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Our understanding of drivers of cyanobacterial harmful algal blooms (cHABs) is evolving, but it is apparent that not all lakes are created equal. Nitrogen (N) is an important component of all cHABs and is crucial for cyanotoxin production. It is generally assumed that external nitrogen inputs are the primary N source for cHABs. However, in northern lakes, nitrogen inputs are typically low, and suggests that internal nitrogen cycling, through heterotrophic organic matter decomposition or nitrogen fixation, may play a significant role in cHAB development and sustainment. Using Lake of the Woods as a testbed, we quantified nutrients, cyanotoxins, nitrogen fixation, and the microbial community in the southern extent of the lake. During our temporal study, inorganic nitrogen species (NO3-+NO2-and NH4+) were either at very low concentrations or below detection, while phosphorus was in excess. These conditions resulted in nitrogen-deficient growth and thereby favored nitrogen fixing cyanobacterial species. In response, nitrogen fixation rates increased exponentially throughout the summer and coincided with theAphanizomenonsp. bloom. Despite nitrogen limitation, microcystin, anatoxin, saxitoxin, and cylindrospermopsin were all detected, with microcystin being the most abundant cyanotoxin detected. Microcystin concentrations were highest when free nitrogen was available and coincided with an increase inMicrocystis.Together, our work suggests that internal nitrogen dynamics are responsible for the dominance of nitrogen fixing cyanobacteria and that additions of nitrogen may increase the likelihood of other cyanobacterial species, currently at low abundance, to increase growth and cyanotoxin production.Statement of SignificanceThis study is the first assessment of nitrogen fixation rates and water column 16S rRNA gene amplicon sequencing in Lake of the Woods during a harmful algal bloom season. The aim of this study is to better understand nitrogen dynamics and the microbial ecology of cyanobacterial harmful algal blooms on Lake of the Woods. Result from this study reveal that internal nitrogen cycling via nitrogen fixation may alleviate nitrogen deficiencies, and structure and control the cyanobacterial community and cyanotoxin production. Molecular analysis reveals that cyanotoxins in Lake of the Woods are produced by less abundant cyanobacteria that are limited by nitrogen. This study has significant management implication as agencies continue to mitigate toxic blooms on Lake of the Woods, the largest shoreline lake in the United States. Our work is an important initial assessment and jumping off point for further research on Lake of the Woods when assessing how nitrogen plays a role in bloom formation and toxicity. Submitting to L&O, we believe would allow for the greatest outreach and access to an audience that will continue to build upon our findings. Additionally, submitting with L&O our work will reach beyond the scientific audience, but also reach other parties participating in the mitigation of harmful algal blooms.

Evidence suggests that boreal-lake ecosystems are changing rapidly, but with variable ecological responses, due to climate warming. Paleolimnological analysis of 27 undeveloped northern forested lakes showed significant and potentially climate-mediated shifts in diatom communities and increased carbon and biogenic silica burial. We hypothesize the sensitivity of northern forested lakes to climate change will vary along two physical gradients: one reflecting direct, in-lake climate effects (propensity to thermally stratify), the other reflecting indirect watershed effects (watershed to lake-surface area ratio). We focus on the historical response of algal communities to test our two-dimensional sensitivity framework. Historical algal response was summarized by measures of diatom community turnover, changes in species and diagnostic species groups, and measures of siliceous algal and overall primary production (biogenic silica, carbon burial). Measures of algal production increased across all lake types, with carbon burial proportionately higher in polymictic lakes. Greater diatom community change occurred in deep, stratified lakes with smaller watersheds, whereas diatom species groups showed variable responses along our two-dimensional sensitivity framework. Physical characteristics of lakes and watersheds could serve as predictors of sensitivity to climate change based on paleo-indicators that are mechanistically linked to direct and indirect limnological effects of climate change.

Consistent identification of diatoms is a prerequisite for studying their ecology, biogeography, and successful application as environmental indicators. However, taxonomic consistency among observers has been difficult to achieve, because taxonomic information is scattered across numerous literature sources, presenting challenges to the diatomist. First, literature is often inaccessible because of cost, or its location in journals that are not widely circulated. Second, taxonomic revisions of diatoms are taking place faster than floras can be updated. Finally, taxonomic information is often contradictory across literature sources. These issues can be addressed by developing a content creation community dedicated to making taxonomic, ecological, and image-based data freely available for diatom researchers. Diatoms.org represents such a content curation community, providing open, online access to a vast amount of recent and historical information on North American diatom taxonomy and ecology. The content curation community aggregates existing taxonomic information, creates new content, and provides feedback in the form of corrections and notice of literature with nomenclatural changes. The website not only addresses the needs of experienced diatom scientists for consistent identification, but is also designed to meet users at their level of expertise, including engaging the lay public in the importance of diatom science. The website now contains over 1000 species pages contributed by over 100 content contributors, from students to established scientists. The project began with the intent to provide accurate information on diatom identification, ecology, and distribution using an approach that incorporates engaging design, user feedback, and advanced data access technology. In retrospect, the project that began as an "extended electronic book" has emerged not only as a means to support taxonomists, but for practitioners to communicate and collaborate, expanding the size of and benefits to the content curation community. In this paper, we outline the development of diatoms.org, document key elements of the project, examine ongoing challenges, and consider the unexpected emergent properties, including the value of diatoms.org as a source of data. Ultimately, if the field of diatom taxonomy, ecology, and biodiversity is to be relevant, a new generation of taxonomists needs to be trained and employed using new tools. We propose that diatoms.org is in a key position to serve as a hub of training and continuity for the study of diatom biodiversity and aquatic conditions.

