Stream Channel Enlargement Response to Urban Land Cover in Small Coastal Plain Watersheds,North Carolina

Stream channel response to urban land use has not been well documented for southeastern Coastal Plain streams. In this study, urban channel response was evaluated in small Inner Coastal Plain watersheds (<5 km²) in eastern North Carolina. Reaches were selected across a range of watershed total impervious area (0-67% TIA). Channel dimensions and sediment grain size data were collected along 20 urban (>10% TIA) and 20 rural reaches (<10% TIA), and at 10 stormwater outfall sites (180 cross-sections). Urban cross-sectional area, channel incision ratio, and channel grain size (gravel%, D₅₀, and D₈₄) were greater, relative to rural channels. Bankfull cross-sectional areas were approximately 1.78 times greater for urban watersheds than for rural watersheds. Channels in urban watersheds were incised and had median full-channel capacities approximately 3.4 times greater than channels draining rural watersheds. Watershed TIA explained 65-72% of channel capacity enlargement. Urban expansion in the region began in the 1960s, with major urbanization occurring over the last 25 years. Channels draining urban watersheds are still responding to this land use change by downcutting and widening. Urban channel incision has frequently cut off streams from their floodplains, reducing floodplain sediment retention and water quality functions.     

Paleolimnological investigations of anthropogenic change in Lake Tanganyika: VIII. Hydrological evaluation of two contrasting watersheds of the Lake Tanganyika catchment

This study was conducted to delineate the impact of human activities on stream flow and water chemistry as well as other factors that influence the chemical character of both surface and groundwater in two contrasting watersheds of the Lake Tanganyika catchment. The study sites the Mwamgongo and Mitumba streams along the northern Tanzanian coastline of the lake are representative of disturbed and undisturbed watersheds, respectively, but are quite similar in other characteristics of slope, bedrock geology and size. Separation of stream flow components was undertaken using classical hydrograph analysis along with chemical methods using both Cl and ¹⁸O data. All the data show that groundwater accounts for the predominant source of total stream flow in both the Mwamgongo and Mitumba watersheds (65 and 70% respectively). The streams have an average ¹⁸O of about -3.0% and less than 10 mg/l for Cl. The basin recession constants of 9.4×10^-3-d^-1 and 9.6×10^-3-d^-1 for Mwamgongo and Mitumba, respectively, indicate existence of both fissured and fractured aquifer systems. The chemical data exhibit low values of all determined ions. This supported the hypothesis that natural processes influence the water chemical character of the study area. An Mg–HCO₃ type of water dominates in the two watersheds. Despite their similar size and bedrock character the Mwamgongo watershed has an order of magnitude in sediment transport than the Mitumba one. The data show that the disturbed watershed discharges less groundwater and more sediments, and has a poorer water quality than the forested Mitumba watershed, which lies within the Gombe National Park. The data show that soil erosion processes are more active at Mwamgongo, and that both the surface runoff component of the total stream flow and increased dissolved salt load is greater in the deforested Mwamgongo watershed than in the Mitumba watershed. The chloride and ¹⁸O data complemented each other in delineating the amounts of groundwater in the total stream flow as the results using both data differed insignificantly. It may be concluded that the undisturbed watershed has a higher retention of good quality water and traps more sediments than the disturbed one. In addition, the groundwater component plays a dominant role in the total annual stream flow at each watershed.     

长江口潮滩沉积物－水界面无机氮交换通量

对长江口滨岸潮滩7个典型断面三态氮的界面交换通量进行了三年多的季节性连续观测,结果表明无机氮的界面交换行为存在复杂的空间分异和季节变化。NO^-₃-N和NH⁺₄-N的界面交换通量正负变化范围较大,分别介于-32.82~24.13 mmol.m^-2.d^-1和-18.45~10.65mmol.m^-2.d^-1之间;而NOsup>-₂-N的界面交换通量很小,仅为-1.15~2.82 mmol.m^-2.d^-1。NO^-₃-N的界面交换具有明显的上下游季节性时空分异特征,而NH⁺₄-N的界面交换则表现为南北岸季节性时空分异现象。盐度是控制长江口滨岸潮滩NH⁺₄-N界面交换行为的主要因素,而沉积物粒度、水体 NO^-₃-N浓度、沉积物有机质含量、水温和溶解氧含量则以不同的组合方式,共同制约着 NO^-₃-N在潮滩界面交换的时空分异格局。     

