### Recent Submissions

• Journal Article

#### Water–rock interactions in the Bruchsal geothermal system by U–Th series radionuclides ﻿

Geothermal Energy. 2020 Sep 08;8(1):24
Uranium and thorium decay series disequilibria in deep geothermal brines are a result of water–rock interaction processes. The migratory behavior of radionuclides provides valuable site-specific information and can therefore be an important tool for reservoir characterization and sustainable management of geothermal sites. In this study, we present data from long-term monitoring of naturally occurring 238U, 232Th and 235U series radionuclides analyzed in brine samples collected from the Permo-Triassic sedimentary reservoir rock at the Bruchsal geothermal site (SW Germany). The results show that radionuclides of the elements radium (226Ra, 228Ra, 224Ra, 223Ra), radon (222Rn), and lead (210Pb, 212Pb) are rather soluble in brine, while isotopes of uranium (238U, 234U, 235U), thorium (232Th, 228Th, 230Th), polonium (210Po), and actinium (227Ac, 228Ac) have low solubilities and are mostly immobile. Activities of radium isotopes in the geothermal brine exceed those of their thorium progenitors (average 226Ra = 29.9 Bq kg−1, about 103 times that of its 230Th parent). Modelling the observed disequilibria allows the following conclusion on water–rock interaction processes: (1) supply from alpha-recoil depends on isotope half-life because it is limited by the rate of diffusion through microfractures causing isotopic fractionation. (2) Radium retardation due to adsorption is low (226Ra/222Rn = 1.3) resulting in adsorption–desorption rate constants in the order of 10−10 s−1 for k1 and 10−9 for k2. (3) Scavenging of 226Ra from brine can best be explained by co-precipitation with barite resulting in an observed 226Ra anomaly in the solids of the reservoir section. The precipitation rate constant amounts to ca. 3.4 × 10−8 s−1 corresponding to a mean removal time of radium from brine by mineral precipitation to approximately 1 year.
• Journal Article

#### Estimating the Aboveground Biomass of an Evergreen Broadleaf Forest in Xuan Lien Nature Reserve, Thanh Hoa, Vietnam, Using SPOT-6 Data and the Random Forest Algorithm ﻿

International Journal of Forestry Research 2020; 2020 p.1-13: Art. 4216160
Forest biomass is an important ecological indicator for the sustainable management of forests. The aim of this study was to estimate forest aboveground biomass (AGB) by integrating SPOT-6 data with field-based measurements using the random forest (RF) algorithm. In total, 52 remote sensing variables, including spectral bands, vegetation indices, topography data, and textures, were extracted from SPOT-6 images to predict the forest AGB of Xuan Lien Nature Reserve, Vietnam. To determine the optimal predictor variables for AGB estimation, 10 different RF models were built. To evaluate these models, 10-fold cross-validation was applied. We found that a combination of spectral and vegetation indices and topography variables offer the highest prediction results ( R$^2_{\textit{adj}}$ = 0.74 and RMSE = 61.24 Mg ha$^{−1}$). Adding texture features into the predictor variables did not improve the model performance. In addition, the SPOT-6 sensor has the potential to predict forest AGB using the RF algorithm.
• Journal Article