Diporeia spp. were a key component of the Great Lakes benthos, converting the pelagic algal rain to secondary production, which is critical for Great Lakes fishes. However, Diporeia declines since the 1980s have been rapid and widespread. While there are temporal relationships between Diporeia declines and spread of zebra and quagga mussels, establishing a mechanistic link has been difficult. Diporeia declines may result from competition for food resources with dreissenid mussels; however, conflicting evidence suggests food limitation may not be the direct link. To test food limitation, we analyzed gut contents of Diporeia collected between the 1980s and 2009 from two deep (>100 m) and one nearshore station (~50 m depth) in southern Lake Michigan. We further analyzed sediment cores from the same stations to resolve relationships among food resources, Diporeia diet, and diet selectivity during pre- and post-dreissenid invasion. In spring, pre-dreissenid Diporeia fed selectively and exclusively on large (Stephanodiscus) and filamentous centric diatoms (Aulacoseira). Diporeia diets showed significant shifts during the 2000s to greater proportions of small centric and araphid diatoms, coincident with Diporeia declines and offshore expansion of quagga mussels. Sediment cores recorded declines in Aulacoseira and large Stephanodiscus from 1960 to 2009 and increases in small centrics after dreissenid introduction. Accounting for high selectivity in springtime Diporeia diets, community changes in sediment records are consistent with changes observed in Diporeia diets and suggest Diporeia declines have been exacerbated by a shift from more nutritious and highly preferred diatom species to less nutritious and negatively selected species.

The genus Semiorbis was erected by R.M.Patrick in 1966 as monotypic based on the relatively rare taxon Semiorbis hemicyclus. Defining characters for Semiorbis include strongly arcuate valves, short eunotioid raphe branches, well-developed external costae with spine-like projections on the virgae, lack of rimoportulae, and a broader dorsal mantle. New populations of Semiorbis were found in the central USA (Wisconsin) on Outer Island, Apostle Islands National Lakeshore, along southeast Lake Superior, from a lake in New Jersey (USA), and from a small arctic lake in Nunavut, Canada. The population in Outer Lagoon, a shallow embayment cut off from Lake Superior by a long-shore bar, provided documentation of living cells and colonies of Semiorbis. We examined the morphology, ecology, and taxonomy of these new populations using light and scanning electron microscopy, traditional morphometrics, and sliding landmarks shape analysis. We compared these populations to European populations of Semiorbis hemicyclus and North American populations of Semiorbis rotundus and Semiorbis catillifera. We determined that the population found in Wisconsin represents a new species herein described as Semiorbis eliasiae Edlund, D.R.L.Burge, N.A.Andresen & VanderMeulen sp. nov., the New Jersey (USA) population is Semiorbis rotundus, and the Nunavut (Canada) population represents a North American population of the generitype Semiorbis hemicyclus.

Modern and fossil populations of a Stephanodiscus Ehrenberg species from June Lake, California (USA) were analysed using light and scanning electron microscopy (SEM). Stephanodiscus valves were a m...

We used light and electron microscopy to characterize a Late Miocene freshwater diatomite deposit in the Chalk Hills Formation, near Payette, Idaho, USA. The diatom assemblage from this sample was ...

Background and aims – Mastogloia grevillei has been shown to be a polymorphic diatom species, producing frustules with morphology of Mastogloia grevillei, frustules with morphology of M. danseyi, and more rarely, heteromorphic or Janus cells with one valve of each morphology. Methods – We investigated a wetland population from Iowa (USA) known to produce heteromorphic valves and the type material of Mastogloia grevillei and M. danseyi to clarify the nomenclature of this taxon. Key results – The polymorphic shift in stria construction and density between Mastogloia grevillei and M. danseyi occurs in populations sampled decades apart, among widely separated populations, within single genotypes, and independent of sexual reproduction. Combining our observations with observations of type material for Mastogloia grevillei and M. danseyi we propose that Mastogloia danseyi f. grevillei stat. nov. be recognized as an ecophenotype of the nominate Mastogloia danseyi, as the latter taxon has nomenclatural priority. We also provide lectotypes for both taxa. Conclusions – Variability in stria structure and density between the two taxa is discontinuous and represents a probable polyphenism for diatoms that is likely triggered by changing total dissolved solids, conductivity, and/or solutes.

Background and aims – Diatoms began to inhabit freshwater by at least the Late Cretaceous, becoming well established by the early to middle Eocene. Aulacoseira, an important diatom in numerous ponds, lakes and rivers today, was one of the earliest known genera to colonize freshwater ecosystems. Members of this genus with characteristics familiar to those found on modern species became increasingly more abundant by the Eocene, and continued to thrive throughout the Miocene to the present. We describe a new species of Aulacoseira from an early to middle Eocene site near the Arctic Circle in northern Canada. Methods – Twelve samples taken from the Giraffe Pipe core were analysed in this study. Light and scanning electron microscopy were used to document morphological characters. Morphometric measurements were made from 200 specimens per sample (n = 1200), and used to investigate changes in valve size over time. Key results – The new species, Aulacoseira giraffensis, has valves with a length:width ratio close to 1, a hyaline valve face, straight mantle striae, a shallow ringleiste, branched linking spines, concave-convex complementarity on adjacent valve faces, and rimoportulae with simple papillae-like structure. The suite of characters, especially the highly branched spines, concave-convex valves and simple rimoportulae, is unique for this species. Large numbers of A. giraffensis specimens were found over a ten-metre section of the core, representing thousands of years. These high concentrations are indicative of abundant, bloom-like, growth. Conclusions – The locality represents one of the earliest known records of Aulacoseira dominating a freshwater community. Findings confirm that the morphological body plan for the genus was well established by the Eocene. Although findings indicate evolutionary stasis in morphological structure for A. giraffensis over a time scale of thousands of years, oscillations in valve morphometrics could potentially be used to trace changes in the environment of this ancient Arctic waterbody.

