Strontium,SO42−/Cl− and Mg2+/Ca2+ ratios as tracers for the evolution of seawater into coastal aquifers: the example of Castell de Ferro aquifer (SE Spain)

The strontium content and the SO₄^2?/Cl^? and Mg²⁺/Ca²⁺ ratios were used as natural tracers of the residence time of seawater intrusion into the Castell de Ferro aquifer. Analysis of these parameters indicated the existence of two principal flowpaths in the aquifer. The first flows through the eastern part of the aquifer, through the karstified Castell de Ferro massif; it accommodates a larger and more rapid flow, so that the residence time is shorter, leading to lower SO₄²⁺/Cl^? ratios, lower Sr²⁺ content and higher Mg²⁺/Ca²⁺ ratios. The second flowpath is in the western sector, and flows exclusively through alluvial deposits; the flow here is slower, particularly that flowing towards the sea. Thus the residence time of the water here will be longer and there is scant flushing of the intruded seawater; this is manifested in the high Sr²⁺ content, high SO₄²⁺/Cl^? and low Mg²⁺/Ca²⁺ ratios. To cite this article: P. Pulido-Leboeuf et al., C. R. Geoscience 335 (2003).     

Methane emission measurements in urban areas in Eastern Germany

We have investigated methane emissions from urban sources in the former East Germany using innovative measurement techniques including a mobile real-time methane instrument and tracer release experiments. Anthropogenic and biogenic sources were studied with the emphasis on methane emissions from gas system sources, including urban distribution facilities and a production plant. Methane fluxes from pressure regulating stations ranged from 0.006 to 24. l/min. Emissions from diffuse sources in urban areas were also measured with concentration maps and whole city flux experiments. The area fluxes of the two towns studied were 0.37 and 1.9 g/m²/s. The emissions from individual gas system stations and total town emissions of this study are comparable to results of similar sites examined in the United States.     

Oceanographic Research Vessel Sharing Plan—A Significant Creation of the National Natural Science Foundation of China

To settle the difficulties of the shortage of oceanographic research vessels in our country, the National Natural Science Foundation Committee of China founded Oceanographic Research Vessel Sharing Plan in 2009. It is aimed at enhancing efficiency and optimization of the vessel resources,and coordinating the use demands of vessels for the different foundation projects and the efficient use of the research vessels. We have summarized the achievements made in the Plan from 2010 to 2014, as well as the use system of the research vessels sharing, the specific operating mode ,the organization and the management framework of the Plan. In the end, we put forward our suggestions on the improvement of the Plan after the primary analysis of the present situation of the sharing of the survey data and the existing problems.     

Ecohydrological modelling with EcH2O‐iso to quantify forest and grassland effects on water partitioning and flux ages

We used the new process‐based, tracer‐aided ecohydrological model EcH₂O‐iso to assess the effects of vegetation cover on water balance partitioning and associated flux ages under temperate deciduous beech forest (F) and grassland (G) at an intensively monitored site in Northern Germany. Unique, multicriteria calibration, based on measured components of energy balance, hydrological function and biomass accumulation, resulted in good simulations reproducing measured soil surface temperatures, soil water content, transpiration, and biomass production. Model results showed the forest “used” more water than the grassland; of 620 mm average annual precipitation, losses were higher through interception (29% under F, 16% for G) and combined soil evaporation and transpiration (59% F, 47% G). Consequently, groundwater (GW) recharge was enhanced under grassland at 37% (~225 mm) of precipitation compared with 12% (~73 mm) for forest. The model tracked the ages of water in different storage compartments and associated fluxes. In shallow soil horizons, the average ages of soil water fluxes and evaporation were similar in both plots (~1.5 months), though transpiration and GW recharge were older under forest (~6 months compared with ~3 months for transpiration, and ~12 months compared with ~10 months for GW). Flux tracking using measured chloride data as a conservative tracer provided independent support for the modelling results, though highlighted effects of uncertainties in forest partitioning of evaporation and transpiration. By tracking storage—flux—age interactions under different land covers, EcH₂O‐iso could quantify the effects of vegetation on water partitioning and age distributions. Given the likelihood of drier, warmer summers, such models can help assess the implications of land use for water resource availability to inform debates over building landscape resilience to climate change. Better conceptualization of soil water mixing processes and improved calibration data on leaf area index and root distribution appear obvious respective modelling and data needs for improved simulations.     

