排序方式： 共有14条查询结果，搜索用时 46 毫秒
1.
Divergence and flow direction as indicators of subsurface heterogeneity and stage‐dependent storage in alluvial floodplains 
下载免费PDF全文
下载免费PDF全文 D. M. Heeren G. A. Fox A. K. Fox D. E. Storm R. B. Miller A. R. Mittelstet 《水文研究》2014,28(3):1307-1317
Assuming homogeneity in alluvial aquifers is convenient, but limits our ability to accurately predict stream‐aquifer interactions. Research is needed on (i) identifying the presence of focused, as opposed to diffuse, groundwater discharge/recharge to streams and (ii) the magnitude and role of large‐scale bank and transient storage in alluvial floodplains relative to changes in stream stage. The objective of this research was to document and quantify the effect of stage‐dependent aquifer heterogeneity and bank storage relative to changes in stream stage using groundwater flow divergence and direction. Monitoring was performed in alluvial floodplains adjacent to the Barren Fork Creek and Honey Creek in northeastern Oklahoma. Based on results from subsurface electrical resistivity mapping, observation wells were installed in high and low electrical resistivity subsoils. Water levels in the wells were recorded real time using pressure transducers (August to October 2009). Divergence was used to quantify heterogeneity (i.e. variation in hydraulic conductivity, porosity, and/or aquifer thickness), and flow direction was used to assess the potential for large‐scale (100 m) bank or transient storage. Areas of localized heterogeneity appeared to act as divergence zones allowing stream water to quickly enter the groundwater system, or as flow convergence zones draining a large groundwater area. Maximum divergence or convergence occurred with maximum rates of change in flow rates or stream stage. Flow directions in the groundwater changed considerably between base and high flows, suggesting that the floodplains acted as large‐scale bank storage zones, rapidly storing and releasing water during passage of a storm hydrograph. During storm events at both sites, the average groundwater direction changed by at least 90° from the average groundwater direction during baseflow. Aquifer heterogeneity in floodplains yields hyporheic flows that are more responsive and spatially and temporally complex than would be expected compared to more common assumptions of homogeneity. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
2.
Understanding species distributions, and how they change in space and time, is vital when prioritising conservation or management initiatives. We assessed the distribution and density patterns of common dolphins (Delphinus sp.), bottlenose dolphins (Tursiops truncatus) and Bryde’s whales (Balaenoptera edeni) in the Hauraki Gulf, New Zealand. Dedicated boat-based surveys were conducted in the inner Hauraki Gulf (IHG) and off Great Barrier Island (GBI) during 2010–2012. Generalised linear models were used to investigate temporal changes in relative densities and kernel density estimation was implemented to examine spatial trends. Common dolphins were widely distributed during all seasons, with higher densities observed during winter and spring in the IHG but during autumn off GBI. There was inter-annual variation in Bryde’s whale distribution, with high densities recorded off GBI in 2011. Bottlenose dolphins were infrequently sighted in the IHG but regularly encountered off GBI, with the highest densities during spring and summer. 相似文献
3.
Green-lipped mussels (Perna canaliculus) formed extensive reefs on soft sediments in sheltered embayments around northern New Zealand until overfishing and/or increased sediment input caused their virtual disappearance by 1980. To determine the role of mussel reefs as habitat for other animals, we located remnant soft-sediment reefs in five locations and compared the density, biomass, productivity and composition of mobile macroinvertebrate communities, and the density of small fishes associated with mussels, with fauna in the surrounding soft sediments. The mussel reefs had a distinct assemblage of macroinvertebrates, which had 3.5 times the density, 3.4 times the biomass and 3.5 times the productivity of surrounding areas. The density of small fishes was 13.7 times higher than in surrounding areas. These results show that soft-sediment mussel reefs support an abundant and productive fauna, highlighting the probable large loss of productivity associated with the historical decline in mussel habitat and the consequent desirability of restoration efforts. 相似文献
4.