典型岩溶农业区地下水质与土地利用变化: 以云南小江流域为例

1 Introduction Ecological environment such as water, soil, etc. are very fragile in the karst area because of the special geological background. With the fast increase of the population and rapid social and economic development in karst area, contradictio…     

Bank Erosion in Fifteen Tributaries in the Glaciated Upper Susquehanna Basin of New York and Pennsylvania

The proportional contributions of cultivated lands and stream banks as sources of fine sediment loads were quantified in 15 rural watersheds in the Glaciated Appalachian Plateau region of the Susquehanna River basin of New York and Pennsylvania. We utilized a relatively simple method of fingerprinting sediment sources by comparing the concentrations of the nuclear bomb-derived radionuclide ¹³⁷ Cs in fluvial sediment samples collected from channel margins with sediment from cultivated fields and stream banks. The proportion of fine sediment from bank erosion ranged from none to 100% in the study tributaries, with a median contribution of 53% across the 15 study streams. In one stream with no evidence of bank sediment, anomalously high ¹³⁷ Cs levels in the samples indicated that the sources were pasture or forest, probably scoured from marshy floodplains upstream of the sampling sites. In the 14 other streams, cultivated lands accounted for an average of 42% of the fine sediment. We discuss sources of eroded bank material and the processes driving stream bank erosion in this glaciated region, and examine the impact of historic mill-dam deposits on bank erosion.     

Hydrologic variation with land use across the contiguous United States: Geomorphic and ecological consequences for stream ecosystems

Using daily discharge data from the USGS, we analyzed how hydrologic regimes vary with land use in four large hydrologic regions that span a gradient of natural land cover and precipitation across the continental United States. In each region we identified small streams (contributing area < 282 km²) that have continuous daily streamflow data. Using a national database, we characterized the composition of land cover of the watersheds in terms of aggregate measures of agriculture, urbanization, and least disturbed (“natural”). We calculated hydrologic alteration using 10 ecologically-relevant hydrologic metrics that describe magnitude, frequency, and duration of flow for 158 watersheds within the Southeast (SE), Central (CE), Pacific Northwest (NW), and Southwest (SW) hydrologic regions of the United States. Within each watershed, we calculated percent cover for agriculture, urbanized land, and least disturbed land to elucidate how components of the natural flow regime inherent to a hydrologic region is modified by different types and proportions of land cover. We also evaluated how dams in these regions altered the hydrologic regimes of the 43 streams that have pre- and post-dam daily streamflow data. In an analysis of flow alteration along gradients of increasing proportion of the three land cover types, we found many regional differences in hydrologic responses. In response to increasing urban land cover, peak flows increased (SE and CE), minimum flows increased (CE) or decreased (NW), duration of near-bankfull flows declined (SE, NW) and flow variability increased (SE, CE, and NW). Responses to increasing agricultural land cover were less pronounced, as minimum flows decreased (CE), near-bankfull flow durations increased (SE and SW), and flow variability declined (CE). In a second analysis, for three of the regions, we compared the difference between least disturbed watersheds and those having either > 15% urban and > 25% agricultural land cover. Relative to natural land cover in each region, urbanization either increased (SE and NW) or decreased (SW) peak flows, decreased minimum flows (SE, NW, and SW), decreased durations of near-bankfull flows (SE, NW, and SW), and increased flow variability (SE, NW, and SW). Agriculture had similar effects except in the SE, where near-bankfull flow durations increased. Overall, urbanization appeared to induce greater hydrologic responses than similar proportions of agricultural land cover in watersheds. Finally, the effects of dams on hydrologic variation were largely consistent across regions, with a decrease in peak flows, an increase in minimum flows, an increase in near-bankfull flow durations, and a decrease in flow variability. We use this analysis to evaluate the relative degree to which land use has altered flow regimes across regions in the US with naturally varying climate and natural land cover, and we discuss the geomorphic and ecological implications of such flow modification. We end with a consideration of what elements will ultimately be required to conduct a more comprehensive national assessment of the hydrologic responses of streams to land cover types and dams. These include improved tools for modeling hydrologic metrics in ungauged watersheds, incorporation of high-resolution geospatial data to map geomorphic and hydrologic drivers of stream response to different types of land cover, and analysis of scale dependence in the distribution of land-use impacts, including mixed land uses. Finally, ecological and geomorphic responses to human alteration of land cover will have to be calibrated to the regional hydroclimatological, geologic, and historical context in which the streams occur, in order to determine the degree to which stream responses are region-specific versus geographically independent and broadly transferable.     