#### Revealing the diversity of amber source plants from the Early Cretaceous Crato Formation, Brazil ﻿

BMC Evolutionary Biology. 2020 Aug 20;20(1):107
Abstract Background Amber has been reported from the Early Cretaceous Crato Formation, as isolated clasts or within plant tissues. Undescribed cones of uncertain gymnosperm affinity have also been recovered with amber preserved in situ. Here, we provide multiple lines of evidence to determine the botanical affinity of this enigmatic, conspicuous cone type, and to better understand the diversity of amber-source plants present in the Crato Formation and beyond. Results A new taxon of amber-bearing pollen cone Araripestrobus resinosus gen. nov. et sp. nov. is described here from complete cones and characteristic disarticulated portions. The best-preserved cone portion has both in situ amber infilling the resin canals inside the preserved microsporophyll tissues and pollen of the Eucommiidites-type. This places this genus within the Erdtmanithecales, an incompletely known gymnosperm group from the Mesozoic. FTIR analysis of the in situ amber indicates a potential araucariacean conifer affinity, although affinity with cupressacean conifers cannot be definitely ruled out. Pyr-GC-MS analysis of the Araripestrobus resinosus gen. nov. et sp. nov. in situ fossil resin shows that it is a mature class Ib amber, thought to indicate affinities with araucariacean and cupressacean, but not pinaceous, conifers. This is the first confirmed occurrence of this class of amber in the Crato Formation flora and in South America, except for an archaeological sample from Laguna Guatavita, Colombia. Conclusions The combined results of the cones’ novel gross morphology and the analyses of the in situ amber and pollen clearly indicate that the new taxon of resinous gymnosperm pollen cones from the Crato Formation is affiliated with Erdtmanithecales. The cone morphology is very distinct from all known pollen cone types of this extinct plant group. We therefore assume that the plant group that produced Eucommiidites-type pollen is much more diverse in habits than previously thought. Moreover, the diversity of potential amber source plants from the Crato Formation is now expanded beyond the Araucariaceae and the Cheirolepidiaceae to include this member of the Erdtmanithecales. Despite dispersed Eucommiidites pollen being noted from the Crato Formation, this is the first time macrofossils of Erdtmanithecales have been recognized from the Early Cretaceous of South America.
• Journal Article

#### Structure of Nanocrystalline, Partially Disordered MoS$_{2+δ}$ Derived from HRTEM—An Abundant Material for Efficient HER Catalysis ﻿

Catalysts 2020; 10(8) p.1-16: Art. 856
Molybdenum sulfides (MoS$_x$, x > 2) are promising catalysts for the hydrogen evolution reaction (HER) that show high hydrogen evolution rates and potentially represent an abundant alternative to platinum. However, a complete understanding of the structure of the most active variants is still lacking. Nanocrystalline MoS$_{2+δ}$ was prepared by a solvothermal method and immobilized on graphene. The obtained electrodes exhibit stable HER current densities of 3 mA cm$^{−2}$ at an overpotential of ~200 mV for at least 7 h. A structural analysis of the material by high-resolution transmission electron microscopy (HRTEM) show partially disordered nanocrystals of a size between 5–10 nm. Both X-ray and electron diffraction reveal large fluctuations in lattice spacing, where the average c-axis stacking is increased and the in-plane lattice parameter is locally reduced in comparison to the layered structure of crystalline MoS$_2$. A three-dimensional structural model of MoS$_{2+δ}$ could be derived from the experiments, in which [Mo$_2$S$_{12}$]$^{2−}$ and [Mo$_3$S$_{13}$]$^{2−}$ clusters as well as disclinations represent the typical defects in the ideal MoS$_2$ structure. It is suggested that the partially disordered nanostructure leads to a high density of coordinatively modified Mo sites with lower Mo–Mo distances representing the active sites for HER catalysis, and, that these structural features are more important than the S:Mo ratio for the activity.
• Journal Article

#### Tracing the Scientific History of Fe$^0$-Based Environmental Remediation Prior to the Advent of Permeable Reactive Barriers ﻿