我们曾提出过一种可能导致地磁和地壳电导率异常的来源：地壳中的二级磁相变,即居里（尼尔）深度附近磁化率的显著提高.这一现象能很好地解释一些来源不明的地磁异常.本文总结了在中地壳深度处、薄且高磁导率异常体的一维和多维大地电磁特征.高磁导率层引起的异常与高电导率层导致的异常相比,大小上可相比拟,但符号相反.无论在什么情况下,经典的大地电磁解释容易导致一个不真实的极厚高阻层,并且在地磁异常附近有与之对应的空间波长,二级磁相变也被认为是这一现象的可能解释.尽管在地壳中是否存在二级磁相变还有一定争议,但最近的一些固体物理实验结果进一步表明它可能是地壳各种地球物理异常的来源之一. 相似文献
5.
ABSTRACTFloodplains are composed of complex depositional patterns of ancient and recent stream sediments, and research is needed to address the manner in which coarse floodplain materials affect stream–groundwater exchange patterns. Efforts to understand the heterogeneity of aquifers have utilized numerous techniques typically focused on point-scale measurements; however, in highly heterogeneous settings, the ability to model heterogeneity is dependent on the data density and spatial distribution. The objective of this research was to investigate the correlation between broad-scale methodologies for detecting heterogeneity and the observed spatial variability in stream/groundwater interactions of gravel-dominated alluvial floodplains. More specifically, this study examined the correlation between electrical resistivity (ER) and alluvial groundwater patterns during a flood event at a site on Barren Fork Creek, in the Ozark ecoregion of Oklahoma, USA, where chert gravels were common both as streambed and as floodplain material. Water table elevations from groundwater monitoring wells for a flood event on 1–5 May 2009 were compared to ER maps at various elevations. Areas with high ER matched areas with lower water table slope at the same elevation. This research demonstrated that ER approaches were capable of indicating heterogeneity in surface water–groundwater interactions, and that these heterogeneities were present even in an aquifer matrix characterized as highly conductive. Portions of gravel-dominated floodplain vadose zones characterized by high hydraulic conductivity features can result in heterogeneous flow patterns when the vadose zone of alluvial floodplains activates during storm events.
EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR X. Chen 相似文献
6.
A borehole permeameter is well suited for testing saturated hydraulic conductivity (K(sat)) at specific depths in the vadose zone. Most applications of the method involve fine-grained soils that allow hand auguring of test holes and require a small water reservoir to maintain a constant head. In non-cohesive gravels, hand-dug test holes are difficult to excavate, holes are prone to collapse, and large volumes of water are necessary to maintain a constant head for the duration of the test. For coarse alluvial gravels, a direct-push steel permeameter was designed to place a slotted pipe at a specific sampling depth. Measurements can be made at successive depths at the same location. A 3790 L (1000 gallons) trailer-mounted water tank maintained a constant head in the permeameter. Head in the portable tank was measured with a pressure transducer and flow was calculated based on a volumetric rating curve. A U.S. Bureau of Reclamation analytical method was utilized to calculate K(sat). Measurements with the permeameter at a field site were similar to those reported from falling-head tests. 相似文献
7.
新疆东天山图拉尔根大型铜镍矿床硫化物珠滴构造的特征及其对通道式成矿的指示 总被引：7，自引：4，他引：3
东天山图拉尔根岩浆铜镍硫化物矿床中产出一种不常见的硫化物珠滴状构造。这些硫化物珠滴粒度在5~20mm左右,是由磁黄铁矿、镍黄铁矿、黄铜矿等硫化物矿物组成的斑杂状硫化物集合体。野外观察发现硫化物珠滴具有各种几何形态,产出在稀疏浸染状硫化物和无矿化的辉石岩之间的部位。对图拉尔根杂岩体中发育的24个硫化物珠滴的统计结果显示,平缓厚层状矿化部位的硫化物珠滴呈水平方向拉长,陡倾薄层状矿化部位的硫化物珠滴呈陡倾拉长,珠滴的拉长方向和矿体的延伸方向一致。这表明在含矿母岩浆上升就位到中上地壳的过程中,硫化物珠滴受到熔浆流动的控制,因而其形态可以很好地指示通道式成矿硫化物熔体运动的方向。 硫化物珠滴的矿相学和电子探针数据表明其具有向地性特征,即磁黄铁矿和镍黄铁矿先结晶,沉淀在下部; 珠滴上部为后结晶的黄铜矿和其它富铜硫化物。这种元素分布可能对贯入块状硫化物矿石同样适用。碲化物和铋化物在硫化物珠滴中的含量明显高于其在早结晶的浸染状硫化物中的含量,表明富Te和Bi等元素及挥发份的熔体是在岩浆演化后期开始富集结晶的。 相似文献
8.
