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1.
来源于微生物膜脂的甘油二烷基甘油四醚类(GDGTs)化合物是近年来被广泛用于古环境定量重建研究的化合物之一,究其原因在于此类化合物对环境响应敏感,特别是温度与pH值等,据此而建立的一系列GDGTs指标有效定量重建海洋、湖泊、泥炭以及土壤等不同沉积载体的环境信息.目前已在全球范围广泛开展湖泊沉积物GDGTs的研究工作,相继建立的全球以及不同区域尺度的湖泊沉积物GDGTs校正方程,已被用于湖泊古环境的定量重建研究,有效记载古湖泊环境变迁信息.相较之下,基于湖泊水体GDGTs的调查工作则起步较晚,但越来越多的研究显示,不同类型湖泊水体普遍贡献GDGTs,然而究竟此类水生来源GDGTs是否与陆源以及湖泊沉积物GDGTs具有类似的分布,以及他们对环境因素的响应如何,这都为湖泊古温度定量重建研究带来不确定性.基于此,本文总结这10年来湖泊水体GDGTs研究工作的进展,首先阐述湖泊水体不同来源(古菌以及细菌)GDGTs的分布情况,研究发现水体不同层位GDGTs浓度以及各组分之间存在差异,并且水深在不同湖泊对GDGTs浓度以及各组分相对比例的影响存在差异.此外还总结湖泊水体中古菌来源isoGDGTs以及细菌来源brGDGTs的生物来源,并进一步分析环境因素对不同深度水体GDGTs分布的影响,虽然温度依然是影响水体中GDGTs分布的首要因素之一,然而湖泊水深、温度以及水体中溶解氧浓度等因素存在着一定的耦合关系,这些因素往往协同作用于水体GDGTs,因此会为评估环境因素对水体GDGTs的影响带来难度. 相似文献
2.
Glycerol dialkyl glycerol tetraethers(GDGTs) in lake sediments are useful biomarkers for the continental paleoclimatic reconstruction. However, the environmental controls on the distribution of these compounds, in particular the 6-methyl isomers of bacterial branched GDGTs(bGDGTs), in the lakes with contrasting pH, are still unknown, hindering their application for paleo-reconstructions. Here, we investigated the environmental impacts on the distribution of GDGTs in 17 alkaline lakes and 1 acid lake in China. It was found that the dissolved oxygen content in water column may have an impact on the distribution of archaeal isoprenoid GDGTs(iGDGTs) by causing the change in archaeal communities. The ratio of GDGT-0/crenarchaeol increases with decreasing oxygen content, indicating that the relative abundance of anaerobic methanogenic archaea or Miscellaneous Crenarchaeotic Group(MCG) vs. aerobic Thaumarchaeota is controlled by the oxygen content dissolved in water of these lakes. Thaumarchaeota are likely to contribute only a small proportion of iGDGTs in the relatively oxygen-depleted lakes, and thus TEX_(86) is not suitable for the reconstruction of the surface temperature of these lakes. The abundance ratio of iGDGTs to bGDGTs(R_(i/b)) appears to show no relationship with water pH in all the lakes, but exhibits a significant positive correlation with the water depth of the acid Lake Qinghai in Tengchong. As expected, the methylation degree of bGDGTs(MBT′) was found to correlate with both mean annual air temperature(MAT) and water pH, and the cyclization degree of bGDGTs(CBT) correlates only with water pH in these lakes. However, the MBT′_(5ME), an index to measure the methylation degree of 5-methyl bGDGTs, exhibits no relationship with MAT, whereas MBT′_(6ME), the methylation degree of 6-methyl bGDGTs, was found to correlate significantly with MAT. This is opposite to the situation observed in the global soils, pointing to a different adaptation of b GDGT-producing bacteria to environmental variables or different microbial sources of bGDGTs in these lakes. The relative abundance of 6- vs. 5-methyl bGDGTs is controlled by pH in these lakes, similar to that observed in worldwide soils. Hence, the isomer ratio(IR) of 6-methyl bGDGTs or CBT′ can be used as a proxy for water pH, although they might be influenced by other environmental factors including temperature in the lakes with a narrow range of pH. 相似文献
3.
