Nils Moosdorf

A glimpse beneath earth's surface: GLobal HYdrogeology MaPS (GLHYMPS) of permeability and porosity

The lack of robust, spatially distributed subsurface data is the key obstacle limiting the implementation of complex and realistic groundwater dynamics into global land surface, hydrologic, and climate models. We map and analyze permeability and porosity globally and at high resolution for the first time. The new permeability and porosity maps are based on a recently completed high-resolution global lithology map that differentiates fine and coarse-grained sediments and sedimentary rocks, which is important since these have different permeabilities. The average polygon size in the new map is ~100 km2, which is a more than hundredfold increase in resolution compared to the previous map which has an average polygon size of ~14,000 km2. We also significantly improve the representation in regions of weathered tropical soils and permafrost. The spatially distributed mean global permeability ~10−15 m2 with permafrost or ~10−14 m2 without permafrost. The spatially distributed mean porosity of the globe is 14%. The maps will enable further integration of groundwater dynamics into land surface, hydrologic, and climate models.

Carbon dioxide efficiency of terrestrial enhanced weathering.

Terrestrial enhanced weathering, the spreading of ultramafic silicate rock flour to enhance natural weathering rates, has been suggested as part of a strategy to reduce global atmospheric CO2 levels. We budget potential CO2 sequestration against associated CO2 emissions to assess the net CO2 removal of terrestrial enhanced weathering. We combine global spatial data sets of potential source rocks, transport networks, and application areas with associated CO2 emissions in optimistic and pessimistic scenarios. The results show that the choice of source rocks and material comminution technique dominate the CO2 efficiency of enhanced weathering. CO2 emissions from transport amount to on average 0.5-3% of potentially sequestered CO2. The emissions of material mining and application are negligible. After accounting for all emissions, 0.5-1.0 t CO2 can be sequestered on average per tonne of rock, translating into a unit cost from 1.6 to 9.9 GJ per tonne CO2 sequestered by enhanced weathering. However, to control or reduce atmospheric CO2 concentrations substantially with enhanced weathering would require very large amounts of rock. Before enhanced weathering could be applied on large scales, more research is needed to assess weathering rates, potential side effects, social acceptability, and mechanisms of governance.

The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust

The terrestrial surface, the “skin of the earth”, is an important interface for global (geochemical) material fluxes between major reservoirs of the Earth system: continental and oceanic crust, ocean and atmosphere. Because of a lack in knowledge of the geochemical composition of the terrestrial surface, it is not well understood how the geochemical evolution of the Earth’s crust is impacted by its properties. Therefore, here a first estimate of the geochemical composition of the terrestrial surface is provided, which can be used for further analysis. The geochemical average compositions of distinct lithological classes are calculated based on a literature review and applied to a global lithological map. Comparison with the bulk composition of the upper continental crust shows that the geochemical composition of the terrestrial surface (below the soil horizons) is significantly different from the assumed average of the upper continental crust. Specifically, the elements Ca, S, C, Cl and Mg are enriched at the terrestrial surface, while Na is depleted (and probably K). Analysis of these results provide further evidence that chemical weathering, chemical alteration of minerals in marine settings, biogeochemical processes (e.g. sulphate reduction in sediments and biomineralization) and evaporite deposition are important for the geochemical composition of the terrestrial surface on geological time scales. The movement of significant amounts of carbonate to the terrestrial surface is identified as the major process for observed Ca-differences. Because abrupt and significant changes of the carbonate abundance on the terrestrial surface are likely influencing CO2-consumption rates by chemical weathering on geological time scales and thus the carbon cycle, refined, spatially resolved analysis is suggested. This should include the recognition of the geochemical composition of the shelf areas, now being below sea level.

