Statistical downscaling of historical monthly mean winds over a coastal region of complex terrain. II. Predicting wind components

A regression-based downscaling technique was applied to monthly mean surface wind observations from stations throughout western Canada as well as from buoys in the Northeast Pacific Ocean over the period 1979–2006. A predictor set was developed from principal component analysis of the three wind components at 500?hPa and mean sea-level pressure taken from the NCEP Reanalysis II. Building on the results of a companion paper, Curry et al. (Clim Dyn 2011, doi:10.1007/s00382-011-1173-3), the downscaling was applied to both wind speed and wind components, in an effort to evaluate the utility of each type of predictand. Cross-validated prediction skill varied strongly with season, with autumn and summer displaying the highest and lowest skill, respectively. In most cases wind components were predicted with better skill than wind speeds. The predictive ability of wind components was found to be strongly related to their orientation. Wind components with the best predictions were often oriented along topographically significant features such as constricted valleys, mountain ranges or ocean channels. This influence of directionality on predictive ability is most prominent during autumn and winter at inland sites with complex topography. Stations in regions with relatively flat terrain (where topographic steering is minimal) exhibit inter-station consistencies including region-wide seasonal shifts in the direction of the best predicted wind component. The conclusion that wind components can be skillfully predicted only over a limited range of directions at most stations limits the scope of statistically downscaled wind speed predictions. It seems likely that such limitations apply to other regions of complex terrain as well.     

Feldspar dissolution rates in the Topopah Spring Tuff, Yucca Mountain, Nevada

Two different field-based methods are used here to calculate feldspar dissolution rates in the Topopah Spring Tuff, the host rock for the proposed nuclear waste repository at Yucca Mountain, Nevada. The center of the tuff is a high silica rhyolite, consisting largely of alkali feldspar (60 wt%) and quartz polymorphs (35 wt%) that formed by devitrification of rhyolitic glass as the tuff cooled. First, the abundance of secondary aluminosilicates is used to estimate the cumulative amount of feldspar dissolution over the history of the tuff, and an ambient dissolution rate is calculated by using the estimated thermal history. Second, the feldspar dissolution rate is calculated by using measured Sr isotope compositions for the pore water and rock. Pore waters display systematic changes in Sr isotopic composition with depth that are caused by feldspar dissolution. The range in dissolution rates determined from secondary mineral abundances varies from 10⁻¹⁶ to 10⁻¹⁷ mol s⁻¹ kg tuff⁻¹ with the largest uncertainty being the effect of the early thermal history of the tuff. Dissolution rates based on pore water Sr isotopic data were calculated by treating percolation flux parametrically, and vary from 10⁻¹⁵ to 10⁻¹⁶ mol s⁻¹ kg tuff⁻¹ for percolation fluxes of 15 mm a⁻¹ and 1 mm a⁻¹, respectively. Reconciling the rates from the two methods requires that percolation fluxes at the sampled locations be a few mm a⁻¹ or less. The calculated feldspar dissolution rates are low relative to other measured field-based feldspar dissolution rates, possibly due to the age (12.8 Ma) of the unsaturated system at Yucca Mountain; because oxidizing and organic-poor conditions limit biological activity; and/or because elevated silica concentrations in the pore waters (50 mg L⁻¹) may inhibit feldspar dissolution.     

Dissolved organic phosphorus speciation in the waters of the Tamar estuary (SW England)

The speciation of dissolved organic phosphorus (DOP) in the temperate Tamar estuary of SW England is described. Eight stations from the riverine to marine end-members were sampled during four seasonal campaigns in 2007 and the DOP pool in the water column and sediment porewater was characterized and quantified using a flow injection manifold after sequential enzymatic hydrolysis. This enabled the enzymatically hydrolysable phosphorus (EHP) fraction and its component labile monoester phosphates, diester phosphates and a phytase-hydrolysable fraction that includes myo-inositol hexakisphosphate (phytic acid), to be determined and compared with the total DOP, dissolved reactive phosphorus (DRP) and total dissolved phosphorus (TDP) pools. The results showed that the DOP pool in the water column varied temporally and spatially within the estuary (1.1-22 μg L⁻¹) and constituted 6-40% of TDP. The EHP fraction of DOP ranged from 1.1-15 μg L⁻¹ and represented a significant and potentially bioavailable phosphorus fraction. Furthermore the spatial profiles of the three components of the EHP pool generally showed non-conservative behavior along the salinity gradient, with apparent internal estuarine sources. Porewater profiles followed broadly similar trends but were notably higher at the marine station throughout the year. In contrast to soil organic phosphorus profiles, the labile monoester phosphate fraction was the largest component, with diester phosphates also prevalent. Phytic acid concentrations were higher in the lower estuary, possibly due to salinity induced desorption processes. The EHP fraction is not commonly determined in aquatic systems due to the lack of a suitable measurement technique and the Tamar results reported here have important implications for phosphorus biogeochemistry, estuarine ecology and the development of efficient strategies for limiting the effects of phosphorus on water quality.     

