There were significant linear relationship between interstitial salinity (SAL) and distance from the mouth (DIST) for the three estuaries (Fig. 2A). These relationships can be described by the equations SAL 1⁄4 1.33 (DIST) þ 43.4, with R2 1⁄4 0.88 for Jaguaripe; SAL 1⁄4 0.79 (DIST) þ 40.8, with R2 1⁄4 0.67 for Paraguaçu and SAL 1⁄4 1.08 (DIST) þ 40.5, with R2 1⁄4 0.81 for Subae estuary.