Climate crisis - Water in lakes is turning brown: cold-water fish are suffering
Climate change is also having a major impact on life in lakes. Fish adapted to colder water areas can be affected in two ways, as a research team has discovered: directly through the warming of the water and indirectly through the increasing turbidity of the water, known as browning.
Many lakes are becoming browner as a result of global warming because more organic material is being produced in them and carried in from the surrounding soil - for example during heavy rainfall. This phenomenon can already be clearly observed in countries such as Sweden and also in some regions of Germany.
Browning can significantly reduce the oxygen content of the cooler deep water in particular, as the team led by Stephen Jane from Cornell University in Ithaca explains in the scientific journal "PNAS". Darker water absorbs more heat, which further increases the climate change effect on the surface of the lakes. As a result, stratification between the warmer surface water and the cooler deep water is increased and mixing decreases. This in turn can lead to a lack of oxygen at the bottom of the water, as oxygen is mainly produced in the upper layers - especially as the browning allows less sunlight to reach the depths, which algae need to produce oxygen, as the researchers explain.
Long-term values analyzed
Between 1994 and 2012, the scientists recorded the development of the surface temperature, the oxygen content in the deep water and the dissolved organic carbon in 28 lakes in the Adirondack region in the north-east of New York State. Surface temperatures and carbon levels increased, while the oxygen content in the deep water decreased.
In a supplementary analysis, the consequences of browning for the habitat of brook trout (Salvelinus fontinalis) were investigated using temperature and oxygen data from 15 of the lakes from 2021. In late summer in particular, the habitat suitable for the fish shrank significantly in a large proportion of the water bodies. Like trout and salmon, brook trout belong to the group of salmonids that need cool, oxygen-rich water to live.
Loss of habitat
When comparing the results with historical records for 1467 Adirondack lakes, the researchers found that the char have suffered a significant loss of suitable habitat in most lakes since the 1980s.
The research team concludes from the results that the browning caused by global warming poses an existential threat to populations of cold-water fish in temperate lakes. Deep areas of lakes are only a refuge for such species in the course of climate change if they remain oxygen-rich. However, this is questionable in many cases due to browning. There is therefore a threat of mass extinctions and the disappearance of species from more and more lakes.
Read also:
- This will change in December
- Fireworks and parties ring in 2024 - turn of the year overshadowed by conflicts
- Attacks on ships in the Red Sea: shipping companies avoid important trade route
- Houthi rebels want to launch further attacks despite international coalition
- The team at Cornell University in Ithaca, USA, has conducted research on the impact of climate change on lake waters, revealing that warming and browning are affecting cold-water fish.
- In some regions of Germany, as well as in countries like Sweden, lakes are turning brown due to global warming, leading to reduced oxygen content in the deep water.
- The increasing turbidity of lakes, known as browning, results from the production of more organic material and its transfer from the surrounding soil, which can be exacerbated by heavy rainfall in the USA.
- The reduced oxygen content in deeper waters, caused by browning, can be attributed to darker water absorbing more heat, which in turn increases heat on the lake surface and decreases mixing, potentially leading to oxygen deprivation at the lake bottom.
- A study by Stephen Jane's team from Cornell University analyzed data from 28 lakes in New York State between 1994 and 2012 and discovered an increase in surface temperatures, carbon levels, and a decrease in oxygen content in the deep water.
- Examining the habitat of brook trout in 15 Adirondack lakes, the researchers found that a significant decrease in suitable habitats has occurred since the 1980s, due to the combined effects of warming water and browning, which impairs their need for cool, oxygen-rich water.
- The impact of global warming-induced browning on lakes poses an existential threat to cold-water fish populations in temperate lakes, as the lack of oxygen in deeper water areas can lead to mass extinctions and the disappearance of species in more and more lakes internationally.
Source: www.stern.de
