Effects of watershed land use on sources and nutritional value of particulate organic matter in temperate headwater streams   总被引：4，自引：0，他引：4  

Yue Han Lu  Elizabeth A. Canuel  James E. Bauer  R. M. Chambers 《Aquatic Sciences - Research Across Boundaries》2014,76(3):419-436

Suspended particulate organic matter (POM) in headwater streams is an important source of food and energy to stream food webs. In order to determine the effects of watershed land use on the sources and characteristics of POM, we compared the lipid composition of POM (fatty acid, aliphatic alcohol and sterol) from streams influenced by different types of watershed land use. Eight first-order streams discharging to the York River Estuary (Virginia, USA) were sampled during baseflow conditions bi-monthly from February to November 2009, including streams draining forest-dominated, pasture-dominated, cropland-dominated, and urban land-dominated watersheds. Allochthonous vs. autochthonous lipids showed that POM in most of these streams was dominated by allochthonous sources (59.5 ± 14.2 vs. 39.6 ± 14.5 % for aliphatic alcohols and 52.9 ± 11.5 vs. 34.1 ± 10.3 % for sterols). The relative abundance of allochthonous vs. autochthonous lipid inputs to POM varied as a function of land use type. POM in streams draining forest-dominated watersheds contained a higher proportion of allochthonous lipids and a lower proportion of autochthonous lipids than the streams influenced by human land use. The contribution of bacterial fatty acids differed significantly among sampling times (P = 0.003), but not among land use types (P = 0.547). Stepwise linear regression model selected nitrate and temperature as the best predictors of variation in bacterial inputs to POM. Proxies used to assess the nutritional value of POM potentially available to stream consumers included C:N ratios, and the concentrations of total long-chain polyunsaturated fatty acids, eicosapentaenoic acid, arachidonic acid, and cholesterol. None of these nutritional proxies differed among sampling months (P ≥ 0.171), but the proxies showed that the nutritional value of POM in forest streams was lower than in urban streams. Collectively, these findings suggest that human land use in upstream watersheds alters the source composition and nutritional value of stream POM, which not only impacts food quality for stream biota, but also potentially changes the characteristics of OM reaching downstream ecosystems.  相似文献   

A Snapshot of the Sun Near Solar Minimum: The Whole Heliosphere Interval     

Barbara J. Thompson  Sarah E. Gibson  Peter C. Schroeder  David F. Webb  Charles N. Arge  Mario M. Bisi  Giuliana de Toma  Barbara A. Emery  Antoinette B. Galvin  Deborah A. Haber  Bernard V. Jackson  Elizabeth A. Jensen  Robert J. Leamon  Jiuhou Lei  Periasamy K. Manoharan  M. Leila Mays  Patrick S. McIntosh  Gordon J. D. Petrie  Simon P. Plunkett  Liying Qian  Peter Riley  Steven T. Suess  Munetoshi Tokumaru  Brian T. Welsch  Thomas N. Woods 《Solar physics》2011,274(1-2):29-56

We present an overview of the data and models collected for the Whole Heliosphere Interval, an international campaign to study the three-dimensional solar?Cheliospheric?Cplanetary connected system near solar minimum. The data and models correspond to solar Carrington Rotation 2068 (20 March??C?16 April 2008) extending from below the solar photosphere, through interplanetary space, and down to Earth??s mesosphere. Nearly 200 people participated in aspects of WHI studies, analyzing and interpreting data from nearly 100 instruments and models in order to elucidate the physics of fundamental heliophysical processes. The solar and inner heliospheric data showed structure consistent with the declining phase of the solar cycle. A closely spaced cluster of low-latitude active regions was responsible for an increased level of magnetic activity, while a highly warped current sheet dominated heliospheric structure. The geospace data revealed an unusually high level of activity, driven primarily by the periodic impingement of high-speed streams. The WHI studies traced the solar activity and structure into the heliosphere and geospace, and provided new insight into the nature of the interconnected heliophysical system near solar minimum.  相似文献   

Is there a link between deep‐sea biodiversity and ecosystem function?     

