Overfertilisation of Baltic Sea Makes Algal Blooms More Toxic
Thursday, December 16, 2010 9:10:52 AM
Surface blooms of cyanobacteria have increased in both frequency and magnitude in the Baltic Sea in recent decades, and researchers are divided on the cause. There are several species of cyanobacteria, that can form surface blooms in the Baltic Sea, and which species ends up dominating a bloom depends partly on how they deal with an increased amount of ultraviolet light and a shortage of nutrients. The cyanobacteria Nodularia spumigena is most toxic when there is little nitrogen in the water but sufficient amounts of phosphorus. Wastewater is to a large extent treated before it flows into the Baltic Sea with processes that concentrate on removing nitrogen. This can make cyanobacterial blooms more toxic. Wastewater therefore needs to be cleared of both nitrogen and phosphorus.
It has been a key question in ecology whether primary production is controlled by nutrient and/or light (bottom-up), or by grazers (top-down). Bottom-up and top-down factors are greatly dependent on each other, but a eutrophic system such as the Baltic Sea, is supposed to be more strongly controlled by bottom-up factors. The new Swedish study is (therefore) focusing on bottom-up factors. (Eutrophic water is water with high primary productivity due to excessive nutrients. Primary production is principally the production of organic material through photosynthesis).
According to the study discussions concerning further increase of nitrogen removal in sewage treatment, should take into account that this may lead to increased toxicity during the Nodularia spumigena blooms. The results suggest that the highest concentrations of the toxin called nodularin (produced by Nodularia spumigena) during a Nodularia spumigena bloom may occur during the initiation of the bloom when phosphorus is still present in excess while nitrogen is limited and when filaments are found deeper in the water column not exposed to ultraviolet radiation.
On the Ecophysiology of Baltic Cyanobacteria, Focusing on Bottom-up Factors
Download Ph.D. thesis as pdf-file here
Ecophysiology (from Greek οἶκος, oikos, "house(hold)"; φύσις, physis, "nature, origin"; and -λογία, -logia) or environmental physiology is a biological discipline which studies the adaptation of organism's physiology to environmental conditions. Physiology deals with the normal (chemical or physical) functions of living organisms and their parts.