Boreal temperature variability inferred from maximum latewood density and tree-ring width data, Wrangell Mountain region, Alaska

Variations in both width and density of annual rings from a network of tree chronologies were used to develop high-resolution proxies to extend the climate record in the Wrangell Mountain region of Alaska. We developed a warm-season (July–September) temperature reconstruction that spans A.D. 1593–1992 based on the first eigenvector from principal component analysis of six maximum latewood density (MXD) chronologies. The climate/tree-growth model accounts for 51% of the temperature variance from 1958 to 1992 and shows cold in the late 1600s–early 1700s followed by a warmer period, cooling in the late 1700s–early 1800s, and warming in the 20th century. The 20th century is the warmest of the past four centuries. Several severely cold warm-seasons coincide with major volcanic eruptions. The first eigenvector from a ring-width (RW) network, based on nine chronologies from the Wrangell Mountain region (A.D. 1550–1970), is correlated positively with both reconstructed and recorded Northern Hemisphere temperatures. RW shows a temporal history similar to that of MXD by increased growth (warmer) and decreased growth (cooler) intervals and trends. After around 1970 the RW series show a decrease in growth, while station data show continued warming, which may be related to increasing moisture stress or other factors. Both the temperature history based on MXD and the growth trends from the RW series are consistent with well-dated glacier fluctuations in the Wrangell Mountains and some of the temperature variations also correspond to variations in solar activity.     

Modelling nitrogen and oxygen isotope fractionation during denitrification in a lacustrine redox-transition zone

The stable isotope composition (δ¹⁵N and δ¹⁸O) of nitrate was measured during Summer 1999 in the anaerobic hypolimnion of eutrophic Lake Lugano (Switzerland). Denitrification was demonstrated by a progressive nitrate depletion coupled to increasing δ¹⁵N and δ¹⁸O values for residual nitrate. Maximum δ¹⁵N and δ¹⁸O values amounted to 27.2 and 15.7‰, respectively.¹⁵N and ¹⁸O enrichment factors for denitrification (ε) were estimated using a closed-system model and a dynamic diffusion-reaction model. Using the Rayleigh equation (closed-system approach), we obtained ε values of −11.2 and −6.6‰ for nitrogen and oxygen, respectively. The average ε values derived using the diffusion-reaction model were determined to be −20.7 ± 3.8 for nitrogen and −11.0 ± 1.7 for oxygen. Both N and O isotope fractionation appeared to be lower when denitrification rates where high, possibly in association with high organic carbon availability. In addition, variations in the isotope effects may be attributed to the variable importance of sedimentary denitrification having only a small isotope effect on the water column. The combined measurement of N and O isotope ratios in nitrate revealed that coupled nitrification-denitrification in the open-water was of minor importance. This is the first study of nitrogen and oxygen isotope effects associated with microbial denitrification in a natural lake. Moreover, this study confirms the high potential of δ¹⁸O of nitrate as a valuable biogeochemical tracer in aquatic systems, complementing nitrate δ¹⁵N.     

Evidence for a regime shift after the 1997–1998 El Niño, based on 1995, 1998, and 2001 acoustic surveys in the Pacific Eastern Boundary Current

Increasing physical oceanographic evidence suggests that a regime shift, which featured increased equatoward surface winds and upwelling in the Eastern Pacific Boundary Current region, occurred following the 1997–1998 El Niño. We expect the signal of this change in biota to be stronger in euphausiids than in pelagic fishes such as Pacific hake (Merluccius productus) because lower trophic levels are more responsive to changes in upwelling and primary production. We used acoustic backscatter data from acoustic surveys in summer 1995, 1998, and 2001 to explore whether significant changes in abundance and distribution of euphausiids and fishes have occurred between 1995 and 2001. Graphical and statistical results show that the density of fish schools and euphausiid patches increased significantly south of Cape Blanco between 1995 and both 1998 and 2001. North of Cape Blanco there was no consistent change in euphausiid abundance, although both fish and euphausiid distributions in 2001 appear to be significantly higher nearshore than in the other years. Pelagic fish abundance distributions appeared more closely linked to El Niño than to regime shifts, with abundance shifted much farther north in 1998, an El Niño year, than in the other years, while 1995 and 2001 fish abundance distributions are similar to each other. The regime shift appears so far to have had a stronger effect on euphausiids than on pelagic fishes. The change in euphausiid abundance and distribution between the survey years was linked, through a conceptual model, to the relative strength of the poleward flowing California undercurrent and equatorward flowing California current and to the distribution and abundance of hake.     

