North American Lakes Research Articles

Evaporation in a Mediterranean environment by energy budget and Penman methods, Lake Baratz, Sardinia, Italy

Abstract. In Mediterranean environments, evaporation is a key component of lake water budgets. This applies to Lake Baratz in Sardinia, Italy, a closed lake that almost dried up in 2008 after a succession of years with low seasonal rainfall. We used the energy budget method and Penman's equation to estimate evaporation over Lake Baratz. We measured, using a raft station, water temperature at the surface, at 1, 2, 4, 6 m depth and at the bottom of the lake, as well as air temperature, relative humidity, wind speed, and net radiation over a period of 3 years. We also compared Penman's equation and the energy budget method in two other climatic zones using published data. Our results indicate that mean yearly evaporation over Lake Baratz was 950 mm. On an annual scale, evaporation estimated by Penman's method omitting heat storage as is usually done was 18% higher than by the energy budget method that included heat storage, with monthly differences ranging between −38 and +60%. Including the heat storage term in Penman's equation changed the monthly values but did not change the yearly value significantly. Solar radiation and heat storage were found to be the most important energy fluxes to and from the lake and had the greatest effect on evaporation rates for the energy budget method. The bias between the two methods has a seasonal cycle due to the storage and release of energy from the lake. Energy advected to and from the lake by precipitation, surface water and ground water had minor effect on evaporation rates. Lake Baratz, like other lakes in a Mediterranean environment, is particularly sensitive to the summer hot and dry climate. In contrast, we found that rates of evaporation estimated from Penman and the energy budget methods over tropical African lakes were nearly constant over the entire year and the difference between the two methods smaller. Difference between the two methods for North American lakes is also smaller probably owing to the ice-cover season and to lower radiation and lower temperatures during summer.

Impact of Fishing and Stocking Practices on Coregonid Diversity

Fish species diversity can be lost through interacting stressors including habitat loss, stocking and overfishing. Although a multitude of stressors have played a role in the global decline of coregonid (Coregonus spp.) diversity, a number of contemporary studies have identified habitat loss stemming from eutrophication as the primary cause. Unfortunately, reconstructing the role of fishing and stocking practices can be difficult, because these records are incomplete or appear only in hard-to-access historic grey literature. Based on an illustrative set of historic and contemporary studies, we describe how fisheries management practices may have contributed to coregonid diversity loss in European and North American lakes. We provide case studies examining how fishing and stocking may reduce coregonid diversity through demographic decline and introgressive hybridization. In some lakes, fisheries management practices may have led to a loss of coregonid diversity well before issues with habitat degradation manifested. Our review suggests that fish conservation policies could beneficially consider the relative importance of all stressors, including management practices, as potential drivers of diversity loss.

Regulation of the KNOX-GA gene module induces heterophyllic alteration in North American lake cress.

Plants show leaf form alteration in response to changes in the surrounding environment, and this phenomenon is called heterophylly. Although heterophylly is seen across plant species, the regulatory mechanisms involved are largely unknown. Here, we investigated the mechanism underlying heterophylly in Rorippa aquatica (Brassicaceae), also known as North American lake cress. R. aquatica develops pinnately dissected leaves in submerged conditions, whereas it forms simple leaves with serrated margins in terrestrial conditions. We found that the expression levels of KNOTTED1-LIKE HOMEOBOX (KNOX1) orthologs changed in response to changes in the surrounding environment (e.g., change of ambient temperature; below or above water) and that the accumulation of gibberellin (GA), which is thought to be regulated by KNOX1 genes, also changed in the leaf primordia. We further demonstrated that exogenous GA affects the complexity of leaf form in this species. Moreover, RNA-seq revealed a relationship between light intensity and leaf form. These results suggest that regulation of GA level via KNOX1 genes is involved in regulating heterophylly in R. aquatica. The mechanism responsible for morphological diversification of leaf form among species may also govern the variation of leaf form within a species in response to environmental changes.

