Anthropogenic contributions to mercury levels in present-day Arctic animals—A review

Background

Because of concern about the recently increasing levels of biological Hg in some areas of the Arctic, we examined the literature concerning the long-term changes of Hg in humans and selected Arctic marine mammals and birds of prey since pre-industrial times (i.e. before 1800 A.D.), to determine the anthropogenic contribution to present-day Hg concentrations and the historical timing of any changes.

Methods

Mercury data from published articles were extracted on historical and pre-industrial concentrations as percentages of the recent maximum, as well as the man-made contribution was calculated and depicted in a uniform manner to provide an overview of the development over time.

Results and discussion

Trends of [Hg] in hard tissues such as teeth, hair and feathers consistently showed that there had been an order-of-magnitude increase of [Hg] in Arctic marine foodweb-based animals that began in the mid- to late-19th Century and accelerated in the 20th Century. The median man-made contribution to present-day Hg concentrations was 92.4% ranging from 74.2 to 94.4%. Confidence in our data was increased by accompanying data in some studies on stable isotopes (δ¹³C, δ¹⁵N), which allowed us to normalize where necessary for changes in animal trophic position and feeding location over time, and by careful attention to the possibility of sample chemical diagenesis (Hg contamination or loss) which can alter the Hg content of ancient hard tissues.

Conclusions

Wildlife hard tissue matrices provide consistent information with respect to the steep onset of Hg exposure of Arctic wildlife beginning in the latter half of the 19th Century. Today the man-made contribution was found to be above 92%. Stable isotope analyses provide important information to normalize for possible changes in diet over time, and are highly relevant to include when interpreting temporal trends, baseline concentrations as well as man-made anthropogenic contribution of Hg.     

参数模糊自整定PID控制器在恒压供水系统中的应用

本文提出了一种基于模糊控制理论的恒压供水系统,针对传统PID控制器的特点,将模糊控制技术引入到PID参数自整定过程中,根据不同情况在线自整定PID参数,并采用变频调速技术,节能效果明显,有一定的理论与实际应用价值.     

Paleolimnological proxies reveal continued eutrophication issues in the St. Lawrence River Area of Concern

Recent surface-water surveys suggest that high nutrient concentrations and nuisance algae remain issues in the St. Lawrence River Area of Concern (AOC) at Cornwall, Ontario, specifically in the tributaries and nearshore zones of Lake St. Francis (LSF). In particular, it is unclear whether management actions designed to reduce nutrient inputs, first implemented in the 1990s as part of the Remedial Action Plan for the AOC, have reduced algal production or influenced assemblage composition. To address this issue, a paleolimnological approach was used to provide a historical context for the present-day nutrient concentrations and to quantify the extent of change in water quality in LSF since the early 1990s. A sediment core was collected near the north shore of LSF and was examined for changes in the concentrations and compositions of fossil diatoms and pigments, as well as stable isotope (δ¹⁵N and δ¹³C) values. Analyses of diatom and pigment concentrations indicated that overall algal abundance has risen in the last few decades, including trends of increasing occurrences of potentially toxic cyanobacteria, despite ongoing remediation efforts. Temporal patterns of stable isotope signatures in the core suggest a steady increase in nutrient influx since the mid-20th century, with the post-1990 increase in algal production likely attributable to recent inputs associated with land-use changes in local contributing watersheds. These patterns suggest that the AOC delisting goals for the LSF tributaries will not be reached without a drastic change in land management practices.     

A Bolasso based consistent feature selection enabled random forest classification algorithm: An application to credit risk assessment

