Duck Lake Research Articles

Research on Typical Plant Spectral Distinguishable Characteristics by Mann-Whitney U-Test in Wild Duck Lake

Wetlands is a superior way to purify water environment. However monitoring and discriminating among vegetation covers types are critical to understanding population distribution, biogeochemical functioning and the process of wetland recovery. Recently, remote sensing technology has become an important tool to monitor wetland vegetation. Typical wetland plants Bidens Pilosa, Scirpus planiculumis, Phragmites australis and Typha angustifolia in Wild duck wetland were chosen, and Mann-Whitney U-test were used to analyze the spectral characteristics. There were typical vegetation spectral characteristics of dominant species spectral reflectance curve. There are differences among reflective spctral characteristic of species, especially in the green peak and steep reflection. According to the results of Mann-Whitney U-test, the highest frequency bands appeared in702-715732-745747nm, the classification precision of Bidens pilosa , Scirpus planiculumis and Phragmites australis are 100%, 100%, 80%. While It is difficult to distinguish Typha angustifolia from other species effectively using the three spectrum regions.

Canopy Water Content Estimation for Typical Emerged Plant Community from Simulation Worldview-2 Data: A Case Study in Wild Duck Lake Wetland, Beijing

Quantitative estimation of vegetation water content with remote sensing technique is of great significance for vegetation physiological status and growth trend monitoring. It also provides a theoretical foundation for actual application of vegetation water content diagnosis using remote sensing images in Wild Duck Lake wetland. In this paper the NDVIs and SRs calculated from simulation WorldVeiw-2 curves can be used to model and predict canopy water content of typical emerged plant. The NDVIs and SRs involving the additional spectral bands of WorldView-2, such as the red-edge and near infrared regions of the electromagnetic spectrum, improve the prediction accuracy compared with the traditional NDVIs and SRs.

不同端元模型下湿地植被覆盖度的提取方法——以北京市野鸭湖湿地自然保护区为例

植被覆盖度作为反映湿地植物生长状况的重要生态学参数,在评估和检测湿地生态环境方面起着关键的作用。以华北内陆典型的淡水湿地——北京市野鸭湖湿地自然保护区为研究对象,中等分辨率的Landsat TM影像为数据源,基于线性光谱混合模型(LSMM)对研究区的植被覆盖度进行了估算。针对湿地植被类型丰富、土地利用类型多样化的特点,利用归一化植被指数(NDVI)在反映植物生长状况、覆盖程度以及区分地表覆盖类型方面的优势,通过对原始Landsat TM影像增加NDVI数据维对影像进行维度扩展,克服了传统研究中通常从Landsat TM影像上提取3-4种端元的局限,经最小噪声分离变换(MNF变换)、纯像元指数(PPI)计算以及人机交互端元选取等一系列运算,构建以陆生植物、水生植物、高反射率地物、低反射率地物、裸露土壤为组分的五端元模型来反映研究区的地物组成;同时,以原始Landsat TM影像为基础,构建植物、高反射率地物、低反射率地物、裸露土壤为组分的四端元模型。针对两种端元模型,采用全约束下的LSMM算法进行混合像元分解以获取研究区的植被覆盖度,其次辅以研究区的纯水体信息对其进行优化。精度检验采用相同时期的高分辨率WorldView-2多光谱影像来进行。研究表明:虽然四端元模型与五端元模型对植被覆盖度的估算结果在空间上具有基本一致的分布趋势,但是前者的估算结果在数值上要普遍低于后者,在研究区的水体及其附近,四端元模型难以体现水生植物的植被覆盖信息;另外,五端元模型的估算结果与检验数据的相关系数<em>R</em>达到0.9023,均方根误差(RMSE)为0.0939,明显优于四端元模型的<em>R</em>=0.8671和RMSE=0.1711。这反映了通过对影像进行维度扩展的方法来改进端元提取的数量是可行的,而由此构建的五端元模型可以更充分的反映研究区地物之间的光谱差异,从而获得更好的估算精度。;Vegetation abundance is a critical indicator for measuring the status of vegetation. It is also important for revealing the rules of spatial change and evaluating the eco-environment of wetland. In this paper, vegetation abundance is estimated through a Linear Spectral Mixture Model (LSMM) using Landsat Thematic Mapper (TM) data within the Wild Duck Lake Wetland, a typical freshwater wetland in North China. Considering the biodiversity of wetland, it is necessary to select enough endmembers to characterize the spectral variability of features. However, a maximum of four endmembers is usually used in spectral mixture analysis when using Landsat TM data due to the high correlation coefficients among the three visible bands. Thus, the Normalized Difference Vegetation Index (NDVI), a widely used vegetation index, is included along with the six reflective bands of Landsat TM image, which extended the dimensionality of the TM data and allowed the use of five endmembers. After performed the Minimum Noise Fraction (MNF) transformation and Pixel Purity Index (PPI) algorithm, five endmembers are selected including Terrestrial plants, Aquatic plants, High albedo, Low albedo and Bare soil using n-Dimensional Visualizer Tool of ENVI software. At the same time, a four-endmember model which consists Plants, High albedo, Low albedo and Bare soil was established using the six reflective bands of Landsat TM data. For both four- and five-endmember model, we used a fully constrained LSMM algorithm to obtain the vegetation abundance of the study area. We modified our result using the pure water information of Wild Duck Lake Wetland, which was obtained by using NDVI and Normalized Difference Water Index (NDWI). The accuracy of vegetation abundance is validated by WorldView-2 multispectral image with a 1.8 meter spatial resolution through randomly selected 60 samples. The result showed that although the vegetation abundance extracted by four- and five-endmember model share almost the same spatial distribution, their values vary much from each other. Generally, the five-endmember model results a much higher value than the four-endmember model and it can reflect the vegetation abundance of aquatic plants better than the other. After the analysis of relationship between predicted and inspection values of both four- and five-endmember models, we found that the correlation coefficients are 0.8671 and 0.9023, respectively. Additionally, the Root Mean Square Error (RMSE) clearly showed that the five-endmember model can achieve a much better result than the other model: the former is 0.0939 and the latter is 0.1771. Our results suggest that it is feasible to improve the number of endmembers by extending the dimension of remote sensing image. By using NDVI as an additional data dimension along with the reflective bands of Landsat TM data, a five-endmember model can estimate vegetation abundance of Wild Duck Lake wetland better due to the inclusion of the fifth endmember. Moreover, four endmembers may be inadequate to spectrally characterize the heterogeneous landscapes of wetland. The use of five endmembers may further improve the representation of the spectral variability of land-cover types within the study area and thus potentially improve the accuracy for estimating vegetation abundance of wetlands.