Sophie discovers Amerika: German-speaking women write the New World

In a 1798 novel by Sophie von La Roche, a European woman swims across a cold North American lake seeking help from the local indigenous tribe to deliver a baby. In a 2008 San Francisco travel guide, Milena Moser, the self-proclaimed Patron Saint of Desperate Swiss Housewives, ponders the guilty pleasures of a media-saturated world. Wildly disparate, these two texts reveal the historical arc of a much larger literary constellation: the literature of German-speaking women who interact with the New World. In this volume, cultural historians from around the world investigate this unique literary bridge between two hemispheres, focusing on New-World texts written by female authors from Germany, Austria, or Switzerland. Encompassing a broad range of genres including novels, films, travel literature, poetry, erotica, and even photography, the essays include women's experiences across both American continents. Many of the primary literary texts discussed in this volume are available in the online collections of Sophie: A Digital Library of Works by German-Speaking Women (http://sophie.byu.edu/). Contributors: Christiane Arndt, Karin Baumgartner, Ute Bettray, Ulrike Brisson, Carola Daffner, Denise M. Della Rossa, Linda Dietrick, Silke R. Falkner, Maureen O. Gallagher, Nicole Grewling, Monika Hohbein-Deegen, Gabi Kathofer, Thomas W. Kniesche, Julie Koser, Judith E. Martin, Sarah C. Reed, Christine Rinne, Tom Spencer, Florentine Strzelczyk, David Tingey, Petra Watzke, Chantal Wright. Rob McFarland and Michelle Stott James are both Associate Professors of German at Brigham Young University.

Invasion of the Allegheny River in Pennsylvania by the spiny water flea (Bythotrephes longimanus Leydig, 1860)

The spiny water flea (Bythotrephes longimanus), has successfully established populations in North American reservoirs and lakes, but little is known of its movement between lake and river systems. Here we document the first longitudinal movement of this aquatic invader in the Allegheny River, Pennsylvania. During spring 2013 we collected samples from the tailrace of Kinzua Dam to the confluence of Oil Creek, Oil City Pennsylvania, a distance of 100 km. The spiny water flea was present along 24 km of the sampled reach, comprising from 10 to 30% of the total zooplankton assemblage. In addition we collected two species of Daphnia, the dominant taxon, and Leptodora kindtii. All three developmental stages of the spiny water flea were present in samples collected (Instars I, II, and III). This study presents one of the first documented expansions of this species from an impoundment to downstream riverine reaches. Its presence warrants further monitoring and appropriate strategies to curb its spread and to investigate its potential impact on the lotic food web.

Trophic interactions between introduced lake trout (Salvelinus namaycush) and native Arctic charr (S. alpinus) in a large Fennoscandian subarctic lake

AbstractIntroduced fishes may have major impacts on community structure and ecosystem function due to competitive and predatory interactions with native species. For example, introduced lake trout (Salvelinus namaycush) has been shown to replace native salmonids and induce major trophic cascades in some North American lakes, but few studies have investigated trophic interactions between lake trout and closely related native Arctic charr (S. alpinus) outside the natural distribution of the former species. We used stomach content and stable isotope analyses to investigate trophic interactions between introduced lake trout and native Arctic charr in large subarctic Lake Inarijärvi in northern Finland. Both salmonids had predominantly piscivorous diets at >280 mm total length and were mainly caught from the deep profundal zone. However, lake trout had a more generalist diet and showed higher reliance on littoral prey fish than Arctic charr, whose diet consisted mainly of pelagic planktivorous coregonids. According to length at age and condition data, lake trout showed slightly faster growth but lower condition than Arctic charr. The results indicate that introduced lake trout may to some extent compete with and prey upon native Arctic charr, but currently have only a minor if any impact on native fishes and food web structure in Inarijärvi. Future monitoring is essential to observe potential changes in trophic interactions between lake trout and Arctic charr in Inarijärvi, as well as in other European lakes where the two salmonids currently coexist.

