Lead Contamination Adjacent to Roadways in Trujillo,Venezuela

This study analyzes the extent and pattern of lead contamination along roadways in Trujillo, Venezuela, using traffic counts and soil samples collected in the field. The normalized mean lead level for frontyard samples along major traffic arteries was 200 μgg ^-1 versus 0 μgg^-1 for backyard samples. Furthermore 55%of the frontyard lead levels were hazardous, versus 7% of the backyard samples. This suggests a strong relationship between traffic and soil lead content. However, a relationship between lead level spatial patterns and traffic volume patterns was not established, suggesting that factors beyond traffic volume, such as slope and erosion, play a significant role in contamination patterns.     

中国公路交通的重金属排放及其对土地污染的初步估算

本文研究了全国各省市机动车Pb、Cu、Zn、Cd排放总量和公路两侧土壤中Pb含量的分布及其面积。结果表明,东部发达省份机动车的重金属排放量较西部地区大。使用含铅汽油的1990~1996年期间,北京市公路两侧土壤中Pb的年输入量为2.48~3.17 mg/ (kg · a)、累积量为11.4 mg/kg;1997~2003年使用无铅汽油后,两者分别下降到0.26~0.29 mg/(kg · a)和1.30 mg/kg。公路两侧的土壤中Pb含量随垂直距离的外延呈指数形式下降。公路交通对道路两侧土壤产生严重和轻度Pb污染的范围分别为距公路0~10 m和10~65 m。2003年北京市和全国受公路交通Pb污染的土地面积为2310 km²和28900 km²。公路交通的重金属排放是导致我国土地污染的重要原因之一。     

金华市街道灰尘磁化率与交通因素的关系

通过对浙江省金华市街道灰尘磁化率测试,从主干道与非主干道磁化率的对比、十字路口与非十字路口磁化率的比较以及磁化率与路网密度相关分析三个方面,定量研究金华市街道灰尘磁化率及其与交通因素的关系。结果表明：灰尘样品磁化率（χlf）变幅为127.57×10^-8~853.91×10^-8 m³ · kg^-1,平均值为322.55×10^-8 m³ · kg^-1,高于本地土壤磁化率;频率磁化率变幅为0.67%~3.99%,平均值为1.61%;磁化率与频率磁化率呈负相关关系;主干道灰尘的磁化率大于非主干道,十字路口灰尘磁化率大于非十字路口;灰尘磁化率和路网密度呈正相关,金华市街道灰尘磁化率可以指示交通污染的分布状况。     

中国东部南北样带森林生态系统WUE和NUE空间格局及驱动因子(英文)

From July 2008 to August 2008, 72 leaf samples from 22 species and 81 soil samples in the nine natural forest ecosystems were collected, from north to south along the North-South Transect of Eastern China (NSTEC). Based on these samples, we studied the geographical distribution patterns of vegetable water use efficiency (WUE) and nitrogen use efficiency (NUE), and analyzed their relationship with environmental factors. The vegetable WUE and NUE were calculated through the measurement of foliar δ 13C and C/N of predominant species, respectively. The results showed: (1) vegetable WUE, ranging from 2.13 to 28.67 mg C g-1 H2O, increased linearly from south to north in the representative forest ecosystems along the NSTEC, while vegetable NUE showed an opposite trend, increasing from north to south, ranging from 12.92 to 29.60 g C g-1 N. (2) Vegetable WUE and NUE were dominantly driven by climate and significantly affected by soil nutrient factors. Based on multiple stepwise regression analysis, mean annual temperature, soil phosphorus concentration, and soil nitrogen concentration were responding for 75.5% of the variations of WUE (p<0.001). While, mean annual precipitation and soil phosphorus concentration could explain 65.7% of the change in vegetable NUE (p<0.001). Moreover, vegetable WUE and NUE would also be seriously influenced by atmospheric nitrogen deposition in nitrogen saturated ecosystems. (3) There was a significant trade-off relationship between vegetable WUE and NUE in the typical forest ecosystems along the NSTEC (p<0.001), indicating a balanced strategy for vegetation in resource utilization in natural forest ecosystems along the NSTEC. This study suggests that global change would impact the resource use efficiency of forest ecosystems. However, vegetation could adapt to those changes by increasing the use efficiency of shortage resource while decreasing the relatively ample one. But extreme impacts, such as heavy nitrogen deposition, would break this trade-off mechanism and give a dramatic disturbance to the ecosystem biogeochemical cycle.     