Derek M. Heeren Garey A. Fox Ronald B. Miller Daniel E. Storm Amanda K. Fox Chad J. Penn Todd Halihan Aaron R. Mittelstet 《水文研究》2011,25(20):3230-3243
Models for contaminant transport in streams commonly idealize transient storage as a well mixed but immobile system. These transient storage models capture rapid (near‐stream) hyporheic storage and transport, but do not account for large‐scale, stage‐dependent interaction with the alluvial aquifer. The objective of this research was to document transient storage of phosphorus (P) in coarse gravel alluvium potentially influenced by large‐scale, stage‐dependent preferential flow pathways (PFPs). Long‐term monitoring was performed at floodplain sites adjacent to the Barren Fork Creek and Honey Creek in northeastern Oklahoma. Based on results from subsurface electrical resistivity mapping which was correlated to hydraulic conductivity data, observation wells were installed both in higher hydraulic conductivity and lower hydraulic conductivity subsoils. Water levels in the wells were monitored over time, and water samples were obtained from the observation wells and the stream to document P concentrations at multiple times during high flow events. Contour plots indicating direction of flow were developed using water table elevation data. Contour plots of total P concentrations showed the alluvial aquifer acting as a transient storage zone, with P‐laden stream water heterogeneously entering the aquifer during the passage of a storm pulse, and subsequently re‐entering the stream during baseflow conditions. Some groundwater in the alluvial floodplains had total P concentrations that mirrored the streams' total P concentrations. A detailed analysis of P forms indicated that particulate P (i.e. P attached to particulates greater than 0·45 µm) was a significant portion of the P transport. This research suggests the need for more controlled studies on stage‐dependent transient storage in alluvial systems. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
9.
Snapper (Chrysophrys auratus) is an important coastal fish species in New Zealand for a variety of reasons, but the large amount of research conducted on snapper has not been reviewed. Here, we review life history information and potential threats for snapper in New Zealand. We present information on snapper life history, defining stages (eggs and larvae, juvenile and adult), and assess potential threats and knowledge gaps. Overall we identify six key points: 1. post-settlement snapper are highly associated with certain estuarine habitats that are under threat from land-based stressors. This may serve as a bottleneck for snapper populations; 2. the largest knowledge gaps relate to the eggs and larvae. Additional knowledge may help to anticipate the effects of climate change, which will likely have the greatest influence on these early life stages; 3. ocean acidification, from land-based sources and from climate change, may be an important threat to larval snapper; 4. a greater understanding of population connectivity would improve certainty around the sustainability of fishery exploitation; 5. the collateral effects of fishing are likely to be relevant to fishery productivity, ecosystem integrity and enduser value; 6. our understanding of the interrelationships between snapper and other ecosystem components is still deficient. 相似文献
10.
We estimated population abundance of New Zealand fur seal (Arctocephalus forsteri) pups on Bench Island off Stewart Island, New Zealand seven times between 1996 and 2012. Overall, there was a 29% increase in pup abundance from 1996 to 2012 at the Main Beach colony, corresponding to a mean annual growth rate of 1.6% and a doubling time of approximately 40 years. At the Sprat Point colony, there was an overall increase of 29% between 2003 and 2012 corresponding to a mean annual growth rate of 2.9% and a doubling time of approximately 25 years. The area occupied by both colonies has also increased. In 2006, we surveyed East Beach and counted a total of 201 pups. We obtained traditional ecological knowledge of fur seal distribution and breeding status from local Māori for 46 locations around Stewart Island, 36 of which have not been surveyed since Wilson in 1971–1974; this supports an expansion of fur seal presence and breeding areas in the region in the last 41 years. 相似文献