*3.1. Sampling*

Two sampling campaigns were carried out in May 2006 and May 2007, under calm weather conditions. Water samples were collected during both campaigns, surface sediments were collected during the first campaign, and core sediments were collected during the second one. Two stations at the seawater inlets represent the seaward boundary conditions (A1, A12), one station the freshwater stream (A13), while the rest of the stations represent the conditions in the inner part of the lagoon (A2–A11; Figure 1). *In situ* measurements of temperature, salinity, conductivity, pH, and dissolved oxygen were conducted by YSI 63 and YSI 57 portable instruments throughout the water column.

Water sampling bottles were soaked in 10% HNO3 for at least 48 h, then thoroughly rinsed with deionized water (18 MΩ·cm) and stored in double polyethylene bags in a laminar flow bench. In the field, the bottles were rinsed twice with ambient water, and then the samples were collected by hand by submersing pre-cleaned polyethylene bottles at up to 20 cm beneath the water surface. During sampling, all necessary precautions were taken to avoid contamination. The samples were transported in two polyethylene bags stored in a portable refrigerator.

Surface sediment samples were collected by an Ekman-Birge grab sampler. A short sediment core was collected from station A8 (Figure 1) with a Plexiglas tube 60 cm-long and 10 cm-wide, attached to a push-tube coring device. The core was sectioned immediately after the collection into 1−2 cm intervals. Sediment samples were stored in pre-cleaned polyethylene vessels and transported in a portable refrigerator.