鲁西北平原夏玉米产量与土壤硝态氮淋失

供水量和氮肥施用量是影响农田硝态氮淋失的主要因素。本文通过田间小区试验,研究了水分和氮肥用量对夏玉米产量和土壤硝态氮的影响。试验表明,高水处理（0～50cm平均含水量控制在85%FC,FC为田间持水量032）和低水处理（0～50cm平均含水量控制在70%FC）间产量差异不显著,施肥量（0、100、200、和300kgNha^-1）则具有显著影响,并且在200kgNha^-1左右时达到最高产量;高水条件下土壤水分硝态氮下渗强,运移深度大,所有施肥处理在200cm处的土壤水硝态氮浓度都要高于国家饮用地下水标准10mgNL-1;低水条件下水分下渗弱,运移深度小于高水处理,但是在200cm处,200、300kgNha^-1处理的土壤溶液硝态氮浓度依然高于10mgNL^-1。     

Benthic diatom communities as indicators of anthropogenic metal contamination at Casey Station,Antarctica

Prior to environmental legislation in the 1980s, anthropogenic waste in Antarctica was often deposited into landfill sites or into the sea. This resulted in metal contamination in terrestrial and near-shore marine environments. In this study, we assess the feasibility of using both past and present diatom assemblages to reconstruct and monitor past and future metal contamination. Our dataset included the analyses of both surface sediment samples and sediment cores from a contaminated site near Casey Station, Antarctica. Redundancy analyses indicated a strong relationship between metal concentrations and the composition of diatom communities. Within the surface sediment samples, tin and lead individually explained 43% of the variation observed in the diatom data; copper and iron explained 42% of this variation. In the sediment cores, tin and lead individually explained 53% of the variation in diatom community composition. In the same samples copper explained 47% of this variation, with iron explaining 46% of the observed variation. Once one metal had been selected, incorporating further metal data into the analyses added little extra information. Modern analog technique (MAT) analyses showed a strong correlation between actual and predicted values within one dataset (R²: Cu 0.75; Pb 0.86; Sn 0.89; p<0.05 for each). MAT reconstructions of metal concentrations closely followed measured concentrations, with both high and low concentrations recorded. MAT analyses performed favorably when compared to predictive techniques based on multivariate linear regression and multilayer perceptron neural networks. This study demonstrates that the composition of benthic diatom communities is a good indicator of anthropogenic metal contamination, and may be useful in monitoring the success of environmental remediation strategies in Antarctica and elsewhere.     

盐碱荒地开垦年限对表层土壤盐分的影响

 以典型荒漠区原生盐碱荒地及开垦农田为研究对象,通过对比研究,以阐明原生盐碱荒地开垦后不同管理措施下土壤可溶盐总量的变化规律,开垦后土壤剖面中可溶盐总量的垂直分布和季节变化规律。结果表明：开垦显著降低了0～50 cm土壤的可溶性盐含量,开垦达100 a以上老耕地的可溶性盐含量（2.31 g/kg）仅为原生盐碱荒地（26.62 g/kg）的11%;长期的耕作改变了土壤可溶性盐分在土层中的分布,原生荒漠土壤盐分具有鲜明的表聚特征,0～30 cm土层的盐分含量占整个土壤剖面的79%,开垦50 a后,土壤中的盐分分布趋于均匀,各离子浓度的垂直分布不再明显;开垦使土壤中的盐分离子组成也发生了变化,Cl^-、K⁺、Na⁺离子浓度降低,而SO₄^2-、Mg²⁺、Ca²⁺离子浓度增加,耕作层土壤由SO₄^-2-Cl^-1盐土转变为Cl^-1-SO₄^-2盐土;盐碱荒地土壤可溶盐浓度伴随着降水变化具有显著的季节变化特征,而季节对开垦耕地没有显著影响。总体而言,盐碱荒地经过多年开垦利用后,土壤可溶性盐分和pH值均显著降低。     