Probabilistic prediction of cyanobacteria abundance in a Korean reservoir using a Bayesian Poisson model

AbstractThere have been increasing reports of harmful algal blooms (HABs) worldwide. However, the factors that influence cyanobacteria dominance and HAB formation can be site‐specific and idiosyncratic, making prediction challenging. The drivers of cyanobacteria blooms in Lake Paldang, South Korea, the summer climate of which is strongly affected by the East Asian monsoon, may differ from those in well‐studied North American lakes. Using the observational data sampled during the growing season in 2007–2011, a Bayesian hurdle Poisson model was developed to predict cyanobacteria abundance in the lake. The model allowed cyanobacteria absence (zero count) and nonzero cyanobacteria counts to be modeled as functions of different environmental factors. The model predictions demonstrated that the principal factor that determines the success of cyanobacteria was temperature. Combined with high temperature, increased residence time indicated by low outflow rates appeared to increase the probability of cyanobacteria occurrence. A stable water column, represented by low suspended solids, and high temperature were the requirements for high abundance of cyanobacteria. Our model results had management implications; the model can be used to forecast cyanobacteria watch or alert levels probabilistically and develop mitigation strategies of cyanobacteria blooms.

Climate change drives coherent trends in physics and oxygen content in North American lakes

Using a 25-year record of monitoring data, we show that recent climate change has affected the thermal properties and oxygen content of seven lakes in south-central Ontario, Canada, and five lakes in north-central Wisconsin, USA. Coherent patterns in autumnal lake warming were driven by increased autumn air temperature in both lake districts. Temperature increases were restricted to the epilimnion and metalimnion of the lakes, resulting in increased thermal stability of the water column. Mixing depths also decreased over the study period. Shallower mixing depths in the Ontario lakes were due to climate-driven increases in lake-water dissolved organic carbon concentrations. Collectively, changes in the thermal regime of the lakes suggest autumn mixing of the water column may be delayed. Metalimnetic oxygen also increased in the Wisconsin lakes, perhaps in response to increased algal production as lake thermal regimes changed. The response of individual lakes to climate change was modified by lake chemistry in the Ontario lake district and by lake chemistry and morphometry in the Wisconsin lake district. Our results demonstrate coherent lake response to climate change and highlight the importance of both regional and local factors in regulating individual lake response to global climate change.

The influence of pre-settlement and early post-settlement processes on the adult distribution and relative dominance of two invasive mussel species

The structure of a community is governed by a complex combination of processes whose relative importance varies over time and space. Larval dynamics, settlement and recruitment are thought to be important processes limiting adult abundance and distribution of benthic invertebrates with planktonic larvae. Two invasive molluscs with similar morphology and resource needs, the Eurasian zebra mussel Dreissena polymorpha and the quagga mussel Dreissena rostriformis bugensis, co-occur in several North American lakes and rivers but often differ in their adult distribution over depth. Following establishment, the quagga mussel typically replaces the zebra mussel in abundance, particularly in deeper waters. A field sampling programme conducted over 3 years in a lotic system (the Soulanges Canal connected to the St. Lawrence River) examined the extent to which adult distribution and the differential dominance of these two species are determined by larval supply (i.e. larval abundance near settlement sites), settlement and recruitment. Total dreissenid larval abundance in the water column at two depths was determined weekly, and larval competence (size) and species-specific larval composition was estimated, during the main settlement period over three consecutive years. The pattern of total dreissenid settlement over the depth gradient was determined by deployment of settlement plates at both depths. Total abundance and proportional abundance of zebra mussel and quagga mussel juveniles and adults in each depth zone were determined monthly from July to September each year. Mean dreissenid larval size did not differ between depths and the supply of late-stage larvae was generally low, but total larval abundance was consistently greater in deeper water. This differential larval abundance established settlement and recruitment patterns in the canal but contrasted predictions based on total adult dreissenid abundance – which was higher in the shallow zone. Therefore, the significant factor dictating the abundance of adult mussels in these two depth zones must be post-recruitment mortality, rather than larval supply, settlement or recruitment. Despite a strong species-specific adult depth zonation, larvae and juveniles showed no consistent differences in species proportions over the depth gradient. In fact, zebra mussels dominated larval abundance at both depths for c. 50% of the sampling dates and dominated juvenile abundance at both depths throughout most of the sampling period. In contrast, the proportional abundance of zebra mussels in the adult dreissenid community was consistently 4–5 times higher in the shallow zone. These results indicate that larval supply, settlement and recruitment processes are not responsible for determining total adult dreissenid distribution or species dominance. Rather, these patterns appear to be governed by post-recruitment factors that manifest themselves in later stages of mussel development and growth.

