磷在富营养化湖泊沉积物-水界面的循环

沉积物中部分固定的磷可通过分解或溶解作用而释放磷酸盐到沉积物间隙水中;再生的磷可能释放到上覆水体中,或在沉积物中作为一种自生相而再沉淀,或被沉积物的其它组分所吸附。本文描述了磷在沉积物-水界面的迁移过程,并对影响磷循环的因子及其磷自沉积物释放的机制作一简要概述。     

Performing Aboriginality: Desiring Pre-contact Aboriginality in Victoria, 1886–1901

This paper re-investigates notions of performed Aboriginality in relation to photographs made at Lake Tyers Mission Station, Victoria, Australia, and argues that Nicholas Caire's photographs reveal complex Aboriginal subjectivities. The photographs, made originally in 1886 and distributed to tourists, were later reproduced and circulated in book format in 1897. The first presentation of the photographs, whilst focusing on historical Aboriginality, contains traces of cross-cultural hybridity. However, the later presentation of the work reinforces historical and traditional material culture over cross-cultural dialogue. This paper argues that the desire to find historical notions of Aboriginality on mission stations in Victoria was not just due to the establishment of hierarchical racial theories in the latter part of the nineteenth century (generating the idea that Aborigines could not change and adapt to notions of ‘civilisation’) and doubts about the success of mission stations, but also because there was an interest in Aborigines who had experienced little assimilation from more remote parts of the continent of Australia. This curiosity in pre-contact Aboriginality fuelled tourism in Victoria to accessible mission stations such as Lake Tyers.     

The perceived risk of the Line 5 Pipeline and spills under ice

Using the psychometric paradigm of risk in conjunction with surveys of the Michigan public (n = 638) and a regional planning organization (n = 65), we examine the perceived risk and concerns associated with underwater oil pipelines, the Enbridge Line 5 pipeline in particular, and oil spills under ice. The fate of Line 5 is heavily debated in Michigan, specifically the portion that traverses the Straits of Mackinac, which can be ice-covered for months. Scant literature examines how individuals perceive the risk associated with Line 5, its alternatives, or potential spills in open water or under ice. Here we identify considerable concern regarding both the pipeline and the potential for spills under ice on behalf of the public, and increased concern about spills under ice on behalf of the planning organization. Organization members' concerns are significantly predicted by beliefs about the difficulty in remediating spills, however not by beliefs about spills' likelihood, difficulty in detection, noticeability, or consequences. Our results identify the need to better examine and communicate the risks associated with underwater pipelines and spills, both in open water and under ice, as well as options for remediating oil captured under ice. Furthermore, we recommend the adoption of decision-making and risk governance processes that explicitly expand analysis of the social, economic and environmental tradeoffs of underwater pipelines such as Line 5.     

Vertical oscillations of the thermocline caused by internal waves modify coldwater pelagic fish distribution: Results from a large stratified lake

Fishes typically occupy a species-specific temperature range, with their occupied depth being related to the lake’s temperature profile. When a fish’s preferred temperature range coincides with the thermocline, the location of their preferred thermal habitat is influenced by the rise and fall of internal waves, leading to possible changes in fish depth. These internal waves are common in large, stratified lakes, yet we do not know how they affect the spatial distribution and behavior of freshwater fishes. We conducted nighttime hydroacoustic surveys in a large, deep embayment of a large thermally stratified lake to observe whether pelagic fish respond to vertical oscillations of the thermocline caused by internal waves. The coldwater pelagic fish in our study (primarily cisco, Coregonus artedi) typically occupied a narrow vertical band approximately 5–8 m thick and temperatures between 10.8 ± 0.8–13.6 ± 1.6 °C (fishes sized 106–500 mm), just below the thermocline (centered around 15–17 °C). Importantly, the upper bound of fish depth varied in response to vertical thermocline movements associated with internal waves, suggesting fish respond to changes in their physical environment on timescales commensurate with basin-scale internal wave periods (hours to days), to remain within their preferred thermal habitat. Dissolved-oxygen levels were typically above avoidance thresholds of these fish, thus not likely exerting a strong influence on fish location. Our findings emphasize the need to account for internal waves when designing hydroacoustic and netting surveys, as thermocline movements can influence where fish are located.     