We observed four Gomphonema taxa with a high abundance of Janus cells, which are cells that have valves of two different morphologies, also termed heterovalvar cells. The specimens were collected from a habitat with periodic drying, alternating with standing water. A high proportion of Gomphonema Janus cells (up to 20% of the frustules for each taxon) were found. Heterovalvy within a frustule is based on stria count, and two types of heterovalvy were observed. Cells produced either coarsely or finely striated valves with discontinuous phenotypic plasticity or highly variable stria density within a frustule along a continuous phenotypic gradient. In our study, we measured stria density in complete frustules and single valves. Other features of the frustules showed no noticeable variation. Variable stria density was found in frustules and single valves, although it is not possible to determine whether the single valves were part of Janus cells or homomorphic frustules. Therefore, our conclusions are based o...

Iran is a large country with a great diversity of aquatic ecosystems including rivers, springs, shallow seas, lakes, waterfalls, lagoons, and wetlands. Despite the many types of aquatic habitats, there has been a limited study of the diatom flora. The purpose of this study is to present the diatom species and characterize their distribution in the Karaj River, which flows in Iran’s Central Alborz region. The Alborz is one of the Irano-Anatolian ecoregions that serve as biodiversity hotspots. The Central Alborz, located in the middle part of this mountainous area, is an outstanding ecological and geological resource. This study uses the diatom flora to determine the biodiversity in one of the major rivers of the Central Alborz. Periphytic diatom samples were collected monthly from six stations along the length of the Karaj River between May 2011 and April 2012. A total of 128 diatom taxa was found from 48 genera expanding our understanding of regional aquatic diversity as 42 species are recorded as new for the diatom flora of Iran. Furthermore, the biogeography of the diatom flora of the Karaj River is considered in relation to the rest of Iran, the Middle East, and Asian and European diatom communities. © 2019, © 2019 The International Society for Diatom Research.

The St. Louis River Estuary (SLRE), a freshwater estuary bordering Duluth, Minnesota, Superior, Wisconsin, and the most western point of Lake Superior (46.74°, − 92.13°), has a long history of human development since Euro-American settlement ~ 200 years ago. Due to degradation from logging, hydrologic modification, industrial practices, and untreated sewage, the SLRE was designated an Area of Concern in 1987. Action has been taken to restore water quality including the installation of the Western Lake Superior Sanitary District in 1978 to help remove beneficial use impairments. A better understanding of historical impacts and remediation is necessary to help document progress and knowledge gaps related to water quality, so a paleolimnological study of the SLRE was initiated. Various paleolimnological indicators (pigments, diatom communities, and diatom-inferred phosphorus) were analyzed from six cores taken throughout the SLRE and another from western Lake Superior. Reductions in eutrophic diatom taxa such as Cyclotella meneghiniana and Stephanodiscus after 1970 in certain cores suggest an improvement in water quality over the last 40 years. However, in cores taken from estuarine bay environments, persistence of eutrophic taxa such as Cyclostephanos dubius and Stephanodiscus binderanus indicate ongoing nutrient problems. Sedimentary pigments also indicate cyanobacteria increases in bays over the last two decades. Diatom model-inferred phosphorus and contemporary monitoring data suggest some of the problems associated with excess nutrient loads have been remediated, but modern conditions (internal phosphorus loading, changing climate) may be contributing to ongoing water quality impairments in some locations. The integrated record of biological, chemical, and physical indicators preserved in the sediments will aid state and federal agencies in determining where to target their resources.

Paleolimnologists have utilized lake sediment records to understand historical lake and landscape development, timing and magnitude of environmental change at lake, watershed, regional and global scales, and as historical datasets to target watershed and lake management. Resurrection ecologists have long recognized lake sediments as sources of viable propagules (“seed or egg banks”) with which to explore questions of community ecology, ecological response, and evolutionary ecology. Most researchers consider Daphnia as the primary model organism in these efforts, but many other aquatic biota, from viruses to macrophytes, similarly produce viable propagules that are incorporated in the sediment record but have been underutilized in resurrection ecology. The common goals shared by these two disciplines have led to mutualistic and synergistic collaborations—a development that must be encouraged to expand. We give an overview of the achievements of paleolimnology and the reconstruction of environmental history of lakes, review the untapped diversity of aquatic organisms that produce dormant propagules, compare Daphnia as a model of resurrection ecology with other organisms amenable to resurrection studies, especially diatoms, and consider new research directions that represent the nexus of these two fields.

Anderson JP, Paterson AM, Reavie ED, Edlund MB, Ruhland, KM. 2017. An introduction to Lake of the Woods – from science to governance in an international water body. Lake Reserv Manage. 33:325–334.Lake of the Woods (LOW), a vast lake covering over 3850 km2, is a waterbody of current and historical significance that spans the borders between Minnesota and the Canadian provinces of Ontario and Manitoba. Over the past 2 decades, there has been concern for the water quality of LOW, sparked by anecdotal evidence of increased intensity and frequency of algal blooms by the public and resource managers. Minnesota's waters of LOW were declared impaired in 2008 due to exceedances of eutrophication criteria, initiating a Total Maximum Daily Load study. LOW's impairment declaration spurred several contrasting challenges and opportunities for water quality management across this diverse lake and basin. Governance challenges are emphasized by the large number of government agencies (>25) with land or water autho...

Edlund MB, Schottler SP, Reavie ED, Engstrom DR, Baratono NG, Leavitt PR, Heathcote AJ, Wilson B, Paterson AM. 2017. Historical phosphorus dynamics in Lake of the Woods (USA–Canada) — does legacy phosphorus still affect the southern basin? Lake Reserv Manage. 33:386–402. A historical phosphorus (P) budget was constructed for southern Lake of the Woods. Sediment cores from 7 bays were radioisotopically dated and analyzed for loss-on-ignition, P, Si, diatoms, and pigments. Geochemical records for cores were combined using focusing factors for whole-basin estimates of sediment, total P, and P fraction accumulation. Although historical monitoring shows that external P loads decreased since the 1950s, sediment P has continued to increase since the mid-20th century. Much sediment P is labile and may be mobile within the sediments and/or available for internal loading and resuspension. Two mass-balance models were used to explore historical P loading scenarios and in-lake dynamics, a static one-box model and a dynamic multi-box model. The one-box model predicts presettlement external loads were slightly less than modern loads. The dynamic model shows that water-column P was higher in the 1950s–1970s than today, that the lake is sensitive to external loads because P losses from burial and outflow are high, and that the lake is moving to a new steady state with respect to water-column P and size of the active sediment P pool. The active sediment pool built up in the mid-20th century has been depleted through outflow and burial, such that its legacy effects are now minimal. Comparison of historical nutrient dynamics and sediment records of algal production showed a counterintuitive increase in production after external P loads decreased, suggesting other drivers may now regulate modern limnoecology, including seasonality of P loading, shifting nutrient limitation, and climate warming.

