Persistent weak thermal stratification inhibits mixing in the epilimnion of north-temperate Lake Opeongo,Canada

Persistent weak temperature stratification characterizes the epilimnion of Lake Opeongo, Ontario, Canada, and reduces the magnitude of turbulent mixing. Throughout July and August 2009, the epilimnion was isothermal for only 34 % of the record, while for 28 % of the record there was at least a 2 °C temperature difference across the 5 m deep epilimnion. During these stratified periods, there were increases in gradient Richardson numbers (Ri _g ), and decreases in rates of dissipation of turbulent kinetic energy ( $\varepsilon$ ), the turbulence activity parameter (I = ε/νN ²), an indicator of active mixing, and vertical eddy diffusivity (K _z ) inferred from temperature microstructure profiles. During periods of shear induced mixing, values of ε approached 10^?6 m² s^?3 and decreased during periods of increasing Ri _g . For 0 < Ri _g  < 1, average values of I were ~1,000 and values of K _z were slightly higher than 10^?4 m² s^?1. For Ri _g >1, average values of I were ~300 and K _z was reduced by one to three orders of magnitude. Mixing during cold fronts occurred over time scales of minutes to hours, which worked to erode diurnal thermoclines. However, during periods of persistent secondary thermoclines, mixing was suppressed throughout the epilimnion.     

Geologic influences on fluvial hydrology and bedload transport in small mountainous watersheds,Northern New Mexico,U.S.A.

Discharge characteristics in six adjacent mountainous watersheds in northern New Mexico, U.S.A., vary substantially between basins underlain by different lithologies. Relatively resistant gneisses and granites underlie two basins (drainage areas: 43 and 94 km²) that have high unit discharge (0·010 to 0·14 m³s^?1 km^?2), high bankfull discharge, and sustained high discharge. Less resistant sandstones and shales underlie four basins (drainage areas: 96 to 215 km²) that have relatively low unit discharge (0·001 to 0·005 m³s^?1 km^?2), relatively low bankfull discharge, and peak discharges that are not sustained as long as those in the crystalline terrane. Analysis of snowmelt-runoff water budgets suggests that three factors control hydrologic conditions in the basins. First, area-elevation distributions appear to control the timing and amounts of water input. These distributions probably reflect the erosional resistance of the different lithologies. Second, lithology appears to control runoff production in areas having minor amounts of storage. Third, glacial deposits in headwater regions control discharge duration and timing via storage and return flow releases. The amount of return flow released by glacial deposits, however, is probably controlled by the permeability of underlying bedrock. Therefore it appears that the duration, timing, and magnitude of discharge events in the study area are controlled both directly and indirectly by lithology. Stream power and shear stress estimates derived from bankfull discharge and bed-material size data suggest that higher bedload transport rates and larger bedload particle sizes exist in streams draining crystalline rocks than in streams draining sedimentary terrane. It appears that source-area lithology, by controlling discharge production, also influences stream power, bedload transport capabilities, and therefore total amounts of bedload transport.     

Carbonate deposition,physical limnology and environmentally controlled chert formation in Paleocene-Eocene Lake Flagstaff,central Utah

Lake Flagstaff (Paleocene-Eocene of central Utah) owed its existence, large size, shallowness and low clastic content to its tectonic setting, but the climate controlled its mostly autochthonous sediments. During the first and most humid of the three lake phases, the lake was fresh, calcareous, large, and highly productive, with abundant vegetation and snails. The first deposits were limestones with gradually increasing detrital dolomite eroded from lake-marginal carbonate mudflats that were undergoing penecontemporaneous dolomitization. Continuous fluctuation in lake level produced many secondary dewatering and pedogenic-paludine fabrics. The lake developed into a playa lake during the very arid second phase, becoming restricted in area and fauna. The water was saline and alkaline, and twice became a gypsum-precipitating brine. Frequent exposure of the lake beds resulted in much calichification and in rapid and complete dolomitization. Under the intermediate climate of the third phase, the lake reexpanded and freshened, snails returned, and many limestones escaped dolomitization. Each phase defines a member of the Flagstaff Formation.Chert, absent in the oldest beds, increases up-section. The lowest chert forms minor small spheres and linings in voids near the top of the lowest member, suggesting limited silica input and post-dolomitization precipitation in areas of greatest groundwater movement. The base of the middle member contains horizons of atextural chert mudcrack fillings and nodules that appear to have been an inorganically precipitated gel. Most of the middle member, however, contains abundant chert nodules that replaced limestone prior to dolomitization. The nodules grew prior to burial (some even prior to mudcrack formation) by the movement of dissolved silica to areas of relatively low pH. In the upper member, chert is even more prevalent: entire thin beds were pervasively but incompletely silicified prior to dolomitization, probably by vertical evaporative pumping of siliceous groundwater moving under mudflats toward the lake.     

Sympatric seagrass shrimp show similar structure and selection along the seashore: a comparison of two cryptic Phycomenes zostericola lineages

Small crustaceans are diverse and abundant in seagrass habitats and provide many ecological services. Further information is needed about their long‐ and short‐term response to habitat fragmentation and loss. Shrimp specimens were sampled from coastal seagrasses: latitudes 9°–27° S (Torres Strait to Moreton Bay, Queensland, Australia) and longitudes 141°–153° E (Weipa to Moreton Bay, Queensland, Australia). The seagrass shrimp Phycomenes zostericola (Caridea: Decapoda) underwent phylogeographic analysis using mitochondrial and nuclear sequence data. Lineage relationships were investigated and two deeply divergent sympatric lineages of P. zostericola were discovered in northern samples. The two lineages display vastly different demographic histories in spite of similar overall phylogeographic patterns. The two lineages appear to be in secondary contact with each other, detailing independent histories of sea level change, long distance colonisation and habitat fragmentation. Their regional structure is evidence that the potential for dispersal is only realised under specific environmental conditions. Nuclear data, used to determine reproductive status between lineages, instead displayed a non‐random latitudinal geographic distribution suggesting directional selection, possibly in response to ocean temperatures. The differences between the two deeply divergent lineages highlight the importance of understanding variability among cryptic taxa and their response to habitat change.     