干旱沙区典型人工植被群落下土壤剖面CO_2浓度变化特征及其驱动因子

对人工固沙植被区柠条(Caragana korshinskii)群落和油蒿(Caragana korshinskii)群落下不同深度的土壤气体采样,主要研究和讨论了不同类型人工植被区下土壤CO2浓度的变化特征及土壤温度和土壤水分对其的影响。结果表明:柠条和油蒿群落0~80cm处的土壤空气CO2浓度随着土壤深度的增加而增加,并且在0~40cm,油蒿群落下的土壤CO2浓度值大于柠条,而在40cm以下则相反。其平均值分别为1 229.3μmol·mol-1和1 242.7μmol·mol-1,大于同一深度流沙下土壤CO2浓度值978.9μmol·mol-1。土壤水分与二者的土壤CO2浓度变化趋势在年际尺度上具有一致性,浅层40cm内油蒿群落下的土壤CO2浓度和土壤水分含量的相关性明显大于柠条和流沙。而在40cm以下,则表现为柠条油蒿流沙。土壤温度对土壤CO2浓度的影响程度一般为流沙油蒿柠条,特别是流沙,在表层达到了极显著的水平,之后随着土壤深度的增加而降低。而土壤温度对油蒿和柠条样地土壤CO2浓度的影响较为复杂,呈现出先增加后减小的趋势。在年际尺度上,土壤水分含量是不同植被群落下土壤剖面CO2浓度的关键限制因子,而在日尺度上,土壤温度则为主要限制因子。据粗略估计,在0~80cm内,柠条和油蒿根系呼吸所占的比例约为30.7%和33.3%。     

Latitudinal variation of leaf morphological traits from species to communities along a forest transect in eastern China

Comprehensive information on geographic patterns of leaf morphological traits in Chinese forests is still scarce. To explore the spatial patterns of leaf traits, we investigated leaf area (LA), leaf thickness (LT), specific leaf area (SLA), and leaf dry matter content (LDMC) across 847 species from nine typical forests along the North-South Transect of Eastern China (NSTEC) between July and August 2013, and also calculated the community weighted means (CWM) of leaf traits by determining the relative dominance of each species. Our results showed that, for all species, the means (± SE) of LA, LT, SLA, and LDMC were 2860.01 ± 135.37 mm², 0.17 ± 0.003 mm, 20.15 ± 0.43 m² kg^–1, and 316.73 ± 3.81 mg g^–1, respectively. Furthermore, latitudinal variation in leaf traits differed at the species and community levels. Generally, at the species level, SLA increased and LDMC decreased as latitude increased, whereas no clear latitudinal trends among LA or LT were found, which could be the result of shifts in plant functional types. When scaling up to the community level, more significant spatial patterns of leaf traits were observed (R ² = 0.46–0.71), driven by climate and soil N content. These results provided synthetic data compilation and analyses to better parameterize complex ecological models in the future, and emphasized the importance of scaling-up when studying the biogeographic patterns of plant traits.     

Exploring spatially varying and scale-dependent relationships between soil contamination and landscape patterns using geographically weighted regression

Landscape pattern is an important determinant of soil contamination at multiple scales, and a proper understanding of their relationship is essential for alleviating soil contamination and making decisions for land planners. Both soil contamination and landscape patterns are heterogeneous across spaces and scale-dependent, but most studies were carried out on a single scale and used the conventional multivariate analyses (e.g. correlation analysis, ordinary least squared regression-OLS) that ignored the issue of spatial autocorrelation. To move forward, this paper examined spatially varying relationships between agricultural soil trace metal contamination and landscape patterns at three block scales (i.e. 5 km × 5  km, 10 km × 10 km, 15 km × 15 km) in the Pearl River Delta (PRD), south China, using geographically weighted regression (GWR). This paper found that GWR performed better than OLS in terms of increasing R square of the model, lowering Akaike Information Criterion values and reducing spatial autocorrelation. GWR results revealed great spatial variations in the relationships across scales, with an increasing explanatory power of the model from small to large block scales. Despite a few negative correlations, more positive correlations were found between soil contamination and different aspects of landscape patterns of water, urban land and the whole landscape (i.e. the proportion, mean patch area, the degree of landscape fragmentation, landscape-level structural complexity, aggregation/connectivity, road density and river density). Similarly, more negative correlations were found between soil contamination and landscape patterns of forest and the distance to the river and industry land (p < 0.05). Furthermore, most significant correlations between soil contamination and landscape variables occurred in the western PRD across scales, which could be explained by the prevailing wind, the distribution of pollutant sources and the pathway of trace metal inputs.     