Small peat-forming ecosystems in arctic landscapes may play a significant role in the regional biogeochemistry of high-latitude systems, yet they are understudied compared to arctic uplands and other major peat-forming regions of the North. We present a new data set of 25 radiocarbon-dated permafrost peat cores sampled around eight low arctic lake sites in northern Manitoba (Canada) to examine the timing of peat initiation and controls on peat accumulation throughout the Holocene. We used macrofossils and charcoal to characterize changes in the plant community and fire, and we explored potential impacts of these local factors, as well as regional climatic change, on rates of C accumulation and C stocks. Peat initiation was variable across and within sites, suggesting the influence of local topography, but 56% of the cores initiated after 3000 B.P. Most cores initiated and remained as drier bog hummock communities, with few vegetation transitions in this landscape. C accumulation was relatively slow and did not appear to be correlated with Holocene-scale climatic variability, but C stocks in this landscape were substantial (mean = 45.4 kg C m−2), potentially accounting for 13.2 Pg C in the Taiga Shield ecozone. To the extent that small peat-forming systems are underrepresented in peatland mapping, soil organic carbon (SOC) stocks may be underestimated in arctic regions. Mean fire severity appeared to be negatively correlated with C accumulation rates. Initiation and accumulation of soil C may respond to both regional and local factors, and substantial lowland soil C stocks have the potential for biogeochemical impacts on adjacent aquatic ecosystems.

The late-Quaternary paleoenvironmental history of the western Hudson Bay region of Subarctic Canada is poorly constrained. Here, we present a regional overview of the post-glacial history of eight lakes which span the forest-tundra biome in northern Manitoba. We show that during the penultimate drainage phase of Lake Agassiz the lake water had an estimated pH of ∼6.0, with abundant quillwort (Isoetes spp.) along the lakeshore and littoral zone and some floating green algae (Botryococcus spp. and Pediastrum sp.). Based on multiple sediment proxies, modern lake ontogeny in the region commenced at ∼7500 cal yrs BP. Pioneering diatom communities were shaped by the turbid, higher alkalinity lake waters which were influenced by base cation weathering of the surrounding till following Lake Agassiz drainage. By ∼7000 cal yrs BP, soil development and Picea spp. establish and the lakes began a slow trajectory of acidification over the remaining Holocene epoch. The natural acidification of the lakes in this region is slow, on the order of several millennia for one pH unit. Each of the study lakes exhibit relatively stable aquatic communities during the Holocene Thermal Maximum, suggesting this period is a poor analogue for modern climatic changes. During the Neoglacial, the beginning of the post-Little Ice Age period represents the most significant climatic event to impact the lakes of N. Manitoba. In the context of regional lake histories, the rate of diatom floristic change in the last 200–300 years is unprecedented, with the exception of post-glacial lake ontogeny in some of the lakes. For nearly the entire history of the lakes in this region, there is a strong linkage between landscape development and the aquatic ecosystems; however this relationship appears to become decoupled or less strong in the post-LIA period. Significant 20th century changes in the aquatic ecosystem cannot be explained wholly by changes in the terrestrial ecosystem, suggesting that future changes to the lakes of N. Manitoba will be strongly influenced by direct climatic effects to the lakes.

Marine diatoms began colonizing freshwater habitats in the early Cenozoic, or possibly earlier, becoming well established by the Eocene. However, because of a sparse fossil record, little is known about the earliest diatom representatives that signalled this important ecological and evolutionary event. We describe a new centric diatom genus, Fideliacyclus, from lake sediments deposited during the Paleocene in the Canadian Arctic. This organism, one of the oldest known freshwater diatoms reported to date, has a unique, highly complex wall structure composed of areolae with large, bulbous, spherical shaped chambers that are open to the external environment but rest on a solid siliceous surface referred to as the solum, and are surrounded by an open space, or hypocaust. The solum is only perforated by marginal labiate processes, which largely isolates the protoplast from ambient conditions hence limiting exchange; this may have represented an adaptive response to living in freshwater. Given the complement of...

Ecological shifts in shallow lakes from clear-water macrophyte-dominated to turbid-water phytoplankton-dominated are generally thought of as rapid short-term transitions. Diatom remains in sediment records from shallow lakes in the Prairie Pothole Region of North America provide new evidence that the long-term ecological stability of these lakes is defined by the legacy of large regime shifts. We examine the modern and historical stability of 11 shallow lakes. Currently, four of the lakes are in a clear-water state, three are consistently turbid-water, and four have been observed to change state from year to year (transitional). Lake sediment records spanning the past 150-200 yr suggest that (1) the diatom assemblage is characteristic of either clear or turbid lakes, (2) prior to significant landscape alteration, all of the lakes existed in a regime of a stable clear-water state, (3) lakes that are currently classified as turbid or transitional have experienced one strong regime shift over the past 150-200 yr and have since remained in a regime where turbid-water predominates, and (4) top-down impacts to the lake food-web from fish introductions appear to be the dominant driver of strong regime shifts and not increased nutrient availability. Based on our findings we demonstrate a method that could be used by lake managers to identify lakes that have an ecological history close to the clear-turbid regime threshold; such lakes might more easily be returned to a clear-water state through biomanipulation. The unfortunate reality is that many of these lakes are now part of a managed landscape and will likely require continued intervention.