湿地资源保护经济学分析——以北京野鸭湖湿地为例

湿地资源保护是全球生态保护的核心问题之一。在分析湿地资源保护的经济属性的基础上,以北京市野鸭湖湿地为案例,运用经济学的理论和方法以及清晰的图表重点分析了野鸭湖湿地资源保护过程中的外部性以及资源利用中成本与收益两个问题。研究结果表明:(1)从正外部性分析,个人收益小于社会收益,个人保护的湿地资源小于社会最优量,会造成湿地资源保护的不足;从负外部性分析,个人成本小于社会成本,个人对湿地资源的利用水平大于社会最优利用水平,造成湿地资源的过度利用;(2)根据湿地资源利用的成本收益分析结果,"搭便车"行为会造成湿地资源的退化甚至恶化;(3)明晰产权有利于湿地资源配置效率的提高。研究结果可以为中国湿地保护过程中出现的资源利用矛盾提供有益的借鉴,特别是为保护北京野鸭湖湿地提供理论支撑和政策建议。;A wetland ecosystem is one of the most important ecosystems on earth. It plays important roles in ecological balances and provides human beings with products such as food, water and entertainment. Therefore, wetland resource conservation is one of the key issues in global ecological environment protection. Based on the analysis of economic attributes of wetland resource conservation and the theories of property rights, public goods and externality, this research, taking the Beijing Wild Duck Lake (BWDL) wetland as an example, emphatically analyzed (1) the externality in the processes of BWDL resource protection and (2) the costs and the profits in the BWDL resource utilization. The results show: (1) Individual profits may not be compensated due to positive externality, which leads to the deficiency of resources during the wetland protection. We hold that a reasonable compensation mechanism should be built in order to compensate the people who participate in the protection of wetlands. Only when their individual profits were safeguarded then can the social optimal point be achieved. In addition, people who destroy wetland resources may not be punished due to negative externality. If there is no valid constraint mechanism for these behaviors of destroying wetland resources, deterioration of wetland resources cannot be avoided. Hence, in the view of externality theory, the primary reason caused the wetland deterioration is the lack of compensation and constraint mechanism of positive and negative externality. (2) Free riding will lead to the deterioration of wetland resources. Taking cage fish culture in the BWDL as an example, we analyzed the negative effect from free riding. Results show that free riding existed in the utilization of wetland resources, resulting in the excessive use of wetland resources. Once the carrying capacity of local wetland ecosystems was broken, wetland resources will deteriorate further. Hence, one of the most challenges facing by wetland resources protection is how to coordinate the contradiction between cost and benefit during the protection and utilization of wetland resources. (3) A clear property rights is good for wetland resources protection. Free riding and externality are, fundamentally, results of unclear property rights of wetland resources. In China, most of natural resources with characteristics of public goods belong to two types: state or collective ownership. The allocation efficient of wetland resources will be low under the condition of unclear property rights. Individual person who protect wetland resources cannot get expect revenue. Converting the operation right and revenue right to individual may be a good way to solve the above problems. Individual is response for cost and benefit during the utilization of wetland resources. The allocation efficient will be improved and market failure can thus be avoided. Thereafter, administers of wetlands should define behaviors and reasonability of damage behaviors of wetland resources. Meanwhile, they should also make clear about the right and responsibility of wetland resource users. These research results would provide references for the problems in wetland protection processes in our country. In particular, it can provide scientific basis and policy options in the BWDL wetland conservation.