HuanYe Wang HaiLiang Dong ChuanLun Zhang HongChen Jiang WeiGuo Liu 《中国科学:地球科学(英文版)》2016,59(5):951-960
Branched and Isoprenoid Tetraether (BIT) index was considered as a proxy for terrestrial organic matter input in lake sediments, based on the assumption that branched glycerol dialkyl glycerol tetraethers (bGDGTs) are mainly derived from terrestrial soils. However, mounting evidences have showed that the in situ production of bGDGTs is widespread in lakes, challenging BIT as a reliable terrestrial input proxy. Recently, BIT has been proven to be a reliable proxy for paleohydrology in a small crater lake (Lake Challa) in accordance with a different mechanism. However, the response of BIT to paleohydrology variation may differ for different lakes. In this study, we investigate the variations in the BIT index and the concentrations of its related GDGTs in a 12-ka sediment core from Lake Qinghai, in combination with our previous results for surface sediments. We find that variations in BIT strongly depend on the concentration of crenarchaeol in both surface and ancient sediments of this lake, whereas bGDGT concentration varies much less remarkably. Considering that crenarchaeol production is positively correlated with water depth in Lake Qinghai, water depth may exert negative control on the BIT index in this lake. This case is inconsistent with the positive relationship between BIT and lake levels or rainfall intensity reported for Lake Challa, suggesting that the response of BIT to local paleohydrology is site specific in lacustrine systems. Hence, the application of sedimentary BIT as a paleohydrological proxy in a specific lake requires caution before confirming the environmental controls on BIT in that lake. 相似文献
4.
Yue Li Shijin Zhao Hongye Pei Shi Qian Jingjie Zang Xinyue Dang Huan Yang 《中国科学:地球科学(英文版)》2018,61(7):925-939
Glycerol Dialkyl Glycerol Tetraethers(GDGTs)serve as important tools for the quantitative reconstruction of paleoclimate and paleoecology in both continental and marine environments.Previous studies of GDGTs in the terrestrial environments focused primarily on the soils from the relatively warm-humid or cold-dry regions.However,it is still unclear how GDGTs respond to environmental variables in the cold-humid regions.Here,we collected soils along an altitudinal transect of Mountain(Mt.)Changbai,which has a typical cold-humid climate,to investigate the distribution of GDGTs and the response of GDGT-based proxies to changes in climate along the transect.The shift in the distribution of archaeal isoprenoidal GDGTs(iso GDGTs)revealed that the archaeal community varied significantly along the transect,which can affect the relationship between TEX_(86)and mean annual air temperature(MAT).In addition,the increased temperature seasonality at higher altitudes exerted a significant impact on TEX_(86).We proposed a global calibration of TEX_(86)for the growing season temperature reconstruction in the soil environments:T=85.19×TEX_(86)-46.30(R~2=0.84,p0.001).The methylation indices for 5-methyl branched GDGTs(br GDGTs)including MBT′_(5me)and MBT_(5/6),showed correlation with soil water content but no relationship with MAT,indicating that MBT′_(5me)and MBT_(5/6)from cold-humid environments may be not suitable for temperature and altitude reconstruction.In contrast,the recently developed p H proxies,including MBT′_(6me)(the methylation index for 6-methyl br GDGTs),CBT(Cyclisation index of Branched Tetraethers),IR_(IIa’)(Isomer ratio of IIa′)and IR_(IIIa′)(Isomer ratio of IIIa′)exhibited significant correlations with soil p H,suggesting these proxies can still be used for soil p H reconstruction in the coldhumid regions.The combination of MBT′_(5me)and MBT′_(6me)was strongly related to different types of climate(cold-dry,warmhumid,cold-humid,and warm-dry).For example,MBT′_(5me)0.65 and MBT′_(6me)0.55 are diagnostic for the cold-humid climate.Thus,the combination of MBT′_(5me)and MBT′_(6me)has the potential as a tool for the identification of different types of paleoclimate. 相似文献
5.
