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.     

Advances in the fatigue assessment of wire ropes

This paper presents the findings from an in-depth analysis of the (axial) stiffness data recorded during tension–tension fatigue tests on wire ropes, particularly in relation to how changes in stiffness during testing relate to changes in rope strength. A linear relationship between stiffness and strength is shown to exist and a methodology presented for quantifying residual strength with applied cycles. New lower bound fatigue lines for six-strand rope and spiral strand are presented which are based on a 10% loss of strength. These new lines have the advantage of having been established using a common discard criterion for wire ropes.     

Evaluation of mine tailings effects on a benthic marine infaunal community over 29 years

Benthic infaunal and sediment data collected over 29 years were used to examine the extent and geographic range of effects and recovery from submarine tailings deposition. Empirical data were used to determine extreme and moderate effects, and identify near-, mid- and far-field zones. A simple probability test using overlap in frequency distributions was then used to determine less obvious effects, identify "normal" or "reference" conditions, and verify the geographic range of effect zones. Tailings thickness and sediment particulate copper were elevated from the outfall to 16-20 km distant, particularly below discharge depth (50 m). Changes in tailings thickness and copper levels before, during and after mining showed three distinct impact zones below discharge depth: near-field (<5 km from outfall); mid-field (5-16 km); and far-field (20 + km). Consistent faunal declines during mining were noted at sediment particulate copper levels >300 microg g(-1), and sediment tailings thickness > 15-20 cm. Extreme impoverishment at these sediment levels were; < 100 animals/m2, <2.5 g/m2 biomass and <7 taxa per station. No stations with >300 microg g(-1) copper and 20 cm tailings had more than 40 taxa. Amphipods were particularly affected by tailings, with distributions reflecting the instability in sediments from heavy deposition and/or shifting of tailings due to resuspension. The probability testing method assumed that reference conditions existed in far-field stations. There was no difference in abundance distributions between near-, mid- and far-field zones. Total taxa per station during mining was significantly reduced (<45) in both near- and mid-field stations compared with far-field (less than 10% overlap in distributions). One midfield station in Quatsino Sound (23) was in reference condition throughout the study period. Post-closure stations in the near- and mid-field had total taxa numbers approaching far-field conditions (overlap of 62% in distributions). Within 3 years following closure, total taxa values were within the far-field range for all stations sampled. Biomass showed a distinct decline in the near-field during mining, but with more overlap in near-field and far-field distributions (27%) than for total taxa per station, and was returning to far-field conditions in the post-closure years. A multivariate (Bray-Curtis) measure of dissimilarity indicated that the near- and mid-field infaunal compositions were distinct from the far-field during mining (< 10% overlap in distributions). The mid-field composition overlapped more with the far-field in the post-closure years, but the near-field composition did not, suggesting that the mine tailings are still affecting the fauna. The most abundant taxon in each of the reference and near-field station groups both showed significantly distinct relative abundance distributions between near- and far-field stations. In summary, the probability method showed that species richness, biomass, species composition and indicator taxa were useful for differentiating affected and non-affected stations. Polychaetes recolonize stable tailings most quickly, and have dominated the tailings stations in the post-closure years. Amphipods have recolonized sporadically, but seem to be highly sensitive to tailings stability. There was no evidence of recovery in dominant bivalves or echinoderms within three years after mine closure.     

Phytoplankton and iron: validation of a global three-dimensional ocean biogeochemical model

The JGOFS program and NASA ocean-color satellites have provided a wealth of data that can be used to test and validate models of ocean biogeochemistry. A coupled three-dimensional general circulation, biogeochemical, and radiative model of the global oceans was validated using these in situ data sources and satellite data sets. Biogeochemical processes in the model were determined from the influences of circulation and turbulence dynamics, irradiance availability, and the interactions among four phytoplankton functional groups (diatoms, chlorophytes, cyanobacteria, and coccolithophores) and four nutrients (nitrate, ammonium, silica, and dissolved iron).Annual mean log-transformed dissolved iron concentrations in the model were statistically positively correlated on basin scale with observations (P<0.05) over the eight (out of 12) major oceanographic basins where data were available. The model tended to overestimate in situ observations, except in the Antarctic where a large underestimate occurred. Inadequate scavenging and excessive remineralization and/or regeneration were possible reasons for the overestimation.Basin scale model chlorophyll seasonal distributions were positively correlated with SeaWiFS chlorophyll in each of the 12 oceanographic basins (P<0.05). The global mean difference was 3.9% (model higher than SeaWiFS).The four phytoplankton groups were initialized as homogeneous and equal distributions throughout the model domain. After 26 years of simulation, they arrived at reasonable distributions throughout the global oceans: diatoms predominated high latitudes, coastal, and equatorial upwelling areas, cyanobacteria predominated the mid-ocean gyres, and chlorophytes and coccolithophores represented transitional assemblages. Seasonal patterns exhibited a range of relative responses: from a seasonal succession in the North Atlantic with coccolithophores replacing diatoms as the dominant group in mid-summer, to successional patterns with cyanobacteria replacing diatoms in mid-summer in the central North Pacific. Diatoms were associated with regions where nutrient availability was high. Cyanobacteria predominated in quiescent regions with low nutrients.While the overall patterns of phytoplankton functional group distributions exhibited broad qualitative agreement with in situ data, quantitative comparisons were mixed. Three of the four phytoplankton groups exhibited statistically significant correspondence across basins. Diatoms did not. Some basins exhibited excellent correspondence, while most showed moderate agreement, with two functional groups in agreement with data and the other two in disagreement. The results are encouraging for a first attempt at simulating functional groups in a global coupled three-dimensional model but many issues remain.     

