Beaver dam analogues drive heterogeneous groundwater–surface water interactions

Beaver dam analogues (BDAs) are a cost-effective stream restoration approach that leverages the recognized environmental benefits of natural beaver dams on channel stability and local hydrology. Although natural beaver dams are known to exert considerable influence on the hydrologic conditions of a stream system by mediating geomorphic processes, nutrient cycling, and groundwater–surface water interactions, the impacts of beaver-derived restoration methods on groundwater–surface water exchange are poorly characterized. To address this deficit, we monitored hyporheic exchange fluxes and streambed porewater biogeochemistry across a sequence of BDAs installed along a central Wyoming stream during the summer of 2019. Streambed fluxes were quantified by heat tracing methods and vertical hydraulic gradients. Biogeochemical activity was evaluated using major ion porewater chemistry and principal component analysis. Vertical fluxes of approximately 1.0 m/day were observed around the BDAs, as was the development of spatially heterogeneous zones of nitrate production, groundwater upwelling, and anaerobic reduction. Strong contrasts in hyporheic zone processes were observed across BDAs of differing sizes. This suggests that structures may function with size-dependent behaviour, only altering groundwater–surface water interactions after a threshold hydraulic step height is exceeded. Patterns of hyporheic exchange and biogeochemical cycling around the studied BDAs resemble those around natural beaver dams, suggesting that BDAs may provide comparable benefits to channel complexity and near-stream function over a 1-year period.     

Aeolian abrasion and modes of fine particle production from natural red dune sands: an experimental study

A series of experiments was conducted to determine the potential for aeolian abrasion of natural dune sands to produce fine particles (< 125 µm) by (1) the release of resident fines; (2) spalling, chipping and breakage of particles; and (3) the removal of grain surface coatings. Parent samples were obtained from the surfaces of four active continental dunes and abraded using a glass ‘test tube’ chamber for up to 120 h. The fine particles produced by this abrasion process were trapped at varying time intervals and subject to detailed particle‐size analyses using a Coulter Multisizer. The abrasion of untreated parent samples produced fine particles in one of two main size classes, < 10 µm and > 50 µm, but when the parent sample was sieved to exclude particles < 250 µm, relatively more material in the range 10–50 µm was produced. For unsieved parent samples, the size range associated with the dominant mode varied according to the length of the abrasion time. The coarsest mode (> 63 µm) was dominant during the first 16 h of abrasion, then became less significant and is thought to be associated with the release of resident fines into suspension. The finest mode (< 10 µm) was absent or very weak during the first 16 h of abrasion, then became more significant and, in some instances, dominated the distribution as abrasion continued. Removal of grain surface coatings is the main source of fine material < 10 µm, and this may be a significant source of fine material in areas where sands are dominated by subrounded and rounded particles. By comparison with previous studies of aeolian particle abrasion, these natural dune sands produced very low quantities of fine material (by weight), but their spatial extent makes them potentially a significant source of dust‐sized particles at the global scale.     

Investigating controls on the thermal sensitivity of Pennsylvania streams

Stream temperature, an important measure of ecosystem health, is expected to be altered by future changes in climate and land use, potentially leading to shifts in habitat distribution for aquatic organisms dependent on particular temperature regimes. To assess the sensitivity of stream temperature to change in a region where such a shift has the potential to occur, we examine the variability of and controls on the direct relationship between air and water temperature across the state of Pennsylvania. We characterized the relationship between air and stream temperature via linear and nonlinear regression for 57 sites across Pennsylvania at daily and weekly timescales. Model fit (r²) improved for 92% (daily) and 65% (weekly) of sites for nonlinear versus linear relationships. Fit for weekly versus daily regression analysis improved by 0·08 for linear and 0·06 for nonlinear regression relationships. To investigate the mechanisms controlling stream temperature sensitivity to environmental change, we define ‘thermal sensitivity’ as the sensitivity of stream temperature of a given site to change in air temperature, quantified as the slope of the regression line between air and stream temperature. Air temperature accounted for 60–95% of the daily variation in stream temperature for sites at or above a Strahler stream order (SO) of 3, with thermal sensitivities ranging from low (0·02) to high (0·93). The sensitivity of stream temperature to air temperature is primarily controlled by stream size (SO) and baseflow contribution. Together, SO and baseflow index explained 43% of the variance in thermal sensitivity across the state, and 59% within the Susquehanna River Basin. In small streams, baseflow contribution was the major determinant of thermal sensitivity, with increasing baseflow contributions resulting in decreasing sensitivity values. In large streams, thermal sensitivity increased with stream size, as a function of accumulated heat throughout the stream network. Copyright © 2011 John Wiley & Sons, Ltd.     

