Prediction of dissolved inorganic nitrogen (DIN) concentrations in deep,seasonally stratified lakes based on rates of DIN input and N removal processes

Mean dissolved inorganic nitrogen concentrations ([DIN]) in deep, seasonally stratified lakes with comparable DIN inputs can differ by up to a factor of 3 depending on hydraulic and morphometric properties and/or different trophic states of the lakes. In such lakes, net N sedimentation rates were estimated with two independent methods (sediment core analysis and input-output mass balances). They were higher in eutrophic lakes (Mean: 5.1; SD: ± 1.6 g m^–2 yr^–1; n = 13) than in oligotrophic lakes (1.6 ± 1.0 g m^–2 yr^–1; n = 3), but independent of [DIN]. Gaseous N loss rates to the atmosphere, as calculated from combined N- and P-mass balances from selected lakes, ranged from 0.9 to 37.4 g m^–2 yr^–1 (n = 10) and were positively correlated with [DIN]. Reduction of NO ₃ ^- to N₂ is assumed to be the main cause for gaseous N losses. A simple one-box mass balance model for [DIN], based on DIN input and rates and kinetics of N removal processes (net sedimentation and gaseous N loss) is proposed, and validated with a data base on [DIN] and DIN input in 19 deep, seasonally stratified lakes of central Europe. The model illustrated that the amount of water loading per unit surface area of a lake (called water discharge height q) is the critical parameter determining mean lake [DIN] relative to mean input [DIN]. Lakes with a q > 50 m yr^–1 have average [DIN] similar to the [DIN] of the inflows regardless of their trophic states, because input and outflow exceed lake-internal N removal processes. A high primary production favors DIN removal in lakes with q < 50 m yr^–1. It is concluded that measures to decrease primary production, e.g. by means of P removal programs, lead to an increase of [DIN] in lakes.     

Adsorption-desorption of phosphate and its availability in the sediment of a saline lake (Fuente de Piedra,southern Spain)

Seasonal changes of soluble reactive phosphorus concentrations in sediments of Fuente de Piedra, a saline lake, have been observed and linked to salinity changes. Phosphate availability in sediments was studied in the laboratory under different salinities, from 10 to 70 g L⁻¹. Changes in adsorption of dissolved phosphate appear to be controlled by salinity variations. The adsorption coefficient increases with salinity and the amount of phosphorus adsorbed ranged between 10 and 30 per cent of the total. Salinity-modulated adsorption is proposed as the primary mechanism explaining the seasonal dynamics of phosphorus in this saline lake and its effects on progressive eutrophication.     

Zooplankton distribution and abundance in saline lakes of Alberta and Saskatchewan,Canada

Zooplankton collections were made during 1985, 1986, 1988 and 1989 from 17 lakes in Saskatchewan and 3 in Alberta. Salinity ranged from 2.8 to 269 g L⁻¹ (total filtrable residue). A total of 35 species was present in four taxa: Anostraca (3 species), Cladocera (11), Copepoda (7) and Rotifera (14). Species richness was greatest at salinities <7 g L⁻¹ (15–16 species). Lakes with salinities between 7 and 100 g L⁻¹ generally had 6–8 zooplankton species, while the most saline lakes (>100 g L⁻¹) had 2–5 species. The largest concentrations of zooplankton occurred at <30 g L⁻¹, but some species (Brachionus plicatilis, Hexarthra polyodonta, Artemia franciscana, Diaptomus connexus) were abundant at salinities >50 g L⁻¹. Eurysaline species included the rotifersAsplanchna girodi (3–111 g L⁻¹),Brachionus plicatilis (13–146) andKeratella quadrata (2.8–103).Artemia franciscana (33–269—but absent from Big Quill Lake, 49–82),Daphnia similis (3–104).D. connexus (9–82),Diacyclops thomasi (3–72), andCletocamptus albuquerquensis (17 to 126—but never abundant in the plankton). About half the species were restricted to hyposaline waters (3–20 g L⁻¹), but some (Hexarthra fennica, Moina hutchinsoni, Hexarthra polyodonta) occurred only at intermediate salinities. The latter two species were also only present at high pH values (>9.2). There was a trend of decreasing species richness with increasing salinity. TWINSPAN classification of 94 lake samples (six parameters) based on zooplankton species abundances yielded a dendrogram with 14 ‘indicator’ species characteristic of seven lake groups related partly to a salinity gradient, but with other environmental factors such as water column depth, pH, Secchi disk transparency, water temperature and month sampled also influenced lake separation. *** DIRECT SUPPORT *** A02GG004 00002     