Increased Terrestrial to Ocean Sediment and Carbon Fluxes in the Northern Chesapeake Bay Associated With Twentieth Century Land Alteration

We calculated Chesapeake Bay (CB) sediment and carbon fluxes before and after major anthropogenic land clearance using robust monitoring, modeling and sedimentary data. Four distinct fluxes in the estuarine system were considered including (1) the flux of eroded material from the watershed to streams, (2) the flux of suspended sediment at river fall lines, (3) the burial flux in tributary sediments, and (4) the burial flux in main CB sediments. The sedimentary maximum in Ambrosia (ragweed) pollen marked peak land clearance (~1900 a.d.). Rivers feeding CB had a total organic carbon (TOC)/total suspended solids of 0.24?±?0.12, and we used this observation to calculate TOC fluxes from sediment fluxes. Sediment and carbon fluxes increased by 138–269% across all four regions after land clearance. Our results demonstrate that sediment delivery to CB is subject to significant lags and that excess post-land clearance sediment loads have not reached the ocean. Post-land clearance increases in erosional flux from watersheds, and burial in estuaries are important processes that must be considered to calculate accurate global sediment and carbon budgets.     

Brønsted reactions on oxide mineral surfaces and the temperature-dependence of their dissolution rates

The pH-dependence of oxide dissolution rates is controlled by Brønsted acid-base reactions at the mineral surface. These reactions are rapid but depend explicitly on temperature, as do the subsequent slow rates of bond hydrolysis. The net result is that dissolution rates vary in a complicated fashion with temperature and solution pH. The enthalpy changes of acid-base reactions on oxide materials are sufficiently similar, however, that general statements can be made about their contribution. The enthalpy changes from proton adsorption to a hydroxyl functional group (SOH), or to a deprotonated functional group (SO ^–), are generally exothermic. The enthalpy changes become increasingly endothermic, however, as charge accumulates on the mineral surface and the charged species interact electrostatically. The result is that mineral dissolution rates are least sensitive to temperature, as measured with an Arrhenius-like rate law, at pH conditions near the Point of Zero Net Proton Charge.     

When the Light of the Home is Abroad: Unskilled Female Migration and the Filipino Family

The migration of women engaged in transnational domestic work reveals how the uneven impacts of globalisation have intruded into the micro‐world of families and households. In this age of globalisation and migration, family membership has become multisited or transnational, with members dispersed in space. The migration of workers and the separation this entails has raised challenges to notions and ideals of “being family”. Unlike other workers on the move, the migration of domestic workers has some distinctive characteristics. It can be framed in terms of women moving between families and households; workers whose departure from their family of origin and insertion into their family of employment reconstitute the structure and content of family relationships in both material and imagined ways. Drawing on in‐depth interviews conducted in the Philippines and Singapore, we explore how migrant women and their family members define and negotiate family ideals, gender identities and family relationships, given the family's transnational configuration. Our findings provide some support to the notion that individual members in transnational families resort to “relativising” in fashioning responses to their situation.     

Contesting ‘Local’ Commemoration of the Second World War: the case of the Changi Chapel and Museum in Singapore

This paper concerns the performance of national war memory at the Changi Chapel and Museum, a site honouring the many prisoners interned in Japanese-Occupied Singapore—especially at Changi—during the Second World War. In the light of the global nature of ‘the Changi story’, and the predominantly transnational nature of its present in situ memorialisation, we first examine how the Singapore state has sought to ‘localise’ the site to make it equally appealing to Singaporeans, as a place where a sense of their ‘shared history’ may be invoked. We then explore the Singaporeans' views about the site and its reconfiguration as a national icon, arguing how the state's task of ‘localising’ the site has been a vexed process due to myriad factors such as ethnic and religious plurality, and the already foreign-centric bias of prevailing knowledge about Changi. Following that, we show how this performance of national memory is also inflected by Australia's national remembrance of the same event. More broadly, we highlight the contested process of ‘localising’ such war memoryscapes as national iconography, suggesting how it may be more fruitful to conceive them as ‘international memoryscapes’, or places to which all individuals can relate regardless of race or national affiliations.