The direction of pan-Arctic ecosystem shifts in response to climate warming is relatively well understood; however, landscape-level linkages among terrestrial, wetland, and lake ecosystems significantly influence the dynamics of each, making it difficult to generalize about lake responses to warming across the Arctic, and at times difficult to interpret paleoclimate records from lake sediments. To investigate differences in lake responses to recent climate change at the boreal-tundra ecotone, we conducted a 2-year survey of diatom assemblages from lakes with varying catchment characteristics in northern Manitoba, Canada. We investigated whether catchment geomorphology and landscape, including slope and vegetative cover, result in characteristic water chemistries and hence diatom assemblage signatures, which could then be used in paleolimnological studies to infer past changes in the catchment. Forty-four lakes were sampled for water chemistry and catchment vegetation was characterized using Landsat Imagery. Lake catchments were generally small (median 702 ha) and dominated by peat (Sphagnum) with or without lowland forest (Picea-Larix), or open tundra, with different amounts of exposed rock/till, upland forest/woodlands, and burn recovery area. Lakes were generally nutrient-poor, with lower nutrient and DOC concentrations in tundra-dominated catchments, and higher nutrients and DOC in catchments with greater forest cover. A diatom-based transfer function for pH (R2 = 0.72, \( {\text{R}}_{\text{boot}}^{2} \) = 0.54) was developed and compared with diatom assemblage turnover and sediment geochemistry in cores from eight lakes to reconstruct limnologic conditions over the past ~200 years. Most cores showed similar increases in biogenic silica and carbon burial, beginning around AD 1880 in the tundra lakes and about 1920 in the more forested catchments, likely in response to regional warming. In contrast to lakes in other Arctic regions, our lakes showed only minor pH changes in recent decades. The shift, however, was more pronounced in higher-latitude lakes with less forest cover, suggesting small-scale watershed influence on lake response to climate, even on short time scales. Diatom assemblages did not follow previously published models of climate-linked community change seen in circum-Arctic and sub-Arctic lakes. Translating local changes detected in the paleolimnological record to the regional level requires an understanding of how different catchment properties mediate the response of lakes, and their diatom assemblages, to climate change.

Atmospheric deposition is a primary source of reactive nitrogen (Nr) to undisturbed watersheds of the Great Lakes region of the U.S., raising concerns over whether enhanced delivery over recent decades has affected lake ecosystems. The National Atmospheric Deposition Program (NADP) has been measuring Nr deposition in this region for over 35 years. Here we explore the relationships among NADP-measured Nr deposition, nitrogen stable isotopes (δ15N) in lake sediments, and the response of algal communities in 28 lakes situated in national parks of the western Great Lakes region of the U.S. We find that 36% of the lakes preserve a sediment δ15N record that is statistically correlated with some form of Nr deposition (total dissolved inorganic N, nitrate, or ammonium). Furthermore, measured long-term (since 1982) nitrogen biogeochemistry and inferred critical nitrogen loads suggest that watershed nitrogen retention and climate strongly affect whether sediment δ15N is related to Nr deposition in lake sediment records. Measurements of algal change over the last ~ 150 years suggest that Nr deposition, in-lake nutrient cycling, and watershed inputs are important factors affecting diatom community composition, in addition to direct climatic effects on lake physical limnology. The findings suggest that bulk sediment δ15N does reflect Nr deposition in some instances. In addition, this study highlights the interactive effects of Nr deposition and climate variability.

Understanding the phenology of emergences can be useful in determining seasonal chironomid life cycle patterns, which are often influenced by ice cover and temperature in cold climates. Lake Superior is the largest lake in North America and with a mean surface temperature of 3.9 °C influences regional climate. Coastal pools at Isle Royale, a wilderness archipelago in the northern part of the lake, occur in dense patches on low-gradient volcanic bedrock between the lakeshore and forest, creating variable microhabitats for Chironomidae. Four sites were sampled monthly from April to October, 2010. Surface-floating pupal exuviae were collected from a series of pools in two zones: a lower zone near the lake influenced by wave splash, and an upper zone near the forest and influenced by upland runoff. We used Jaccard’s and Whittaker’s diversity indexes to test community similarity across months. Temperature loggers in pools collected hourly readings for most of the study. Assemblage emergences were stable in upper pools, with significant similarity across late spring and summer months. Assemblages were seasonally variable in lower pools, with significant dissimilarity across spring, summer, and fall months. Few species in either zone were unique to spring or fall months. However, many summer species in the splash zone had a narrow emergence period occurring during calm weather following distinct increases in mean water temperature. Regardless of input of cold lake water to the lower zone, pools from both zones generally had corresponding temperature trends.

To better understand aquatic–terrestrial linkages in the sub-Arctic, and specifically the relative importance of landscape position versus land cover, we surveyed lakes, soils, land cover, and lake/basin characteristics in a 14 000 km 2 region of acidic forest–tundra landscape near northern Manitoba, Canada (59.56°N, 97.72°W) in 2009. We analyzed 39 different biological, chemical, and physical variables for lakes and soils. We used a remote-sensing– based classification to determine that the landscape was 21% water, 46% peat-forming lowland, and 24.9% open tundra, and we assigned lake order to all lakes based on the order of the outlet stream for each lake. Lakes were oligotrophic to mesotrophic (median total phosphorus: TP = 11.8 µg L −1 ), N-limited (median dissolved inorganic nitrogen: TP = 1.6), acidic (median pH 5.7), and had moderate amounts of dissolved organic carbon (median DOC = 5.2 mg L −1 ). We identified 2 principle groups of variables represented by DOC and conductivity/ cations, respectively, that captured major axes of lake variation. DOC, 2 measures of DOC quality (a 250 /a 365 [a proxy for molecular weight and aromaticity] and specific ultraviolet absorbance), and Fe and were significantly correlated with percent cover of lowland forest, but conductivity/cations were not correlated with variation in land cover. Soils were generally acidic (pH 2.7–4.4) and nutrient-poor, and wetland soils contained more carbon and higher concentrations of calcium, magnesium, and other cations than upland open tundra. Landscape position of lakes (measured as lake order) did not capture systematic differences in land cover or lake biogeochemistry. Our results highlight the importance of lowland export of DOC to lakes and further suggest the need for additional regional studies of aquatic–terrestrial connections in Arctic and sub-Arctic landscapes.

