NITRATE TRANSFORMATIONS IN SOUTHERN ONTARIO STREAM SEDIMENTS1

The transformation of nitrate was investigated in diverse stream sediments from six areas of Southern Ontario, Canada. Laboratory Experiments conducted with intact 0-5 cm depth sediment cores overlain with aerated 5 mg/l nitrate-N solution reveald considerable nitrate depletion during a six-day period as a resuit of denitrification and nitrate reduction to ammonium. Nitrification and ammonification also occurred simultaneously with nitrate reduction in many stream sediments. Mixed 0-5 cm depth sediments collected from 81 stream sites were used to examine the relationship between microbial nitrate removal and sediment characteristics. Rates of nitrate-N loss from aerated 5 mg/l nitrate-N solutions overlying these sediments ranged between 11 and 171 mg/m²/day for a 24-hour incubation period. Rates of nitrate loss for the 24-hour period exhibited a significant positive correlation (r=0.72) with sediment ammonium content. Organic carbon, total nitrogen and sediment texture also had significant but weak correlations with nitrate loss.     

Trace Element Concentrations in Fish, Surficial Sediments and Water from Northern Part of the Persian Gulf

Concentrations of cadmium, lead, nickel and vanadium were determined in water, surficial sediments and the muscle of three demersal fish species (Epinephelus coioides, Psettodes erumei and Solea elongate) from 15 sampling sites in the northern part of Persian Gulf. Concentrations of the elements were determined using Inductively Coupled Plasma Mass Spectrometer. There were no significant differences among the sampling sites in Cd and Pb levels in the sediments. The highest concentrations of Ni and V in sediments were found near the southern coast of Qeshm Iland and Bandar Lengeh. Concentrations of Cd, Pb and Ni in the sediments were notably higher than global baseline values. Nearly in all cases the element concentrations in the sediments were considerably greater than RSA (ROPME Sea Area) and the ERL (Effects Range Low) guidelines. Significant differences among the sampling sites could be found for concentrations of all the four metals in water. The mean Ni, Pb and Cd levels in the water samples were relatively higher than those in some other regions of the Persian Gulf. Except few cases, the mean concentrations of the elements in muscle of the selected fish species were markedly below the international guidelines for human consumption.     

东海特定海区沉积物-水界面附近P释放的实验研究

以采自长江口外东海表层沉积物为对象，对不同类型的沉积物在模拟海水环境中进行了释P实验。研究表明，在静态条件下，沉积物释P量的高点出现在摇晃后10min左右，大约3h后基本趋于平衡。释P动力学可用Elovich公式与双常数速率公式进行拟合。最大释P量与沉积物的组成密切相关，以粉砂、粘土为主的沉积物释P量高，而砂质为主者释P量低。在释P实验中，铁磷(Fe-P)最为活跃，释放比例最高，其次是吸附态磷(Ad-P)和有机态磷(OP)。它们均属于生物可获得P的范畴。实验结果表明，在合适的水动力条件下，沉积物中的P可以迅速释放到水体．并影响水体的营养状杰和初级生产力。     

SPATIAL AND TEMPORAL DYNAMICS OF WOOD IN HEADWATER STREAMS OF THE PACIFIC NORTHWEST1

This paper synthesizes information on the spatial and temporal dynamics of wood in small streams in the Pacific Northwest region of North America. The literature on this topic is somewhat confused due to a lack of an accepted definition of what constitutes “small” streams and what is the relative size of woody debris contained within the channel. This paper presents a matrix that defines woody debris relative to channel size and then discusses the components of a wood budget. Headwater streams are in close proximity to wood sources and, in steeplands, are often tightly constrained by steep hillslopes. Special consideration is given to ecosystem characteristics and to management practices that affect the wood dynamics in this context. Knowledge gaps and uncertainties that can be used to guide future research are identified. Very little is currently known about the role of mass wasting in wood recruitment and storage relative to other processes, such as bank erosion and mortality, in larger streams. Further, very little work has addressed the relative importance of different wood depletion processes, especially those associated with wood transport. The effect of other ecosystem variables on wood dynamics locally across a watershed (from valley bottom to mountaintop) and regionally across the landscape (from maritime to continental climates) is not addressed. Finally, the scientific community has only begun to deal with the effects of management practices on wood quantity, structure, and movement in small streams.     

