Changes in Aquatic Macrophytes after Liming Thrush Lake, Minnesota

Thrush Lake, Minnesota, was treated with limestone in 1988 to evaluate the efficacy of protective base addition against the loss of sport fisheries in a sensitive, mildly acidic lake. Prior to treatment, the lake was stressed (pH 6.46, ANC 64 μeq/L) but not severely degraded by acidic deposition and had a macrophyte community typical of lakes in northeastern Minnesota with low acid-neutralizing capacity (ANC). This paper describes the changes observed in aquatic plant communities during the 5 years after treatment, as pH and ANC slowly returned to pretreatment levels. Sphagnum platyphyllum, intolerant of non-acid conditions, was completely eliminated from the lake. The charo-phyte, Nitella, that originally shared dominance in the deep littoral zone with S. platyphyllum, decreased in importance during the first 2 years after treatment. Two vascular plants, Potamogeton pusillus and Najas flexilis, were first found in the lake the year after treatment and were abundant for 2 years after liming, probably in response to a combination of more neutral pH and reduced cover of Nitella. As the ANC and pH slowly returned to pretreatment conditions, Nitella again increased in coverage and depth range, with a concomitant decrease in P. pusillus and N. flexilis. The moss, S. platyphyllum, had not reinvaded the lake by 1993, 2 years after its dramatic decline.     

Impact of a Protective Limestone Treatment on the Water Chemistry and Zooplankton Community of Thrush Lake, Minnesota

A limestone slurry was sprayed on the surface of Thrush Lake, a small headwater lake in northeastern Minnesota, to test a treatment designed to protect acid-sensitive waters from anthropogenic acidification. The 6-year study, consisting of pretreatment, transition, and post-treatment phases, was part of the four-state Acid Precipitation Mitigation Program directed by the U.S. Fish and Wildlife Service. Measured water-chemistry parameters, including acid-neutralizing capacity, pH, dissolved calcium, and dissolved inoroganic carbon, increased following treatment, although local climatic conditions influenced the magnitude and duration of the chemical changes. Physical changes to the lake, other than an increase in conductivity and a short-term alteration of water clarity subsequent to treatment, were not documented. The composition of the zooplankton community was altered, with the proportion of rotifers increasing after treatment. Individual zooplankton species showed a variety of changes in abundance that were associated with treatment over both seasonal and multi-year intervals. For example, Holopedium gibbemm was absent from lake samples immediately following treatment and recovered within a season, whereas Diaptomus minutus and Keratella taurocephala populations were reduced after treatment and had not recovered by the end of the study. Alternately, Asplanchna priodonta increased in abundance after treatment. These observed abundance patterns were generally consistent with previzous acidification or base-addition studies. In contrast, the changes in community composition of zooplankton did not consistently fit patterns developed from regional studies across water-chemistry gradients. These differences emphasize the importance of biotic as well as abiotic factors in controlling zooplankton community composition.     

Lake sturgeon population characteristics in Rainy Lake, Minnesota and Ontario

Rainy Lake contains a native population of lake sturgeon Acipenser fulvescens that has been largely unstudied. The aims of this study were to document the population characteristics of lake sturgeon in Rainy Lake and to relate environmental factors to year‐class strength for this population. Gill‐netting efforts throughout the study resulted in the capture of 322 lake sturgeon, including 50 recaptures. Lake sturgeon in Rainy Lake was relatively plump and fast growing compared with a 32‐population summary. Population samples were dominated by lake sturgeon between 110 and 150 cm total length. Age–structure analysis of the samples indicated few younger (<10 years) lake sturgeon, but the smallest gill net mesh size used for sampling was 102 mm (bar measure) and would not retain small sturgeon. Few lake sturgeon older than age 50 years were captured, and maximum age of sampled fish was 59 years. Few correlations existed between lake sturgeon year‐class indices and both annual and monthly climate variables, except that mean June air temperature was positively correlated with year‐class strength. Analysis of Rainy Lake water elevation and resulting lake sturgeon year‐class strength indices across years yielded consistent but weak negative correlations between late April and early June, when spawning of lake sturgeon occurs. The baseline data collected in this study should allow Rainy Lake biologists to establish more specific research questions in the future.     

