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81.
Suria Tarigan Christian Stiegler Kerstin Wiegand Alexander Knohl Kukuh Murtilaksono 《水文科学杂志》2020,65(7):1239-1248
ABSTRACTOver the last decade, monoculture plantations have rapidly developed in Jambi Province on Sumatra, Indonesia. Meanwhile, there has been intensification of discharge fluctuation in the study area. We examined the relative contribution of changes in evapotranspiration and soil compaction to the catchment discharge by using the Soil Water Assessment Tool model. Evapotranspiration values based on the catchment water balance analysis in intensively cultivated oil palm plantations, smallholder oil palm plantations, rubber plantations, and the secondary forest are 5.03 ± 0.30, 4.11 ± 0.38, 3.36 ± 0.32, and 4.50 ± 0.18 mm d?1, respectively. Infiltration rate in active interrows of oil palm, rubber plantations, agroforest, oil palm frond pile is 2.6 ± 1.7, 16.3 ± 6.8, 28.0 ± 3.9, 58.2 ± 21.8 cm h?1, respectively. We found that increased evapotranspiration and soil compaction increased the frequency of low discharge by 30%, with increased evapotranspiration contributing 10% and increased soil compaction contributing 20%. 相似文献
82.
83.
Amy F. Ritter Kerstin Wasson Steve I. Lonhart Rikke K. Preisler Andrea Woolfolk Katie A. Griffith Sarah Connors Kimberly W. Heiman 《Estuaries and Coasts》2008,31(3):554-571
One of the most conspicuous anthropogenic disturbances to estuaries worldwide has been the alteration of freshwater and tidal influence through the construction of water control structures (dikes, tide gates, culverts). Few studies have rigorously compared the responses of differing groups of organisms that serve as contrasting conservation targets to such anthropogenic disturbances in estuarine ecosystems. Elkhorn Slough in central California includes a spectrum of tidally restricted habitats behind water control structures and habitats experiencing full tidal exchange. To assess community composition for several different taxa in habitats with varying tidal exchange, we employed a variety of field approaches and synthesized results from several different studies. Overall, we found that communities at sites with moderately restricted tidal exchange were fairly similar to those with full tidal exchange, but those with extremely restricted tidal exchange were markedly different from other categories. These differences in community composition are likely the result of several factors, including restricted movement due to physical barriers, differences in water quality characteristics, and differences in habitat structure. Indeed, in this study, we found that water quality characteristics strongly vary with tidal restriction and may strongly influence patterns of species presence or absence. We also found that different conservation targets showed contrasting responses to variation in tidal exchange. Full exchange appears to favor native oysters, commercially valuable flatfish, migratory shorebirds, and site-level biodiversity. Minimal tidal exchange due to water control structures supports a suite of estuarine endemics (including the tidewater goby and California brackish snail) not represented elsewhere and minimizes invasions by non-native marine species. Altogether, our results suggest that total estuary-wide biodiversity may be enhanced with a mosaic of tidal exchange regimes. 相似文献
84.
Fluid mud dynamics in the Weser estuary turbidity zone tracked by high-resolution side-scan sonar and parametric sub-bottom profiler 总被引:1,自引:0,他引:1
Kerstin Schrottke Marius Becker Alexander Bartholomä Burghard W. Flemming Dierk Hebbeln 《Geo-Marine Letters》2006,26(3):185-198
Fluid mud in estuarine turbidity maximum zones (TMZ) can pose considerable navigation risks due to potentially substantial reductions in nautical depth, coupled with an inherent difficulty of detection by conventional echo-sounders. Despite intensive research efforts, however, our knowledge about the spatial and temporal dynamics of fluid mud is still not sufficient. In this study, the combined use of a side-scan sonar (Sportscan®, Imagenex) and a parametric sub-bottom profiler (SES-2000®, Innomar Technology GmbH) has proved successful for high-resolution fluid mud detection and volumetric quantification in an estuarine environment. In 2004 and 2005, repeated surveys were conducted in the navigation channel of the upper meso- to lower macrotidal Weser estuary TMZ (German North Sea coast) at different tidal stages and river discharges. Current velocity data were simultaneously collected by 1,200-kHz broadband ADCP (RDInstruments) measurements. Ground-truthing was carried out by means of grab sampling and gravity coring, adapted to fluid mud conditions. It was found that fluid mud occurrence in the Weser estuary is highly variable on time scales of a few hours and spatial scales of several metres. The riverbed is characterised by sand and mud deposits, and a complex morphology including subaqueous dunes and smooth bed deposits intermittently overlain by fluid mud. Thus, a continuous, coherent fluid mud body covering the entire TMZ riverbed was not observed. Rather, spatial distribution was patchy and highly dependent on suspended particulate matter (SPM) concentrations in the water column, as a result of which local fluid mud deposits varied in thickness from centimetres to metres. The formation of fluid mud was largely restricted to slack water, although slack-water conditions were not necessarily associated with large-scale fluid mud appearance. Advective SPM transport of resuspended fluid mud seems to be the most plausible explanation for the high spatial variability observed, even between two successive tides. The amount of fluid mud deposited and resuspended in the course of a tidal cycle can reach several 10s of tons even in small riverbed depressions. 相似文献
85.
