Coastal marine environments are critical transitional zones between the continents and the oceans. They are also strongly impacted by human activities on land and at sea. Understanding the cycling of carbon, nutrients and other elements in coastal environments means studying inputs from land, uptake in and release from biomass, and burial in sediments. Elements are transformed by numerous processes whose interactions eventually control water quality and the health of coastal ecosystems. Our research focuses on biogeochemical processes in sediments, where organic matter is broken down by microbes, releasing nutrients and methane.
Our group participates in the CoastClim Centre, a collaboration between University of Helsinki and Stockholm University (primary funding Erkko Foundation, Academy of Finland, Swedish Research Council). CoastClim brings together scientists from various disciplines to study links between biodiversity and climate change in the coastal zone of the Baltic Sea. Carbon cycling is a critical theme of the research; carbon can be stored in coastal ecosystems in the form of blue carbon biomass and associated sediments, but can also be released to the atmosphere as carbon dioxide and methane, powerful greenhouse gases. Our group uses a range of inorganic and organic geochemical approaches to study the sources of carbon to sediments in coastal areas and the contribution of these sources to long-term carbon burial. This includes studying the recycling of organic matter in sediments and production of methane.
Examples of recent publications:
Myllykangas et al., Estuaries and Coasts 2020
Myllykangas et al., Biogeochemistry 2020
Jilbert et al., Frontiers in Earth Science 2021
Through an Academy of Finland Research Fellowship to Tom Jilbert (2018-2023), the group studies the accumulation of trace metals (e.g. molybdenum, uranium, cadmium, lead, tin, zinc) in coastal sediments. These metals can be used as indicators of human impacts and hence to provide information on past environmental conditions in areas where monitoring records are sparse. Some trace metals from seawater can become naturally enriched in sediments under anoxic conditions, hence in areas of human-induced deoxygenation, sediment trace metal contents provide a record of historical oxygen concentrations. At the same time, other metals provide a record of direct pollution inputs to coastal systems. We study the mechanisms of enrichment of each metal and historical changes in their accumulation. This work is mainly focused on the Baltic Sea, Black Sea and other human impacted areas of the European coastal zone.
Examples of recent publications:
Jokinen et al., Science of the Total Environment 2020
Jilbert et al., Geophysical Research Letters 2021
Paul et al., Chemical Geology 2023
Freshwater systems worldwide are under intense pressure from human activities, including nutrient loading, industrial pollution and overfishing. Eutrophication is the dominant stressor in most lake ecosystems, caused by inputs of nitrogen and phosphorus from populated catchment areas. Eutrophication is exacerbated by processes in sediments that retain and recycle nutrients within the aquatic system, leading to so-called internal loading. Many lake ecosystems are now the subject of attempts to restore good water quality and usability of ecosystem services. At the same time, the importance of lakes as carbon sinks is being increasingly recognized. Our research focuses on understanding the timescales of internal loading following eutrophication, developing practical approaches to reduce sediment phosphorus pools, and understanding the role of lakes in carbon burial.
Through funding from a range of sources (Vesijärvi Foundation, LUVY, Hyvinkään kaupunki) the group studies the long-term accumulation and recycling of phosphorus in eutrophic lakes. Phosphorus is a key limiting nutrient for primary production and its accumulation in lake sediments is the main cause of internal loading. A host of microbial and geochemical processes control what happens to phosphorus after its has accumulated in the sediments, including release from organic matter, uptake into sedimentary minerals, and permanent burial. The relative importance of these processes vary widely between different lake systems, impacting on the timeline of the recovery from eutrophication. Our research aims to determine the role of additional elements such as iron and manganese in regulating the burial rates and phases of phosphorus, as well as the role of oxygen conditions in controlling internal loading.
Examples of recent publications:
Jilbert et al., Hydrobiologia 2020a
Jilbert & Zhao, Kytäjärvi project report 2021 (in Finnish)
Hypolimnetic withdrawal is a restoration technique in which phosphorus is removed from lakes through pumping of nutrient-rich deep water. In a new application currently being tested in Lahti, Finland (combined funding from Finnish Environment Ministry, Hämeen ELY-keskus, Maa ja vesitekniikan tuki, Renlund Foundation), a closed circuit version of the technique allows phosphorus to be extracted by filtration. Our group studies optimization of the pumping and filtration system for maximum efficiency of phosphorus extraction. This includes studying seasonal cycles of phosphorus dynamics in the lake itself, as well as the oxidation and precipitation processes occurring in the filtration systems.
Examples of recent publications:
Jilbert et al., Hydrobiologia 2020b
Silvonen et al., Science of the Total Environment 2021
Silvonen et al., Water Research 2022
Boreal lake sediments may be a hitherto underestimated long-term sink for carbon. Organic matter from both autochthonous (in-lake) and allochthonous (external) sources accumulates in lake sediments and may be sequestered (buried) on geological timescales. Similarly to forests and soils, this carbon sink function of lakes is an important consideration for authorities planning carbon-neutral management strategies on various scales. In shallow boreal lakes, carbon can accumulate in near-shore areas associated with macrophyte stands, as well as open water areas where fine-grained sediments are focused into bathymetric depressions. In the new project "Blue Lakes" funded by the EU Recovery and Resilience Facility via the Academy of Finland, our group will quantify carbon sequestration in these environments. The work is a collaboration with the Geological Survey of Finland (GTK) and Finnish Environment Institute (SYKE), and will include development of the VEMALA catchment model to simulate carbon cycling in Finnish aquatic systems.