Reavie ED, Edlund MB, Andresen NA, Engstrom DR, Leavitt PR, Schottler S, Cai M. 2017. Paleolimnology of the Lake of the Woods southern basin: continued water quality degradation despite lower nutrient influx. Lake Reserv Manage. 33:369–385. Despite decades of reduced nutrient inputs, Lake of the Woods, a large, shallow boreal lake on the US-Canadian border, shows little evidence of water quality improvements in the pelagic system. Here we analyzed sediments from 6 sites in the southern basin for diverse biogeochemical (loss-on-ignition, biogenic silica, pigments) and microfossil (diatoms, chrysophytes) remains to reconstruct the environmental history of the lake. Our objectives were to quantify the magnitude and direction of historical trophic change and evaluate reasons for an apparent lack of basin recovery following documented nutrient diversion. Evidence came from fossil indicator profiles and comparisons of these long-term trends with historical land use and monitoring data. Results indicate major changes in algal communities during and following peak nutrient loading in the mid-20th century as well as more recent increases in colonial cyanobacteria and high-nutrient diatom taxa. Combined, fossil indicators reflect an anthropogenically enriched system that has undergone substantial ecological change, particularly since ∼1980, due to multiple drivers. Physical changes in lake thermal regime resulting from climate warming may be exacerbating internal phosphorus release from sediments, thereby lowering nitrogen:phosphorus ratios and enhancing cyanobacterial abundance. These drivers of lake condition in the lake may apply to other large shallow lakes that exhibit only limited biological recovery from reduced external nutrient loading.

The past few decades have brought about a significant expansion in our understanding of the diatom life cycle, particularly its sexual part. Presented here is a set of proposals for the terminology of processes and structures associated with sexual reproduction and for the resting stages of diatoms, some of which have at times been confused with each other. The proposals fill the void present in widely used publications offering standardized terminology related to diatom frustule micro-architecture.

Intensified warming in the Arctic and Subarctic is resulting in a wide range of changes in the extent, productivity, and composition of aquatic and terrestrial ecosystems. Analysis of remote sensing imagery has documented regional changes in the number and area of ponds and lakes as well as expanding cover of shrubs and small trees in uplands. To better understand long-term changes across the edaphic gradient, we compared the number and area of water bodies and dry barrens (>100 m2) between 1956 (aerial photographs) and 2008–2011 (high-resolution satellite images) for eight ∼25 km2 sites near Nejanilini Lake, Manitoba (59.559°N, 97.715°W). In the modern landscape, the number of water bodies and barrens were similar (1162 versus 1297, respectively), but water bodies were larger (mean 3.1 × 104 versus 681 m2, respectively) and represented 17% of surface area compared with 0.4% for barrens. Over the past 60 years, total surface area of water did not change significantly (16.7%–17.1%) despite a ∼30% decrease in numbers of small (2) water bodies. However, the number and area of barrens decreased (55% and 67%, respectively) across all size classes. These changes are consistent with Arctic greening in response to increasing temperature and precipitation. Loss of small water bodies suggests that wet tundra areas may be drying, which, if true, may have important implications for carbon balance. Our observations may be the result of changes in winter conditions in combination with low permafrost ice content in the region, in part explaining regional variations in responses to climate change.

A 7-year-old spayed female German Wirehaired Pointer was presented with difficulty breathing after being found seizing in a water-filled drainage ditch while out hunting. Aspirates from a tracheal wash contained numerous degenerate neutrophils, fewer macrophages, some of which contained basophilic debris, low numbers of extracellular diatoms, and a single intracellular short bacterial rod. As the dog continued to clinically decline and could not be weaned from oxygen support, the owners chose euthanasia. The major necropsy finding was a severe granulomatous bronchopneumonia that was likely due to aspiration of foreign material based on the microscopic presence of plant-like material, bi-refringent crystalline material, non-cellular debris, and occasional fungal structures. Diatoms are a class of algae that live primarily in water. Diatom analysis has been used, with some controversy, in human forensics to assist in documenting drowning as the cause of death. In this case, given the clinical history, the presence of diatoms and inflammation in the tracheal wash were interpreted as a likely result of the aspiration of surface water. To our knowledge, this is the first reported case of diatoms observed in a cytologic specimen in a nonhuman mammal with aspiration pneumonia.

Paleolimnological information is often extracted from diatom records using weighted averaging calibration and regression techniques. Larger calibration sample sets yield better inferences because they better characterize the environmental characteristics and species assemblages of the sample region. To optimize inferred information from fossil assemblages, however, it is worth knowing if fewer calibration samples can be used. Furthermore, confidence in environmental reconstructions is greater if we consider the relative importance of (A) similarity between fossil and calibration assemblages and (B) how well fossil taxa respond to the environmental variable of interest. We examine these issues using ~200-year sediment profiles from four Minnesota lakes and a 145-lake surface sediment training set calibrated for total phosphorus (TP). Training set sample sizes ranging from 10 to 145 were created through random sample selection, and models based on these training sets were used to calculate diatom-inferred (DI) TP data from fossil samples. Relationships between DI-TP variability and sample size were used to determine the minimum sample size needed to optimize the model for paleo-reconstruction. Similarly, similarities between fossil and modern assemblages were calculated for each size training set. Finally, fossil and modern assemblages were compared to determine whether older fossil samples had poorer similarity with modern analogs. More than 50–80 samples, depending on lake, were needed to stabilize variability in DI-TP results, and >110 training set samples were needed to minimize modern-fossil assemblage dissimilarities. Dissimilarities appeared to increase with sample age, but only one of the four studied cores displayed a significant trend. We have two recommendations for future studies: (1) be cautious when dealing with smaller training sets, especially if they are used to interpret older fossil assemblages and (2) understand how well fossil taxa are attuned to the variable of interest, as it is critical to evaluating the quality of the diatom-inferred data.