Credit risk assessment has been a crucial issue as it forecasts whether an individual will default on loan or not. Classifying an applicant as good or bad debtor helps lender to make a wise decision. The modern data mining and machine learning techniques have been found to be very useful and accurate in credit risk predictive capability and correct decision making. Classification is one of the most widely used techniques in machine learning. To increase prediction accuracy of standalone classifiers while keeping overall cost to a minimum, feature selection techniques have been utilized, as feature selection removes redundant and irrelevant attributes from dataset. This paper initially introduces Bolasso (Bootstrap-Lasso) which selects consistent and relevant features from pool of features. The consistent feature selection is defined as robustness of selected features with respect to changes in dataset Bolasso generated shortlisted features are then applied to various classification algorithms like Random Forest (RF), Support Vector Machine (SVM), Naïve Bayes (NB) and K-Nearest Neighbors (K-NN) to test its predictive accuracy. It is observed that Bolasso enabled Random Forest algorithm (BS-RF) provides best results forcredit risk evaluation. The classifiers are built on training and test data partition (70:30) of three datasets (Lending Club’s peer to peer dataset, Kaggle’s Bank loan status dataset and German credit dataset obtained from UCI). The performance of Bolasso enabled various classification algorithms is then compared with that of other baseline feature selection methods like Chi Square, Gain Ratio, ReliefF and stand-alone classifiers (no feature selection method applied). The experimental results shows that Bolasso provides phenomenal stability of features when compared with stability of other algorithms. Jaccard Stability Measure (JSM) is used to assess stability of feature selection methods. Moreover BS-RF have good classification accuracy and is better than other methods in terms of AUC and Accuracy resulting in effectively improving the decision making process of lenders.     

Seasonal patterns in hydrochemical mixing in three Great Lakes rivermouth ecosystems

Rivermouth ecosystems in the Laurentian Great Lakes represent complex hydrologic mixing zones where lake and river water combine to form biologically productive areas that are functionally similar to marine estuaries. As urban, industrial, shipping, and recreational centers, rivermouths are the focus of human interactions with the Great Lakes and, likewise, may represent critical habitat for larval fish and other biota. The hydrology and related geomorphology in these deltaic systems form the basis for ecosystem processes and wetland habitat structure but are poorly understood. To this end, we examined hydrogeomorphic structure and lake-tributary mixing in three rivermouths of intermediate size using water chemistry, stable isotopes, and current profiling over a five-month period. In rivermouths of this size, the maximum depth of the rivermouth ecosystem influenced water mixing, with temperature-related, density-dependent wedging and layering that isolated lake water below river water occurring in deeper systems. The inherent size of the rivermouth ecosystem, local geomorphology, and human modifications such as shoreline armoring and dredging influenced mixing by altering the propensity for density differences to occur. The improved scientific understanding and framework for characterizing hydrogeomorphic processes in Great Lakes rivermouths across a disturbance gradient is useful for conservation, management, restoration, and protection of critical habitats needed by native species.     

Trophic ecology of salmonine predators in northern Lake Huron with emphasis on Atlantic salmon (Salmo salar)

Pacific salmon were introduced to the Great Lakes in the 1960s and now support major recreational fishery. Population declines resulting from invasive species have prompted agencies to consider diversifying sport fisheries through stocking. Atlantic salmon are native to Lake Ontario, but a small fishery has developed in northern Lake Huron since the 1990s that appears suited to the Lake Huron food web leading to requests for increased stocking by anglers and consideration by agencies. However, no study has evaluated the trophic ecology of Atlantic salmon in relation to other salmonine predators in northern Lake Huron. In this study, we used stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N), along with mercury (Hg) concentrations to assess resource use, niche overlap, and contaminant accumulation in Atlantic salmon compared to select Lake Huron predators. Atlantic salmon exhibited considerable niche overlap with Chinook and coho salmon but were strongly differentiated from lake trout. In addition, we observed that Atlantic salmon had similar Hg concentrations as coho but were lower than both Chinook salmon and lake trout. Based upon the relationship between fish size, δ¹⁵N, and Hg, Atlantic salmon bioaccumulate Hg similarly to Pacific salmon but likely have lower consumptive demands than Chinook salmon. Continued attention should be placed on understanding how Atlantic salmon fit into the current Lake Huron food web in order to evaluate the long-term efficacy of the Atlantic salmon stocking program.     