Processes 2020; 8(8) p.1-14: Art. 977
The technology of using metallic iron (Fe$^0$) for in situ generation of iron oxides for water treatment is a very old one. The Fe$^0$ remediation technology has been re-discovered in the framework of groundwater remediation using permeable reactive barriers (PRBs). Despite its simplicity, the improvement of Fe$^0$ PRBs is fraught with difficulties regarding their operating modes. The literature dealing with Fe$^0$ remediation contains ambiguities regarding its invention and its development. The present paper examines the sequence of contributions prior to the advent of Fe$^0$ PRBs in order to clarify the seemingly complex picture. To achieve this, the current paper addresses the following questions: (i) What were the motivations of various authors in developing their respective innovations over the years?, (ii) what are the ancient achievements which can accelerate progress in knowledge for the development of Fe$^0$ PRBs?, and (iii) was Fe$^0$ really used for the removal of organic species for the first time in the 1970s? A careful examination of ancient works reveals that: (i) The wrong questions were asked during the past three decades, as Fe$^0$ was premised as a reducing agent, (ii) credit for using Fe$^0$ for water treatment belongs to no individual scientist, and (iii) credit for the use of Fe$^0$ in filtration systems for safe drinking water provision belongs to scientists from the 1850s, while credit for the use of Fe$^0$ for the removal of aqueous organic species does not belong to the pioneers of the Fe$^0$ PRB technology. However, it was these pioneers who exploited Fe$^0$ for groundwater remediation, thereby extending its potential. Complementing recent achievements with the chemistry of the Fe$^0$/H$_2$O system would facilitate the design of more sustainable Fe$^0$-remediation systems.
• Journal Article

#### Benefits and Constraints of the Agricultural Land Acquisition for Urbanization for Household Gender Equality in Affected Rural Communes: A Case Study in Huong Thuy Town, Thua Thien Hue Province, Vietnam ﻿

Land 2020; 9(8) p.1-19: Art. 249
The Vietnamese Government has implemented agricultural land acquisition for urbanization (ALAFU) since 2010 which has caused a high level of social-economic transition in the country. In this paper, we applied the gender and development approach to discover how ALAFU has influenced the household gender equality in affected areas in Thua Thien Hue province, Vietnam. The data for this paper was mainly collected from two household group surveys, four group discussions, and six key informant interviews. Group 1 covers 50 affected households whose agricultural land was acquired for urbanization, while Group 2 consists of 50 households whose agricultural land was not taken away. The findings reveal that ALAFU has led to reduced access to agricultural land for group 1, but has contributed to an increase of economic status for women in both groups by creating non-farming job opportunities with a good income. However, most of their new jobs are still informal, contain potential risks, and the unpaid care work burden is heavy. Moreover, although the rate of women participating in household decision making has increased, the quality of participation is limited. Their participation in social activities and vocational training courses has improved insignificantly. Therefore, if the Government continues to promote ALAFU, they should take structural gender inequalities into account to achieve their sustainable development goals.
• Journal Article

#### Designing the Next Generation of Fe$^0$-Based Filters for Decentralized Safe Drinking Water Treatment: A Conceptual Framework ﻿

Processes 2020; 8(6) p.1-16: Art. 745
The ambitious United Nations Sustainable Development Goal for 2030 to “leave no one behind” concerning safe drinking water calls for the development of universally applicable and affordable decentralized treatment systems to provide safe drinking water. Published results suggest that well-designed biological sand filters (BSFs) amended with metallic iron (Fe$^0$-BSFs) have the potential to achieve this goal. Fe$^0$-BSFs quantitatively remove pathogens and a myriad of chemical pollutants. The available data were achieved under various operating conditions. A comparison of independent research results is almost impossible, especially because the used Fe$^0$ materials are not characterized for their intrinsic reactivity. This communication summarizes the state-of-the-art knowledge on designing Fe$^0$-BSFs for households and small communities. The results show that significant research progress has been made on Fe$^0$-BSFs. However, well-designed laboratory and field experiments are required to improve the available knowledge in order to develop the next generation of adaptable and scalable designs of Fe$^0$-BSFs in only two years. Tools to alleviate the permeability loss, the preferential flow, and the use of exhausted filters are presented.
• Journal Article

