Remote sensing estimation of carbon fractions in the Chinese Yellow River estuary     

Xiang Yu  Yebao Wang  Xiangyang Liu 《Marine Georesources & Geotechnology》2018,36(2):202-210

Reliable and consistent carbon fraction estimates are crucial in studying the role of coasts in the global carbon cycle. Remote sensing offers the potential to estimate carbon fractions with its advantages of large spatial coverage and real-time surveys. Colored dissolved organic matter (CDOM) absorption was generally used as a proxy to estimate dissolved organic carbon (DOC). However, the CDOM–DOC relationship varies by region and remains inconstant. Thus, the correlation between the reflectivity of visible band and DOC concentration was directly adopted in DOC estimation and performed well in former studies. Atomic groups of the various components of carbon fractions produce electronic transition by absorbing photons, and this process occurs both in the visible bands and in the near-infrared bands. Thus, the wide range of absorption band provides an approach to estimate carbon fractions using the correlation between the reflectivity of the whole visible/near-infrared bands of optical satellite sensors and carbon fractions. A new ratio band combination was developed and performed well in carbon fraction concentration retrievals, and the yielded estimation accuracies (R²?>?0.77, RPD >2.02) were sufficient to map the spatial distributions of carbon fractions with the moderate resolution imaging spectroradiometer image.  相似文献   

白洋淀沉积物重金属潜在生态风险及生物可利用性分析     

刘成  黄蔚  古小治  张雷  陈开宁 《湖泊科学》2022,34(6):1980-1992

沉积物是湖泊水体重金属的主要汇集场所,也是湖泊重金属污染研究及整治的重点.本文分析了白洋淀多个淀区沉积物中16种重金属含量水平及垂向分布特征,解析了其中典型有害重金属潜在生态风险,并基于酸可挥发性硫（AVS）及同步可提取金属（SEM）、间隙水溶解态金属、可转化态金属形态分级等研究,对重金属生物可利用性进行了分析.结果表明：沉积物重金属含量均值高低依次为Fe （29630.50 mg/kg）>Ti （3213.07 mg/kg）>Mn （539.44 mg/kg）>Zn （104.01 mg/kg）>V （76.63 mg/kg）>Cr （52.60 mg/kg）>Cu （43.49 mg/kg）>Ni （35.83 mg/kg）>Pb （26.75 mg/kg）>Co （10.32 mg/kg）>As （8.96 mg/kg）>Mo （2.06 mg/kg）>Sb （1.57 mg/kg）>Tl （0.43 mg/kg）>Cd （0.31 mg/kg）>Hg （0.16 mg/kg）;其中,10种重金属在各淀区沉积物中呈现出自北往南逐渐降低的趋势,各金属在不同淀区分布差异性主要由污染输入所致.除北部烧车淀区域外,其余区域重金属潜在生态风险总体处于较低水平.重金属污染主要来源于该区域周边河道,但近10年来污染输入及在沉积物中的富集总体趋于稳定并呈逐渐降低的趋势.入淀污染不仅增加了该区域沉积物中重金属总量,也使得其中可转化态重金属比例较高,大多在30%~90%之间,提升了重金属生物可利用潜力.水生植物等内生性有机质的大量富集导致沉积物还原性较强,AVS含量较高,沉积物中AVS和ΣSEM均值分别为（10.59±6.37）和（2.23±1.53）μmol/g （dw）.Cd、Cu、Ni、Pb、Zn等金属由于高含量还原态硫的固定而生物可利用性较低.然而,As和Hg在这样的高有机质和强还原环境下更容易溶解和释放,是潜在生物可利用性相对较高的金属,在间隙水中的浓度分别达到（17.07±0.23）和（2.39±0.94）μg/L,未来研究及整治中应给予更多关注.  相似文献   

Social interactions can affect feeding behaviour of fish in tanks     

S.A.L.M. Kooijman   《Journal of Sea Research》2009,62(2-3):175

Fish from the same clutch of eggs, so of the same age and family, can differ substantially in size after some time in a tank as result of social interactions. On the basis of computer simulation studies I here demonstrate that it is possible to mimic this empirical observation using the rules of the standard Dynamic Energy Budget (DEB) model, supplemented with a simple stochastic module for interaction between individuals that have identical parameters. The remarkable result is that length-at-age of two individuals in a tank where the number of food particles is kept constant closely follows von Bertalanffy growth curves with very different parameters, while in reality the individuals have identical parameters. The empirical observation demonstrates that fish are close to the supply end of the supply–demand spectrum and that age-based models for growth don't apply to supply systems. The significance of the result is discussed.  相似文献   