FRACTAL RESEARCH ON DYNAMIC CHANGE OF THE BEIJING WILD DUCK LAKE WETLAND RESOURCES BASED ON GIS AND RS

The theory and characteristics of the fractal theory are described. The wetland data of the Beijing Wild Duck Lake in 1998, 2000 and 2002 were obtained on the basis of RS and GIS technology. Using the fractal dimension numerical model on two dimensional Euclidean space, the authors worked out the fractal dimension values and the stability levels of all kinds of wetland resources. The dynamic changes of wetland resources in the study area was finally obtained according to the physical meaning of fractal dimension and the level of stability. The results of the study indicate that marshes and lakes constitute the most key elements and also the most unstable wetland elements in wetland environments. It has been proved in practice that fractal theory has ample application scope in the study of wetland dynamic change. The fractal dimension and the level of stability can supply the decision-making basis for the appraisal of wetland environments and the sustainable utilization of wetland resources.

Chironomids as indicators of the Holocene climatic and environmental history of two lakes in Northeast Greenland

Schmidt, S., Wagner, B., Heiri, O., Klug, M., Bennike, O. & Melles, M. 2010: Chironomids as indicators of the Holocene climatic and environmental history of two lakes in Northeast Greenland. Boreas, 10.1111/j.1502-3885.2010.00173.x. ISSN 0300-9483. Two Holocene sediment sequences from arctic lakes on Store Koldewey, an island in Northeast Greenland, were investigated for fossil chironomid assemblages. A total of 18 and 21 chironomid taxa were identified in 290- and 252-cm-long sediment sequences from Duck Lake and Hjort Lake, respectively. The chironomid assemblages were very similar in the two lakes. Canonical correspondence analysis (CCA) was used to compare fossil chironomid assemblages from Store Koldewey with chironomid assemblages and environmental conditions presently found in Canadian Arctic lakes and, hence, to infer environmental changes for Northeast Greenland. The first chironomids appeared at c. 9500 cal. a BP in Hjort Lake, and 500 years later in Duck Lake. Taxa typical for cold and nutrient-poor arctic lakes dominated the earliest assemblages. Chironomid assemblages with taxa typical of higher summer air temperatures and lakes with higher nutrient availability occur between 8000 and 5000 cal. a BP. This period probably marks the regional Holocene thermal maximum, which is relatively late compared with some palaeoenvironmental records from East Greenland. One possible reason could be the location of Store Koldewey at the very outer coast, with local climatic conditions strongly influenced by the cold East Greenland Current. From around 5000 cal. a BP, chironomid assemblages in Duck Lake and Hjort Lake again became more typical of those presently found in Northeast Greenland, indicating relatively cold and nutrient-poor conditions. This shift coincides with an increase of ice-rafting debris off East Greenland and an intensification of the East Greenland Current.

Climate-related cyclic deposition of carbonate and organic matter in Holocene lacustrine sediment, Lower Michigan, USA

Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene. Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon, total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich) to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate) and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year) from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years, hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper, zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP.

