岱海湖泊沉积物频率磁化率对历史时期环境变化的反映*

在探讨封闭湖泊沉积物频率磁化率的环境意义的基础上,根据岱海DH₃₂孔湖泊沉积物磁化率的测量结果,结合粒度、孢粉、历史资料和硅藻分析结果,对岱海历史时期的环境变化进行了探讨。研究认为:历史时期内陆封闭湖泊沉积物频率磁化率高值段指示气候偏湿阶段;低值段指示气候干旱阶段;DH₃₂孔湖泊沉积物频率磁化率反映的近300年来岱海气候变化可划分七个阶段,并与粒度、孢粉、硅藻和历史资料的分析结果基本一致。湖泊沉积物频率磁化率是恢复历史时期环境变化的重要环境指标之一。     

阳宗海硅藻群落对水体污染和水文调控的长期响应模式

在人类活动持续干扰的背景下,云南部分湖泊面临着污染物输入增加的环境压力,特别是营养盐富集和重金属污染。以云南地区遭受过严重工业污染的阳宗海为研究对象,通过沉积物硅藻群落、砷浓度、营养元素与稳定同位素、粒度等多指标分析,结合文献记录和湖泊调查结果,揭示了阳宗海硅藻群落对湖泊富营养化和砷污染的长期响应特征,并识别了不同时期的主要环境压力与其驱动强度。结果表明：长期的营养盐累积使得浮游硅藻逐渐占据优势地位,且耐污染的底栖硅藻种的快速增加与砷污染出现的时段一致。在阳宗海长期富营养化的背景下,当水体砷污染物浓度达到一定阈值水平后,硅藻群落结构的改变和多样性的降低都指示了湖泊生态系统发生了灾难性的转变。同时1965年开始的湖泊引水工程导致了贫营养种的突然增加。因此,水体富营养化、重金属污染与湖泊水文调控是导致阳宗海硅藻群落长期变化的主控因子,对阳宗海的生态修复与综合治理需要综合考虑不同胁迫因子的长期影响与驱动作用。     

阳宗海硅藻群落对水体污染和水文调控的长期响应模式北大核心CSCDCSSCI

在人类活动持续干扰的背景下,云南部分湖泊面临着污染物输入增加的环境压力,特别是营养盐富集和重金属污染。以云南地区遭受过严重工业污染的阳宗海为研究对象,通过沉积物硅藻群落、砷浓度、营养元素与稳定同位素、粒度等多指标分析,结合文献记录和湖泊调查结果,揭示了阳宗海硅藻群落对湖泊富营养化和砷污染的长期响应特征,并识别了不同时期的主要环境压力与其驱动强度。结果表明:长期的营养盐累积使得浮游硅藻逐渐占据优势地位,且耐污染的底栖硅藻种的快速增加与砷污染出现的时段一致。在阳宗海长期富营养化的背景下,当水体砷污染物浓度达到一定阈值水平后,硅藻群落结构的改变和多样性的降低都指示了湖泊生态系统发生了灾难性的转变。同时1965年开始的湖泊引水工程导致了贫营养种的突然增加。因此,水体富营养化、重金属污染与湖泊水文调控是导致阳宗海硅藻群落长期变化的主控因子,对阳宗海的生态修复与综合治理需要综合考虑不同胁迫因子的长期影响与驱动作用。     

沉积物记录的亚高山湖泊环境变化——以鄂东南云中湖为例

根据云中湖27 cm长沉积岩芯进行元素、粒度和硅藻多指标分析以及²¹⁰Pb测年,结合流域气候和人类活动等历史资料,反演1958年以来云中湖在气候变化和人类活动影响下的环境变化。冗余分析结果显示云中湖沉积硅藻组合变化与Al、Fe、Pb和温度四个变量显著相关。硅藻属种聚类分析的结果表明云中湖环境变化经历了两个阶段：1958-1993年间喜碱性水体的Achnanthes minutissima和Fragilaria nanana属种大量出现与较高CIA指数响应于气候调控下的流域侵蚀过程;1993年以来气候变暖与旅游发展引起入湖营养盐增加是Cyclotella pseudostelligera和Aulacoseira alpigena等中—富营养硅藻种增殖的主要诱因。重建亚高山湖泊在气候变化以及人类活动影响下湖泊生态系统的演化,为保护亚高山湖泊生态环境和改善流域水质提供参考。     