The low-Arctic region of western Hudson Bay in interior Canada is one of the most poorly described areas of North America in terms of Holocene climate history. Here, we present new data from a well-dated lake sediment core from northern Manitoba, Canada. We assemble one of the richest multi-proxy datasets to date for a low-Arctic lake and characterize terrestrial and lake processes and exchanges between them. These proxies include fossil pollen and diatom assemblages, charcoal, magnetic properties (susceptibility and remanance), mineral grain size, bulk density, organic-matter content, elemental geochemistry, sediment cation (K+, Mg2+, Ca2+, Fe2+/Fe3+) and macronutrient (P, N, C) contents, biogenic-silica content, basal peat dates (wetland initiation), and stable isotopes (δ13C, δ15N). The sediment proxies record both broad- and fine-scale (millennial and sub-millennial) climate change. We find indirect evidence for a cool and dry post-glacial period from 9,000 to 6,500 cal yr BP, a warm and moist mid-Holocene period from 6,500 to 2,500 cal yr BP, and a cool and moist late-Holocene period from 2,500 cal yr BP to present. High-resolution geochemical data suggests 300- to 500-year-long dry periods at ~6,500–6,100, 5,300–5,000, 3,300–2,800, and 400–0 cal yr BP. These results suggest that terrestrial and aquatic ecosystem dynamics in the western Hudson Bay region are sensitive to past climate change and are likely to respond to future changes in temperature and precipitation.

Arctic and sub-arctic lake sediment sequences from the Pleistocene are uncommon due to multiple glacial–interglacial cycles and the associated advances and retreats of Pleistocene ice sheets. Pleistocene strata are preserved in a 9-m-long sediment core recovered from Pingualuit Crater Lake, Nunavik, northern Quebec (Canada). In addition to tychoplanktonic Aulacoseira species, the Pleistocene planktonic flora comprises representatives from the thalassiosiroid genera Cyclotella, Discostella and Puncticulata, of which most species are extant in perennially ice-free sub-arctic and arctic lakes. One Cyclotella species, C. pingualuitii is described as new and is characterized by a small central area, multiple central and scattered marginal fultoportulae with triangular satellite pore covers, a single large submarginal rimoportula and alveolate striae of unequal length. Cyclotella pingualuitii is the most prominent species during the oldest diatom-rich interval (DR3) recovered, which was deposited during the Lat...

A new Eunotia species, E. charliereimeri, is described from Bear Meadows Bog near State College, Pennsylvania. Bear Meadows is an open, montane, nutrient-poor fen that is about 1.6 km long and 0.5 km wide with its open wetlands dominated by Sphagnum, sedges, swamp laurel, blueberry, sundews, Rhododendron spp., alder, Spiraea spp., and mountain holly. Eunotia charliereimeri has been collected intermittently from Bear Meadows over the last decade. Among the eunotioid diatoms, E. charliereimeri is characterized by its arcuate-lunate valve, prominent terminal raphe ends, and two rimoportulae per valve. Most importantly, it has amphoroid frustule symmetry, a character recently used to support the description of the new eunotioid genus Amphorotia Williams et Reid. However, E. charliereimeri does not share several other key features with Amphorotia including marginal spines or silica-rimmed external raphe fissures. A sister taxon, E. sarraceniae Gaiser et Johansen, described from South Carolina bays, s...

The Reimer Diatom Herbarium (ILH) at Iowa Lakeside Laboratory (ILL), a field station of Iowa's state universities, contains 3,280 permanent diatom slides of collections made from prairie potholes, alkaline fens, acid bogs, eutrophic lakes, saline lakes, Pleistocene paleolakes, and Miocene fossil deposits near ILL. The herbarium has a focus on collections made within Dickinson County, a region with an important legacy of study by students and visiting researchers from the US, Canada, and international institutions. The herbarium is well documented by taxon and location catalogues. The taxon card catalogue contains over 2,800 records referencing 67 genera, and the location card catalogue references collection sites from 51 counties in 16 North American states. Curated slides include over 300 species identifications made, or verified, by C.W. Reimer. Most curated slides have diatom specimens identified to species, circled with a diamond objective marker, and indicated on the slide label. Six holotypes are included in the herbarium and we present the first light micrograph images of these type specimens. We present documentation of the contents and current condition of the herbarium and report that it is now available to researchers for scientific study. Many of the sites represented in the Reimer Diatom Herbarium are the same locations visited each year by students and visiting researchers at ILL, resulting in an important resource for monitoring environmental change, resolving taxonomic issues, and understanding species distributions in unique habitats.

SUMMARY Several populations identified and reported from North America and Mongolia under the names Fragilaria elliptica Schumann or Staurosira elliptica (Schumann) Williams et Round were analyzed in detail using light microscopy (LM) and scanning electron microscopy (SEM). The analysis yielded three variants that can not be ascribed to ‘elliptica’ of the type. Furthermore, two of the variants could not be related to published taxa and we describe them as new species, Staurosira ambigua sp. nov. and Staurosira dimorpha sp. nov. A third variant was identified as Pseudostaurosira trainorii Morales, a taxon originally reported from ponds and a river in the north-eastern USA. The combined LM and SEM analysis used here allowed for a more thorough circumscription of taxonomic boundaries among morphologically similar taxa and for better delimitation of their geographic distributions. A discussion of the taxonomy and ecology of these taxa based on literature and recent ecological data is presented.

