CHARACTERISTICS OF LONG‐TERM FRESHWATER TRANSPORT IN APALACHICOLA BAY1

ABSTRACT: Long‐term freshwater transport is an important factor affecting estuarine aquatic ecosystems. In this study, a primitive equation, prognostic, three‐dimensional, hydrodynamic model was applied to Apalachicola Bay, Florida, for the summer and fall seasons of 1993. In response to the river freshwater discharge, tide, and wind forces, the model simulations were used to characterize the long‐term freshwater transport processes in the bay. Analysis of spatial distributions of seasonal average salinity and currents shows that the long‐term freshwater transport was strongly affected by the forcing functions of wind and density gradient in the bay. Average freshwater input was approximately the same in the summer and fall seasons of 1993. However, in the summer season, more freshwater moved to the east direction due to the predominant wind from the west, while in the fall season more freshwater moved to the west in response to the wind primarily from the east. The water column was strongly stratified near the river mouth, and it gradually changed to well mixing near the ocean boundaries. Vertical stratification in the bay changed due to wind‐induced mixing and mass transport. Due to the density gradient effect, surface residual currents carrying fresher water were in the direction from the river toward the Gulf, while the bottom residual currents with saltier water entered the bay from the Gulf of Mexico.     

Transport of a decay chain in homogenous porous media: analytical solutions

With the aid of integral transforms, analytical solutions for the transport of a decay chain in homogenous porous media are derived. Unidirectional steady-state flow and radial steady-state flow in single and multiple porosity media are considered. At least in Laplace domain, all solutions can be written in closed analytical formulae. Partly, the solutions can also be inverted analytically. If not, analytical calculation of the steady-state concentration distributions, evaluation of temporal moments and numerical inversion are still possible. Formulae for several simple boundary conditions are given and visualized in this paper. The derived novel solutions are widely applicable and are very useful for the validation of numerical transport codes.     

Modelling the closure-related geochemical evolution of groundwater at a former uranium mine

A newly developed reactive transport model was used to evaluate the potential effects of mine closure on the geochemical evolution in the aquifer downgradient from a mine site. The simulations were conducted for the K?nigstein uranium mine located in Saxony, Germany. During decades of operation, uranium at the former mine site had been extracted by in situ acid leaching of the ore underground, while the mine was maintained in a dewatered condition. One option for decommissioning is to allow the groundwater level to rise to its natural level, flooding the mine workings. As a result, pore water containing high concentrations of dissolved metals, radionuclides, and sulfate may be released. Additional contamination may arise due to the dissolution of minerals contained in the aquifer downgradient of the mine. On the other hand, dissolved metals may be attenuated by reactions within the aquifer. The geochemical processes and interactions involved are highly non-linear and their impact on the quality of the groundwater and surface water downstream of the mine is not always intuitive. The multicomponent reactive transport model MIN3P, which can describe mineral dissolution-precipitation reactions, aqueous complexation, and oxidation-reduction reactions, is shown to be a powerful tool for investigating these processes. The predictive capabilities of the model are, however, limited by the availability of key geochemical parameters such as the presence and quantities of primary and secondary mineral phases. Under these conditions, the model can provide valuable insight by means of sensitivity analyses.     

Impact of Atmospheric Long Range Transport of Lead,Mercury and Cadmium on the Swedish Forest Environment

Emissions of Hg, Pb, and Cd to air aretransported over wide areas in Europe and deposited far awayfrom their sources. About 80% of the atmospheric depositionof these metals in south Sweden originate from emissions inother countries. As a result of the increased anthropogenicdeposition the concentrations of Hg, Pb, and Cd in the morlayer of forest soils have increased considerably, mainlyduring the 20th century. Although the atmosphericdeposition of these elements has declined during the mostrecent decades, the reduction of the input of Hg and Pb isnot sufficient to prevent a further accumulation. Theconcentrations of Hg and Pb are still increasing by ca. 0.5and ca. 0.2% annually in the surface layer of forest soils.In contrast, the Cd concentration is currentlydecreasing in a large part of Sweden as a result of bothdeposition decreases and enhanced leaching induced by soilacidification. The accumulation factors of Hg and Pb,especially in the forest topsoils of south Sweden, arealready above those at which adverse effects on soilbiological processes and organisms have been demonstrated instudies of gradients from local emission sources andlaboratory assessment. There are also indications of sucheffects at the current regional concentrations of Hg and Pbin mor layers from south Sweden, judging from observationsin field and laboratory studies. There is an apparent riskof Pb induced reduction in microbial activity over parts ofsouth Sweden. This might cause increased accumulation oforganic matter and a reduced availability of soil nutrients.At current concentrations of Hg in Swedish forest soils,effects similar to those of Pb are likely. Increasedconcentrations of these elements in organs of mammals andbirds have also been measured, though decreases have beendemonstrated in recent years, related to changes inatmospheric deposition rates. As a result of current andpast deposition in south Sweden, concentrations of Hg infish have increased about fivefold during the 20thcentury. This implies risks for human health, when fish frominland waters are used for food. Although the concentrationof Hg in fish has decreased ca. 20% during the last decade,probably as a result of the reduced deposition, the levelstill exceeds the general limit (0.5 mg kg^-1) in about half(ca. 40 000) of the Swedish lakes. In order to reduceconcentrations in fish to the level recommended, and avoidfurther accumulation of Hg in soils, the atmosphericdeposition has to be reduced to ca. 20% of the current deposition rate. This can only be achieved by international co-operation.     

