Evaluation of riverbed magnetic susceptibility for mapping biogeochemical hot spots in groundwater-impacted rivers     

Chen Wang  Martin A. Briggs  Frederick D. Day-Lewis  Lee D. Slater 《水文研究》2021,35(5):e14184

Redox hot spots occurring as metal-rich anoxic groundwater discharges through oxic wetland and river sediments commonly result in the formation of iron (Fe) oxide precipitates. These redox-sensitive precipitates influence the release of nutrients and metals to surface water and can act as ‘contaminant sponges’ by absorbing toxic compounds. We explore the feasibility of a non-invasive, high-resolution magnetic susceptibility (MS) technique to efficiently map the spatial variations of magnetic Fe oxide precipitates in the shallow bed of three rivers impacted by anoxic groundwater discharge. Laboratory analyses on Mashpee River (MA, USA) sediments demonstrate the sensitivity of MS to sediment Fe concentrations. Field surveys in the Mashpee and Quashnet rivers (MA, USA) reveal several discrete high MS zones, which are associated with likely anoxic groundwater discharge as evaluated by riverbed temperature, vertical head gradient, and groundwater chemistry measurements. In the East River (CO, USA), widespread cobbles/rocks exhibit high background MS from geological ferrimagnetic minerals, thereby obscuring the relatively small enhancement of MS from groundwater induced Fe oxide precipitates. Our study suggests that, in settings with low geological sources of magnetic minerals such as lowland rivers and wetlands, MS may serve as a complementary tool to temperature methods for efficiently mapping Fe oxide accumulation zones due to anoxic groundwater discharges that may function as biogeochemical hot spots and water quality control points in gaining systems.  相似文献   

Swelter in the city: Urban greenery and its effects on temperature in Guwahati,India     

Monjit Borthakur  Anup Saikia  Kiran Sharma 《Singapore journal of tropical geography》2020,41(3):341-366

Changing urban landscape with multistoried high rises, roads and pavements is continuously reducing urban green space. These structures result in high surface temperature variation within cities. To explore the relationship between surface temperature and normalized difference vegetation index (NDVI), this study estimates two models—geographically weighted regression (GWR) and a fixed effect panel data model in relation to the Guwahati Metropolitan Area (GMA), a secondary city in north east India. The results indicate the superiority of GWR regression in presence of spatial dependence. Panel data analysis shows that the densely populated urban areas in the GMA with less than 10 per cent greenery are 1°C warmer than the sub-urban areas with 50 per cent greenery.  相似文献   

Seismic‐stratigraphic constraints on the age of the Faroe Islands Basalt Group,Faroe–Shetland region,Northeast Atlantic Ocean     

Jana lavsdttir  Martyn S. Stoker  Lars O. Boldreel  Morten Sparre Andersen   luva R. Eidesgaard 《Basin Research》2019,31(5):841-865

Lower Palaeogene extrusive igneous rocks of the Faroe Islands Basalt Group (FIBG) dominate the Faroese continental margin, with flood basalts created at the time of breakup and separation from East Greenland extending eastwards into the Faroe‐Shetland Basin. This volcanic succession was emplaced in connection with the opening of the NE Atlantic; however, consensus on the age and duration of volcanism remains lacking. On the Faroe Islands, the FIBG comprises four main basaltic formations (the pre‐breakup Lopra and Beinisvørð formations, and the syn‐breakup Malinstindur and Enni formations) locally separated by thin intrabasaltic sedimentary and/or volcaniclastic units. Offshore, the distribution of these formations remains ambiguous. We examine the stratigraphic framework of these rocks on the Faroese continental margin combining onshore (published) outcrop information with offshore seismic‐reflection and well data. Our results indicate that on seismic‐reflection profiles, the FIBG can be informally divided into lower and upper seismic‐stratigraphic packages separated by the strongly reflective A‐horizon. The Lower FIBG comprises the Lopra and Beinisvørð formations; the upper FIBG includes the Malinstindur and Enni formations. The strongly reflecting A‐horizon is a consequence of the contrast in properties of the overlying Malinstindur and underlying Beinisvørð formations. Onshore, the A‐horizon is an erosional surface, locally cutting down into the Beinisvørð Formation; offshore, we have correlated the A‐horizon with the Flett unconformity, a highly incised, subaerial unconformity, within the juxtaposed and interbedded sedimentary fill of the Faroe‐Shetland Basin. We refer to this key regional boundary as the A‐horizon/Flett unconformity. The formation of this unconformity represents the transition from the pre‐breakup to the syn‐breakup phase of ocean margin development in the Faroe–Shetland region. We examine the wider implications of this correlation considering existing stratigraphic models for the FIBG, discussing potential sources of uncertainty in the correlation of the lower Palaeogene succession across the Faroe–Shetland region, and implications for the age and duration of the volcanism.  相似文献   

