Agriculture causes nitrate fertilization of remote alpine lakes

Humans have altered Earth’s nitrogen cycle so dramatically that reactive nitrogen (Nr) has doubled. This has increased Nr in aquatic ecosystems, which can lead to reduced water quality and ecosystem health. Apportioning sources of Nr to specific ecosystems, however, continues to be challenging, despite this knowledge being critical for mitigation and protection of water resources. Here we use D17O, d18O and d15N from Uinta Mountain (Utah, USA) snow, inflow and lake nitrate in combination with a Bayesian-based stable isotope mixing model, to show that at least 70% of nitrates in aquatic systems are anthropogenic and arrive via the atmosphere. Moreover, agricultural activities, specifically nitrate- and ammonium-based fertilizer use, are contributing most (B60%) Nr, and data from other North American alpine lakes suggest this is a widespread phenomenon. Our findings offer a pathway towards more effective mitigation, but point to challenges in balancing food production with protection of important water resources

Genomic investigations of unexplained acute hepatitis in children

Since its first identification in Scotland, over 1,000 cases of unexplained paediatric hepatitis in children have been reported worldwide, including 278 cases in the UK1. Here we report an investigation of 38 cases, 66 age-matched immunocompetent controls and 21 immunocompromised comparator participants, using a combination of genomic, transcriptomic, proteomic and immunohistochemical methods. We detected high levels of adeno-associated virus 2 (AAV2) DNA in the liver, blood, plasma or stool from 27 of 28 cases. We found low levels of adenovirus (HAdV) and human herpesvirus 6B (HHV-6B) in 23 of 31 and 16 of 23, respectively, of the cases tested. By contrast, AAV2 was infrequently detected and at low titre in the blood or the liver from control children with HAdV, even when profoundly immunosuppressed. AAV2, HAdV and HHV-6 phylogeny excluded the emergence of novel strains in cases. Histological analyses of explanted livers showed enrichment for T cells and B lineage cells. Proteomic comparison of liver tissue from cases and healthy controls identified increased expression of HLA class 2, immunoglobulin variable regions and complement proteins. HAdV and AAV2 proteins were not detected in the livers. Instead, we identified AAV2 DNA complexes reflecting both HAdV-mediated and HHV-6B-mediated replication. We hypothesize that high levels of abnormal AAV2 replication products aided by HAdV and, in severe cases, HHV-6B may have triggered immune-mediated hepatic disease in genetically and immunologically predisposed children

Paleolimnology and the Frontiers of Biogeography

For almost a century biogeographers have used paleoecological methods, including tree-ring, pollen, macrofossil, and charcoal analysis, to reconstruct climate and environmental conditions for the late Quaternary, but paleolimnological proxies and approaches provide new opportunities for biogeographers. In the last two decades, paleolimnology has grown rapidly as a result of several technical advancements: (1) the development of new proxies, (2) improved coring, sampling, and dating techniques that provide finer temporal resolution, and (3) more sophisticated statistical techniques and greater computing power, which allow for enhanced quantitative calibration of climate and environmental signals from paleolimnological proxies. These advances have led to a plethora of research projects, many using novel approaches, on climate change, anthropogenic impacts, conservation and restoration, aquatic/terrestrial links, resource management, succession, biodiversity, and introduced species. Paleolimnologists are working at the frontiers of biogeographical research, particularly contributing to research on climate change, biogeochemical cycles, and anthropogenic impacts on Earth systems

A 19,000-year record of hydrologic and climatic change inferred from diatoms from Bear Lake, Utah and Idaho

Changes in diatom fossil assemblages from lake sediment cores indicate variations in hydrologic and climatic conditions at Bear Lake (Utah-Idaho) during the late glacial and Holocene. From 19.1 to 13.8 cal ka there is an absence of well-preserved diatoms because prolonged ice cover and increased turbidity from glacier-fed Bear River reduced light and limited diatom growth. The first well-preserved diatoms appear at 13.8 cal ka. Results of principal components analysis (PCA) of the fossil diatom assemblages from 13.8 cal ka to the present track changes related to fluctuations of river inputs and variations of lake levels. Diatom abundance data indicate that the hydrologic balance between 13.8 and 7.6 cal ka is strongly tied to river inputs, whereas after 7.6 cal ka the hydrologic balance is more influenced by changes in lake evaporation. Wet conditions maintained high river inputs from 13.8 to 10.8 cal ka and from 9.2 to 7.6 cal ka, with a dry interval between 10.8 and 9.2 cal ka. After 9.2 cal ka until 2.9 cal ka lake levels were high except for two periods, one between 7.6 and 5.8 cal ka and one between 4.3 and 3.8 cal ka, as a result of decreased effective moisture. After 2.9 cal ka, fossil diatom assemblages suggest drier conditions until 1.6 cal ka to the present, when fragments of large, pennate diatoms appear, possibly the result of a rapid lake transgression. Although similarities exist between the Bear Lake records and other western hydrologic and climatic records, the covariations are not strong. Our data suggest that climatic regimes at Bear Lake have changed frequently over time, perhaps as a consequence of the position of several important climatic boundaries near Bear Lake

Development of a Midge-Based Summer Surface Water Temperature Inference Model for the Great Basin of the Western United States