Molecular Phylogeny Determined Using Chloroplast DNA Inferred a New Phylogenetic Relationship of <i>Rorippa aquatica</i> (Eaton) EJ Palmer & Steyermark (Brassicaceae)—Lake Cress

North American lake cress, Rorippa aquatica (Eaton) EJ Palmer & Steyermark (Brassicaceae), is listed as an endangered or threatened species. Lake cress shows heterophyllic changes in leaf form in response to the surrounding environment. Therefore, this species has received considerable attention from ecological and morphological perspectives. However, its phylogenetic position and taxonomic status have long been a subject of debate. To analyze the phylogenetic relationship of lake cress, we investigated chloroplast DNA sequences from 17 plant species. The results of phylogenetic reconstruction performed using trnL intron, trnG (GCC)-trnM (CAU), and psbC-trnS (UGA) indicated that lake cress is a member of Rorippa. Moreover, we found that the chromosome number of lake cress is 2n = 30. This result indicated that lake cress might have originated from aneuploidy of triploid species or via intergeneric crossing. Taken together, our results suggest an affinity between lake cress and Rorippa at the molecular level, indicating that lake cress should be treated as Rorippa aquatica (Eaton) EJ Palmer & Steyermark.

Threatened fishes of the world: the end of a series

Our series of manuscripts on Threatened Fishes of the World came to an end after a prolonged and increasingly depressing and frustrating history. Prolonged because the series extended from 1995 to 2013, much longer than was anticipated. Increasingly depressing because it became clear to even the most skeptical reader that the status of a great many fishes is a matter of real concern. Frustrating because the accounts mostly presented the same picture for almost every species. The species accounts range from the largest fish species, the whale shark (Rhincodon typus) to one of the smallest (Tanichthys albonubes), in freshwater, marine and brackish water systems (Table 1). The list includes some species that almost certainly are extinct, such as the Yangtze paddlefish (Xiphurus gladius), and some that are relatively abundant and widespread, such as the North American lake sturgeon (Acipenser fulvescens). Some species have global distributions, other are restricted to a single desert spring (Cyprinodon diabolis). Several cautions are obvious for this species list. Since contributions were unsolicited, and judged on their individual merits, it is not possible to analyze or interpret these reports as any objective measure of the number or distribution of threatened fish species. That was never the intention of this series. Other publications (Helfman 2007) are definitive efforts that were designed to address those important questions (Albins et al. 2013). Similarly, it is not possible to draw any conclusions from our series on Threatened Fishes as to the geographic, phylogenetic or systematic distribution of species. In fact, some papers must be regarded as doubtful reports of threatened species, since they probably represent only local color variants of broadly distributed species that cannot be considered as threatened (e.g., the aurora form of Salvelinus fontinalis, Salmo trutta caspias). We still receive a few manuscript submission each year, although the journal website clearly states that we are no longer accepting manuscripts for the series. It proved to be increasingly difficult to judge the claimed threatened status for taxonomic units reported from areas with very limited information on species distributions and abundance. Helfman (2013) has done an admirable job to demonstrate the profound differences and difficulties that exist among different countries and jurisdictions where there is reasonable confidence for species identification and knowledge of population status. It is a simple exercise for any undergraduate ichthyology class in almost any place on earth to demonstrate that we have very limited information on the biology, ecology and population status of most local fish species (Scott and Crossman 1973). I organized an invited session on Threatened Fishes for the annual meeting of the AAAS in Chicago in February 2011. Several papers from that session are Environ Biol Fish (2013) 96:1135–1149 DOI 10.1007/s10641-013-0174-y

THE GENETIC ARCHITECTURE OF REPRODUCTIVE ISOLATION DURING SPECIATION-WITH-GENE-FLOW IN LAKE WHITEFISH SPECIES PAIRS ASSESSED BY RAD SEQUENCING