Web-cam’s potential for collaborative activities in the Earth sciences

We report here our experiences from using easily acquired web-cam components for collaborative ventures in the Earth sciences. We have used a variety of hardware and different software. We demonstrate from various locations in the U.S.A. the feasibility of using web-cam in multitudinous activities, relevant for conducting research and knowledge dissemination. We summarize the quality of the connections from the various combinations of communicating parties. Today, web-cams can be utilized as an economical and viable means of point-to-point communication in the Earth science community. Greater bandwidth is sorely needed for activities such as multi-party conferencing on the present internet network. We propose that web-cam can be readily deployed as a web-service for facilitating collaborative research over the GRID infrastructure, using the middleware Narada-Brokering. Web-cam will play an important role in the emerging field of geoinformatics.     

Structuring subjectivities? Using Q methodology in human geography

This paper presents a critical and reflexive account of using Q methodology in human geography. Q methodology has a long pedigree in psychological, political and sociological research, but is only recently beginning to be used by human geographers. We discuss, in particular, the parts of the process(es) of Q methodology that are often glossed over in the literature, through reflecting on our learning in using Q within a project examining the use and production of environmental science by NGOs. We conclude that Q may be a useful supplement to existing methods in human geography, as long as it is used creatively and reflexively and with full awareness of its interpretative dimensions.     

Groundwater control of mangrove surface elevation: Shrink and swell varies with soil depth

We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table with new rod-surface elevation tables to separately track changes in the mid zone (0–4 m), the shallow root zone (0–0.35 m), and the full sediment profile (0–6 m) in response to site hydrology (daily river stage and daily groundwater piezometric pressure). We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above 0 m], shallow zone [0–0.35 m], middle zone [0.35–4 m], and bottom zone [4–6]) that comprise the entire soil column. Changes in groundwater pressure correlated strongly, with changes in soil elevation for the entire profile (Adjusted R² = 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the bottom soil zone accounted for the majority (R² = 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions on coastal wetland systems.     

Uranyl adsorption onto montmorillonite: Evaluation of binding sites and carbonate complexation

The fate and transport of uranium in contaminated soils and sediments may be affected by adsorption onto the surface of minerals such as montmorillonite. Extended X-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the adsorption of uranyl (UO₂²⁺) onto Wyoming montmorillonite. At low pH (∼4) and low ionic strength (10⁻³ M), uranyl has an EXAFS spectrum indistinguishable from the aqueous uranyl cation, indicating binding via cation exchange. At near-neutral pH (∼7) and high ionic strength (1 M), the equatorial oxygen shell of uranyl is split, indicating inner-sphere binding to edge sites. Linear-combination fitting of the spectra of samples reacted under conditions where both types of binding are possible reveals that cation exchange at low ionic strengths on SWy-2 may be more important than predicted by past surface complexation models of U(VI) adsorption on related montmorillonites. Analysis of the binding site on the edges of montmorillonite suggests that U(VI) sorbs preferentially to [Fe(O,OH)₆] octahedral sites over [Al(O,OH)₆] sites. When bound to edge sites, U(VI) occurs as uranyl-carbonato ternary surface complexes in systems equilibrated with atmospheric CO₂. Polymeric surface complexes were not observed under any of the conditions studied. Current surface complexation models of uranyl sorption on clay minerals may need to be reevaluated to account for the possible increased importance of cation exchange reactions at low ionic strengths, the presence of reactive octahedral iron surface sites, and the formation of uranyl-carbonato ternary surface complexes. Considering the adsorption mechanisms observed in this study, future studies of U(VI) transport in the environment should consider how uranium retardation will be affected by changes in key solution parameters, such as pH, ionic strength, exchangeable cation composition, and the presence or absence of CO₂.     

