The peat bog at Zinnwald-Georgenfeld revisited after 25 years: Geochemical investigation of water,Sphagnum moss and peat cores

From 1992 to 1994, trace metal concentrations of bog water, Sphagnum mosses and peat cores of the bog “Georgenfelder Hochmoor” at Zinnwald-Georgenfeld in the Eastern Ore Mountains (Germany) were investigated. A sampling campaign in September 2019 allows the comparison of the older measurements with today's trace metal concentrations. No changes were found in the bog waters, while the trace metal concentrations of the Sphagnum mosses have decreased significantly. Due to the low growth rate of the peat and despite certain heterogeneity between the peat cores, the investigated elemental data for the peat sampled in the 1990s and in 2019 are in the same concentration range. The maximum concentrations are measured in the upper samples of all peat cores for the analysed elements (except sulphur). Compared to upper crustal data, a different behaviour of the elements is observed: Cr, Sc, Ti, and V, rare earth elements show crustal ratios, while Al and Si are also influenced by crust-air fractionation. Cd, Cu, Ni, Pb, and Zn are additionally enriched by anthropogenic atmospheric inputs from industry and transport. These results confirm the assumption that peat cores record past atmospheric deposition.     

Origins of Xenolithic Eclogites and Pyroxenites from the Central Slave Craton, Canada

Major- and trace-element and Sr–Nd–Hf isotopic compositionsof garnet and clinopyroxene in kimberlite-borne eclogite andpyroxenite xenoliths were used to establish their origins andevolution in the subcontinental lithospheric mantle beneaththe central Slave Craton, Canada. The majority of eclogitescan be assigned to three groups (high-Mg, high-Ca or low-Mgeclogites) that have distinct trace-element patterns. Althoughpost-formation metasomatism involving high field strength element(HFSE) and light rare earth element (LREE) addition has partiallyobscured the primary compositional features of the high-Mg andhigh-Ca eclogites, trace-element features, such as unfractionatedmiddle REE (MREE) to heavy REE (HREE) patterns suggestive ofgarnet-free residues and low Zr/Sm consistent with plagioclaseaccumulation, could indicate a subduction origin from a broadlygabbroic protolith. In this scenario, the low REE and smallpositive Eu anomalies of the high-Mg eclogites suggest moreprimitive, plagioclase-rich protoliths, whereas the high-Caeclogites are proposed to have more evolved protoliths withhigher (normative) clinopyroxene/plagioclase ratios plus trappedmelt, consistent with their lower Mg-numbers, higher REE andabsence of Eu anomalies. In contrast, the subchondritic Zr/Hfand positive slope in the HREE of the low-Mg eclogites are similarto Archaean second-stage melts and point to a previously depletedsource for their precursors. Low ratios of fluid-mobile to lessfluid-mobile elements and of LREE to HREE are consistent withdehydration and partial melt loss for some eclogites. The trace-elementcharacteristics of the different eclogite types translate intolower _Nd for high-Mg eclogites than for low-Mg eclogites. Withinthe low-Mg group, samples that show evidence for metasomaticenrichment in LREE and HFSE have lower _Nd and _Hf than a samplethat was apparently not enriched, pointing to long-term evolutionat their respective parent–daughter ratios. Garnet andclinopyroxene in pyroxenites show different major-element relationshipsfrom those in eclogites, such as an opposite CaO–Na₂Otrend and the presence of a CaO–Cr₂O₃ trend, independentof whether or not opx is part of the assemblage. Therefore,these two rock types are probably not related by fractionationprocesses. The presence of opx in about half of the samplesprecludes direct crystallization from eclogite-derived melts.They probably formed from hybridized melts that reacted withthe peridotitic mantle. KEY WORDS: eclogites; pyroxenite xenoliths; mantle xenoliths; eclogite trace elements; eclogite Sr isotopes; eclogite Hf isotopes; eclogite Nd isotopes     

Immuno-localisations (GSSP) of subcellular accumulation sites of phenanthrene, aroclor 1254 and lead (Pb) in relation to cytopathologies in the gills and digestive gland of the mussel Mytilus edulis

Cell and tissue pathology of both, gill and digestive tissue, has been the subject of many studies for the elucidation of contaminant-induced biological effects. In the present study, cellular pathological alterations were linked to subcellular sites of chemical accumulation in gills and digestive gland tissues. For this purpose, mussels (Mytilus edulis) were exposed to the organic contaminants aroclor 1254 (PCB) (20 microg/L), phenanthrene (PAH) (150 microg/L) or the metal lead (Pb) (2.5mg/L). The localization of chemicals at the subcellular level was analysed by an antibody-based detection system (GSSP) by the use of commercially available antibodies specifically directed against the chemicals. Pathological changes were analysed in parallel in identical samples by transmission electron microscopy. After exposure to the different contaminants, cell organelles such as mitochondria, the endo-lysosomal system as well as endoplasmic reticulum showed clear evidence of chemically-induced alterations. Large numbers of crystalloid inclusions were found in mitochondria and in autophagic lysosomes as well as multi-lamellated whorls after PAH and aroclor exposure. Immunocytochemical detection of the chemicals showed their accumulation inside of various cell organelles such as lysosomes, mitochondria, and nuclei. Additionally, chemicals were localized in association to membranes, cilia and microvilli of gill and digestive gland cells. Furthermore, the chitinous rod and mucus secretions of gill epithelial cells were positively labelled for contaminants indicating their role in protection. Localization of contaminants by immuno-detection in combination with pathological diagnosis gives insights into the cellular targets of chemical attack.     

