Drivers of change in chlorophyll fluorescence data (RED)

Local meteorological conditions play a major role in controlling the concentration and photosynthetic efficiency of phytoplankton in lakes. Photosynthesis is dependent on light energy from the sun, specifically on photosynthetically active radiation (PAR), 400nm - 700nm. However, an excess of light energy can result in the damage to the plant and algal photosynthetic pathways. In lakes, the level of PAR to which phytoplankton are exposed is a function not only of irradiance levels, but also of physical conditions in the lake, which are also affected by local weather. We used high resolution chlorophyll fluorescence data to give us two metrics: maximum night-time fluorescence, a proxy for algal biomass, and the ratio between this value and the subsequent mid-day fluorescence, which we are using as an index for the degree of light-induced stress. The relationship between these two metrics and potential climatic and lake physical drivers was quantified for 17 lakes using a general additive mixed modelling approach. In addition, the strength and direction of the relationships were assessed using seasonally decomposed data.