G5 Doctoral dissertation (article)
The impact of optical properties on spectral light availability and biomass of phytoplankton in boreal lakes (2024)
Veden valo-ominaisuuksien vaikutukset kasviplanktonin spektraaliseen valosaatavuuteen ja biomassaan boreaalisissa järvissä

Ahonen, S. (2024). The impact of optical properties on spectral light availability and biomass of phytoplankton in boreal lakes [Doctoral dissertation]. University of Jyväskylä. JYU Dissertations, 781. https://urn.fi/URN:ISBN:978-952-86-0150-0

JYU authors or editors

Publication details

All authors or editors: Ahonen, Salla

eISBN: 978-952-86-0150-0

Journal or series: JYU Dissertations

eISSN: 2489-9003

Publication year: 2024

Number in series: 781

Number of pages in the book: 1 verkkoaineisto (57 sivua, 23 sivua useina numerointijaksoina, 3 numeroimatonta sivua)

Publisher: University of Jyväskylä

Place of Publication: Jyväskylä

Publication country: Finland

Publication language: English

Persistent website address: https://urn.fi/URN:ISBN:978-952-86-0150-0

Publication open access: Openly available

Publication channel open access: Open Access channel

Abstract

Many boreal lakes have a high content of chromophoric dissolved organic matter (CDOM), which affects light attenuation and thermal structure of water columns, with poorly known consequences on phytoplankton that are essential energy source in aquatic food webs. In this thesis, I used water samples from 128 boreal Finnish lakes and water column monitoring of one lake to study the impact of CDOM on the spectral underwater light field and responses of phytoplankton to the changes in light availability and mixed layer. In most study lakes, CDOM was the highest light absorbing component and strongly controlled the attenuation of solar radiation in water columns. Higher CDOM content in lakes was associated to shallower euphotic layer and a shift in the most available waveband towards red waveband of visible light. Consequently, red light covered > 50 % of the total absorption of visible light by phytoplankton in most study lakes. There was no photoacclimation through the regulation of chlorophyll a (Chla) content by phytoplankton in response to the lower light availability in high-CDOM lakes, but both Chla concentration and phytoplankton biomass were higher in lakes with higher CDOM. A browning scenario assuming increases in both CDOM and nutrients decreased the fraction of light absorbed by phytoplankton but only moderately, presumably due to a compensatory effect of nutrients by promoting higher phytoplankton biomass. In the daily monitoring of Lake Jyväsjärvi during summer stratification, phytoplankton biomass was higher on windy and colder days when mixed layer was deeper. Improving light availability increased the biomass only when light levels were low. Collectively, these findings suggest that despite the strong control of light field by CDOM, phytoplankton biomass can be high even in CDOM-rich lakes, likely owing to higher nutrient export to the lakes. Hence, nutrient availability appears to have a key role in limiting phytoplankton biomass in boreal non-eutrophic lakes. A shallow mixed layer due to a combined effect of browning and climate warming have the potential to limit phytoplankton biomass in stratified lakes during summer heatwave periods, if nutrient availability is low.

Keywords: boreal zone; lakes; light (electromagnetic radiation); absorption; organic material; humus; climate changes; plankton; biomass (ecology); doctoral dissertations

Free keywords: CDOM; browning; climate change; mixed layer; phytoplankton; spectral absorption

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