Differentiation between lake whitefish and cisco eggs based on diameter

Cisco (Coregonus artedi) and lake whitefish (Coregonus clupeaformis) are native fish species of management concern in the Laurentian Great Lakes that often overlap in spawning locations and timing. Thus, species-level inference from in situ sampling requires methods to differentiate their eggs. Genetic barcoding and hatching eggs to visually identify larvae are used but can be time and cost intensive. Observations in published literature indicate that lake whitefish eggs may be larger than cisco eggs in the Great Lakes, but this has not yet been substantiated. Samples from shared spawning grounds are unlikely to contain similarly sized or colored eggs from other species. Thus, we assessed whether lake whitefish and cisco eggs could be separated based on size alone. Fertilized, hardened eggs were collected in situ during spawning at Elk Rapids, Lake Michigan and Chaumont Bay, Lake Ontario and preserved in ethanol. Individual eggs were measured and genetically identified. Mean diameter for cisco (2.45 mm, SD = 0.22, n = 444) was smaller than for lake whitefish (3.21 mm, SD = 0.20, n = 99). We used classification trees to identify a species-separating size threshold of 2.88 mm (95% bootstrap CI = [2.877, 2.976]), which classified eggs with an accuracy rate of 96%. Differences between species across other samples from the same locations were mostly consistent with the threshold size, but we suggest validation if applying this method to other populations. Separation of cisco and lake whitefish eggs by diameter can be accurate, efficient, and especially suitable for large sample sizes.     

Dynamics of beach-ridge formation along a migrating strandplain with implications for paleo-environmental assessment,Illinois Beach State Park,southwestern Lake Michigan

This paper provides insights into shoreline morphodynamics and ridge-plain physiographic compartmentalization along the migrating Zion Beach-ridge Plain, a mainland-attached strand along the high-energy, wave-dominated SW coast of Lake Michigan. Results of UAS-based topographic monitoring during the recent decadal lake-level high (2018–2020) captured the earliest phase of the ridge-formation process along several beach sites. This process-based study of net-erosional (i.e., littoral updrift) and net-accretionary (i.e., littoral downdrift) parts of the system offers much-needed context for assessing relict strand architectures. Embayed beach-ridge plains of the Laurentian Great Lakes have long served as paleo-environmental archives. They form from water-level changes and can be used to interpret isostacy. The preservation of beach ridges here is facilitated by unidirectional infilling. Much less is known about how nearshore littoral processes impact unconfined strand systems and whether useful paleoenvironmental information absent within embayed system analogs might be elucidated from their complex architecture. We herewith promote a model of punctuated development. Major episodes of shoreline transgression are manifested as continuous ridgelines of topographic prominence that, along the northern, erosive strand, truncate older ridges and are onlapped by younger ones. These major discontinuities reflect environmental changes greater in magnitude than decadal water-level oscillations observed to have formed ridgelines in recent decades. The temporal offset across the most lakeward of these major erosional strandlines is on the order of 1 kyrs and it formed between 1.8 ka and 0.9 ka, based on available C-14 ages, coincidental with a regional shift in dominant storm-wind pattern to one promoting higher-energy littoral dynamics.     

鄱阳湖五河入湖水沙通量及典型断面形态变化特性分析

五河入湖水沙通量及河道形态变化对五河尾闾演变、湖区低枯水位、江湖关系等研究有重要意义。以1956—2018年实测资料为基础,利用Mann-Kendall 检验法和河道特征对五河入湖水沙通量、典型断面形态变化特性及其影响因素进行了研究。结果表明:①五河入湖径流量总体呈小幅度减小态势,2003—2018年五河入湖平均径流量较1956—2002年减小5.3%;②除饶河外,入湖泥沙通量均有不同幅度的减小,其中赣江和信江大幅度减小,2003年后分别减少约72.3%和52.6%;③五河典型断面形态2014年前变化较大,断面多呈锯齿状;随后逐渐恢复正常;④水利枢纽工程、水土保持工程和人工采砂是影响五河入湖泥沙通量和河道形态的主要人为因素。     

Shifting status and distribution of range margin chorus frog (Pseudacris) populations in eastern Great Lakes watersheds