Lake restoration by biomanipulation: Round Lake, Minnesota, the first two years

SUMMARY. 1. Rotenone was applied to Round Lake in the autumn of 1980 in order to eliminate predominantly planktivorous and benthivorous fish. The lake was subsequently restocked with a higher population density of piscivores. The effect of this biomanipulation on the phytoplankton and zooplankton communities and on total nutrient concentrations was monitored at fortnightly intervals during the summers, from May 1980 to September 1982.
2. The abundance of phytoplankton was much lower after biomanipulation and was consistent with observed changes in Secchi disc transparency, total attenuation coefficient and chlorophyll a concentration. Zooplankters were also less abundant in 1981 and 1982 but the decrease in numbers was more than offset by the large increase in the mean sizes of the zooplankters present, so that the estimated grazing pressures in 1981 and 1982 were at least double the 1980 value.
3. Daphnia , rare in 1980, became the dominant genus in 1981 and 1982, and a shift to progressively larger-bodied Daphnia species was observed.
4. Although total nitrogen and total phosphorus levels were generally lower after biomanipulation, their decline could not explain the reduction in phytoplankton abundance which was attributed to the increased grazing pressure. Possible causes of the observed declines in nutrient concentrations are discussed.     

Limnology of Shagawa Lake,Minnesota, prior to reduction of phosphorus loading

Various limnological parameters have been measured in Shagawa Lake, a culturally eutrophic lake in northeastern Minnesota, from 1970–1972. These included temperature; specific conductance; dissolved oxygen; alkalinity; pH; total and orthophosphate phosphorus; nitrate, nitrite and ammonia nitrogen; chlorophyll a; transparency; major cations; and selected trace elements. The lake exhibited many characteristics of high productivity. Concentrations of chlorophyll a reached 60 µg/l during summer months and were reflected in pH values in excess of 9. Anaerobic conditions developed during both summer and winter and, during these intervals, large pools of available nutrients developed in the lower waters. Manganese and iron concentrations varied greatly as a consequence of changes in the oxygen regime. Major cations and other trace elements showed no yearly pattern.     

Strelkovimermis amphidis n. sp. from chironomid adults emerging from Lake Itasca and Long Lake, Minnesota

Mermithid nematodes, Strelkovimermis amphidis n. sp., emerged from chironomid imagos from Lake Itasca in Minnesota in the fall of 1996, 1997 and from Long Lake in the fall of 1998. The species is distinguished from the other 11 members of the genus by the long cephalic papillae, absence of an excretory pore, pointed termini in both sexes, large amphids, body diameter decrease at the vulva, long vagina, and the absence of lateral genital papillae. Strelkovimermis amphidis n. sp. is the fifth member of this genus recorded from Lake Itasca. The presence of and nature of the bursal sleeve is suggested as a useful distinguishing characteristic. The ratios involving spicule axis length, diameter of the body at the genital pore, and the length of the tail are also discussed in distinguishing species of Strelkovimermis. An expanded key to the species of Strelkovimermis is included.     

Effects of macronutrients upon buoyancy regulation by metalimnetic Oscillatoria agardhii in Deming Lake, Minnesota

