Invasive floating macrophytes reduce greenhouse gas emissions from a small tropical lake

Floating macrophytes, including water hyacinth (Eichhornia crassipes), are dominant invasive organisms in tropical aquatic systems, and they may play an important role in modifying the gas exchange between water and the atmosphere. However, these systems are underrepresented in global datasets of greenhouse gas (GHG) emissions. This study investigated the carbon (C) turnover and GHG emissions from a small (0.6 km2) water-harvesting lake in South India and analysed the effect of floating macrophytes on these emissions. We measured carbon dioxide (CO2) and methane (CH4) emissions with gas chambers in the field as well as water C mineralization rates and physicochemical variables in both the open water and in water within stands of water hyacinths. The CO2 and CH4 emissions from areas covered by water hyacinths were reduced by 57% compared with that of open water. However, the C mineralization rates were not significantly different in the water between the two areas. We conclude that the increased invasion of water hyacinths and other floating macrophytes has the potential to change GHG emissions, a process that might be relevant in regional C budgets

An unusual carbon cycle budget of a small stream in a mountain silicate terrain: The case of the Gravona river (Corsica)

Abstract The current research of carbon cycling in inland waters lacks a sound knowledge of carbon outgassing from small streams. As a consequence, these compartments of the terrestrial water cycle might still be seriously underrepresented in estimates of global carbon transfer budgets from land surfaces. This study investigated carbon sources and sinks of a mountain river in a silicate catchment. For this purpose, the high‐relief Gravona river, in the western part of the island of Corsica (France) in the Western Mediterranean, was investigated for field parameters, dissolved inorganic carbon (DIC) and its stable carbon isotopes (δ13CDIC). The source region was characterized by low DIC contents and high δ13CDIC values that decreased further downstream due to increasing soil respiration. Associated increasing DIC concentrations and elevated seasonality in the lower river section also indicated more respiration and subsequent DIC‐input by weathering. The aqueous partial pressure (pCO2(aq)) was lowest at the source of the Gravona river and samples from the cold season even showed undersaturation that led to uptake of atmospheric CO2. Further downstream, the seasonality of pCO2(aq) increased and was particularly pronounced near the river mouth where CO2 degassing took place. Average DIC flux along the river was 0.129 Gg C year−1 and was almost equal to CO2 degassing from the river surface with 0.128 Gg C year−1. Our study showed that on an annual basis the river is an overall weak to medium source of CO2 to the atmosphere even though headwater parts of the river seasonally act as CO2 sinks

Tritium as a hydrological tracer in Mediterranean precipitation events

Climate models are in need of improved constraints for water vapor transport in the atmosphere, and tritium can serve as a powerful tracer in the hydrological cycle. Although the general principles of tritium distribution and transfer processes within and between the various hydrological compartments are known, variation on short timescales and aspects of altitude dependence are still under debate. To address questions regarding tritium sources, sinks, and transfer processes, the sampling of individual precipitation events in Corte on the island of Corsica in the Mediterranean Sea was performed between April 2017 and April 2018. Tritium concentrations of 46 event samples were compared to their moisture origin and corresponding air mass history. Air mass back-trajectories were generated from the novel high-resolution ERA5 dataset from the ECMWF (European Centre for Medium-Range Weather Forecasts). Geographical source regions with similar tritium concentrations were predefined using generally known tritium distribution patterns, such as the “continental effect”, and from data records derived at long-term measurement stations of tritium in precipitation across the working area. Our model-derived source region tritium concentrations agreed well with annual mean station values. Moisture that originated from continental Europe and the Atlantic Ocean was most distinct regarding tritium concentrations with values up to 8.8 TU (tritium units) and near 0 TU, respectively. The seasonality of tritium values ranged from 1.6 TU in January to 10.1 TU in May, and they exhibited well-known elevated concentrations in spring and early summer due to increased stratosphere–troposphere exchange. However, this pattern was interrupted by extreme events. The average altitude of trajectories was correlated with the tritium concentrations in precipitation, especially in spring and early summer and if outlier values of extreme tritium concentrations were excluded. However, in combination with the trajectory information, these outlier values proved to be valuable for improving the comprehension of tritium movement in the atmosphere. Our work shows how event-based tritium research can advance the understanding of its distribution in the atmosphere

From Global to Local and Vice Versa: On the Importance of the 'Globalization' Agenda in Continental Groundwater Research and Policy-Making.

