Chemistry,Mineralogy, and Morphology of Lake Erie Suspended Matter

Suspended matter was collected from different depths at three stations in spring and summer, 1978, in Lake Erie. Chemistry, mineralogy, and morphology of the suspended particles were measured to investigate spatial and temporal changes. The determined elements (Si, Fe, Ca, K, Mn, P, Al, Ti, and Mg) were partitioned between inorganic and biological material and the majority of these elements were present in at least two different chemical forms. Flocculates > 3 μm composed of organic material and mineral fragments were common at the water surface and the middle of the water column. Mineral fragments < 3 μm were the major constituent of suspended matter at the bottom at the deepest sampling station (62 m). The concentration of the major components of the suspended matter, organic material, alumino-silicates, and calcite, varied significantly from spring until later summer. The high concentration of organic material and the fluctuations of calcite concentration result from high rates of photosynthesis and respiration and temperature increases in spring and summer.     

Hypolimnion Flow Between the Central and Eastern Basins of Lake Erie During 1977 (Interbasin Hypolimnion Flows)

The shallow central basin of Lake Erie (mean depth 19 m) is separated from the deeper eastern basin (mean depth 28.5 m) by the Pennsylvania Ridge which extends southward from the base of Long Point to Erie, Pennsylvania. The crest of the ridge lies at a depth of 15 m except for a narrow notch near Erie, Pennsylvania, where communication between the two basins extends to 24 m depth. Both basins are stratified in summer, and the thin (2 m) hypolimnion of the central basin becomes depleted of oxygen by late summer. Flows to the hypolimnion of the central basin from the mid thermocline water of the eastern basin have been thought to be important sources of dissolved oxygen to the central basin.Data from ship cruises and current meter moorings made in 1977 have been used to form an estimate of the hypolimnion flux across the sill area. A strong correlation between winds and mean flux is observed and the dynamic balance appears to be one where surface pressure gradient created by wind stress is opposed by internal pressure gradients and by bottom friction. While the total quantity of oxygen transported by the subsurface flow is significant in terms of the later summer oxygen consumption of the central basin hypolimnion, its effects are confined to the eastern half of that basin due to the relatively weak horizontal diffusion in the mid-basin hypolimnion.     

Cone-Shaped Hypolimnion and Local Reactor as Outstanding Features in Eutrophication of Lake Maracaibo

Between 1974 and 1979 a large-scale research program to identify and evaluate the pollution problems in tropical Lake Maracaibo was undertaken. Two unique limnological features investigated during this program were a cone-shaped hypolimnion in the center of the lake and an area of unusually high biologic activity within the northeastern coastal area. With respect to the cone-shaped hypolimnion, epilimnetic water moves counterclockwise around the cone like a large-scale vortex. Anoxic conditions, high salinity, and exceedingly high N and P concentrations are found in the hypolimnetic cone. It functions as an internal source of nutrients throughout the year at tropical temperatures. The northeastern coastal area, where massive blooms of algae are an established feature, is likened to a biological reactor. It is characterized as a relatively low energy zone in relation to the horizontal movement of the water in the rest of the lake.     

Observations of Sediment Transport in Lake Erie during the Winter of 2004–2005

Time series measurements of current velocity, wave action, and water transparency were made at two sites—one in 24 m of water and the other in 53 m—in Lake Erie during the fall and winter of 2004–2005. The observations at the shallow site show that bottom resuspension occurred several times during the deployment. Although local resuspension did not occur at the deeper station, several advection episodes were observed. The storms during the observation period were not unusually large, so the processes observed are probably typical of those that occur on a yearly basis. The observations agree reasonably well with previous estimates for both the bottom shear stress during storms, and for the critical shear stress needed to resuspend bottom sediment, but previous estimates of the particle settling velocity are probably too low, while previous estimates of the sediment entrainment rate are too high. The results show that bottom material in the central basin is reworked numerous times before it is finally buried. Deposition in the eastern basin is a more continuous process, but the events observed were not sufficient to match the long-term accumulation rate, so deposition at this site is probably also due in part to larger, more infrequent storms.     

