Variation in the Settling Velocity of Suspended Particulate Matter in Shallow Lakes,with Special Implications for Mass Balance Modelling

Measurements of sedimentation were combined with water samples to calculate settling velocity of suspended particulate matter (SPM) in lakes. The study sites were open water stations and enclosures in Lake Erken (Sweden) and Lake Balaton (Hungary). Settling velocities were found to vary considerably both inside and outside the enclosures. Within sites, the differences between 25th and 75th percentiles of measured settling velocities of SPM were two‐ or three‐fold. Median settling velocities of SPM ranged from around 0.5 m/d in the enclosures of Lake Erken to more than 8 m/d in the open water of Lake Balaton. Special relevance was attributed to flocculation, which is known to be affected by, e.g., SPM concentration and turbulence. Even though not directly measured, the less turbulent environment inside the enclosures was suggested to explain the low settling velocity compared to the open water environment. Settling velocity apparently correlated with water current speed (r² = 0.66; n = 12). Stepwise multiple linear regressions were used to relate the variability in settling velocity of SPM to the variability of possible controlling factors in a number of data subsets. In most cases, one variable describing the total amount of settling material (e.g., SPM) and one variable reflecting the composition of settling material (e.g., total phosphorus) were chosen. The use of suspended solids concentration to predict settling velocity in mass balance models was discussed. It was found that the mean slope between SPM and v_SPM was close to 0.1 (m⁴d^–1 g^–1). (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The relationship between planktonic algae and bacteria in a small lake

The seasonal changes and vertical distribution of the aerobic and anaerobic bacteria in a small edaphically eutrophic lake which exhibited thermal and chemical stratification are described. There was some correspondence between the phytoplankton and particularly the aerobic bacteria but this was not consistent. Increases in the numbers of anaerobic bacteria coincided with the low dissolved oxygen concentrations in the hypolimnion when algal populations were first senescent and then increasing actively in size.     

中亚热带人工针叶林对未来气候变化的响应

利用基于生理生态学过程的EALCO模型,探讨了千烟洲中亚热带人工针叶林生态系统对未来气候变化的响应.结果表明:CO₂浓度、温度和降水的变化对该人工林生态系统碳水通量影响的程度不同,其中CO₂浓度＞温度＞降水.CO₂浓度是生态系统总光合生产力(GPP)的主要驱动因子,温度与CO₂浓度均是控制生态系统呼吸的主要环境因子,温度的升高使植物地上部分呼吸明显增加,而CO₂浓度升高则对土壤呼吸影响较大.温度升高使蒸散(ET)增加,而CO₂浓度升高则使ET减少.在未来气候变化情景(2100年)下,该人工林生态系统的净初级生产力将增加22%,说明其仍具有较强的固碳潜力.     

Recent research in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a cytosine–guanine–guanine repeat expansion neurological disease that occurs in a subset of aging carriers of the premutation (55–200 cytosine–guanine–guanine repeats) in the FMR1 gene located on the X chromosome. The clinical core involves intention tremor and gait ataxia. Current research seeks to clarify the pathophysiology and neuropathology of FXTAS, as well as the development of useful biomarkers to track the progression of FXTAS. Efforts to implement quantitative measures of clinical features, such as kinematics and cognitive measures, are of special interest, in addition to characterize the differences in progression in males compared with females and the efficacy of new treatments.     

脑白质功能——来自BOLD-fMRI的证据

白质是组成大脑神经网络不可缺少的部分,对白质的探索多采用解剖形态学方法.血氧水平依赖功能性磁共振成像(blood oxygen level dependent functional magnetic resonance imaging,BOLD-fMRI)作为一种研究大脑功能的非侵入性工具已得到了广泛的应用,但是大多数BOLD-fMRI研究集中在大脑灰质,将白质BOLD信号作为噪声处理.事实上,白质的BOLD信号允许我们探索其动态功能特性,构建白质的功能连接网络,进而从功能角度来评估白质的完整性.因此,在已有研究基础上,我们对白质功能研究相对较少的原因以及BOLD信号可能的神经生理基础进行探讨,并概述了近年来已经发表的相关证据.最后,我们梳理了白质BOLD-fMRI研究存在的问题以及未来研究方向.     

