Predicting median monthly chlorophyll-a concentrations

Chlorophyll-a (Chl-a) is a plant pigment which is used in many environmental monitoring programs as a water quality indicator for lakes. However, monthly Chl-a data are often lacking in many monitored lakes as measurements are concentrated to certain periods of the year. This study investigates two methods of how monthly Chl-a medians can be predicted (i) new monthly regression models from median summer total phosphorus concentrations and latitude, (ii) and with monthly constants added to regression models from the literature. Data from 308 lakes were used and the trophic status of the lakes ranged from oligotrophic to hypertrophic, they were located from northern Sweden (Europe) to southern Florida (North America). These models may be useful for understanding the general Chl-a seasonality in lakes and for managing lakes in which Chl-a measurements are not made over the whole year.