Round Goby and Mottled Sculpin Predation on Lake Trout Eggs and Fry: Field Predictions from Laboratory Experiments

The accidental introduction of round gobies (Neogobius melanostomus) into the North American Great Lakes has raised concerns about their potential impacts on local fauna. Gobies have similar habitat and spawning requirements to mottled sculpins (Cottus bairdi) and slimy sculpins (C. cognatus), and may already be displacing sculpins where the ranges of the species overlap. Like sculpins, gobies are capable of penetrating interstitial spaces to acquire food, and therefore may become predators of interstitially incubating lake trout eggs. Laboratory experiments were conducted to compare egg consumption rates and critical size (the minimum size at which a fish was capable of ingesting an egg) between round gobies and mottled sculpins. Predation by both species on lake trout eggs and fry was also examined in two grades of substrate (cobble and gravel). Mottled sculpins consumed larger numbers of eggs than round gobies of similar size, and were capable of ingesting eggs at smaller sizes than gobies. Both gobies and sculpins had lower foraging success on smaller substrates (gravel) than on cobble. Gobies are currently present at higher densities than sculpins in areas where they are established in the Great Lakes. The similar predation of lake trout eggs by round gobies and mottled sculpin and high densities the goby has achieved at some Great Lakes sites leads to the prediction that the round goby may negatively affect lake trout reproduction and therefore rehabilitation.     

Calibration of a Hydraulic Transport Model for Green Bay,Lake Michigan

The U.S. Environmental Protection Agency (USEPA) has developed and implemented a comprehensive plan for modeling the transport and fate of toxic chemicals in Green Bay, Lake Michigan. Characterization of the hydrodynamic behavior of Green Bay was a key step in the model calibration process. To accomplish this, the WASP4 finite-segment model framework was calibrated to describe chloride dynamics during an 18-month period (Jan 1989 to May 1990). Extensive use was made of field data (currents, water temperature, wind, and ice cover), and new interpretations of these data were developed. The direction of circulation in Green Bay typically reverses every three to five days during open water periods; these reversals are closely correlated to wind direction relative to the axis of the Bay. Inflows from Lake Michigan exceed the combined inflows of all tributaries by over twenty times; the circulation of these inflows through Green Bay are greatly enhanced each spring when the ice cover melts. During open water periods, bulk dispersion coefficients typically range from 20 to 120 m²/s in the longitudinal direction, and from 5 to 40 m²/s in the transverse direction. The calibrated advection and dispersion fields accurately describe the major hydrodynamic features of Green Bay, and were incorporated into input data sets for models of eutrophication, organic carbon sorbents, and toxic chemicals.     

Seasonal Hypoxia and the Genetic Diversity of Prokaryote Populations in the Central Basin Hypolimnion of Lake Erie: Evidence for Abundant Cyanobacteria and Photosynthesis

The reoccurring region of seasonal hypoxia in the central basin of Lake Erie (“the dead zone”) has been of significant interest to researchers over the past several years. Surprisingly however, no efforts to characterize the endemic microbial community, responsible for the consumption of oxygen in this system, have been published. To understand how the microbial community may be interacting with this event, we have begun to characterize microbial members by using molecular tools. Phycoerythrinrich cyanobacteria appear abundant and active in a narrow region (∼ 1.5 m) below the thermocline during hypoxic conditions, reaching abundances of greater than 10⁵ mL⁻¹ and being the primary agent releasing 1.5 mg O₂ L⁻¹ above the daytime demands in this region. Sequencing of 16S rDNA amplicons, generated with universal eubacterial primer sets, from the Lake Erie's hypolimnion during seasonal oxygen depletion demonstrated that cyanobacteria, most closely related to phycoerythrin-rich Synechococcus spp., dominate during rapid drawdown of oxygen (0.083 mg L⁻¹ d⁻¹ in 2004) in this region. Analyses of another conserved marker of phylogeny (RuBisCO) has been used to confirm the presence of these cell types. Numerous distinct taxa of heterotrophic bacteria are also represented in the 16S library. The results of this study suggest that novel groups of cyanobacteria may persist within the Lake Erie dead zone during hypoxic conditions and, along with the heterotrophic community, strongly influence system geochemistry.     

