Blue-green algal situation in inland waters
|Updated: 1.11.2013 - Next update: 15.9.2014|
A better-than-average summer in terms of blue-green algae
In summer 2013, Finnish lakes had a better than average year in terms of blue-green algae. In July, the number of reported blue-green algae observations was much below normal. Most of the monitored lakes were not affected by heavy and long-term blooms. The peak of blue-green algae observations was in August and September. In early autumn, the number of blooms slightly exceeded a level typical of that time of the year.
During the summer, the number of blue-green algal blooms in the lakes varied according to the weather.
In June, the numbers of blue-green algae remained normal until midsummer. However, the warm spring and a warm start to the summer resulted in early growth of blue-green algae. With the heatwave at the end of June, the reported observations of blue-green algal bloom in lakes exceeded the average.
In early July, thunderstorms and windy weather broke up the algal blooms and dispersed the algae in the water. Because of the unsettled weather in July, the blue-green algae remained dispersed in the water and few blooms occurred.
The level of blue-green algae was better than average until mid-August after which warmer and less windy weather created conditions which resulted in blue-green algal blooms. In August, algal growth was enhanced through conditions such as strong short-term winds and the gradual cooling of lake waters, which resulted in the release of nutrients and the uptake by algae.
Blue-green algae are most noticeable in southern and eastern Finland where the impacts of human activities on watercourses are also the greatest. Abundant blooms that lasted for more than four weeks were only observed in a small number of monitored lakes.
The blooms consisted of the most common genera of blue-green algae: Dolichospermum (Anabaena), Microcystis, Woronichinia and Aphanizomenon. Species within these genera may produce harmful toxins that are released into lake water. In summer 2013, the environmental administration analysed 203 freshwater algal samples. In 95% of the samples, the blooms were mainly caused by blue-green algae.
The Finnish Environment Institute SYKE
Description of indicator
The algae barometer describes the development of blue-green algal blooms on a weekly basis. The columns indicate the relative number of blue-green algae findings, weighted with the abundance of algae. The background indicates the average for the relative amount of blue-green algae calculated for 1998-2010. If the column is higher than the background, this means that, during the week in question, algae in excess of the long-term average was found. Long-term averages for the autumn, from week 36 onwards, are indicative only, being based on limited observation material.