Daniel Leduc  Ashley A. Rowden  Conrad A. Pilditch  Elizabeth W. Maas  P. Keith Probert 《Marine Ecology》2013,34(3):334-344

Studying the diversity‐ecosystem function relationship in the deep sea is of primary importance in the face of biodiversity loss and for our understanding of how the deep sea functions. Results from the first study of diversity‐ecosystem function relationships in the deep sea (Danovaro et al. 2008; Current Biology, 18, 1–8) are unexpected and show an exponential relationship between deep‐sea nematode diversity and ecosystem function and efficiency, although this relationship appears largely restricted to relatively low diversities [ES(51) <25]. Here, we investigate the relationship between nematode diversity and several independent measures/proxies of ecosystem function (sediment community oxygen consumption, bacterial biomass, bacterial extracellular enzyme activity) and efficiency (ratio of bacterial/nematode carbon to organic C content of the sediment) on the New Zealand continental slope. Nematode diversity at our study sites was relatively high [ES(51) = 30–42], and there was no relationship between species/functional diversity and ecosystem function/efficiency after accounting for the effects of water depth and food availability. Our results are consistent with a breakdown of the exponential diversity‐function relationship at high levels of diversity, which may be due to increased competition or greater functional redundancy. Future studies need to take into account as many environmental factors and as wide a range of diversities as possible to provide further insights into the diversity‐ecosystem function relationship in the largest ecosystem on Earth.  相似文献   

Interaction between the controls on fluvial system development: tectonics,climate, base level and river capture – Rio Alias,Southeast Spain     

Elizabeth Whitfield  Adrian M. Harvey 《地球表面变化过程与地形》2012,37(13):1387-1397

Fluvial systems in uplifting terrain respond to tectonic, climatic, eustatic and local base‐level controls modified by specific local factors, such as river capture. The Rio Alias in southeast Spain is an ephemeral, transverse‐to‐structure fluvial system. The river drains two interconnected Neogene sedimentary basins, the Sorbas and Almeria basins, and crosses two major geological structures, the Sierras de Alhamilla/Cabrera and the Carboneras Fault Zone. Regional epeirogenic uplift resulted in sustained fluvial incision during the Quaternary, punctuated by major climatically driven periods of aggradation and dissection, which created a suite of five river terraces. The river terrace sequence was radically modified in the late Pleistocene by a major river capture (itself a response to regional tectonics), localized tectonic activity and eustatic base‐level change. The Rio Alias is defined by four reaches; within each the climatically‐generated, region‐wide, fluvial response was modified by tectonics, base‐level change or river capture to varying degrees. In the upper part of the basin (Lucainena reach), climate was the dominant control on river development, with limited modification of the sequence by uplift of the Sierra Alhamilla and local drainage reorganization by a local river capture. Downstream of the Sierra Alhamilla in the Polopus reach, the climatic signal is dominant, but its expression is radically modified by the response to a major river capture whereby the Alias system lost up to 70% of its pre‐capture drainage area. In the reach adjacent to the Carboneras Fault Zone (Argamason reach), modification of the terrace sequence by local tectonic activity and a resultant local base‐level fall led to a major local incisional event (propagating c. 3–4 km upstream from the area of tectonic disturbance). At the seaward end of the system (El Saltador reach) Quaternary sea‐level changes modified the patterns of erosion and incision and have resulted in steep incisional terrace profiles. The signals generated by regional tectonics and the Quaternary climate change can be identified throughout the basin but those generated by ongoing local tectonics, river capture and sea‐level change are spatially restricted and define the four reaches. The connectivity of the system from the headwaters to the coast decreased through time as incision progressed, resulting in changes in local coupling characteristics. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

High‐frequency water quality monitoring in an urban catchment: hydrochemical dynamics,primary production and implications for the Water Framework Directive          下载免费PDF全文

Sarah J. Halliday  Richard A. Skeffington  Andrew J. Wade  Michael J. Bowes  Emma Gozzard  Jonathan R. Newman  Matthew Loewenthal  Elizabeth J. Palmer‐Felgate  Helen P. Jarvie 《水文研究》2015,29(15):3388-3407