#### Quantifying forest cover at Mount Kenya: Use of Sentinel-2 for a discrimination of tropical tree composites ﻿

African Journal of Environmental Science and Technology 2020; 14(6) p.159-176
The aim of the present study is totest ESA’s Sentinel-2 (S2) satellites (S2A and S2B) for an efficient quantification of land cover (LC) and forest compositions in a tropical environment southwest of Mount Kenya. Furthermore, outcome of the research is used to validate ESA’s S2 prototype LC 20m map of Africa that was produced in 2016. A decision tree that is based on significant altitudinal ranges was used to discriminatefour natural tree compositions that occur within the investigation area. In addition, the classification process was supported by Google Earthimages, and land use (LU) data that wereprovided by the local Kenyan Forest Service(KFS). Final classification products include four LC classes and five subclasses of forest (four natural forestsubclasses plus one non-natural forest class). Results of theJeffries-Matusita (JM) distance test show significant differences in spectral separability between all classes. Furthermore, the study identifies spectral signatures and significant wavelengths for a classification of all LC classes and forest subclasseswherewavelengths of SWIR and the red-edge domain show highestimportancefor the discrimination of tree compositions.Finally, considerable differences can be seen between the utilized multi-temporal classification set (total of 39 bands fromthree acquisition dates) and ESA’s S2 prototype LC 20m map of Africa 2016. A visual comparison of ESA’s prototypemapwithin the investigation area indicates an overrepresentation of tree cover areas (as confirmed in previous studies) andalso an underrepresentation of water.
• Journal Article

#### Authigenic formation of Ca-Mg carbonates in the shallow alkaline Lake Neusiedl, Austria ﻿

Biogeosciences 2020; 17(7) p.2085-2106
Despite advances regarding the microbial and organic-molecular impact on nucleation, the formation of dolomite in sedimentary environments is still incompletely understood. Since 1960, apparent dolomite formation has been reported from mud sediments of the shallow, oligohaline and alkaline Lake Neusiedl, Austria. To trace potential dolomite formation or diagenetic alteration processes in its deposits, lake water samples and sediment cores were analyzed with respect to sediment composition, hydrochemistry and bacterial community composition. Sediments comprise 20 cm of homogenous mud with 60 wt % carbonate, which overlies dark-laminated consolidated mud containing 50 wt % carbonate and plant debris. Hydrochemical measurements reveal a shift from oxic lake water with pH 9.0 to anoxic sediment pore water with pH 7.5. A decrease in SO$_2^{−4}$ with a concomitant increase in ΣH$_2$S and NH$^+_4$ from 0 to 15 cm core depth indicates anaerobic heterotrophic decomposition, including sulfate reduction. The bacterial community composition reflects the zonation indicated by the pore water chemistry, with a distinct increase in fermentative taxa below 15 cm core depth. The water column is highly supersaturated with respect to (disordered) dolomite and calcite, whereas saturation indices of both minerals rapidly approach zero in the sediment. Notably, the relative proportions of different authigenic carbonate phases and their stoichiometric compositions remain constant with increasing core depth. Hence, evidence for Ca–Mg carbonate formation or ripening to dolomite is lacking within the sediment of Lake Neusiedl. As a consequence, precipitation of high-magnesium calcite (HMC) and protodolomite does not occur in association with anoxic sediment and sulfate-reducing conditions. Instead, analytical data for Lake Neusiedl suggest that authigenic HMC and protodolomite precipitate from the supersaturated, well-mixed aerobic water column. This observation supports an alternative concept to dolomite formation in anoxic sediments, comprising Ca–Mg carbonate precipitation in the water column under aerobic and alkaline conditions.
• Journal Article

#### Characterizing the Reactivity of Metallic Iron for Water Treatment: H$_2$ Evolution in H$_2$SO$_4$ and Uranium Removal Efficiency ﻿

