Search

Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication.We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10‐fold larger catchment and an abrupt increase in production around 1990.Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low‐light‐adapted benthic diatoms. Analysis of pigment time‐series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N2‐fixing cyanobacteria despite persistent eutrophication.Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg.These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment. [ABSTRACT FROM AUTHOR]

Aquatic sediments record past climatic conditions while providing a wide range of ecological niches for microorganisms. In theory, benthic microbial community composition should depend on environmental features and geochemical conditions of surrounding sediments, as well as ontogeny of the subsurface environment as sediment degraded. In principle, DNA in sediments should be composed of ancient and extant microbial elements persisting at different degrees of preservation, although to date few studies have quantified the relative influence of each factor in regulating final composition of total sedimentary DNA assemblage. Here geomicrobiological and phylogenetic analyses of a Patagonian maar lake were used to indicate that the different sedimentary microbial assemblages derive from specific lacustrine regimes during defined climatic periods. Two climatic intervals (Mid-Holocene, 5 ka BP; Last Glacial Maximum, 25 ka BP) whose sediments harbored active microbial populations were sampled for a comparative environmental study based on fossil pigments and 16S rRNA gene sequences. The genetic assemblage recovered from the Holocene record revealed a microbial community displaying metabolic complementarities that allowed prolonged degradation of organic matter to methane. The series of Archaea identified throughout the Holocene record indicated an age-related stratification of these populations brought on by environmental selection during early diagenesis. These characteristics were associated with sediments resulting from endorheic lake conditions and stable pelagic regime, high evaporative stress and concomitant high algal productivity. In contrast, sulphatereducing bacteria and lithotrophic Archaea were predominant in sediments dated from the Last Glacial Maximum, in which pelagic clays alternated with fine volcanic material characteristic of a lake level highstand and freshwater conditions, but reduced water column productivity. Comparison of sedimentary DNA composition with that of fossil pigments suggested that post-depositional diagenesis resulted in a rapid change in the initial nucleic acid composition and overprint of phototrophic communities by heterotrophic assemblages with preserved pigment compositions. Long DNA sequences (1400-900 bp) appeared to derive from intact bacterial cells, whereas short fragments (290-150 bp) reflected extracellular DNA accumulation in ancient sediments. We conclude that sedimentary DNA obtained from lacustrine deposits provides essential genetic information to complement paleoenvironmental indicators and trace post-depositional diagenetic processes over tens of millennia. However, it remains difficult to estimate the time lag between original deposition of lacustrine sediments and establishment of the final composition of the sedimentary DNA assemblage. [ABSTRACT FROM AUTHOR]

Increases in atmospheric temperature and nutrients from land are thought to be promoting the expansion of harmful cyanobacteria in lakes worldwide, yet to date there has been no quantitative synthesis of long-term trends. To test whether cyanobacteria have increased in abundance over the past ~ 200 years and evaluate the relative influence of potential causal mechanisms, we synthesised 108 highly resolved sedimentary time series and 18 decadal-scale monitoring records from north temperate-subarctic lakes. We demonstrate that: (1) cyanobacteria have increased significantly since c. 1800 ce, (2) they have increased disproportionately relative to other phytoplankton, and (3) cyanobacteria increased more rapidly post c. 1945 ce. Variation among lakes in the rates of increase was explained best by nutrient concentration (phosphorus and nitrogen), and temperature was of secondary importance. Although cyanobacterial biomass has declined in some managed lakes with reduced nutrient influx, the larger spatio-temporal scale of sedimentary records show continued increases in cyanobacteria throughout the north temperate-subarctic regions. [ABSTRACT FROM AUTHOR]

Supply of anthropogenic nitrogen (N) to the biosphere has tripled since 1960; however, little is known of how in situ response to N fertilisation differs among phytoplankton, whether species response varies with the chemical form of N, or how interpretation of N effects is influenced by the method of analysis (microscopy, pigment biomarkers). To address these issues, we conducted two 21-day in situ mesocosm (3140 L) experiments to quantify the species- and genus-specific responses of phytoplankton to fertilisation of P-rich lake waters with ammonium (NH4+), nitrate (NO3-), and urea ([NH2]2CO). Phytoplankton abundance was estimated using both microscopic enumeration of cell densities and high performance liquid chromatographic (HPLC) analysis of algal pigments. We found that total algal biomass increased 200% and 350% following fertilisation with NO3- and chemically-reduced N (NH4+, urea), respectively, although 144 individual taxa exhibited distinctive responses to N, including compound-specific stimulation (Planktothrix agardhii and NH4+), increased biomass with chemically-reduced N alone (Scenedesmus spp., Coelastrum astroideum) and no response (Aphanizomenon flos-aquae, Ceratium hirundinella). Principle components analyses (PCA) captured 53.2-69.9% of variation in experimental assemblages irrespective of the degree of taxonomic resolution of analysis. PCA of species-level data revealed that congeneric taxa exhibited common responses to fertilisation regimes (e.g., Microcystis aeruginosa, M. flos-aquae, M. botrys), whereas genera within the same division had widely divergent responses to added N (e.g., Anabaena, Planktothrix, Microcystis). Least-squares regression analysis demonstrated that changes in phytoplankton biomass determined by microscopy were correlated significantly (p<0.005) with variations in HPLC-derived concentrations of biomarker pigments (r²=0.13-0.64) from all major algal groups, although HPLC tended to underestimate the relative abundance of cyanobacteria. Together, these findings show that while fertilisation of P-rich lakes with N can increase algal biomass, there is substantial variation in responses of genera and divisions to specific chemical forms of added N. [ABSTRACT FROM AUTHOR]

