A critical evaluation of multi‐proxy dendroclimatology in northern Finland

Twentieth‐century summer (July–August) temperatures in northern Finland are reconstructed using ring widths, maximum density and stable carbon isotope ratios (δ¹³C) of Scots pine tree rings, and using combinations of these proxies. Verification is based on the coefficient of determination (r²), reduction of error (RE) and coefficient of efficiency (CE) statistics. Of the individual proxies, δ¹³C performs best, followed by maximum density. Combining δ¹³C and maximum density strengthens the climate signal but adding ring widths leads to little improvement. Blue intensity, an inexpensive alternative to X‐ray densitometry, is shown to perform similarly. Multi‐proxy reconstruction of summer temperatures from a single site produces strong correlations with gridded climate data over most of northern Fennoscandia. Since relatively few trees are required (<15) the approach could be applied to long sub‐fossil chronologies where replication may be episodically low. Copyright © 2010 John Wiley & Sons, Ltd.     

Precessional forcing of tropical vegetation carbon storage

Since the Mid Pleistocene Revolution, which occurred about one million years ago, global temperatures have fluctuated with a quasi‐periodicity of ca. 100 ka. The pattern of past change in the extent of woodlands, and therefore by inference vegetation carbon storage, has been demonstrated to have a strong positive link with this global temperature change at high and mid latitudes. However, understanding of climate systems and ecosystem function indicates that the pattern of woodland change at low latitudes may follow a fundamentally different pattern. We present output from the intermediate complexity model GENIE‐1, comprising a single transient simulation over the last 800 ka and a 174‐member ensemble of 130 ka transient simulations over the last glacial cycle. These simulations suggest that while vegetation carbon storage in mid–high northern latitudes robustly follows the characteristic ca. 100 ka cycle, this signal is not a robust feature of tropical vegetation, which is subject to stronger direct forcing by the precessional (21 ka) orbital cycle (albeit with a highly uncertain response). We conclude that the correlation of palaeoenvironmental records from low latitudes with global temperature change must be done with caution. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrological regulation of chemical weathering and dissolved inorganic carbon biogeochemical processes in a monsoonal river

To better understand the mechanisms relating to hydrological regulations of chemical weathering processes and dissolved inorganic carbon (DIC) behaviours, high-frequency sampling campaigns and associated analyses were conducted in the Yu River, South China. Hydrological variability modifies the biogeochemical processes of dissolved solutes, so major ions display different behaviours in response to discharge change. Most ions become diluted with increasing discharge because of the shortened reactive time between rock and water under high-flow conditions. Carbonate weathering is the main source of major ions, which shows strong chemostatic behaviour in response to changes in discharge. Ions from silicate weathering exhibit a significant dilution effect relative to the carbonate-sourced ions. Under high temperatures, the increased soil CO₂ influx from the mineralisation of organic material shifts the negative carbon isotope ratios of DIC (δ¹³C_DIC) during the high-flow season. The δ¹³C_DIC values show a higher sensitivity than DIC contents in response to various hydrological conditions. Results from a modified isotope-mixing model (IsoSource) demonstrate that biological carbon is a dominant source of DIC and plays an important role in temporal carbon dynamics. Furthermore, this study provides insights into chemical weathering processes and carbon dynamics, highlighting the significant influence of hydrological variability to aid understanding of the global carbon cycle.     

Changes in dissolved organic matter (DOM) amount and composition along nested headwater stream locations during baseflow and stormflow

Amount and composition of dissolved organic matter (DOM) were evaluated for multiple, nested stream locations in a forested watershed to investigate the role of hydrologic flow paths, wetlands and drainage scale. Sampling was performed over a 4‐year period (2008–2011) for five locations with drainage areas of 0.62, 3.5, 4.5, 12 and 79 ha. Hydrologic flow paths were characterized using an end‐member mixing model. DOM composition was determined using a suite of spectrofluorometric indices and a site‐specific parallel factor analysis model. Dissolved organic carbon (DOC), humic‐like DOM and fluorescence index were most sensitive to changes with drainage scale, whereas dissolved organic nitrogen, specific UV absorbance, Sr and protein‐like DOM were least sensitive. DOM concentrations and humic‐like DOM constituents were highest during both baseflow and stormflow for a 3.5‐ha catchment with a wetland near the catchment outlet. Whereas storm‐event concentrations of DOC and humic DOM constituents declined, the mass exports of DOC increased with increasing catchment scale. A pronounced dilution in storm‐event DOC concentration was observed at peak stream discharge for the 12‐ha drainage location, which was not as apparent at the 79‐ha scale, suggesting key differences in supply and transport of DOM. Our observations indicate that hydrologic flow paths, especially during storms, and the location and extent of wetlands in the catchment are key determinants of DOM concentration and composition. This study furthers our understanding of changes in DOM with drainage scale and the controls on DOM in headwater, forested catchments. Copyright © 2014 John Wiley & Sons, Ltd.     