Simulation of Runoff and Suspended Sediment Transport Rate in a Basin with Multiple Watersheds

Accurate runoff and suspended sediment transport rate models are critical for watershed management. In this study, a physiographic soil erosion–deposition (PSED) model is used in conjunction with GIS, to simulate the runoff and sediment transport process during storm events in a multi-watershed basin. This PSED model is verified using three typhoon events and 33 storm events in Cho-Shui River Basin, located in central Taiwan. Cho-Shui River Basin has 11 sub-watersheds displaying a variety of hydrologic and physiographic conditions as well as high concentrations of suspended sediment in river flow and a steep average channel bed slope of 2%. The results show the capability, applicability, and accuracy of the PSED model for multi-watershed basins.     

Seasonal variation in trophic structure and restoration effects in a deep perialpine lake (Lake Lugano,Switzerland and Italy)

Using monitoring data from the South Basin of Lake Lugano (Switzerland and Italy), we examined seasonal responses of phytoplankton and herbivorous zooplankton biomass to nearly three decades (1989–2017) of phosphorus (P) management to ask: [1] what is the trophic structure of the lake, [2] whether trophic structure and the effects of nutrient management varied seasonally, and [3] what are the implications of the existent trophic structure for the restoration of the lake. Trophic structure varied seasonally, including a structure consistent with strong consumer control (exploitation food chain) in spring and fall, and an unexpected structure in summer, characterized by a negative correlation between phytoplankton biomass and phosphorus. This structure was explained by accumulation of inedible phytoplankton (mainly cyanobacteria) at low P concentrations. Owing to a lack of apparent resource (P) control, P-management had no detectable effects on phytoplankton biomass. The trophic structures identified in the lake provides explanations for this lack of response to P-management and for the differences between the responses of the South Basin of Lake Lugano and other perialpine lakes. Based on the results, lake restoration practice would benefit from a greater understanding and an increased ability to predict trophic structure within and across lakes.     

大窑湾潮及悬浮物沉降扩散的数值模拟

本文结合大窑湾港区建设的实际工程，计算了大窑湾潮流场及悬浮物浓度的沉降扩散。采用垂向平均的二维潮流场模型，其开边界条件考虑了海湾内潮波反射的影响，潮流场的计算结果与实测值比较符合。对具有沉降项的悬浮物浓度对流扩散方程也采用垂向平均处理，给出了其合理的表达，结合潮流场的实测及计算数据，确定了沉降项中的参数，计算的浓度分布结果为工程环境评价提供了有益的依据。     

汕尾电厂进港航道疏浚悬浮物扩散数值模拟

利用交替方向隐格式(ADI法),首先对工程海域潮流场进行了数值模拟,进而建立了工程海域疏浚悬浮物的二维输运——扩散模型,并应用于汕尾电厂进港航道疏浚区的悬浮物输运扩散数值模拟预测,根据预测结果分析了进港航道疏浚区施工期间悬浮物对附近水环境的影响。     