During speciation-with-gene-flow, effective migration varies across the genome as a function of several factors, including proximity of selected loci, recombination rate, strength of selection, and number of selected loci. Genome scans may provide better empirical understanding of the genome-wide patterns of genetic differentiation, especially if the variance due to the previously mentioned factors is partitioned. In North American lake whitefish (Coregonus clupeaformis), glacial lineages that diverged in allopatry about 60,000 years ago and came into contact 12,000 years ago have independently evolved in several lakes into two sympatric species pairs (a normal benthic and a dwarf limnetic). Variable degrees of reproductive isolation between species pairs across lakes offer a continuum of genetic and phenotypic divergence associated with adaptation to distinct ecological niches. To disentangle the complex array of genetically based barriers that locally reduce the effective migration rate between whitefish species pairs, we compared genome-wide patterns of divergence across five lakes distributed along this divergence continuum. Using restriction site associated DNA (RAD) sequencing, we combined genetic mapping and population genetics approaches to identify genomic regions resistant to introgression and derive empirical measures of the barrier strength as a function of recombination distance. We found that the size of the genomic islands of differentiation was influenced by the joint effects of linkage disequilibrium maintained by selection on many loci, the strength of ecological niche divergence, as well as demographic characteristics unique to each lake. Partial parallelism in divergent genomic regions likely reflected the combined effects of polygenic adaptation from standing variation and independent changes in the genetic architecture of postzygotic isolation. This study illustrates how integrating genetic mapping and population genomics of multiple sympatric species pairs provide a window on the speciation-with-gene-flow mechanism.

Evaluating the fate and behaviour of cyclic volatile methyl siloxanes in two contrasting North American lakes using a multi-media model

The behaviour of cyclic volatile methyl siloxanes (cVMS) in lakes was explored using a fugacity-based steady-state non-equilibrium multimedia fate and transport model (a modified version of QWASI). Three substances were investigated: Octamethylcyclotetrasiloxane (D4), Decamethylcyclopentasiloxane (D5) and Dodecamethylcyclohexasiloxane (D6) in two contrasting North American lakes: Lake Ontario and Lake Pepin (a natural shallow lake on the Mississippi river between Minnesota and Wisconsin). Values for the principal partition coefficients and the hydrolysis rate constant were adjusted for the mean annual temperatures of each lake. Hydrolysis rate constants were also adjusted for the fraction of chemical calculated to be in the freely dissolved phase. Half-lives in sediment were calculated from partitioning theory, assuming hydrolysis can occur only in the dissolved phase. Best estimates of substance-specific emissions were obtained by combining current per capita approximations of usage and fraction lost to domestic waste water, the population of the lake catchment and cVMS removal in waste water treatment. Concentrations were generally lower and chemical residence times longer in Lake Ontario than in Lake Pepin, owing to greater depth, a higher hydraulic retention time and a higher degree of dilution. Overall persistence in Lake Pepin is significantly influenced by the high rate of sediment burial assumed in the model, as well as by a relatively high rate of water discharge. Despite the many similarities of the compounds considered, the dominant loss mechanisms vary significantly and are not the same in each lake system. This highlights the pitfalls of subjective evaluation of chemical fate and illustrates the important role which models have to play in providing a quantitative framework for assessing chemical behaviour objectively under the influence of a complex and interacting set of factors.

Climate-driven changes in water level: a decadal scale multi-proxy study recording the 8.2-ka event and ecosystem responses in Lake Sarup (Denmark)

A two-stage change in lake level during the 8.2-ka event was identified in Lake Sarup, Denmark (55°N), using a multiproxy approach on precise radiocarbon wiggle-matched annually laminated sediments deposited 8740–8060 cal. yr BP. Changes in δ13C and δ18O indicated closed lake hydrology driven by precipitation. The isotopic, sedimentary and plant macrofossil records suggested that the lake level started to decrease around 8400 cal. yr BP, the decrease accelerating during 8350–8260 before an abrupt increase during 8260–8210. This pattern shows that the climate anomaly started ~150 years before the onset of the 8.2-ka cooling event registered in Greenland ice cores, but was synchronous with hydrologic change in the North American Lake Agassiz drainage. The lake level decrease was accompanied by a higher accumulation rate of inorganic matter and lower accumulation rates of cladoceran subfossils and algal pigments, possibly due to increased turbidity and reduced nutrient input during this drier period. Pigment analysis also showed added importance of diatoms and cryptophytes during this climate anomaly, while cyanobacteria became more important when the water level rose. Moreover, Nymphaeaceae trichosclereids were abundant during the period of algal enrichment. Cladoceran taxa associated with floating leaved plants or benthic habitats responded in a complex way to changes in water level, but the cladoceran assemblages generally reflected deep lake conditions throughout the period. The lake did not return to its pre-8.2-ka event status during the period of analysis, but remained more productive for centuries after the climatic anomaly as judged from the pigment accumulation and assemblage composition. The change to more eutrophic conditions may have been triggered by erosion of marginal deposits. Together, these data confirm the chronology of hydrologic changes and suggest, for the first time, that lake levels exhibited both a decline and an increase in rapid succession in response to the 8.2-ka event in southern Scandinavia.