Application of a Bayesian model to infer the contribution of coalbed natural gas produced water to the Powder River,Wyoming and Montana

The Powder River Basin (PRB) of Wyoming and Montana contains significant coal and coal bed natural gas (CBNG) resources. CBNG extraction requires the production of large volumes of water, much of which is discharged into existing drainages. Compared to surface waters, the CBNG produced water is high in sodium relative to calcium and magnesium, elevating the sodium adsorption ratio (SAR). To mitigate the possible impact this produced water may have on the quality of surface water used for irrigation, the State of Montana passed water anti‐degradation legislation, which could affect CBNG production in Wyoming. In this study, we sought to determine the proportion of CBNG produced water discharged to tributaries that reaches the Powder River by implementing a four end‐member mixing model within a Bayesian statistical framework. The model accounts for the ⁸⁷Sr/⁸⁶Sr, δ¹³C_DIC, [Sr] and [DIC] of CBNG produced water and surface water interacting with the three primary lithologies exposed in the PRB. The model estimates the relative contribution of the end members to the river water, while incorporating uncertainty associated with measurement and process error. Model results confirm that both of the tributaries associated with high CBNG activity are mostly composed of CBNG produced water (70–100%). The model indicates that up to 50% of the Powder River is composed of CBNG produced water downstream from the CBNG tributaries, decreasing with distance by dilution from non‐CBNG impacted tributaries from the point sources to ~10–20% at the Montana border. This amount of CBNG produced water does not significantly affect the SAR or electrical conductivity of the Powder River in Montana. Copyright © 2013 John Wiley & Sons, Ltd.     

中全新世以来呼伦湖沉积物碳埋藏及其影响因素分析

通过对内蒙古高原呼伦湖沉积物样品总有机碳含量(TOC)及其稳定同位素(δ13Corg)、总氮含量(TN)和TOC/TN(C/N)值的测定,结合沉积岩芯AMS14C年代标尺,分析了中全新世以来呼伦湖沉积物有机碳埋藏速率随时间变化的趋势及有机质的来源,并探讨了影响呼伦湖有机碳埋藏的主要因素.结果表明,中全新世以来呼伦湖有机碳埋藏速率平均值约为2.06 g/(m~2·a),碳储量约为35.25 Tg C,且总体上呈现增加趋势.呼伦湖沉积物中有机质主要来源于外源输入,但近1000 a以来内源输入逐渐增加并占据优势.呼伦湖有机碳埋藏速率与温度和降水均呈负相关,表明在长时间尺度上,升温及降水量的增加可能对呼伦湖的碳埋藏起到一定的抑制作用.     

碳氮稳定同位素比值在潮间带大型底栖动物组织间差异性研究

近年来，稳定同位素技术已被广泛应用于食物网研究中。然而，生物样品取样部位对食物网构建的影响的研究相对少见。大型底栖动物作为潮间带食物网的重要组成部分，在食物网研究中有必要对其采样部位进行统一，以增加研究结果的准确性及可比较性。本研究选取黄河三角洲和烟台潮间带10种代表性的大型底栖动物，比较δ13C和δ15N在不同采样部位中的差异。结果显示，对于大多数底栖动物而言，采样部位将直接影响到δ13C和δ15N的测定结果。当底栖动物作为摄食者，需分析其食性和营养级时，应统一采用肌肉组织，如贝类的闭壳肌或足部肌肉，蟹类的鳌足肌肉，鱼类的背部肌肉；当底栖动物作为被摄食者，需分析次级消费者的食性和营养级时，除多毛类采用去除消化道内容物的体壁外，其他种类应选取整体（难以被消化的组织除外），如贝类的软体部，蟹类肌肉与鳃等的混合组织。     