Lake sediments from Store Koldewey, Northeast Greenland, as archive of Late Pleistocene and Holocene climatic and environmental changes

A 2.9 m long sedimentary record was studied from a small lake, here referred to as Duck Lake, located at 76°25′N, 18°45′W on Store Koldewey, an elongated island off the coast of Northeast Greenland. The sediments were investigated for their geophysical and biogeochemical characteristics, and for their fossil chironomid assemblages. Organic matter began to accumulate in the lake at 9.1 cal. kyr BP, which provides a minimum age for the deglaciation of the basin. Although the early to mid‐Holocene is known as a thermal maximum in East Greenland, organic matter accumulation in the lake remained low during the early Holocene, likely due to late plant immigration and lack of nutrient availability. Organic matter accumulation increased during the middle and late Holocene, when temperatures in East Greenland gradually decreased. Enhanced soil formation probably led to higher nutrient availability and increased production in the lake. Chironomids are abundant throughout the record after 9.1 cal. kyr BP and seem to react sensitively to changes in temperature and nutrient availability. It is concluded that relative temperature reconstructions based on biogeochemical data have to be regarded critically, particularly in the period shortly after deglaciation when nutrient availability was low. Chironomids may be a suitable tool for climatic reconstructions even in those high arctic environments. However, a better understanding of the ecology of chironomids under these extreme conditions is needed.

Using three-dimensional visualization to represent hydrological influence on wetland plants

Wild Duck Lake (WDL) wetland, a Nature Reserve of Beijing, China is suffering from regional groundwater table declining and potential flood inundation. This paper aims to visualize the hydrological influence on plant species in this area. The photorealistic plants were rendered at 3D scale with exact georeferencing on the Digital Elevation Model (DEM) covered with an aerial photo. The simplified relationship between plants and hydrology was established according to the field survey of individual height, population density, depth to shallow groundwater table, and depth to surface water level. Seed-spread algorithm was used to simulate flood inundation with a given flood level. Plant species with the influenced individual height and population density were then represented according to specified shallow groundwater table and flood level. Navigation, animation and some other 3D handling tools were developed to improve interactive and immersive abilities for exploring. The result shows that 3D visualization can be an effective way to understand interaction between hydrology and ecology, which usually hides behind of some complicated and interdisciplinary processes. It provides us a visual decision-making support for water resource management on considering of ecological response.

Mantle petrology and mineralogy of the Thetford Mines Ophiolite Complex

The Ordovician Thetford Mines ophiolite complex (TMOC) formed by boninite-fed seafloor-spreading, probably in a fore-arc environment. The mantle section is dominated by foliated harzburgite (≤ 5–6% clinopyroxene), cut by dunitic (± chromitite cores) and orthopyroxenitic veins and dykes. Contrasting structures, textures and mineral compositions allow us to subdivide the mantle. The granular-textured rocks of the Duck Lake Block (DLB) have two steeply-dipping foliations. The older foliation strikes NW, is sub-perpendicular to the Moho, and is interpreted to have resulted from upflow of the asthenosphere beneath the spreading ridge. This fabric is overprinted by a 2nd ductile foliation striking ENE, oriented sub-parallel to the Moho, which we interpreted as having formed by crust–mantle shear as the lithosphere migrated away from the spreading ridge. The DLB mantle has a limited range of spinel Cr# (100Cr / (Cr + Al) = 51–71). Comparison with experimentally determined residual spinel compositions (equilibrium melting) implies a maximum loss of 27–38% melt if the protolith had a fertile MORB mantle composition. However, interstitial-textured clinopyroxene may have high TiO 2 (< 0.04wt.%) and Na 2O (< 0.27wt.%), and some interstitial spinel has higher TiO 2 (< 0.09wt.%), suggesting interaction with (or crystallization from) an “impregnating” melt. Interstitial tremolitic amphibole also indicates the passage of late hydrous fluids. The harzburgite in the Caribou Mountain Block (CMB) has a porphyroclastic texture, with a strong, locally mylonitic foliation striking roughly N–S, parallel to the orientation of seafloor-spreading related paleo-normal faults in the crust. These fabrics and textures imply a colder, lithospheric deformation, possibly related to tectonic denudation (oceanic core complex). This would explain problematic lava/mantle contacts, favour infiltration of seawater, serpentinization, and reduced fO 2 conditions. The CMB mantle shows a wider range of mineral compositions than the DLB, with spinel Cr# (28–86) implying ≤ 15–45% of equilibrium melting. Locally higher TiO 2 in spinel (< 0.05wt.%) and clinopyroxene (< 0.11wt.%), a local rimward decrease in spinel Cr#, clinopyroxene Cr#, and olivine Fo-content, and traces of interstitial amphibole, are attributed to the circulation of an evolved hydrous melt during peridotite deformation. This suggests that the lower limit to the extent of melting inferred for the CMB (15%), established on the basis of Al-rich spinel rims and neoblasts, is probably too low. On the other hand, the higher inferred degree of depletion of the CMB is probably unaffected by the metasomatic overprint and is a more robust conclusion.