Short-term declines in curlyleaf pondweed in Minnesota: potential influences of snowfall

Curlyleaf pondweed (Potamogeton crispus) is a long-established, nonnative aquatic plant common throughout southern and central Minnesota that is thought to be expanding northward. Curlyleaf pondweed typically grows abundantly in spring in productive lakes and then senesces in midsummer, often followed by algae blooms. We report observations of widespread, short-term declines in curlyleaf pondweed cover that appear linked to winter snow depth on frozen lakes. These findings suggest that climate change may greatly affect habitat suitability for curlyleaf pondweed. As Minnesota lakes warm with less snow cover limiting light penetration, curlyleaf pondweed growth will likely increase. These observations form the foundation for targeted follow up studies that more precisely describe conditions limiting the growth and expansion of curlyleaf pondweed in north-temperate, North American lakes.

Comparative Metagenomics of Toxic Freshwater Cyanobacteria Bloom Communities on Two Continents

Toxic cyanobacterial blooms have persisted in freshwater systems around the world for centuries and appear to be globally increasing in frequency and severity. Toxins produced by bloom-associated cyanobacteria can have drastic impacts on the ecosystem and surrounding communities, and bloom biomass can disrupt aquatic food webs and act as a driver for hypoxia. Little is currently known regarding the genomic content of the Microcystis strains that form blooms or the companion heterotrophic community associated with bloom events. To address these issues, we examined the bloom-associated microbial communities in single samples from Lake Erie (North America), Lake Tai (Taihu, China), and Grand Lakes St. Marys (OH, USA) using comparative metagenomics. Together the Cyanobacteria and Proteobacteria comprised >90% of each bloom bacterial community sample, although the dominant phylum varied between systems. Relative to the existing Microcystis aeruginosa NIES 843 genome, sequences from Lake Erie and Taihu revealed a number of metagenomic islands that were absent in the environmental samples. Moreover, despite variation in the phylogenetic assignments of bloom-associated organisms, the functional potential of bloom members remained relatively constant between systems. This pattern was particularly noticeable in the genomic contribution of nitrogen assimilation genes. In Taihu, the genetic elements associated with the assimilation and metabolism of nitrogen were predominantly associated with Proteobacteria, while these functions in the North American lakes were primarily contributed to by the Cyanobacteria. Our observations build on an emerging body of metagenomic surveys describing the functional potential of microbial communities as more highly conserved than that of their phylogenetic makeup within natural systems.

Morphological and Molecular Characterization of Paramecium (Viridoparamecium nov. subgen.) chlorelligerum Kahl (Ciliophora)

We redescribe Paramecium chlorelligerum, a forgotten species, which Kahl (Tierwelt Dtl., 1935, 30:651) briefly but precisely described in the addendum to his ciliate monographs as a Paramecium with symbiotic green algae. The redescription is based on classical morphological methods and the analysis of the small subunit (SSU) rDNA. Morphologically, P. chlorelligerum differs from P. (C.) bursaria, the second green species in the genus, by having a special swimming shape, the length of the caudal cilia, the size of the micronucleus, the size of the symbiotic algae, the contractile vacuoles (with collecting vesicles vs. collecting canals), and the number of excretory pores/contractile vacuole (1 vs. 2-3). The molecular investigations show that P. chlorelligerum forms a distinct branch distant from the P. (Chloroparamecium) bursaria clade. Thus, we classify P. chlorelligerum in a new subgenus: Paramecium (Viridoparamecium) chlorelligerum. The symbiotic alga belongs to the little-known genus Meyerella, as yet recorded only from the plankton of a North American lake.

