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1.
Cristián Frêne Juan J. Armesto Freddy Véliz Fernando D. Alfaro Kathleen C. Weathers 《水文研究》2021,35(5):e14175
The variability of rainfall-dependent streamflow at catchment scale modulates many ecosystem processes in wet temperate forests. Runoff in small mountain catchments is characterized by a quick response to rainfall pulses which affects biogeochemical fluxes to all downstream systems. In wet-temperate climates, water erosion is the most important natural factor driving downstream soil and nutrient losses from upland ecosystems. Most hydrochemical studies have focused on water flux measurements at hourly scales, along with weekly or monthly samples for water chemistry. Here, we assessed how water and element flows from broad-leaved, evergreen forested catchments in southwestern South America, are influenced by different successional stages, quantifying runoff, sediment transport and nutrient fluxes during hourly rainfall events of different intensities. Hydrograph comparisons among different successional stages indicated that forested catchments differed in their responses to high intensity rainfall, with greater runoff in areas covered by secondary forests (SF), compared to old-growth forest cover (OG) and dense scrub vegetation (CH). Further, throughfall water was greatly nutrient enriched for all forest types. Suspended sediment loads varied between successional stages. SF catchments exported 455 kg of sediments per ha, followed by OG with 91 kg/ha and CH with 14 kg/ha, corresponding to 11 rainfall events measured from December 2013 to April 2014. Total nitrogen (TN) and phosphorus (TP) concentrations in stream water also varied with rainfall intensity. In seven rainfall events sampled during the study period, CH catchments exported less nutrients (46 kg/ha TN and 7 kg/ha TP) than SF catchments (718 kg/ha TN and 107 kg/ha TP), while OG catchments exported intermediate sediment loads (201 kg/ha TN and 23 kg/ha TP). Further, we found significant effects of successional stage attributes (vegetation structure and soil physical properties) and catchment morphometry on runoff and sediment concentrations, and greater nutrients retention in OG and CH catchments. We conclude that in these southern hemisphere, broad-leaved evergreen temperate forests, hydrological processes are driven by multiple interacting phenomena, including climate, vegetation, soils, topography, and disturbance history. 相似文献
2.
Water quality is often highly variable both in space and time, which poses challenges for modelling the more extreme concentrations. This study developed an alternative approach to predicting water quality quantiles at individual locations. We focused on river water quality data that were collected over 25 years, at 102 catchments across the State of Victoria, Australia. We analysed and modelled spatial patterns of the 10th, 25th, 50th, 75th and 90th percentiles of the concentrations of sediments, nutrients and salt, with six common constituents: total suspended solids (TSS), total phosphorus (TP), filterable reactive phosphorus (FRP), total Kjeldahl nitrogen (TKN), nitrate-nitrite (NOx), and electrical conductivity (EC). To predict the spatial variation of each quantile for each constituent, we developed statistical regression models and exhaustively searched through 50 catchment characteristics to identify the best set of predictors for that quantile. The models predict the spatial variation in individual quantiles of TSS, TKN and EC well (66%–96% spatial variation explained), while those for TP, FRP and NOx have lower performance (37%–73% spatial variation explained). The most common factors that influence the spatial variations of the different constituents and quantiles are: annual temperature, percentage of cropping land area in catchment and channel slope. The statistical models developed can be used to predict how low- and high-concentration quantiles change with landscape characteristics, and thus provide a useful tool for catchment managers to inform planning and policy making with changing climate and land use conditions. 相似文献
3.
David J. Dunlop Hironobu Hyodo Todd Knight Alan G. Steele 《Geophysical Journal International》1985,83(3):699-720
Summary. After thermal and alternating field (AF) cleaning, the characteristic high blocking temperature A component of natural remanent magnetization (NRM) of the Tudor gabbro of southern Ontario has a mean direction D = 326°, I =–46° ( k = 132, α95 = 4.8°, N = 8 sites). The corresponding palaeopole, 133°E, 12°N ( dp = 4°, dm = 6°), confirms the palaeopole 137°E, 17°N (α95 = 8.4°) reported earlier by Palmer & Carmichael, based on AF cleaning only. The A NRM has unblocking temperatures > 515–525°C which exceed the estimated 500°C peak temperature reached locally during ∼ 1050 Ma Grenvillian regional metamorphism. The A NRM therefore predates metamorphism and is probably a primary thermoremanence (TRM). The age of the Tudor NRM has previously been taken to be about 675 Ma, but recent 40 Ar/39 Ar dating by Baksi has shown that this is the time of post-metamorphic cooling to 200–250°C. Hornblendes record initial cooling of the intrusion to 590±20°C at 1110 Ma and this is the best estimate of the age of the A remanence. Successful Thellier-type palaeointensity determinations on 11 Tudor samples confirm that the A NRM is a TRM and indicate a palaeofield at this time of 18–27 μT, about 50–70 per cent of the present field intensity at 27° magnetic latitude. The anomalous Tudor A palaeopole, which lies well to the west of both 1000–800 Ma Grenvillian palaeopoles and 1100–1050 Ma poles from Interior Laurentia, is interpreted as recording divergence between Grenvillia and Interior Laurentia just before the Grenvillian orogeny, rather than a post-metamorphic extension of the apparent polar wander path as previously assumed. 相似文献
4.