The Duck Lake Site and Implications for Late Archaic Copper Procurement and Production in the Southern Lake Superior Basin

Few sites relating to Archaic procurement of copper have been archaeologically investigated in the southern part of the Lake Superior basin. The Duck Lake site, located in the Ontonagon River watershed of Michigan's Upper Peninsula, is within the source area for native copper. Investigations at this site reveal a field camp consisting of one or more occupations by Late Archaic groups. Lithic analysis demonstrates a strong reliance on non-local raw materials, and suggests a degree of residential mobility within a region known to the occupants. Lithic material was obtained through embedded procurement and exchange with more distant groups. Copper likely entered the early Late Archaic exchange system in the Midwest through frequent interactions and trade between groups, and appears consistent with a down-the-line model of exchange.

Paleoproterozoic arc and ophiolitic rocks on the northwest-margin of the Trans-Hudson Orogen, Saskatchewan, Canada: their contribution to a revised tectonic framework for the orogen

A new lithotectonic framework for the northwestern Reindeer Zone of the Trans-Hudson Orogen divides rocks into five northwest- to north-dipping volcano-sedimentary assemblages: (1) at the structural base, the 1.92–1.87 Ga largely sedimentary Levesque Bay Assemblage (partly equivalent to former ‘MacLean Lake gneisses’), which lies within the confines of the Kisseynew Domain and is tectonically imbricated with metasedimentary rocks of the <1.85 Ga McLennan and Burntwood groups; (2) the turbiditic Duck Lake Assemblage, also located along the northern edge of the Kisseynew Domain; it contains detrital zircons ranging in age between 1.92 and 1.87 Ga; (3) the ?1.92 Ga mafic–ultramafic volcano-plutonic Lawrence Point Assemblage of the La Ronge Domain; (4) the ≥1.88 Ga felsic to intermediate volcano-plutonic Reed Lake Assemblage of the La Ronge Domain; and (5) the turbiditic Milton Island Assemblage of the Rottenstone Domain, which contains detrital zircons ranging in age between 2.83 and 1.86 Ga. The assemblages are intruded by a variety of 1.91–1.78 Ga mafic to felsic plutons. The Lawrence Point Assemblage is interpreted as a dismembered supra-subduction zone ophiolite. High-MgO refractory harzburgite (‘Group 1’ ultramafic rocks), at the structural base of the assemblage, is geochemically identical to the upper mantle section of selected supra-subduction zone ophiolites and mantle tectonites. Chromite and olivine compositions of the ‘Group 1’ ultramafic rocks are also comparable to those of ophiolitic harzburgite and mantle tectonite. Mafic metavolcanic rocks of the assemblage are classified as subalkaline tholeiitic basalts. Their trace element patterns and Hf, Ta, Th, Y, Nb, and La element ratios resemble those of modern back-arc basin basalts. The Reed Lake Assemblage represents a subduction-generated arc complex that was built on top of the Lawrence Point Assemblage; its mafic metavolcanic rocks are subalkaline basalts, with calc-alkaline trends, and elevated Th and Ce concentrations and negative Nb anomalies. Feldspar porphyry dykes intruding the Lawrence Point and Duck Lake assemblages constrain timing of Lawrence Point ophiolite emplacement onto the Duck Lake Assemblage to 1.86–1.84 Ga. The trace element geochemistry of the dykes suggests continued arc volcanism after ophiolite emplacement. Mafic metavolcanic rocks of the Levesque Bay Assemblage are geochemically similar to those of the Lawrence Point Assemblage. Other ultramafic rocks (peridotite to pyroxenite) are abundant in the Lawrence Point Assemblage, but have similar geochemistry to small ultramafic bodies intruding the Reed Lake, Duck Lake and Levesque Bay Assemblages. They represent a separate, later phase (?1.86 Ga) of ultramafic plutonism, which post-dates ophiolite emplacement. Timing of Lawrence Point ophiolite emplacement (between 1.86 and 1.84 Ga) and geochemistry of later felsic and mafic/ultramafic volcanism suggest that the Lawrence Point ophiolite and overlying Reed Lake arc assemblage were not accreted to the Hearne Craton prior to 1.86 Ga, but were first accreted to the Flin Flon–Glennie Complex after 1.86 Ga.

