Seasonal comparison of the molar ratio of water and periphyton in a tropical dam (Lago das Niféias, São Paulo/SP)

Abstract

The molar ratio of water and periphytic material in a shallow mesotrophic dam was evaluated at four times of the year (spring, summer, autumn and winter) from isolated and combined enrichments by N and P. Four treatments were designed using nutrient diffuser substrate (polystyrene cups, filled with Agar solution and nutrients – control: no addition of nutrients; N+: 0.75 M; P+: 0.05 M; NP+: combined addition of the two salts, molar ratio N:P = 15). The opening of the cups was coated with a 20 μm mesh as a substrate for the periphyton. Collections were carried out on the 15th, 20th, 25th and 30th days of colonization. The greatest variability of abiotic limnological data was attributed to the type of treatment, followed by the annual scale. The PCA indicated a strong association between the addition of phosphorus and, mainly, combined addition with the higher levels of periphyton phosphorus content, as well as the treatments without phosphorus addition with the N:P ratio of periphyton. Phosphorus can be considered the driver of the molar ratio values found in both water and periphyton, followed by low temperature in the cold months.