to snowmelt runoff during the 2013 water year. We also sampled the furthest downstream site in the Utah Valley urban area during a major flood event. Trace element concentrations indicate that a variety of factors potentially influence Provo River chemistry, including inputs from weathering of carbonate/siliciclastic rocks (Sr) and black shales (Se and U), geothermal groundwater (As, Cs, Li, and Rb), soil erosion during snowmelt runoff (Ce, Cr, Fe, La, Pb, and Ti), legacy mining operations (Mo, Sb, and Tl), and urban runoff (Cr, Pb, and Zn). Although specific elements overlap between different groups, the combination of different elements together with isotopic measurements and streamflow observations may act as diagnostic tools to identify sources. ⁸⁷Sr/⁸⁶Sr ratios indicate a strong influence of siliciclastic bedrock in the headwaters with values exceeding 0.714 and carbonate bedrock in the lower reaches of the river with values approaching 0.709. δD and δ¹⁸O changed little throughout the year in the Provo River, suggesting that the river is primarily fed by snowmelt during spring runoff and snowmelt-fed groundwater during baseflow. Based on nonmetric multidimensional scaling (NMS) water chemistry was unique across the upper, middle, and lower portions of the river, with high temporal variability above the first reservoir but minimal temporal variability below the reservoir. Thus, the results show that dams alter water chemistry by allowing for settling of particle-associated elements and also by homogenizing inflows throughout the year to minimize dilution during snowmelt runoff. Taken together, trace element concentrations and isotopic measurements can be used to evaluate the complex geochemical patterns of rivers and their variability in space and time. These measurements are critical for identifying natural and anthropogenic impacts on river systems.     

长江流域水资源、灾害及水环境状况初步分析

长江是我国第一、世界第三大河流,发源于青藏高原,全长6300多公里,流域面积180×104km²,占中国陆地面积的1/5。长江及其流域不仅以其不可替代的自然资源优势和其他江河无法比拟的区位优势,在我国国民经济和社会发展中扮演着举足轻重的角色,特别是约占全国的36%、拥有9616×10⁸m³的年径流量(为黄河的20倍),是我国最重要的水源地。这不仅对长江流域资源优势的发挥和缓解我国北方地区日趋严重的水资源短缺问题至关重要,而且对全国的可持续发展也将产生深远影响。然而,在长江流域大规模开发及经济快速发展的同时,人类活动与自然规律的负面效应相互叠加,导致了流域环境的生态调节和自我恢复功能大幅降低,引起了日趋严重的水环境退化、洪涝灾害威胁加剧等问题。文章首先对长江流域水资源的重要性及其作用做了分析,肯定了其丰富的资源和重要的战略地位,该流域在占全国不足18%的土地上,集中了40%以上的人口及国民生产总值,而且其经济地位有进一步上升的趋势,在水量及水能的蕴藏上,全流域湖泊面积达10323km²,占我国淡水湖泊总面积的37.2%,水能蕴藏总计达2.7×10⁸kW。另外,对长江流域日趋严重灾害及水环境问题做了探讨,尤其中游的洪水、淤积以及随着经济发     

长江流域水资源、灾害及水环境状况初步分析

长江是我国第一、世界第三大河流,发源于青藏高原,全长6300多公里,流域面积180×104km²,占中国陆地面积的1/5。长江及其流域不仅以其不可替代的自然资源优势和其他江河无法比拟的区位优势,在我国国民经济和社会发展中扮演着举足轻重的角色,特别是约占全国的36%、拥有9616×10⁸m³的年径流量(为黄河的20倍),是我国最重要的水源地。这不仅对长江流域资源优势的发挥和缓解我国北方地区日趋严重的水资源短缺问题至关重要,而且对全国的可持续发展也将产生深远影响。然而,在长江流域大规模开发及经济快速发展的同时,人类活动与自然规律的负面效应相互叠加,导致了流域环境的生态调节和自我恢复功能大幅降低,引起了日趋严重的水环境退化、洪涝灾害威胁加剧等问题。文章首先对长江流域水资源的重要性及其作用做了分析,肯定了其丰富的资源和重要的战略地位,该流域在占全国不足18%的土地上,集中了40%以上的人口及国民生产总值,而且其经济地位有进一步上升的趋势,在水量及水能的蕴藏上,全流域湖泊面积达10323km²,占我国淡水湖泊总面积的37.2%,水能蕴藏总计达2.7×10⁸kW。另外,对长江流域日趋严重灾害及水环境问题做了探讨,尤其中游的洪水、淤积以及随着经济发     