Long-range sidescan sonar can be used to map sediment distributions over wide expanses of deep ocean floor. Seven acoustic facies that arise from differing sediment or rock types have been mapped over the low-relief Saharan continental rise and Madeira abyssal plain. These have been calibrated with sampling, profiling and camera studies and the facies can be traced confidently on a regional scale using the sidescan data. The mapping of the sediment distribution shows that a complex interplay of turbidity current and debris flow processes can occur at a continental rise/abysaal plain transition over 1000 km from the nearest continental slope. 相似文献
5.
Berry Head, a limestone headland in Torbay, southwest England, exhibits a series of subaerial marine erosion platforms and raised beaches spanning an altitude range of 97 m. Solution caves on the headland show preferred horizontal development at elevations that are correlated with the marine erosion platforms, and developed in a marine/freshwater mixing zone whose position was controlled by high sea-level still-stands. Corbridge Cave in Berry Head Quarry lies below the raised beaches in Torbay, and contains evidence of three marine transgressions in the form of fine-grained marine ponding deposits with a marine microfauna. Uranium-series dating of intercalated speleothems indicates that a transgression during oxygen isotope stage 5e reached an elevation of 5.8 m OD, while an earlier transgression (probably during stage 7) reached at least 7.2 m OD. These findings are used to constrain possible interpretations of the aminostratigraphy of raised beaches in Southwest Britain, and a correlation of the Unnamed Stage of Bowen, Sykes, Reeves, Miller, Andrews, Brew and Hare with oxygen isotope stage 5e is proposed. 相似文献
6.
A new analysis of all 346 published 14C dated Holocene alluvial units in Britain offers a unique insight into the regional impacts of global change and shows how surprisingly sensitive British rivers have been to relatively modest but repeated changes in climate. Fourteen major but probably brief periods of flooding are identified bracketed within the periods 400–1070, 1940–3940, 7520–8100 and at ca. 10 420 cal. yr BP. There is a strong correspondence between climatic deteriorations inferred from mire wet shifts and major periods of flooding, especially at ca. 8000 cal. yr BP and since ca. 4000 cal. yr BP. The unusually long and complete British record also demonstrates that alterations in land cover have resulted in a step change in river basin sensitivity to variations in climate. This has very important implications for assessing and mitigating the impact of increasing severe flooding. In small and medium‐sized river basins land use is likely to play a key role in either moderating or amplifying the climatic signal. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
7.
The solubility of iron sulphides in synthetic and natural waters at ambient temperature 总被引:1,自引:1,他引:0
W. Davison 《Aquatic Sciences - Research Across Boundaries》1991,53(4):309-329
A critical evaluation of literature values for the solubility products, K
sp
NBS
= [Fe2+][HS–] Fe2+
HS– (H
NBS
+
)–1, of various iron sulphide phases results in consensus values for the pKs of 2.95 ± 0.1 for amorphous ferrous sulphide, 3.6 ± 0.2 for mackinawite, 4.4 ± 0.1 for greigite, 5.1 ± 0.1 for pyrrhotite, 5.25 ± 0.2 for troilite and 16.4 ± 1.2 for pyrite.Where the analogous ion activity products have been measured in anoxic freshwaters in which there is evidence for the presence of solid phase FeS, the values lie within the range of 2.6–3.22, indicating that amorphous iron sulphide is the controlling phase. The single value for a groundwater of 2.65 (2.98 considering carbonate complexation) agrees. In seawater four values range between 3.85 to 4.2, indicating that mackinawite or greigite may be the controlling phase. The single low value of 2.94 is in a situation where particularly high fluxes of Fe (II) and S (–II) may result in the preferential precipitation of amorphous iron sulphide. Formation of framboidal pyrite in these sulphidic environments may occur in micro-niches and does not appear to influence bulk concentrations. Calculations show that the formation of Fe2S2 species probably accounts for very little of the iron or sulphide in most natural waters. Previously reported stability constants for the formation of Fe (HS)2 and (Fe (HS)3)– are shown to be suspect, and these species are also thought to be negligible in natural waters. In completely anoxic pore waters polysulphides also have a negligible effect on speciation, but in tidal sediments they may reach appreciable concentrations and lead to the direct formation of pyrite. Concentrations of iron and sulphide in pore waters can be controlled by the more soluble iron sulphide phase. The change in the IAP with depth within the sediment may reflect ageing of the solid phase or a greater flux of Fe (II) and S (–II) nearer the sediment surface. This possible kinetic influence on the value of IAPs has implications for their use in geochemical studies involving phase formation. 相似文献
8.