Surface water oxygen and hydrogen isotopic values are commonly used as proxies of precipitation isotopic values to track modern hydrologic processes while proxies of water isotopic values preserved in lake and river sediments are used for paleoclimate and paleoaltimetry studies. Previous work has been able to explain variability in USA river‐water and meteoric‐precipitation oxygen isotope variability with geographic variables. These studies show that in the western United States, river‐water isotopic values are depleted relative to precipitation values. In comparison, the controls on lake‐water isotopic values are not well constrained. It has been documented that western United States lake‐water input values, unlike river water, reflect the monthly weighted mean isotopic value of precipitation. To understand the differing controls on lake‐ and river‐water isotopic values in the western United States, we examine the seasonal distribution of precipitation, evaporation and snowmelt across a range of seasonality regimes. We generate new predictive equations based on easily measured factors for western United States lake‐water, which are able to explain 69–63% of the variability in lake‐water hydrogen and oxygen isotopic values. In addition to the geographic factors that can explain river and precipitation values, lake‐water isotopic values need factors related to local hydrologic and climatic characteristics to explain variability. Study results suggest that the spring snowmelt runs off the landscape via rivers and streams, depleting river and stream‐water isotopic values. By contrast, lakes receive seasonal contributions of precipitation in proportion to the seasonal fraction of total annual precipitation within their watershed. Climate change may alter the ratio of snow to rain fall, affecting water resource partitioning between rivers and lakes and by implication of groundwater. Paleolimnological studies must account for the multiple drivers of water isotopic values; likewise, studies based on the isotopic composition of fossil material need to distinguish between species that are associated with rivers versus lakes. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Archaeal and bacterial glycerol dialkyl glycerol tetraethers (GDGTs) play a unique role in discerning the biogeochemical processes and climate change in terrestrial (e.g. soil, peat, stalagmites, lakes, rivers, hot springs) and marine environments. Organic proxies based on GDGTs (e.g. TEX86, MBT/CBT and BIT) have made impressive applications in the open ocean and terrestrial environments. However, the applicability of these proxies in marginal seas has not been thoroughly evaluated, which is necessary given the complexity and dynamics of these systems, such as organic matter (OM) flux, hydrodynamic conditions, and human impact. This review aims to summarize recent studies of GDGTs and GDGT-based proxies in the Chinese marginal seas (CMS), which are characterized by diverse gradient in terrigenous supplies and ocean productivity and hold rich information on climate and sea level changes, ocean current dynamics, sedimentary evolution and biogeochemical processes. 相似文献
7.
甘油二烷基甘油四醚脂(GDGTs)是目前生物地球化学研究的热点之一.与GDGTs有关的指标已成功地应用在海洋环境中有关来源判识和古环境古气候重建的研究,但是在湖泊环境中的应用目前还比较有限.通过开展巢湖柱状沉积物中GDGTs的组成测定,为GDGTs类脂分子标志物在湖泊系统中的应用提供依据.研究表明由柱状沉积物中支链GDGTs参数计算得到的量化结果与巢湖周围流域的环境温度、pH等历史记录能较好地吻合;柱状沉积物中类异戊二烯类GDGTs来源的不确定性可能是造成TEX_(86)指标的量化结果和实际的水体温度出现较大偏差的重要原因.另外,沉积物中GDGTs指标和TOC、C/N、δ~(13)C_(org)、δ~(15)N等传统湖泊总体有机质参数以及其它分子标志物指标相比,具有高分辨性和抗干扰等特点.因此,湖泊中GDGTs有望成为湖泊古气候和古环境重建的重要指标. 相似文献
8.
目前,甘油二烷基甘油四醚(GDGTs)组成和分布特征已被成功应用于古气候古环境重建中。然而,越来越多的研究表明除温度和pH值外,GDGTs也受其他环境因素影响,这导致了在同一地区运用多种温度和pH校准公式得到的结果差异较大,特别是在干旱地区尤为显著。因此,有必要开展现代过程GDGTs分布及其影响因素的调查,以提高温度和pH校准公式的适用性。为此,我们以北方察汗淖尔湖泊为中心,分析流域内24个湖泊沉积物和土壤GDGTs组成和分布。结果显示,所有样品GDGTs分布模式相似,其中古菌类异戊二烯GDGTs(简称isoGDGTs)以crenarchaeol为主,GDGT-0次之,crenarchaeol’含量较低,指示GroupⅠ.1b型奇古菌输入较多;细菌支链GDGTs(简称brGDGTs)中五甲基化brGDGTs丰度最高,其次是六甲基化和四甲基化brGDGTs。群落指数(community index,CI)表明,产brGDGTs的细菌群落属于冷簇,且冗余分析显示pH值对brGDGTs分布影响显著,二者可能共同导致了应用多种校准公式计算结果与器测记录之间的差异。通过该项工作我们认为在利用GD... 相似文献
9.
