Changed thinning regimes may increase carbon stock under climate change: A case study from a Finnish boreal forest

A physiological growth and yield model was applied for assessing the effects of forest management and climate change on the carbon (C) stocks in a forest management unit located in Finland. The aim was to outline an appropriate management strategy with regard to C stock in the ecosystem (C in trees and C in soil) and C in harvested timber. Simulations covered 100 years using three climate scenarios (current climate, ECHAM4 and HadCM2), five thinning regimes (based on current forest management recommendations for Finland) and one unthinned. Simulations were undertaken with ground true stand inventory data (1451 hectares) representing Scots pine (Pinus sylvestris), Norway spruce (Picea abies) and silver birch (Betula pendula) stands. Regardless of the climate scenario, it was found that shifting from current practices to thinning regimes that allowed higher stocking of trees resulted in an increase of up to 11% in C in the forest ecosystem. It also increased the C in the timber yield by up to 14%. Compared to current climatic conditions, the mean increase over the thinning regimes in the total C stock in the forest ecosystem due to the climate change was a maximum of 1%; but the mean increase in total C in timber yield over thinning regimes was a maximum of 12%.     

An integrated thermodynamic mixing model for sphalerite geobarometry from 300 to 850°C and up to 1 GPa

An asymmetric, Margules-type, solid solution model was used to model the mixing behavior of Fe-Zn sphalerites. The model is based on an analysis of experimental results from fifteen independent data sources. After a careful, stepwise, analysis of the available runs, the solid solution model was constrained using a refined experimental database of 279 experiments which were simultaneously regressed to obtain the excess parameters and a general geobarometric equation. The model indicates that, when pressures are low, the value of γ_FeS^Sph, which is always greater than one, is higher at low FeS contents and an increase in temperature causes it to decline. However, for certain compositions γ_FeS^Sph values might be slightly less at low T than at high T. This behavior is corrected when pressure increases, regardless of the composition. The excess Gibbs free energy has positive values at any P&T while it is asymmetric. Pressure increases the value of the excess free energy. On the other hand, the Gibbs free energy of mixing is always negative, with a single minimum that tends to move towards Fe-poorer compositions as the pressure goes up. An increase in temperature leads to a more negative Gibbs free energy mixing function suggesting that increasingly Fe-poorer sphalerite would be expected at high temperatures and pressures. The application of the solid solution model to a selection of case-studies provided results which are consistent with independent pressure estimates. However, the pressure determinations for sphalerite + pyrite + pyrrhotite and sphalerite + pyrrhotite assemblages are very sensitive to uncertainties in the composition of the phases involved and, to a lesser extent, to temperature. The results of the application of the model to a field case (scheelite-mineralized Hercynian veins from the Central Pyrenees) were also consistent when compared with independent pressure-constraining silicate assemblages. Thus, the solid solution model described in this paper provides a workable framework with which to compute the pressures of the formation of rocks over a wide range of geological conditions.     

Quantitative assessment of the residual risk in a rockfall protected area

Quantitative Risk Assessment (QRA) has become an indispensable tool for the management of landslide hazard and for planning risk mitigation measures. In this paper we present the evaluation of the rockfall risk at the Solà d’Andorra slope (Andorra Principality) before and after the implementation of risk mitigation works, in particular, the construction of protective fences. To calculate the risk level we have (i) identified the potential rockfall release areas, (ii) obtained the volume distribution of the falling rocks, (iii) determined the frequency of the rockfall events, and (iv) performed trajectographic analysis with a 3D numerical model (Eurobloc) that has provided both the expected travel distances and the kinetic energy of the blocks. The risk level at the developed area located at the foot of the rock cliff has been calculated taking into account the nature of the exposed elements and their vulnerability. In the Forat Negre basin, the most dangerous basin of the Solà d’Andorra, the construction of two lines of rockfall protection fences has reduced the annual probability of loss of life for the most exposed person inside the buildings, from 3.8×10⁻⁴ to 9.1×10⁻⁷ and the societal risk from 1.5×10⁻² of annual probability of loss of life to 1.2×10⁻⁵.     

