Peter Escher

Early diagenesis of sulfur in a tropical upwelling system, Cabo Frio, southeastern Brazil

The early diagenesis of sulfur was assessed in four short sediment cores on the continental shelf off southeastern Brazil that were deposited under the influence of an upwelling tropical system. This tropical upwelling area allows a direct focus on the coupled roles of hydrodynamic- and bioturbation-driven influences on sulfate reduction, sulfide re-oxidation and corresponding stable sulfur isotope signal formation. Under the depositional conditions of Cabo Frio, the degree of reactive iron pyritization was limited by both dissolved sulfide availability and pyrite oxidation events. Textural analyses of pyrite framboids provide evidence of re-oxidation processes, reflecting dynamic redox conditions in the sediments. The isotope composition of pore-water sulfate remained close to the modern seawater value, but very light stable sulfur isotope ratios ( 34 S/ 32 S) of chromium reducible sulfur (essentially pyrite) are found that reflect intense bioturbation-induced sulfur re-cycling. The sulfur isotope signatures developing in these tropical upwelling sites are similar to those of modern euxinic systems, although they are caused by a superimposition of sulfate reduction and an intense oxidative sulfur cycle.

Concrete under sulphate attack: an isotope study on sulphur sources.

The formation of secondary sulphate minerals such as thaumasite, ettringite and gypsum is a process causing severe damage to concrete constructions. A major key to understand the complex reactions, involving concrete deterioration is to decipher the cause of its appearance, including the sources of the involved elements. In the present study, sulphate attack on the concrete of two Austrian tunnels is investigated. The distribution of stable sulphur isotopes is successfully applied to decipher the source(s) of sulphur in the deteriorating sulphate-bearing minerals. Interestingly, δ34S values of sulphate in local groundwater and in the deteriorating minerals are mostly in the range from+14 to+27 ‰. These δ34S values match the isotope patterns of regional Permian and Triassic marine evaporites. Soot relicts from steam- and diesel-driven trains found in one of the tunnels show δ34S values from−3 to+5 ‰, and are therefore assumed to be of minor importance for sulphate attack on the concretes. In areas of pyrite-containing sedimentary rocks, the δ34S values of sulphate from damaged concrete range between−1 and+11 ‰. The latter range reflects the impact of sulphide oxidation on local groundwater sulphate.

Variability of photosynthetic capacity and water relations of Pinus sylvestris L. in the field

Measurements of dependence of photosynthetic electron transport on irradiance and analyses of stable isotope ratios (δ18O, δ13C, δ15N) were performed on 4 to 6-year-old pine trees (Pinus sylvestris L.) in the primeval forest reserve of Białowieża and on 21-year-old pine trees of a plantation of different provenances at the Sękocin Forest Station near Warsaw, Poland. Small differences in maximum photosynthetic electron transport rates, ETRmax were related to growth. Stable isotope analyses suggest that water relations play an important role for the performance of P. sylvestris at the sites studied. The intraspecific comparisons showed a very high variability of photosynthetic capacity between needles of given trees and between individual trees under similar conditions. Differences between specific provenances were also observed. This is relevant for ecological niche occupation in a wide geographical growth range, where P. sylvestris is actually occurring. The high physiological plasticity demonstrated reveals a conspicuous trait of this tree species.

Does plant diversity affect the water balance of established grassland systems

Evidence from experimental grasslands indicated that plant biodiversity modifies the water cycle but it is unclear if this is also true for established land-use systems. Therefore, we investigated how evapotranspiration (ETa), downward flux (DF), and upward flux (UF) in soil are related with land use and plant diversity in agriculturally managed grassland. In three Central European regions (“Biodiversity Exploratories”), we studied 29 grassland plots (50m x 50m; 9-11 plots per region) covering the land-use classes pasture, mown pasture, and meadow in at least triplicate per region. From 2010 to 2015, we measured soil moisture, meteorological conditions, plant species richness, cover and number of species in the functional groups of grasses, herbs, and legumes, aboveground biomass and root biomass on each plot. Annual ETa, DF, and UF were calculated for two soil layers with a soil water balance model and statistically analyzed for land-use and biodiversity effects with analysis of variance. Water fluxes were not significantly affected by land-use class. UF did not vary between plots with different species richness and plant functional group composition. DF from topsoil increased with increasing number of grass species. ETa from topsoil decreased with increasing species richness and with the number of herb or legume species, while ETa from subsoil increased. Our results demonstrate that plant diversity influences the soil depth partitioning of water use, but the complex drivers of this relationship in agriculturally managed grassland still need to be disentangled.