We have revised the regional crustal structure, oceanic age distribution, and conjugate margin segmentation in and around the Lena Trough, the oceanic part of the Fram Strait between the Norwegian–Greenland Sea and the Eurasia Basin (Arctic Ocean). The Lena Trough started to open after Eurasia–Greenland relative plate motions changed from right-lateral shear to oblique divergence at Chron 13 times (33.3 Ma; earliest Oligocene). A new Bouguer gravity map, supported by existing seismic data and aeromagnetic profiles, has been applied to interpret the continent–ocean transition and the influence of Eocene shear structures on the timing of breakup and initial seafloor spreading. Assuming that the onset of deep-water exchange depended on the formation of a narrow, oceanic corridor, the gateway formed during early Miocene times (20–15 Ma). However, if the initial Lena Trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep-water circulation, the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around Chron 5 times (9.8 Ma; Late Miocene). Paleoceanographic changes at ODP Site 909 (northern Hovgård Ridge) are consistent with both hypotheses of gateway formation. We cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the Lena Trough. The gravity, seismic and magnetic observations question the prevailing hypotheses on the Yermak Plateau and the Morris Jesup Rise as Eocene oceanic plateaus and the Hovgård Ridge as a microcontinent. 相似文献
9.
Based on our detailed structural characterization, we examine possible relationships between thrust faults and strike-slip faults and thrust-cored folds and depositional units in the Silla Syncline, a 4 km wide fold composed of fine-grained mudstone, coarse sandstone and conglomerate deposits of the Cerro Toro Formation in the Magallanes foreland basin, Chilean Patagonia. The syncline is bounded on its western flank by an asymmetric anticline and on its eastern flank by a broad zone of thrust faults and associated folds, which are oriented sub-parallel to the syncline axis. Deposition of the coarse-grained units of the Silla Syncline appears to have taken place in this structurally defined trough controlled primarily by thrust fault related growth structures flanking the syncline.The syncline and surrounding area have also been deformed by two sets of strike-slip faults, one right-lateral and one left-lateral. The strike-slip and thrust faulting operated contemporaneously for much of their active periods, although it appears that thrust faulting, confined within the fine-grained units, initiated slightly earlier than strike-slip faulting. In addition, younger igneous intrusions at high angle to bedding generally localize along the strike-slip faults. The cross-cutting relationships among the intrusions, strike-slip faults, and flexural slip faults show that all these structures were active during the same period, which extends beyond mid-Miocene.These conclusions support the premise that structures in deep-water sediments are important for understanding not only the deformation of a foreland basin, but also its depositional architecture. 相似文献
10.
Three discriminant function models are raised and cross-compared in order to distinguish geochemical patterns characteristic
for the Drava River floodplain sediments. Based on data representing total element concentrations in samples collected from
alluvium (A), terrace (T), and unconsolidated bedrock (B) at the border of a floodplain, four element clusters emerged accounting
for discrimination between the referred groups of sediments. The most prominent is contaminant/carbonate cluster characteristic
for alluvium. The other two are: silicate cluster typical for unconsolidated geological substrate (Neogene sedimentary rocks);
and naturally dispersed heavy metal cluster separating terrace from the former two groups. Models introducing depth intervals
and single profiles as grouping criteria reveal identical sediment-heavy metal matrices. The second important issue of this
paper is possibility of reclassification of samples originally assigned to one of the a priori defined groups of sediments,
based on established geochemical pattern. The mapped geological units can be reconsidered by the post hoc assignments to a
different group if geological border between alluvium and terrace or between terrace and bedrock can not be established geologically
with absolute certainty. 相似文献