2020-2023: Timescales of recovery from eutrophication in Finnish lakes

In this project we study the recovery of lakes in Finland from eutrophication. Many lakes in the urban and agricultural areas of southern Finland experienced declining water quality during the late 20th century due to external loading of nutrients, primarily nitrogen and phosphorus (P). Actions to reduce external loading have improved water quality to some extent, but problems remain. In many cases, this is due to “legacy P” accumulated in lake sediments that takes decades to be buried and hence removed from the lake biogeochemical cycles. Here we will study the possible future recovery trajectories of specific lakes, based on a detailed understanding of their sediment biogeochemistry and its impact on the balance between P regeneration and burial. We will attempt to model the rate of change in internal phosphorus loading due to long-term burial of sedimentary P during the recovery, and how different restoration actions may influence this.

This project is funded by a China Scholarship Council grant to Siqi Zhao under the supervision of Tom Jilbert. Additional funding is sourced in collaboration with the Lake Vesijärvi Foundation and Länsi Uudenmaan Vesi ja Ympäristö ry.

For more details contact Assistant Professor Tom Jilbert.

2018-2023: Sedimentary trace metals: unlocking the archives of coastal marine hypoxia

"Dead zones" are areas of the ocean where the water contains no oxygen, and most marine organisms cannot survive. These zones are increasingly common in coastal areas of Europe, including the Baltic Sea, where inputs of waste water and agricultural runoff have caused widespread eutrophication. It is important to know how dead zones have expanded in the past, in order to estimate sustainable inputs of nutrients for the future. Unfortunately, many coastal areas have not been monitored sufficiently well to provide this information. This project will fill in these gaps by studying sediment cores from coastal regions of Europe. Using advanced chemical analyses, the project will focus on "trace" metals in sediments, which provide a natural archive of the size of dead zones in the past. New information about the past expansion of dead zones will be used to improve existing models of nutrient cycling in the Baltic Sea.

This project is funded by an Academy of Finland Research Fellowship to Tom Jilbert. The project is a collaboration with Bo Gustafsson, Christoph Humborg and Alf Norkko of Marine Ecosystems Research Group and Stockholm University, Sweden; Caroline Slomp of Utrecht University, Netherlands; and Helena Filipsson of Lund University, Sweden.

For more details contact Assistant Professor Tom Jilbert.

2019- 2022: BaSeMent: Baltic Sea monitoring on microplastic sedimentation processes

Microplastics are recognized as a risk for environment and health, however current understanding on processes controlling the faith of plastic particles in aquatic environments are poorly understood as is the flux rate of these pollutants to the natural waters. Microplastics are reported from sediments of coastal regions to the remote deep basins of the ocean, however, so far no flux rates with respect of time is reported. This project will increase our knowledge on spatially and temporally varying flux rates in coastal estuarine zones. As the deposition of any material transported to aquatic environment is controlled by the seasonal changes, climate, hydrology, catchment and anthropogenic actions, the same processes are expected to control microplastics entering to natural waters. However, as a heterogenic group of different physical and chemical characteristics the processes controlling the faith of each synthetic polymer type must be investigated and understood individually.

This project is funded by the Academy of Finland.

For more details contact Saija Saarni.



2020-2021: Elucidating seasonal substrate limitation of benthic nitrate reduction in the coastal Baltic Sea

The reduction of bioavailable nitrate to non-bioavailable di-nitrogen gas via denitrification is an important ecosystem service particularly in eutrophic coastal areas. At the Baltic Sea coast, benthic denitrification displays a pronounced seasonality with contrasting patterns between photic and aphotic sediments, which is particularly obvious in early spring when process activity is limited in aphotic sediments only. This limitation has been attributed to seasonally low availability of labile organic carbon, the electron donor in heterotrophic denitrification; yet, it remains elusive how labile organic carbon can become limiting in a eutrophic system such as the Baltic coastal zone.