地表暖化影响下温度示踪地下水流速方法     

董林垚  任洪玉  雷俊山  刘纪根 《吉林大学学报(地球科学版)》2019,49(3):773-783

为构建温度示踪方法测算地下水流速技术体系，并应用于区域地下水资源评价，基于最小二乘法和垂向一维非稳定流水-热运移方程数值解法，提出地表暖化情形下地下水流速计算方法，并对雷州半岛东北部地下水流速进行测算。结果表明：研究区域地下水补给速度为0.796 m/a，入渗以西北部降水和运河渗漏为主；地下水排泄速度为0.269 m/a，排泄入海主要发生在东海岛、南三岛和硵州岛附近。温度示踪解析区域地下水流动情况与地下水位分布情况基本一致，观测和计算地温数据具有较强相关性（R²>0.50）和较低均方根误差（均值0.748），表明提出方法率定得到的地下水流速具有较强的可靠性。参数敏感性分析结果表明，地质体热扩散率和地表温度均对地温计算结果产生较明显的影响，参数的准确率定对利用地温计算地下水流速十分重要。  相似文献   

辽宁省积雪对自动气象站观测地气温差的影响     

朱玲  顾正强  龚强  晁华  李杨  徐红  周晓宇  沈历都  蔺娜 《冰川冻土》2019,41(2):293-303

利用1971—2016年辽宁省61个气象站气温、地表温度、积雪日数和积雪深度资料，分析了积雪的保温作用及其对地气温差的影响。结果表明：更换自动站前后地表温度观测方式的差异导致地气温差显著增大，地气温差的增大程度受所在区域积雪日数、积雪深度的影响显著。在积雪期较长、积雪较厚的地区，积雪引起反照率增大，使得雪面温度降低，导致雪气温差减小，而雪的保温作用使得地气温差显著增大。因此，更换自动站前地（雪）气温差与积雪日数呈显著负相关，而更换自动站后地气温差与积雪日数呈显著正相关。各台站之间地气温差随积雪深度的变化系数差异较大，为0.045~0.858 ℃?cm^-1，在年平均积雪日数＜40 d、年平均极端积雪深度＜10 cm的区域，积雪的保温作用随积雪深度增大而显著增大；在年平均积雪日数＞40 d、年平均极端积雪深度＞10 cm的区域，10 cm以下的积雪对土壤保温作用随积雪深度增大显著，当积雪深度＞10 cm后，其保温作用随积雪深度增大的幅度明显减小。  相似文献   

