Hidrology and phytoplankton biomass in the Orange and Catuama inlets (Santa Cruz Channel), Itamaracá Island, Pernambuco State: nictemeral variation

Abstract

The Santa Cruz Channel is linked to the sea through the Orange inlet (34º55’W), and Catuama inlet (7º40’S), which make up two hydrodynamic systems with intense interchange of fresh- and salt-water. The present work objective was to study their hydrology and relate it to the phytoplankton biomass, in order to assess its relationships with the environment. Climatological and hydrological parameters were accounted for. Hydrological data were collected at Orange and Catuama sandbanks in August, 2001, during spring and neap tides, each one with a 3-hour interval, corresponding to a nyctemeral cycle. The method of Principal Com ponent Analysis (PCA) was applied to the data, with the following results; (a) the ammonia, nitrite and nitrate nutrients were positively correlated with salinity and dissolved oxygen, and inversely with silicates; (b) the phytoplankton biomass is related to phosphate, showing that this nutrient can be the limiting factor to the primary productivity. A higher salinity at the bottom layer was registered during the spring tide, in both inlets. Dissolved oxygen values were higher at Orange and Catuama inlets, which may be classified as oxygen-saturated zones. The pH was always alcaline in both inlets. The ammonia, nitrite and nitrate contents were higher during high tide, mainly at spring tides. Silicate values were more pronounced at the Catuama inlet, during low tide. The high phytoplankton biomass, with 10 - 42 mg.m-3 (Orange inlet) and 0.87 - 42 mg.m-3 (Catuama inlet) ranges has allowed those biotopes to be classified as euthrophic.