Slow post-orogenic cooling in a deeply eroded orogen: Reindeer Zone, Trans-Hudson Orogen, Saskatchewan

We present 40Ar/39Ar hornblende and muscovite data from a 200 km transect across the northern flank of the Paleoproterozoic Trans-Hudson Orogen (THO) exposed along Reindeer Lake in Saskatchewan, Canada. The transect crosses a series of distinct lithotectonic domains that experienced pressure–temperature (P–T) conditions of 600–730 °C at 4.5–6.0 kbar (1 kbar = 100 MPa) during D2 peak metamorphism at 1820–1790 Ma. The distribution of 40Ar/39Ar hornblende ages shows that most of the transect cooled through approximately 500 °C by ca. 1765 Ma, with two significant exceptions. At the north end of the transect, older ages in the Peter Lake Domain (up to 2200 Ma) suggest that this region did not experience high-grade metamorphism that affected the rest of the transect and may indicate a structural break between these Archean rocks and the Cree Lake Zone to the north. In the south-central part of the transect, U–Pb (monazite, titanite) and 40Ar/39Ar (hornblende, muscovite) ages indicate that rocks in the vicinity of the Duck Lake Shear Zone, a ductile thrust zone separating the Kisseynew and La Ronge domains, cooled at a rate of 6 °C/Ma and that cooling was delayed by ca. 20–25 million years relative to that of adjacent regions. Based on generic thermal–tectonic models for large hot orogens, we suggest that delayed cooling in the vicinity of the shear zone reflects post-orogenic thermal relaxation of lower crustal isotherms that were perturbed by the effects of convergence.

Geology of the Two Duck Lake Intrusion and the Marathon Cu-PGE Deposit, Coldwell Complex, Northern Ontario

Detailed mapping of the Eastern Gabbro, Coldwell Complex, Ontario, revealed that the copper and platinum-group-element deposit on the Marathon property is confined to a coarse-grained to pegmatitic gabbro-diorite intrusion, the Two Duck Lake intrusion (TDLI). Exposed along the eastern boundary of the Coldwell Complex, the TDLI was emplaced as a sill whose orientation is slightly oblique to the general structure of the Eastern Gabbro. The TDLI has been subdivided into lower , middle and upper sub-units on the bases of lithological, textural, mineralogical, and geochemical criteria. Both border sub-units are sulfide-, base- and precious metal-enriched, and exhibit abundant evidence of host-rock assimilation. The primary mineral assemblage in the TDLI is plagioclase, olivine, clinopyroxene, Fe-Ti oxides, with accessory orthopyroxene, biotite, apatite; this primary mineral assemblage is essentially preserved in the core of the intrusion (i.e., the middle subunit). The Cu-PGE Marathon deposit, delineated mainly in the upper sub-unit of the intrusion, consists of disseminated Fe-Cu-Ni sulfides, and platinum-group-minerals derived by hydrothermal remobilization from primary magmatic sulfides. Enrichment in Cu and PGE resulted from partial replacement of original Fe-Ti oxides and pyrrhotite in the primary mineral assemblage by reaction with (a) residual magmatic fluid, and (b) fluids derived from the breakdown of host rock xenoliths and hydrothermal alteration along the lower contact of the TDLI.

Trophic Classification of Selected Lakes in Yellowstone National Park

The purpose of this study is to evaluate the trophic state of five lakes in southern Yellowstone National Park in order to determine if the human activity in the local area is having a negative environmental impact and possibly increasing the eutrophication rate. While some previous analyses have been done on these lakes, this study is intended to be a preliminary trophic state evaluation to which future analyses can be compared. The five lakes sampled are Shoshone Lake, Lewis Lake, Heart Lake, Riddle Lake, and Duck Lake. Each lake, with the exceptions of Riddle Lake and Duck Lake, was sampled at several locations. These samples were taken during the months of June through August of 1999 by Woodruff Miller and Dave Anderson of the BYU Civil &amp; Environmental Engineering Department.

Platinum-group minerals in fluid inclusions from the Marathon deposit, Coldwell Complex, Canada

Platinum-group minerals (PGM) project into fluid inclusions that occur in chalcopyrite and cubanite from the Marathon deposit, Two Duck Lake gabbro, Coldwell Complex, Ontario. Semi-quantitative analyses of the micron-sized PGM were made by SEM-EDS; they reveal Ag-bearing intermetallic compounds of Pd3Sn-Pd3Pb-Pd3Te (i.e., atokitezvyagintsevite-keithconnite) and telargpalite (Pd2AgTe) on broken, irregular surfaces of the Cu-Fe-S minerals. Halite daughter minerals, and quenched brine occur in and around some opened fluid inclusions. These data confirm the hypothesis based on petrography and mineral compositions that saline fluids remobilized PGE, Cu, and other elements and precipitated them well after crystallization of sulfide and silicate magmas in the Marathon deposit.