Water content and land use history controlling soil CO2 respiration and carbon stock in savanna soil and groundnut fields in semi-arid Senegal

Decomposition of soil organic carbon (SOC) regulates the partitioning between soil C-stock and release of CO₂ to the atmosphere and is vital for soil fertility. Agricultural expansion followed by decreasing amounts of SOC and soil fertility is a problem mainly seen in tropical agro-ecosystems where fertilizers are in short supply. This paper focuses on factors influencing temporal trends in soil respiration measured as CO₂ effluxes in grass savanna compared with groundnut (Arachis hypogaea L.) fields in the semi-arid part of Senegal in West Africa. Based on laboratory experiments, soil CO₂ production has been expressed as a function of temperature and soil water content by fit equations. Field measurements included soil CO₂ effluxes, soil temperatures and water contents. Effluxes in grass savanna and groundnut fields during the dry season were negligible, while effluxes during the rainy season were about 3–8 μmol CO₂ m^?2 s^?1, decreasing to less than 1 μmol by the end of the growing season. Annual soil CO₂ production was simulated to be in the range of 31–38 mol C m^?2. Furthermore, a controlled water addition experiment revealed the importance of rain during the dry season for the overall turnover of soil organic matter.     

Soil sodium and potassium adsorption ratio along a Mediterranean–arid transect

Changes in the relationship between soil soluble ions and rainfall were studied on hillslopes at seven research sites that represent four climatic regions: Mediterranean, semi-arid, mildly arid and arid. At each site, soil samples were taken in several seasons and the ratio between the Na⁺ plus K⁺ content and the Ca²⁺ plus Mg²⁺ content (sodium and potassium adsorption RATIO=SPAR) was determined. In general, SPAR increased with increasing aridity except for the most arid site in which the soil contains a gypsic layer. The relationship between SPAR and rainfall was non-linear. An abiotic threshold, characterized by a sharp change in the SPAR, was found around the 200 mm isohyet: sites that receive less than 200 mm annual rainfall showed significantly higher SPAR than those that receive more than 200 mm, where SPAR was very low.     

Vegetation development and carbon storage on a glacier foreland in the High Arctic, Ny-Ålesund, Svalbard

The distribution of organic carbon and its relationship to vegetation development were examined on a glacier foreland near Ny-Ålesund, Svalbard (79°N). In a 0.72-km² area, we established 43 study plots on three line transects along primary succession from recently deglaciated area to old well-vegetated area. At each plot, we measured the type and percent coverage of vegetation types. The organic carbon content of vegetation, organic soil, and mineral soil samples was determined based on their organic carbon concentration and bulk density. Cluster analysis based on vegetation coverage revealed five types of ground surfaces representing variations in the amounts and allocation patterns of organic carbon. In the later stages of succession, 7%–24% and 31%–40% of organic carbon was contained in the organic and deeper soil layers, respectively. Organic carbon storage in the later stages of succession ranged from 1.1 – 7.9 kg C m⁻². A larger amount of organic carbon, including ancient carbon in a raised beach deposit, was expected to be contained in much deeper soil layers. These results suggest that both vegetation development and geological history affect ecosystem carbon storage and that a non-negligible amount of organic carbon is distributed in this High Arctic glacier foreland.     

Isotope composition and anion chemistry of soil profiles along the Kalahari Transect

Savannas cover about 20% of the Earth's land area across a wide range of climatic conditions. As an important and distinct biome, savannas produce approximately 29% of global terrestrial net primary productivity. In these ecosystems the distribution of belowground resources remains poorly investigated and the relationship to the climatic conditions remains unclear. In the present study, vertical profiles of soil nutrients (chloride, nitrate, phosphate and sulfate) and nitrogen stable isotopes were analyzed at four sites along the Kalahari mega-transect, where a distinct rainfall gradient exists on a homogeneous soil substrate. The results show clear differences in nutrients and δ¹⁵N vertical distributions between wet and dry seasons. The results also show how the formation of “fertility islands” (i.e., the concentration of soil nutrients in the soils beneath tree canopies) is not necessarily coupled with belowground processes in that the distribution of soil nutrients at the surface does not match belowground patterns. The results also indicate that phosphorus may be a limiting nutrient in these savanna ecosystems with seasonal dynamics in its cycling.     

