Funded by LBAYS: The effects of water color on the spectral composition of light

Researcher Kari Sainio investigates brownification in the Humic Load Indicators project, aiming to identify key indicators for understanding the process. His focus is on how water color impacts the spectral composition of light within this research framework.

Especially in boreal region lakes, gradual and long-term increase of water color has been recognized. This phenomenon is called brownification and it has major impacts on freshwater ecosystems. Changes in thermal stratification, volume of the productive layer, as well as species composition and behavior of biotic communities have been identified to be caused by the brownification of lakes. Albeit the diverse and multidimensional impacts of brownification, the water framework directive of the European Union does not recognize water color as an ecological state parameter of waterbodies. Land use changes, like forest and peatland ditching in catchment areas, are known to cause elevations of water color in waterbodies. It is important to better understand and identify the widespread ecological impacts of brownification, for better policy making and protection of the ecological states of our lakes.

I started my master thesis research in the summer of 2022 in the Humic Load Indicators project, that aims to identify and develop indicators of brownification. In my thesis, I examine the effects of water color on the spectral composition of light. It is known that shorter wavelengths of photosynthetically active radiation are more intensely attenuated in the water column when the elevation of water color occurs. Water color also affects the chlorophyll a:b ratio in primary producers such as macrophytes.

Exploring light quality variations in differently colored lakes for a master's thesis on Nuphar lutea chlorophyll content

For my masters thesis research, we selected twelve differently colored lakes from a color value range of 20 mg Pt/l to 350 mg Pt/l. The goal was to study the light quality variations along a water colour gradient of lakes, and to find out the possible effects of light quality on the chlorophyll content of the yellow water lily (Nuphar lutea).

We measured the attenuation of different light wavelengths from each lake from the same locations where Nuphar lutea samples were gathered. The spectral composition of light was measured by a Ramses radiometric spectrometer from the surface to the depth of 50 cm, both down- and upwelling light was measured. After data collection we arranged and familiarized ourselves with the huge amount of data that we had collected. It appears that the quality of light correlates with the a:b ratio of Nuphar lutea. The finalization and interpretation of results is underway.

So far the process of learning of how to do research has been rewarding. New ideas and research avenues are widespread and open in my mind.  The phenomenon of photosynthesis as an interface between the abiotic and biotic world is fascinating. The carbon sequestration of primary producers in lakes and the impact that brownification may have on the process is a topic of interest.

Life at the station

During the field research we stayed at the Lammi Biological Station (LBS). The field work was mainly done in Evo area. It was great to get to the stations after a long day of fieldwork. Getting in to a clean room, showering in a nice shower, and laying down to a nice bed was wonderful. I want to thank the good people of LBS and the Environmental Research Foundation of Lammi Biological Station for the warm-hearted accommodation and for the grant that made this work possible.

More research funded by LBAYS