electric conductivity

BSc Thesis

Abstract

Mangrove forests are among the most productive ecosystems on the planet. However, the global mangrove area is decreasing annually by 0.7% - 3%. For mangrove areas in semi-arid to arid climates, salinity is one of the causes for a decrease in mangrove canopy and tree die-off. This process occurs in mangrove forests and the backwaters near the main land. Because of their location and the presence of sediments, water circulation from the seaside becomes limited.

The backwaters near the mainland become shallow, warmer and isolated compared to the rest of the seawater, which results in increasing evapotranspiration and salinity rates. Lac Bay on Bonaire is a place where the salinity of the backwaters increase and where sediments limit the water circulation. In this case study, the electrical conductivity (EC) and sediment depths (SD) are measured to assess the current situation concerning the EC and SD variety in the backwaters of the mangrove forest at Lac Bay. This is done in two different areas in the backwaters: Area 1 and Area 2. In addition, the EC is measured twice to see if the EC changes over time and a third area is used as a reference site. The results show that the measured range of the EC in Area 1 and Area 2 is between 85 mS/cm - 128 mS/cm. The measured range of the sediment depths in Area 1 and Area 2 is between 1 cm – 379 cm. Furthermore, the EC values change over time and, with some exceptions, the greatest values are found the furthest from the feeder channels, which provide water from Lac Bay towards the backwaters. The tides are also a possible factor for the water to flow over a broader mangrove area towards the backwaters. This causes exceptions on the general pattern where EC increases with distance to feeder channels. Overall, the SD gradually increases with distance to the mainland. Some local exceptions from this pattern were measured in Area 2 and could be possible due to irregularities in the underlaying bedrock. In addition, the sediment inflow in the northern part of Area 1 causes some greater values than the surround areas.

These results and conclusions provide a baseline for follow-up research. This follow-up research should focus on factors which will prevent sediment inflow and help to reduce the EC values to make it possible to restore the previous state of the mangroves.