Sources and transport of organic carbon from the Dongjiang River to the Humen outlet ofthe Pearl River,southern China简

Transport of organic carbon via rivers to estuary is a significant geochemical proc- ess in the global carbon cycle. This paper presents bulk total organic carbon （TOC） from the Dongjiang catchment to the adjacent Humen outlet, and discusses the applicability of 613C and ratio of carbon to nitrogen （C/N） as indicators for sources of organic matter in the surface sediments. Survey results showed that organic carbon concentration in summer were higher than in the winter. An elevated trend of TOC occurred along the river to the Humen outlet in both surveys, and the highest mean values of dissolved and particular organic carbon （DOC-279 μmol L-1 and POC-163μmol L-1） were observed in the urban deltaic region in summer flood flow. Winter samples had a wide range of b＇13C and C/N （5-3C -24.6%o to -30.0%o, C/N 4-13）, and summer ones varied slightly （8-3C -24.2%o to -27.6%0, C/N 6-18）. As results suggest that POC in the three zones of upstream-delta-outlet dominantly came from riverbank soil, phytoplankton and agricultural C3 plants in winter, whereas main sources were from the riverbank and mangrove soil in summer. Moreover, anthropogenic sewage inputs had 11% and 7% contribution to POC in the deltaic and outlet. Transport accompanied with seasonal freshwater variation, phytoplankton production and degradation, and removal be- havior caused variation of organic carbon concentration. The results also discovered that TOC export bulk in Dongjiang was approximately one quarter of Humen flux in the dry flow, and anthropogenic activity significantly impacted the river export contribution.     

Organochlorine pesticide and metal residues in a cichlid fish, Tilapia, Sarotherodon (=Tilapia) alcalicus grahami Boulenger from Lake Nakuru, Kenya

29 specimens of a cichlid fishSarotherodon (=Tilapia) alcalicus grahami were collected from Lake Nakuru between September and October 1990 and samples of liver, kidney, muscle, brain and fat were removed for analysis of organochlorine pesticide and metal residues. Fat was extracted and the concentration of three lindane (BHC/HCH) isomers (alpha, beta andgamma), aldrin, heptachlor, heptachlor-epoxide, endrin, dieldrin, DDD, DDE and DDT was determined. Fish muscle samples were digested and the concentration of mercury, arsenic and cadmium was also determined. No residues of o,p¹-DDD, p,p¹-DDD, aldrin, endrin and dieldrin were detected. The highest residue concentration detected was 0.062 mg kg⁻¹ of p,p¹-DDT. The mean pesticide residue concentration levels were generally low. The [p,p¹-DDT]/[p,p¹-DDE] ratio of 1.22 indicated that the residues of the parent DDT compound exist in the Lake Nakuru ecosystem. There was a negative fish length: DDE concentration relationship. Similarly, there was a very weak negative relationship between arsenic concentration and length of fish. The concentrations of metal residues were considerably low. The median arsenic and cadmium concentrations were 0.03 mg kg⁻¹ and <0.1 mg kg⁻¹, respectively. The concentrations of mercury, with a median level of <0.01 mg kg⁻¹, were particulary low and did not approach a level that would give rise to public health concern. Metal and pesticide residue concentration in fish in 1970 and 1990 does not show a significant increase. From these results, Lake Nakuru is presently not exposed to heavy pesticide and metal contamination, but there is a gradual build-up of these residues in the biota.     

孑遗植物四合木(Tetraena mongolica)异地保护条件下的气候生物学特征与光合效率

为了廓清异地保护条件下孑遗濒危植物四合木(Tetraena mongolica)的气候生物学特征、光合生理生态适应性及生境适宜性,应用1971—2011年的地面气象资料进行了不同试验区的气候生物图解与分析,测定了四合木及其伴生种白刺(Nitraria tangutorum)的叶片气体交换参数及光合效率。结果表明:①四合木自然分布区(内蒙古乌海地区)与异地保护区的气候生物学特征存在明显分异;②当年种植的四合木实生苗的生长量大小依次为:乌海四合木核心区实生苗鄂尔多斯实生苗阿拉善实生苗;③自然条件下,5个处理的净光合速率(Pn)依次为阿拉善移植的四合木成株(24.05±1.68μmol·m-2·s-1)乌海客土栽培的四合木(19.97±1.05μmol·m-2·s-1)乌海栽培的四合木实生苗(18.96±1.04μmol·m-2·s-1)鄂尔多斯栽培的四合木实生苗(16.64±0.92μmol·m-2·s-1)阿拉善栽培的四合木实生苗(16.48±0.13μmol·m-2·s-1);异地保护试验区栽培的四合木实生苗的Pn没有明显差异(p≥0.05),即原生境条件下栽培的四合木实生苗的Pn较高。同时,异地保护栽培四合木实生苗中,鄂尔多斯栽培的四合木实生苗的Pn阿拉善栽培的四合木实生苗。从四合木光合作用特征中的Pn、蒸腾速率、气孔导度和胞间CO2浓度、气候生物学特征和生长量等综合研究结果可以推断,从原生境区东移的实生苗迁地保护,使四合木具有更高的生理生态适宜性和环境适应性。     