Gas-vacuolate filaments of Oscillatoria agardhii form a metalimneticlayer in Oeming Lake, Minnesota. The environmental factors whichaffect buoyancy and the physiological processes which mediatechanges in buoyancy were determined. Buoyant filaments losttheir buoyancy in a few hours when incubated at light intensitiesabove those found in situ ({small tilde}15 µnol photonsm^–2 s^–1, or 1% of the surface value). The rate ofbuoyancy loss was accelerated by the addition of 10 µMphosphate at irradiances >200mol photons m^–2 s^–1.The effect of nutrient additions on buoyancy was also investigatedover a longer time period by incubating metalimnetic samplesin situ. The samples were deployed for 6 days at a depth wherethe irradiance was 8% of the surface value. As found in short-termexperiments, the addition of phosphate resulted in the largestdecrease in buoyancy. However, the addition of ammonia in additionto phosphate attenuated the buoyancy loss on day 2, and on day6 the filaments in these treatments were almost completely buoyant.The physiological status of the filaments in these treatmentswas assayed by analysis of elemental ratios of C, N and P, andby measurement of cellular chlorophyll, polysaccharide and protein.In addition, the cellular content of gas vesicles was determined.The construction of ballast balance sheets from these data indicatedthat changes in buoyancy were primarily due to differences inthe amount of polysaccharide ballast in the cells. However,in another set of in situ experiments, the increase in measuredballast molecules did not explain the observed loss of buoyancy.We hypothesized that another, undetected ballast-providing moleculehad accumulated in the cells.     

江苏南京发现赤颈鸫和宝兴歌鸫?

正2013年3月31日,在江苏省南京市老山九峰寺附近(118°89'21"E,31°32'75"N)发现1只在林间地面活动的鸫类,并拍摄照片(图1a)。所拍摄的个体上体灰褐色,眉纹、颈侧、喉及胸为红褐色,腹部和尾下覆羽为白色,根据相关资料(约翰·马敬能等2000)鉴定为赤颈鸫(Turdus ruficollis)雄性个体。2015年11月11日再次于南京老山发现赤颈鸫。     

Lake sturgeon population attributes and reproductive structure in the Namakan Reservoir,Minnesota and Ontario

Quantified were the age, growth, mortality and reproductive structure of lake sturgeon (Acipenser fulvescens) collected in the US and Canadian waters of the Namakan Reservoir. The hypotheses were tested that (i) age and growth of lake sturgeon in the Namakan Reservoir would differ by sex and reproductive stage of maturity, and (ii) that the relative strength of year‐classes of lake sturgeon in the reservoir would be affected by environmental variables. To quantify age, growth and mortality of the population, existing data was used from a multi‐agency database containing information on all lake sturgeon sampled in the reservoir from 2004 to 2009. Lake sturgeon were sampled in the Minnesota and Ontario waters of the Namakan Reservoir using multi‐filament gillnets 1.8 m high and 30–100 m long and varying in mesh size from 178 to 356 mm stretch. Reproductive structure of the lake sturgeon was assessed only during spring 2008 and 2009 using plasma testosterone and estradiol‐17β concentrations. Ages of lake sturgeon >75 cm ranged from 9 to 86 years (n = 533, mean = 36 years). A catch‐curve analysis using the 1981–1953 year classes estimated total annual mortality of adults to be 4.8% and annual survival as 95.2%. Using logistic regression analysis, it was found that total annual precipitation was positively associated with lake sturgeon year‐class strength in the Namakan Reservoir. A 10 cm increase in total annual precipitation was associated with at least a 39% increase in the odds of occurrence of a strong year class of lake sturgeon in the reservoir. Plasma steroid analysis revealed a sex ratio of 2.4 females: 1 male and, on average, 10% of female and 30% of male lake sturgeon were reproductively mature each year (i.e. potential spawners). Moreover, there was evidence based on re‐captured male fish of both periodic and annual spawning, as well as the ability of males to rapidly undergo gonadal maturation prior to spawning. Knowledge of lake sturgeon reproductive structure and factors influencing recruitment success contribute to the widespread conservation efforts for this threatened species.     

Deposition,resuspension, and decomposition of particulate organic matter in the sediments of Lake Itasca,Minnesota, USA