The Vertical Distribution of Runoff and its Suspended Load in Lake Malawi

Lake Malawi, in south-eastern Africa, is subject to increasing loading of suspended solids caused by land use pressure in its watershed. Whether this load is transported into the lake as overflow, interflow or deep underflow determines to a large extent its effect on the lake ecosystem. In this paper, vertical distributions of suspended solids in the Linthipe River delta region of the lake are described from multiple surveys during two rainy seasons. These data are supplemented by data from a single survey near four northern rivers also tributary to the lake. Profiles of temperature, conductance, and suspended solids concentrations (SSC, estimated from optical backscatter and beam transmission) are used to identify fluvial intrusions into the water column. Most inflow plunged to the seasonal metalimnion where it spread along high density gradients as interflow. While SSC in surface plumes rarely exceeded 10 g m⁻³, and in intrusions in the lower metalimnion was rarely greater than 1 g m⁻³, concentrations up to 420 g m⁻³ were recorded in interflow near the thermocline. Although storm runoff density often exceeded 100 m depth-equivalence in the lake, underflow density was reduced to metalimnion-equivalence (30–50 m depth) within a few 100s of meters of the river mouth. We attribute bottom-attached turbid layers, and the few unattached turbid layers in the lower metalimnion, all with positive conductance anomalies, to sediment resuspension and not to runoff. We conclude that the upper metalimnion is the prevailing pathway carrying watershed runoff horizontally throughout Lake Malawi.     

丰满水库入库悬移质输沙特性变化及其原因分析

本文通过对红石砬子、五道沟等站河道输沙量及不同时期输沙量分布特性等资料的分析,论述了该水域水沙关系的变化趋势和规律,指出了水利工程拦沙、水土流失治理是丰满水库入库悬移质输沙量特性发生变化的主要原因。     

Trophic evolution of Lake Lugano related to external load reduction: Changes in phosphorus and nitrogen as well as oxygen balance and biological parameters

Lake Lugano is located at the border between Italy and Switzerland and is divided into three basins by two narrowings. The geomorphologic characteristics of these basins are very different. The catchment area is characterized by calcareous rock, gneiss and porphyry; the population amounts to approximately 290 000 equivalent inhabitants. The external nutrient load derives from anthropogenic (85%), industrial (10%) and agricultural (5%) sources. The limnological studies carried out by Baldi et al. (1949) and EAWAG (1964) revealed early signs of eutrophication, with a phosphorous concentration of about 30–40 mg m^–3 and an oxygen concentration of less than 4 g m^–3 in the deepest hypolimnion. Subsequently Vollenweider et al. (1964) confirmed these data and was the first to point out the presence of a meromictic layer in the hypolimnion of the northern basin. From the 1960s, as a result of an increase in the population and internal migration, the lake became strongly eutrophic with the P concentration reaching 140 mg m^–3 and the oxygen in the hypolimnion reduced to zero. Fifty‐five per cent of the P was from metabolic sources and 45% from detergents and cleaning products. In 1976, a partial diversion of waste water from the northern to the southern basin was begun, and gradually eight waste water treatment plants came into operation using mechanical, chemical and biological treatments. In 1986, Italy and Switzerland began to eliminate the P in detergents and cleaning products. Since 1995, the main sewage treatment plants have improved their efficiency by introducing P post‐precipitation, denitrification and filtration treatments. The recovery of the lake is due to be completed by the year 2005. Altogether, during the last 20 years recovery measures have reduced the external P load from about 250 to 70–80 tonnes year^–1; the goal to be reached is 40 tonnes year^–1. In‐lake phosphorous concentrations have decreased from 140 to 50–60 mg m^–3, with the target at 30 mg m^–3. Dissolved oxygen concentration is satisfactory only between the depths of 0 and 50 m, falling rapidly to zero in the deepest layers. Below a depth of 90 m, high CH₄, HS^–, NH₄⁺, Fe²⁺ and Mn²⁺ concentrations exist. Primary production has decreased from 420 to 310 g C_ass m^–2 year^–1, notwithstanding an increase in the thickness of the trophogenic layer. Structure and dynamic biomass show marked changes: phytoplankton dry weight has decreased from 16 to 7 g m^–2, while zooplankton dry weight has increased from 3 to 4.5 g m^–2. Chlorophyll concentration has fallen from 14 to 9 mg m^–3 and Secchi disk transparency has increased from 3.5 to 5.5 m. The current sources of the external load are uncollected small urban conglomerations, storm‐water overflows from outfall sewers, and the residual load from sewage treatment plants, particularly those without P post‐precipitation.     