Transport of South Atlantic water through the passages south of Guadeloupe and across 16°N, 2000–2004 总被引:1,自引:1,他引:1
Monika Rhein Kerstin Kirchner Christian Mertens Reiner Steinfeldt Maren Walter Ulrich Fleischmann-Wischnath 《Deep Sea Research Part I: Oceanographic Research Papers》2005,52(12):2234-2249
CTD, vessel-mounted ADCP and LADCP measurements in the Caribbean passages south of Guadeloupe (three repeats) and along 16°N (five repeats) were carried out between December 2000 and July 2004. The CTD data were used to calculate the contribution of South Atlantic water (SAW) in the upper 1200 m between the isopycnals σθ=24.5 and 27.6. Northern and southern source water masses are defined and an isopycnal mixing approach is applied. The SAW fractions are then combined with the ADCP flow field to calculate the transport of SAW into the Caribbean and across 16°N. The SAW inflow into the Caribbean through the passages south of Guadeloupe ranges from 7.6 to 11.6 Sv, which is 50–75% of the total inflow. The mean (9.1±2.2 Sv) is in the range of previous estimates. Ambiguities in the northern and southern source water masses of the salinity maximum water permitted us only to calculate the contribution of SAW from the eastern source in this water mass. We estimated the additional SAW transport by the western source to be of the order of 1.9±0.7 Sv. The calculation of the SAW transport across 16°N was hampered by the presence of several anticyclonic rings from the North Brazil Current (NBC) retroflection region, some of the rings were subsurface intensified. Provided that the rings observed at 16°N are typical rings and that all rings which are annually produced in the NBC retroflection area (6.5–8.5 per year) reach 16°N, the SAW ring transport across 16°N is calculated to 5.3±0.7 Sv. From the 5 repeats at 16°N, only two showed a net northward flow, suggesting that the mean northward SAW transport is dominated by ring advection. The joint SAW transports of the Caribbean inflow (9.1 Sv) and the flow across 16°N (5.3 Sv) sum up to 14.4 Sv. The transport increases to 16.3 Sv if the additional SAW transport from the western source of SMW (1.9±0.7 Sv) is included. These transport estimates and the following implications depend strongly on the assumption that the surface water in the Caribbean inflow is of South Atlantic origin. The transport estimates are, however, in the range of the inverse model calculations for the net cross-hemispheric flow. About 30–40% of this transport is intermediate water from the South Atlantic, presumably supporting studies which found the contributions of intermediate and upper warm water to be of a comparable magnitude. For the upper warm water (σθ<27.1), the Caribbean inflow seems to be the major path (7.9±1.6 Sv), the ring induced transport across 16°N is about 30% of that value. The intermediate water transport across 16°N was calculated to be 2.3–3.6 Sv, the inflow into the Caribbean is slightly smaller (1.5–2.4 Sv). 相似文献
86.
The degree of association between geoeffective (SID producing) flares (hereafter called SID flares) and sunspot morphology is examined. It is found that: (1) the frequency of SID flares associated with sunspot groups is linear function of sunspot area and rate of change in area; (2) the SID flare intensity is dependent on the sunspot area and on the magnetic morphology (field geometry); (3) the probability of a sunspot group being magnetically complex (henceforth called complex ratio) is a linear function of spot area, the larger this area the more likely a group is in the βγ or δ magnetic class; (4) the complex ratio exhibits the greatest degree of association to SID flare frequency. We conclude from these results that a higher frequency of D-region ionizing flares (emitting a soft X-ray flux >2 × 10?3 erg cm?2 s?1) is likely to accompany the disk transit of large area, complex spot groups. This combination of morphological factors reflects a shearing of the associated force-free magnetic field, with accumulation of free magnetic energy to power SID flares. Mutual polarity intrusion would be one observational signature of the pre-flare energy storing process. 相似文献
87.
A laboratory experiment has been made where a plasma stream collides with targets made of different materials of cosmic interest. The experiment can be viewed as a process simulation of the solar wind particle interaction with solid surfaces in space — e.g., cometary dust. Special interest is given to sputtering of OH and Na.It is also shown that the erosion of solid particles in interplanetary space at large heliocentric distances is most likely dominated by sputtering and by sublimation near the Sun. The heliocentric distance of the limit between the two regions is determined mainly by the material properties of the eroded surface, e.g., heat of sublimation and sputtering yield, a typical distance being 0.5 AU.It is concluded that the observations of Na in comets at large solar distances, in some cases also near the Sun, is most likely to be explained by solar wind sputtering. OH emission in space could be of importance also from dry, water-free, matter by means of molecule sputtering. The observed OH production rates in comets are however too large to be explained in this way and are certainly the results of sublimation and dissociation of H2O from an icy nucleus. 相似文献
88.