Size-Biased Predation and Prey Life Histories: A Comparative Study of Freshwater Amphipod Populations

A prior survey of Michigan populations of a freshwater amphipod, Hyalella azteca, indicted that populations occur as one of two morphotypes that differ in body size and life history traits. Population types, which may represent separate species, are associated with distinct habitat types. Generally, lakes with centrarchid fish contain a small—bodied form, and fishless ponds and marshes contain a large—bodied form. In this comparative study of two Hyalella populations, I examine the potential role of size—biased feeding by major predators in maintaining, and perhaps generating, the pattern of association between Hyalella morphotype and habitat type. In Duck Lake (Centrarchid fish present), overall mortality generally increased with body size in each of two study years, and adult mortality exceeded juvenile mortality. The opposite pattern was observed in a nearby fishless habitat, Duck Marsh, where mortality generally declined with size, so that juvenile mortality exceeded adult mortality. To determine the degree to which size—biased predation might cause the observed mortality patterns, I used stomach content analysis to assess prey size preferences of fish in the lake habitat and laboratory foraging trials to examine size—biased predation by invertebrate predators from the marsh. Fish predators displayed a strong tendency to prey on larger, adult Hyalella. Size preferences exhibited by larval dragonflies, the principal invertebrate predators in the marsh habitat, depended on predator body size, with small larvae preferring juvenile Hyalella and the largest larvae preferring adults. In general, size—selective predation by major predators in each habitat appeared to contribute importantly to overall mortality patterns, the exception being the marsh habitat in a year of low predator density. Observed differences in life history traits between populations are in close agreement with predictions derived from life history models addressing the influence of size—biased mortality on the evolution of reproductive allocation, size at maturity, and egg size. Life history characteristics of Hyalella were measured both on field—collected individuals and on individuals reared for approximately two generations in replicated predator—free artificial ponds. In field samples, the lake Hyalella population exhibited a smaller mean adult body size, smaller size at maturity, smaller egg size, and higher size—specific fecundity and reproductive investment that the marsh population. These life history differences were also observed in the artificial pond experiment, indicating that these traits are genetically based and nonplastic.

The Mechanistic Basis of Body Size Differences Between TwoHyalella(Amphipoda) Species

Abstract The mechanistic basis of differences in adult body size between two closely related freshwater amphipod species (Hyalella spp.) are investigated. The study populations, Duck Lake and George Pond, are representative of two sibling species found in southeast Michigan, U.S.A that differ in adult body size and life history. An analysis of relative growth rates across size classes indicated that growth rates were similar in small size classes, but divergent at larger size classes, with higher growth rates in Hyalella from George Pond. Because the timing of the divergence coincides with the onset of reproduction in the Duck Lake population, which reaches sexual maturity at a smaller body size than individuals in the George Pond population, tradeoffs in allocation of resources between growth and reproduction probably contribute substantially to population differences in adult body size. Resource consumption rates were similar between populations in small and intermediate size classes, but large Duck Lake adults had lower consumption rates than George Pond individuals of similar size. Thus, differences in resource consumption rate may also contribute to differences in adult growth rate and body size.

Genesis of the Marathon Cu-platinum-group element deposit, Port Coldwell alkalic complex, Ontario; a Midcontinent rift-related magmatic sulfide deposit