云南洱海流域人类活动的湖泊沉积记录分析

根据湖泊沉积记录的环境指标变化,对云南洱海地区人类活动的湖泊沉积响应进行了系统的讨论。洱海湖泊沉积物记录显示,湖泊沉积物磁化洱海流域土地利用方式变化特别是耕作农业的出现有显著响应;沉积物元素Ｆｅ、Ａｌ含量的变化也与流域人类活动影响下的地表水土流失有密切联系。沉积物色素的变化则指标湖泊富人为营养化的历史。湖泊沉积物磁化率、元素、色素指标的变化是不湖泊流域人类活动的有效指标并具有重要的科学考古学意义。     

松嫩平原湖泊水质演化研究

以松嫩平原湖泊为研究对象,2008年6～8月对27个湖泊水体总氮、总磷、高锰酸盐指数等指标进行了测试和分析。结果显示,松嫩平原湖泊水体高锰酸盐指数、总磷含量和总氮含量普遍较高。湖泊营养状态综合评价结果表明,27个湖泊中只有牛心套宝泡水体处于中营养状态,其营养状态指数为53.69,目前其他湖泊营养状态指数均高于54,都已呈富营养化状态。不同时期月亮泡、查干湖水质指标的对比显示,这两个湖泊水体的总磷含量和总氮含量都有所上升,富营养化程度加剧。     

乌鲁木齐东道海子剖面的硅藻记录与环境演变

通过分析乌鲁木齐河尾闾湖泊东道海子剖面的硅藻记录,结合孢粉、磁化率、烧失量和粒度分析资料,以^14C测年数据为基础,讨论了天山北麓古尔班通古特沙漠南部边缘的环境演变。研究认为：东道海子地区在4900aBP～3120aBP这一时段气候较稳定,3120aBP以来,有几次波动;湖泊的高湖面期与气候的冷期对应,湖泊的盐碱度较低,硅藻以及水生、沼生植物生长较繁盛;湖泊的中湖面期与气候的暖期对应,湖泊的盐碱度较高,硅藻以及水生、沼生植物生长较稀少。     

蒙古国北部Gun Nuur湖表层沉积物花粉分布特征

 蒙古国北部Gun Nuur湖20个表层沉积物孢粉组合与数量分析研究揭示,孢粉组合及浓度分布存在显著空间差异。结果表明：双束松型花粉百分含量由湖泊东南向西北降低,桦属、蒿属、藜科以及禾本科百分含量增加,湖泊东南侧赤松林是造成孢粉组合空间分异的主要原因。孢粉浓度分布与湖泊水深具有良好的对应关系,体现了湖水流对孢粉的二次搬运和富集作用。现代森林草原地带Gun Nuur湖表层孢粉组合中松属含量较高,具超代表性;受松属影响蒿属和藜科花粉含量较低,代表性较低。     