Hence, in this project I investigate the link between organic carbon composition and heterotrophic benthic nitrate reduction processes (denitrification and dissimilatory nitrate reduction to ammonium) to identify key compounds of organic carbon preferentially used in nitrate reduction. I do this by characterizing the biochemical composition of in situ organic carbon in both photic and aphotic Baltic coastal sediments before, during and after the spring bloom, while concurrently quantifying benthic nitrate reduction rates and  applying substrate addition experiments. The methodological approach includes both established and cutting-edge analysis techniques, such as isotope pairing techniques and Fourier-transform ion cyclotron resonance mass spectrometry. The results obtained will render it possible to better understand the observed substrate limitation and to establish a more distinct view on the ʻlabilityʼ characteristics of organic carbon.

This project is funded by the Walter and Andrée de Nottbeck Foundation and is carried out in collaboration with Mikko Kiljunen (University of Jyväskylä), Boris Koch (Alfred-Wegener-Institute Bremerhaven, Germany), Eero Asmala (University of Helsinki), and Joanna and Alf Norkko (Tvärminne Zoological Station).

For more details contact Dana Hellemann.

2016-2020: Phosphorus burial in Lake Vesijärvi

In this project we study the mechanisms by which the key nutrient element phosphorus is buried in the sediments of Vesijärvi, a eutrophied lake close to Lahti, Finland. Sedimentary phosphorus burial is a critical natural process that lowers the content of phosphorus in the lake water, and therefore improves the water quality. Many eutrophic lakes worldwide are experiencing strong changes in phosphorus cycling due to anthropogenic activities, hence understanding the natural processes influencing phosphorus burial in these systems is of global importance.

There are many biogeochemical processes in lake sediments that influence the cycling of phosphorus. These include the decay of organic matter such as algae accumulating on the lake bed, and the precipitation of phosphate minerals in the sediments. Some processes release phosphorus, while others retain and capture it.  Environmental conditions such as oxygen, pH and the presence of benthic organisms all influence the balance of these processes, and hence the amount of phosphorus that is eventually buried in the sediments.

Using sediment and pore water geochemical analyses, we study the rates of biogeochemical processes in the sediments to determine their influence on the burial of phosphorus. In turn, we couple our results to existing nutrient budgets and models of biogeochemical cycling in the lake itself. A key goal is to estimate the timescale of the future recovery from eutrophication in the lake, and to integrate the results into planning management strategies. The work is carried out in collaboration with the Lake Vesijärvi Foundation, City of Lahti Environment Services, and University of Turku.

This project is funded by the Faculty of Biological and Environmental Sciences as part of the Tenure Track first phase of Tom Jilbert.

For more details contact Assistant Professor Tom Jilbert.



2016-2020: Iron and manganese cycling in boreal estuaries

In this project we study the processes influencing iron and manganese cycling in boreal estuaries. Iron and manganese are two commonly occurring metals that take part in microbially mediated chemical reactions.  As such, they are an important source of energy for microorganisms in a range of envrionments. Estuaries are transitional aquatic systems with strong gradients of salinity, oxygen and pH conditions, which influence the cycling of iron and manganese and hence their potential role in microbial processes. 

Eutrophication, land use change and climate change are causing major disruptions in biogeochemical cycling in boreal estuaries today. In particular, the rapid accumulation of organic materials in estuarine sediments has stimulated microbial processes such as methanogenesis and altered the oxygen balance of coastal waters. Using geochemical analyses of both water column and sediments, we study the effects of these changes on the cycling of iron and manganese.

The project is closely connected to "Biogeochemical links between climate change and eutrophication in the Baltic Sea".

This project is funded by the Faculty of Biological and Environmental Sciences as part of the Tenure Track first phase of Tom Jilbert.

For more details contact Assistant Professor Tom Jilbert.

2014-2019: Microbiology: the missing link in benthic foraminiferal ecology

The discovery of nitrate accumulation and denitrification in benthic foraminifera challenges our current understanding of the physiology of these common marine eukaryotes. Deeper investigation of foraminiferal ecology, and its impact on benthic carbon and nutrient cycling, are required to provide a comprehensive understanding of modern-day biogeochemical processes in surface sediments. Understanding of the role of potential endosymbionts in foraminiferal carbon and nitrogen processing is currently also lacking and must be critically assessed in relation to sediment biogeochemical processes.