Submarine groundwater discharge from tropical islands: a review

Submarine groundwater discharge (SGD) is a rarely recognized pathway for nutrients and other solutes from land to sea. The sensitive coastal ecosystems around tropical islands could be particularly affected by nutrient discharge associated with SGD in relation to surficial nutrient transport by rivers, but have received comparatively little attention to date. This study reviews the findings of local assessments of submarine groundwater discharge from tropical islands. In addition, the ratio of coast length and land area of individual land bodies is suggested as an appropriate first-order estimate of the relevance of SGD versus river discharge, demonstrating the potential relative importance of SGD from tropical islands over rivers. The review highlights the need for targeted research of submarine groundwater discharge from tropical islands and highlights its relevance for biogeochemical fluxes in these geographic settings.ZusammenfassungSubmariner Grundwasserabfluss (SGD) vom Land in die Ozeane ist ein wenig beachteter Transportweg für gelöste Stoffe. Existierende Studien betonen allerdings seine Wichtigkeit für die Nährstoffversorgung der Küstengewässer. Insbesondere in Küstenökosystemen im Bereich tropischer Inseln kann SGD im Verhältnis zum Flusseintrag die Nährstoffbudgets dominieren, dort hat SGD aber bisher nur wenig Interesse erfahren. Diese Studie beleuchtet die Erkenntnisse lokaler Untersuchungen des SGD tropischer Inseln. Darüber hinaus wird das Verhältnis von Küstenlänge und Landfläche einer Insel als grobe Abschätzung des Verhältnisses von SGD und Flusseinträgen vorgeschlagen und damit die potenzielle Wichtigkeit von SGD von tropischen Inseln gezeigt. Das Review zeigt den Bedarf an systematischen Feldstudien über SGD von tropischen Inseln und hebt dessen Bedeutung für biogeochemische Stoffkreisläufe dieser Regionen hervor.

Lithological composition of the North American continent and implications of lithological map resolution for dissolved silica flux modeling

Lithological maps are important tools for applications sensitive to physical or chemical attributes of rocks. They aggregate rock types into a limited set of classes. Most studies on river elementary fluxes derived from chemical weathering use local lithological maps, and some upscale their results to global scales, using global lithological maps. It remains unclear if those maps sufficiently represent the heterogeneous local lithological settings. To analyze this in more detail a new lithological map of North America containing 262,111 polygons is presented and compared to three global lithological maps. The impact of the differences is demonstrated using four models of dissolved silica mobilization from the terrestrial land system into river systems (DSi mobilization), calibrated using each map. According to the new map, North America is composed of 62.8% sediments, 14.8% plutonics, 13.3% metamorphics, and 7.2% volcanics. In all four maps, the total proportions of rock types are comparable for North America, but their spatial distribution differs largely. The calculated DSi mobilization differs weakly between the maps (−20% to +9%) compared to the results of the model calibrated on the new map for North America but strongly (−59% to +38%) for tributary regions of regional seas around North America. The map comparison suggests that lithological classes of different data sets may represent different attributes although they may share the same name. Applications (e.g., Earth system models) considering lateral weathering derived matter fluxes should use data derived from different lithological source data sets with care.

The World Karst Aquifer Mapping project: concept, mapping procedure and map of Europe