Biogeomorphic Relationships and Riparian Vegetation Changes Along Altered Ephemeral Stream Channels: Florence to Marana,Arizona

This study examines riparian vegetation cover changes along ephemeral channels due to the emplacement of the Central Arizona Project (CAP) canal. Two research questions examined are the following: (1) How has riparian vegetation changed over the course of twenty-eight years due to altered flow conditions? (2) How has channel morphology affected changes in vegetation cover? Five Landsat TM images acquired in 1982, 1989, 1996, 2003, and 2010 were classified. The average change of vegetation cover per 0.5-km section over the twenty-eight-year period is approximately 100,436 m² over 25.5-km length of the canal on the upstream section. In addition, the total amount of vegetation cover increase in the twenty-eight years over the 25.5-km length of the canal is approximately 5,122,239 m². Larger streams experienced a greater increase in vegetation cover upslope than smaller streams. In addition, streams of similar width dimensions that were completely closed off resulted in greater vegetation cover than streams that were semiconnected. A significant relationship between changes in vegetation green-up and channel widths was examined. Results from this study suggest that there is a quasi-linear relationship between channel widths and increases in vegetation cover for altered and impounded channels due to the presence of the CAP canal.     

High spatial resolution hyperspectral mapping of in-stream habitats, depths, and woody debris in mountain streams

This article evaluates the potential of 1-m resolution, 128-band hyperspectral imagery for mapping in-stream habitats, depths, and woody debris in third- to fifth-order streams in the northern Yellowstone region. Maximum likelihood supervised classification using principal component images provided overall classification accuracies for in-stream habitats (glides, riffles, pools, and eddy drop zones) ranging from 69% for third-order streams to 86% for fifth-order streams. This scale dependency of classification accuracy was probably driven by the greater proportion of transitional boundary areas in the smaller streams. Multiple regressions of measured depths (y) versus principal component scores (x₁, x₂,…, x_n) generated R² values ranging from 67% for high-gradient riffles to 99% for glides in a fifth-order reach. R² values were lower in third-order reaches, ranging from 28% for runs and glides to 94% for pools. The less accurate depth estimates obtained for smaller streams probably resulted from the relative increase in the number of mixed pixels, where a wide range of depths and surface turbulence occurred within a single pixel. Matched filter (MF) mapping of woody debris generated overall accuracies of 83% in the fifth-order Lamar River. Accuracy figures for the in-stream habitat and wood mapping may have been misleadingly low because the fine-resolution imagery captured fine-scale variations not mapped by field teams, which in turn generated false “misclassifications” when the image and field maps were compared.The use of high spatial resolution hyperspectral (HSRH) imagery for stream mapping is limited by the need for clear water to measure depth, by any tree cover obscuring the stream, and by the limited availability of airborne hyperspectral sensors. Nonetheless, the high accuracies achieved in northern Yellowstone streams indicate that HSRH imagery can be a powerful tool for watershed-wide mapping, monitoring, and modeling of streams.     

赣江上游河流水化学的影响因素及DIC来源

对赣江上游38 处水体采样点的水化学特征和溶解无机碳稳定同位素的分析, 发现其总溶解质浓度较低, 其中, 阳离子以Na⁺、Ca²⁺ 为主, 阴离子以Cl^- 和HCO₃ ^- 为主, Si 的浓度较高, 表征了典型硅酸盐地区河流的水化学组成特征。通过海盐校正分析得出, 研究区大气降水对河水溶解质的贡献率为11.5%, 扣除降水的贡献部分, 利用主成分分析的方法, 计算得出赣南流域受硅酸盐岩风化作用强烈, 同时由于受附近盐矿的影响, 蒸发盐岩的风化作用显著。另外, 根据δ¹³C 溶解无机碳DIC 的测量值约为-8.35‰~-13.74‰, 平均为-11.65‰, 利用质量平衡计算得出, 研究区DIC 的主要来源, 约68.5%来自于土壤CO₂, 31.5%来自于碳酸盐矿物的溶解, 进而得出流域岩石化学风化过程消耗的土壤CO₂ 为2.11×105 mol/yr·km², 来自碳酸盐本身的HCO₃ ^-含量为9.6×104 mol/yr·km²。由于地理位置和流域环境以及人为因素的差异, 各支流DIC 来源的比例亦有所差异。     