秋季连续打捞蓝藻对水-气界面温室气体通量的影响     

荀凡  杜先  陈新芳  刘高飞  齐天赐  冯慕华 《湖泊科学》2020,32(6):1707-1722

在巢湖西北半湖近岸带设置大型围隔研究秋季连续打捞蓝藻对湖泊温室气体通量的影响，应用YL-1000型大型仿生式水面蓝藻清除设备进行原位打捞蓝藻，通过便携式温室气体分析仪-静态箱法对大型围隔内水-气界面CH₄、CO₂通量特征及其影响因素进行观测.结果表明：对比未打捞区，蓝藻连续打捞下打捞区水体中叶绿素a（Chl.a）、悬浮物（SS）浓度不断下降，两者削减率分别为72%、85%，Chl.a、SS浓度分别下降到29.6±2.5 μg/L、12.5±1.2 mg/L，打捞对围隔内颗粒态物质去除效果十分明显；打捞过程中水体溶解性有机物（DOM）中微生物代谢类腐殖质（C1）、类蛋白（C3）显著下降趋势，打捞区C1、C3组分（0.18±0.02、0.06±0.01 RU）强度明显低于未打捞区（0.26±0.05、0.12±0.03 RU），打捞能有效控制藻源性溶解性有机质释放.同时，打捞区水-气界面CH₄通量呈显著下降趋势，未打捞区CH₄通量平均值（17.473±1.514 nmol/（m²·s））为打捞区（7.004±4.163 nmol/（m²·s））近2倍，CH₄通量与Chl.a、C1、C3组分均呈显著正相关，水体中藻源性溶解态有机质对CH₄通量具有促进作用；打捞区CO₂释放通量呈显著上升趋势，打捞区CO₂吸收通量（-0.200±0.069 μmol/（m²·s））明显低于未打捞区（-0.344±0.017 μmol/（m²·s）），CO₂通量与Chl.a、温度均呈显著负相关.秋季打捞对CH₄、CO₂综合日平均通量减排量值为0.275±0.076 mol/（m²·d）（以CO₂当量计）.研究结果揭示了巢湖秋季连续打捞蓝藻过程对水-气界面温室气体具有显著减排作用，且能在一定程度上减缓蓝藻水华与湖泊富营养化、气候变暖之间的恶性循环，为湖泊碳循环和蓝藻水华灾害防控提供科学数据支撑和理论参考.  相似文献   

华南上扬子区深部温度估算及其油气地质意义     

李香兰  刘绍文  徐明  李旭东  郝春艳 《地质学报》2020,94(6):1896-1910

盆地热体制及深部温度估算对油气和区域地热能资源评估具有重要意义。南方上扬子区是海相油气勘探的重要区块,近年来更是我国页岩气勘探的主要选区。然而,由于数据不足及研究目标的分散,该区的盆地热体制特征还有待深化。结合前人已有地热数据,并整合新近开展的稳态测温数据,我们揭示了上扬子区现今地温梯度、大地热流分布特征,继而估算了1000～6000m埋深处的深部地层温度和2套主要古生界海相烃源岩底界面处的温度。结果表明,上扬子区具有中-低温的地热状态,其现今地温梯度和大地热流的范围(平均值)分别为10～74℃/km(24℃/km)和27～118mW/m~2(64mW/m~2),整体上从东北向西南方向递增,呈现出"东北低、西南高"的分布趋势。1000～6000m埋深处估算温度的分布格局与地温梯度及热流的分布趋势基本一致。东北部的鄂西-湘北地区为低温区,中部的四川盆地其大部分为中温区,西南的云南地区为高温区。上扬子区现今地热分布格局受区域差异构造和岩浆作用控制。结合储层温度估算并综合其他油气地质资料,提出川东的石柱-涪陵、川南的威远-自贡-泸州和宜宾-长宁等区的下志留统龙马溪组页岩层系是上扬子区油气勘探有利区带。  相似文献   

The effects of floods on the temperature of riparian groundwater          下载免费PDF全文

Jeffery A. Watson  M. Bayani Cardenas  Stephen B. Ferencz  Peter S.K. Knappett  Bethany T. Neilson 《水文研究》2018,32(9):1267-1281

