Timo Kairesalo

Foodweb structure and functioning
Recognizing and quantifying the links between terrestrial (watershed), littoral, benthic and pelagic subsystems and food webs is of crucial importance for a better understanding of the complex interactions and community structure in freshwater ecosystems. For instance, through their ontogeny fish occupy and use pelagic, benthic and littoral habitats. In this way, fish may be considered to be important spatial vectors. As they develop and move through various habitats, their top-down effects shift from one food web to another. On the other hand, watershed area and littoral communities are in key positions when considering the responses of the high latitude lacustrine ecosystems to the climate change, i.e. elevated CO 2 and temperature with more intensive and irregular drainage from surrounding terrestrial areas and with shorter ice- and snow-covered winter periods in water bodies.
Spatial and temporal scales
Functional relationships and productivity of freshwater communities are regulated by the dynamics of their physical, chemical and biotic environments and their spatio-temporal scales. For instance, biological processes in relation to generation time and life-time range of the aquatic life-form in question, together with relevant physical processes (hydrodynamics) which operate at different spatio-temporal scales, are essential to know when considering key mechanisms behind the observed patterns in freshwater systems (e.g. community structure and periodicity, habitat patchiness, species diversity, vertical stratification).
Disturbance vs. recovery and restoration
Effluent waters from urban and rural areas contain nutrients and ‘natural’ organic material but also often a myriad of different xenobiotic chemicals which may cause disturbance in the functioning of recipient aquatic ecosystems. Their impacts should be understood in order to make relevant interpretations of the observed dynamics within the foob webs. For instance, sewage effluent contains heavy metals from industrial sources as well as nutrients that cause eutrophication. The heavy metals are present in the sediments of eutrophicated lakes but are normally not easily mobilised under turbid, phytoplankton dominating conditions. Restored, clear water conditions favour submerged plants which colonise deeper sediment areas. The plants exploit the substances contained in sediments through their roots and may accumulate and transfer the heavy metals back to the open water and to the littoral food webs. On the other hand, the capacity of littoral and benthic habitats for handling the incoming pollution load is still poorly known and factors affecting the biorestoration potential of the lakeshore-littoral biota should be understood better.

TIMO KAIRESALO Professor in Freshwater Ecology University of Helsinki Department of Ecological and Environmental Sciences Timo.Kairesalo(at)helsinki.fi

Major fields of research and teaching Selected Publications

Major fields of research and teaching In my research and teaching in Freshwater Ecology I would like to highlight three major fields of study, (1) Foodweb structure and functioning; (2) Spatial and temporal scales; and (3) Disturbance vs. recovery and restoration
Foodweb structure and functioning Recognizing and quantifying the links between terrestrial (watershed), littoral, benthic and pelagic subsystems and food webs is of crucial importance for a better understanding of the complex interactions and community structure in freshwater ecosystems. For instance, through their ontogeny fish occupy and use pelagic, benthic and littoral habitats. In this way, fish may be considered to be important spatial vectors. As they develop and move through various habitats, their top-down effects shift from one food web to another. On the other hand, watershed area and littoral communities are in key positions when considering the responses of the high latitude lacustrine ecosystems to the climate change, i.e. elevated CO 2 and temperature with more intensive and irregular drainage from surrounding terrestrial areas and with shorter ice- and snow-covered winter periods in water bodies. *Spatial and temporal scales* Functional relationships and productivity of freshwater communities are regulated by the dynamics of their physical, chemical and biotic environments and their spatio-temporal scales. For instance, biological processes in relation to generation time and life-time range of the aquatic life-form in question, together with relevant physical processes (hydrodynamics) which operate at different spatio-temporal scales, are essential to know when considering key mechanisms behind the observed patterns in freshwater systems (e.g. community structure and periodicity, habitat patchiness, species diversity, vertical stratification). *Disturbance vs. recovery and restoration* Effluent waters from urban and rural areas contain nutrients and ‘natural’ organic material but also often a myriad of different xenobiotic chemicals which may cause disturbance in the functioning of recipient aquatic ecosystems. Their impacts should be understood in order to make relevant interpretations of the observed dynamics within the foob webs. For instance, sewage effluent contains heavy metals from industrial sources as well as nutrients that cause eutrophication. The heavy metals are present in the sediments of eutrophicated lakes but are normally not easily mobilised under turbid, phytoplankton dominating conditions. Restored, clear water conditions favour submerged plants which colonise deeper sediment areas. The plants exploit the substances contained in sediments through their roots and may accumulate and transfer the heavy metals back to the open water and to the littoral food webs. On the other hand, the capacity of littoral and benthic habitats for handling the incoming pollution load is still poorly known and factors affecting the biorestoration potential of the lakeshore-littoral biota should be understood better.
In all, restoration and management of freshwater ecosystems will demand professionals who are broadly trained to view water bodies as systems that are integrated with the surrounding landscape and in which biological, physical and chemical processes are interrelated.