The exceptional Oder flood in summer 1997 — distribution patterns of the oder discharge in the Pomeranian Bight

The exceptional Oder flood in summer 1997 was a unique event in order to investigate the impacts on and the consequences for the ecosystem of the Baltic Sea of about 6.5 km³ additional water loaded with nutrients and contaminants and discharged within only 5 weeks. About 15 institutions participated in this investigation in both the Szczecin Lagoon and the Pomeranian Bight. The Baltic Sea Research Institute Warnemünde studied the water and nutrient inflow, the spreading of the Oder discharge, and the impact of the discharge on the ecosystem. The main topic of the presented investigations is a detailed study of the spatial and temporal spreading of the extreme river discharge in the Pomeranian Bight and the southern Baltic Sea by satellite data, ship observations and continuous buoy measurements as well as numerical modelling. The meteorological conditions were characterized by mainly easterly winds which guided the outflowing riverine water along the German coast into the Arkona Sea. The spatial and temporal development of the distribution patterns of the Oder discharge was monitored by about 80 Sea Surface Temperature (SST) images of NOAA satellites. Shipborne measurements showed that the vertical extent of the Oder plume ranged between 5 and 7 metres. The concentrations of inorganic nutrients, except higher silicate, were comparable to typical winter/early spring values (seasonal maximum) in this region. The high dilution effect of the flood water reduced the concentration of contaminants and thus, prevented a direct negative impact of trace metals and chlorinated organic compounds on the marine environment. Coupled physical-biochemical modelling in combination with SST-images demonstrated the temporal development and satellite data in the visible spectral range delivered the maximum extent of discharged river water into the southern Arkona Sea where a further western transport was limited by the upwelling region off Hiddensee. Thus, all detected effects of the Oder flood were confined to the Pomeranian Bight and the southern Arkona Sea, without long-term consequences for the ecosystem.     

On the relative nature of adequate measures: Media representations of the EU energy and climate package

This paper aims to contribute to media studies on climate change through a study of the ways in which the adequacy of transnational measures of tackling climate change are represented in media outlets in the UK, Ireland, Sweden and Finland. Media texts on the European Union Energy and Climate Package, introduced in January 2008 and approved in modified form in December 2008, are analyzed in-depth. Through an exploratory cross-societal comparison of media representations, the paper traces some of the dynamics of contemporary environmental debates. We argue that the adequacy of proposed transnational measures for tackling climate change becomes a relative concept in the media: measures are not adequate or inadequate per se, but contingent upon social context and relative with regard to time and to the comparisons made.     

Isotopic tracers of paleohydrologic change in large lakes of the Bolivian Altiplano

We have developed an ⁸⁷Sr/⁸⁶Sr, ²³⁴U/²³⁸U, and δ¹⁸O data set from carbonates associated with late Quaternary paleolake cycles on the southern Bolivian Altiplano as a tool for tracking and understanding the causes of lake-level fluctuations. Distinctive groupings of ⁸⁷Sr/⁸⁶Sr ratios are observed. Ratios are highest for the Ouki lake cycle (120-95 ka) at 0.70932, lowest for Coipasa lake cycle (12.8-11.4 ka) at 0.70853, and intermediate at 0.70881 to 0.70884 for the Salinas (95-80 ka), Inca Huasi (~ 45 ka), Sajsi (24-20.5 ka), and Tauca (18.1-14.1 ka) lake cycles. These Sr ratios reflect variable contributions from the eastern and western Cordilleras. The Laca hydrologic divide exerts a primary influence on modern and paleolake ⁸⁷Sr/⁸⁶Sr ratios; waters show higher ⁸⁷Sr/⁸⁶Sr ratios north of this divide. Most lake cycles were sustained by slightly more rainfall north of this divide but with minimal input from Lake Titicaca. The Coipasa lake cycle appears to have been sustained mainly by rainfall south of this divide. In contrast, the Ouki lake cycle was an expansive lake, deepest in the northern (Poópo) basin, and spilling southward. These results indicate that regional variability in central Andean wet events can be reconstructed using geochemical patterns from this lake system.     

