MELIMEX,an experimental heavy metal pollution study: Chemical speciation and biological availability of copper in lake water

The chemical speciation of dissolved copper was investigated in waters from the limno-corrals of the MELIMEX project and compared with speciation data from other Swiss lakes. Copper is complexed primarily by organic ligands having molecular sizes between 10⁴ and 10³ daltons. The mean concentration of the ligands is approximately 5×10⁻⁷ mole/mg DOC. The conditional stability constants (pH=8.8) are about 10¹¹. An increased metal load did not induce an increase of binding ligands. A comparison of calculated Cu²⁺ concentration with corresponding copper contents in the biomass leads to the conclusion that organic ligands and pH are the most important factors in deciding the biological availability of copper. However the sorption capacity of the biomass depends as well on the variety of plankton species.     

MELIMEX,an experimental heavy metal pollution study: Regulation of trace metal concentrations in limno-corrals

In three limno-corrals of the MELIMEX project the transport paths of the trace metals Cu, Zn, Cd, Hg and Pb and the reaction of the systems on increased metal loads were investigated. The metal balances lead to the conclusion that the biomass is the main factor responsible for the regulation of trace metal concentration. The observed sequence of relative residence times of the trace metals can be described with a steady-state model. Additional metal load decreases the ability of the limnic system to lower the metal concentration. The production of phytoplankton and its assimilation capacity for metals are reduced leading to relatively higher metal concentrations in the lake.     

MELIMEX,an experimental heavy metal pollution study: Particle size distributions in limno-corrals

The particle size distributions in three limno-corrals, located in Baldeggersee, Switzerland, have been determined by means of a Zeiss Micro-Videomat image analyzer as a function of depth and time. The distributions were measured biweekly over a period of 1 year at depths of 0 m, 2.5 m, 5 m, 7.5 m and 10 m (=above bottom). Two of the limno-corrals were charged with heavy metals, whereas the third was uncharged and served as a reference. The shape of the distributions as well as the particle concentrations in the uncharged container did not differ from the ones in the charged limno-corrals. The distributions were found to be self-preserving and independent on heavy metal load, time, depth and particle concentrations. As an average, the dependence of the distributions on the particle diameter was found to be ?1.5 to ?2.5.     

MELIMEX,an experimental heavy metal pollution study: Oligochaetes and chironomid larvae in heavy metal loaded and control limno-corrals

In two limno-corrals loaded with heavy metals the density of tubificid worms and chironomid larvae was higher than in the control. The better oxygen conditions observed in the heavy metal loaded corrals might explain this discrepancy. The higher oxygen concentration at the sediment-water interface was due to lower organic sedimentation, consequence of the primary production reduced by heavy metals. In all limno-corrals, the tubificid populations consisted ofTubifex tubifex. The size structure of tubificid populations in the heavy metal loaded corrals indicated a delayed reproduction compared to the control.     

MELIMEX,an experimental heavy metal pollution study: Effects of increased heavy metal loads on phytoplankton communities

Long-term impacts of increased metal loading (Hg, Cu, Cd, Zn and Pb) on phytoplankton communities of large limno-corrals (diameter 12 m, depth 10 m) were studied. Increased metal concentrations initially lowered phytoplankton biomass, as well as species number and photosynthetic activity of phytoplankton. They caused changes in metal speciation and shifts in phytoplankton community structure, favoring less susceptible species. Although adaptation was not sufficient to completely prevent the metal-induced depression of photosynthesis, due to depressed zooplankton grazing, at the end of the experiment even higher phytoplankton densities were observed in the metal-loaded corrals than in the control.     

MELIMEX,an experimental heavy metal pollution study: Behaviour of heavy metals in an aquatic food chain

Phytoplankton, periphyton and zooplankton samples, chironomid andSialis sp. larvae, and fry of trout and bream collected from unpolluted and artificially metal-polluted limno-corrals were analyzed for mercury, copper, cadmium, zinc and lead. The results indicate that these metals are not accumulated through the food chain and suggest that increased metal concentrations in the environment favor the growth of phytoplankton organisms with a low metal sorption capacity.     

