Seasonal fluctuations in pigment content of macrophytes: implications for monitoring brownification

Abstract

Seasonal variations of floating-leaved macrophyte Nuphar lutea chlorophyll content were studied in lakes with different water quality. The aim was to investigate whether chlorophyll content of the plants could be used as an indicator of brownification. The relationship between chlorophyll a and b (CHL a:b) of the petioles decreased with increasing water colour. The relationship between CHL a:b and turbidity was less clear. The sum concentration of chlorophyll a and b of the petioles did not respond to water colour consistently. The strong effect of water colour on petiole CHL a:b was probably due to the effect of colour on the attenuation of short-wavelength light. CHL b absorbs short-wavelength light more effectively than CHL a. To maximize the harvesting of short-wavelength light, macrophytes increase their CHL b concentration relative to CHL a. The results suggested that petiole CHL a:b of N. lutea can be used as an indicator of brownification. High phytoplankton biomass may, however, disturb the relationship between water colour and CHL a:b. Therefore, the most reliable results are obtained by sampling several times during the growing season. The floating leaves cannot be recommended as brownification indicators because the relationship between their CHL content and water colour is weak.