Performance of a pavement foundation system based on the partial compensation of masses method

The system of the partial compensation of masses in the lacustrine zone of the Mexico Basin has been conceptualized, developed, used and improved over the past five decades as a foundation alternative for different types of roadways. This kind of foundation has been used in highways and runways built on lacustrine soils to reduce the settlement that can affect the service and operation conditions of those structures. In the construction of the new Mexico City International Airport in the Texcoco Lake area, various alternatives for runway foundations were evaluated through different test sections that were constructed to identify which of them would yield an adequate transfer of stress and prevent excessive total and differential deformations of the soil deposits. In this work, the behavior of the test section of the system of the partial compensation of masses, built in the Texcoco Lake area, is studied. An exploration campaign was performed; it consisted of different field and laboratory tests to determine the stratigraphic profile and the index and mechanical properties of the soil strata. Numerical models were applied using the finite element software PLAXIS 2D to analyze the behavior of the test section and to determine the maintenance frequency required to preserve the functionality of future runways. To validate the capability of the numerical models to properly simulate the stress-strain behavior of the test section, a comparative analysis was performed between the data obtained from the instrumentation installed on the test section and the results obtained from the finite element software. Once the numerical models were calibrated, the medium- and long-term behaviors of the test section were predicted, and the evolution over time of its surface geometry and transverse slopes were obtained.     

Development and application of a real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands,Lake Superior

Assessing all pertinent environmental variables to categorize a skill level to safely navigate the water environment can be difficult for inexperienced kayakers, especially at a remote site where internet access is limited. A real-time kayaker safety assessment of water environmental conditions at the Mainland Sea Caves of the Apostle Islands National Lakeshore, Lake Superior is achieved. We present a new cyberinfrastructure that provides kayakers with real-time data access and a Safety Index (SI) with consideration of multiple environmental factors to characterize the degree of navigational difficulty for classifying kayaker skill levels. Specifically, radar reflectivity is added to improve forecasts of dangerous conditions caused by convective storms using state-of-the-art weather and wave modeling. Spectral characteristics of surface waves are employed to correlate the occurrences of extreme and freak waves. In addition, unexpectedly dangerous conditions like coastal upwelling and freak wave occurrence due to changing wind directions are considered. A contingency plan is implemented to handle the issue of possibly missing required environmental data. Display of the SI and visualization of other real-time environmental data are communicated by a power-efficient kiosk. Web analytics demonstrates a public interest in real-time water conditions and the need for the on-site kiosk to provide the latest information before kayakers enter the water. The new real-time water environment cyberinfrastructure for kayaker safety in the Apostle Islands, Lake Superior has been successfully operated since 2014.     

Diet composition and overlap for adult walleye,lake whitefish,and yellow perch in Green Bay,Lake Michigan

Interspecific interactions among walleye Sander vitreus, lake whitefish Coregonus clupeaformis, and yellow perch Perca flavescens in Green Bay could influence the population status of each species, but potential trophic interactions are poorly understood. Our objectives were to determine if diet assemblages for each species and diet overlap among species varied spatially and temporally within Green Bay. Adult walleye (≥381 mm total length (TL); N = 981), lake whitefish (≥432 mm TL; N = 1507), and yellow perch (≥150 mm TL; N = 1174) were collected during May-October of 2018 and 2019 from multiple locations in southern and northern Green Bay. Diet assemblages of each species varied between northern and southern Green Bay, but walleye diets were more temporally variable (among months within zones and between years) than diets of lake whitefish or yellow perch. Lake whitefish represented a seasonally important prey item for walleye in southern Green Bay, composing 10 % and 41 % of walleye diets by weight in May and June, respectively. Yellow perch generally composed <15 % of walleye diets by weight but were consumed at a broader spatiotemporal scale than lake whitefish. Diet overlap between walleye and both lake whitefish and yellow perch was generally weak or moderate, whereas diet overlap between whitefish and perch was generally strong. Our assessment of adult trophic interactions suggests that changes in the population status of one species could influence fisheries for all three, and we identify additional research questions to address potential population-level effects of these trophic interactions.     