Abstract: The trophic history of Lake Champlain''s northeastern arm was assessed using a multi-proxy paleolimnological approach to provide sub-basin specific information for restoration planning. Sediment cores collected from Missisquoi Bay, St. Albans Bay, and the central Northeast Arm (Inland Sea) were analyzed for nutrients, organic carbon, carbon stable isotopes, biogenic silica, pigments, diatoms and soft algae microfossils. Results indicate that this arm of Lake Champlain was oligotrophic when Europeans arrived in 1609, and that clearance of >70% of catchment forest cover had minor impact on algal production. Instead, eutrophication of St. Albans Bay was concurrent with sewer installation and expansion in early 20th century, and again with urban development in the 1960–70s. In contrast, less urbanized Missisquoi Bay remained mesotrophic until agriculture intensified after 1970. Interpretation of central Northeast Arm trophic history is complicated because road and railroad causeways built in 19th century reduced sediment input to this basin for several decades. Nevertheless, high surface-sediment concentrations of nutrients, pigments and organic matter along with replacement of Cyclotella bodanica with more eutrophic Fragilaria crotonensis suggest substantial eutrophication in deep as well as shallow water after 1970. We conclude that effective restoration of the northeastern arm is possible, but will require stringent control of animal and human wastes and reduced use of crop fertilizers. [Copyright &y& Elsevier]

Photography has long been a part of the Library of Congress classification tables. At the time of its inclusion, photography was not considered an art form and thus was placed in the T – Technology schedule instead of the N – Fine Arts schedule. This article will discuss various aspects of photography classification, including its history, the reasons behind and development of alternative schedules, the challenges of classifying artists’ books with a photographic basis, and the feasibility of maintaining alternative schedules with the proliferation of shelf-ready books. [ABSTRACT FROM AUTHOR]

Migratory animals, such as Pacific salmon, can significantly shape communities in recipient habitats both by altering the flux of resources, and changing community composition and subsequent trophic interactions. Here we mainly used paleoecological records from natural sockeye salmon nursery lakes to quantify the response of plankton communities to the influx of salmon-derived nutrients and consumers (juvenile salmon). Our long-term data show that increases in the density of spawning salmon often elevated influx of nutrients, and, in turn, zooplankton production over the past few centuries. In contrast, significant correlations were not detected in two lakes with extremely low or high average spawner densities (i.e. 1.5 and 34.7 × 103 spawners km−2 year−1 respectively). With increasing spawner densities across lakes, analysis of the size structure of subfossils in sediments revealed a strong decrease in body size of a main juvenile salmon prey item ( Eubosmina longispina; r2= 0.36, p < 0.001, n = 67), consistent with an overriding effect of predation in lakes with high salmon densities. These long-term data not only highlight the key role of salmon-derived nutrients in stimulating plankton communities, but also suggest that the relative effect of nutrient and consumer subsidies varies along gradients of lake production, despite a single ultimate causal mechanism (migrating fish). [ABSTRACT FROM AUTHOR]

1. Pacific salmon are a textbook example of migratory animals that transfer nutrients between ecosystems, but little is known about how salmon-derived nutrients (SDN) affect the biodiversity of recipient freshwater ecosystems. We examined paleolimnological records from six Alaskan lakes to define how changes in SDN from sockeye salmon ( Oncorhynchus nerka) influenced sedimentary diatom community structure and beta-diversity among lakes and through time. 2. Using an isotopic mixing model, we showed that SDN loading could account for >80% of the lake total nitrogen budgets and strongly regulated diatom community composition. Spatial dissimilarity in diatom communities was positively related to differences in SDN among lakes ( r = 0.69, P < 0.01, n = 10). Likewise, temporal dissimilarity in diatom communities was positively related to differences in SDN in a sediment core with substantial variation in salmon spawner dynamics between 1700 and 1950 AD ( r = 0.34, P < 0.01, n = 19). Finally, beta-diversity metrics quantifying temporal turnover within each lake's sediment record were also positively related to the variance in SDN loading among lakes ( r = 0.88, P < 0.05, n = 5). Mean SDN was only negatively correlated to temporal diatom beta-diversity. 3. Spatially subsidised systems often receive temporally variable resource inputs, and thus, it is not surprising that, unlike previous studies, we found that resource variability was the key driver of community composition and beta-diversity. In habitats that receive strongly fluctuating external nutrient loads, environment heterogeneity may overweigh stochastic community processes. In addition, freshwater diatoms are characterised by great dispersal capabilities and short life cycles and therefore may be a more sensitive indicator for evaluating the role of resource variability than previously used model organisms. These results suggest that productivity-diversity relationship vary with the nature of nutrient loading and the life history of the community studied. 4. Overall, our study highlights that the transport of nutrients by sockeye salmon across ecosystem boundaries is a significant driver of algal community and biodiversity in nursery lakes, mainly through changing the magnitude of nutrient variation. As such, freshwater species diversity in regions like the U.S. Pacific Northwest may become impoverished where there have been long-term declines in salmon populations and decreases in nutrient variability among lakes. [ABSTRACT FROM AUTHOR]

The article discusses issues related to digital image overload in museums in the U.S. It states that the bulk of digital images in the institutions consisted of exhibition documentation, general research, surrogates as well as permanent collection. In addition, the authors mention that the national efforts to maintain a complete centralized digital archive can be hindered by the immediate demands of museums and the absence of collaboration between them.