Terrestrial sediment yield and the lifetimes of reservoirs, lakes, and larger basins

Water reservoirs, lakes, and larger basins, including their drainage areas, represent sedimentologically closed to semi-closed denudation-accumulation systems. The mean rates of mechanical denudation, DR_me, and clastic sedimentation, SR_me, are related by the ratio of the drainage/lake area, A_d/A_l. If the latter is known, DR_me (or the specific sediment yield SY in t per km²/a) can be calculated from SR_me, or vice versa. The best data for modern SY mainly come from the sediment fills of artificial reservoirs. Small drainage areas of mountainous regions show SY values up to two orders of magnitude higher than lowlands and approximately one order higher than larger regions of mixed relief. This is also true of arid to semi-arid zones which often provide approximately as much sediment (SY) as humid temperate and even tropical zones of comparable relief. Lithology and climate (river runoff) also may play some role for SY from catchments of limited size. The importance of these factors is exemplified by perialpine lakes and two East African lakes. Sediment yields gained from some large reservoirs compare well with long-term denudation rates derived from geological studies (e.g., the Tarbela dam reservoir along the Indus River). In many other cases, human activities have raised SY by factors of 2–10, locally up to >100. Artificial reservoirs in mountainous regions with SY in the range of 300–2000?t?per?km²/a tend to become filled within several tens to hundreds of years; some have even shorter lifetimes. Perialpine lakes of the Alps and British Columbia are strongly affected by delta prograding and have lifetimes mostly between 15 and 40?ka. Closed lake systems in deep morphological depressions (Lake Bonneville, Aral Sea, northern Caspian Sea) have a high potential for sediment storage up to the level of spillover and therefore can persist over long time periods. Basins with markedly subsiding basin floors (lakes of the East African rift zone, the southern Caspian Sea, and the Black Sea, both on oceanic crust) can survive for many Ma in the future, despite relatively high terrigenous input.     

Major ion chemistry of the Ganga source waters: Weathering in the high altitude Himalaya

A systematic study of the major ion chemistry of the Ganga source waters—the Bhagirathi, Alaknanda and their tributaries—has been carried out to assess the chemical weathering processes in the high altitude Himalaya. Among major ions, Ca, Mg, HCO₃ and SO₄ are the most abundant in these river waters. These results suggest that weathering of carbonate rocks by carbonic and sulphuric acids dominates in these drainage basins. On an average, silicate weathering can contribute up to ∼ 30% of the total cations. The concentration of total dissolved salts in the Bhagirathi and the Alaknanda is 104 and 115mg/l, respectively. The chemical denudation rate in the drainage basins of the Bhagirathi and the Alaknanda is, respectively, 110 and 137 tons/km²/yr, significantly higher than that derived for the entire Ganga basin, indicating intense chemical erosion of the Himalaya.     