TRANSIENT STORAGE ASSESSMENTS OF DYE‐TRACER INJECTIONS IN RIVERS OF THE WILLAMETTE BASIN,OREGON1

ABSTRACT: Rhodamine WT dye‐tracer injections in rivers of the Willamette Basin yield concentration‐time curves with characteristically long recession times suggestive of active transient storage processes. The scale of drainage areas contributing to the stream reaches studied in the Willamette Basin ranges from 10 to 12,000 km². A transient storage assessment of the tracer studies has been completed using the U.S. Geological Survey's One‐dimensional Transport with Inflow and Storage (OTIS) model, which incorporates storage exchange and decay functions along with the traditional dispersion and advection transport equation. The analysis estimates solute transport of the dye. It identifies first‐order decay coefficients to be on the order of 10^?5/sec for the nonconservative Rhodamine W.T. On an individual subreach basis, the first‐order decay is slower (typically by an order of magnitude) than the transient storage process, indicating that nonconservative tracers may be used to evaluate transient storage in rivers. In the transient storage analysis, a dimensionless parameter (A_s/A) expresses the spatial extent of storage zone area relative to stream cross section. In certain reaches of Willamette Basin pool‐and‐riffle, gravel‐bed rivers, this parameter was as large as 0.5. A measure of the storage exchange flux was calculated for each stream subreach in the simulation analysis. This storage exchange is shown subjectively to be higher at higher stream discharges. Hyporheic linkage between streams and subsurface flows is the probable physical mechanism contributing to a significant part of this inferred active transient storage. Hyporheic linkages are further suggested by detailed measurements of river discharge with an Acoustic Doppler Current Profiler system delineating zones in two large rivers where water alternately enters and leaves the surface channels through gravel‐and‐cobble riverbeds. Measurements show patterns of hyporheic exchange that are highly variable in time and space.     

OPTIMAL CONTROL OF RESERVOIR RELEASES TO MINIMIZE SEDIMENTATION IN RIVERS AND RESERVOIRS1

ABSTRACT: An optimal control methodology and computational model are developed to evaluate multi‐reservoir release schedules that minimize sediment scour and deposition in rivers and reservoirs. The sedimentation problem is formulated within a discrete‐time optimal control framework in which reservoir releases represent control variables and reservoir bed elevations, storage levels, and river bed elevations represent state variables. Constraints imposed on reservoir storage levels and releases are accommodated using a penalty function method. The optimal control model consists of two interfaced components: a one‐dimensional finite‐difference simulation module used to evaluate flow hydraulics and sediment transport dynamics, and a successive approximation linear quadratic regulator (SALQR) optimization algorithm used to update reservoir release policies and solve the augmented control problem. Hypothetical two‐reservoir and five‐reservoir networks are used to demonstrate the methodology and its capabilities, which is a vital phase towards the development of a more robust optimal control model and application to an existing multiple‐reservoir river network.     