Water 2020; 12(6) p.1-18: Art. 1523
Metallic iron (Fe$^0$) has been demonstrated as an excellent material for decentralized safe drinking water provision, wastewater treatment and environmental remediation. An open issue for all these applications is the rational material selection or quality assurance. Several methods for assessing Fe$^0$ quality have been presented, but all of them are limited to characterizing its initial reactivity. The present study investigates H$_2$ evolution in an acidic solution (pH 2.0) as an alternative method, while comparing achieved results to those of uranium removal in quiescent batch experiments at neutral pH values. The unique feature of the H$_2$ evolution experiment is that quantitative H$_2$ production ceased when the pH reached a value of 3.1. A total of twelve Fe$^0$ specimens were tested. The volume of molecular H$_2$ produced by 2.0 g of each Fe$^0$ specimen in 560 mL H$_2$SO$_4$ (0.01 M) was monitored for 24 h. Additionally, the extent of U(VI) (0.084 mM) removal from an aqueous solution (20.0 mL) by 0.1 g of Fe$^0$ was characterized. All U removal experiments were performed at room temperature (22 ± 2 °C) for 14 days. Results demonstrated the difficulty of comparing Fe$^0$ specimens from different sources and confirmed that the elemental composition of Fe$^0$ is not a stand-alone determining factor for reactivity. The time-dependent changes of H$_2$ evolution in H$_2$SO$_4$ confirmed that tests in the neutral pH range just address the initial reactivity of Fe$^0$ materials. In particular, materials initially reacting very fast would experience a decrease in reactivity in the long-term, and this aspect must be incorporated in designing novel materials and sustainable remediation systems. An idea is proposed that could enable the manufacturing of intrinsically long-term efficient Fe$^0$ materials for targeted operations as a function of the geochemistry.
• Journal Article

#### Application of Wavelet De-Noising for Travel-Time Based Hydraulic Tomography ﻿

Water 2020; 12(6) p.1-23: Art. 1533
Travel-time based hydraulic tomography is a promising method to characterize heterogeneity of porous-fractured aquifers. However, there is inevitable noise in field-scale experimental data and many hydraulic signal travel times, which are derived from the pumping test’s first groundwater level derivative drawdown curves and are strongly influenced by noise. The required data processing is thus quite time consuming and often not accurate enough. Therefore, an effective and accurate de-noising method is required for travel time inversion data processing. In this study, a series of hydraulic tomography experiments were conducted at a porous-fractured aquifer test site in Goettingen, Germany. A numerical model was built according to the site’s field conditions and tested based on diagnostic curve analyses of the field experimental data. Gaussian white noise was then added to the model’s calculated pumping test drawdown data to simulate the real noise in the field. Afterward, different de-noising methods were applied to remove it. This study has proven the superiority of the wavelet de-noising approach compared with several other filters. A wavelet de-noising method with calibrated mother wavelet type, de-noising level, and wavelet level was then determined to obtain the most accurate travel time values. Finally, using this most suitable de-noising method, the experimental hydraulic tomography travel time values were calculated from the de-noised data. The travel time inversion based on this de-noised data has shown results consistent with previous work at the test site.
• Journal Article

#### Understanding the Operating Mode of Fe$^0$/Fe-Sulfide/H$_2$O Systems for Water Treatment ﻿

Processes 2020; 8(4) p.1-15: Art. 409
The general suitability of water treatment systems involving metallic iron (Fe$^0$) is wellestablished. Various attempts have been made to improve the effciency of conventional Fe$^0$ systems. One promising approach combines granular Fe$^0$ and an iron sulfide mineral to form Fe$^0$/Fe-sulfide/H$_2$O systems. An improved understanding of the fundamental principles by which such systems operate is still needed. Through a systematic analysis of possible reactions and the probability of their occurrence, this study establishes that sulfide minerals primarily sustain iron corrosion by lowering the pH of the system. Thus, chemical reduction mediated by Fe$^{\text{II}}$ species (indirect reduction) is a plausible explanation for the documented reductive transformations. Such a mechanism is consistent with the nature and distribution of reported reaction products. While considering the mass balance of iron, it appears that lowering the pH value increases Fe$^0$ dissolution, and thus subsequent precipitation of hydroxides. This precipitation reaction is coupled with the occlusion of contaminants (co-precipitation or irreversible adsorption). The extent to which individual sulfides impact the effciency of the tested systems depends on their intrinsic reactivities and the operational conditions (e.g., sulfide dosage, particle size, experimental duration). Future research directions, including the extension of Fe$^0$/Fe-sulfide/H$_2$O systems to drinking water filters and (domestic) wastewater treatment using the multi-soil-layering method are highlighted.
• Journal Article