Karst aquifers contribute substantially to freshwater supplies in many regions of the world, but are vulnerable to contamination and difficult to manage because of their unique hydrogeological characteristics. Many karst systems are hydraulically connected over wide areas and require transboundary exploration, protection and management. In order to obtain a better global overview of karst aquifers, to create a basis for sustainable international water-resources management, and to increase the awareness in the public and among decision makers, the World Karst Aquifer Mapping (WOKAM) project was established. The goal is to create a world map and database of karst aquifers, as a further development of earlier maps. This paper presents the basic concepts and the detailed mapping procedure, using France as an example to illustrate the step-by-step workflow, which includes generalization, differentiation of continuous and discontinuous carbonate and evaporite rock areas, and the identification of non-exposed karst aquifers. The map also shows selected caves and karst springs, which are collected in an associated global database. The draft karst aquifer map of Europe shows that 21.6% of the European land surface is characterized by the presence of (continuous or discontinuous) carbonate rocks; about 13.8% of the land surface is carbonate rock outcrop.ZusammenfassungKarstgrundwasserleiter leisten in vielen Regionen der Welt einen wichtigen Beitrag zur Wasserversorgung, sind aber aufgrund ihrer hydrogeologischen Eigenschaften besonders verletzlich gegenüber Schadstoffeinträgen und schwierig zu bewirtschaften. Viele Karstsysteme sind über weite Gebiete hydraulisch verbunden und erfordern daher grenzüberschreitende Ansätze zur Erkundung, zum Schutz und zur Bewirtschaftung. Um einen besseren globalen Überblick der Karstaquifere zu erhalten, eine Grundlage für nachhaltiges und internationales Wasserressourcenmanagement zu etablieren und das Bewusstsein in der Öffentlichkeit und bei Entscheidungsträgern zu erhöhen, wurde das Welt-Karstaquifer-Kartierprojekt (WOKAM) ins Leben gerufen. Ziel dieses Projektes ist es, eine Weltkarte und Datenbank der Karstaquifere zu erstellen, als Weiterentwicklung existierender Kartenwerke. Dieser Fachbeitrag präsentiert die grundlegenden Konzepte und die detaillierte Vorgehensweise bei der Kartierung. Am Beispiel von Frankreich wird der Arbeitsablauf Schritt für Schritt illustriert, von der Generalisierung über die Differenzierung von Gebieten mit kontinuierlichen und diskontinuierlichen Carbonatgesteinen bzw. Evaporiten, bis hin zur Identifizierung von tiefen und bedeckten Karstaquiferen. Die Karte zeigt auch ausgewählte Höhlen und Karstquellen, welche in einer assoziierten globalen Datenbank gesammelt werden. Die Karstaquifer-Karte von Europa zeigt, dass 21.6% der Landfläche durch (kontinuierliche oder diskontinuierliche) Carbonatgesteinen charakterisiert sind; anstehende Carbonatgesteine sind auf etwa 13.8% der Fläche anzutreffen.RésuméLes aquifères karstiques contribuent pour une part significative à l’alimentation en eau potable de nombreuses régions du monde, mais ils sont vulnérables à la pollution et sont difficiles à gérer du fait de leurs caractéristiques hydrogéologiques particulières. De nombreux systèmes karstiques présentent des connections hydrauliques sur de vastes étendues et requièrent de ce fait des études, une protection et une gestion transfrontalières. Afin de disposer d’une meilleure vue d’ensemble des aquifères karstiques, de créer une base pour une gestion internationale durable de leurs ressources en eau et de mieux sensibiliser le public et surtout les décideurs, le programme de la Carte Mondiale des Aquifères Karstiques (World Karst Aquifer Mapping, WOKAM) a été réalisé. Son but est de créer une carte et une base de données mondiales des aquifères karstiques, pour améliorer les cartes antérieures. Cet article présente les concepts de base et le détail de la procédure de cartographie, en prenant la France comme exemple pour illustrer la démarche pas à pas, comprenant la généralisation, la différenciation des zones