This paper describes the hydrochemistry of a lowland, urbanised river‐system, The Cut in England, using in situ sub‐daily sampling. The Cut receives effluent discharges from four major sewage treatment works serving around 190 000 people. These discharges consist largely of treated water, originally abstracted from the River Thames and returned via the water supply network, substantially increasing the natural flow. The hourly water quality data were supplemented by weekly manual sampling with laboratory analysis to check the hourly data and measure further determinands. Mean phosphorus and nitrate concentrations were very high, breaching standards set by EU legislation. Although 56% of the catchment area is agricultural, the hydrochemical dynamics were significantly impacted by effluent discharges which accounted for approximately 50% of the annual P catchment input loads and, on average, 59% of river flow at the monitoring point. Diurnal dissolved oxygen data demonstrated high in‐stream productivity. From a comparison of high frequency and conventional monitoring data, it is inferred that much of the primary production was dominated by benthic algae, largely diatoms. Despite the high productivity and nutrient concentrations, the river water did not become anoxic, and major phytoplankton blooms were not observed. The strong diurnal and annual variation observed showed that assessments of water quality made under the Water Framework Directive (WFD) are sensitive to the time and season of sampling. It is recommended that specific sampling time windows be specified for each determinand, and that WFD targets should be applied in combination to help identify periods of greatest ecological risk. © 2015 The Authors. Hydrological Processes published by John Wiley & Sons Ltd.  相似文献   

Abyssal and hydrated mantle wedge serpentinised peridotites: a comparison of the 15$$^\circ$$20$$'$$′N fracture zone and New Caledonia serpentinites     

Fiona?Elizabeth?Mothersole  Katy?EvansEmail authorView author&#;s OrcID profile  B.?Ronald?Frost 《Contributions to Mineralogy and Petrology》2017,172(8):69

Subduction of serpentinised mantle transfers oxidised and hydrated mantle lithosphere into the Earth, with consequences for the oxidation state of sub-arc mantle and the genesis of arc-related ore deposits. The role of subducted serpentinised mantle lithosphere in earth system processes is uncertain because subduction fluxes are poorly constrained. Most subducted serpentinised mantle is serpentinised on the ocean floor settings. Yet this material is poorly represented in the literature because it is difficult to access. Large volumes of accessible serpentinite are available in ophiolite complexes, and most interpretations of subduction fluxes associated with ultramafic rocks are based on ophiolite studies. Seafloor and ophiolite serpentinisation can occur under different conditions, so it is necessary to assess if ophiolite serpentinites are a good proxy for seafloor serpentinites. Serpentinites sampled during ODP cruise 209 were compared with serpentinites from New Caledonia. The ODP209 serpentinites were serpentinised by modified seawater in a shallow hydrothermal seafloor setting. The New Caledonia serpentinites were serpentinised in a mantle wedge setting by slab-derived fluids, with possible contributions from oceanic serpentinisation and post-obduction serpentinisation. Petrological, whole rock and mineralogical analyses were combined to compare the two sample sets. Petrologically, the evolution of serpentinisation was close to identical in the two environments. However, more oxidised iron, Cl, S and C is present in serpentine from the ODP209 serpentinites relative to the New Caledonia serpentinites. Given these observations, the use of serpentinites from different geodynamic settings as a proxy for abyssal serpentinites from spreading settings must be undertaken with caution.  相似文献   

Erratum to “Metal–silicate partitioning of tungsten at high pressure and temperature: Implications for equilibrium core formation in Earth” [Earth and Planetary Science Letters 281 (2009) 275–287]     

Elizabeth Cottrell  Michael J. Walter  David Walker 《Earth and Planetary Science Letters》2010,289(3-4):631-634

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Mantle transition zone beneath the Caribbean-South American plate boundary and its tectonic implications     

Jianping Huang  Elizabeth Vanacore  Fenglin Niu  Alan Levander 《Earth and Planetary Science Letters》2010,289(1-2):105-111

We analyzed receiver-function data recorded by a temporary broadband array deployed as part of the BOLIVAR project and the permanent seismic network of Venezuela to study the mantle transition zone structure beneath the Caribbean-South American plate boundary and Venezuela. Significant topography on both the 410-km and the 660-km discontinuities was clearly imaged in the CCP (common-conversion-point) stacked images. Beneath the southeastern Caribbean, the 410-km is featured by a narrow (～ 200 km EW) ～ 25-km uplift extending in the NS direction around 63° west, while the 660-km is depressed by ～ 20 km in a narrow region slightly west to the uplift, a scenario that is more consistent with westward descent of the oceanic South American plate rather than a break-off of NNW dipping proto-Caribbean oceanic lithosphere along the El Pilar Fault. We also found a thick transition zone beneath the Falcon region in northwestern Venezuela, possibly associated with the subducted Nazca plate. A flat 410-km was observed beneath the Guayana shield, suggesting that the shield has a stable and moderately deep keel, which has little effect on the underlying transition zone structure.  相似文献