#### Middle Class, Tradition and the Desi-Realm—Discourses of Alternative Food Networks in Bengaluru, India ﻿

Sustainability 2020; 12(7) p.1-15: Art. 2741
It has repeatedly been claimed that persistent traditional agriculture and marketing in countries of the Global South, such as India, are a fruitful basis for the foundation of alternative food networks (AFNs). However, literature on AFNs in the Global South is scarce and it thus remains uncertain how the appropriation of traditional agri-food practices plays out. We conducted semi-structured expert interviews with representatives of 14 AFNs in Bengaluru, India, in order to explore their aims and approaches. We found that there is a high variety of different AFNs in the city. One salient discourse among the representatives was that the agri-food system can be improved by a revitalization of tradition. In this paper, we discuss the implications of this conviction on representatives of AFNs. Traditionalism, we argue, does rather represent a deflection from achieving the stated goals of the AFN, namely the improvement of the livelihood of Indian farmers.
• Journal Article

#### Steel Wool for Water Treatment: Intrinsic Reactivity and Defluoridation Efficiency ﻿

Processes 2020; 8(3) p.1-21: Art. 265
Studies were undertaken to characterize the intrinsic reactivity of Fe$^0$-bearing steel wool (Fe$^0$ SW) materials using the ethylenediaminetetraacetate method (EDTA test). A 2 mM Na$_2$-EDTA solution was used in batch and column leaching experiments. A total of 15 Fe$^0$ SW specimens and one granular iron (GI) were tested in batch experiments. Column experiments were performed with four Fe$^0$ SW of the same grade but from various suppliers and the GI. The conventional EDTA test (0.100 g Fe$^0$, 50 mL EDTA, 96 h) protocol was modified in two manners: (i) Decreasing the experimental duration (down to 24 h) and (ii) decreasing the Fe$^0$ mass (down to 0.01 g). Column leaching studies involved glass columns filled to 1/4 with sand, on top of which 0.50 g of Fe$^0$ was placed. Columns were daily gravity fed with EDTA and effluent analyzed for Fe concentration. Selected reactive Fe$^0$ SW specimens were additionally investigated for discoloration effciency of methylene blue (MB) in shaken batch experiments (75 rpm) for two and eight weeks. The last series of experiments tested six selected Fe$^0$ SW for water defluoridation in Fe$^0$/sand columns. Results showed that (i) the modifications of the conventional EDTA test enabled a better characterization of Fe$^0$ SW; (ii) after 53 leaching events the Fe$^0$ SW showing the best k$_{\text{EDTA}}$ value released the lowest amount of iron; (iii) all Fe$^0$ specimens were effcient at discoloring cationic MB after eight weeks; (iv) limited water defluoridation by all six Fe$^0$ SW was documented. Fluoride removal in the column systems appears to be a viable tool to characterize the Fe$^0$ long-term corrosion kinetics. Further research should include correlation of the intrinsic reactivity of SW specimens with their effciency at removing different contaminants in water.
• Journal Article

#### Nonlinear Autoregressive Neural Networks to Predict Hydraulic Fracturing Fluid Leakage into Shallow Groundwater ﻿

Water 2020; 12(3) p.1-14: Art. 841
Hydraulic fracturing of horizontal wells is an essential technology for the exploitation of unconventional resources, but led to environmental concerns. Fracturing fluid upward migration from deep gas reservoirs along abandoned wells may pose contamination threats to shallow groundwater. This study describes the novel application of a nonlinear autoregressive (NAR) neural network to estimate fracturing fluid flow rate to shallow aquifers in the presence of an abandoned well. The NAR network is trained using the Levenberg–Marquardt (LM) and Bayesian Regularization (BR) algorithms and the results were compared to identify the optimal network architecture. For NAR-LM model, the coeffcient of determination ($R^2$) between measured and predicted values is 0.923 and the mean squared error ($MSE$) is $4.2\times 10^{-4}$, and the values of $R^2 = 0.944$ and $MSE = 2.4\times 10^{-4}$ were obtained for the NAR-BR model. The results indicate the robustness and compatibility of NAR-LM and NAR-BR models in predicting fracturing fluid flow rate to shallow aquifers. This study shows that NAR neural networks can be useful and hold considerable potential for assessing the groundwater impacts of unconventional gas development.
• Journal Article