continues et discontinues de carbonates et d’évaporites et l’identification des aquifères karstiques sous couverture. La carte montre également une sélection de cavités et de sources dont les informations ont été rassemblées dans une base de données globale. L’ébauche de la carte des aquifères karstiques d’Europe montre que 21.6% du territoire européen sont caractérisés par la présence de roches carbonatées, continues ou discontinues, et qu’environ 13.8% de la surface sont des affleurements de roches carbonatées.ResumenLos acuíferos kársticos contribuyen sustancialmente al suministro de agua dulce en muchas regiones del mundo, pero son vulnerables a la contaminación y difíciles de manejar debido a sus singulares características hidrogeológicas. Muchos sistemas kársticos están conectados hidráulicamente en grandes áreas y requieren exploración, protección y manejo transfronterizo. Se estableció el proyecto World Karst Aquifer Mapping (WOKAM) con el fin de obtener una mejor visión global de los acuíferos kársticos, crear una base para una gestión internacional sostenible de los recursos hídricos y aumentar la concientización en el público y entre los responsables de la toma de decisiones. El objetivo es crear un mapa mundial y una base de datos de acuíferos kársticos, como un desarrollo adicional de mapas previos. Este trabajo presenta los conceptos básicos y el procedimiento detallado del mapeo, utilizando a Francia como ejemplo para ilustrar el flujo de trabajo paso a paso, que incluye la generalización, la diferenciación de las áreas continuas y discontinuas con rocas carbonatadas y evaporíticas, y la identificación de acuíferos kársticos no expuestos. El mapa también muestra cavernas y manantiales kársticos seleccionados, que se recopilan en una base global de datos asociados. El mapa del acuífero kárstico de Europa muestra que el 21.6% de la superficie europea se caracteriza por la presencia de rocas carbonatadas (continuas o discontinuas); aproximadamente el 13.8% de la superficie es roca carbonatada aflorante.摘要在全世界范围内岩溶含水层提供了重要的淡水资源,但由于独特的水文地质特征,使其极易受到污染且难以开发和管理。许多大型的岩溶含水系统不仅分布范围广,而且其内部水力联系通畅,因此需要跨国界的调查、保护和管理。为了更好地获得对全球范围内岩溶含水层空间分布的认识,为国际水资源可持续性利用创造基础,并且提高公众和决策者对岩溶水资源的认识,国际水文地质学家协会建立了世界岩溶含水层制图项目(WOKAM)。该计划的目标是参考现有文献资料,绘制世界范围内岩溶含水层分布图,并且建立相关的地理信息数据库。本文记述了制图过程所使用的概念和编制步骤,并且以法国及周边地区为例逐步说明了制图流程,重点讨论了怎样界定连续及非连续型碳酸盐岩的空间分布特征,如何显示蒸发岩,如何识别非出露型即覆盖型和埋藏型岩溶含水层等关键问题。除此以外地图上还简要地显示了具有重要区域水文地质意义的洞穴及岩溶泉,更加详细的数据可以参考数据库。世界岩溶含水层分布图欧洲部分样图显示,在欧洲有21.6%的陆地面积具有岩溶水文地质特征,其中碳酸盐岩出露面积大约占13.8%。ResumoAquíferos cársticos contribuem significativamente para a suprimento de água doce em muitas regiões do globo, mas são vulneráveis à contaminação e apresentam dificuldades de gerenciamento devido a características hidrogeológicas peculiares. Muitos sistemas cársticos são hidraulicamente conectados em vastas áreas e requerem exploração, proteção e manejo que ultrapassam limites políticos. O Projeto Mapeamento Global de Aquíferos Cársticos (WOKAM – World Karst Aquifer Mapping Project) foi estabelecido de modo a se obter uma síntese mais abrangente sobre aquíferos cársticos no planeta, assim como para se criar uma base para manejo sustentável de recursos hídricos em âmbito internacional e para aumentar a conscientização tanto do público em geral quanto entre responsáveis por tomadas de decisões. O objetivo é elaborar um mapa mundial e banco de dados sobre aquíferos cársticos tomando como base mapas anteriores. Baseando-se na França como exemplo, este artigo apresenta os conceitos básicos e procedimentos adotados de modo a ilustrar as etapas executadas para a confecção do mapa, que inclui generalização, diferenciação de áreas contínuas e descontínuas de carbonatos e evaporitos e identificação de aquíferos cársticos não expostos superficialmente. O mapa também mostra algumas cavernas e nascentes cársticas, selecionadas a partir de um banco de dados global. Esta versão do mapa de aquíferos cársticos da Europa mostra que 21.6% da superfície europeia caracteriza-se pela presença (sob forma contínua ou descontínua) de rochas carbonáticas e cerca de 13.8% da superfície apresenta afloramentos de carbonatos.