Performance of an inshore fishery in the absence of regulatory enforcement     

Edward Fahy   《Marine Policy》2008,32(6):1037-1042

The principal inshore fishery in the southwest Irish Sea is currently for whelk Buccinum undatum, which expanded in the 1990s and yielded almost 10,000 t in 2003. The fleet exploiting it consisted largely of old boats many of which previously used a variety of gears but which cannot any longer compete with more modern towing craft. Whelk is the only target species for the majority. The fishery is in open access and is not regulated and the paper examines the consequences of this for the fishers, particularly the problems associated with maintaining a way of life traditionally associated with remuneration by share rather than wage. Lack of regulation, it is argued, encourages a short term, opportunistic harvesting regime, which is not conducive to maintain a biologically sustainable fishery.  相似文献   

Changes in fine sediment size distributions due to interactions with streambed sediments     

Jianhong Ren  Aaron I. Packman 《Sedimentary Geology》2007,202(3):529-537

In the classical view of fine sediment transport and deposition in streams, particles are expected to be removed from flowing water simply by direct sedimentation onto the streambed. However, recent research has demonstrated that fine sediments can propagate into pore spaces in the streambed due to hyporheic exchange and be removed by a combination of physical and chemical processes. This behaviour can significantly alter fine sediment size distributions during in-stream sediment transport because the physical transport of fine particles and their attachment to bed sediment grains are both a function of the particle size. Herein, we present model simulations for deposition of suspended sediments with a bimodal size distribution. We also applied this approach to analyse the results of laboratory flume observations of suspended sediment deposition. Results from model simulations and flume experiments clearly show that the rate of particle deposition increases with increasing particle size. Thus, the larger particles are preferentially removed from mixtures and there is a fining of the mixed suspensions over time. Both particle deposition mechanisms, i.e. particle sedimentation and filtration, contribute to the fining of the mixed fine particle suspensions over time, and their effects are clearly demonstrated using the fundamental process-based model. These results clearly demonstrate the effects of stream-subsurface exchange on the temporal evolution of the suspended fine sediment size distribution in downstream transport.  相似文献   

茶园土壤不同形态镍的含量及其影响因素   总被引：3，自引：2，他引：1  

谢忠雷  杨佰玲  包国章  董德明 《吉林大学学报(地球科学版)》2006,36(4):599-604

通过自然茶园土壤采样和室内实验分析,探讨浙江、江苏和安徽13个茶园土壤镍的污染状况、形态分布规律以及不同形态镍的含量与土壤镍总量和土壤理化性质的关系。结果表明：部分茶园土壤受到不同程度的镍污染;茶园土壤镍的形态分布有一定差异,按镍的含量多少排序,一般为残渣态＞交换态＞铁锰氧化物结合态＞有机结合态＞碳酸盐结合态;除了交换态以外的所有其他形态的镍含量均随土壤镍含量的增加而显著增加;碳酸盐结合态、铁锰氧化物结合态和残渣态镍含量随土壤pH的升高呈显著增加趋势,而交换态镍则呈减少趋势,但不显著;随土壤有机质含量的增加,铁锰氧化物结合态镍显著减少,而其他形态增加或减少的趋势均不显著;碳酸盐结合态、有机结合态和残渣态的镍含量均随阳离子交换量的增加显著增加;随粘粒含量的增加所有形态中的镍呈增加趋势,但除了残渣态外增加趋势均不显著。  相似文献   

Seasonal variability of phytoplankton biomass and composition in the major water masses of the Indian Ocean sector of the Southern Ocean     

《Polar Science》2014,8(3):283-297

Long-term changes in phytoplankton biomass and community composition are important in the ecosystem and biogeochemical cycle in the Southern Ocean. We aim to ultimately evaluate changes in phytoplankton assemblages in this region on a decadal scale. However, yearly continuous data are lacking, and long-term datasets often include seasonal variability. We evaluated the seasonal changes in phytoplankton abundance/composition across latitudes in the Indian Ocean sector of the Southern Ocean via multi-ship observations along the 110°E meridian from 2011 to 2013. The chlorophyll a concentration was 0.3–0.5 mg m⁻³ in the Subantarctic Zone (40–50°S) and 0.4–0.6 mg m⁻³ in the Polar Frontal Zone (50–60°S); pico-sized phytoplankton (<10 μm), mainly haptophytes, were dominant in both zones. In the Antarctic Divergence area (60–65°S), the chlorophyll a concentration was 0.6–0.8 mg m⁻³, and nano-sized phytoplankton (>10 μm), mainly diatoms, dominated. Chlorophyll a concentrations and phytoplankton community compositions were the same within a latitudinal zone at different times, except during a small but distinct spring bloom that occurred north of 45°S and south of 60°S. This small seasonal variation means that this part of the Southern Ocean is an ideal site to monitor the long-term effects of climate change.  相似文献   

