Did fires drive Holocene carbon sequestration in boreal ombrotrophic peatlands of eastern Canada?

Wildfire is an important factor on carbon sequestration in the North American boreal biomes. Being globally important stocks of organic carbon, peatlands may be less sensitive to burning in comparison with upland forests, especially wet unforested ombrotrophic ecosystems as found in northeastern Canada. We aimed to determine if peatland fires have driven carbon accumulation patterns during the Holocene. To cover spatial variability, six cores from three peatlands in the Eastmain region of Quebec were analyzed for stratigraphic charcoal accumulation. Results show that regional Holocene peatland fire frequency was ~ 2.4 fires 1000 yr^? 1, showing a gradually declining trend since 4000 cal yr BP, although inter- and intra-peatland variability was very high. Charcoal peak magnitudes, however, were significantly higher between 1400 and 400 cal yr BP, possibly reflecting higher charcoal production driven by differential climatic forcing aspects. Carbon accumulation rates generally declined towards the late-Holocene with minimum values of ~ 10 g m^? 2 yr^? 1 around 1500 cal yr BP. The absence of a clear correlation between peatland fire regimes and carbon accumulation indicates that fire regimes have not been a driving factor on carbon sequestration at the millennial time scale.     

Regional soil erosion in response to land use and increased typhoon frequency and intensity,Taiwan

Reservoir sedimentation data and sediment yields from Taiwanese rivers show increased soil erosion in response to both 20th century changes in land use and a more recent increase in typhoon frequency and intensity. Decadal variations of up to 5- to 20-fold in suspended-sediment rating curves demonstrate supply-limited transport and correspond to increased sediment delivery from hillslopes due to changes in land use, regional ground shaking during the Chi-Chi earthquake, and post-2000 changes in typhoon frequency and intensity. While accelerated erosion in central Taiwan after the Chi-Chi earthquake has been documented previously, our results show that periods of increased upland erosion also occurred earlier, in response to 20th century changes in land use. Analyses of rainfall records and typhoon frequency for the period 1900–2009 further point to an island-wide increase in erosion rates corresponding to increased typhoon frequency and intensity after 1990.     

Impacts of a raw sewage spill on water and sediment quality in an urbanized estuary

A sewer main serving a large municipal wastewater system ruptured, discharging approximately 3,000,000 gallons (11,355,000 L) of raw human sewage into a multi-branched tidal creek estuary along the US East Coast. The biochemical oxygen demand caused severe hypoxia in the system, causing a large fish kill. The sewage load led to high fecal coliform bacteria concentrations in the creek (maximum of 270,000 CFU 100ml(-1)), which declined in an approximate logarithmic manner over the first few days. The spill caused elevated sediment fecal coliform bacteria and enterococcus counts that declined much more gradually than water column counts. Persistence of relatively high concentrations of fecal indicator bacteria in sediments for several weeks after the spill suggests that sediment sampling should be included in response to major sewage spills. The high concentration of nutrients in the spilled sewage led to several algal blooms. However, nutrient concentrations in the water column declined rapidly, demonstrating the value of conserving marshes because of their pollutant filtration function.     

Climate, agriculture, and cycles of human occupation over the last 4000 yr in southern Zacatecas, Mexico

Scholars attribute the growth and decline of Classic period (AD 200-900) settlements in the semi-arid northern frontier zone of Mesoamerica to rainfall cycles that controlled the extent of arable land. However, there is little empirical evidence to support this claim. We present phytolith, organic carbon, and magnetic susceptibility analyses of a 4000-yr alluvial record of climate and human land use from the Malpaso Valley, the site of one such Classic frontier community. The earliest farming occupation is detected around 500 BC and appears related to a slight increase of aridity, similar to the level of the modern day valley. By AD 500, the valley's Classic period Mesoamerican settlements were founded under these same dry conditions, which continued into the Postclassic period. This indicates that the La Quemada occupation did not develop during a period of increased rainfall, but rather an arid phase. The most dramatic changes detected in the valley resulted from the erosion associated with Spanish Colonial grazing and deforestation that began in the 16th century. The landscape of the modern Malpaso Valley is thus primarily the product of a series of intense and rapid transformations that were concentrated within the last 400 yr.     

Using Stable Isotope Mixing in a Great Lakes Coastal Tributary to Determine Food Web Linkages in Young Fishes

We characterized stable isotope mixing along a river-Great Lake transition zone in the St. Louis River, an important fish nursery in western Lake Superior, and used it to identify food web linkages supporting young fish production. We observed a broad, spatial pattern in the carbon stable isotope ratio (δ¹³C); downriver enrichment in particulate organic carbon and aquatic vegetation δ¹³C, as well as pelagic, benthic and littoral invertebrate δ¹³C, reflected isotope mixing along the river-lake transition zone. Fishes with similarly enriched δ¹³C were used to identify benthopelagic and littoral trophic pathways. River and Lake Superior organic matter (OM) sources contributed to both pathways. Differences between the δ¹³C in fishes and invertebrate prey revealed that fish production was supported at multiple spatial scales. The result was that the food web specific to any location along the transition zone incorporated multiple OM sources from across the watershed.     