A note on the general concept of wave breaking for Rossby and gravity waves

A recently proposed general definition of wave breaking is further discussed, in order to deal with some points on which misunderstanding appears to have arisen. As with surface and internal gravity waves, the classification of Rossby waves into breaking and not breaking is a generic classification based on dynamical considerations, and not a statement about any unique signature or automatically recognizable shape. Nor is it a statement about passive tracers uncorrelated with potential vorticity on isentropic surfaces. A strong motivation for the definition is that proofs of the nonacceleration theorem of wave, mean-flow interaction theory rely, explicitly or implicitly, on a hypothesis that the waves do not break in the sense envisaged.The general definition refers to the qualitative behaviour of a certain set of material contours, namely those, and only those, which would undulate reversibly, with small slopes, under the influence of the waves' restoring mechanism, in those circumstances for which linearized, nondissipative wave theory is a self-consistent approximation to nonlinear reality. The waves' restoring mechanism depends upon the basic-state vertical potential density gradient in the case of gravity waves, and upon the basic-state isentropic gradient of potential vorticity in the case of Rossby waves. In the usual linearized theory of planetary scale Rossby waves on a zonal shear flow, the relevant material contours lie along latitude circles when undisturbed.     

Comparison of ground-based and UAV a-UHF artificial tracer mobility monitoring methods on a braided river

Radio frequency identification (RFID) technologies, which allow wireless detection of individual buried or immersed tracers, represent a step forward in sediment tracking, especially passive integrated transponders (PIT tags) that have been widely used. Despite their widespread adoption in the scientific community, they typically have low efficiency when deployed in river systems with active bedload transport or deep wet channels, attributed to their technical specifications. A recent evaluation of active ultra-high frequency transponders (a-UHF tags) assessed their larger detection range and provided a methodology for their geopositioning. In this study, we test five different survey methods (one including an unmanned aerial vehicle [UAV]) in a sediment tracking study, and compare them in terms of recovery rate, field effort, geopositioning error, and efficiency. We then tested the method on a larger reach following a Q₅ flood and performed cross-comparisons between active and passive RFIDs. The results confirmed that the a-UHF RFID technology allowed rapid (1.5 h ha⁻¹) survey of a large area (<34 ha) of emerged bars and shallow water channels with recovery of a high percentage of tracers (72%) that had travelled large distances (mean ≈ 1000 m; max ≈ 3400 m). Moreover, the tracers were identified with low geopositioning error (mean ≈ 7.1 m, ≤1% of their travel distance). We also showed that a UAV-based survey was fast (0.38 h ha⁻¹), efficient (recovery rate = 84%), and low error (mean ≈ 4.2 m). Thus, a-UHF RFID technology permits the development of a variety of survey methods, depending on the study objectives and the human and financial resources available. This allows field efforts to be optimized by determining an appropriate balance between the high equipment cost of a-UHF tracers and the resulting reduced survey costs. © 2019 John Wiley & Sons, Ltd.     

Depth profiles of chlorofluoromethanes in the Norwegian sea

Depth profiles of the chlorofluoromethanes (CFM), CFCl₃ and CF₂Cl₂, have been obtained together with tritium profiles from water samples collected in the Norwegian Sea between surface and 2800 m depth. CFM analysis was performed by vacuum extraction of the dissolved gases from 500 ml samples of seawater and subsequent gaschromatographic measurement. The CFM concentration decreases with depth to about 10 percent of surface concentration at depths below 2000 m. The same behaviour is found for the tritium content. From a correlation of the CFM and tritium concentration the upper limit of the preindustrial atmospheric CFM levels can be estimated to 5 percent of the present day concentrations.     