Quan Li 《中国科学:地球科学(英文版)》2018,61(3):270-284
Pollen diversity offers abundant clues into the floristic diversity and history of vegetation change. Few palynological studies investigated modern pollen diversity or the past floristic diversity on the Tibetan Plateau (TP). Based on modern pollen assemblages from 37 topsoils and 63 surface lake sediments in the Nam Co catchment on the central TP, this study quantitatively explored spatial distribution of modern pollen diversity using Shannon-Wiener index (H) and palynological richness (E(T n ), n=600). Pollen diversity indices showed spatial variability among vegetation types, reflecting the differences in terrestrial floristic diversity in the lake catchment. Their values were high in the southeastern region of the lake catchment which is covered by alpine steppe, while values were low for alpine meadow and marsh meadow. The pollen diversity in lacustrine pollen assemblage could be an effective proxy to document past floristic diversity. The past floristic diversity in the lake catchment, recovered from a fossil pollen record of NMLC-1, showed a long-term change of ascending overlaid by several rapid diversity changes during the last 8400 years due to the downward shift of altitudinal vegetation belt driven by a general climatic cooling. The results imply that under the environmental challenge of climate warming and vegetation degradation, alpine vegetation restoration in the Nam Co catchment and the central TP should pay attention to altitudinal vegetation belt and zonal vegetation of alpine steppe, and use the long-term change of floristic diversity as a historical analogue. 相似文献
10.
中国晚新生代湖泊沉积及其反映的环境概貌 总被引：4，自引：1，他引：3
在地球历史上湖泊沉积大规模的发育或缺失,都和一定的构造背景和气候环境条件相关。本文依据我国晚新生代以来,湖泊沉积时空规模和分布的变化,来探讨我国大环境的变迁过程。上新世和早更新世我国西部存在许多大湖泊,发育巨厚的湖泊沉积,而东部分布的范围很局限,造成这种情况的原因,除了构造运动的差别外,当时大气环流的形势与今不同,西部的气候条件相当湿润。中—晚更新世西部的大湖大都萎缩,甚至消失,东部却表现出大湖增加的趋势,这显然与青藏高原的迅速隆起、东亚季风的加强有关。末次冰期以来,对应于冰期、间冰期的气候变化,不同气候带湖泊的响应差异颇大,既表现出区域环境的特点,也有全球变化事件的反映。 相似文献
11.
The paleoenvironmental significance of spatial distributions of grain size in groundwater‐recharged lakes: A case study in the hinterland of the Badain Jaran Desert,northwest China 
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下载免费PDF全文 For lakes in desert hinterlands that are not recharged by river runoff, sediment input solely comes from wind transport. While the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge, the spatial distribution of sediment grain size in these groundwater‐recharged lakes remains largely unknown. Moreover, whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear. In this study, five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the Badain Jaran Desert of north‐western China, and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size. Moreover, an end‐member‐modeling algorithm was used to calculate end members from all grain size measurements. Our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore, deep‐water zone. However, the lowest median and mean grain sizes were not found in the center of the lakes, in contrast to lakes recharged by surface runoff. The median grain size of sediment in the lake center was negatively correlated with lake level, and thus could help reveal lake evolution at low resolutions. Moreover, EM1 and EM2 were interpreted as wind transported sediment, and sediment perturbed by lake waves after wind transport, respectively. The modal grain size of EM1 varied slightly between lakes, while changes in the modal grain size of EM2 were related to lake area. Given the positive relationship found between EM2 content and lake level, changes in the EM2 content (%) can serve as a rough indicator of lake level fluctuations at low temporal resolutions. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
12.
