Doctoral hat in the snow

Thesis defence in the University of Oulu

Friday, March 26, 2021

Doctoral Candidate

Master of Science Marja Lindholm

Faculty and research unit

University of Oulu Graduate School, Faculty of Science, The Geography Research Unit
+358 294 48 0000

Field of study

Geography

Date and time of the thesis defence

26.3.2021 15:00

Place of the thesis defence

Remote connection: https://oulu.zoom.us/j/63020701528

Topic of the dissertation

Spatial and temporal trends in different dimensions of macrophyte biodiversity in boreal lakes

Opponent

Associate Professor Sapna Sharma, York University

Custos

Adjunct professor Janne Alahuhta, University of Oulu

Surprisingly few changes in lake vegetation over the past 70 years

According to the doctoral thesis of geographer Marja Lindholm, aquatic vegetation in the study lakes in Tampere region is not homogenised over time, as has been observed elsewhere in the world.

Global change threatens the vegetation of lakes. This is alarming as aquatic plants are vital to the well-being of lakes. In the doctoral thesis carried out at the University of Oulu, spatial and temporal changes in the aquatic plants of small lakes during the last seventy years were investigated. The changes were studied by using vegetation surveys carried out in four different decades in lakes near the city of Tampere and by surveying the same lakes again in summer 2017.

“Surprisingly little has happened in the presence and absence of aquatic plants in the lakes. Globally, the pressure of human activities in the research area has not been very high. That is why the changes would be probably seen in the abundances of species, not in what species grow in the lakes”, Lindholm says.

According to the results of Lindholm’s doctoral thesis, the location of the lakes and water pH are affecting how aquatic vegetation has varied between lakes. Environmental changes, such as the increase in urbanisation and drainage ditching that have taken place over the decades have caused species extinctions and dispersal at the individual lake level. For example, species that grow submerged or floating in the water have benefitted from declining of agriculture and nutrient load in the littoral zone of the lakes.

The results of the doctoral thesis show that environmental changes through decades, such as declining of agriculture, are related to functional diversity of aquatic plant communities to some extent. Functional diversity was studied through functional traits of species, such as size and growth form. According to Lindholm, the functional role of aquatic plants would be important to take into account in protection and restoration of lakes.

Lindholm's doctoral thesis shows how important long-term monitoring is in biodiversity research. Therefore, there is a need to continue ongoing monitoring programs and conduct more re-surveys of historical data, to be able to estimates the impacts of human activities on temporal variation of biodiversity.

 

Dissertation

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Last updated: 18.3.2021