Nearshore-offshore exchanges in multi-basin coastal waters: Observations and three-dimensional modeling in Lake Erie

Nearshore-offshore exchanges through upwelling events and subsequent formation of internal Kelvin waves and coastal-jets are expected in the multi-basin coastal waters of Lake Erie; however, these phenomena have yet to be confirmed in the field or numerically modeled. Here, we demonstrate these physical processes in Lake Erie through extensive field data analysis and high-resolution three-dimensional hydrodynamic modeling. The validated model successfully reproduces dominant physical processes in the offshore and nearshore waters including surface seiches (~14?h), near-inertial waves (~17?h) and upwelling events (5–10?days). We show that upwelling events are the predominant nearshore physical processes, and are energized when winds accelerate the epilimnetic waters to the south, causing the thermocline front to move up into the north shore. After the wind subsides, the elevated thermoclines simultaneously form two separate cyclonically propagating internal Kelvin waves in the central and the eastern basins following by two coastal-jets at phase speeds of 0.22?ms^?1 and 0.37?ms^?1 within 5–15?km off the shoreline, respectively. The predominant south-west winds limit the presence of Kelvin waves only to the northern parts of each basin, where the bathymetry allows, and disappear when shoreline morphology no longer maintain these waves due to nonzero cross-shore transports at the coastal boundary layer. Intrusions of hypolimnetic waters through upwelling events contribute 10–30% to the net cross-shore transport, and are most pronounced in May and June when the offshore thermocline is shallow. The intermittent strong westward nearshore currents by Kelvin waves are in the opposite direction of seasonal eastward currents.     

Observations of Hydra from a Submersible at Two Deepwater Sites in Lake Superior

During a series of submersible dives at depths of 300 m and 400 m in southeastern Lake Superior, Hydra were observed attached to a variety of hard substrates including individual rocks, the edges of large boulders, and the undersurfaces of sandstone ledges. Although widespread, populations were generally found in distinct clumps. Based strictly on morphological features, the species resembled H. littoralis or H. carnea. The finding of Hydra at depths of 400 m in Lake Superior, the deepest sounding in the Great Lakes, would indicate that Hydra are not limited by depth.     

A Semi-Lagrangian Study of Circulation and Transport in Lake Ontario

A particle tracking model (PTM) is linked with a hydrodynamic model to evaluate mean seasonal circulation patterns in Lake Ontario, and also to provide a basis for predicting movement of algal blooms. The PTM is based on a random walk algorithm that combines a deterministic advective component with a stochastic component associated with the turbulent diffusivity field to calculate trajectories of neutrally buoyant particles, where both the advective and diffusive velocities are obtained from the hydrodynamic model. Mean circulation is calculated using 30-year average meteorological forcing data collected from five stations around the lake. Seasonal variations in lake circulation are demonstrated, and a clockwise flow in the eastern basin during summer and early fall is identified, contrary to some previous observations that suggest counterclockwise flow. The impacts of Niagara and St. Lawrence river flows on general lake circulation are found to be small, except within approximately 10 km of the river mouth. Development and application of the PTM demonstrate its potential to provide calculations of (Lagrangian) movements as determined from the hydrodynamic output, and to serve as a first step toward development of an algal transport model. Particle tracking helps to visualize flow patterns and provides a means of evaluating the probability a bloom will reach a specified area, given an initial position and the predicted velocity and diffusivity fields. This capability, when set up for real-time applications, can provide an important tool to support management decisions that may be needed when a bloom is observed, for example in predicting potential impacts of the bloom on a beach or a water intake.     

悬移质模型沙级配的模拟计算方法探讨

对于研究泥沙问题的动床模型试验，模型沙的选择是模型设计的关键。模型沙的选择是指综合考虑所研究问题的性质，已知条件，模型几何比尺，以满足模型与原型的水沙运动相似为目的，选定，设计模型沙的材料，比重和粒径级配，作者主要阐述悬移质模型沙级配的模拟方法，并提出利用沙玉清公式计算，设计模型沙级配的另一种方法，以尽可能严格满足模型相似条件。克服老方法的不足和缺陷。