Using the deuterium isotope composition of permafrost meltwater to constrain thermokarst lake contributions to atmospheric CH4 during the last deglaciation

Thermokarst lakes are thought to have been an important source of methane (CH4) during the last deglaciation when atmospheric CH4 concentrations increased rapidly. Here we demonstrate that meltwater from permafrost ice serves as an H source to CH4production in thermokarst lakes, allowing for region‐specific reconstructions ofδDCH4 emissions from Siberian and North American lakes. δDCH4 reflects regionally varying δD values of precipitation incorporated into ground ice at the time of its formation. Late Pleistocene‐aged permafrost ground ice was the dominant H source to CH4production in primary thermokarst lakes, whereas Holocene‐aged permafrost ground ice contributed H to CH4 production in later generation lakes. We found that Alaskan thermokarst lake δDCH4 was higher (−334 ± 17‰) than Siberian lake δDCH4 (−381 ± 18‰). Weighted mean δDCH4values for Beringian lakes ranged from −385‰ to −382‰ over the deglacial period. Bottom‐up estimates suggest that Beringian thermokarst lakes contributed 15 ± 4 Tg CH4 yr−1 to the atmosphere during the Younger Dryas and 25 ± 5 Tg CH4 yr−1during the Preboreal period. These estimates are supported by independent, top‐down isotope mass balance calculations based on ice coreδDCH4 and δ13CCH4 records. Both approaches suggest that thermokarst lakes and boreal wetlands together were important sources of deglacial CH4.

Tribute to an ‘obnoxious’ ecocatalytical demotechnician: Jack Vallentyne on population

The late John R. Vallentyne was a limnologist and one of Canada’s most influential scientists in the latter half of the last century. While his work in institution-building and in improving water quality in North American lakes is widely known, his creative, if infrequent, writings on human overpopulation and its environmental consequences are less so. This tribute analyzes these, starting with his concept of demotechnic growth, relating his thoughts to those of David Suzuki and Garrett Hardin, 2 admirers who encouraged him to write his cry-from-the-heart book, Tragedy in Mouse Utopia, which was published shortly before his death. His ideas are related to current population issues such as immigration and the estimation of environmentally sustainable population levels. An attempt is made to explain his relative silence on Canada’s population and immigration policies. He has left some of the heavy-lifting to his colleagues and the next generation.

Regulatory versus coding signatures of natural selection in a candidate gene involved in the adaptive divergence of whitefish species pairs (Coregonus spp.)

While gene expression divergence is known to be involved in adaptive phenotypic divergence and speciation, the relative importance of regulatory and structural evolution of genes is poorly understood. A recent next-generation sequencing experiment allowed identifying candidate genes potentially involved in the ongoing speciation of sympatric dwarf and normal lake whitefish (Coregonus clupeaformis), such as cytosolic malate dehydrogenase (MDH1), which showed both significant expression and sequence divergence. The main goal of this study was to investigate into more details the signatures of natural selection in the regulatory and coding sequences of MDH1 in lake whitefish and test for parallelism of these signatures with other coregonine species. Sequencing of the two regions in 118 fish from four sympatric pairs of whitefish and two cisco species revealed a total of 35 single nucleotide polymorphisms (SNPs), with more genetic diversity in European compared to North American coregonine species. While the coding region was found to be under purifying selection, an SNP in the proximal promoter exhibited significant allele frequency divergence in a parallel manner among independent sympatric pairs of North American lake whitefish and European whitefish (C. lavaretus). According to transcription factor binding simulation for 22 regulatory haplotypes of MDH1, putative binding profiles were fairly conserved among species, except for the region around this SNP. Moreover, we found evidence for the role of this SNP in the regulation of MDH1 expression level. Overall, these results provide further evidence for the role of natural selection in gene regulation evolution among whitefish species pairs and suggest its possible link with patterns of phenotypic diversity observed in coregonine species.