Property impacts on Carbon Capture and Storage (CCS) processes: A review

Odjel za geografiju u osamnaest godina djelovanja razvio se u respektabilnu nastavno istraživacku jedinicu visokog skolstva i znanosti Republike Hrvatske. Postupnim jacanjem kadrovske strukture, s dvadesetak zaposlenih djelatnika i nekoliko vanjskih suradnika, surađuje s brojnim ustanovama u domovini i inozemstvu. Uz nastavnu djelatnost, kroz znanstveno-istraživacku i izdavacku djelatnost, uspjesno je ostvarena nova, jadranska jezgra visokoskolskog obrazovanja, znanstveno- istraživacke, izdavacke i međunarodne djelatnosti u geografiji u Republici Hrvatskoj. Daljnje usavrsavanje kadrova, postizanje maticnosti, unaprjeđenje nastavne, znanstveno-istraživacke, izdavacke i međunarodne aktivnosti važni su prioriteti u njezinu daljnjem razvoju, jednako kao i zadržavanje visoke kvalitete rada i postignuca na svim razinama. Ujedno, svojim rezultatima rada i napretkom, odgovornoscu prema potrebama nastave, studenata, istraživanja, izdavastva, administracije itd., Odjel za geografiju jedna je od najuspjesnijih i najaktivnijih sastavnica Sveucilista u Zadru.

Department of Geography

Unique worldwide, Lake Kivu stores enormous amounts of CH 4 and CO 2 . A recent study reported that CH 4 concentrations in the lake have increased by up to 15% in the last 30 years and that accumulation at this rate could lead to catastrophic outgassing by ∼2100. This study investigates the present-day CH 4 formation and oxidation in Lake Kivu. Analyses of 14C and 13C in CH 4 and potential carbon sources revealed that below 260 m, an unusually high ∼65% of the CH 4 originates either from reduction of geogenic CO 2 with mostly geogenic H 2 or from direct inflows of geogenic CH 4 . Aerobic CH 4 oxidation, performed by close relatives of type X CH 4 -oxidizing bacteria, is the main process preventing CH 4 from escaping to the atmosphere. Anaerobic CH 4 oxidation, carried out by CH 4 -oxidizing archaea in the SO 4 2--reducing zone, was also detected but is limited by the availability of sulfate. Changes in 14C CH4 and 13C CH4 since the 1970s suggest that the amount of CH 4 produced from degrading organic material has increased due to higher accumulation of organic matter. This, as well as the sudden onset of carbonates in the 1960s, has previously been explained by three environmental changes: (1) introduction of nonnative fish, (2) amplified subaquatic inflows following hydrological changes, and (3) increased external inputs due to the fast growing population. The resulting enhancement of primary production and organic matter sedimentation likely caused CH 4 to increase. However, given the large proportion of old CH 4 carbon, we cannot exclude an increased inflow of geogenic H 2 or CH 4 . Copyright 2011 by the American Geophysical Union.

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Methane sources and sinks in Lake Kivu

The African great lakes are of utmost importance for the local economy (fishing), as well as being essential to the survival of the local people. During the past decades, these lakes experienced fast changes in ecosystem structure and functioning, and their future evolution is a major concern. In this study, for the first time a set of one-dimensional lake models are evaluated for Lake Kivu (2.28°S; 28.98°E), East Africa. The unique limnology of this meromictic lake, with the importance of salinity and subsurface springs in a tropical high-altitude climate, presents a worthy challenge to the seven models involved in the Lake Model Intercomparison Project (LakeMIP). Meteorological observations from two automatic weather stations are used to drive the models, whereas a unique dataset, containing over 150 temperature profiles recorded since 2002, is used to assess the model’s performance. Simulations are performed over the freshwater layer only (60 m) and over the average lake depth (240 m), since salinity increases with depth below 60 m in Lake Kivu and some lake models do not account for the influence of salinity upon lake stratification. All models are able to reproduce the mixing seasonality in Lake Kivu, as well as the magnitude and seasonal cycle of the lake enthalpy change. Differences between the models can be ascribed to variations in the treatment of the radiative forcing and the computation of the turbulent heat fluxes. Fluctuations in wind velocity and solar radiation explain inter-annual variability of observed water column temperatures. The good agreement between the deep simulations and the observed meromictic stratification also shows that a subset of models is able to account for the salinity- and geothermal-induced effects upon deep-water stratification. Finally, based on the strengths and weaknesses discerned in this study, an informed choice of a one-dimensional lake model for a given research purpose becomes possible. Keywords: lake modelling, model intercomparison, surface–atmosphere interactions, tropical lakes, Lake Kivu (Published: 5 February 2014) Citation: Tellus A 2014, 66 , 21390, http://dx.doi.org/10.3402/tellusa.v66.21390 This publication is part of a Thematic Cluster entitled "Parameterization of lakes in numerical weather prediction and climate models". Read the other papers from this thematic cluster here

https://biblio.vub.ac.be/vubirfiles/31314598/Thiery_etal_TA_2014.pdf

LakeMIP Kivu: Evaluating the representation of a large, deep tropical lake by a set of one-dimensional lake models

