Interstitial water salinity, organic matter content and sediment were sampled at each quadrat, during low tide. The interstitial water samples were collected in July 2011 (winter) and March 2012 (summer) on all estuaries. A random sample of interstitial water was collected at each quadrat, at 50 cm depth. Interstitial water was collected using a hose, syringe and a PVC tube with small holes near a capped end (adapted from Schaeffer-Novelli and Cintron, 1986). After collection, the interstitial water samples were stored in glass vials and kept under refrigeration until the decantation of the suspended sediments. After decantation, interstitial water was carefully extracted and measured with an optical refractometer.