Decoupled trophic responses to long‐term recovery from acidification and associated browning in lakes

Increases in the concentration of dissolved organic matter (DOM) have been documented in many inland waters in recent decades, a process known as “browning”. Previous studies have often used space‐for‐time substitution to examine the direct consequences of increased DOM on lake ecosystems. However, browning often occurs concomitant with other ecologically important water chemistry changes that may interact with or overwhelm any potential ecological response to browning itself. Here we examine a long‐term (~20 year) dataset of 28 lakes in the Adirondack Park, New York, USA, that have undergone strong browning in response to recovery from acidification. With these data, we explored how primary producer and zooplankton consumer populations changed during this time and what physical and chemical changes best predicted these long‐term ecosystem changes. Our results indicate that changes in primary producers are likely driven by reduced water clarity due to browning, independent of changes in nutrients, counter to previously hypothesized primary producer response to browning. In contrast, declines in calcium concomitant with browning play an important role in driving long‐term declines in zooplankton biomass. Our results indicate that responses to browning at different trophic levels are decoupled from one another. Concomitant chemical changes have important implications for our understanding of the response of aquatic ecosystems to browning.     

Influence of substrate concentration and moisture content on the specific methanogenic activity of dry mesophilic municipal solid waste digestate spiked with propionate

The objective of this study was to evaluate the influence of substrate concentration and moisture content on the specific methanogenic activity (SMA) of a fresh dry mesophilic digestate from a municipal solid waste digester plant. For this purpose, SMA tests were performed under mesophilic conditions into glass bottles of 500 mL volume used as batch reactors, during a period of 20-25 days. Propionate was used as substrate at concentrations ranging from 1 to 10 gCOD/kg. Four moisture contents were studied: 65%, 75%, 80% and 82%. Experimental results showed that propionate concentration and moisture content strongly influenced the SMA. The highest SMA was observed at a substrate concentration of 10 gCOD/kg (11.3 mgCOD gVS⁻¹ d⁻¹ for the second dose of propionate) and at a moisture content of 82% (7.8 mgCOD gVS⁻¹ d⁻¹ for the second dose of propionate, at a concentration of 5 gCOD/kg). SMA was found to decrease linearly when decreasing the moisture content.     

Influence of natural dissolved organic matter (DOM) on acute and chronic toxicity of the pesticides chlorothalonil, chlorpyrifos and fipronil on the meiobenthic estuarine copepod Amphiascus tenuiremis

Dissolved organic matter (DOM) represents an important carbon phase in coastal environments and influences the partitioning of organic contaminants. In this study, we evaluated the role of salt-marsh sediment-derived DOM vs. DOM-free seawater on the acute and chronic toxicity of three pesticides (chlorothalonil—CHTH, chlorpyrifos—CHPY and fipronil—FIP) to the meiobenthic copepod Amphiascus tenuiremis. Acute toxicity was evaluated via standard 96-h median lethal concentration (LC₅₀), while chronic toxicity was evaluated for 16 days using a 96-well microplate life-cycle bioassay. DOM significantly reduced (p<0.05) acute toxicity of CHTH and CHPY to male and female copepods relative to copepods exposed in DOM-free seawater. In contrast, DOM elevated the acute toxicity of FIP to male copepods. In chronic exposures with/without DOM, CHTH and CHPY did not significantly affect copepodite-to-adult development. In these treatments, plus controls, the majority (95%) of copepodites developed into adults by 8 days. Individuals exposed to FIP in the presence of DOM showed a slower development rate than FIP individuals in DOM-free seawater. Overall, FIP exposed copepodites developed into adult copepods 4 days later than controls. CHTH, CHPY and FIP significantly reduced reproductive success by 33%, 31% and 89%, respectively. DOM, however, mitigated 30% (p=0.006) and 20% (p=0.05) of the reproductive failure attributed to CHTH and CHPY. FIP-induced reproductive failure was high (∼80%) in all exposures regardless of DOM presence/absence. An exponential growth model predicted that exposure to CHTH, CHPY and FIP in the absence of DOM significantly reduced (≥38%) projected naupliar production relative to DOM-free controls. In the presence of DOM, naupliar production under CHTH and CHPY exposures was not significantly different (p>0.05) from control projections. These results indicate that DOM generally reduced the acute and chronic toxicity of CHTH and CHPY to A. tenuiremis, while certain compound-specific pesticide (FIP): organic associations may enhance acute toxicity of FIP, particularly to male copepods.