Dissolved organic nutrients (C, N, P) in seawater on the continental shelf in the Southwestern South Atlantic with emphasis State Marine Park of Laje de Santos (SMPLS) - São Paulo - Brazil

Abstract

The main objective of this work is evaluate seasonal and spatial distribution of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP) and urea in 10 stations of the State Marine Park of Laje de Santos (SMPLS). Stations 1 to 4 (nearest the continent) and the stations 5 to 10 (nearest the marine park) all of them were on the continental shelf. The results show that no statistic significant seasonal variations were found for the DOC and DOP nevertheless DOC and DON in summer period were lightly above the winter period showing the increase in biological activities and continental influence. On the other hand, DON showed high values in June (2014 - winter) to January 2015, ranging from 12.51 to 32.76 µmol L-1 according to the ANOVA method (p <0.01). Low values of DON in January 2014 (0.32 to 8.98 µmol L-1) was observed in a summer unusually dry, while the highest values were observed in July 2014 (27.50 µmol L-1). Urea presented low values in SMPLS region and coastal areas reaching 4.00 µmol L-1. Sometimes, the urea concentration can be associated with diving activity in the park. DOC, DON and urea showed differences between SMPLS stations (5-10) and coastal stations (1-4). DOC coastal stations reached 267 µmol L-1, while the SMPLS the maximum value was 100 µmol L-1. No significant spatial variation between coastal stations and park were observed for the DOP (ANOVA p <0.01). Considering that dissolved organic compounds can also be monitored by means of the evaluation of C, N, P in their organic fraction, it was concluded that in the studied region the impact of eutrophic waters under continental and anthropic influence is minimal and these parameters could be monitored to support monitoring in the region.