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.
MEDIWA - Meteorological Drivers of Mass and Energy Exchange between Inland Waters and the Atmosphere
The correct quantification of the mass and energy exchange between inland waters and the atmosphere is of great importance for both scientific and practical issues. Exact direct measurements are possible, but expensive and technically challenging. Thus, different gradient approaches, such as the ‘turbulent boundary layer’ (TBL) approach, provide the methodological backbone to determine diffusive gas fluxes, energy fluxes and evaporation rates from inland water utilizing easy–to–measure limnologic and atmospheric variables. However, the reliability of such flux approximations significantly depends on (i) the parameterisation of the transfer coefficient and (ii) the representativeness of input data. In order to enhance our capabilities to determine fluxes from inland waters, exchange processes will be intensively studied in this project. In particular, we aim to (A) improve the predictive power of gradient approaches and (B) quantify effects of spatial and short-term variations of meteorological and limnological drivers on flux approximations.
Two long-term and four additional short-term intensive measurement experiments will be performed at Bautzen reservoir in Lusatia (Germany) to observe mass and energy fluxes under different weather and limnic conditions as well as on different scales of space and time. A floating outdoor laboratory equipped with an eddy covariance measurement system and several meteorological, hydro-chemical and hydro-physical sensors will be used for direct continuous measurements of fluxes and variables that are unaffected by land surfaces and are representative for the pure water-atmosphere-interaction. Three additional satellite platforms with a simplified set-up will be utilized to detect the spatial variations of atmospheric and limnic conditions along the fetch. Furthermore, the occurrence and the effects of surface films and micro-stratification in the uppermost water layers will be examined by additional hydro–chemical field and laboratory experiments.
The combination of experimental fieldwork, statistical analyses and model–based investigations as well as the nexus between limnological and micrometeorological researches provide the foundations to better understand the processes that are relevant for the mass and energy exchange on different temporal and spatial scales. Our analyses will focus on the development of novel methods to (a) parameterise atmospheric transfer coefficients, especially under low turbulence conditions, (b) evaluate effects of limnological phenomena such as micro-stratification and surface films, and (c) quantify influences of atmospheric and limnologic heterogeneities on flux estimates. Additionally (d), we will examine atmospheric turbulence structures and develop models for the numerical description of spectra and cospectra of atmospheric variables to improve the correction of damping losses and therefore the fidelity of eddy covariance measurements above water surfaces.
Little is known about the ecology of lakes in winter because limnologists have historically focused on the “vegetation period” from spring through autumn. Winter is generally considered to be ecologically dormant because there is insufficient light for phytoplankton to grow until spring. Contrary to this view, there are many lakes in which phytoplankton – specifically large-celled diatoms – can form dense blooms in late winter. This phenomenon is little known yet apparently not uncommon in temperate lakes and there is evidence that these blooms can strongly alter lake ecosystems in the subsequent seasons by sequestering nutrients and decreasing phytoplankton biomass. In the DIAtom BLOoms (DIABLO) project, we want to find out what causes these blooms and investigate how they influence lake ecology and nutrient availability in the other seasons.
Project duration: 1.1.2021 – 31.12.2023
EventNut - Rapid, event-driven shortcuts between benthic nutrients and phytoplankton in inland and coastal waters
Algal blooms remain a major challenge in many lakes and coastal waters because they continue to persist even where external nutrient loads have been reduced. The vast amounts of “legacy” nutrients in the sediments continue to provide nutrients pulses, which trigger algal blooms. The objective of this project is to measure, analyze and conceptualize the short time scale effects of benthic nutrient dynamics on algal dynamics (including species composition changes) and physiology (respecting for species specific responses) under in-situ conditions. This will be conducted in a shallow freshwater and a brackish water system, using combination of high temporal resolution wet chemical sensors (P), UV spectral sensors (C, N) and methods for characterization of phytoplankton photo-physiology status (in-situ flow cytometry, gas exchange measurements and various kinds of pulse-amplitude-modulated fluorometers).