Stream Temperature Spatial Variability Reflects Geomorphology,Hydrology, and Microclimate: Navarro River Watershed,California

Stream temperatures are critical to coldwater fish and vary with microclimate, geomorphology, and hydrology, including influx of groundwater. Spatial variability of stream temperatures was examined at reach and watershed scales within the 816 km² Navarro River watershed in California. Field monitoring and numerical modeling illustrate that stream temperatures were highest at sites with high solar incidence (low shading and wide streams), long travel times, and low discharge. Microclimate helps explain deviation from the general pattern of streams warming with increasing drainage area. Reach-scale field observations of channel width and groundwater influx explain variation in stream temperatures not captured by watershed-scale models.     

The analysis of nitrate in highly saline waters

The analysis of nitrate in seawater and hypersaline waters should take account of a significant “salt effect”. Procedures developed for fresh water and marine waters must be applied cautiously to highly saline waters. The most widely used standard method for the determination of nitrate-nitrogen (NO₃-N) in fresh and marine waters involves the quantitative reduction of nitrate by the Cd column technique followed by colorimetric procedures. In our study, three approaches to estimate NO₃-N in highly saline waters were examined. The first involved dilution. This approach overcame the salt effect but dilution limited the detection of low concentrations of nitrate in highly saline waters. The second involved the use of standard nitrate solutions in saline water. This method is not recommended because of nitrate impurities in AR grade salts. The third- and preferred approach-involved the use of standard additions. “Spikes” of a known volume of NO₃-N standard solution were added to natural saline waters. Nitrate values estimated by the stadard addition method were used to calculate an equation for salt error correction at different salinities applicable to waters with the same relative ionic composition as seawater. This could then be used to correct nitrate determinations in highly saline waters where standards made in distilled water were used for calibration. Many previously published data for NO₃-N in saline water used methods of analysis which do not take account of salt error and are therefore probably in error.     

Geochemistry of waters and brines from the Salinas Grandes basin,Córdoba,Argentina. I. Geomorphology and hydrochemical characteristics

This paper reports on hydrochemical features of diluted waters in the source areas and the brine end-members dominant in the playa of the Salinas Grandes Basin, Córdoba, Argentina. Special emphasis was placed on the study of the relationship between geomorphology and the resulting hydrochemical fractionation. Inflow is from springs and mountain streams which disappear before reaching the saline complex. The playa and intermittent saline lakes are mainly fed by groundwater flow and a few moderately saline and perennial springs. Conversely, ephemeral lakes are fed by atmospheric precipitation and groundwater, whereas small ponds are only fed by atmospheric precipitation. The absence of a clear linkage between geomorphological units and water types was evident in the source areas. Up to four types of water were recognized in a given geomorphological unit. From the sandflat downward towards the playa, the correspondence between geomorphological units and water types was clear, coinciding with a decreased hydrochemical heterogeneity. In this subenvironment, I have recognized two dominant types of water (SO ₄ ^2– –Cl^––HCO ₃ ^– –Na⁺ and Cl^––SO ₄ ^2– –HCO ₃ ^– –Na⁺), which can be considered the original members of the neutral brine in the playa (Cl^––SO ₄ ^2– –Na⁺ where Ca²⁺+Mg²⁺ do not surpass 5 meq per cent), and an intermediate type in the mudflat (Cl^––SO ₄ ^2– –Na⁺ where the contribution of Ca²⁺+Mg²⁺ reaches up to 15 meq per cent). It seems evident that in the zone between the source areas and the sandflat, hydrochemistry is governed by chemical weathering. In stream floodplains and in the distal alluvial plain, close to the saline complex, the increase in water types as well as the increase of HCO ₃ ^– with respect to SO ₄ ^2– , were explained by the mixture of aquifers controlled by the Salinas Grandes-Salinas de Ambargasta fracture. In the saline complex, the more concentrated end-members are the result of evaporation of the two more frequent water-types in the sandflat subenvironment, and salt dissolution of ancient evaporite deposit.     