Early burial mud diapirism and its impact on stratigraphic architecture in the Carboniferous of the Shannon Basin,County Clare,Ireland

Delta fronts are often characterized by high rates of sediment supply that result in unstable slopes and a wide variety of soft‐sediment deformation, including the formation of overpressured and mobile muds that may flow plastically during early burial, potentially forming mud diapirs. The coastal cliffs of County Clare, western Ireland, expose Pennsylvanian (Namurian) delta‐front deposits of the Shannon Basin at large scale and in three dimensions. These deposits include decametre‐scale, internally chaotic mudstone masses that clearly impact the surrounding sedimentary strata. Evidence indicates that these were true mud (unlithified sediment) diapirs that pierced overlying strata. This study documents a well‐exposed ca 20 m tall mud diapir and its impact on the surrounding mouth‐bar deposits of the Tullig Cyclothem. A synsedimentary fault and associated rollover dome, evident from stratal thicknesses and the dip of the beds, define one edge of the diapir. These features are interpreted as recording the reactive rise of the mud diapir in response to extensional faulting along its margin. Above the diapir, heterolithic sandstones and siltstones contain evidence for the creation of localized accommodation, suggesting synsedimentary filling, tilting and erosion of a shallow sag basin accommodated by the progressive collapse of the diapir. Two other diapirs are investigated using three‐dimensional models built from ‘structure from motion’ drone imagery. Both diapirs are interpreted to have grown predominantly through passive rise (downbuilding). Stratal relationships for all three diapirs indicate that they were uncompacted and fluid‐rich mud beds that became mobilized through soft‐sediment deformation during early burial (i.e. <50 m, likely <10 m depth). Each diapir locally controlled the stratigraphic architecture in the shallow subsurface and potentially influenced local palaeocurrents on the delta. The mud diapirs studied herein are distinct from deeper ‘shale diapirs’ that have been inferred from seismic sections worldwide, now largely disputed.     

A Climate Change Adaptation Strategy for Management of Coastal Marsh Systems

Sea level rise is causing shoreline erosion, increased coastal flooding, and marsh vulnerability to the impact of storms. Coastal marshes provide flood abatement, carbon and nutrient sequestration, water quality maintenance, and habitat for fish, shellfish, and wildlife, including species of concern, such as the saltmarsh sparrow (Ammodramus caudacutus). We present a climate change adaptation strategy (CCAS) adopted by scientific, management, and policy stakeholders for managing coastal marshes and enhancing system resiliency. A common adaptive management approach previously used for restoration projects was modified to identify climate-related vulnerabilities and plan climate change adaptive actions. As an example of implementation of the CCAS, we describe the stakeholder plans and management actions the US Fish and Wildlife Service and partners developed to build coastal resiliency in the Narrow River Estuary, RI, in the aftermath of Superstorm Sandy. When possible, an experimental BACI (before-after, control-impact) design, described as pre- and post-sampling at the impact site and one or more control sites, was incorporated into the climate change adaptation and implementation plans. Specific climate change adaptive actions and monitoring plans are described and include shoreline stabilization, restoring marsh drainage, increasing marsh elevation, and enabling upland marsh migration. The CCAS provides a framework and methodology for successfully managing coastal systems faced with deteriorating habitat, accelerated sea level rise, and changes in precipitation and storm patterns.     

Recent changes in heavy metal storage in flood-plain soils of the Lahn River,central Germany

Between 1995 and 2007, the concentrations of Pb and Zn in floodplain soils increased along a 60-km reach of the Lahn River, Germany, suggesting that the storage of some metals in the fluvial system is out of phase with recent declines in the release of metals to the environment. Re-sampling of surface soils to 5 cm along five transects perpendicular to the river indicated that the concentration of Pb increased between 1995 and 2007 along two transects and was statistically unchanged at the other three. The concentration of Zn increased at three of five transects and was statistically unchanged at two transects over the same time period. Between 1995 and 2007, concentrations of Cu were statistically equal along four of five transects and declined at the other transect. The increase in Pb and Zn was greater in a more rural than in a more urbanized reach of the Lahn River. Soil texture and organic matter content had virtually no impact on the concentration of metals. The increase in Pb concentration suggests a lag between the decline in Pb releases to the environment and its movement through the fluvial system. Increased Zn storage may result from the high solubility of the metal and the relative ease with which it moves through the environment. Environmental controls appear to have slowed Cu storage along the Lahn River, but are not yet reflected in Pb and Zn storage.     

A systematic field-based testing program of hydraulic conductivity and dispersivity over a range in scale

In a small watershed underlain by relatively homogeneous (nonlayered), sandy, glacial outwash, hydraulic conductivity (K) and longitudinal dispersivity (α _L) were systematically measured over a range in scale. Test methods employed in the investigation are conventional and/or based on accepted principles, measurement scales are those typically encountered in applied field problems, and the hydrogeologic setting is typical of large areas within the northern hemisphere and similar to many alluvial environments worldwide. The results show that K measured under radial flow is scale-dependent up to a radius of influence (r _i) of approximately 15 m but reaches an asymptotic value above this threshold. This asymptotic value of K is consistent with results obtained at the regional scale (～10⁴ m) for the same aquifer using non-radial three-dimensional techniques; the initial increase appears to reflect increasing dimensionality of the radial tests with larger r _i. Although α _L was evaluated over a much smaller interval relative to K, α _L proved to be independent of scale over the full range tested, from 2 to 29 m, an unexpected result. The findings support the idea that there is, as yet, no predictable relationship between scale effects in K and α _L at scales normally encountered in applied field hydrogeology.     

Trends in Abundance of Coastal Birds and Human Activity on a Texas Barrier Island Over Three Decades

Trends in abundance of the 28 most common species of coastal birds on Mustang Island, Texas, were assessed for a 29-year period (1979–2007) during which the study area experienced a substantial increase in human activity. Ten of the 28 species examined declined significantly (P < 0.05) over the study period. Six of these were larids (herring gull, Forster’s tern, royal tern, gull-billed tern, Caspian tern, black skimmer), which exhibited declines in mean abundance of 53% to 88%. Other significant species declines were the great blue heron (39% decline) and the shorebirds Wilson’s plover (63%), red knot (54%), and black-bellied plover (34%). Four species showed significant increases in local abundance. Mean number of people on the beach increased fivefold during the study period. This unique dataset allows for an extremely rare assessment of bird populations in direct relation to human disturbance and may have implications for managing coastal birds worldwide.