#### Exfoliated near infrared fluorescent silicate nanosheets for (bio)photonics ﻿

Nature Communications 2020; 11(1) p.1-11: Art. 1495
Imaging of complex (biological) samples in the near-infrared (NIR) is beneficial due toreduced light scattering, absorption, phototoxicity, and autofluorescence. However, there arefew NIRfluorescent materials known and suitable for biomedical applications. Here weexfoliate the layered pigment $CaCuSi_4O_{10}$ (Egyptian Blue, EB) via ball milling and facile tipsonication into NIRfluorescent nanosheets (EB-NS). The size of EB-NS can be tailored todiameters <20 nm and heights down to 1 nm. EB-NSfluoresce at 910 nm and thefluorescenceintensity correlates with the number of $Cu^{2+}$ ions. Furthermore, EB-NS display no bleachingand high brightness compared with other NIRfluorophores. The versatility of EB-NS isdemonstrated by in-vivo single-particle tracking and microrheology measurements inDro-sophila melanogasterembryos. EB-NS can be uptaken by plants and remotely detected in alow-cost stand-off detection setup. In summary, EB-NS have the potential for a wide range ofbioimaging applications.
• Journal Article

#### Biomass, Morphology, and Dynamics of the Fine Root System Across a 3,000-M Elevation Gradient on Mt. Kilimanjaro ﻿

Frontiers in Plant Science 2020; 11 p.1-16: Art. 13
Fine roots (≤2 mm) consume a large proportion of photosynthates and thus play a key role in the global carbon cycle, but our knowledge about fine root biomass, production, and turnover across environmental gradients is insufficient, especially in tropical ecosystems. Root system studies along elevation transects can produce valuable insights into root trait-environment relationships and may help to explore the evidence for a root economics spectrum (RES) that should represent a trait syndrome with a trade-off between resource acquisitive and conservative root traits. We studied fine root biomass, necromass, production, and mean fine root lifespan (the inverse of fine root turnover) of woody plants in six natural tropical ecosystems (savanna, four tropical mountain forest types, tropical alpine heathland) on the southern slope of Mt. Kilimanjaro (Tanzania) between 900 and 4,500 m a.s.l. Fine root biomass and necromass showed a unimodal pattern along the slope with a peak in the moist upper montane forest (~2,800 m), while fine root production varied little between savanna and upper montane forest to decrease toward the alpine zone. Root:shoot ratio (fine root biomass and production related to aboveground biomass) in the tropical montane forest increased exponentially with elevation, while it decreased with precipitation and soil nitrogen availability (decreasing soil C:N ratio). Mean fine root lifespan was lowest in the ecosystems with pronounced resource limitation (savanna at low elevation, alpine heathland at high elevation) and higher in the moist and cool forest belt (~1,800–3,700 m). The variation in root traits across the elevation gradient fits better with the concept of a multi-dimensional RES, as root tissue density and specific root length showed variable relations to each other, which does not agree with a simple trade-off between acquisitive and conservative root traits. In conclusion, despite large variation in fine root biomass, production, and morphology among the different plant species and ecosystems, a general belowground shift in carbohydrate partitioning is evident from 900 to 4,500 m a.s.l., suggesting that plant growth is increasingly limited by nutrient (probably N) shortage toward higher elevations.
• Journal Article

