The emissions of carbon dioxide (CO2) and methane (CH4) from inland waters are an important source in the global greenhouse gas (GHG) balance. Reservoirs are particular hot spots of GHG emissions. The GHG emissions are temporally and spatially highly variable. Currently, not much is known about the actual flux rates from temperate reservoirs, and the processes involved are not completely understood. In this project, we would like to quantify the GHG emissions from two German reservoirs. The central topic is the understanding of the regulation of CO2 and CH4 emissions and, especially, to comprehend effects of altering water levels, trophic state and meteorological drivers. We would like to test three major hypotheses:
(1) Short term events contribute significantly to the overall balance.
(2) Temporal pattern of CO2 and CH4 emission depend on the trophic state of the reservoir and are complexly overlaid by atmospheric effects.
(3) The spatial distribution of the flux of the two gasses CO2 and CH4 depends differently on internal (e.g., hydro-chemical parameters and water depth) and external interacting factors (e.g., wind, air pressure, radiation and energy balance).
The proposed project is placed in the nexus between limnology, hydrology and boundary layer meteorology. We will investigate two different reservoirs – the oligotrophic Rappbode reservoir in the Harz Mountains and the eutrophic reservoir Bautzen in Lusatia. Temporal patterns of CO2 and CH4 emissions will be quantified by a combination of micro-meteorological and water side measurements. Central to the project will be a floating Eddy Covariance (EC) measurement system. The conflation of EC flux measurements, concentration measurements in the water body, and meteorological basic data allows the determination of the physical gas transfer coefficient. The spatial variability of GHG emissions will be analysed by floating chamber measurements and ebullition funnels. The measurements of emission rates are accompanied by the analysis of sediment and hydro-chemical parameters, e.g., pH and concentrations of O2, CO2 and CH4 as well as by continuous measurements of energy balance, radiation budget and classical meteorological variables. Proper modelling approaches will be used for generalisation and regionalisation of measurements and project results.
ORCWAR - ORganic Carbon cycling in WAter Reservoirs of Brazil and Germany: influence of land use and hydrology
The project "ORganic Carbon cycling in WAter Reservoirs of Brazil and Germany: influence of land use and hydrology – ORCWAR” will characterize and quantify the input and output of organic carbon to the Itupararanga dam south of Sorocaba as well as the transformation processes occurring within the water column and the sediments with the special aid of isotope analyses. Similar investigations are performed at the Rappbode Reservoir in the Harz Mountains of Germany. The project aims to quantify the particle removal and carbon storage in the sediments as well as the identification of sources within the catchment by using different extraction and fractionation schemes for carbon and humic substances. To get these ambiguous goals the following steps have to be conducted:
• Sampling of water and suspended particulate matter (SPM) at the main inflows at different season and within the lake water column
• Measurement of discharge of the main tributaries during the water sampling
• Chemical analyses of nutrients and major ions within the water samples
• Isotopic analyses of organic carbon of the water and the SPM
• Fluorescence characterization of the water samples
• Installation of sediment traps within the water column to collect settling particles (seston)
• Sampling of seston and determination of carbon and nitrogen concentrations and organic carbon isotopic composition
• Sampling of sediment material at several positions along the reservoir to quantify the amount of carbon within the top layer of the sediment
• Analyses of the isotopic composition of the sediment for organic carbon
• Extraction, purification and enrichment of humic substances from sediment, porewater, soil, and soil water
• Determination of HS concentration and chemical and isotopic characterization
• Evaluation of the land use within the catchment of the dam (preferentially by GIS)
• Sampling of typical soil within the different subcatchments and determination of carbon and nitrogen concentrations and organic carbon isotopic composition
• Calculation and balance for the organic carbon cycles of the dams
Goal: In this project, we investigate the processes that control the abundance and characteristics of gas bubbles in freshwater ecosystems, along with an assessment of their role in transporting gases, dissolved and particulate matter. We distinguish between bubbles generated by air entrainment at the water surface, bubbles nucleating in the pelagic zone due to excess dissolved gas pressure and bubbles formed in aquatic sediments. We hypothesize that these three different types of bubbles have distinct properties.
The ISIMIP (www.isimip.org) is a framework for projecting the impacts of climate change across sectors and spatial scales. The project has created an international network of climate-impact modellers contributing to a comprehensive and consistent picture of the world under different climate-change scenarios. In the Department of Lake Research at UFZ, scientists are using one- and two-dimensional models to simulate how climate change will affect lakes and reservoirs. We are firstly investigating the physical changes that occur as a result of warming, such as an increase in water temperature, decrease in ice cover, and changes in stratification and mixing. Ultimately, modelling results from different sectors will be combined to assess the integrated and more indirect effects of climate warming, like how land-use change and altered patterns of nutrient export from catchments will affect freshwater ecology and water quality.
The ISIMIP enables a large number of international scientists to join forces towards a common goal. For instance, we are working together with lake modelling teams from Switzerland, Belgium, Sweden, the United States, Ireland, and other countries. Each team is using different models to simulate the same climate warming scenarios in the same set of lakes. This method, called “ensemble” modelling, delivers more reliable model projections and a better idea of the uncertainty in our results. The initiative is ongoing and funded independently for each researcher, including contributions from UFZ.