MELIMEX,an experimental heavy metal pollution study: Effects of increased heavy metal load on uptake of glucose by natural planctonic communities

Glucose uptake in lake water samples has been determined with short-time¹⁴C-experiments at different additions of the single heavy metals Cu⁺⁺, Zn⁺⁺, Cd⁺⁺, Pb⁺⁺, Hg⁺⁺ and at different additions of a combination of all metals. The degree of a metal induced inhibition of glucose uptake varied from lake to lake and from season to season, whereby the addition of legally tolerated concentrations of 10 μg Cu/l and 200 μg Zn/l inhibited glucose uptake in most samples significantly, as well as the simultaneous addition of all metals. The legally tolerated limit of 1 μg Hg/l inhibited glucose uptake in Lake Lucerne samples almost completely, showed however no effect in samples of Lake Baldegg. The equimolar toxicity sequence of heavy metals for heterotrophic microorganisms has been determined as: Hg>Cu>Cd>(Zn. Pb). Glucose uptake of plankton sampled from metal polluted limno-corrals was less inhibited than that of the control plankton, when heavy metals were added to the samples singly or in combination. It is assumed that this effect is due to the natural selection of more resistant plankton species.     

MELIMEX,an experimental heavy metal pollution study: Effects of increased heavy metal load on crustacea plankton

The crustacea plankton of three artificial model lakes in Lake Baldegg was observed during 15 months. Two were loaded continuously with low concentrations of five heavy metals (Hg, Cu, Cd, Zn, Pb). It was attempted to explain the significant lower abundances of the loaded limno-corrals. The results suggest that the decrease was not, or only partially, caused by the lower food supply in the loaded limnocorrals, but directly by the heavy metals. Accompaning laboratory tests show significantly increased egg-development-times for two species of those animals from the loaded limno-corrals. Two other species show a decrease of the egg production/♀. It cannot be determined if increased mortality of particular animal stages was caused by heavy metals.

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Résumé On a observé pendant 15 mois les crustacés planctoniques des trois modèles de lac installés dans le lac de Baldegg. Dans deux de ceux-ci, une charge constante de cinq métaux lourds (Hg, Cu, Cd, Zn, Pb) de faible concentration a été maintenue. On a essayé d'expliquer la faible concentration significative de plancton dans les bassins limnologiques chargés. Les résultats montrent que la diminution n'était que partiellement ou pas du tout causée par le faible approvisionnement en nourriture dans les bassins chargés, mais directement par les métaux lourds. Les tests de laboratoire montrent significativement l'augmentation du temps de développement des œufs pour deux espèces animales des bassins chargés. Deux autres espèces montrent une diminution de la production d'œufs/♀. On ne peut pas déterminer l'augmentation de la mortalité des animaux causée par les métaux lourds à des stades particuliers de développement.

     

From experimental plots to experimental landscapes: topography,erosion and deposition in sub‐humid badlands from Structure‐from‐Motion photogrammetry

In the last decade advances in surveying technology have opened up the possibility of representing topography and monitoring surface changes over experimental plots (<10 m²) in high resolution (~10³ points m^‐1). Yet the representativeness of these small plots is limited. With ‘Structure‐from‐Motion’ (SfM) and ‘Multi‐View Stereo’ (MVS) techniques now becoming part of the geomorphologist's toolkit, there is potential to expand further the scale at which we characterise topography and monitor geomorphic change morphometrically. Moving beyond previous plot‐scale work using Terrestrial Laser Scanning (TLS) surveys, this paper validates robustly a number of SfM‐MVS surveys against total station and extensive TLS data at three nested scales: plots (<30 m²) within a small catchment (4710 m²) within an eroding marl badland landscape (~1 km²). SfM surveys from a number of platforms are evaluated based on: (i) topography; (ii) sub‐grid roughness; and (iii) change‐detection capabilities at an annual scale. Oblique ground‐based images can provide a high‐quality surface equivalent to TLS at the plot scale, but become unreliable over larger areas of complex terrain. Degradation of surface quality with range is observed clearly for SfM models derived from aerial imagery. Recently modelled ‘doming’ effects from the use of vertical imagery are proven empirically as a piloted gyrocopter survey at 50m altitude with convergent off‐nadir imagery provided higher quality data than an Unmanned Aerial Vehicle (UAV) flying at the same height and collecting vertical imagery. For soil erosion monitoring, SfM can provide data comparable with TLS only from small survey ranges (~5 m) and is best limited to survey ranges ~10–20 m. Synthesis of these results with existing validation studies shows a clear degradation of root‐mean squared error (RMSE) with survey range, with a median ratio between RMSE and survey range of 1:639, and highlights the effect of the validation method (e.g. point‐cloud or raster‐based) on the estimated quality. Copyright © 2015 John Wiley & Sons, Ltd.     