G. Proft 《洁净——土壤、空气、水》1994,22(4):177-184
The BSi content has been investigated in the surface sediments of lakes of different trophic state in the Mecklenburgian Lake District. The BSi content differs between 1 to 1000 mg BSi/g dry matter. High values were found in deep eutrophic lakes. Litoral sediments and shallow eutrophic lakes have lower contents. BSi content was found to be correlated with lake morphometry, depth, trophic level, sediment composition and especially with calcite. With the CaCO3/BSi-value, 3 groups of lakes can be characterized:
- CaCO3/BSi = 0 oligotrophic and dystrophic lakes
- CaCO3/BSi ≤ 10 mesotrophic and eutrophic deep lakes
- CaCO3/BSi ≤ 10 eutrophic shallow lakes
13.
Based on the total phosphorous (TP) concentration in sediment core, the TP concentration in lake water quantitatively reconstructed from fossil diatoms and diatom-TP transfer function in the Longgan Lake during the last 200 years, the temperature and precipitation data from meteorological observation for the last 50 years, the temperatures and precipitation sequences of climate simulation for the last 200 years, as well as the amount of the agricultural phosphate fertilizer in Longgan area for nearly 50 years, the characteristic and the law of the nutrient status evolution were analyzed, and the influence of the climatic factor, the anthropologic factor and the aquatic biology factor on the nutrient status evolution and its mechanism were discussed for the Longgan Lake during the last 200 years. The results showed that, in the nearly 200 years, the TP concentration in the sediment core of the Longgan Lake gradually increased, its range of variation was situated between 330–580 mg/kg, the mean value was 388 mg/kg, a nearly 30-year vibration adjustment period existed at 1950 around. The TP concentration in lake water changed in a different way. Before 1950, it had a slow increasing tendency in fluctuated background, to 1950 around it reached up to the mean value (52.18 μg/L), and vibrated and adjusted around the mean value, then it fast declined, its change range was situated between 37.75–62.33 μg/L. The analyses indicated that, in the centennial time scale, the climate change was the main controlling factor, while in the decadal time scale in the recent 50 years, human activities were the leading factors for the nutrient status evolution of the Longgan Lake. 60% of the variability of the TP concentration in the sediments and 57% of that in lake water were due to human activities. The differentiation between phosphorus concentration in the sediment and in the lake water reflected the response processes and the adjustment abilities of the lake aquatic ecosystems to the lake nutrient level, implying the maintenance and the destruction of the balances between the algae and the aquatic plants, as well as the corresponding accumulating characteristics of the phosphorus. 相似文献
14.
Understanding the relative impacts of natural processes and human activities on the hydrology of the Central Rift Valley lakes,East Africa 下载免费PDF全文
下载免费PDF全文 Significant changes have been observed in the hydrology of Central Rift Valley (CRV) lakes in Ethiopia, East Africa as a result of both natural processes and human activities during the past three decades. This study applied an integrated approach (remote sensing, hydrologic modelling, and statistical analysis) to understand the relative effects of natural processes and human activities over a sparsely gauged CRV basin. Lake storage estimates were calculated from a hydrologic model constructed without inputs from human impacts such as water abstraction and compared with satellite‐based (observed) lake storage measurements to characterize the magnitude of human‐induced impacts. A non‐parametric Mann–Kendall test was used to detect the presence of climatic trends (e.g. a decreasing or increasing trends in precipitation), while