Imaging Thermal Stratigraphy in Freshwater Lakes Using Georadar

Thermal stratification exerts significant control over biogeochemical processing in freshwater lakes. Thus, the temporal and spatial distribution of the thermal structure is an important component in understanding lake ecosystems. We present the first reported observations of lake thermal stratification from surface based georadar measurements acquired over two small freshwater lakes. This method is very useful because it can provide rapid acquisition of 2D or 3D lotic stratification

Salting our Freshwater Lakes

The highest densities of lakes on Earth are in north temperate ecosystems, where increasing urbanization and associated chloride runoff can salinize freshwaters and threaten lake water quality and the many ecosystem services lakes provide. However, the extent to which lake salinity may be changing at broad spatial scales remains unknown, leading us to first identify spatial patterns and then investigate the drivers of these patterns. Significant decadal trends in lake salinization were identified using a dataset of long-term chloride concentrations from 371 North American lakes. Landscape and climate metrics calculated for each site demonstrated that impervious land cover was a strong predictor of chloride trends in Northeast and Midwest North American lakes. As little as 1% impervious land cover surrounding a lake increased the likelihood of long-term salinization. Considering that 27% of large lakes in the United States have \u3e1% impervious land cover around their perimeters, the potential for steady and long-term salinization of these aquatic systems is high. This study predicts that many lakes will exceed the aquatic life threshold criterion for chronic chloride exposure (230 mg L−1), stipulated by the US Environmental Protection Agency (EPA), in the next 50 y if current trends continue

Widespread occurrence of distinct alkenones from Group I haptophytes in freshwater lakes: Implications for paleotemperature and paleoenvironmental reconstructions

Alkenones are C35-C42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature. However, their use in coastal seas and saline lakes can be hindered by species-mixing effects. We recently hypothesized that freshwater lakes are immune to species-mixing effects because they appear to exclusively host Group I haptophyte algae, which produce a distinct distribution of alkenones with a relatively consistent response of alkenone unsaturation to temperature. To evaluate this hypothesis and explore the geographic extent of Group I haptophytes, we analyzed alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid- and high latitudes of the Northern Hemisphere (n = 30). Our results indicate that Group I-type alkenone distributions are widespread in freshwater lakes from a range of different climates (mean annual air temperature range: -17.3-10.9 degrees C; mean annual precipitation range: 125-1657 mm yr(-1); latitude range: 40-81 degrees N), and are commonly found in neutral to basic lakes (pH > 7.0), including volcanic lakes and lakes with mafic bedrock. We show that these freshwater lakes do not feature alkenone distributions characteristic of Group II lacustrine haptophytes, providing support for the hypothesis that freshwater lakes are immune to species-mixing effects. In lakes that underwent temporal shifts in salinity, we observed mixed Group I/II alkenone distributions and the alkenone contributions from each group could be quantified with the RIK37 index. Additionally, we observed significant correlations of alkenone unsaturation (U-37(K)) with seasonal and mean annual air temperature with this expanded freshwater lakes dataset, with the strongest correlation occurring during the spring transitional season (U-37(K) = 0.029 * T - 0.49; r(2) = 0.60; p < 0.0001). We present new sediment trap data from two lakes in northern Alaska (Toolik Lake, 68.632 degrees N, 149.602 degrees W; lake E5, 68.643 degrees N, 149.458 degrees W) that demonstrate the highest sedimentary fluxes of alkenones in the spring transitional season, concurrent with the period of lake ice melt and isothermal mixing. Together, these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a lake temperature proxy. (C) 2018 Elsevier B.V. All rights reserved

Dissolved carbon and CDOM in lake ice and underlying waters along a salinity gradient in shallow lakes of Northeast China