Improved efficiency,stable spectra and low efficiency roll-off achieved simultaneously in white phosphorescent organic light-emitting diodes by strategic exciton management

Despite their merits of high efficiency and environmental friendliness, phosphor based white organic light-emitting diodes (WOLEDs) for commercial applications still face tough challenges of efficiency roll-off and color stability. Herein, we fabricated high-efficiency phosphor WOLEDs with extremely low roll-off and stable white emission by employing mixed spacer layer between the two complementary emissions as well as mixed host in the orange layer. The strategic exciton management in our proposed device structure greatly balanced the transport of charge carriers due to the excellent exciton manipulation of the mixed spacer, and significantly suppressed the exciton quenching owing to the extended exciton recombination region, which significantly minimized the efficiency roll-off of the fabricated WOLEDs. The resulting phosphor WOLED exhibited the maximum current efficiency (CE) and power efficiency (PE) of 47.5 cd A⁻¹ and 44.7 lm W⁻¹, respectively, and the CE still had 43.1 cd A⁻¹ at 5000 cd m⁻², showing a suppressed efficiency roll-off of only 9.2%. Additionally, the device achieved fairly stable spectra over a wide range of luminance with suitable CIE coordinates for indoor lighting and outdoor displays.     

Importance of environmental flow on feeding and distribution of juvenile Labeobarbus species in the Gumara River,Lake Tana Sub-basin,Ethiopia

The tributary rivers of Lake Tana are important nursery grounds for larvae and juveniles of the migratory endemic Labeobarbus species, but very little is known about their functional habitat and feeding preferences. This study investigated nursery grounds, habitat shifts, and potential energy sources for juvenile Labeobarbus species. Electrofishing point abundance sampling for juvenile sampling and stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) were applied to trace potential energy sources. Habitat use shifting was observed among labeobarbus size classes from weak or no flow pool to fast-flowing riffle mesohabitats. The young-of-the-year (YOY) were mainly found in microhabitats with a weak to moderate water velocity (i.e., < 0.3 m s^?1), while 1⁺ juveniles (>7 cm FL) adapted to velocities of > 0.3 m s^?1. Juveniles suffered from limited access to run and riffle habitats during the peak dry season (March-April). They were subsequently exposed to resource competition and predation risk which led to lower catches. Juveniles of different size classes used different food sources. C1 (<3 cm) and C3 (5.1–7 cm) size classes mainly relied on algal sources, while C2 (3 – 5 cm) and C4 (>7 cm) on zooplankton. Insect larvae were a relatively important source for larger juveniles. Maintaining appropriate flow that permits juveniles to access preferred foraging and nursery habitat in the Gumara River is crucial for the sustainable management and conservation of the Labeobarbus population in Lake Tana.     

Seventy years of food-web change in South Bay,Lake Huron

Though aquatic ecosystems (and the Laurentian Great Lakes in particular) have faced many stressors over the past century, including fisheries collapses and species invasions, rarely are data available to evaluate the long-term impacts of these stressors on food web structure. Stable isotopes of fish scales from the 1940s to the 2010s in South Bay, Lake Huron were used to quantify trophic position and resource utilization for fishes from offshore (alewife, cisco, lake trout, lake whitefish, rainbow smelt) and nearshore (rock bass, smallmouth bass, white sucker, yellow perch) habitats, providing one of the longest continuous characterizations of food webs in the Laurentian Great Lakes. Mean δ¹⁵N and δ¹³C values for each species were compared across twenty-year time periods. Using directional statistics, no significant community-wide changes were detected between time periods from 1947 to 1999. In contrast, a significant change was detected between 1980-1999 and 2000–2017, with all species showing increased reliance on nearshore resources. The increase in nearshore resource reliance for lake whitefish between these time periods was the greatest in magnitude compared with any other species between any two adjacent time periods. Besides lake whitefish, the increased reliance on nearshore resources was more pronounced for nearshore compared to offshore species. The timing of these shifts coincided with the invasion of dreissenid mussels and round goby, and declines in offshore productivity and prey densities. These results show the unprecedented magnitude of recent food-web change in Lake Huron after 50 years of relative stability.     

Sex pheromone of the stable fly

The cuticular alkenes of the female stable fly,Stomoxys calcitrans (L), which were responsible for inducing male fly copulatory behavior are (Z)-9-hentriacontene, (Z)-9-tritriacontene, 13-methyl-1-hen-triacontene and 13-methyl-1-tritriacontene. The identifications of the branched alkenes and the synthesis of these four compounds are described. Bioassays indicate that these materials in combination with previously described methyl branched alkanes are more active than the individual components.Diptera=Muscidae.Mention of proprietary or commercial products in this paper does not constitute an endorsement of this product by the U.S.D.A.