Variation on the Fluxes of Nutrients in an Urban Lagoon by Seasonal Effects and Human Activities

Abstract

This document to examine the changes occurred in the flux of nutrients and NEM during dry season and rainy + north wind season in the Caleta system located within the Terminos lagoon natural reserve which presents negative impacts caused by discharges of urban wastewater. Salinity, dissolved oxygen, chlorophyll a, nitrogen and phosphorus were monitored during nine months considering the dry, rainy and north wind season. Storms caused sediment disturbances which increased the amount of nutrients into the Caleta system as well as the phytoplankton production (25 mg m-3). The system shows longer times of water renovation during the summer (21 d) unlike (6 d) during the rainy + north wind season. On one hand, the ΔDIP values during dry season (0.0049 μmol m-2 d-1), establishes the system as producer and exporter of DIP into the ocean; on the other hand, the ΔDIP during rainy + north wind seasons (-0.0039 μmol m-2 d-1) suggests the importation of phosphorus from the ocean. Likewise, the system exports DIN (0.0031 μmol m-2 d-1) during the summer and imports DIN (-0.0048 μmol m-2 d-1), during the rainy + north wind seasons. The negative values of fixation-denitrification and NEM during the summer turn the system into a nitrogen sink. Seasonal changes were present in the system, dominated by heterotrophic NEM during summer with higher nitrogen fixation; while an autotrophic NEM dominated during winter.