Eutrophication in Malta

Abstract

A number of results, in particular the vertical distribution of temperature, salinity and oxygen content, show that there is a lack of stratification in the harbours but for certain localised zones. This indicates that the harbour waters are subject to a certain amount of mixing probably on account of winter storms. The temperature results contrast with summer observations made by Harvard where a surface to bottom difference of up to 10°C over a 30m depth was detected in calm conditions off the coast of Malta. The temperature difference at Station 8 in January 1991 was only 0.8°C within the 20m sampled, storms and strong currents being the causative factors. The increased mixing in winter, however, does not imply that it is accompanied by a pronounced exchange of water from the harbours to the open seas. The mean temperatures within the harbours remain slightly higher than those at Station 8. Whether this effect is significant or not can only be tested by knowing the temperature differences in summertime too. From the results of October 1990 compared with those of January 1991, there does seem to have been a small drop in difference between the harbours and Station 8 with the onset of winter. The volume and type of data and data collection techniques however were not intended to measure the effect of water exchange and a separate study would be needed to throw light on this subject. [excerpt]