Surface sediment recovered from 51 lakes in the Uinta Mountains of northeast Utah was analyzed for subfossil chironomid remains, and incorporated in a midge-based inference model for summer surface water temperature (SSWT). The lakes in the calibration set spanned elevation, depth, and summer surface water temperature ranges of 900 m, 12.7 m, and 11.3°C, respectively. Redundancy analysis (RDA) identified four variables, SSWT, depth, specific conductivity, and Al concentration, that could account for a statistically significant amount of variance in the chironomid distribution, with SSWT accounting for the largest amount of variance. The Uinta Mountain calibration set was merged with a previously developed calibration set from the Sierra Nevada, California, in order to develop a midge-based inference model for SSWT applicable to subfossil chironomid stratigraphies from the Great Basin. A variety of statistical approaches, such as weighted averaging (WA), weighted averaging-partial least squares (WA-PLS), and partial least squares (PLS) were used to assess model performance. The best inference model for SSWT, based on a 3-component WA-PLS approach, had robust performance statistics (r2jack = 0.66, RMSEP = 1.4°C). The newly expanded inference model will enable more accurate estimates of late Pleistocene and Holocene thermal regimes and help address many outstanding questions relating to long-term and recent climate change in this region

Ecology and Distribution of Diatoms from Boreal Forest Lakes in Wood Buffalo National Park, Northern Alberta and the Northwest Territories, Canada

Diatoms were identified from the surface sediments of 35 small to intermediate-sized boreal forest lakes in Wood Buffalo Nat. Park, located on the border of Alberta and the NW Terr., Canada. A total of 276 diatom taxa were recorded; of these, 112 taxa, belonging to 29 genera, are illustrated. Detailed taxonomic descriptions and ecological info. are provided for 62 of these taxa. Striking differences in diatom assemblages were observed between the lakes sampled, which included 3 types: Shield lakes, situated in the granites and granitic gneisses of the Canadian Shield; sinkhole lakes, located in Palaeozoic-aged limestones and gypsums; and muskeg lakes, found in poorly drained areas characterized by Palaeozoic-aged calcareous shales

Late Pleistocene and Early Holocene Climate and Limnological Changes in the Sierra Nevada, California, USA Inferred from Midges (Insecta: Diptera: Chironomidae)

Chironomid and stratigraphic analyses of a lake sediment core recovered from a high-elevation lake in the central Sierra Nevada, California, USA, was undertaken to assess chironomid community development during the Pleistocene–Holocene transition and to quantitatively reconstruct the thermal regime that existed during this interval. Between 14 800 cal yr BP and 13 700 cal yr BP the chironomid community consisted almost exclusively of Heterotrissocladius, suggesting this period was characterized by extremely cold climatic conditions. Evidence of post-glacial climatic amelioration, as manifested by increases in thermophilous chironomid taxa, head capsule concentrations, and taxon richness and diversity, commenced at approximately 13 300 cal yr BP. In order to quantify the magnitude of the water temperature changes associated with post-glacial climatic amelioration, a recently developed chironomid-based inference model for surface water temperature was applied to the subfossil chironomid assemblages. The one-component, weighted-averaging partial least squares (WA-PLS) model has an r2jack=0.72, RMSEPjack=1.1°C and a maximum bias of 1.24°C. The reconstructed surface water temperatures suggest a minimum warming of approximately 4.7°C occurred during the Pleistocene–Holocene transition. However, warming during this interval may not have been monotonic. Evidence of the Younger Dryas has been previously discovered in the study area and adjacent regions; Our research indicates that changes in chironomid community composition and an inferred short-term cooling event occurred between 12 000 cal yr BP and 11 500 cal yr BP, which may represent a local manifestation of the Younger Dryas. Chironomid community development during the Pleistocene–Holocene transition appears to primarily reflect the influence of changing climate conditions

Paleolimnological Evidence of Change in a Shallow, Hypereutrophic Lake: Upper Klamath Lake, Oregon, USA

Sediment cores were collected from Upper Klamath Lake in October, 1998 and analyzed for 210Pb, 14C, 15N, N, P, C, Ti, Al, diatoms, Pediastrum, and cyanobacterial akinetes. These results were used to reconstruct changes in water quality in Upper Klamath Lake over the last 150 years. The results showed that there was substantial mixing of the upper 10 cm of sediment, representing the previous 20 to 30 years. However, below that, 210Pb activity declined monotonically, allowing reasonable dating for the period from about 1850 to 1970. The sediment accumulation rates (SAR) showed a substantial increase in the 20th century. The increase in SAR corresponded with increases in erosional input from the watershed as represented by the increases in sediment concentrations of Ti and Al. The upper 20 cm of sediment, representing the last 150 years, also showed increases in C, N, P, and 15N. The increases in nutrient concentrations may be affected to various degrees by diagenetic reactions within the sediments, although the changes in concentrations also were marked by changes in the N:P ratio and in a qualitative change in the source of N as reflected in increasing delta15N. The diatoms showed modest changes in the 20th century, with increases in Asterionella formosa, Stephanodiscus hantzschii, and S. parvus. Pediastrum, a green alga, was well-preserved in the sediments and exhibited a sharp decline in relative abundance in the upper sediments. Total cyanobacteria, as represented by preserved akinetes, exhibited only minor changes in the last 1000 years. However, Aphanizomenon flos-aquae, a taxon which was formerly not present in the lake 150 years ago, but that now dominates the summer phytoplankton, has shown major increases over the past 100 years. The changes in sediment composition are consistent with activities including timber harvest, drainage of wetlands, and agricultural activities associated with livestock grazing, irrigated cropland, and hydrologic modifications