the Standard Precipitation Index (SPI) analysis was used to assess the long‐term, inter‐annual climate variability within the basin. Results indicate human activities (e.g. abstraction) significantly contributed to the changes in the hydrology of the lakes, while no statistically significant climatic trend was seen in the basin, however inter‐annual natural climate variability, extreme dryness, and prolonged drought has negatively affected the lakes. The relative contributions of natural and human‐induced impacts on the lakes were quantified and evaluated by comparing hydrographs of the CRV lakes. Lake Abiyata has lost ~6.5 m in total lake height between 1985 and 2006, 70% (~4.5 m) of the loss has been attributed to human‐induced causes, whereas the remaining 30% is related to natural climate variability. The relative impact analysis utilized in this study could potentially be used to better plan and create effective water‐management practices in the basin and demonstrates the utility of this integrated methodology for similar studies assessing the relative natural and human‐induced impacts on lakes in data sparse areas. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
Based on the total phosphorous (TP) concentration in sediment core, the TP concentration in lake water quantitatively reconstructed from fossil diatoms and diatom-TP transfer function in the Longgan Lake during the last 200 years, the temperature and precipitation data from meteorological observation for the last 50 years, the temperatures and precipitation sequences of climate simulation for the last 200 years, as well as the amount of the agricultural phosphate fertilizer in Longgan area for nearly 50 years, the characteristic and the law of the nutrient status evolution were analyzed, and the influence of the climatic factor, the anthropologic factor and the aquatic biology factor on the nutrient status evolution and its mechanism were discussed for the Longgan Lake during the last 200 years. The results showed that, in the nearly 200 years, the TP concentration in the sediment core of the Longgan Lake gradually increased, its range of variation was situated between 330-580 mg/kg, the mean value was 388 mg/kg, a nearly 30-year vibration adjustment period existed at 1950 around. The TP concentration in lake water changed in a different way. Before 1950, it had a slow increasing tendency in fluctuated background, to 1950 around it reached up to the mean value (52.18μg/L), and vibrated and adjusted around the mean value, then it fast declined, its change range was situated between 37.75-62.33μg/L. The analyses indicated that, in the centennial time scale, the climate change was the main controlling factor, while in the decadal time scale in the recent 50 years, human activities were the leading factors for the nutrient status evolution of the Longgan Lake. 60% of the variability of the TP concentration in the sediments and 57% of that in lake water were due to human activities. The differentiation between phosphorus concentration in the sediment and in the lake water reflected the response processes and the adjustment abilities of the lake aquatic ecosystems to the lake nutrient level, implying the maintenance and the destruction of the balances between the algae and the aquatic plants, as well as the corresponding accumulating characteristics of the phosphorus. 相似文献
16.
长江中下游典型湖泊营养盐历史变化模拟 总被引：2，自引：1，他引：1
湖泊营养盐变化在自然条件下受到气候水文因素控制,同时受到湖泊生态系统生物群落作用和反馈.作为动力机制探讨,本文试图基于水文和生态动力学方法,分别构建气候-流域水文作用于湖泊营养盐的外源模式和湖泊生物群落作用于湖泊营养盐的內源模式.针对长江中下游典型湖泊,经过控制实验和率定,发现营养盐模拟与观测数据在时间序列上达到90%百分位的正相关,因此用来模拟1640 1840 A.D.期间的营养盐演变历史.研究表明:(1)模拟的湖泊营养盐变化与沉积钻孔揭示的历史营养盐变化基本一致,沉积记录与模式模拟的7个湖泊的营养盐变化均显著相关;(2)气候因素是湖泊营养盐历史演变的主控因子,来自于湖泊生物群落的反馈作用贡献约占40%;(3)在温度和降水因子的驱动下,湖泊营养盐历史变化主要受降水控制,在极端干旱时期,60%的营养盐变化同步响应于降水变化.同时,面积在400 km2以下的湖泊营养盐对气候变化的响应比2000 km2以上的大湖更为敏感.研究结果对长江中下游湖泊营养状态的长期变化机理认识和趋势控制提供科学依据. 相似文献
17.