The influence of local hydrogeologic forcings on near‐stream event water recharge and retention (Upper San Pedro River,Arizona)

The rise in stream stage during high flow events (floods) can induce losing stream conditions, even along stream reaches that are gaining during baseflow conditions. The aquifer response to flood events can affect the geochemical composition of both near‐stream groundwater and post‐event streamflow, but the amount and persistence of recharged floodwater may differ as a function of local hydrogeologic forcings. As a result, this study focuses on how vertical flood recharge varies under different hydrogeologic forcings and the significance that recharge processes can have on groundwater and streamflow composition after floods. River and shallow groundwater samples were collected along three reaches of the Upper San Pedro River (Arizona, USA) before, during and after the 2009 and 2010 summer monsoon seasons. Tracer data from these samples indicate that subsurface floodwater propagation and residence times are strongly controlled by the direction and magnitude of the dominant stream–aquifer gradient. A reach that is typically strongly gaining shows minimal floodwater retention shortly after large events, whereas the moderately gaining and losing reaches can retain recharged floodwater from smaller events for longer periods. The moderately gaining reach likely returned flood recharge to the river as flow declined. These results indicate that reach‐scale differences in hydrogeologic forcing can control (i) the amount of local flood recharge during events and (ii) the duration of its subsurface retention and possible return to the stream during low‐flow periods. Our observations also suggest that the presence of floodwater in year‐round baseflow is not due to long‐term storage beneath the streambed along predominantly gaining reaches, so three alternative mechanisms are suggested: (i) repeated flooding that drives lateral redistribution of previously recharged floodwater, (ii) vertical recharge on the floodplain during overbank flow events and (iii) temporal variability in the stream–aquifer gradient due to seasonally varying water demands of riparian vegetation. Copyright © 2011 John Wiley & Sons, Ltd.     

DEVELOPMENT AND VALIDATION OF AN ISOTOPIC METHOD FOR ESTIMATING LAKE EVAPORATION

A study designed to test the validity of an isotopic method for estimating evaporation was conducted within a small, tundra lake situated in the continental Arctic of Canada. Evaporation was determined using an isotope mass balance approach which accounted quantitatively for isotopic fractionation, progressive evaporative enrichment of δ¹⁸O and δ²H in lake water, and attenuation of enrichment by liquid inputs and atmospheric moisture. Concurrent determinations made using standard mass balance, energy balance, aerodynamic profile and class A pans permitted rigorous comparisons between methods. Results are presented for two summers which had distinct weather conditions and hydrological balances. Overall, the δ¹⁸O balance was found to be in good agreement with standard methods during both years over time intervals greater than about one week. Owing to a less systematic response of δ²H over short time periods, it use is not recommended for quantitative mass balance determinations over time intervals of less than about 50 days in this setting.     

Distribution of clay minerals in surface sediments from the eastern Barents and south-western Kara seas

Surface samples from the eastern Barents and south-western Kara seas have been analysed for clay mineralogy. Transport paths, the role of regional sources and local bedrock outcrops and the influence of hydrodynamic and glacigenous processes for clay distribution on the shelves are discussed in relation to central Arctic Ocean deep sea and sea ice sediments. Franz Josef Land and Novaya Zemlya show significantly different clay mineral associations. Although smectite concentrations are fairly high, Franz Josef Land can be excluded as a source for central Arctic sea ice sediments, which are relatively rich in smectite. In the Kara Sea, smectite concentrations in coastal sediments surpass even the Franz Josef Land concentrations. The large cyclonic gyre in the eastern Barents Sea between Novaya Zemlya and Franz Josef Land, which serves as a mixing zone between Arctic and North Atlantic water, is apparently reflected within the smectite distribution pattern. With the exception of Franz Josef Land, the area of investigation is typically low in kaolinite. In particular, coastal areas and areas north of Novaya Zemlya, influenced by the inflow of Arctic waters, show the lowest kaolinite concentrations. A high kaolinite occurrence within the Nansen Basin is most probably related to Franz Josef Land and emphasizes the importance of long-range downslope transport of sediments across the continental slope. The surface water circulation pattern in close interaction with local outcrops onshore Novaya Zemlya and locally restricted occurrences within the eastern Barents Sea significantly alter the illite dispersal pattern. Illite concentrations are lowest around Franz Josef Land. Chlorite is generally low in the area of investigation. Submarine outcrops and important chlorite occurrences onshore Novaya Zemlya bias its distribution pattern.