#### Fresh groundwater discharge insignificant for the world’s oceans but important for coastal ecosystems ﻿

Nature Communications 2020; 11(1) p.1-12: Art. 1260
The flow of fresh groundwater may provide substantial inputs of nutrients and solutes to the oceans. However, the extent to which hydrogeological parameters control groundwater flow to the world’s oceans has not been quantified systematically. Here we present a spatially resolved global model of coastal groundwater discharge to show that the contribution of fresh groundwater accounts for ~0.6% (0.004%–1.3%) of the total freshwater input and ~2% (0.003%–7.7%) of the solute input for carbon, nitrogen, silica and strontium. However, the coastal discharge of fresh groundwater and nutrients displays a high spatial variability and for an estimated 26% (0.4%–39%) of the world’s estuaries, 17% (0.3%–31%) of the salt marshes and 14% (0.1–26%) of the coral reefs, the flux of terrestrial groundwater exceeds 25% of the river flux and poses a risk for pollution and eutrophication.
• Journal Article

#### Geothermal play typing in Germany, case study Molasse Basin: a modern concept to categorise geothermal resources related to crustal permeability ﻿

Netherlands Journal of Geosciences 2019; 98
The majority of running geothermal plants worldwide are located in geological settings with convection- or advection-dominant heat transport. In Germany as in most regions in Europe, conduction is the dominating heat transport mechanism, with a resulting average geothermal gradient. The geothermal play type concept is a modern methodology to group geothermal resources according to their geological setting, and characteristic heat transport mechanisms. In particular, the quantity of heat transport is related to fluid flow in natural or engineered geothermal reservoirs. Hence, the permeability structure is a key element for geothermal play typing. Following the existing geothermal play type catalogue, four major geothermal play types can be identified for Germany: intracratonic basins, foreland basins and basement/crystalline rock provinces as conduction-dominated play types, and extensional terrains as the convection-dominated play type. The installed capacity of geothermal facilities sums up to 397.1 MWth by the end of 2018. District heating plants accounted for the largest portion, with about 337.0 MWth. The majority of these installations are located in the play type ‘foreland basin’, namely the Molasse Basin in southern Germany. The stratigraphic unit for geothermal use is the Upper Jurassic, also known as ‘Malm’ formation, a carbonate reservoir with high variability in porosity and permeability. Recently drilled wells in the southernmost Molasse Basin indicate the Upper Jurassic as a tight, fracture-controlled reservoir, not usable for conventional hydrothermal well doublets. Our new data compilation including the recently drilled deep geothermal well Geretsried reveals the relation of porosity and permeability to depth. The results suggest that obviously diagenetic processes control permeability with depth in carbonate rock, diminishing the predictability of reservoir porosity and permeability. The play type concept helps to delineate these property variations in play type levels because it is based on geological constraints, common for exploration geology. Following the general idea of play typing, the results from this play analysis can be transferred to geological analogues as carbonate rock play levels in varying depth.
• Journal Article

#### Siboglinidae Tubes as an Additional Niche for Microbial Communities in the Gulf of Cádiz—A Microscopical Appraisal ﻿

Microorganisms 2020; 8(3): Art. 367
Siboglinids were sampled from four mud volcanoes in the Gulf of Cádiz (El Cid MV, Bonjardim MV, Al Gacel MV, and Anastasya MV). These invertebrates are characteristic to cold seeps and are known to host chemosynthetic endosymbionts in a dedicated trophosome organ. However, little is known about their tube as a potential niche for other microorganisms. Analyses by scanning and transmission electron microscopy showed dense biofilms on the tube in Al Gacel MV and Anastasya MV specimens by prokaryotic cells. Methanotrophic bacteria were the most abundant forming these biofilms as further supported by 16S rRNA sequence analysis. Furthermore, elemental analyses with electron microscopy and energy-dispersive X-ray spectroscopy point to the mineralization and silicification of the tube, most likely induced by the microbial metabolisms. Bacterial and archaeal 16S rRNA sequence libraries revealed abundant microorganisms related to these siboglinid specimens and certain variations in microbial communities among samples. Thus, the tube remarkably increases the microbial biomass related to the worms and provides an additional microbial niche in deep-sea ecosystems.