dc.description.abstract | Eutrophication together with its subsequent effects, increased levels of phytoplankton, algae,
decreased water transparency and oxygen depletion poses a significant threat to our limnic
systems. Cultural eutrophication, in particular, significantly shortens the lifespan of freshwater
bodies compared to natural processes. Lake Årungen, a dimictic lake, undergoes seasonal
mixing, impacting its oxygen levels and nutrient distribution. During stratification, the lake
experiences anoxic conditions in the hypolimnion, affecting the nitrogen and phosphorus cycles.
The presence of nitrate in the hypolimnion can buffer against phosphorus release from
sediments, mitigating eutrophication. The degree of mixing in Lake Årungen, influenced by wind
and weather conditions, is crucial for maintaining water quality. Increased air temperatures due
to climate change are contributing to the earlier onset and greater stability of thermal
stratification in lakes such as Lake Årungen. This prolonged stratification period can lead to
extended anoxic conditions in the hypolimnion and increases chances of internal phosphorus
loading. Effective management of nutrient inputs, particularly from agriculture, is essential to
counteract eutrophication and preserve freshwater ecosystems. Increased thermal stratification
stability from increased air temperatures early in the season reduces oxygen distribution,
increasing anoxia duration and necessitating higher nitrate levels to prevent reducing conditions.
Comparative data from previous years (2017, 2013, and 2009) indicated that sufficient nitrate
levels are critical in buffering phosphorus release from sediments. In 2023, nitrate levels at the
onset of anoxia were 2.6 mg/l, maintaining a high redox potential and preventing significant
internal phosphorus loading. In contrast, lower nitrate levels in earlier years led to substantial
phosphorus release. Threshold levels for nitrate concentration, crucial in preventing internal
phosphorus loading, are influenced by various biogeochemical and environmental factors,
including sediment composition, pH, and microbial activity. Effective management strategies
should focus on reducing external nitrate inputs and maintaining higher nitrate levels to mitigate
the impacts of prolonged thermal stratification and prevent eutrophication in Lake Årungen. | |