Multi‐year water balance assessment of a newly constructed wetland,Fort McMurray,Alberta

Oil sands mining in Alberta transforms the boreal landscape of forests and wetlands into open pits, tailings ponds and overburden piles. Whereas reclamation efforts have primarily focused on upland forests, rebuilding wetland systems has recently become a motivation for research. Wetland creation and sustainability in this region is complicated by the sub‐humid climate and salinity of underlying mining material. In 2012, Syncrude Canada Ltd. completed the construction of the Sandhill Fen Watershed (SFW), a 52‐ha upland‐wetland system to evaluate wetland reclamation strategies on soft tailings. SFW includes an active pumping system, upland hummocks, a fen wetland and underdrains. To evaluate the influence of management practices on the hydrology of the system, this study reports the water balance from January 2013 to December 2014, the first 2 years after commissioning. A semi‐distributed approach was taken to examine the fluxes and stores of water in uplands and lowlands. Natural and artificial inputs and outputs were measured using a series of precipitation gauges and pumps, and evapotranspiration was quantified using three eddy covariance towers. A series of near surface wells recorded water table position. Both 2013 and 2014 were normal rainfall years, with 2013 having more and 2014 less snow than normal. In 2013, inflow/outflow from pumping was the predominant hydrological fluxes, resulting in considerable variability in water table position and storage changes throughout the summer. In 2014, the artificial addition of water was negligible, yet the water table remained near the surface in lowland locations, suggesting that wetland conditions could be maintained under current conditions. Evapotranspiration rates between uplands and lowlands were similar between years and sites, ranging from 2.2 ± 1.8 to 2.5 ± 1.2 mm/day and were largely controlled by climate. These rates were less than nearby older upland systems, suggesting that water balance partitioning will change as vegetation develops. Comparison between years and with natural systems provides insight on how management practices influence hydrologic dynamics and the overall water balance of the SFW. Copyright © 2016 John Wiley & Sons, Ltd.     

Mercury and methylmercury biogeochemistry in a thawing permafrost wetland complex,Northwest Territories,Canada

In arctic and sub‐arctic environments, mercury (Hg), more specifically toxic methylmercury (MeHg), is of growing concern to local communities because of its accumulation in fish. In these regions, there is particular interest in the potential mobilization of atmospherically deposited Hg sequestered in permafrost that is thawing at unprecedented rates. Permafrost thaw and the resulting ground surface subsidence transforms forested peat plateaus into treeless and permafrost‐free thermokarst wetlands where inorganic Hg released from the thawed permafrost and draining from the surrounding peat plateaus may be transformed to MeHg. This study begins to characterize the spatial distribution of MeHg in a peat plateau–thermokarst wetland complex, a feature that prevails throughout the wetland‐dominated southern margin of thawing discontinuous permafrost in Canada's Northwest Territories. We measured pore water total Hg, MeHg, dissolved organic matter characteristics and general water chemistry parameters to evaluate the role of permafrost thaw on the pattern of water chemistry. A gradient in vegetation composition, water chemistry and dissolved organic matter characteristics followed a toposequence from the ombrotrophic bogs near the crest of the complex to poor fens at its downslope margins. We found that pore waters in poor fens contained elevated levels of MeHg, and the water draining from these features had dissolved MeHg concentrations 4.5 to 14.5 times higher than the water draining from the bogs. It was determined through analysis of historical aerial images that the poor fens in the toposequence had formed relatively recently (early 1970s) as a result of permafrost thaw. Differences between the fens and bogs are likely to be a result of their differences in groundwater function, and this suggests that permafrost thaw in this landscape can result in hotspots for Hg methylation that are hydrologically connected to downstream ecosystems. Copyright © 2016 John Wiley & Sons, Ltd.