A late Mesozoic – early Cenozoic sedimentary recycling system on the Gondwana rifted margin of southeast Africa

Detrital zircons in late Cretaceous – Palaeogene, calcareous sandstone and conglomerate deposited in continental basins on the southeastern African margin after the breakup of Gondwana have characteristic combinations of age and epsilon-Hf that indicate an origin by recycling of Palaeoproterozoic (Waterberg, Soutpansberg and Pretoria groups) and Phanerozoic (Karoo Supergroup) cover successions. The latter is dominant in the south and east (Boane, Mahosi, Chilojo Cliffs), and the Palaeoproterozoic sources in the northwest (Pafuri, Wright’s Tower, Masisi). This recycling and mixing regime was restricted to late Mesozoic and Palaeogene time in northeastern South Africa and adjoining parts of Mozambique and Zimbabwe. Detrital zircon distribution patterns in these deposits reflect the denudation history of the southern African continental surface after breakup of the Gondwana supercontinent.

Tools to forecast climate change effects on lakes's water column

<p>Lakes and reservoirs are environments with many important uses in social activities, such as hydropower generation, water supply, landscape element, irrigation and flood containment. An ecosystem with so many environmental services needs to have its water quality well preserved, and besides that, inland waters have a key role in climate change studies, because of their faster response to variability in external forces.</p><p>Water circulation in a reservoir is the result of a combination of morphometry and energetic driving forces. A lake’s hydrodynamic characteristics vary with morphometric, meteorological and hydrological conditions. The heat balance involves exchanges at the surface, which are actively mixed and energised by the transfers occurring at the air-water interface, and also the exchanges in the water-soil interface near the banks and bottom, which depend on currents and internal waves; while in the main water column, the heat transfer is influenced by light penetration.</p><p>In the context of climate changes and water scarcity worldwide, the development of tools to better understand, maintain and improve water quality in lakes and reservoirs becomes an essential ally to environmental research and limnology. This research aims to demonstrate the lake mixing regime by a different approach, testing two different methods to forecast the climate change influence on a lakes’ mixing regime, using data from climate models.</p><p>The first tool is a thermal limit curve proposed by the authors which can forecast water column thermal limits for stability or mixing condition in a lake, based on wind speed, radiation and water profile temperature data. The second applied tool is a quasi-3D mathematical model, well known and reputed in the simulation field.</p><p>The results obtained for different experimental lakes in temperate and tropical zones showed that both methods have a good performance in representing lakes hydrodynamics accurately. The curve allows a faster response and minor need for data input, on the other hand, the quasi-3D models are capable to produce more detailed results. Possibly in the lakes’ management, it would be more indicated the use of those two methods together, using the curve to analyse faster the period's trend and be able to delimitate the exact period which needs more detailed studies.</p><p>The climate change simulations conducted for two experimental lakes considering different scenarios of climate changes showed the driving forces' strong influence on the lake's mixing regime. The number of mixing events is an interesting proxy to analyse this influence. It was greater in the pessimistic scenarios but still less than in the current situation. This means longer periods of stratification, which can cause dissolved oxygen depletion in the deeper layers.</p><p>The pessimistic scenarios have mixing events with greater amplitude, which results from a powerful stratification in previous periods. Mixing events with greater amplitudes create higher vertical velocities, resuspending more organic load and dropping dissolved oxygen levels along the water column, impairing the water quality.</p>

