Relating nautical traffic and copper concentration in coastal waters: a case-study in the Krka River estuary (Croatia)

Abstract

Abstract:Copper (Cu) is essential metal needed for the growth of aquatic organisms. However, above certain level, it behaves as toxicant. Hence, the monitoring of its level in natural waters is of primary interest. Copper is used as a biocide in anti-biofouling Cu-based paints, and as such it is released in the water as contaminant. Previous studies carried out in the Krka River estuary in last several years, have showed that during summer season concentrations of Cu are up to 20 times higher compared to winter season. It was presumed that such increase is due to Cu leaching from the boat-paints, enhanced during touristic season. However this relation was not fully confirmed, because the traffic intensity in Estuary was unknown. To evaluate impact of nautical traffic on Cu concentrations in surface layer of the Krka River estuary, one-year monitoring study was undertaken. Monitoring program consisted of two main activities: 1) counting vessels by video observing system and 2) measuring copper content in water. It was shown that the number of vessels are dramatically increased in summer season, when compared to winter season: the average number of boats passes was ~50/day in winter, and in summer it increased over 1000/day. Similar trend of Cu concentration increase was recorded, with ~5× higher concentrations in summer season. The conducted research confirmed strong relation between nautical traffic and Cu content in water. However, it was found that at selected monitoring location not only number of vessels is factor on which Cu concentrations are linked, but also other variables are having influence: salinity, the Krka River flow, intensity and direction of the wind and rainfall.