The Valley of the Great Lakes in western Mongolia is a unique ecosystem comprising a wide variety of terrestrial and aquatic habitats. Relatively little is known about the long-term climate history of the area or the relative impact of changes in climate and land use in the region. Tree-ring records have established an understanding of regional temperature fluctuations; however, the few records of moisture balance from Mongolia offer little insight into potential changes in the precipitation-to-evaporation balance in the region with warming temperatures. Modern and paleoclimatic records from across arid Central Asia show substantial temporal and spatial variability in the correlation between temperature and moisture availability and climate models are inconsistent in predictions for future changes with continued warming. In order to refine the understanding of moisture balance in the region, we developed six diatom-inferred records of lake salinity between 200 and 2000 years in length, demonstrating a negative correlation between temperature and effective moisture (warm-dry and cool-wet conditions) over most of this time period. In addition to climate warming, Mongolian grasslands have seen substantial human impacts over the last several decades. Recent core records show evidence of eutrophication and must be interpreted carefully to understand the individual and combined impacts of climate and land use on sedimentary records and the potential for human—environment interactions to confound inferences about climate changes.

Climate warming and major land-use changes have profoundly affected the Mongolian landscape in the past several decades. Previous studies have recognized the impacts of a warmer, more arid climate and Mongolia’s 1991 transition from a command to a market economy on terrestrial ecosystems, including impaired sustainability of subsistence herding and threats to wild animals. In this study, we examined the combined effects of changing climate and herding practices on lake eutrophication in Western Mongolia. We sampled 65 lakes for modern nutrients and found the majority of lakes were eutrophic to hyper-eutrophic. Sediment cores were taken from five of the lakes to compare current lake status to paleolimnologial measures of lake eutrophication over the past 100–2000 years, including changes in diatom assemblages, diatom-inferred total phosphorus, biogenic silica, organic matter, and sediment accumulation rates. Variance partitioning analysis showed that recent shifts in diatom assemblages were related to changes in both climate and herding practices. The results presented here demonstrate a need for further study and long-term monitoring of water quality in Mongolia to understand the complicated interactions of climate and land use on aquatic resources and to preserve water quality in this remote and ecologically important region.

Paleolimnological studies show that phosphorus (P) loads to the federally protected St. Croix River, a tributary of the Upper Mississippi River, have increased about threefold over the last century. Ongoing management efforts to protect and restore the river hinge on the question of whether the increased nutrient load results from point-source discharges or nonpoint runoff from agricultural intensification and urban expansion. Here we determine the historical contribution of point source phosphorus (P) loads to the St. Croix watershed from 1900–2000 A.D. Historical point source loads were estimated based on discharge volumes, demographics, industrial sources, wastewater technologies, and facility discharge records, where available. Sewering in the basin began in 1905, and since that time, there have been as many as 169 permitted point source dischargers basinwide, including municipal, industrial, and agricultural facilities. Early wastewater management typically discharged untreated sewage; technological advances had secondary treatment in place at most facilities by the 1960s–1970s and much of the municipal population was served by tertiary treatment by the 1990s. Peak nutrient discharges from point sources occurred in the 1960s–1970s. Detergent phosphorus bans instituted in the late 1970s for Minnesota and Wisconsin, greater use of land and groundwater effluent disposal, and improvements in treatment technology brought about decreases in P loads in the 1980s and 1990s. Point-source discharges were compared to historical total phosphorus loads estimated in a whole-basin phosphorus mass balance to calculate the historical contribution of point sources, anthropogenic nonpoint sources, and natural or background sources. We estimated 1990s point source loads at 48 t P yr−1, which represents about 10% of the total phosphorus load (459 t P yr−1, flow-corrected to 412 t P yr−1) to the basin. Without further controls on nutrient inputs to the St. Croix River, annual flow-corrected P loads are projected to increase to 498 t P yr−1 by the 2020s with point source phosphorus loading contributions at 65 t P yr−1 or 13% of the total load. However, if we exclude background P loads to the St. Croix (166 t P yr−1), recent nutrient loads are primarily from anthropogenic nonpoint sources. Point sources also contribute over 19% of the current and future phosphorus load that can be attributed to human activities in the watershed. Interstate and federal efforts to decrease P loading to the St. Croix River by 20% will need to target both point and nonpoint sources.

Lake St. Croix is a natural impoundment of the lowermost 37 km of the St. Croix River in Minnesota and Wisconsin, making this one of a few large river systems in the world possessing a long-term depositional basin at its terminus. The river’s relatively pristine condition led to its designation as a National Scenic Riverway in 1968, but increasing urbanization in its lower reaches has raised concerns about impacts on water quality. This study was initiated to reconstruct historical loadings of suspended sediment and phosphorus (P) from the sediment record in Lake St. Croix. Twenty-four piston cores, with an average length of 2 m, were collected along eight transects of the lake. Dated chronologies from 210Pb, 137Cs and 14C were used to calculate the rate of sediment accumulation in the lake over the past 100+ years. Diatom microfossil analysis was used to reconstruct historical lakewater P concentrations over the same time period, and sediment P analysis quantified the amount of P trapped in lake sediments. Using a whole-lake mass balance approach, the loading of sediment and P to Lake St. Croix over the last 100+ years was calculated. Beginning in 1850, sediment accumulation increased dramatically to a peak in 1950–1960 of eight times background rates prior to European settlement. The peak is driven largely by sediment contributions from small side-valley catchment tributaries to the downstream half of the lake. The total P load to the lake increased sharply after 1940 and remains high, at around four times the level of pre-European settlement conditions. The timing of peak sediment and P loading to the lake shows that early settlement activities, such as logging and the conversion of forest and prairie to agricultural land between 1850 and 1890, had only modest impacts on the lake. By contrast, the mid-1900s brought major increases in sediment and P loading to the lake, suggesting that relatively recent activities on the landscape and changes to nutrient balances in the watershed have caused the current eutrophic condition of this important recreational and natural resource.