The applicability and limitations of thermodynamic geochemical models to simulate trace element behaviour in natural waters. Lessons learned from natural analogue studies

Natural analogue investigations aim to understand key phenomena and processes in natural systems related to those expected to occur in radioactive waste repositories. One of the key applications of natural analogue studies has been the possibility to test the geochemical models to be used to describe the migration of radionuclides in a future radioactive waste repository system. To this end, several geochemical modelling testing exercises (commonly denoted as blind predictive modelling, BPM) have formed an integral part of these studies over the last decade.

We have reviewed, discussed and compared the results obtained from geochemical modelling BPM exercises carried out within six natural analogue studies: Poços de Caldas, Cigar Lake, Maqarin, El Berrocal, Oklo and Palmottu. To make this comparison meaningful, we present the main geochemical characteristics of each site in order to highlight the most relevant mineralogical and hydrochemical differences. The elements selected for discussion are: Sr, Ba, Sn, Pb, Se, Ni, Zn, REEs, Th and U. We have based our discussion on the results obtained from the calculated aqueous speciation as well as by comparing solubility calculations with the actually observed concentrations.

Results can be differentiated into two categories of elemental behaviour:

1. those elements like Th and U under reducing conditions that can be fairly well described by assuming solubility control exerted by pure solid phases as their oxyhydroxides;

2. elements such as Sr, Zn, REEs and U under oxidising conditions for which the association to major geochemical components of the system must be considered in order to explain their concentrations in groundwaters.

Additionally, we discuss the main improvements made to the thermodynamic databases and the geochemical calculation methodologies due to the BPM exercises. Furthermore, the most important characterisation geochemical data needed to complete predictive solubility and speciation calculations are identified.     

Flow characteristics of a gravity current induced by differential cooling in a small lake

Extensive field data of a density current driven by the differences in the cooling rates between the two lobes of a small lake are presented. These data illustrate the fact that this gravitational motion affects the whole system and dominates its lakewide circulation. Moreover, data are used to evaluate the entrainment into the density current and also to discuss the regime of the flow from a scaling analysis of the horizontal momentum equations. This analysis is specifically applied to the central area of the lake, where the density current flows from one lobe to the other. Results of this study show that in the longitudinal direction there is a balance between the pressure gradient and the turbulent viscous term. Further, it is found that geostrophy correctly describes the transversal pattern of the passage of the gravity current from the northern lobe to the southern, where it flows confined to the western shoreline.     

The ratio between chrysophycean cysts and diatoms in temperate,mountain lakes: some recommendations for its use in paleolimnology

The ratio between chrysophycean cysts and diatom valves (CD ratio) in lake sediments has been suggested as a useful indicator of changing trophic state conditions in oligotrophic lakes. Other environmental factors, however, may influence the CD ratio because chrysophycean cysts usually reflect conditions in the planktonic environment and diatoms reflect benthic conditions. We investigated the CD ratio in 76 mountain lakes in the Pyrenees to determine the environmental drivers that influence the ratio and assess its value for paleoenvironmental inference. The lakes surveyed included a broad range with respect to bedrock type, altitude and surface area, characteristics that cover much of the variability that can be found in cold, oligotrophic mountain lakes. Lake depth and Ca²⁺ concentration explain most of the variation in the CD ratio. Trophic state factors (e.g. total phosphorus, TP) play a secondary role. As a predictor, CD ratio performs primarily as a lake depth indicator. The predictive models can be improved if trophic state (i.e. TP) and chemical conditions (Ca²⁺) are known or can be estimated independently. Use of the CD ratio for inferring Ca²⁺ oscillations only makes sense in lakes with Ca²⁺ <200 µeq/L or in those that oscillate below and above this threshold through time. Other interpretations of the CD ratio (e.g. lake trophic state changes, ice-cover duration) make sense if complementary paleolimnological evidence indicates that neither water depth nor Ca²⁺ concentration changed significantly. Indeed, paleolimnological interpretation of the CD ratio requires considering the particular characteristics of the lake and may vary depending on the temporal scale considered. This study provides some guidelines for evaluating critically the use of the CD ratio.