Nature and Dynamics of an Active Block Stream, Kunlun Pass, Qinghai Province, People's Republic of China

Active block streams are common on the slopes of mountains on the northern, drier portion of the Qinghai-Xizang (Tibetan) Plateau. Between 1990 and 1995, the authors studied a block stream northeast of the crest of the Kunlun Pass at latitude 35°50’N, longitude 94°05’ E. It occurs on a 31° slope facing southwest at 4800 m altitude and consists of a 15 cm layer of blocks moving downslope over a sandy loam of lacustrine origin. The blocks are derived from both frost shattering of exposed bedrock and by ejection of blocks from the till capping the hill. No water flows in the block stream and its surface is level with the surrounding slope. Mean annual air temperature is –6°C and mean annual precipitation is about 320 mm. The few plants growing between the blocks exhibit elongated stems and/or roots, indicating movement of the upper layers of blocks relative to the underlying materials. Average mean annual downslope movement of the surface blocks ranges up to 95 cm but varies both across the block stream and also along its long axis. The blocks are gradually extending further downslope. Comparison of movement of lines painted on stones in summer and winter shows that most of the movement occurs in winter. The stones usually rotate randomly as they move, probably by sliding on ice. There is no obvious sorting or rounding of the blocks during movement downslope. The deposits produced differ from talus/scree sediments as they have a dip of less than the maximum angle of rest of dry sediment (c. 33°) and also show no sorting downslope. The movement of material takes place predominantly in winter, rather than in summer and the deposits occur in areas of negligible snow cover. Ground temperatures suggest exceptionally rapid temperature changes under the blocks, indicating air exchange in the voids. Mean ground temperatures in the loams beneath the blocks are about 7°C colder than in the adjacent soils. Winter snow covers are noticeably absent, and summer precipitation is often in the form of snow, which soon melts. Permafrost is present beneath the block stream but is absent in the sandy loam soils. The ground is also moister beneath the blocks. It appears that the surface blocks tend to slide downslope on the icy surface of the underlying blocks, perhaps aided by water from melting snow. This and the lack of sorting by clast size clearly differentiates them from talus slopes or avalanche deposits.     

平原河网地区河流结构特征及其对调蓄能力的影响

平原河网地区是河流高度发育并受到城市化深刻影响的区域。本文以上海为例,基于上海及周边城市普遍采用的河流分类和水利片管理系统,分析不同城市化水平地区河流结构的共同特征及其差异性,探讨河流结构对河网调蓄能力的可能影响,提出估算河网调蓄能力的方法。研究表明,平原河网地区河流结构指标反映了该地区河流数量、长度以及低等级河流高度发育的自然地理特征,城市化在达到一定程度后即会干扰河流结构的自身发育规律,并表现为河流发育能力的下降;河流结构在城市化影响下表现出由复杂到简单、由多元到单一的变化趋势;河网调蓄能力受低等级河流数量及结构的影响更大,并随着城市化水平的提高而下降;就整体而言,城市化对河网调蓄能力的影响大于对河流结构的影响;以水面数量和河流结构两项指标作为参数能够更准确地估算河网调蓄能力。     

Relationships between land-use and forced-pool characteristics in the Colorado Front Range

