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Published: 22 Nov, 2018

More knowledge about respiration to understand oxygen-free seabeds

NEWS The findings of Kevin Vikström's thesis from a coastal area in the Baltic Sea show that a decrease in nutrient salts, and thereby growth, does not necessarily reduce oxygen consumption. Kevin Vikström proposes a new perspective of marine environmental management, where maintenance respiration must be taken into account. He will defend his thesis on 9 November at Umeå University.

An increase in oxygen-free areas and a decrease in oxygen in coastal areas have been observed globally in recent years. This leads to areas where no fish or crustaceans can live. In order to counteract the occurrence of oxygen deficit, more knowledge is needed about the distribution of oxygen consumption caused by growth and maintenance respiration.

Respiration means that carbon compounds and oxygen are converted into energy. All living marine animals need energy for growth, as well as for maintenance functions, which means that the energy is used for example to be able to move around, maintain vital functions and repair injuries.

As early as the 1970s, a need for oxygen was able to be measured even without growth in bacteria, and a model was developed that described the so-called bacterial maintenance respiration. This model was further developed in the 1980s, but to-date, everything has been based on cultures in a lab environment. Another concept, which is similar to maintenance respiration, has also been developed at an ecosystem level, where growth of photosynthesising plants was used as an explanatory variable. This concept is called baseline respiration and is defined as oxygen consumption when photosynthesis is negligible. Carbon from e.g. rivers and ground water can be used for respiration and the primary production is thereby disconnected from the respiration in the ecosystem. The effect that the baseline respiration and maintenance respiration have on ecosystems has not been studied.

Kevin Vikström studied these concepts in a coastal zone in the Baltic Sea and presents an initial estimate of annual contributions by both baseline respiration and bacterial maintenance respiration. His findings show that the model that describes bacterial maintenance respiration works to some extent under highly productive conditions and would entail a 58-per-cent contribution by maintenance respiration to the annual bacterial respiration. Baseline respiration was also significant and contributed 50 per cent to the annual oxygen consumption in the water.

"In a broader perspective, the findings show that a decrease in bacterial growth with the help of lower amounts of nutrients does not necessarily reduce the oxygen consumption for bacteria. Instead, the growth-based respiration converts to maintenance respiration with a marginal difference in total consumption of oxygen as a result," says Kevin Vikström.

The baseline respiration was primarily driven by the coal that is added to the coast through the rivers. There may thereby be different levels of baseline respiration in different environments. In an ecosystem where baseline respiration is high, a decrease in nutrients will not necessarily reduce oxygen consumption. However, this is achieved in an environment where the sea's own production of algae is the main source of carbon.

Respiration for maintaining vital functions, but not growth, in the ecosystem can be high in coastal areas. The current environmental management strategy that focuses on growth may thereby be deficient.

"Baseline and maintenance respiration are crucial to take into account to understand and manage the development of oxygen-depleted coastal areas in a suitable and economical way," says Kevin Vikström.

Read the thesis digitally