Climate‐driven changes in chemical weathering and associated phosphorus release since 1850: Implications for the land carbon balance

Chemical weathering and associated nutrient release act as a control on atmospheric carbon dioxide (CO2) concentration. To globally quantify the contribution of chemical weathering and associated phosphorus (P) release on the historical trend in terrestrial carbon uptake, we applied a weathering model under climate reconstructions from four Earth System Models. In these simulations, CO2 consumption and P release increased from 1850 to 2005 by 11 ± 3% and 12 ± 4%, respectively. Thereby the intensification of weathering due to climate change could have contributed to a small extent to the trend in terrestrial carbon uptake since the pre–Industrial Period. Using a back of the envelope calculation, we found a feedback strength of CO2 consumption and P release of −0.02 ± 0.01Wm−2K−1 and −0.02 ± 0.01Wm−2K−1, respectively. Although being one magnitude smaller than the carbon cycle feedback, the weathering feedbacks are comparable in strength to small second-order feedbacks such as methane, fire, or ozone.

Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks

Significance We compile data showing that, as hypothesized previously, waters draining glaciers have solute chemistry that is distinct from nonglacial rivers and reflects different proportions of mineral weathering reactions. Elevated pyrite oxidation during glacial weathering could generate acidity, releasing carbon to the atmosphere. We show that this effect could contribute to changes in CO2 during glacial cycles of the past million years. Over the longer, multimillion-year timescales that Earth transitions into and out of glaciated states, sustained addition of pyrite-derived sulfate to the oceans could shift the balance of the global carbon cycle toward increasing CO2 in the ocean–atmosphere, thus providing a negative-feedback mechanism preventing runaway glaciation. This mechanism depends on oxidation and thus sufficient O2. Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.

Groundwater nutrient inputs into an urbanized tropical estuary system in Indonesia

Groundwater discharge is known to transport nutrients into estuaries at several locations around the world. However, few studies report groundwater-associated nutrient fluxes from tropical developing regions such as Southeast Asia, even though this area shows the strongest human modifications in the coastal zone worldwide. We investigated groundwater nutrient flux into two streams and estuaries (Awur and Sekumbu Bay) in the urban area of Jepara, Indonesia, and its relation with the land usage surrounding the estuaries. We found that average concentrations of NO3, NH4, and PO4 in Jeparas aquifer reached 145μM, 68μM, and 14μM, respectively, and our results indicate that these were mainly originated from untreated sewage, agriculture, and manure input. Approximately 2200tonNyear-1 and 380tonPyear-1 were removed in the soil and aquifer before the nutrients were discharged into the river. The total groundwater discharge into the river and estuary was estimated to 461×103m3d-1, or up to 42% of the river discharge. Discharge of groundwater-associated NO3 (72×103mold-1), NH4 (34×103mold-1), PO4 (5×103mold-1), and additional surface runoff may contribute to eutrophication and a decrease of nearshore surface water quality. Nutrient concentrations in groundwater, river, and coastal seawater in the Jepara region are similar to those found in major urban areas in Southeast Asia, e.g. Manila and Bangkok, even though Jepara has smaller size and population. Thus, our results indicate that medium populated cities with highly modified regional land use can contribute a significant amount of nutrient discharge in the coastal area and should be included in global assessments of nutrient budget calculation.

Radium tracing nutrient inputs through submarine groundwater discharge in the global ocean

Riverine and atmospheric inputs are often considered as the main terrestrial sources of dissolved inorganic nitrogen (DIN), phosphorus (DIP), and silicon (DSi) in the ocean. However, the fluxes of nutrients via submarine groundwater discharge (SGD) often exceed riverine inputs in different local and regional scale settings. In this study, we provide a first approximation of global nutrient fluxes to the ocean via total SGD, including pore water fluxes, by combining a global compilation of nutrient concentrations in groundwater and the SGD-derived 228Ra fluxes. In order to avoid overestimations in calculating SGD-derived nutrient fluxes, the endmember value of nutrients in global groundwater was chosen from saline groundwater samples (salinity >10) which showed relatively lower values over all regions. The results show that the total SGD-derived fluxes of DIN, DIP, and DSi could be approximately 1.4-, 1.6-, and 0.7-fold of the river fluxes to the global ocean (Indo-Pacific and Atlantic Oceans), respectively. Although significant portions of these SGD-derived nutrient fluxes are thought to be recycled within sediment-aquifer systems over various timescales, SGD-derived nutrient fluxes should be included in the global ocean budget in order to better understand dynamic interactions at the land-ocean interface.