浙江温州山地丘陵区土壤碳储量研究

基于温州市山地丘陵区开展的多目标地球化学调查获得的深、表层土壤有机碳和全碳数据,采用直线模型法计算了研究区表层(0~0.2 m)、中层(0~1.0 m)和深层(0~2 m)土壤无机碳的单位储量及密度;采用指数模型法计算了研究区表层(0~0.2 m)、中层(0~1.0 m)和深层(0~2 m)土壤有机碳的单位储量及密度。利用这些数据分别编制了表层、中层、深层无机碳和有机碳的碳密度图,分析了无机碳、有机碳的分布范围和特点以及它们在不同土壤类型中的分布特征。结果表明研究区单位土壤无机碳平均储量为2881.333t,平均密度为0.720 kg/m^2,单位土壤有机碳平均储量为43128.667t,平均密度为10.782 kg/m^2;有机碳和无机碳在表层、中层和深层土壤中含量分布趋势一致;在不同土壤类型中含量分布趋势也一致,均为滨海岩土中最高,粗骨土中最低。     

富营养化对湖泊消费者群落碳源和氮源的影响——以白洋淀为例

富营养化对湖泊生态系统能流和物流的影响具有不确定性，多数研究仅关注富营养化对浅水湖泊食物网结构和功能的影响，而富营养化对消费者群落碳源和氮源的影响及其时空分异特征较少关注.鉴于此，本研究选取华北平原最大的浅水富营养化湖泊——白洋淀为研究区，依据生境理化参数将白洋淀划分为3类生境（生境1（Ⅰ和Ⅱ区）主要遭受上游府河废水排放影响；生境2（Ⅴ、Ⅶ和Ⅷ区）主要遭受水产养殖和生活污水的影响；生境3（Ⅲ、Ⅳ和Ⅵ区）遭受人为干扰较小）.在2018年4月和8月分别收集了浮游生物、底栖生物和鱼类样品，运用碳、氮稳定同位素技术定量估算3类生境中底栖和浮游生物对消费者群落碳源和氮源贡献百分比的时空分异特征；同时收集水体和沉积物样品进行常规理化参数分析，明晰富营养化对白洋淀消费者群落碳源和氮源贡献百分比的影响.结果表明：1）就水体和沉积物理化参数季节变化而言，除pH相对稳定外，化学需氧量（COD）、沉积物氨氮（NH₃-Ns）、总氮（TN）和沉积物总磷（TPs）4月高于8月，而其他理化参数则8月高于4月；就空间分布而言，温度（T）、水深（WD）、溶解氧（DO）和沉积物总碳（TCs）值在生境3中最高，而其他理化参数的值则在生境1中最高；2）就δ¹³C和δ¹⁵N空间分布而言，对于同一群落，δ¹³C和δ¹⁵N在3类生境中富集程度呈现显著差异；就时间分布而言，不同季节消费者群落的δ¹³C值存在显著差异，而δ¹⁵N值未呈现显著差异，且消费者群落的δ¹³C和δ¹⁵N呈显著负相关；3）就消费者营养级的空间分布而言，3类生境存在显著差异，同一消费者营养级在生境1中最高，在生境3中最低；就时间分布而言，消费者营养级未呈现显著差异；4）浮游生物对消费者群落碳源和氮源贡献百分比4月高于8月，生境1高于其他生境；而底栖生物对消费者群落碳源和氮源贡献百分比则8月高于4月，生境3高于其他生境；5）通过相关分析，结果表明白洋淀消费者群落的δ¹³C与总磷（TP）、TCs、沉积物总氮（TNs）、总有机碳（TOCs）、TPs呈现负相关关系；δ¹⁵N值与TP、TCs、TNs、TOCs、TPs呈正相关关系.因此，湖泊富营养化会影响消费者群落的碳源和氮源，进而改变湖泊生态系统的能流和物流.     

内陆水体溶解无机碳同位素研究进展及展望

碳是陆地生态系统中最重要的生命元素，能够在各个圈层之间相互转换和运移。碳循环作为地球各圈层相互连接的纽带，被认为是地表系统最重要的元素地球化学循环。碳在水体中主要以溶解性有机碳（dissolved organic carbon，简称DOC）和溶解性无机碳（dissolved inorganic carbon，简称DIC）形式存在。内陆水体（包括河水、地下水、湖水和水库等）尽管只占陆地表面1%，但它们在碳循环过程中发挥了重要作用。其DIC浓度(CDIC)和DIC同位素组成(δ13CDIC)可以为碳循环研究提供线索，因此成为近年来国际研究的热点之一。本文系统总结了全球内陆水体DIC同位素的研究进展。DIC同位素具有广泛的地质应用，不同碳源具有独特的同位素特征。因此，DIC同位素被用于定性和定量地示踪碳源，指示碳循环过程以及确定河水补给端元。