Andmebaasi logo

Sirvi Autor "Tuvikene, Arvo (advisor)" järgi

Nüüd näidatakse 1 - 2 2
  • Pisipilt
    Kirje
    How phytoplankton pigments reflect historical and contempoarary status of large shallow lakes?
    (Eesti Maaülikool, 2012) Freiberg, Rene; Tuvikene, Arvo (advisor); Tõnno, Ilmar (advisor)
    Phytoplankton is the most important primary producer in the aquatic ecosystems and account for half of all photosynthetic activity on earth, thus creating the base for most aquatic food chains. It also plays key role in the oxygen- carbon dioxide balance of the atmosphere and helping to ameliorate green-house gases, by removing nearly a third of the anthropogenic carbon released to the atmosphere. In Europe, the EU has implemented the Water Framework Directive, which is focused on assessing water quality in all waterbodies spanning from ground water to coastal marine waters. The directive requires that undisturbed or reference conditions should be defined for these aquatic environments. Monitoring records rarely go back more than a few decades and in order to define reference conditions other approaches are needed. Phytoplankton pigments that capture and transform light energy are important source of historical information, because if buried in sediments they preserve for centuries and can give information about algal communities in the past. As opposed to deep lakes, the use of phytoplankton pigments in palaeolimnological studies is complicated, because constant resuspension of sediments disturbs the formation of clear sediment archives. This dissertation is focused on phytoplankton pigment analysis of two interconnected large shallow lakes Võrtsjärv and Peipsi. The first issue that is covered is how the pigments in the upper sediment layer of the lake Võrtsjärv follow the annual dynamics of phytoplankton pigments in the water column. Thereafter eutrophication history and palaeolimnological aspects of these two lakes on the 20th century are compared in a multi-proxy studies. As a result of contemporary pigment flux and multi-proxy palaeolimnological studies of lakes Peipsi and Võrtsjärv we can conclude that according to fossil pigments and other palaeoindicators three periods in the evolution of lakes Peipsi and Võrtsjärv can be distinguished on the 20th century: from 1900 to 1950s, from 1950s to 1990s and from 1990s to 2000. Palaeoindicators show that eutrophication of both lakes started to increase rapidly in 1950s. This is also supported by the monitoring data that is available. Although some palaeoindicators peaked in 1970s no significant recovery to more natural state was observed. Results do show, that phytoplankton pigments can be used in multi-proxy palaeolimnological studies to track changes in phytoplankton communities and work out reference conditions even in large shallow lakes.
  • Pisipilt
    Kirje
    Non-native species invasion strategies and effects on freshwater native communities
    (Estonian University of Life Sciences, 2025) Teesalu, Paul; Ercoli, Fabio (advisor); Tuvikene, Arvo (advisor); Institute of Agricultural and Environmental Sciences; Tricarico, Elena (opponent)
    ABSTRACT. The spread of invasive species has been forecasted to increase, particularly in freshwater ecosystems due to anthropogenic and environmental changes taking place at increasing rates. Invasive species generally adapt quickly to new environments, have high reproductive rates and can tolerate a wide range of conditions. This thesis studied three invasive species in the Narva reservoir area and found that their success is linked to dietary flexibility, behaviour, and tolerance to temperature changes. The Amur sleeper fish (Percottus glenii) can inhabit various waterbodies, for example, we found it in a warm-water channel, a large reservoir and a small pond. The Amur sleeper demonstrated great dietary plasticity, or the ability to consume a wide range of prey items. As Amur sleeper individuals grew, their diet shifted from a benthivorous diet to a piscivorous diet. The small amphipod Gmelinoides fasciatus, which has outcompeted and displaced native gammarid Gammarus lacustris in Lake Peipsi, exhibits superior predator avoidance and shows a more pronounced behavioural response to predators than its native counterpart, increasing its survivability. Marbled crayfish (Procambarus fallax virginalis) can shift from a protein rich macroinvertebrate based diet to a macrophyte based diet, indicating great dietary plasticity. Additionally, marbled crayfish, despite being considered a warm-water species, could withstand a wide range of water temperatures ranging from 0-30 °C over an extended period at our study site. During the implementation of invasive species management programs, it is important to consider their environmental tolerance, dietary adaptability and behavioural traits. As conditions change in our freshwater lakes and reservoirs, it is likely that invasive species will continue to be a problem, highlighting the need to understand and manage their spread to protect native freshwater ecosystems.