This Academy of Finland funded project focusses on developing a mechanistic understanding of interactions between benthic foraminifera, their potential endobiont community and the sediment microbial community in the context of sediment carbon and nitrogen dynamics. The project applies state-of-the-art molecular approaches, including Next Generation Sequencing, to study foraminiferal endobiont communities, and their direct links with the ambient sediment bacterial community and biogeochemical processes. In addition, trophic interactions between foraminifera and other sedimentary (micro-)organisms are assessed in the context of benthic food webs and carbon transfer.

For more details contact Academy Research Fellow Karoliina Koho

2018-2019: Optimizing the efficiency of the Kymijärvi hypolimnetic withdrawal filter

Hypolimnetic withdrawal is a relatively new technique for the restoration of eutrophic lakes. In this method, nutrient-rich deep waters are extracted from lakes, thereby reducing the overall nutrient concentrations and improving the water quality. It is regarded as a relatively low-impact solution to eutrophication, in contrast to for example dredging or the addition of chemicals for phosphorus retention. However, one hindrance to the development of effective hypolimneitc withdrawal systems is the fact that the lake level is lowered due to the extraction of deep waters. Also, the extracted nutrients are typically released back into the envrionment downstream.

A new project funded by the Finnish Ministry of the Environment (PI. Prof. Jukka Horppila) will construct a pilot hypolimnetic withdrawal and treatment system (HWTS) at Kymijärvi in Lahti, Finland in 2018. In the HWTS, the extracted deep water will be processed to remove phosphorus before being returned to the lake, hence capturing this key nutrient and maintaining the water level.

In this related project, we test the efficiency of various filter materials in the HWTS. We employ a range of geochemical analyses to determine the mineral phases in which phosphorus is retained filter beds of varying composition, for future optimization of the technology.

This project is funded by a grant from Maa ja Vesitekniikan Tuki (MVTT) to Tom Jilbert.

For more details contact Assistant Professor Tom Jilbert.

2013-2018: Biogeochemical links between climate change and eutrophication in the Baltic Sea

Climate change and eutrophication are two major stressors which deteriorate the health of the Baltic Sea, in particular by driving the expansion of low-oxygen conditions. However, the feedbacks between climate change and eutrophication have remained largely unexplored. The research on greenhouse gases has mainly focused on concentrations and sea-air interface fluxes, with hardly any data gathered on the actual microbial processes that in the end construct these fluxes, or on the factors controlling the production/consumption balance. In this project we evaluate the Baltic Sea sources and sinks of two essential greenhouse gases, nitrous oxide and methane. We focus on the factors controlling the balance between production and consumption of the gases, hypothesized to link directly to the mineralisation processes in which these gases are formed. Mineralisation, in turn, affects and is affected by eutrophication and climate change.

Nitrous oxide sources and sinks are related to overall nitrogen mineralization. The microbial processes denitrification and anammox remove nitrogen from the water ecosystem, mitigating eutrophication and reducing nitrous oxide to harmless dinitrogen gas. During oxygen stress, caused by climate change and eutrophication, nitrous oxide production in both nitrification and denitrification increases. When oxygen conditions deteriorate further, the nitrogen removal ecosystem service is partly or completely replaced by dissimilatory nitrate reduction to ammonium, which recycles, instead of removing, nitrogen in the water ecosystem. Decreasing nitrogen removal further boosts eutrophication, and increasing nitrous oxide production enhances climate change.

Methane source and sink balance changes with growing organic loading, caused by increasing algal biomass (due to eutrophication) and higher runoff (inflicted by climate change). The growing load intensifies methanogenesis and deteriorates the oxygen status, leading to weakening of both aerobic and anaerobic methane oxidation. Increasing production and decreasing consumption both enhance the fluxes towards atmosphere.

In this Academy of Finland funded project, we measure processes in coastal sediments (including sandy sediments) and pelagic redoxclines that are hot spots of mineralization. Samples are collected at Tvärminne Zoological Station, Finland (coastal sediments) and on international research cruises (coastal sediments in southern Baltic, redoxclines). Field data is supplemented with experimental work. We use stable isotope and radiotracer techniques to test the stability of the greenhouse gas sources and sinks in the alternating oxygen conditions. The relationships between oxygen, nitrogen removal and greenhouse gas production will be implemented in the biogeochemical components of large ecosystem models, increasing their prognostic accuracy. Such models are powerful tools in creating scenarios for the development of the Baltic Sea in the changing environment.