Contiguous with their range across major rivers into Canada, two different species of chorus frogs are now thought to inhabit the Great Lakes watersheds of New York. Pseudacris triseriata is found along the western Lake Ontario and Lake Erie plains while P. maculata (tentatively a new frog species in NY) inhabits the lowlands of eastern Lake Ontario and the St. Lawrence River. Both species are on their extreme range margins in NY. In 2010 we detected distributional declines of both putative chorus frog species based on a broad survey following standardized occupancy detection protocols. Causes are unclear but could relate to reforestation and urbanization of formerly more extensive agricultural lands, climate change, pathogenic fungal outbreaks and/or the contaminant effects of intensive agriculture. On the other hand, the prior overestimation of ranges because of misidentification may have inflated earlier perceived distributions (positive survey bias) because false positives are problematical for this cryptic frog. At broad geographical scales, chorus frog (meta)populations are highly dynamic and are likely shifting their ranges in response to rapidly changing overall environmental conditions in the northeastern U.S. and Canada.     

堰塞湖成因与工程地质问题

为减小堰塞湖的危害,对其成因进行了分析：特殊的地质地貌与河谷斜坡,是形成堰塞湖的内因;降水、地震、加载、坡脚淘蚀或开挖、水位骤然升降、火山爆发、冰河崩解等是形成堰塞湖的诱因。论述了堰塞坝的工程地质问题,并以唐家山堰塞湖为实例,对其抢险处理方案作了介绍,具体为：机械开挖泄流明渠,借水力将其拓宽,逐渐扩大泄流能力,避免发生突然溃坝。对指导堰塞湖的应急处置具有一定的指导作用。     

太湖蓝藻成因分析与清淤方法探讨

分析氮磷比和温度对太湖蓝藻生长与消亡的影响,结果表明,较高质量浓度的TN、TP是太湖富营养化的根本原因,适宜的氯磷比是太湖蓝藻大规模暴发的内因,25℃左右的水温是太湖蓝藻暴发的突变点。针对太湖传统清淤工作中存在的问题,提出了利用高频微幅振动清淤的湖泊淤泥疏浚新技术和清淤与淤灌相结合的综合清淤方案。     

基于马尔科夫模型的污染物质量浓度变化规律

采用马尔科夫模型模拟调水过程中太浦河练塘大桥断面处污染物质量浓度变化过程,并通过构建转移矩阵,确定进步度,对污染物质量浓度的变化情况进行动态评价,研究污染物质量浓度变化规律。结果表明,调水指标的进步度计算结果整体为正,但局部地区出现负值;随着调水量的增加,水体自净能力增强,各指标的进步度普遍提高;调水试验结束进入水资源常规调度期间,水质长时间保持良好。本研究旨在为制定河湖连通调水方案提供借鉴。     

Sediment transport following water transfer from Yangtze River to Taihu Basin

To meet the increasing need of fresh water and to improve the water quality of Taihu Lake, water transfer from the Yangtze River was initiated in 2002. This study was performed to investigate the sediment distribution along the river course following water transfer. A rainfall-runoff model was first built to calculate the runoff of the Taihu Basin in 2003. Then, the flow patterns of river networks were simulated using a one-dimensional river network hydrodynamic model. Based on the boundary conditions of th...     

星海湖湿地综合整治中生态规划与景观设计的思考

通过对近几年星海湖滨水湿地整治建设过程中景观和生态两个方面的问题进行分析思考,总结成功经验和教训,探求一种城市滨水湿地型景观开发与生态保护的新思路、新途径。     

Effects of habitat and fishing on fish assemblages in a tropical reservoir: Lake Kariba,Zimbabwe

This study investigated the effects of habitat and fishing on fish communities along inshore areas of the Sanyati Basin, Lake Kariba. A one‐year experimental gillnet survey was carried out in 2007 from eight sampling sites located in two different habitats (river mouths and sheltered bays), and in areas open or closed to fishing. A total of 16 species were captured, although the numbers caught at each site varied widely, with only four species recorded at each of the eight sampling sites. The numbers of fish were higher in the fished areas, mainly because of large numbers of Synodontis zambezensis, although the differences were not significant. In contrast, there were significant differences in the abundance of all species between habitats, with the exception of Cyphomyrus discorhynchus and Marcusenius macrolepidotus. There were no significant differences in the diversity of fish in these areas, although mean diversity and evenness were slightly higher in unfished areas and in sheltered bays. Overall, 90% of the fish specimens caught were within a 10–25 cm size range, although there were no systematic differences in the mean length in relation to fishing. In contrast, most fish were generally larger in river mouth areas than in sheltered bays. These data suggest that fishing had little effect on fish communities. This is in contrast to general habitat, which had a significant effect, a finding consistent with earlier studies showing that vegetation, in particular, had a significant effect on fish stocks.