Can otolith microchemistry identify the natal origin of larval lake whitefish Coregonus clupeaformis in the waters of Green Bay?

Lake whitefish Coregonus clupeaformis play a key role in the socioeconomics of the Laurentian Great Lakes region and serve as an important conduit of energy among trophic levels. Lake wide declines in adult abundance creates the need for improved understanding of population dynamics, currently hampered by a lack of early life history information and resolution of subpopulation structure. We predicted that otolith microchemistry had the potential to broaden our understanding of lake whitefish ecology by determining the natal origin of larvae at a resolution (e.g., spawning location) unachievable with other techniques. To test this prediction, in 2017 and 2018, recently hatched, pelagically-drifting lake whitefish larvae were collected from the open waters of Green Bay, Lake Michigan and four large tributaries (Menominee, Fox, Oconto and Peshtigo Rivers), where spawning activity has been recently documented. Linear discriminant function analyses conducted at the broadest level of resolution (i.e., river vs. open-water origin) correctly assigned 80.5% and 75.0% of individuals to their natal location in 2017 and 2018, respectively. Reclassification success at a finer resolution (i.e., specific rivers) ranged from 75.9% in 2017 to 42.1% in 2018. We discuss these promising results with respect to underlying variation in geological features, water chemistry and interannual river conditions that eggs and larvae experience during incubation and before prolonged drift.     

The thermal behaviour of French water bodies: From ponds to Lake Geneva

The management of French freshwater bodies (lakes, reservoirs, ponds, etc.) needs to face the challenges imposed by the effects of climate change and by legal requirements to develop standards for water temperature and other physicochemical indicators. While 1D hydrodynamical models could be helpful in improving the knowledge of the thermal and hydrodynamic behaviour of French water bodies, the scarcity of data for calibration and validation, in addition to the unavailability of some forcing data, makes their application difficult for most French water bodies. In this article we explore an alternative statistical approach that takes advantage of the available data in order to inform future modelling applications. We used official monitoring data and satellite measurements to study the thermal characteristics of more than 400 French water bodies (depth: 1–310 m, surface area: 0.1–577 km², volume: 0.1–89,000 hm³). The objective was to identify the importance of size on their thermal behaviour. For this we analysed the annual temperature cycle, the summer temperature profiles and within-lake spatial variability. Together with size, geography and transparency determine the thermal behaviour of water bodies through complex interactions. As a result of the analysis we propose a classification of French water bodies as a function of depth and surface area that reflects the summer vertical temperature gradient and the processes influencing the deepening of the thermocline.     

The distribution,density, and biomass of the zebra mussel (Dreissena polymorpha) on natural substrates in Lake Winnipeg 2017–2019

The distribution, density, biomass and size-structure of the zebra mussel (Dreissena polymorpha) population in Lake Winnipeg were examined between 2017 and 2019. Zebra mussels have colonized most of the available hard substrate in the south basin and Narrows region, but colonization of the north basin remains low at present, even on suitable substrate. Numerical densities and shell free biomass peaked at 5530 ± 953 m^?2 and 64.7 ± 57.9 g shell free dry mass m^?2 respectively. The distribution appeared to be strongly limited by substrate type and availability, with further limitations on the distribution imposed by physical disturbance in shallow waters and unsuitable substrate in deeper areas of the lake. Zebra mussels <1 year old dominated the populations, and individuals >18 mm were exceedingly rare. Poor recruitment was observed at sites along the eastern side of the south basin compared to elsewhere in the lake. The proximate causes of these differences in colonization success and recruitment are not clear, but may be in part due to heterogeneous patterns of key physico-chemical environmental conditions such as calcium concentrations required for successful development of juvenile mussels and colder water temperatures in the north basin. This study provides a baseline of information on which to track further expansion of zebra mussels in Lake Winnipeg and assist efforts to develop an understanding of how zebra mussels may affect the ecology of Lake Winnipeg.