内蒙古嘎顺诺尔湖泊沉积物磁化率与粒度的古环境意义

湖泊沉积物磁化率和粒度已被广泛地应用于古环境和古气候研究,但在不同地区两者的关系不同,一般与磁性矿物来源、种类和赋存粒级有关。查明磁性矿物来源和赋存状态是利用粒度和磁化率恢复古环境的重要基础。通过测定干旱区嘎顺诺尔GXN剖面湖泊沉积物的磁化率与粒度及两者的相关关系,结合代表性样品的岩石磁学特征,揭示此类地区湖泊沉积物磁性矿物来源和赋存状态,探讨它们在干旱区湖泊沉积物中所反映的环境变化信息。结果显示,剖面下部（200~105 cm）和上部（36~0 cm）沉积物磁化率与粗砂含量呈正相关,中部（105~36 cm）与粉砂含量呈正相关,表明磁性矿物主要富集于粗颗粒和较粗颗粒组分中。剖面下部和中部沉积物以顺磁性矿物为主,含少量亚铁磁性矿物（如磁铁矿+磁赤铁矿）,含少量顺磁性矿物;剖面上部沉积物以亚铁磁性矿物为主（如磁赤铁矿+磁铁矿）,含少量顺磁性矿物。根据嘎顺诺尔晚全新世湖泊沉积物剖面的岩性、磁化率和粒度组合特征,可将其划分为河漫滩相沉积（200~105 cm）、浅湖相沉积（105~36 cm）和滨浅湖相沉积（36~0 cm）3个阶段。该湖粒度组分中<4 μm和4~64 μm颗粒主要反映了湖泊水动力的变化,受碎屑物来源和水动力条件的控制;而河漫滩相中>64 μm粗颗粒组分的峰值是风力作用的结果。河漫滩相及滨浅湖相的磁化率高值则指示了湖面较低,水动力较强,有较多的磁性矿物随粗颗粒入湖;浅湖相的磁化率低值则指示该时期湖面较高,水动力较弱,磁性矿物随入湖粗颗粒含量的减少而降低。     

内蒙古查干淖尔湖东湖水体富营养化特征及其影响因素

为了探究内蒙古查干淖尔湖东湖水体富营养化特征及影响因素,于2011年至2021年每年的2月10日、5月10日、8月10日和10月5日,对查干淖尔湖东湖水体水质指标进行监测,采用综合营养状态指数法,对查干淖尔湖东湖水体富营养化程度进行评价,采用冗余分析法,确定影响查干淖尔湖东湖水体富营养化的主要因素。研究结果表明,2011年至2021年查干淖尔湖东湖水体整体属于中度富营养化,水体中总氮质量浓度为0.14～5.81 mg/L,总磷质量浓度为0.15～0.80 mg/L,高锰酸盐指数为6.56～39.52 mg/L,叶绿素a质量浓度为0.63～7.66 mg/L;水体富营养化程度随季节变化明显,冬季查干淖尔湖东湖水体为重度富营养,夏季和秋季水体为中度富营养,春季水体为轻度富营养;气温和湖泊水量是影响查干淖尔湖东湖水体富营养化的主要因素。     

Diatom assemblage response to Iroquoian and Euro-Canadian eutrophication of Crawford Lake,Ontario, Canada

Diatom and geochemical data from Crawford Lake, Ontario, have been used to document limnological responses to periods of cultural disturbance resulting from native Iroquoian occupation of the watershed (1268–1486 AD) and Euro-Canadian agriculture and deforestation (1867 AD–present). Here, we further develop the high-resolution nature of the Crawford Lake sediment record to examine the physical, chemical and biological aspects of limnological response to human disturbances in the lake catchment area with exceptional detail. We report detailed diatom abundance and flux data for individual taxa from Crawford Lake, and further describe the relationship between assemblage composition and environmental conditions using canonical correspondence analysis (CCA). Diatom assemblage data are used to calculate diatom inferred-total phosphorus (DI-TP) concentrations for the past ∼1,000 years. We also examine the diatom community response during and after periods of disturbance by Iroquoian and Euro-Canadian populations, and compare this response to existing geochemical proxies of lake production and new elemental geochemical indicators of catchment area erosion. In particular, we explore the differing limnological response to the two distinct periods of cultural eutrophication and examine the limnological processes that occurred during the period of␣low (or no) human activity (1487–1866 AD), when geochemical indicators of lake production recovered to pre-disturbance conditions, but diatom assemblages notably did not. Our results illustrate the highly susceptible nature of diatom communities to periods of anthropogenic disturbance, and emphasize that ecological indicators (such as diatom assemblages) should be included with other proxies (such as nutrient concentrations and physical characteristics) when assessing disturbance and recovery in lake systems.     