高磷沉积物有机磷形态分布及释放动力学特征——以宜昌西北口水库为例

为探究高磷背景水库沉积物中有机磷(OP)的空间分布及OP释放动力学特征, 本文采用Ivannoff法对西北口水库沉积物中的OP进行分级提取, 通过沉积物OP释放动力学模拟实验, 探讨了表层沉积物OP的释放特征, 以及沉积物理化性质对其响应.结果表明, 西北口水库沉积物OP含量为210.3~455.2mg/kg, 平均含量为322.9mg/kg, 占总磷(TP)的18.3%.OP含量空间分布呈现库中(363.2mg/kg)>库首(339.3mg/kg)>库尾(266.1mg/kg)的变化规律, 垂向上随深度的增加而减小.西北口水库不同形态OP的含量表现为: 非活性有机磷(NOP)>中活性有机磷(MLOP)>活性有机磷(LOP), 其中NOP含量占OP的65.3%, 是西北口水库沉积物OP的主要存在形式.准一级动力学模型是描述西北口水库库首、库中和库尾沉积物OP释放动力学曲线的最优方程(R²=0.98~0.99, P < 0.01), 在0~1h表征为快速释放过程, 所释放的OP含量占最大释放量(Q_max)的55.68%~79.55%, 随后进入慢速释放过程, 逐渐达到Q_max, Q_max在1.4~3.1mg/kg之间.该水库沉积物中LOP和MLOP是主要向上覆水体释放的磷形态.     

胶州湾沉积物中的磷及其环境指示意义

研究了胶州湾沉积物中磷形态的地球化学分布特征、控制因素及环境意义,将胶州湾沉积物中的磷分为可交换态磷、铝结合态磷、铁结合态磷、闭蓄态磷、自生钙磷、碎屑态磷和有机磷7种不同的形态,并结合210Pb测年法计算了不同年代各形态磷的埋藏通量,在此基础上,分析了胶州湾沉积物中磷所给出的环境信息.结果表明,无机磷是胶州湾沉积物中磷的主要形态,有机磷只占较小的比例,无机磷中钙磷占的比例相对较大,其中碎屑态磷是含量最高.磷的含量及埋藏通量的垂向分布受到pH、盐度、温度、生物扰动、沉积速率等环境因子的影响.相关分析及元素的OC/OP比值分析证明,近20a,陆源输入是胶州湾沉积物主要来源,并且沉积速率不断增大.由于近年来采取的较为得力的治污与排放措施,胶州湾的环境状况已有明显改观.研究还表明,Fe-P,Al-P和Oc-P的含量与海域污染程度有较密切的关系,可作为表征海洋沉积环境污染状况的指示因子之一.     

PCB Levels and Trends Within the Detroit River-Western Lake Erie Basin: A Historical Perspective of Ecosystem Monitoring

An international workshop held in the spring of 2002 convened a group of technical experts to address monitoring, modeling, and management of PCBs within the Detroit River-Western Lake Erie basin. Participants shared and discussed a diverse set of research data bases pertaining to PCB levels within the region, discussed observed changes within different components of the local ecosystem, and identified several primary issues impacting future PCB management strategies. Results presented at the workshop indicate dramatic reductions in PCB contamination levels have been observed in much of study area between the late 1970s and mid-1990s. Estimates of loadings attributable to water and atmospheric sources have generally declined, as have PCB concentrations in herring gull eggs, smelt and walleye. Nevertheless, additional improvements have not been observed during recent years and elevated contamination levels remain a concern within local hot spots, particularly in the lower Detroit River and Trenton Channel. A primary recommendation broadly supported by workshop participants is the need to maintain, support, and coordinate a comprehensive ecosystem monitoring program for the Detroit River-Western Lake Erie basin, one that incorporates both near-field and far-field monitoring elements. Such a program is crucial to provide necessary data in support of understanding ecosystem trends, calculating annual mass loadings to the system, assessing impacts of remediation actions, developing improved modeling frameworks, and formulating cost-effective management strategies for the future.     

