Background
Climate change has emerged as a major global challenge in recent decades, with significant impacts on natural ecosystems and human societies. Lake is one of the most vulnerable ecosystems to climate change (Råman Vinnå et al. 2021). The phenomenon known as Arctic amplification has caused the rate of warming in the Arctic to accelerate, potentially leading to more severe impacts on lakes located at high latitudes. These high latitude lakes are mainly distributed at North America and Europe and have the characteristics, such as low temperatures, short growing seasons, and limited nutrient inputs, which make them highly sensitive to the effects of climate change. The Arctic amplification phenomenon also amplifies these impacts and highlights the importance of studying the high-latitude lakes.
Picture 1: Global average temperature from 2000 to 2009 compared to 1951-1980. The Arctic warmed by about 2°C, much higher than other regions. (Adapted from: NASA Earth)
Climate change is expected to have a profound impact on these high latitude lakes, with potential consequences for their trophic state and the growth of algae. Algae is critical to the function of high-latitude lake ecosystems, acting as primary producers that support the food web. Lakes usually have slower water currents, which are more likely to cause algae to aggregate and grow. The growth of algae in lakes depend on nutrient availability which can be affected by a variety of local climate factors, such as, temperature, and precipitation, etc. (Juneja et al. 2013). Changes in climate variables can cause shifts in the trophic state of lakes, with some becoming eutrophic or even hypertrophic and others becoming more oligotrophic. The trophic state index (TSI) is a classification which is commonly used to evaluate the level of biological productivity that can be maintained by water bodies (E. 1997). The higher the value, the more serious the eutrophication of the water body.
The uncontrolled growth of algae caused by high trophic level can lead to harmful algal blooms (HABs) which can negatively impact the local ecosystems. Excessive growth of algae can create a layer of biomass on water surface that blocks sunlight from reaching other aquatic plant species, preventing them from photosynthesis process and resulting in death. And the dead aquatic plants will release nutrients back to water and facilitate the eutrophication process through decomposition. As the algae die and decompose, they consume large amounts of dissolved oxygen and release carbon dioxide, which create dead zones where aquatic life cannot survive.
Picture 2: These diagrams demonstrate the oxygen content of the water body under different trophic states. (Adapted from: ResearchGate)
This can also promote the growth of bacteria, fungi, etc. in the water, which may increase potential risks to local aquatic organisms and surrounding terrestrial animals. Some algae species such as Cyanobacteria, Dinoflagellates and Pseudo-nitzschia, etc. can also emit toxic compounds. For example, Dinoflagellates can produce toxic hemolytic and neurotoxic that are lipid-soluble, while Pseudo-nitzschia algae is known for producing domoic acid (Macintyre et al. 2011). Toxic compounds like domoic acid can be accumulated in the food chain of aquatic species, which can have harmful effects on animals and humans that consume them (Marquez et al. 2020). This can have significant ecological and socio-economic implications, including the loss of biodiversity, and reduced recreational and economic opportunities.
Picture 3: Lake Dora in Florida shows the Harmful algal blooms. (Adapted from: U.S. Geological Survey)
Objective
Despite the critical importance of high-latitude lakes in North America and Europe, the understanding of the impacts of climate change on these ecosystems remains limited. While previous studies have investigated the impact of individual climate variables on the growth of algae, few studies have examined the combined effects of multiple climate variables and compared the lakes at North America with Europe. The objective of this paper is to explore the impact of spatial variations in climate variables on the trophic states and growth of algae in high-latitude lakes in North America and Europe. By studying this, we can better understand the interactions between algae growth, tropic states, and climate factors on algae growth, so that improve our ability to monitor and manage the health of aquatic ecosystems based on spatial differentiation, especially under global climate. And the hypothesis is that the growth of algae in lakes is affected by both spatial factors and climate variables and that these effects vary depending on the trophic status of the lake.