MELIMEX,an experimental heavy metal pollution study: Vertical mixing in a large limno-corral

In a limno-corral (diameter 12 m, depth to sediments 10 m), located in Baldeggersee (Switzerland), vertical mixing has been measured during more than one year and compared to the conditions in the open lake (maximum depth 65 m, surface area 5.3 km²). The temperature method by McEwen and Hutchinson yields K_z values between 5×10⁻² cm²s⁻¹ at the upper boundary of the thermocline and 2×10⁻³ cm²s⁻¹ at the bottom, a value near the molecular diffusion of heat at 4°C (1.36×10⁻³ cm²s⁻¹). K_z calculated from profiles of excess radon-222 generally agree with those from the temperature data. Compared to the open lake, the corral has a more shallow epilimnion. However, during calm meteorological conditions, vertical mixing in the upper 10 m is similar outside and inside the corral. Supported by the Swiss National Science Foundation within the framework for its National Research Program on ‘Lake Currents.’     

Volume,energy and cyclicity of eruptions of Arenal volcano,Costa Rica

The 1968–73 (and continuing) eruption of Arenal Volcano, Costa Rica, a small 1633 m strato-volcano with long periods of repose, defines an eruptive cycle which is typical of Arenal’s pre-historic eruptions. An intense, short explosive phase (July 29–31, 1968) grades into an effusive phase, and is followed by a block lava flow. The eruptive rocks become increasingly less differentiated with time in a given cycle, ranging from andesite to basaltic andesite. Nuées ardentes are a characteristic of the initial explosions, and are caused by fall-back ejecta on slopes around the main crater — an explosion crater in the 1968 eruption — which coalesce into hot avalanches and descend major drainage channels. Total volume of pyroclastic flows was small, about 1.8 ± 0.5 × 10ⁿ m³, in the July 29–31 explosions, and are block and ash flows, with much accidental material. Overpressures, ranging up to perhaps 5 kilobars just prior to major explosions, were estimated from velocities of large ejected blocks, which had velocities of up to 600 m/sec. Total kinetic energy and volume of ejecta of all explosions are an estimated 3 × 10²² ergs and 0.03 km³, respectively. The block lava flow, emitted from Sept., 1968 to 1973 (and continuing) has a volume greater than 0.06 km³, and covers 2.7 km² at thicknesses ranging from 15 to over 100 m. The total volumes of the explosive and effusive phases for the 1968–73 eruption are about 0.05 km³ and 0.06 km³, respectively. The last eruption of Arenal occurred about 1500 AD. based on radiocarbon dating and archaeological means, and was about twice as voluminous as the current one (0.17 km³ versus 0.09 km³). The total thermal energies for this pre-historic eruption and the current one are 8 × 10²³ and 18 × 10²³, respectively. The total volume of Arenal’s cone is about 6 km³ from 1633 m (summit) to 500 m, and, estimates of age based on the average rate of cone growth from these two eruptions, suggest an age between 20,000 to 200,000 years.     

The age of the Mistastin Lake crater,Labrador, Canada

⁴⁰Ar/³⁹Ar age determinations have been carried out on eight samples of melt rocks and one of the maskelynite from Mistastin Lake impact crater, Labrador. The observed⁴⁰Ar^* evolution spectra of the impact melts fall into distinct groups which correlate with petrographic variations. The release patterns of six of the melt rock samples define an age plateau in the range 34–41 m.y.; the other two have complex spectra which indicate incomplete equilibration of inclusions. Four of the samples with well-defined plateaux exhibit a high-temperature sag in their⁴⁰Ar/³⁹Ar ratio similar to that observed in some lunar samples. Maskelynite gives a partially overprinted spectrum which rises monotonically to a final age near 700 m.y., approximately half the age of the country rocks. The data from the melt samples are interpreted as indicating an age of 38 ± 4 m.y. for the Mistastin Lake impact event. Previously, it had been considered that this crater was 202 ± 25 m.y. old.     