Experimental research of thermohydraulic dispatcher operating regimes

Heat carrier transportation in district heating (DH) systems is an issue of a significant energy saving potential. This potential can be achieved by applying a thermohydraulic dispatcher (THD) into DH systems. THD is a vertical or horizontal shunt pipe of a large diameter with relatively low hydraulic resistance in comparison with that of connected circuits. Installation of THD along with distributed variable speed pumps in DH systems can lead to reducing or even eliminating electric energy losses caused by throttling of redundant hydraulic head. It also leads to decreasing pressure in heat supply network which improves reliability of the network. But the opportunity of further rational implementation of THD in DH systems is limited because of insufficient amount of theoretical and experimental research. This paper is concerned with the experimental research of THD operating regimes. Already known aspects of THD operation were checked and proved. New dependencies were obtained for bypassing regime and for mixing regime of THD. Besides, different types of the primary circuit connection to THD were considered: connection for non-condensing boilers and connection for condensing boilers. Simplified models describing bypassing and mixing regimes of THD were proposed. It is possible to estimate return temperature of primary circuit with the help of the bypassing regime model with an error less than 1%. At the same time the mixing regime model is suitable for finding supply temperatures of primary circuits with an error less than 2%.The results of this paper can be used for further research and development of DH systems with THD. Such systems could be traditional as well as prospective ones (low temperature and pressure DH systems).

Effect of Mixing Regimes on Cow Manure Digestion in Impeller Mixed, Unmixed and Chinese Dome Digesters

This study examines the effect of mixing on the performance of anaerobic digestion of cow manure in Chinese dome digesters (CDDs) at ambient temperatures (27–32 °C) in comparison with impeller mixed digesters (STRs) and unmixed digesters (UMDs) at the laboratory scale. The CDD is a type of household digester used in rural and pre-urban areas of developing countries for cooking. They are mixed by hydraulic variation during gas production and gas use. Six digesters (two of each type) were operated at two different influent total solids (TS) concentration, at a hydraulic retention time (HRT) of 30 days for 319 days. The STRs were mixed at 55 rpm, 10 min/hour; the unmixed digesters were not mixed, and the Chinese dome digesters were mixed once a day releasing the stored biogas under pressure. The reactors exhibited different specific biogas production and treatment efficiencies at steady state conditions. The STR 1 exhibited the highest methane (CH4) production and treatment efficiency (volatile solid (VS) reduction), followed by STR 2. The CDDs performed better (10% more methane) than the UMDs, but less (approx. 8%) compared to STRs. The mixing regime via hydraulic variation in the CDD was limited despite a higher volumetric biogas rate and therefore requires optimization.

Future projections of temperature and mixing regime of European temperate lakes

The physical response of lakes to climate warming is regionally variable and highly dependent on individual lake characteristics, making generalizations about their development difficult. To qualify the role of individual lake characteristics in their response to regionally homogeneous warming, we simulated temperature, ice cover, and mixing in four intensively studied German lakes of varying morphology and mixing regime with a one-dimensional lake model. We forced the model with an ensemble of 12 climate projections (RCP4.5) up to 2100. The lakes were projected to warm at 0.10–0.11 ∘C decade−1, which is 75 %–90 % of the projected air temperature trend. In simulations, surface temperatures increased strongly in winter and spring, but little or not at all in summer and autumn. Mean bottom temperatures were projected to increase in all lakes, with steeper trends in winter and in shallower lakes. Modelled ice thaw and summer stratification advanced by 1.5–2.2 and 1.4–1.8 days decade−1 respectively, whereas autumn turnover and winter freeze timing was less sensitive. The projected summer mixed-layer depth was unaffected by warming but sensitive to changes in water transparency. By mid-century, the frequency of ice and stratification-free winters was projected to increase by about 20 %, making ice cover rare and shifting the two deeper dimictic lakes to a predominantly monomictic regime. The polymictic lake was unlikely to become dimictic by the end of the century. A sensitivity analysis predicted that decreasing transparency would dampen the effect of warming on mean temperature but amplify its effect on stratification. However, this interaction was only predicted to occur in clear lakes, and not in the study lakes at their historical transparency. Not only lake morphology, but also mixing regime determines how heat is stored and ultimately how lakes respond to climate warming. Seasonal differences in climate warming rates are thus important and require more attention.

Experimental observation of nonadiabatic bifurcation dynamics at resonances in the continuum

In the strong vibronic state mixing regime, both Herzberg type-I and type-II predissociations coexist and proceed in a competitive way.