The relative contributions of unicellular and filamentous diazotrophs to N2 fixation in the South China Sea and the upstream Kuroshio     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

We studied the seasonal, diel, and vertical distribution of phytoplankton N₂ fixation to understand the relative contributions of unicellular and filamentous nitrogen fixers (diazotrophs) to N₂ fixation and nitrogen recycling in the northern South China Sea (SCS) and the neighboring upstream Kuroshio. N₂-fixation rates were measured by the ¹⁵N₂ tracer technique (addition by bubble) on unicellular (<10 or 20 µm) and the filamentous diazotrophs (>10 or 20 µm, mostly Trichodesmium and Richelia) fractionated by 10- or 20-µm mesh sizes. The mean depth-integrated total (unicellular+filamentous) N₂-fixation rates in the SCS (51.7±6.2 µmol N m⁻² d⁻¹) averaged 1/3 of that in the Kuroshio (142.7±29.6 µmol N m⁻² d⁻¹), with higher rates in the winter than in other seasons in the SCS and the opposite seasonal pattern in the Kuroshio. Unicellular diazotrophs contributed 65% of the total N₂ fixation in the SCS, which were negatively correlated with surface temperature and, as for total N₂ fixation, were higher in the winter when Trichodesmium spp. were scarce. In comparison, the unicellular diazotrophs contributed 50% of total N₂ fixation in the Kuroshio, and their contributions were not significantly correlated with surface temperature. In both the SCS and the Kuroshio, the unicellular N₂ fixation was more important during the night than during the day, and in the deep euphotic layer than in the surface layer, even in the daytime. Our results show that the unicellular diazotrophs were important N₂ fixers and contributed significantly to N₂ fixation in the tropical marginal seas, more so in the SCS than the Kuroshio.  相似文献   

一次多层云系云物理垂直结构探测研究          下载免费PDF全文

王维佳  董晓波  石立新  刘建西  刘平  张世林 《高原气象》2011,30(5):1368-1375

利用飞机PMS探测数据、雷达回波资料和FY-2卫星云图,分析了2009年6月四川盆地上空一次未形成地面降水的多层云系。结果表明,云系为Cs-As2-As1-Sc2-Sc1结构,夹有干层。云系中暖层厚,过冷层很薄。液态含水量随高度分布很不均匀,出现多个峰值。云系中液态含水量主要由小云粒子浓度决定,并且存在大量的小云滴、一...  相似文献   

Size-dependent uptake of nitrate and ammonium as a function of light in well-mixed temperate coastal waters     

Jean-François Maguer  Stéphane L'HelguenJulien Caradec  Cécile Klein 《Continental Shelf Research》2011,31(15):1620-1631

The effect of light on nitrate (NO₃⁻) and ammonium (NH₄⁺) uptake by natural communities was investigated in relation to cell size (<10 and >10 μm) in the well-mixed coastal waters of the English Channel. Nitrogen (N) uptake kinetics as a function of irradiance were assessed using ¹⁵N tracer techniques, for a seasonal cycle of populations collected at 50% and 1% light penetration depth. The nitrogen uptake responses to irradiance can be represented by the formulation used to describe the photosynthesis versus irradiance relationships and modified by the addition of a dark uptake parameter. The response curves of two size fractions of phytoplankton collected at 50% and 1% of incident light did not differ significantly, which suggested that the physiological characteristics of N uptake were not affected by the light intensity at which the phytoplankton assemblages were sampled. The kinetics parameters indicated that the NO₃⁻ uptake system was more strongly dependent on light than the NH₄⁺ uptake system. They also showed that N uptake was less limited by the light intensity in the small size fraction than it was in the large size fraction. At the mean light intensity in the water column, kinetics analysis predicted a NH₄⁺ uptake that was on average 1.8 (±0.6) and 2.4 (±1.0) times greater than the NO₃⁻ uptake, for <10 and >10 μm size fractions, respectively. The kinetics also predicted, at the in situ mean light intensity, that the mean ability to take up nitrogen was twice as high (1.8±0.5) for the small than for the large cells when the N substrate was NH₄⁺ and more than twice as high (2.6±1.5) when the substrate was NO₃⁻. These results added to our understanding of the light effect on N uptake processes in well-mixed waters, and can largely explain the phytoplankton production, mainly regenerated and dominated by small cells, that has been observed in these waters.  相似文献