Interannual water quality changes at the head of a tropical estuary.

Waters entering the small estuaries of the Brazilian north-east originate from drainage basins that cross semi-arid and tropical rainforest areas at various levels of use and conservation. Such rivers are often under heavy demand for water supply and other services, such as effluent dilution. The present study examines four consecutive years (2006-2009) of water quality-monitoring data divided by season (rainy and dry) just before the Goiana River enters its estuary.