**4. Sediment as geo-marker**

**Figure 5.** Concentration of Arsenic (As) in sediment of South Brittany waters (Bay of Quiberon and Gulf of Morbihan),

GIS is a tool for decision making, using information stored in a geographical form. Some researchers defined major requirements and functions of GIS and mentioned spatial data handling tool for solving complex geographical problems [7–9]. Besides, GIS is increasingly used in environmental pollution studies because of its ability in spatial analysis and interpolation,

**Figure 4.** Example of geographical information system (GIS) mapping in environmental studies. Photo adapted from

https://technofaq.org/posts/2017/07/thoughts-on-the-future-of-gis-what-will-change-in-50-years/ [6].

32 Wetlands Management - Assessing Risk and Sustainable Solutions

France. Figure by Ong Meng Chuan using ArcGIS software 9.3.

Sediments are widely used as geo-markers for monitoring and identifying the possible sources of pollution in the coastal environments since sediments are the main sink for various pollutants (**Figure 6**). Sediments can serve as a metal pool that can release metals to the overlying water via natural or anthropogenic processes, causing potential adverse health effects to the ecosystems. Most metals are bound in the fine-grained fraction (<63 μm), mostly because of its high surface area-to-grain size ratio and humic substance content, where they have a potentially greater biological availability than those in the larger (2 mm–63 μm) sediment fraction.

Meanwhile, sediment cores (**Figure 7**) can provide chronologies of contaminant concentrations and a record of the changes in concentration of chemical indicators in the environment. Metal accumulation rates in sediment cores can reflect variations in metal inputs in a given system over long periods of time. Hence, the study of sediments core provides historical record of various influences on the aquatic system by indicating both natural background levels and the man-induced accumulation of metals over an extended period of time.

**Figure 6.** Different types of sediment can be collected from wetlands ecosystem. Photo by Ong Meng Chuan.

**Figure 7.** Core sample collected from mangrove environment used for metals proxy study. Photo by Ong Meng Chuan.