The sedimentary record of spheroidal carbonaceous fly-ash particles in shallow Danish lakes

Spheroidal carbonaceous particles (SCP) from combustion of oil and coal have been quantified in cores from top sediments of Danish shallow lakes. Chronologies were provided by ²¹⁰Pb-dating supplemented by measurements of other radionuclides (¹³⁷Cs, ¹³⁴Cs, ²⁴¹Am). All cores show indications of sediment mixing but most still retain a characteristic SCP record. Deposition rates of SCP were low until the 1920s, increased strongly after World War II, reached maximum levels around 1970 and decreased thereafter. These results were used to infer a new chronology for a sediment core from a shallow lake, from which a ²¹⁰Pb chronology had previously been published.SCP inventories are positively correlated with ²¹⁰Pb inventories and dry matter accumulated since 1900, suggesting that absolute SCP accumulation rates may be more influenced by sedimentary processes than by atmospheric fluxes. The concentrations of SCP in surface sediments of the six lakes do, however, correlate with regional SO₂ emissions.     

Recent limnological changes in a saline lake of the Bolivian Altiplano,Lake Poopo

During the past twelve years, Lake Poopo, located on the Bolivian Altiplano, has had two main types of morphometry. Before 1985, its level was low and the depth shallow (maximum 3 m); there was no outlet and a strong salinity gradient existed from north to south. After 1985, the depth doubled, an outlet developed and the salinity became uniform throughout the lake (∼10 g L⁻¹). Before 1985, the phytoplankton was distinguished by a high number of diatom taxa and by the dominance of diatoms in the algal biomass. After 1985, while diatoms were still numerous in terms of species composition, Peridiniales or Chlorophyceae dominated the algal biomass. *** DIRECT SUPPORT *** A02GG003 00002     

土质对人工冻土冻结温度影响的试验研究

不同土质的冻结温度是人工冻结法冻结壁设计重要依据。为研究土质对人工冻土冻结温度的影响,选取不同地区人工冻结法施工典型土层开展冻结温度试验,提供了不同地区典型土层的冻结温度范围,并结合水泥土、含盐土冻结温度试验进行对比分析。结果表明：同一地区不同土层的冻结温度随其土颗粒粒径的增大而增大;随水泥掺入比及龄期的增加,水泥土的冻结温度降低;随含盐量的增加,NaCl含盐土冻结温度线性降低,含盐量对氯盐土比对硫酸盐土的冻结温度影响更显著。研究成果对不同土性的冻结壁设计具有指导意义。     

盐湖生物发育特征及其烃源意义

盐湖类盆地(咸化湖盆)发育了许多陆相大油气田,但其生物发育特征却因组成复杂与种类独特而认识较模糊,是石油地质地球化学和湖相沉积学领域的重要科学问题。为加深对其理解,本文综述了盐湖(咸化湖盆)环境中生物发育的特征,并讨论了其烃源意义。结果表明,盐湖(咸化湖盆)并不是传统认为的"生物荒漠",而是随盐度增加生物种类减少但生物量并不减少,可以有较高生产力,形成优质烃源岩。盐湖(咸化湖盆)中的生物系统组成异常复杂,包括高等植物、藻类、缺氧光合细菌、厌氧化能自养细菌、脊椎动物、无脊椎动物、古菌等,且生物不是均匀而是呈层分布,不同种类生物的耐盐度也各不相同。盐湖(咸化湖盆)生物的生物标记物及其数量关系对环境具有指示意义,生物及其盐度变化影响着与烃源岩有机质丰度相关的生产量、破坏量和稀释量等,进而影响油气生烃。未来仍有许多科学问题有待进一步深化研究,如盐湖(咸化湖盆)生物种类及数量、各生物生烃贡献比例、生物生产量、破坏量和稀释量的影响机制、成烃模式和机制、盐湖(咸化湖盆)形成的机制等。     