The Marathon copper and platinum-group element (PGE) deposit is hosted by the Two Duck Lake intrusion, located at the eastern margin of the Port Coldwell alkalic complex, northwestern Ontario. The Two Duck Lake intrusion is subdivided into an upper layered zone and a lower unlayered zone that consists of olivine gabbro and pegmatite with trace amounts of granophyre. The sulfides are hosted in the lower zone which is referred to here as Two Duck Lake gabbro. Petrography, mineral-chemistry, and geochemical data imply that Two Duck Lake gabbro crystallized in situ from a plagioclase crystal mush. There is no geochemical evidence for metasomatic alteration of the gabbro. The sulfides are disseminated in gabbro and pegmatite and consist of approximately equal proportions of chalcopyrite and pyrrhotite and minor amounts of pentlandite and pyrite. Samples of Two Duck Lake gabbro exhibit a significant correlation between sulfur and Ni, Ir, Rh, Pt, Pd, Au, and Cu. Further, the Pd/Ir and Pd/Ni ratios increase with increasing concentrations of Rh, Pt, Pd, Au, and Cu. Consequently, bulk sulfide compositions are best explained by the separation of a sulfide liquid from a gabbroic magma. This origin is contrary to that proposed by previous workers. They presented detailed petrographic and mineral-chemical data that imply inter-action of Cl-bearing hydrous fluids and sulfides at low temperatures. In the light of our study, we interpret these observations to indicate that elements migrated over very short distances and that bulk sulfides were not enriched with Cu and PGE, as previously proposed. A model for the genesis of the Marathon deposit is proposed.Many characteristics of the Marathon deposit bear a striking resemblance to observations reported in disseminated sulfide deposits at the base of the Duluth Complex, Minnesota. The features include mineral textures, abundances, and compositions; crystallization paths for the host gabbroic bodies; silicate-sulfide associations; trace element trends; and chalcophile element fractionation trends. The similarities imply that the Marathon deposit and deposits in the Duluth Complex formed by analogous processes.

Waterflooding Increases Gas Recovery

Summary Injecting water into a low-pressure gas reservoir nearing abandonment will displace gas and increase ultimate recovery. This paper examines the theory and reports the results of a case history. Water was injected into a southern Louisiana gas reservoir for more than 10 years, successfully increasing recovery by 25 Bcf [710×106 m3]. This paper also discusses the importance of considering all possible producing mechanisms early in a reservoir's life to predict future performance properly and shows that straight-line p/z performance does not necessarily indicate that a gas reservoir has a depletion drive, as is frequently assumed in practice. Introduction Natural gas is a major source of energy production and consumption in the U.S. As reserves decline, investigators are studying the potential of increased supplies from several unconventional sources1 and from waterdrive reservoirs with high production rates in the gas zones2,3 and the aquifers.4 Production at high rates from a waterdrive reservoir is an attempt to reduce reservoir pressure to a low value, thereby minimizing the actual gas volume occupying residual pore space. A reservoir with little water influx that depletes to low pressure has the opposite problem because all the pore space is still filled with gas. This paper shows that increased recovery can be obtained by waterflooding a low-pressure gas reservoir and discusses an actual field case. The Discorbis 1 reservoir (Reservoir D-1) in the Duck Lake field of southern Louisiana (St. Martin Parish) initially produced by limited aquifer influx. Water injection was initiated after reservoir pressure had fallen below 1,000 psi [6.9 MPa] and continued for 11 years. An incremental recovery of 25 Bcf [710×106 m3] was attributed to water injection. This project was primarily a low-cost expansion of the field's existing saltwater disposal system, providing a unique opportunity for an economic project at the gas prices of the 1970's, which were about 15% of current prices. Analysis of Reservoir D-1 also provides the opportunity to show that straight-line p/z performance does not necessarily mean that a gas reservoir has a depletion drive. Theory showing that depletion-drive gas reservoirs will exhibit a straight-line p/z plot has been developed. The corollary - that a straight-line p/z plot proves the existence of a depletion drive - has not been proven, although it is frequently assumed in practice. Theory If a gas reservoir produces strictly by pressure depletion, hydrocarbon pore space at abandonment pressure should be equal to that at initial pressure. A significant amount of gas, however, can remain in the reservoir. Injecting water at abandonment pressure displaces a fraction of the PV to production wells, leaving a residual gas saturation that contains a minimal standard volume because of the low trapping pressure. Thus, the good features of pressure depletion and water displacement are combined in a controlled production mechanism to maximize recovery. Craft and Hawkins5 showed that recovery for a waterdrive reservoir can be expressed asEquation 1 and that recovery for a depletion-drive reservoir can be expressed asEquation 2 For imbibition fluid displacements, Naar and Henderson6 concluded that residual nonwetting-phase saturation should be about one-half the initial nonwetting-phase saturation, so thatEquation 3 Substituting Eq. 3 into Eq. 1 and subtracting Eq. 2 yieldsEquation 4 Eq. 4 presents a simple means to calculate a theoretical incremental recovery, as a percentage of original gas in place (OGIP), that results from waterflooding a gas reservoir that is pressure depleting. This recovery factor is representative of a homogeneous reservoir where permeability is uniform areally and vertically, and water coning is neglected.