Rafael Santana Guilherme C. Lessa John Haskins Kerstin Wasson 《Estuaries and Coasts》2018,41(1):99-113
Estuarine ecosystem diversity and function can be degraded by low oxygen concentrations. Understanding the spatial and temporal patterns of dissolved oxygen (DO) variation and the factors that predict decreases in DO is thus essential to inform estuarine management. We investigated DO variability and its drivers in Elkhorn Slough, a shallow, well-mixed estuary affected by high nutrient loading and with serious eutrophication problems. Long-term (2001–2012), high-resolution (15 min) time series of DO, water level, winds, and solar radiation from two fully tidal sites in the estuary showed that hypoxia events close to the bottom are common in the summer at the more upstream estuarine station. These events can occur in any lunar phase (spring to neap), at any time of the day, and both on sunny or cloudy days. They are, however, short-lived (lasting in average 40 min) and mainly driven by momentary low turbulent diffusion around slack tides (both at high and low water). Tidal advective transport explains up to 52.1% of the daily DO variability, and the water volume (or DO reservoir) contained in the estuary was not sufficient to avoid hypoxia in the estuary. Solar radiation was responsible for a positively correlated DO daily cycle but caused a decreased in the averaged DO in the summer at the inner station. Wind-driven upwelling reduced the average DO at the more oceanic station during spring. The approach we employed, using robust techniques to remove suspect data due to sensor drift combined with an array of statistical techniques, including spectral, harmonic, and coherence spectrum analysis, can serve as a model for analyses of long-term water quality datasets in other systems. Investigations such as ours can inform coastal management by identifying key drivers of hypoxia in estuaries. 相似文献
89.
Kerstin Huber Kaarina Weckström Ruth Drescher-Schneider Johann Knoll Jutta Schmidt Roland Schmidt 《Journal of Paleolimnology》2010,43(1):131-147
A sediment core section from Längsee, a small meromictic lake in the southern Alpine lowland (Carinthia, Austria) close to the Würmian ice margin, was investigated by means of diatoms and pollen. The main aims of the study were to reconstruct water temperature as a signal of climate change during the last glacial termination, compare the aquatic and terrestrial response to the changing climate, and place our findings into a climatic frame on the northern hemispheric scale. A calibration data set (ALPS06) of 116 lakes was constructed using data from newly studied lakes and from two previously published data sets and we established a transfer function for predicting summer epilimnetic water temperatures (SEWT). A locally weighted weighted average regression and calibration model (R jack 2 = 0.89; RSMEP = 1.82°C) was applied to the fossil diatom assemblages in order to reconstruct SEWT. Three major sections were distinguished in the time window of approximately 19–13 cal ka BP, which fitted well with the oxygen isotope curve and the isotope-event stratigraphy from the Greenland ice-core GRIP. The first section was a warming period (SEWT range from 11.6 to 18.0°C; average 15.8°C = ca. 6°C below present) called the Längsee oscillation, which probably correlates with the warmer sub-section (GS-2b) of the Greenland Stadial 2. The subsequent section represents a climate cooling, called the Längsee cold period (SEWT range between 10.6 and 15.9°C; average 12.9°C), which probably corresponds with the sub-section GS-2a of the Greenland Stadial 2, the Heinrich 1 cold event of the North Atlantic, and partially the Gschnitz Stadial in the Alps. The Längsee cold period shows a tri-partition: Two colder phases are separated by a warmer inter-phase. The passive ordination of the core sample scores along maximum water depth indicated that the Längsee cold period was drier than the Längsee oscillation. Strong short-term fluctuations during the Längsee oscillation and the Längsee cold period indicate climate instability. The third section represented climate warming during the Längsee late glacial interstadial (=Greenland Interstadial 1, GI-1) with an average SEWT of 17.5°C. From the minor climatic fluctuations during this interstadial, mainly indicated by pollen, the fluctuation most likely related to the Gerzensee oscillation showed a SEWT decline. During the early immigration and expansion period of shrubs and trees, aquatic and terrestrial records showed distinct discrepancies that might have arose because of time lags in response and differences in sensitivity. 相似文献
90.
Henny A.J. Van Lanen Gregor Laaha Daniel G. Kingston Tobias Gauster Monica Ionita Jean‐Philippe Vidal Radek Vlnas Lena M. Tallaksen Kerstin Stahl Jamie Hannaford Claire Delus Miriam Fendekova Luis Mediero Christel Prudhomme Ekaterina Rets Renata J. Romanowicz Sébastien Gailliez Wai Kwok Wong Mary‐Jeanne Adler Veit Blauhut Laurie Caillouet Silvia Chelcea Natalia Frolova Lukas Gudmundsson Martin Hanel Klaus Haslinger Maria Kireeva Marzena Osuch Eric Sauquet James H. Stagge Anne F. Van Loon 《水文研究》2016,30(17):3097-3104