For more details contact Academy Research Fellow Susanna Hietanen

2016-2018: Next generation tool for environmental assessment

This Academy of Finland funded Key Project aims to develop a new, economically sound tool for ecosystem assessment, which is able to deliver extensive information on biodiversity and environmental status of marine environments. Marine dead zones, areas of seafloor devoid of animal life, are expanding as a result of increased anthropogenic nutrient loading in coastal environments. Furthermore direct anthropogenic impacts such as trace metal pollution are observed in some areas. As a consequence, there is a growing demand for assessment of human impacts on marine habitats and to provide important information to decision and policy makers. However, the traditional monitoring approaches are very labor intensive, and are under financial pressure to become more cost-effective. To respond to this need, the project will develop a monitoring tool based on genetic sequencing of sediment samples. The project has a high affinity to environmental agencies such as the Finnish Environment Institute (SYKE), as well as industry and environmental consultancies, who are interested in quantification and monitoring of ecosystem health in a cost-effective manner.

For more details contact Academy Research Fellow Karoliina Koho

2014-2017: BONUS COCOA: Nutrient cocktails in the coastal zone of the Baltic Sea

The BONUS COCOA consortium, funded byt the BONUS EEIG+ (EU and national sources) includes 14 institutes representing 7 countries around the Baltic. The objective of BONUS COCOA is to identify major pathways of nutrients and organic material in various coastal ecosystems around the Baltic Sea. Nutrients and organic matter are transformed and retained along the land-sea continuum, and BONUS COCOA will quantify how physical and chemical conditions as well as the biological components of the coastal zone affect the biogeochemical processes. We will investigate if transformation and retention processes may have changed over time, and how coastal ecosystem services are affected by these changes. As a result, BONUS COCOA will outline management responses to improve the ecological status for coastal ecosystems degraded by eutrophication.

For more details, regarding our share of BONUS COCOA work, contact Academy Research fellow Susanna Hietanen.

Read more about BONUS COCOA on the coordinator homepage, BONUS homepage, and on its blog page.

2011-2016: Nitrogen processes in the water column of the Baltic Sea

The Baltic Sea is a shallow inland sea suffering from heavy anthropogenic pressure. The large cyanobacterial blooms are a visible demonstration of the intense eutrophication of the Sea and have raised public interest in the protection of the Baltic Sea and triggered a heated discussion on the measures that should be taken to counteract eutrophication, such as nitrogen versus phosphorus versus nitrogen and phosphorus removal from the waste waters. A vicious circle seems to operate in the Baltic Sea, with internal feedbacks boosting the eutrophication. A key factor is the effect increasing hypoxia has on the biogeochemical cycles of the nutrients. Phosphorus is released from the sediments during anoxic spells, but the effect on nitrogen is still uncertain. While the nitrogen removing processes, denitrification and anammox, are both anaerobic, they rely on an aerobic nitrification process for substrates. A significant negative relationship exists between the total dissolved inorganic nitrogen and the volume of hypoxic water in the Baltic Sea, indicating enhanced nitrogen removal in hypoxic conditions. In this Academy of Finland funded project, to evaluate the role of natural nitrogen removal in current conditions in the Baltic Sea we measure in situ rates of nitrification and nitrogen removal processes in the water column on research cruises. We use stable isotope techniques for measuring denitrification and anammox and regulation of these. We use several approaches to quantify in situ nitrification, including stable isotope ammonium oxidation coupled to denitrifier-based NO3 analysis and specific inhibitor use. To clarify the environmental conditions needed for the efficient co-operation of these processes we will do experimental research, and use environmental databases to map the actual volume of water in which such conditions exist. The information gained will be used to improve the accuracy of the biogeochemical components of large ecosystem models such as Nest (Baltic Nest Institute, Stockholm Resilience Centre) and RCO-SCOBI (Swedish Meteorological and Hydrological Institute). That, in turn, will reduce the uncertainty in the models used for calculating the costs and effects of possible nutrient reduction measures. Additionally, models with a better description of the factors regulating nitrogen removal can be used to predict how the self-purification (nitrogen removal) capacity adjusts to changes in the ecosystem, such as climate change or increase or decrease in nutrient loading.

For more details contact Academy Research Fellow Susanna Hietanen