Alternate trajectories in historic trophic change from two lakes in the same catchment, Huayang Basin, middle reach of Yangtze River, China

In order to assess how best to manage impacted lake systems, one needs to understand the trophic functioning of the lake system and the recent states through which the lake may have transitioned. Lakes in the middle and lower reaches of the Yangtze have been heavily impacted over recent decades. In order to understand recent changes in functional status, we examined sediment cores covering the last 120?years from two lakes in the same catchment with differing status: one algal-dominated (Taibai Lake) and the other macrophyte-dominated (Longgan Lake). Chironomid head capsules were identified from both sites and an expanded chironomid-total phosphorus (TP) transfer function (21 sites were added to the 30-lake model previously developed by Zhang et al. 2006) was used to assess the lakes?? response to recent anthropogenic change. Quantitative chironomid-inferred TP (CI-TP) reconstructions showed that Taibai Lake experienced clear changes in trophic status since the 1860s. Before the 1950s, the CI-TP concentration was relatively stable around 50?C80???g?L^?1, while it reached to 80?C130???g?L^?1 in the latter period. CI-TP for Longgan Lake, however, showed a relative decline from the range of 50?C75???g?L^?1 since the 1880s to 30?C40???g?L^?1 in recent years, accompanied by strong evidence from the chironomids for increased macrophyte biomass as TP levels declined. Both reconstructions agreed with diatom inferences of TP from the same lakes. The stark difference between these two sites is thought to reflect a function of macrophyte development, with Taibai Lake losing its plants through increased nutrient levels and internal recycling, whereas Longgan Lake, which is much bigger in area and hence potentially more resilient to change, was able to develop macrophyte communities over the same time period. The positive feedbacks associated with abundant macrophytes retained the clear water state of Longgan Lake, but a further increase in nutrients might lead to decrease in resilience of the relatively stable macrophyte state and loss of benthic pathways of primary production, which would push the lake towards eutrophication. Unless nutrient inputs to Longgan are controlled, Longgan Lake might lose macrophyte communities and follow a developmental pathway similar to that observed in Taibai Lake.     

长江中游网湖近代沉积环境演变及其对人类活动的响应

采用放射性核素²¹⁰Pb和¹³⁷Cs计年方法,建立了长江中游网湖近代沉积物的年代序列,并对网湖沉积物的粒度组成、磁性参数、重金属元素、花粉组合以及营养盐含量等指标进行了分析。根据沉积指标垂直分布的综合特征,结合湖区史料,重建了网湖100年来沉积环境的演变过程。通过对沉积指标与湖区人口变化、工农业产值等数据的比对,发现中华人民共和国成立以后沉积物中TOC和TN浓度与人口变化存在较高的相关性,相关系数分别达到0.8892和0.8928(P<0.001);沉积物中重金属元素富集序列、营养盐富集序列与孢粉含量的变化序列与湖区人类活动具有较好的耦合性。表明网湖沉积指标可以敏感地反映湖区的人类活动。     

Paleohydrology of Lake Nhaucati (southern Mozambique), ∼400 AD to present

This paper investigates the correlations between lake level change, rainfall variability and general atmospheric forcing in southern Africa. The analysis of fossil diatom assemblages in a sediment sequence from the small, rain-fed Lake Nhaucati, southern Mozambique, is presented and discussed in relation to regional palaeoclimate data. The accumulation of organic sediments in Lake Nhaucati began 1,600 years ago when the lake level was rising. Lithology and pollen suggest a low stand at 800 AD, which correlates with other climate proxies from the summer rainfall region of southern Africa. The diatom assemblage suggests that lake levels were high between 900 and 1300 AD, with shorter low stands at c.1100 and 1200 AD. The period after 1400 AD was marked by a slow rate of accumulation and consequently a low temporal resolution. The correlation with other climate proxies in the summer rainfall region, written sources, and pollen data suggests repeated droughts corresponding to the Little Ice Age, though the driest periods may have caused complete desiccation of the lake. Higher lake levels are suggested after 1800 AD, though written sources suggest droughts in the beginning of the twentieth century. The analysis shows a good correlation with palaeoclimate data from the summer rainfall region and confirms the presence of an anti-phase relationship between the summer rainfall region of southern Africa and the bi-modal rainfall region of east tropical Africa. It also supports the general hypothesis that variation in the intensity of the Inter Tropical Convergence Zone is the main agent modulating rainfall over southern and eastern Africa on centennial timescales.     