A spatial approach to baseline and leakage in CDM forest carbon sinks projects

Abstract

Forestry projects under the Clean Development Mechanism (CDM) face specific challenges with regard to determination of a baseline for carbon sequestration. We propose a semi-standardized approach called PARAPIA for calculation of a baseline that is built on the concept of a reference area around the project area whose land-use characteristics determine the baseline scenario. The land-use shares in the reference area are checked at each verification. Baseline carbon stocks are then derived ex post using the average carbon content of each land-use type. The reference area is between five and ten times larger than the project area. To determine indirect effects (the so-called ‘leakage’), a political influence area such as province or state is assessed with regards to migration flows due to the project and related emissions.     

Additionality revisited: guarding the integrity of market mechanisms under the Paris Agreement

ABSTRACT

The Paris Agreement requires mitigation contributions from all Parties. Therefore, the determination of additionality of activities under the market mechanisms of its Article 6 will need to be revisited. This paper provides recommendations on how to operationalize additionality under Article 6. We first review generic definitions of additionality and current approaches for testing of additionality before discussing under which conditions additionality testing of specific activities or policies is still necessary under the new context of the Paris Agreement, that is, in order to prevent increases of global emissions. We argue that the possibility of ‘hot air’ generation under nationally-determined contributions (NDCs) requires an independent check of the NDC’s ambition. If the NDC of the transferring country does contain ‘hot air’, or if the transferred emission reductions are not covered by the NDC, a dedicated additionality test should be required. While additionality tests of projects and programmes could continue to be done through investment analysis, for policy instruments new approaches are required. They should be differentiated according to type of policy instrument. For regulation, we suggest calculating the resulting pay-back period for technology users. If the regulation generates investments exceeding a payback period threshold, it could be deemed additional. Similarly, carbon pricing policies that generate a carbon price exceeding a threshold could qualify; for trading schemes an absence of over-allocation needs to be shown. The threshold should be differentiated according to country categories and rise over time.

Key policy insights

• Without additionality testing, market mechanisms under the Paris Agreements might lead to an international diffusion of ‘hot air’. To avoid this, an independent assessment of NDC ambition is in order. Otherwise, activities under the mechanisms need to undergo specific additionality tests.

• Additionality testing of projects and programmes should build on the experience developed under the Kyoto Protocol mechanisms.

• Bold approaches are needed for assessing additionality of policies. To avoid cumbersome assessment of all activities triggered by such policies, highly aggregated approaches are suggested, ranging from payback period thresholds for technologies mandated by regulation to minimum price levels triggered by carbon pricing policies. Over time, the stringency of threshold values should increase.

     

A sediment record of trophic state change in an Arkansas (USA) reservoir

Reservoir sediments are used cautiously in paleolimnological studies because of dating uncertainties, possible sediment disturbances and even concerns that indicators of trophic status may behave differently in reservoirs as opposed to natural lakes. We measured loss on ignition (LOI), carbon to nitrogen ratio (C:N), diatom abundance, total nitrogen (TN), total phosphorus (TP), TN:TP ratio, and carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) in an 83-cm sediment core to track recent trophic status changes in Beaver Reservoir, Northwest Arkansas, USA. Measurements showed that LOI, TN, TP and diatom abundance increased significantly from the bottom to the top of the core (p < 0.001). The C:N ratio and δ¹³C indicated a predominantly algal source for organic matter in the sediments. Increases in TN and TP were positively correlated with human population growth (p < 0.01) and the TN:TP ratio recorded a shift from phosphorus to nitrogen limitation around 1990. This shift may have encouraged cyanobacterial growth that caused episodes of taste and odor problems in the reservoir. This study suggests that despite concerns about sediment dating and disturbance, reservoir sediments can provide valuable information on past water quality changes.     

How hydrofractures become arrested

Fluids in the earth's crust are commonly transported by hydrofractures, such as dykes and mineral veins, many of which become arrested at various crustal depths. Hydrofractures are commonly arrested – some showing blunt tips – at contacts between soft (low Young's modulus) and stiff (high Young's modulus) layers. For example, many dyke tips are arrested at contacts between soft pyroclastic rocks and stiff basaltic lava flows, and vein tips at contacts between soft marl and stiff limestone. Theoretical models indicate that overpressured, buoyant hydrofractures in homogeneous, isotropic host rocks should normally reach the surface. In layered host rocks, however, abrupt changes in Young's moduli, horizontal discontinuities, and layers with unusually high fracture-perpendicular stresses encourage hydrofracture arrest. It is proposed that for layer-parallel loading, stiff layers favour hydrofracture arrest during active compression but soft layers during extension. It is concluded that for hydrofracture propagation to occur, the stress field along its potential pathway must be essentially homogenous.