4种改良剂对紫色土Cd生物有效性及土壤酶活性的影响

探究4种改良剂施用对酸性花椒园土壤有效Cd和花椒各部位Cd含量及土壤酶活性的影响,为紫色土酸化改良及重金属污染治理提供科学依据.采用田间试验,设置不施肥（CK）、单施化肥（F）、石灰+化肥（SF）、有机肥+化肥（OM）、生物炭+化肥（BF）和酒糟灰渣+化肥（JZ）这6个处理,研究不同处理土壤pH、有效态Cd（DTPA-Cd）、花椒枝条、叶片、椒壳、椒籽Cd含量及土壤过氧化氢酶（S-CAT）、酸性磷酸酶（S-ACP）和脲酶（S-UE）活性,阐明其相互关系.结果表明:①酒糟灰渣+化肥和石灰+化肥两处理均显著提高土壤pH（P < 0.05）,分别比对照提高了3.39和2.25个单位;与对照处理相比,酒糟灰渣+化肥处理和石灰+化肥两处理土壤有效态Cd含量分别降低了28.91 %和20.90 %.②酒糟灰渣+化肥处理显著降低了花椒叶片、椒壳和椒籽的Cd含量,降幅分别为31.33 %、30.24 %和34.01 %;花椒各部位对Cd的富集能力不同,具体表现为:叶片 > 枝条 > 椒籽 > 椒壳,与对照相比,酒糟灰渣+化肥处理的花椒各部位富集系数降低最为显著（P < 0.05）,降幅为27.54 %~40.0 %.③改良剂处理下土壤过氧化氢酶和脲酶活性的变化规律相似,相较对照,酒糟灰渣+化肥处理对以上两种酶活性提高最为显著,分别提高了191.26 %和199.50 %,而酸性磷酸酶活性则降低了16.45 %.相关性分析表明,土壤有效Cd含量与土壤pH值呈极显著负相关（P < 0.01）,过氧化氢酶和脲酶活性与土壤pH呈极显著正相关（P < 0.01）,与土壤有效Cd含量呈极显著负相关（P < 0.01）,酸性磷酸酶则完全相反.酸性紫色土壤施用石灰、酒糟灰渣中和土壤酸度效果最显著,在降低土壤有效Cd含量、改善土壤环境的同时,抑制花椒各部位对Cd的吸收和转运,是改良酸性紫色土及防治重金属污染的有效措施.     

水库汞污染研究进展

汞污染是水库环境存在的一个重要问题,本文概述了目前水库汞污染现状、汞的存在形态、汞的迁移转化过程及其动力学模型的研究进展,指出了不足之处,以促进下一步研究。     

北京夏季近地面臭氧及其来源的数值模拟研究

高浓度的近地面臭氧一直是北京夏季面临的主要污染问题,本文利用自主发展的空气质量数值模式WRF-NAQPMS(Weather Research and Forecasting Model-Nested Air Quality Prediction Modelling System)以及生物源排放模式MEGAN(Model of Emission of Gases and Aerosols from Nature),数值模拟了2017年6月华北区域臭氧的时空分布,评估了生物源排放可挥发有机物对臭氧的影响,并对北京臭氧的关键源区和形成时间进行量化解析.结果发现:NAQPMS (Nested Air Quality Prediction Modelling System)模式合理再现了北京及其周边臭氧的时空演变规律,特别是生物源的加入有效改善臭氧浓度的模拟效果.生物源对北京6月臭氧浓度月均值的贡献为4%～6%,对最大1小时浓度的贡献最高可达8%以上.源解析结果发现,本地当天排放的臭氧前体物对北京城区浓度影响最大,对最大1小时浓度和8小时移动平均浓度的贡献达到50.2%和45.4%,远高于1～2天前排放污染物的影响.河北对北京的影响主要集中在当天和1天前排放的污染物,对最大1小时浓度的贡献分别为7.9%和6.5%.河南和山东对北京城区最大1小时浓度的贡献较小,分别为2.4%和3.7%,且主要为1～2天前排放的污染物在区域输送过程中的化学反应所贡献.对于北京区域平均来讲,本地的贡献率较城区明显偏小,河北的贡献显著增加,这也说明北京市臭氧来源的空间不均匀性较大.北京地区生成的臭氧沿怀柔区向北输送,到达承德市西侧,对月均值的贡献达到20～30μg·m~(-3).     

苯酚在饱水细砂土层中的迁移转化规律

本文研究苯酚在细砂土层中的迁移转化规律,包括静态吸附、降解及动态土柱实验三部分.实验结果用计算机进行线性拟合和参数估值.研究结果表明:细砂土对苯酚的吸附能力较差而降解能力较强;在好氧条件下,苯酚更易降解;水中存在的其它有机物在一定时间内会影响苯酚的降解,但随着微生物对苯酚逐渐适应,这种影响可被消除。