Seasonality modulates the predictive skills of diatom based salinity transfer functions

The value of diatoms as bioindicators of contemporary and palaeolimnological studies through transfer function development has increased in the last decades. While they represent a tremendous advance in (palaeo) ecology, these models also leave behind important sources of uncertainties that are often ignored. In the present study we tackle two of the most important sources of uncertainty in the development of diatom salinity inference models: the effect of secondary variables associated to seasonality and the comparison of conventional cross-validation methods with a validation based on independent datasets. Samples (diatoms and environmental variables) were taken in spring, summer and autumn in the freshwater and brackish ditches of the province of North Holland in 1993 and sampled again different locations of the same province in 2008-2010 to validate the models. We found that the abundance of the dominant species significantly changed between the seasons, leading to inconsistent esti...