Land use practices in Colorado during the last two centuries altered the supply of sediment and water to many channels in the upper South Platte Basin. As a result of increased supply of sediment and mobility and reduced peak flows, the characteristics of pools associated with channel constrictions, referred to as forced pools, may have been altered. Increased supply of sediment and reduced transport capacity of high flows could lead to aggradation in forced pools. Channel confined by road corridors could lead to high velocities at normal flows, increased energy dissipation from riprap, or even increased pool frequency resulting from failed riprap. To assess potential alterations, four hypotheses were tested: (1) impacted streams will show significantly different mean volume of pools than a control stream; (2) mean volume of pools on streams where land-use activities increased the supply of sediment will be significantly different from streams solely affected by flow regulation; (3) the strongest change in characteristics of pools of impacted streams will be a reduced volume of pools; (4) streams affected by road corridors will show statistically lower spacing of pools than streams unaffected by roads. The downstream spacing and residual volume of twenty consecutive forced pools were surveyed on five streams in the Colorado Front Range that varied from no contemporary impact to multiple historical and contemporary impacts. ANCOVA with stepwise model selection indicated that degree of land-use (categorical), bankfull spacing of pools, upstream riffle slope and expansion ratio were all significant (α = 0.1) predictors of volume of pools (R² = 0.73). Simple linear regression of mean volume of pools and stream specific variables (gradient, drainage area and discharge) and least square means comparison of mean volume of pools indicated a need to standardize volumes of pools by slope and discharge so that the volumes of pools could be compared among different levels of land-use. Significant correlations between drainage area and volume of pools allowed volume of pools to be standardized by drainage area and thereby discharge. This dimensionless variable was also significantly correlated with channel slope, which permitted the construction of a new variable, PV_QS (volume of pools standardized by discharge and slope). Least square means comparison of mean PV_QS revealed that the control reach was significantly different from road-impacted reaches. Mean volume of pools was significantly larger in the control reach compared to all but one road-impacted stream. This was likely a function of higher wood loading in the control reach and the competence of high flows in the road-impacted reach. Streams affected by road corridors did not have significantly different bankfull spacing of pools from streams not impacted by roads. The multiple interactions among control and response variables explored in this study indicate the need to identify the most constrained and sensitive response variables when attempting to assess channel response to land use.     

Water chemistry and its diversity in relation to local factors in the Latnjavagge drainage basin, arctic–oceanic Swedish Lapland

The chemistry of precipitation, snow pack and surface water has been analysed on 205 samples collected during the 2001 field season at 25 selected sites within the Latnjavagge drainage basin in arctic–oceanic northern Swedish Lapland. Additionally, daily discharge and yield of dissolved solids have been calculated for several subcatchments and the entire Latnjavagge catchment during the years 2000, 2001 and 2002. Chemical water analysis included the components Ca²⁺, Mg²⁺, Na⁺, K⁺, Fe²⁺, Mn²⁺, Cl⁻, NO₃⁻, SO₄²⁻ and PO₄³⁻, with SO₄²⁻ and Ca²⁺ being the dominant ones in the surface water. Solute concentrations and chemical denudation were low, but showed significant differences within the basin. In areas of shade, longer snow cover, frozen ground and thin regolith, concentrations over the summer were perceptible but so low that solutes brought into the basin from precipitation could be detected in the surface water. In one locality, it was even found that lake water could reflect snowmelt to such an extent that the solute concentration was less than that of summer precipitation. The highest concentrations were found at a radiation-exposed, W-facing, vegetated, moderately steep slope with relatively thick regolith that was thawed at the time of snowmelt in early June. In such well-drained sites with continuous subsurface water flow, a maximum of contact between water and mineral particles could take place. The concentration values revealed differences in the rate of thawing of frozen ground between shaded areas and/or areas at higher altitude on the one hand and radiation-exposed areas on the other. A comparison with published results from Kärkevagge a few kilometres to the northwest as well as from other periglacial locations indicates that the chemical denudation values from Latnjavagge are more representative of periglacial oceanic environments than the values from the Kärkevagge catchment, which shows especially high chemical denudation rates. The investigation in Latnjavagge stresses the importance of spatial variability within even small catchments of homogeneous lithology as it demonstrates that solute concentrations from different subbasins can differ substantially dependent on exposure to radiation, duration of snow cover and frozen ground conditions, regolith thickness and possibly also to vegetation cover and slope angle as factors steering water turbulence and retention of drainage.     