Chemical weathering in the Three Rivers region of Eastern Tibet

Three large rivers - the Chang Jiang (Yangtze), Mekong (Lancang Jiang) and Salween (Nu Jiang) - originate in eastern Tibet and run in close parallel over 300 km near the eastern Himalayan syntaxis. Seventy-four river water samples were collected mostly during the summer season from 1999 to 2004. Their major element compositions vary widely, with total dissolved solids (TDS) ranging from 31 to 3037 mg/l, reflecting the complex geologic makeup of the vast drainage basins. The major ion distribution of the main channel samples primarily reflects the weathering of carbonates. Evaporite dissolution prevails in the headwater samples of the Chang Jiang in the Tibetan Plateau interior, as evidenced by the high TDS (928 and 3037 mg/l) and the Na-Cl dominant major element composition. Local tributary samples of the Mekong and Salween, draining the Lincang Batholith and the Tengchong Volcano, show distinctive silicate weathering signatures. We used five reservoirs - rain, halite, sulfate, carbonate, and silicate - in a forward model to calculate the contribution from silicate weathering to the total dissolved load and to estimate the consumption rate of atmospheric CO₂ by silicate weathering. Carbonate weathering accounts for about 50% of the total cationic charge (TZ⁺) in the samples of the Mekong and the Salween exiting the Tibetan Plateau. In the “exit” sample of the Chang Jiang, 45% of TZ⁺ is from halite dissolution inherited from the extreme headwater tributaries in the interior of the plateau, and carbonates contribute only 26% to the TZ⁺. The net rate of CO₂ consumption by silicate weathering is (103-121) × 10³ mol km⁻² year⁻¹, lower than the rivers draining the Himalayan front. GIS-based analyses indicate that runoff and relief can explain 52% of the spread in the rate of atmospheric CO₂ drawdown by silicate weathering, but other climatic (temperature, precipitation, potential evapotranspiration) and geomorphic (elevation, slope) factors also show collinearity. Only qualitative conclusions can be drawn for the significance of lithology due to lack of digitized lithologic information. The effect of the peculiar drainage pattern due to tectonic forcing is not readily apparent in the major element composition or in increased chemical weathering rates. The ⁸⁷Sr/⁸⁶Sr ratios and the silicate weathering rates are in general lower in the Three Rivers than in the rivers draining the Himalayan front.     

京津冀地区国土资源环境地质条件分析

统计分析了京津冀地区土地资源、地下水、湿地、矿产、地热和地质景观等资源条件分布,结果显示,平原区土壤质量总体良好,良好及以上等级土壤分布面积约占平原区面积的80.89%,适宜种植绿色农产品的面积为96363 km~2,富硒耕(园)地面积为1894 km~2;地下水可开采资源总量为188亿m~3/a,但呈现空间分布不均的特征;衡水湖等五大湿地分布面积约为614 km~2,近30年来减少了35.57%;金属矿产和非金属矿产资源丰富,例如铁矿资源储量98.4亿t,铜矿资源量111.50万t,石油地质储量249635.02万t;地热资源丰富,开发利用地热资源可替代3.43亿t标准煤;地质遗迹资源丰富,约有300余处可纳入环首都国家公园规划建设。同时,分析了活动断裂与地震、地面沉降、地裂缝、崩滑流和地面塌陷、地下水污染和湿地退化等主要环境地质问题现状;在此基础上,针对城镇发展和重要基础设施建设、湿地保护与修复、地下水资源开发利用、优质耕地资源保护和地质遗迹资开发利用等方面提出了地学建议,为区域规划建设提供地质安全保障和资源保障。     

Suspended sediment load in the Amazon basin: An overview

In this report the state of knowledge of sediment transport by rivers of the Amazon drainage basin is reviewed. On an annual basis the Amazon river transports about 1200×10⁶ tons of sediment from the South American continent to the ocean, which puts it among the world's largest rivers in this respect. The main source of sediment is erosion in the Andes mountains and this material is progressively diluted with sediment poor runoff from lowland draining tributaries. Almost half of the Amazon river transport is attributable to one tributary, the Rio Madeira (488×10⁶ t/y). The Rio Negro, which drains the N crystalline shield, has a comparable water discharge to the Rio Madeira, but only contributes 7×10⁶ t/y. In general the sediments in transport are about 1% organic carbon by weight and this results in an annual particulate carbon to the oceans of 13×10⁶ t/y. Total carbon transport, particulate plus dissolved, is about twice this amount.