Lakes over the inner Tibetan Plateau (TP) are very sensitive to the regional environmental transformations and climate changes. Well-preserved lake sediments around these lakes provide critical geomorphological and sedimentary evidence that can be used to infer the past hydroclimate changes. In this study, a lacustrine section from a sandy shoreline (∼74 m above the modern lake) situated to the northwest of modern Dawa Co in the inner TP was investigated using both luminescence and radiocarbon dating methods. Our results demonstrated: (1) the quartz optically simulated luminescence (OSL) dating yielded much younger ages (∼4 ka) than that of the post-infrared IRSL (pIRIR) dating of the K-feldspar fraction; (2) fading test showed g-values ranging between 1.34 and 4.46%/decade for quartz OSL signals, which is considered to be responsible for the underestimation of the corresponding ages; (3) the AMS 14C age of the charcoal sample from the section is in line with the K-feldspar pIRIR225 ages, confirming the reliability of the pIRIR225 dates and the underestimation of the quartz OSL ages. The anomalous fading of quartz OSL signals and the consequent age underestimation have been reported in several other lakes on the TP, we presented here for the first time firm evidence of the phenomenon with the help of a robust independent control of AMS 14C age of the charcoal. Based on the pIRIR225 and AMS 14C ages, we conclude that Dawa Co underwent a prominent highstand during the early Holocene (∼9–7 ka), which was probably controlled by the large amounts of glacial meltwater input and the increased monsoonal precipitation. 相似文献
18.
We used a comparative data set for 25 lakes in Denmark sampled during summer to explore the influence of lake morphometry,
catchment conditions, light availability and nutrient input on lake metabolism. We found that (1) gross primary production
(GPP) and community respiration (R) decline with lake area, water depth and drainage ratio, and increase with algal biomass
(Chl), dissolved organic carbon (DOC) and total phosphorus (TP); (2) all lakes, especially small with less incident light,
and forest lakes with high DOC, have negative net ecosystem production (NEP < 0); (3) daily variability of GPP decreases with
lake area and water depth as a consequence of lower input of nutrients and organic matter per unit water volume; (4) the influence
of benthic processes on free water metabolic measures declines with increasing lake size; and (5) with increasing lake size,
lake metabolism decreases significantly per unit water volume, while depth integrated areal rates remain more constant due
to a combination of increased light and nutrient limitation. Overall, these meta-parameters have as many significant but usually
weaker relationships to whole-lake and benthic metabolism as have TP, Chl and DOC that are directly linked to photosynthesis
and respiration. Combining water depth and Chl to predict GPP, and water depth and DOC to predict R, lead to stronger multiple
regression models accounting for 57–63% of the variability of metabolism among the 25 lakes. It is therefore important to
consider differences in lake morphometry and catchment conditions when comparing metabolic responses of lakes to human impacts. 相似文献
19.
Variation characteristics of heavy metals and nutrients in the core sediments of Taihu Lake and their pollution history 总被引：1，自引：0，他引：1
The sedimentary environment change, trophic evolution and heavy metals pollution history of the northern Taihu Lake in the last 100 years are studied according to the sedimentary geochemical proxies of the core sediments, such as grain size, nutrients, heavy metals, diatom, etc. The nutrients in the sediments depended mainly on the lake internal circulation and the heavy metals were from natural geogenic sources before the 1920s, which were not influenced by human activities generally, and grain size was one of the key factors influencing heavy metals content in the sediments. The alternation of manner and strength of human activities in Taihu Lake catchment before and after the 1920s made the lake sediments coarser, and hence heavy metals and TP content decreased contrasted with that before the 1920s. TP content in sediments and water increased from the 1950s to late 1970s due to anthropogenic pollutants discharge, and the lake belonging to mesotrophic state. TN and TOC content and C/N ratio increased due to the increasing external pollutants into Taihu Lake by human activities, TP content also increased obviously in water and sediments, and the diatom association was dominated by eutrophic species since the late 1970s, indicating the eutrophication state of Taihu Lake in this period. Meanwhile the increasing in heavy metals content, such as Cu, Mn, Ni, Pb and Zn, and their proportion of valid fractions in the sediments indicates that they all result from human pollutants since the late 1970s. The heavy metals in the surface sediments have certain potential biological toxicity due to the higher SEM/AVS ratio. 相似文献
20.
The use of TN:TP and DIN:TP ratios as indicators for phytoplankton nutrient limitation in oligotrophic lakes affected by N deposition 总被引：1，自引：0，他引：1
Ann-Kristin Bergström 《Aquatic Sciences - Research Across Boundaries》2010,72(3):277-281
The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and
DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate
whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton.
Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes)
and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the
study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios
was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate
addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton.
Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating
P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes
with high to very high amounts of N deposition. 相似文献