Groundwater is one of the most important environmental resources and its use continuously rises globally for industrial, agricultural, and drinking water supply purposes. Because of its importance, more knowledge about the volume of usable groundwater is necessary to satisfy the global demand. Due to the challenges in quantifying the volume of available global groundwater, studies which aim to assess its magnitude are limited in number. They are further restricted in scope and depth of analysis as, in most cases, they do not explain how the estimates of global groundwater resources have been obtained, what methods have been used to generate the figures and what levels of uncertainty exist. This article reviews the estimates of global groundwater resources. It finds that the level of uncertainty attached to existing numbers often exceeds 100 % and strives to establish the reasons for discrepancy. The outcome of this study outlines the need for a new agenda in water research with a more pronounced focus on groundwater. This new research agenda should aim at enhancing the quality and quantity of data provision on local and regional groundwater stocks and flows. This knowledge enhancement can serve as a basis to improve policy-making on groundwater resources globally. Research-informed policies will facilitate more effective groundwater management practices to ensure a more rapid progress of the global water sector towards the goal of sustainability

Monitoring of cap-rock integrity during CCS from field data at the Ketzin pilot site (Germany): Evidence from gas composition and stable carbon isotopes

Cap-rock integrity is a key issue in Carbon Capture and Storage (CCS) technologies. At the Ketzin pilot site, new drill cores of sealing- and reservoir formations were retrieved from a depth range of 620⬜701 m below ground level (b.g.l.). These strata have been exposed to injected CO2 under field conditions for more than four years. Here we present data on cap-rock and reservoir lithologies, CO2 concentrations and their stable carbon isotope ratios (View the MathML sourceδCCO213). CO2 concentrations within the mudstone-dominated cap-rock were <1% (i.e. 10 000 ppmV) with corresponding carbon isotope values between ↙18.6⬰ and ↙29.4⬰. Below the boundary between the cap-rock and the reservoir, CO2 concentrations of more than 90% with mean View the MathML sourceδCCO213 values around ↙36.5⬰ were measured. Below this section, between 648 and 655 m b.g.l., CO2 concentrations decreased again in the clayey and silty lithology of the reservoir to less than 2%, but maintained a depleted View the MathML sourceδCCO213 value of around ↙34.2⬰. At depths below 662 m b.g.l., the CO2 concentrations decreased to values of less than 10 000 ppmV and showed corresponding increases to View the MathML sourceδCCO213 values between ↙15.9⬰ and ↙27.6⬰. Both isotope and CO2 concentration confirm that no CO2 from the reservoir penetrated the cap-rock at the Ketzin pilot site after four years of injection

Stable water isotope patterns in a climate change hotspot: The isotope hydrology framework of Corsica (western Mediterranean)

International audienceThe Mediterranean is regarded as a region of intense climate change. To better understand future climate change, this area has been the target of several palaeoclimate studies which also studied stable isotope proxies that are directly linked to the stable isotope composition of water, such as tree rings, tooth enamel or speleothems. For such work, it is also essential to establish an isotope hydrology framework of the region of interest. Surface waters from streams and lakes as well as groundwater from springs on the island of Corsica were sampled between 2003 and 2009 for their oxygen and hydrogen isotope compositions. Isotope values from lake waters were enriched in heavier isotopes and define a local evaporation line (LEL). On the other hand, stream and spring waters reflect the isotope composition of local precipitation in the catchment. The intersection of the LEL and the linear fit of the spring and stream waters reflect the mean isotope composition of the annual precipitation (δP) with values of-8.6(±0.2) ‰ for δ18O and-58(±2) ‰ for δ2H. This value is also a good indicator of the average isotope composition of the local groundwater in the island. Surface water samples reflect the altitude isotope effect with a value of-0.17(±0.02) ‰ per 100 m elevation for oxygen isotopes. At Vizzavona Pass in central Corsica, water samples from two catchments within a lateral distance of only a few hundred metres showed unexpected but systematic differences in their stable isotope composition. At this specific location, the direction of exposure seems to be an important factor. The differences were likely caused by isotopic enrichment during recharge in warm weather conditions in south-exposed valley flanks compared to the opposite, north-exposed valley flanks.</p