快速城市化地区水系结构变化特征——以深圳市为例

为了探讨城市化对水系结构的影响,应用深圳市1982、2002年的二期水系详查图,定量分析了水系长度、密度、分枝比、分枝能力和分维数等参数的变化特征。结果表明: 快速城市化过程中, 深圳市的河道总长度减少、密度减小, 河道数目减少, 特别是低级别的支流减少较多; 河道的分枝比和分枝能力都有不同程度的弱化, 单个水系片区和全市的河流分维数都下降,河流具有简单化的趋势, 河流的多元化特征削弱; 对于不同水系片区来说, 其变化速度不同, 表明城市化过程对水系结构的干扰存在空间差异性。建议强力推进河流的蓝线规划和滨水区的开发管理, 将水网的保护和规划纳入到城市规划的管理范围; 注重在开发利用中的保护, 减少各类新建城市用地、农用地整理过程中对水系的破坏; 加大水土保持力度, 减少因水土流失导致河流淤塞; 加强管理, 严禁向河道中倾倒垃圾。     

The Organic Component of Particulate Matter in Small Streams of the Northern Yenisei Region During the Summer-Autumn Period

A quantitative assessment is made of suspended sediment load, including particulate organic matter and organic carbon, in 2014 for the small streams of the Northern Yenisei region, in the taiga–tundra transition zone (near the city of Igarka, Krasnoyarsk krai). It was found that the suspended sediment concentration (SSC) of the streams under investigation fluctuated between 2 and 18 mg/L during the summer–autumn low-water period of 2014. The proportion of dissolved organic matter (DOM) in the total sediment yield varied from 16.4% to 74.1%, depending on landscape-geomorphological conditions for suspended sediment formation: it is higher for streams with tundra catchments and lower on forest watersheds underlain by sandy and clayey loams. The DOM content varies from catchment to catchment from 1.63 to 2.42 mg/L, and the mean concentration of dissolved organic carbon (DOC) is estimated at 0.73 to 1.09 mg C/L. It is shown that the local channel transformations serve as the main source of POM and DOC input to the water of two out of three streams under study. Surface runoff or fast subsurface flow in the organic soil horizon is the external source of DOM input to the water of the third stream during flooding. Regional empirical dependencies were obtained, which correlate the water discharge, total SSC and the proportion of DOM are obtained. The long-term proportion of DOM in the annual suspended sediment flow of the Graviika river makes up 25% and DOC, 11%, or, in absolute values, 406 and 183 t/year, and in units of layer 1.26 and 0.57 t/km², respectively.     

Assessing the Influence of the Mining Operations on the State of Streams in the Northern Part of the Red River Basin (Viet Nam)

A study was made of the influence of extraction of lead and zinc ores in the northern part of Vietnam (the Red river basin, Chodon district of Bac Can Province, and the basins of the Dai, Ban Thi, Ta Dieng and Cau rivers). Background concentrations of macro- and microelements and biogenic elements are determined in the river waters and water extracts from bottom sediments of small streams of the study area. A significance exceedance of background concentrations was revealed in stretches of the headwaters of the Ban Thi and Dai rivers caused by a combination of natural and anthropogenic factors. It is established that the river waters near the pollution sources contain increased (compared with the geochemical background) concentrations of Zn, Pb, Fe, Ni, Co, As, Bi, Cd, Cs, Sb, Ag,NO₂^? and SO₄^2?. The waters are estimated as moderately and heavily polluted, and at the other points as minimally polluted. It is determined that the level of accumulation of matter in water extracts from bottom sediments with respect to the geochemical background in the vicinity of the ore dressing factories corresponds to weakly and heavily polluted bottom sediments, and further downstream, to thy minimum level of pollution. It is shown that the influence of extraction of lead and zinc ores on the state of small streams is observed in stretches as long as 11–12 km (with a maximum in stretches of up to 4.5 km). The mathematical model of Pb and Zn distribution in the river waters of the study area has been developed and tested.     

于桥水库流域地表水非点源N时空变化特征

在野外水样监测（1999年5月－2000年10月）和土地利用调查的基础上，利用遥感影像和数字化地形图，运用GIS的空间分析和图形叠置功能，研究于桥水库域地表水非点源N的时空变化特征。结果表明，在时间上，NH4^ －N的峰值出现在枯水期，而NO3^-N的峰值出现在丰水期；在空间上，NH4^ －N含量在中部平原区最高，南部丘陵和北部山区居其次，NO3^-N含量的变化则不具有明显的规律性。NH4^ －N和NO3^-不同的时空分布特征与它们的化学性质及流域内土地利用格局有关。