Spatio-temporal variability in debris-flow activity: a tree-ring study at Geisstriftbach (Swiss Alps) extending back to AD 1736

Past debris-flow activity on the forested cone of the Geisstriftbach torrent (St. Niklaus, Valais, Swiss Alps) was assessed from growth disturbances in old conifer trees, providing a much improved record of past events. The study of 633 tree-ring sequences sampled from 252 European larch (Larix decidua Mill.), Norway spruce (Picea abies (L.) Karst.) and Silver birch (Betula pendula Roth.) trees allowed reconstruction of 53 debris-flow events since AD 1736. The spatial analysis of trees affected during particular events on the geomorphic map allowed for a spatial representation of individual events and a reconstruction of four flow patterns. Based on our results and Siegfried maps, we believe that before the formation of a dogleg near the cone apex in the late 1890s, debris flows preferentially used the channels located in the west-southwestern part of the Geisstriftbach cone. This study contributes to our understanding of debris-flow processes on cones and provides an example of how dendrogeomorphic techniques may help in the reconstruction and understanding of debris flows in Alpine areas.     

Impacts of Oyster Reef Restoration on Primary Productivity and Nutrient Dynamics in Tidal Creeks of the North Central Gulf of Mexico

The ability of oysters to remove large quantities of particulates from the water column, thereby potentially improving water quality, has been cited as one of the reasons for oyster reef restoration. However, this ability has not yet been effectively demonstrated in the field. As part of the Alabama Oyster Reef Restoration Project, this study was designed to assess impacts of restored eastern oyster (Crassostrea virginica) reefs on primary production, nutrient dynamics, and water quality in shallow tidal creeks. Using a Before–After-Control–Impact (BACI) design, we monitored tidal creeks around Dauphin Island, AL, for changes induced by the introduction of oyster reefs. Reef placement resulted in increased ammonium (NH₄⁺) in two of the three experimental creeks. Interestingly, oyster reefs did not seem to reduce water column particulates or have an impact on phytoplankton or microphytobenthic biomass or productivity. We do not believe that our data discount the importance and/or usefulness of oysters in modifying the water column. Rather, we acknowledge that it is difficult to detect these impacts/environmental services in this type of system (i.e., a tidal creek system), because they seem to be very localized and short-lived (i.e., not ecologically relevant on a creek-wide scale). This study highlights the need to consider location and habitat in planning oyster restoration projects. Also, it demonstrates that the types, magnitudes, and spatial extent of changes in ecosystem services that should be expected after reef restoration might need to be re-evaluated.     

Using chloride and other ions to trace sewage and road salt in the Illinois Waterway

Chloride concentrations in waterways of northern USA are increasing at alarming rates and road salt is commonly assumed to be the cause. However, there are additional sources of Cl⁻ in metropolitan areas, such as treated wastewater (TWW) and water conditioning salts, which may be contributing to Cl⁻ loads entering surface waters. In this study, the potential sources of Cl⁻ and Cl⁻ loads in the Illinois River Basin from the Chicago area to the Illinois River’s confluence with the Mississippi River were investigated using halide data in stream samples and published Cl⁻ and river discharge data. The investigation showed that road salt runoff and TWW from the Chicago region dominate Cl⁻ loads in the Illinois Waterway, defined as the navigable sections of the Illinois River and two major tributaries in the Chicago region. Treated wastewater discharges at a relatively constant rate throughout the year and is the primary source of Cl⁻ and other elements such as F⁻ and B. Chloride loads are highest in the winter and early spring as a result of road salt runoff which can increase Cl⁻ concentrations by up to several hundred mg/L. Chloride concentrations decrease downstream in the Illinois Waterway due to dilution, but are always elevated relative to tributaries downriver from Chicago. The TWW component is especially noticeable downstream under low discharge conditions during summer and early autumn when surface drainage is at a minimum and agricultural drain tiles are not flowing.     

Early Cretaceous Archaefructus eoflora sp. nov. with Bisexual Flowers from Beipiao, Western Liaoning, China

Recently, whether Archaefructus has bisexual multi-parted flowers or just inflorescences of unisexual flowers, and whether it is ancestral to all angiosperms or a derived eudicot have been debated. Here, from the same Yixian Formation, NE China, we report a new Archaefructus species, A. eoflora sp. nov., with the generic characteristics of dissected leaves and bisexual reproductive axes. It is entirely preserved with roots, rhizome, shoots and protogynous reproductive organs at different developmental stages. Its lateral and main fertile shoots form a pseudo-indeterminate pattern, while the reproductive branches on the main shoot form a cymose inflorescence. Subtended by 1-2 bract-like leaves, the section of stamen clusters changes into a much shorter section of carpels that have one row of orthotropous ovules. Significantly, one cluster bearing two carpels and one stamen between the two sections demonstrates a true bisexual flower, an important step of the origin of floral bisexuality, and the homology