The transition area between rivers and their adjacent riparian aquifers, which may comprise the hyporheic zone, hosts important biochemical reactions, which control water quality. The rates of these reactions and metabolic processes are temperature dependent. Yet the thermal dynamics of riparian aquifers, especially during flooding and dynamic groundwater flow conditions, has seldom been studied. Thus, we investigated heat transport in riparian aquifers during 3 flood events of different magnitudes at 2 sites along the same river. River and riparian aquifer temperature and water‐level data along the Lower Colorado River in Central Texas, USA, were monitored across 2‐dimensional vertical sections perpendicular to the bank. At the downstream site, preflood temperature penetration distance into the bank suggested that advective heat transport from lateral hyporheic exchange of river water into the riparian aquifer was occurring during relatively steady low‐flow river conditions. Although a small (20‐cm stage increase) dam‐controlled flood pulse had no observable influence on groundwater temperature, larger floods (40‐cm and >3‐m stage increases) caused lateral movement of distinct heat plumes away from the river during flood stage, which then retreated back towards the river after flood recession. These plumes result from advective heat transport caused by flood waters being forced into the riparian aquifer. These flood‐induced temperature responses were controlled by the size of the flood, river water temperature during the flood, and local factors at the study sites, such as topography and local ambient water table configuration. For the intermediate and large floods, the thermal disturbance in the riparian aquifer lasted days after flood waters receded. Large floods therefore have impacts on the temperature regime of riparian aquifers lasting long beyond the flood's timescale. These persistent thermal disturbances may have a significant impact on biochemical reaction rates, nutrient cycling, and ecological niches in the river corridor.  相似文献   

Bacteria‐sediment associations in an alpine,freshwater environment and their effects on particle size,density and settling velocity          下载免费PDF全文

David C. Barrett  Kyle R. Hodder 《地球表面变化过程与地形》2018,43(10):2232-2242

This study measures the presence of bacteria‐sediment associations (BSAs) in an alpine, glacier‐fed watershed in the Southern Coast Mountains of British Columbia, Canada. The impact of BSAs on the creation of flocculated particles and their settling velocity are quantified using a laser transmissometer. Results from the study indicate that BSAs are present in the watershed and vary over both space and time. The percentage of bacteria associated with sediment particles was found to range from < 1% to 40%. Major sources of planktonic bacteria such as agricultural land and wastewater treatment outflow co‐occur with large decreases in the BSA ratio. Laboratory analysis demonstrates that an increase in the concentration of bacteria was associated with a decrease in the volume concentration of small particles, and a decrease in both estimated density and measured settling velocity for particles in larger size classes; consistent with flocculated particles of increasing complexity arising from combinations of primary particles and/or BSAs. Paleoenvironmental reconstructions using laminated lake sediments in alpine, glacier‐fed systems benefit from a fuller understanding of the geomorphologic processes by which they formed. While bacteria are noted to enhance formation of flocculated particles in laboratory systems, their impact upon geomorphic processes in natural systems have yet to be fully explored. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

In situ measurements of wind‐driven salt fluxes through constructed channels in a coastal wetland ecosystem          下载免费PDF全文

Alex K. Manda  Enrique Reyes  James M. Pitt 《水文研究》2018,32(5):636-643

A suite of instruments was deployed in a coastal wetland ecosystem in the Albemarle estuarine system, North Carolina (USA), to characterize wind‐driven transport of saltwater through a constructed (man‐made) channel. Flow velocity, electrical conductivity, and stage were measured in a representative channel over a 2‐month period from May to July 2014, during which 4 wind tides were observed. Collected data show that thousands of metric tons of salt were advected through the channel into coastal wetlands during each event, which lasted up to 4 days. The results reveal that as much as 36% of advected salts accumulated in the wetlands, suggesting that the cumulative effects of these events on the health of coastal wetlands in the Albemarle system may be substantial due to the abundance of constructed channels and the frequency of wind‐driven tidal events. This study is the first to quantify wind‐driven salt fluxes through constructed channels in coastal wetland settings.  相似文献