A land surface data assimilation framework using the land information system: Description and applications

The Land Information System (LIS) is an established land surface modeling framework that integrates various community land surface models, ground measurements, satellite-based observations, high performance computing and data management tools. The use of advanced software engineering principles in LIS allows interoperability of individual system components and thus enables assessment and prediction of hydrologic conditions at various spatial and temporal scales. In this work, we describe a sequential data assimilation extension of LIS that incorporates multiple observational sources, land surface models and assimilation algorithms. These capabilities are demonstrated here in a suite of experiments that use the ensemble Kalman filter (EnKF) and assimilation through direct insertion. In a soil moisture experiment, we discuss the impact of differences in modeling approaches on assimilation performance. Provided careful choice of model error parameters, we find that two entirely different hydrological modeling approaches offer comparable assimilation results. In a snow assimilation experiment, we investigate the relative merits of assimilating different types of observations (snow cover area and snow water equivalent). The experiments show that data assimilation enhancements in LIS are uniquely suited to compare the assimilation of various data types into different land surface models within a single framework. The high performance infrastructure provides adequate support for efficient data assimilation integrations of high computational granularity.     

Geochemistry,chronology and stratigraphy of Neogene tuffs of the Central Andean region

Tuff layers are vital stratigraphic tools that allow correlations to be made between widely dispersed exposures. Despite their widespread occurrence in the central Andes, tuffs from both natural exposures and sedimentary cores extracted from the region's extensive salars (salt pans) are relatively unstudied. Here we lay the foundation for a tephrostratigraphic framework in the central Andes (14–28°S) by chemically and morphologically characterizing ash shards, and in some cases dating 36 Neogene distal tuffs. These tuffs occur in lacustrine and alluvial deposits from the southern Bolivian Altiplano and adjacent Atacama Desert. All tuffs are calc-akaline rhyolites, consistent with their setting in the Central Andean Volcanic Zone. Five of the older tuffs were ⁴⁰Ar/³⁹Ar dated and yield an age range of 6.63–0.75 Ma. Organic material associated with tuffs deposited into paleolake sediments, paleowetland deposits, or urine-encrusted rodent middens provide constraints on the age of several Late Pleistocene and Holocene tuffs.These tuffs provide key stratigraphic markers and ages for lake cycles and archeological sites on the Bolivian Altiplano and for assessing rates of surficial processes and archeology in both the Atacama and Altiplano. While modern climate, and consequently questions about geomorphic processes and climate change, differs in the hyperarid Atacama and the semi-arid Altiplano, the most extensive air-fall tuffs covered both regions, placing the Atacama and the Bolivian Altiplano in the same tephrostratigraphic province. For example, the Escara B tuff (～1.85 Ma), can be securely identified in both the Altiplano and Atacama. On the Altiplano, dates from the Escara B and E tuffs securely establish the age of the Escara Formation—representing the oldest expansive lake documented on the Bolivian Altiplano. By contrast, the presence of the Escara B tuff below ～6 m of alluvial sediment at the Blanco Encalado site in the Atacama desert yields information about sedimentation rates in this hyperarid region. Indeed, most tuffs from the Atacama Desert are older than 600,000 years, even though they occur within fluvial terraces immediately adjacent to the alluvial fans that are still active. Most of these geomorphic surfaces in the Atacama also possess well-developed saline soils that, when combined with the radiometric ages of the distal tuffs, suggest slow rates of geomorphic change and exceptional landscape stability for this area during the Quaternary.In contrast, younger tuffs are more abundant in the more recent lake records of the Altiplano. The Chita tuff was deposited at ～15,650 cal yr B.P., during the regressive phase of the region's deepest late Quaternary lake cycle—the “Tauca lake cycle”—which spanned 18.1–14.1 cal yr B.P. Two Holocene tuffs, the Sajsi tuff and the Cruzani Cocha tuff, are widespread. The Sajsi tuff was deposited just before 1700 cal yr B.P., whereas the Cruzani Cocha tuff appears to be mid-Holocene in age and shows some chemical affinities to a Holocene tuff (202B) deposited between 4420 and 5460 cal yr B.P. in a urine-encased rodent midden in the Atacama Desert.