Natural and anthropogenic forcing of Holocene lake ecosystem development at Lake Uddelermeer (The Netherlands)

Lake Uddelermeer (The Netherlands) is characterized by turbid conditions and annual blooms of toxic cyanobacteria, which are supposed to be the result of increased agricultural activity in the twentieth century AD. We applied a combination of classic palaeoecological proxies and novel geochemical proxies to the Holocene sediment record of Lake Uddelermeer (The Netherlands) in order to reconstruct the natural variability of the lake ecosystem and to identify the drivers of the change to the turbid conditions that currently characterize this lake. We show that the lake ecosystem was characterized by a mix of aquatic macrophytes and abundant phytoplankton between 11,500 and 6000 cal year BP. A transition to a lake ecosystem with clear-water conditions and relatively high abundances of ‘isoetids’ coincides with the first signs of human impact on the landscape around Lake Uddelermeer during the Early Neolithic (ca. 6000 cal year BP). An abrupt and dramatic ecosystem shift can be seen at ca. 1030 cal year BP when increases in the abundance of algal microfossils and concentrations of sedimentary pigments indicate a transition to a turbid phytoplankton-dominated state. Finally, a strong increase in concentrations of plant and faecal biomarkers is observed around 1950 AD. Canonical Correspondence Analysis suggests that reconstructed lake ecosystem changes are best explained by environmental drivers that show long-term gradual changes (sediment age, water depth). These combined results document the long-term anthropogenic impact on the ecosystem of Lake Uddelermeer and provide evidence for pre-Industrial Era signs of eutrophication.     

Tracking eutrophication in Taihu Lake using the diatom record: potential and problems

Taihu Lake is the third largest freshwater lake in China and has been experiencing eutrophication problems for several decades. Diatoms in short sediment cores from three bays in northern Taihu Lake were studied in addition to 1-year of seasonal phytoplankton samples in order to evaluate the rate and magnitude of nutrient enrichment. The dominant species found in the phytoplankton samples appeared in high percentages in the surface sediment samples, suggesting that the latter faithfully record the modern diatom flora. The diatom preservation status varied among the three cores, while in all cores the preservation deteriorated with sediment depth. Due to the superior diatom preservation in the core from Mashan Bay, the fossil diatom record of this core and an established diatom total phosphorus (TP) transfer function were used to reconstruct the nutrient history of Taihu Lake. Diatom assemblages changed from Aulacoseira-dominated to other eutrophic planktonic species, such as Stephanodiscus minutulus, Cyclostephanos tholiformis, Cyclotella atomus, C. meneghiniana and S. hantzschii in ca. 1980. Diatom-inferred TP concentrations exhibited little change prior to 1980, with values around 50 μg/l. However, after 1980 TP concentrations increased significantly and remained in excess of 100 μg/l, reflecting eutrophication of Taihu Lake. Comparison with TP measurements in the water column from 1988 to 2004, as well as the analogue analysis among fossil and modern samples, demonstrates that the diatom-TP inference model can reliably hindcast past TP concentrations. Therefore, the baseline TP value of about 50 μg/l, can be used as a restoration target for Taihu Lake. However, due to the complexity of this very large, shallow aquatic ecosystem, caution should be exercised when employing the diatom record to track eutrophication. Further studies on the mechanism of diatom distribution, evolution and preservation are recommended for Taihu Lake.     