Distribution,source, and ecological risk assessment of PAHs among size and density fractions in contaminated sediments from the Yellow River of Henan section

This study investigated particle size and density distributions of polycyclic aromatic hydrocarbons (PAHs) in two surface sediments (JZ and KF), collected from the Yellow River of Henan section, China. The concentrations of Σ₁₅PAHs ranged from 35.6 to 45862?ng g^?1 dry wt, which were greatly elevated in coarse particles and low-density fractions. The Σ₁₅PAHs concentrations in low-density fractions were 533 (JZ) and 996 (KF) times higher than those in the corresponding high-density fractions. However, due to relatively less quantities of low-density fractions (0.27–2.33%), most of the PAHs were contributed by the high-density components. For both sediments, the influence factors of PAHs source in the environment were very complex, more so than the level of TOC and BC content. JZ sediment was dominated by 4-ring to 6-ring PAHs (61.5–75.1%), while, 2-ring to 3-ring PAHs were abundant in KF samples (39.8–72.6%). Ratios of specific PAHs reflected PAHs among the size- and density-fraction of each sediment may be contaminated by mixed of pyrolytic and petrogenic origin. Additionally, ecological risk assessment of PAHs suggested that total toxic equivalent values of PAHs in the low-density fractions were much higher than those of the corresponding high-density fractions in the studied area.     

Decadal and Episodic Changes in Morphology and Migration of the Confluence Bar of Two Alluvial Rivers in Louisiana,USA

Past research on fluvial dynamics at the confluence of two alluvial rivers has mainly focused on downstream flow structure and bed scoring, often using laboratory experiments and numerical modeling. Little is investigated about yearly and episodic dynamics of confluence mouth bars that can affect downstream morphology using field measurements. In this study, we analyzed the migration of a confluence mouth bar of two free meandering alluvial rivers, the Amite and Comite Rivers in coastal Louisiana, USA from 2002 to 2017. Remote sensing images were utilized to investigate the decade‐long morphologic changes. To assess episodic dynamics, we employed terrestrial laser scanning measurements to acquire high‐accuracy digital elevation models at the confluence before and after three floods in 2017. Our study found that the Amite‐Comite confluence mouth bar migrated downstream 55 m in the past 15 years, and its angle reduced by 55° from 100° to 45°. The fast migration was a result of sediment deposition and channel deformation around the confluence mainly during the years when the tributary‐to‐main channel discharge was lower (<0.25). The study further reveals that a single moderate flood could strongly affect the mouth bar, as shown by an increase of the projected surface area by 114% and an increase of volume of the confluence mouth bar by 68%.     

三峡库区典型次级支流表层沉积物中PAHs的分布特征及来源分析

本文表征了三峡库区典型次级支流(梁滩河)表层沉积物中18种多环芳烃(PAHs)的浓度,并对其分布特征和污染来源进行了探讨。18种PAHs的总浓度(∑18 PAHs)范围为198.5～4349 ng/g-dw(干重),平均浓度为1441ng/g,中值为1160 ng/g。与其他地区沉积物污染情况相比,梁滩河沉积物中PAHs浓度处于中等偏低的污染程度,支流污染程显著高于干流,流经城镇的右支污染程度显著高于流经农村或人口较少的左支和主干流。大部分采样点以高环(4～6环)PAHs污染为主。PAHs源解析结果表明,梁滩河表层沉积物中PAHs污染以燃烧源为主,主要源于化石燃料和生物质的不完全燃烧。沉积物中苯并[a]芘的毒性当量因子(TEF)值为39.38～384.37 ngTEQ/g,平均值110.94 ngTEQ/g。生态风险评价的结果表明,右支流的两个采样点R3和R4点沉积物中PAHs可能存在生物负效应影响,R4点的高风险可能与附近白市驿机场污染有关。