Strontium and oxygen isotopic composition of some basalts from Hole 504B,Costa Rica Rift,DSDP Legs 69 and 70

Seventeen whole-rock samples, generally taken at 25–50 m intervals from 5 to 560 m sub-basement in Hole 504B, drilled in 6.2 m.y. old crust, were analysed for⁸⁷Sr/⁸⁶Sr ratios, Sr and Rb concentrations, and¹⁸O/¹⁶O ratios. Sr isotope ratios for 8 samples from the upper 260 m of the hole range from 0.70287 to 0.70377, with a mean of 0.70320. In the 330–560 m interval, 5 samples have a restricted range of 0.70255–0.70279, with a mean of 0.70266, the average value for fresh mid-ocean ridge basalts (MORB). In the 260–330 m interval, approximately intermediate Sr isotopic ratios are found.δ¹⁸O values (‰) range from 6.4 to 7.8 in the upper 260 m, 6.2–6.4 in the 270–320 m interval, and 5.8–6.2 in the 320–560 m interval. The values in the upper 260 m are typical for basalts which have undergone low-temperature seawater alteration, whereas the values for the 320–560 m interval correspond to MORB which have experienced essentially no oxygen isotopic alteration.The higher⁸⁷Sr/⁸⁶Sr and¹⁸O/¹⁶O ratios in the upper part of the hole can be interpreted as the result of a greater overall water/rock ratio in the upper part of the Hole 504B crust than in the lower part. Interaction of basalt with seawater(⁸⁷Sr/⁸⁶Sr=0.7091) increased basalt⁸⁷Sr/⁸⁶Sr ratios and produced smectitic alteration products which raised whole-rock δ¹⁸O values. Seawater circulation in the lower basalts may have been partly restricted by the greater number of relatively impermeable massive lava flows below about 230 m sub-basement. These flows may have helped to seal off lower basalts from through-flowing seawater.     

Tidal and residual currents in the Bransfield Strait,Antarctica

During the 1992–1993 oceanographic cruise of the Spanish R/V Hespérides, recording equipment was deployed in the Bransfield Strait. Six Aanderaa RCM7 current meters and three Aanderaa WLR7 tide gauges were successfully recovered after an operation period of 2.5 months. Relevant features of the time series obtained are presented and discussed in this paper. The emphasis is placed on the tidal character of the currents and the relative importance of tidal flow in the general hydrodynamics of the strait. For these purposes a dense grid of hydrographic stations, completed during the BIOANTAR 93 cruise, is used. Preliminary geostrophic calculations relative to a 400 m depth, yield current velocities of around 0.20 m s⁻¹ in the study area, whereas the magnitude of tidal currents is seen to be 0.30-0.40 m s⁻¹.     

Observations of contemporary arroyo cutting near Santa Fe,New Mexico,U.S.A.

Arroyo cutting that began in the American Southwest in the 1880s is associated with sudden runoff, a circumstance characteristic of this semiarid region in which occasional intense rainfall exceeds the capacity of the ground to absorb water. This report describes two arroyos in an area of moderately dissected bolson deposits southwest of Santa Fe, Cañada de la Cueva and Pueblo Cañon, where arroyo cutting since 1970 has been closely related to runoff from summer rain. The area is vegetated chiefly by grama grass and scattered juniper. Cutting is monitored by repeated surveys of channel floors, cross-sections, and headcuts, and by repeated photographs taken as stereopairs. Rainfall and discharge are measured simultaneously in 5-minute intervals by dual digital recorders at a gauging station on Cañada de la Cueva (drainage area 4.64 km²). Discharge has been as much as 18.2 m³/s from rainfall of 25.2 mm. The maximum 15-minute intensity for this storm was 64.0 mm/hr, and runoff was 7.9 mm. The flood peak arrived in 20 minutes, by which time 80 per cent of the rain had fallen, and the flow subsided to a tenth of its maximum in less than an hour. This storm at Pueblo Cañon (drainage area 13.3 km² above the place of measurement) resulted in an estimated discharge of 140 m³/s, and features produced by hail on the channel floor suggest that the duration of flow could have been as brief as 30 minutes. Observed increments of headward cutting at Cañada de la Cueva range from 0.28 m for 1.8 mm of runoff to 4.9 m for 12 mm of runoff. Aggregate cutting in 5 years has been as much as 13.7 m, resulting in erosion of 570 m³ of alluvium. Headward cutting near the mouth of Pueblo Cañon has been observed in increments of 10.3, 14.6, and 20.7 m, for an aggregate of 45.6 m, as measured from 1971 to 1974. This cutting removed 1,770 m³ of alluvium.     