[1] On 17 January 2002, Nyiragongo volcano erupted along a 20 km-long fracture network extending from the volcano to the city of Goma. The event was captured by InSAR data from the ERS-2 and RADARSAT-1 satellites. A combination of 3D numerical modeling and inversions is used to analyze these displacements. Using Akaike Information Criteria, we determine that a model with two subvertical dikes is the most likely explanation for the 2002 InSAR deformation signal. A first, shallow dike, 2 km high, is associated with the eruptive fissure, and a second, deeper dike, 6 km high and 40 km long, lies about 3 km below the city of Goma. As the deep dike extends laterally for 20 km beneath the gas-rich Lake Kivu, the interaction of magma and dissolved gas should be considered as a significant hazard for future eruptions. A likely scenario for the eruption is that the magma supply to a deep reservoir started ten months before the eruption, as indicated by LP events and tremor. Stress analysis indicates that the deep dike could have triggered the injection of magma from the lake and shallow reservoir into the eruptive dike. The deep dike induced the opening of the southern part of this shallow dike, to which it transmitted magma though a narrow dike. This model is consistent with the geochemical analysis, the lava rheology and the pre- and post-eruptive seismicity. We infer low overpressures (1–10 MPa) for the dikes. These values are consistent with lithostatic crustal stresses close to the dikes and low magma pressure. As a consequence, the dike direction is probably not controlled by stresses but rather by a reduced tensile strength, inherited from previous rift intrusions. The lithostatic stresses indicate that magmatic activity is intense enough to relax tensional stresses associated with the rift extension.

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Magma sources involved in the 2002 Nyiragongo eruption, as inferred from an InSAR analysis

Double-diffusive staircases with a total of 230-350 mixed layers and sharp interfaces were observed in nine microstructure temperature profiles measured during February 2004 in Lake Kivu. The presence of these staircases at depths. 120 m indicates that diapycnal turbulent mixing is weak and vertical diffusive transport is dominated by double diffusion. Contrary to previously investigated natural or laboratory double-diffusive systems, the dissolved gases CO(2) and CH(4) contribute significantly to the density stratification, thereby influencing the formation and the structure of the staircases. The density ratio (i.e., the ratio of the stabilizing effect of dissolved substances to the destabilizing effect of temperature) ranges between 2.0 and 4.5 in large sections of the deep waters, implying a high susceptibility to the formation of staircases. The mixed layers (average thickness 0.48 m) are shown to be in a state of active convection. The average thickness of the interfaces (0.18 m) is surprisingly constant and independent of the large-scale stratification. The vertical heat fluxes correlate well with the temperature steps across the interfaces. Lake Kivu receives inflows from subaquatic springs at several depths that maintain the large-scale structure of the density stratification and disturb the staircases. In comparison to earlier observations from 1972, the double-diffusive heat fluxes appear to have been reduced, leading to a heat accumulation in the deep waters. Conversely, the strengthening of the main chemocline indicates an increased discharge of the subaquatic springs that could be responsible for recent changes in the nutrient cycling and methane production in the lake.

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Double-diffusive convection in Lake Kivu.

Lake Kivu is one of the large African Rift lakes situated between the Democratic Republic of the Congo and Rwanda. In its permanently stratified hypolimnion, unusually high methane concentrations have increased further in recent decades. Because methanogenesis is, in part, dependent on supply of organic material from the photic zone, it is necessary to quantify upward nutrient fluxes from the saline, nutrient-rich deep waters. These upward fluxes are mainly driven by advection caused by subaquatic springs. Biogenic calcite precipitation drives surface-water depletion and deep-water enrichment of Ca2+ ,S r 2+, and Ba2+. Methane is mainly oxidized aerobically at the redox interface at 60 m, with a small contribution of anaerobic methane oxidation. A subaquatic spring that sustains the major chemocline at 250 m depth was depleted of N, P, and CH4, and concentrations of major ions were slightly lower than in the lake water of the same depth. Enrichment of the deep waters with nutrients and CH4 are driven by mineralization of settling organic material, whereas SiO2 is influenced by uptake and mineralization of diatoms and inputs through subaquatic springs. Dissolved inorganic phosphorus and Si fluxes supplied by internal loading through upwelling were found to be lower than the estimations for Lakes Malawi and Tanganyika. In contrast, N flux was within the lower range for Lake Malawi, whereas it was assumed to be totally lost by denitrification in Lake Tanganyika. In Lake Kivu, nutrient uptake by primary production is three times higher than nutrient upward fluxes.

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Alfred Wu #x Fc est

Papers

Double-diffusive convection in Lake Kivu.

Physical and biogeochemical limits to internal nutrient loading of meromictic Lake Kivu