Sediment traps were used to investigate the settling, resuspension, and decomposition of particulate organic matter in Lake Itasca, MN (USA). Traps were deployed in the epilimnion and hypolimnion of the deepest basin during June, 1988, sampled twice during stratified conditions (August, September) and once after the lake had mixed (October). The downward flux of particulate material increased from summer to fall. The net sedimentation of organic matter ranged from 0.6 to 2.3 g m^–2 d^–1 at 4 m and increased to 2.1 to 3.2 g m^–2 d^–1 two meters above the bottom sediment indicating that resuspended sediment was at least 33% of the settling mass during all periods. The C:N ratios of captured particles (6.8–9.5) were between the ratios of plankton (5.8 to 6.8) and the sediments (9.9 to 10.2) but smaller than the ratios of terrestrial organic materials (13.5 to 222). The monosaccharide compositions of the entrapped particles were similar to plankton samples and different from the distinct composition of the sediments. Capture of rebound particles similar to the primary flux and not decomposition may have been responsible for this similarity. Total monosaccharide concentrations were lower in the sediments than in entrapped particles. Individual sugars exhibited different patterns of accumulation in the sediments. Glucose was lowest in sediments when the relative concentrations were compared to those in source materials and entrapped particles. In contrast, sediments had the highest rhamnose and fucose concentrations. Bacterial biomass could only account for small portions of these sugars in the sediment. The distinct monosaccharide composition of resuspended sediments was not strongly recorded in materials captured by the sediment traps even after the lake had mixed.     

湖南八大公山发现长尾地鸫

正在对湖南八大公山国家级自然保护区野生动物科学考察的过程中,我们采用了红外相机(Ltl-6210MC,Ltl Acorn,珠海市猎科电子有限公司)陷阱法。其中,安放在天平山保护站的第676号相机(位点坐标:29°46′46.11″N,110°5′44.63″E,海拔1 463 m)分别于2015年11月26日、11月28日和12月19日拍摄到1种鸫科鸟类(图1)。其主要形态特征为:上体呈单一     

The identification of gas vacuoles and their abundance in the hypolimnetic bacteria of Arco Lake,Minnesota

Bright refractile granules in bacterial cells are identified as gas vacuoles if they disappear on application of a few atmospheres pressure. This paper describes a simple method for observing individual cells under the light microscope before and after application of pressure and the use of this method in making a comprehensive survey of gas-vacuolate organisms in a sample. In water samples from the hypolimnion of a stratified lake (Arco Lake) in Northern Minnesota, gas vacuoles were found in nearly 30 different bacteria, representing possibly 60% or more of those present. The pressure sensitivity of gas vacuoles in these organisms is illustrated by micrograph pairs. Gas vacuoles, which are otherwise uncommon in bacteria, are evidently of great selective value in the hypolimnia of stratified lakes, perhaps by regulating cell buoyancy.     

贵州省宽阔水发现褐头鸫

正2015年9月30日利用Ltl6210型红外相机(深圳猎科电子有限公司)在贵州省宽阔水国家级自然保护区松林垭口处(28°12′N,107°09′E,海拔1 497m)拍摄到鸫科(Muscicapidae)鸟类1种。照片中的鸟中等体型,具白眉和标志性白色下眼圈,上体、腰及尾上覆羽棕褐色,颏至腹部灰白色,两胁灰色,与白眉鸫(Turdus obscurus)相似,但其胸及两胁灰色而非黄褐色,白色眉纹稍短,经查阅《中     

Hydromermis contorta (Kohn) and Hydromermis pseudocontorta n. sp. from chironomids of Lake Itasca and Long Lake, Minnesota

Hydromermis contorta (Kohn) and Hydromermis pseudocontorta n. sp. are described from chironomids in Lake Itasca and Long Lake, Minnesota, respectively. The former was recovered from adult females of Glyptotendipes paripes (Edwards) and the latter from fourth-instar larvae of Chironomus sp. Hydromermis pseudocontorta n. sp. resembles H. contorta in cephalic structures, overall size, and the presence of a restricted trophosome in the female. The terminal mouth, long uterine and vulvar limbs of the vagina, and the strongly chitinized brownish spicule of H. contorta contrast with the subventral mouth, short vaginal limbs, and the light yellow spicule of H. pseudocontorta n. sp. Both nematode species emerge from the host as sexually mature adults and both species give evidence of mating while in the host. The H. contorta described by Welch is designated as a new species, Hydromermis albionis n. sp.     

江西发现宝兴歌鸫

2015年4月2日在江西官山发现宝兴歌鸫。