Crystallization and welding variations in a widespread ignimbrite sheet; the Rattlesnake Tuff,eastern Oregon,USA

The 7.05 Ma Rattlesnake Tuff covers ca. 9000 km², but the reconstructed original coverage was between 30000 and 40000 km². Thicknesses are remarkably uniform, ranging between 15 and 30 m for the most complete sections. Only 13% of the area is covered with tuff thicker than 30 m, to a maximum of 70 m. The present day estimated tuff volume is 130 km³ and the reconstructed magma volume of the outflow is 280 km³ DRE (dense rock equivalent). The source area of the tuff is inferred to be in the western Harney Basin, near the center of the tuff distribution, based mainly on a radial exponential decrease in average pumice size, and is consistent with a general radial decrease in welding and degree of post-emplacement crystallization. Rheomorphic tuff is found to a radius of 40–60 km from the inferred source.Four facies of welding and four of post-emplacement crystallization are distinguishable. They are: non-welded, incipiently welded, partially welded and densely welded zones; and vapor phase, pervasively devitrified, spherulite and lithophysae zones. The vapor phase, pervasively devitrified and lithophysae zones are divided into macroscopically distinguishable subzones. At constant thickness (20±3 m), and over a distance of 1–3 km, nonrheomorphic sections can cary between two extremes: (a) entirely vitric sections grading from nonwelded to incipiently welded; and (b) highly zoned sections. Highly zoned sections have a basal non- to densely welded vitric tuff overlain by a spherulite zone that grades upward through a lithophysae-dominated zone to a zone of pervasive devitrification, which, in turn, is overlain by a zone of vapor-phase crystallization and is capped by partially welded vitric tuff. A three-dimensional welding and crystallization model has been developed based on integrating local and regional variations of 85 measured sections.Strong local variations are interpreted to be the result of threshold-governed welding and crystallization controlled by residence time above a critical temperature, which is achieved through differences in thickness and accumulation rate.     

U-Pb ages of uraniferous opals and implications for the history of beryllium,fluorine, and uranium mineralization at Spor Mountain,Utah

The U-Pb isotope systematics of uraniferous opals from Spor Mountain, Utah, were investigated to determine the suitability of such material for geochronologic purposes, and to estimate the timing of uranium and associated beryllium and fluorine mineralization. The results indicate that uraniferous opals can approximate a closed system for uranium and uranium daughters, so that dating samples as young as ～1 m.y. should be possible. In addition, the expected lack of initial²³⁰Th and²³¹Pa in opals permits valuable information on the initial²³⁴U/²³⁸U to be obtained on suitable samples of ?10 m.y. age. The oldest²⁰⁷Pb/²³⁵U apparent age observed, 20.8 ± 1m.y., was that of the opal-fluorite core of a nodule from a beryllium deposit in the Spor Mountain Formation. This age is indistinguishable from that of fission-track and K-Ar ages from the host rhyolite, and links the mineralization to the first episode of alkali rhyolite magmatism and related hydrothermal activity at Spor Mountain. Successively younger ages of 13 m.y. and 8–9 m.y. on concentric outer zones of the same nodule indicate that opal formed either episodically or continuously for over 10 m.y. Several samples of both fracture-filling and massive-nodule opal associated with beryllium deposits gave²⁰⁷Pb/²³⁵U apparent ages of 13–16 m.y., which may reflect a restricted period of mineralization or perhaps an averaging of 21?and<13?m.y. periods of opal growth. Several samples of fracture-filling opal in volcanic rocks as young as 6 m.y. gave²⁰⁷Pb/²³⁵U ages of 3.4–4.8 m.y. These ages may reflect hot-spring activity after the last major eruption of alkali rhyolite.