Anthropogenic influences on seasonal changes of nutrients, physical and chemical factors in three coastal freshwater shallow lakes (Portugal)

Abstract

Braças, Vela and Mira lakes (near Figueira da Foz - Portugal) are eutrophic bodies of water largely as a result ot nutrient loading from the runnof from agricultural areas and suburban watersheds. Despite this situation, Mira lake provides sport fishing/angling and Vela and Braças lakes are, respectively, important environments for community recreation and protection of wildlife. The algal production in the three lakes has varied with nutrient concentrations, primarily phosphorus and nitrogen, and the anthropogenic landuse activities increased the mobilisation of the nutrients in the drainage basin and subsequent loading into the lakes. In Mira lake, the external loading from bait used in sport fishing increases temporally phosphorus and nitrogen into the water body. This finding is the main disturbance within this system. The present study was made to compare the three lakes in order to examine seasonal and spatial variations on the environmental parameters and to assess the impact of human activities on physical and chemical structure. © Asociación Española de Limnología.