渤南洼陷古近系早期成藏作用再认识及其地质意义

传统观念认为渤南洼陷古近系具有三期成藏、晚期为主的特点。随着咸化湖盆烃源岩具有早生早排、生排烃量大的新认识的提出,利用钻井、地震及分析化验资料开展了渤南洼陷古近系早期成藏作用的重新评估。结果显示:渤南洼陷沙四上亚段发育有咸化环境下形成的烃源岩,地球化学参数表明其具有生成大量油气的能力,是早期成藏的物质基础;流体包裹体荧光颜色、均一温度共同指示出渤南洼陷罗家地区和三合村洼陷存在早期成藏,三合村洼陷古近系油气是在东营组沉积早期孤南断层断距较小时由渤南洼陷罗家地区运移而来;早期成藏作用的再认识不但使三合村洼陷古近系的油气勘探取得突破,而且构建了完整的油气成藏期次序列;早期成藏造成的岩石润湿性反转利于优势运移通道继承性发育,同时成藏过程中伴随的有机酸充注利于储集空间发育,更重要的是早期成藏作用的再次认识将会转变勘探思路、拓展勘探选区,带来了重要的地质意义和勘探启示。     

The lateglacial lakes of Glens Roy,Spean and vicinity (Lochaber district,Scottish Highlands)

This paper summarises the evidence for glacial ice advance into lower Glen Spean during the Loch Lomond Stadial which involved the blockage of westward-flowing drainage to form a series of ice-dammed lakes, the former surfaces of which are marked by prominent shorelines. Detailed mapping of glacigenic landforms and instrumental levelling of the shorelines reveals a dynamic interplay between the glacier margins and lake formation. Subsequent deglaciation led to lowering of the lake levels, at times by catastrophic drainage beneath the ice (jökulhlaup). The abandoned shorelines have been warped and dislocated in numerous places as a result of glacio-isostatic deformation, faulting and landslip activity. The pattern of retreat of the ice can be deduced from the mapped distributions of retreat moraines and the levelled altitudes of numerous kame and fluvial terrace fragments. The sequence of events outlined in this paper provides important context for understanding the evolution of the landscape of the Glen Roy area during the Loch Lomond Stadial, and a prelude to more recent studies reported in other contributions to this thematic issue.     

东濮凹陷北部盐湖相原油特征与成因

东濮凹陷盐湖相油气成因与成藏机理研究薄弱。采用色谱/质谱(GC/MS)等常规技术,结合傅立叶变换离子回旋共振质谱、单体烃碳同位素技术,对东濮凹陷北部文明寨、卫城地区油气特征及其成因进行了解剖。结果表明,该区原油具有植烷对姥鲛烷优势显著、伽马蜡烷富集、升藿烷“翘尾”、甾烷异构化程度较低等咸水、盐湖相原油的典型特征。原油还具有正构烷烃单体烃碳同位素呈低碳重、高碳轻、近两段式分布的特征,与柴达木盐湖相原油有所差异。原油中检测到丰富的S1、S2、O1S1、N1、O1、O2、O3等芳构化程度较低的NSO化合物,其与该区低熟油的形成关系密切。油-油、油-岩详细对比表明,东濮凹陷北部原油主要来自埋深超过3 000 m的沙三—沙四段烃源岩、存在不同成熟度原油混合聚集现象。研究结果对该区进一步油气勘探具有重要指示意义。