The carbohydrate‐to‐protein ratio as a biological indicator of water movement

We investigated temporal (day‐to‐day and season) and spatial (reach) variability of drift with the aim of guiding sampling protocol for quantifying drift at the whole river or reach scale. Overall, we found aquatic drift density and biomass varied considerably seasonally (CV = 72.9, 88.1) and to a lesser extent spatially (CV = 31.3, 30.7) and from day‐to‐day (CV = 45.2, 39.4). Although spatial and day‐to‐day variation in drift density and biomass were similar, sampling logistics suggest spatial sampling would be more cost‐effective and less time consuming. Drift density and biomass estimated from top samplers was often higher than estimates from samplers near the streambed or mid‐water column. A reliable estimate of mean densities and biomass at a site may require only two samplers— a top sampler and either a middle or bottom sampler. In our study, we calculated that sampling at four sites over 1 or 4 days at one site would be required to obtain a 95% CI within 50% of the mean drift density. Eight sites over 1 or 10 days at one site would be required to achieve a 95% CI within 25% of the mean drift density.     

Applying Resilience Thinking to Natural Resource Management through a “Planning-By-Doing” Framework

Natural resource management (NRM) organizations are increasingly looking to resilience thinking to provide insights into how social and environmental systems interact and to identify points of intervention. Drawing on complex systems analysis, resilience thinking emphasizes that landscapes constantly change from social and ecological interactions, and focuses NRM planners’ attention on identifying key variables, feedbacks, and thresholds that can help improve intervention strategies. More deliberative approaches are being developed to use resilience thinking in ways that engage and build human capacity for action. This article documents experiences shared with NRM agencies in rural Australia as we developed new approaches to link resilience thinking with collective learning principles. We present an emerging framework through which heuristics associated with resilience thinking is being used as part of a planning-by-doing process. The framework is being tested to assess whether and how it can enable change agents to advance their capacities for adaptation and transformation.     

Effectiveness and toxicity of an oil dispersant in large outdoor salt water tanks

Use of the dispersant, Oilsperse 43, increased the dispersion of Venezuelan Guanipa crude oil. The resulting mixture was more homogeneous and the oil slick less viscous than in the oil tank. The dispersant appeared to retard formation of the familiar “crust” on the surface. A weathered crude oil plus dispersant mixture with an oil concentration of 250 μg/l was lethal to over 50% of the test organisms, green sea urchins, within 4 days. No mortalities occurred among urchins exposed to the crude oil treatment.     

Sediment detachment and transport processes associated with internal erosion of soil pipes

Subsurface flow can be an important process in gully erosion through its impact on decreasing soil cohesion and erosion resistance as soil water content or pressure increases and more directly by the effects of seepage forces on particle detachment and piping. The development of perched water tables fosters lateral flow that can result in seepage at the surface and/or formation of soil pipes by internal erosion of preferential flow paths. Continued internal erosion of soil pipes can lead to gullies, dam and levee failures. However, the processes involved in particle and aggregate detachment from soil pipe walls and transport processes within soil pipes have not been well studied or documented. This paper reviews the limited research on sediment detachment and transport in macropores and soil pipes and applies the knowledge learned from the much more extensive studies conducted on streams and industrial pipes to hydrogeologic conditions of soil pipes. Knowledge gaps are identified and recommendations are made for future research on sediment detachment and transport in soil pipes. Copyright © 2017 John Wiley & Sons, Ltd.     

Radio source calibration for the Very Small Array and other cosmic microwave background instruments at around 30 GHz

Accurate calibration of data is essential for the current generation of cosmic microwave background (CMB) experiments. Using data from the Very Small Array (VSA), we describe procedures which will lead to an accuracy of 1 per cent or better for experiments such as the VSA and CBI. Particular attention is paid to the stability of the receiver systems, the quality of the site and frequent observations of reference sources. At 30 GHz the careful correction for atmospheric emission and absorption is shown to be essential for achieving 1 per cent precision.
The sources for which a 1 per cent relative flux density calibration was achieved included Cas A, Cyg A, Tau A and NGC 7027 and the planets Venus, Jupiter and Saturn. A flux density, or brightness temperature in the case of the planets, was derived at 33 GHz relative to Jupiter which was adopted as the fundamental calibrator. A spectral index at ∼30 GHz is given for each.
Cas A, Tau A, NGC 7027 and Venus were examined for variability. Cas A was found to be decreasing at 0.394 ± 0.019 per cent yr⁻¹ over the period 2001 March to 2004 August. In the same period Tau A was decreasing at 0.22 ± 0.07 per cent yr⁻¹. A survey of the published data showed that the planetary nebula NGC 7027 decreased at 0.16 ± 0.04 per cent yr⁻¹ over the period 1967–2003. Venus showed an insignificant (1.5 ± 1.3 per cent) variation with Venusian illumination. The integrated polarization of Tau A at 33 GHz was found to be 7.8 ± 0.6 per cent at position angle =148°± 3°.