邻避或迎臂效应：东莞豪华酒店与社区的互动关系

“酒店—社区”是一个不同行动者进行角力的场所。本文采用参与式观察和深度访谈方法,援引邻避效应与迎臂效应的相关理论,试图探究东莞豪华酒店与社区的景观模式及其互动关系。研究发现：① 权力与资本逻辑推动着“酒店—社区”景观的建构。东莞豪华酒店特有的迎臂因子形成了酒店与社区互动的四种景观类型：“酒店+房地产”型、“酒店+村庄”型、“酒店+镇中心”型、“酒店+政府”型。② 酒店黄色产业的存在是“迎臂”或“邻避”矛盾的焦点。豪华酒店所衍生的“精神垃圾——黄色文化”成为邻避的主要因子,促使社区居民进行非暴力反抗,然而,地方情感与现代性促使社区居民在反抗与选择性消费中和“精神垃圾”共存,豪华酒店成为社区居民的一种日常生活方式。③ 居民的生活实践、记忆与想象共同强化了社区的豪华酒店情结。迎臂效应最终战胜邻避效应,形成“请到我家后院来”的社区与酒店共存画面。研究丰富了邻避与迎臂效应的理论,在社会、生态和心理维度上补充了邻避效应的文化维度——“精神垃圾”,同时提出迎臂效应的物质维度——“酒店房地产”和心理维度——“地方情感和主体想象”,并且指出邻避与迎臂效应并非矛盾对立的存在,其影响因素的抗衡会促使“邻避效应”与“迎臂效应”在特定的时空相互转化。     

Diatom taxonomic and morphological changes as indicators of metal pollution and recovery in Lac Dufault (Québec, Canada)

We studied diatom taxonomic composition and the presence of morphological alterations (size and deformations) along a sediment core collected in Lac Dufault, Abitibi, whose watershed has a long history of mining pollution presently undergoing mitigation. According to sediment dating with ²¹⁰Pb and metal profiles along the core, we could identify four periods in the contamination history of the lake, which were characterized by different diatoms. Tabellaria flocculosa was dominant in the pre-mining period but was drastically reduced at the onset of pollution when Fragilaria cf. tenera became important. This diatom, together with other Fragilaria species and cysts of Chaetoceros muelleri, typified the transition period in which Cu reached its maximum value and other metals started to increase. During the period of maximum contamination with Zn, Cd, and Fe accompanied by acid mine drainage, Achnanthes minutissima and Brachysira vitrea were dominant. These taxa started to wane in the most recent sediments representing a partial chemical recovery. Asterionella formosa, which almost vanished at mining onset, reappeared with high abundance in these superficial sections. Beside these taxonomical shifts, we observed during the contamination period significant reduction in valve length together with increased percentages of valve deformations. Because available data on water chemistry and a diatom-based pH reconstruction suggest that Lac Dufault escaped severe acidification, diatom patterns observed in the core can be mostly ascribed to metal contamination. Individual diatom abundance and valve length had strong statistical relationships with the different metals identified in the core. Diatom changes both taxonomic and morphological can be excellent specific indicator of metal contamination and early recovery.     

Cleaning of lake sediment samples for diatom oxygen isotope analysis

Detrital grain contamination in a diatom sample can considerably influence the δ¹⁸O_diatom signal. In order to obtain a meaningful signal, pure samples must be used. This can be achieved via a series of cleaning stages including organic and carbonate material removal, sieving, differential settling and heavy liquid separation. The method described here works best for sediments with >20% diatom content. Based on testing various clean-up methods, we propose a sequence of four clean-up stages to produce pure diatom samples from a range of lake sediments types starting with a few grams of sediment. The diatom content and the oxygen isotope composition of the samples at each stage were measured in order to assess the effect of differential amounts of contamination. Results show that a four stage clean-up is necessary to produce clean diatom samples and that contamination by silt and clay causes lower δ¹⁸O values.