Natural and anthropogenic aquatic environmental changes reconstructed by paleolimnological analyses in Lake Kitaura,central Japan

In order to assess the recent anthropogenic environmental changes in Lake Kitaura, central Japan, changes during the past few centuries were reconstructed from results of radiometric and tephrochlonological age determination, magnetic susceptibility measurements, total organic carbon analyses, total nitrogen analyses and fossil diatom analyses on a sediment core from the lake. A total of six major and sub-zones are recognized according to the diatom fossil assemblages, and we discuss aquatic environmental change in Lake Kitaura mainly based on these diatom assemblage change. Zone Ia and Zone Ib (older than AD 1707) are marine to brackish. In Zone IIa (AD␣1707–AD 1836), most of the brackish diatoms disappeared, and were replaced by freshwater species indicating a decrease in salinity. We interpret the salinity decrease in Zone I–IIa as a sea-level fall during the Little Ice Age. The salinity of the lake decreased to near freshwater conditions in Zone IIb (AD 1836–AD 1970), which could arise from alteration in River Tone or development of a sandspit in the mouth of River Tone in addition to sea-level change. In Zone IIIa (AD 1970–AD 1987), the diatom assemblage indicates a freshwater environment, and sedimentation rates increase rapidly. These changes reflect sedimentary environment change and an ecosystem transition due to the construction of the tide gate. In Zone IIIb (AD 1987–AD 2002), the diatom flux (valves cm⁻² y⁻¹) increased and species composition changed. The changes in Zone IIIb show a good agreement with limnological monitoring data gathered from the lake. These paleolimnological data suggest that the recent human-induced changes of the aquatic environment of the lake after the 1970s exceed rates during the period concerned in this study.     

基于滇池水生态系统演替的富营养化控制策略

自20世纪80年代以来,滇池开始爆发大规模蓝藻水华。滇池治理一直以提高水质为主要目标,以污染控制为主要手段。近10年来,滇池水质虽呈现明显好转趋势,但长期实施的污染控制工程并未有效抑制蓝藻水华爆发。通过浅析滇池富营养化特征,分析当前治理思路和方法中存在的不足,并结合生态系统稳态转换理论和一些国内外富营养湖泊治理经验,认为滇池具备在较高营养盐浓度(V类水质)下恢复清水草型生态系统的可能性,提出滇池治理可以适当降低对水质的要求,在污染物控制的基础上辅以生态修复措施的治理思路,最终实现滇池生态系统由浊水-藻型向清水-草型演替。     

Effects of spring warming and mixing duration on diatom deposition in deep Tiefer See,NE Germany

Monitoring during three meteorologically different spring seasons in 2012, 2013, and 2014 revealed that temperature increase in spring, which influences spring lake mixing duration, markedly affected nutrient availability and diatom deposition in a sediment trap close to the bottom of deep Tiefer See, NE Germany. Deposition of Stephanodiscus taxa and small Cyclotella taxa was much higher after late ice out and a deep, short lake mixing period in spring 2013, compared to that after gradual warming and lengthy lake mixing periods in spring 2012 and 2014, when only brief or marginal ice cover occurred. Availability of dissolved Si and P was 33 and 20 % higher, respectively, in 2013 compared to 2014. The observed relation between high (low) diatom deposition and short (lengthy) mixing duration in spring was applied to varved sediments deposited between AD 1924 and 2008. Low detrital Si content in trapped material and a sediment core enabled use of µXRF-counts of Si as a proxy for diatom silica. The spring mixing duration for 1951–2008 was derived from FLake-model calculations. The spring warming duration related to lake mixing was approximated from air temperatures for 1924–2008 using the dates when daily mean air temperature exceeded 5 °C (start) and 10 °C (end). Diatom silica deposition showed a significant (p < 0.0001) inverse linear relationship with the modeled spring mixing duration (R² = 0.36) and the spring warming duration (R² = 0.28). In both cases, the relationship is strengthened when data from the period of low diatom production (1987–2005) is excluded (R² = 0.59 and R² = 0.35). Part of this low diatom production is related to external nutrient supply that favored growth of cyanobacteria at the expense of diatoms. This approach shows that diatom Si deposition was strongly influenced by the availability of light and nutrients, related to the duration of lake mixing and warming in spring, during most of the studied period. The remaining unexplained variability, however, indicates that additional factors influence Si deposition. Further tests in other deep, temperate lakes are necessary to verify if this relation is a common feature and consequently, if diatom Si can be used as a proxy for spring mixing duration in such lakes.