The variations of DOC and DIC concentrations in lake ice and underlying waters were examined in 40 shallow lakes across the Songnen Plain, Northeast China. The lakes, frozen annually during winter, included freshwater and brackish systems (EC > 1000 μS cm−1; range: 171–12607 μS cm−1 in underlying water). Results showed that lake ice contained lower DOC (7.2 mg L−1) and DIC (6.7 mg L−1) concentration compared to the underlying waters (58.2 and 142.4 mg L−1, respectively). Large differences in DOC and DIC concentrations of underlying waters were also observed between freshwater (mean ± SD: 22.3 ± 11.5 mg L−1, 50.7 ± 20.6 mg L−1) and brackish lakes (83.3 ± 138.0 mg L−1, 247.0 ± 410.5 mg L−1). A mass balance model was developed to describe the relative distribution of solutes and chemical attributes between ice and the underlying waters. Results showed that water depth and ice thickness were the key factors regulating the spatial distribution of solutes in the frozen lakes. Chromophoric dissolved organic matter (CDOM) absorption coefficient at 320 nm, aCDOM(320) and specific UV absorbance (SUVA254) were used to characterize CDOM composition and quality. Compared to the underlying waters, CDOM present in ice largely included low aromaticity organic substances, an outcome perhaps facilitated by ice formation and photo-degradation. In ice and underlying freshwaters, CDOM predominantly included organic C fractions of high aromaticity, while low aromaticity organic substances were observed for brackish lakes. Results of this study suggest that, if water salinity increases due to climate change and anthropogenic activities, significant changes can occur in the dissolved carbon and fate of CDOM in these shallow lakes

Investigating Changes in Chlorophyll a and Other Water Chemistry Variables in Response to Global Environmental Change

Changes in water quality are influenced by climate change and other anthropogenic stressors. We 1) assessed changes in water quality in lakes in the Laurentian Great Lakes region, and 2) compiled water quality data for lakes across the world to assess global patterns in chlorophyll a. We found that at the regional scale water quality (specifically chlorophyll a, total phosphorus, total nitrogen, and dissolved organic carbon) were influenced by temperature, precipitation, morphology, and the presence of dreissenids. We also compiled chlorophyll a and water chemistry data together with morphometric characteristics for 8557 lakes worldwide. This global dataset will allow researchers to associate global water quality patterns to different pressures such as changes climate or land use

Rotifers, and other aquatic invertebrates, from the Larsemann Hills, Antarctica

Seventeen species of rotifer (11 Monogononta and six Bdelloidea) three tardigrades, two arthropods, as well as protozoans, a plathyhelminth and nematodes were found in 13 freshwater lakes in the Larsmann Hills, Antartctic

Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Mid-Atlantic): Alewife/Blueback Herring

This profile covers life history and environmental requirements of both alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis), since their distribution is overlapping and their morphology, ecological role, and environmental requirements are similar. The alewife is an anadromous species found in riverine, estuarine, and Atlantic coastal habitats, depending on life cycle stage, from Newfoundland (Winters et al. 1973) to Soutn Carolina (Berry 1964). Landlocked populations are i n the Great Lakes, Finger Lakes, and many other freshwater lakes (Bigelow and Sch roeder 1953; Scott and Crossman 1973). The blueback herring is an anadromous species found in riverine, estuarine, and Atlantic coastal habitats, depending on life stage cycle, from Nova Scotia to the St. Johns River, Florida (Hildebrand 1963

Systematics of Beringian threespine sticklebacks

Thesis (M.S.) University of Alaska Fairbanks, 2000In Pleistocene Beringia, large-scale glaciations exposed high latitude species to variable environmental conditions that created disjunct populations of terrestrial and marine species. The general nature of the dynamic biogeographic history of Beringia can be assessed by studying genetic patterns across many Beringian organisms. Mitochondrial DNA sequences were used to study the phylogenetic and phylogeographic structure of the threespine stickleback, Gasterosteus aculeatus. A 714 bp fragment of the cytochrome b gene was sequenced from 66 individuals from 17 locations extending from southeast Alaska northwest to coastal Siberia. These data were combined with 36 homologous cyt-b sequences from a previous study to provide a preliminary assessment of patterns of genetic variation in threespine stickleback- with a particular emphasis on Alaskan populations. Cytochrome b data show the existence of two major clades in the Pacific, with an extensive zone of overlap that spans the Bering Straits

Draft genome sequences of two unclassified Chitinophagaceae bacteria, IBVUCB1 and IBVUCB2, isolated from environmental samples

We report here the draft genome sequences of two Chitinophagaceae bacteria, IBVUCB1 and IBVUCB2, assembled from metagenomes of surface samples from freshwater lakes. The genomes are >99% complete and may represent new genera within the Chitinophagaceae family, indicating a larger diversity than currently identified

A River Otter's, Lontra canadensis, Capture of a Double-crested Cormorant, Phalacrocorax auritus, in British Columbia's Gulf Island Waters

Direct and apparent predation events by River Otters (Lontra canadensis) on birds have been recorded on marine islands and freshwater lakes. We add to this the first known observation of a River Otter capturing a marine bird on the ocean