Domino effects and feedback mechanisms

Nature is complex. Various processes, dynamics, and energy exchanges occur at the same time - fast and slow, with long and short duration, on large and small scales - and involve all sorts of physical, chemical, and biological aspects. Within these complex processes, parameters affect each other continuously and “everything is interaction and reciprocal”, as Alexander von Humboldt already stated in 1803. These interactions lead to domino effects and feedback mechanisms when a chain of effects reaches back to the initial driver of the process.

One way to structure the complexity of natural and environmental processes is to use the methodology of the system dynamics approach developed by Jay W. Forrester in the 1950s. This approach examines system structures by determining the interactions between parameters as either positive (enhancing) or negative (decreasing). This allows an easy determination whether evolving feedback mechanisms are reinforcing (positive) or balancing (negative).

Warming and hydrological changes act as drivers of further changes in Arctic wetland systems and their interactions with permafrost and ecology. Illustration: NG

Climate change and tipping points

Understanding complex systems becomes especially important when certain drivers change or intensify over time and thereby induce an imbalance in the system. In some cases, these instabilities might be irreversible when certain tipping points are reached.  The most relevant example of a driver with such a large impact is climate change. In the Arctic, warming is already twice the global average which has drastic impacts on landscapes and ecosystems. In this context, a recent scientific paper published in the journal WIREs WATER investigates the structure and functioning of Arctic wetland systems in order to understand the process chains and feedback mechanisms caused by climate change.

Arctic wetland. Photo: Private

The role of wetlands

Wetlands are landscapes that combine ecological and hydrological processes. They are of high importance as they represent vital habitats and valuable grazing grounds in the polar desert landscape. They act as relevant water sources by storing, filtering and buffering water to other water bodies. These functions are very important for Arctic communities that make use of wetlands within their fishing and hunting activities. Furthermore, wetlands store vast amounts of carbon and contribute to the greenhouse gas effect. Changes within Arctic wetlands are therefore crucial to investigate, as they impact local ecosystems and communities as well as global processes.

In the Arctic, wetlands are highly influenced by permafrost which is defined as ground that is frozen for at least two consecutive years. The thaw of permafrost as a consequence of rising temperatures has received great attention in both academia and media, mainly in the context of subsequent carbon emissions.

However, permafrost thaw also impacts other environmental parameters and hence also wetlands. Wetlands can either shrink or expand depending on local factors. Expansion is caused by so-called thermokarst processes that describe the formation of depressions following the thaw of ice-rich permafrost. The disappearance of permafrost can, on the other hand, also create new pathways for water to flow underground and therefore induce drainage of wetlands.

The future of Arctic wetlands still uncertain

The intensification of the hydrological cycle as a consequence of warming additionally alters water sources in the Arctic. This might ultimately lead to inundation or desiccation, causing wetland expansion or shrinkage. The future of Arctic wetlands is still uncertain, and more research is needed to identify the relevant local factors that might determine whether a specific wetland will disappear or enlarge. Again, the interaction of different environmental parameters complicates this process.

Generally, the recently published article confirms that permafrost and air temperatures are highly relevant factors for changes within Arctic wetlands. Feedbacks and process chains, that reinforce or balance warming and permafrost thaw, are therefore of great importance.

Surface albedo and feedback mechanisms

Vegetation has been identified as a crucial system parameter within these feedback mechanisms, including, for instance, the surface albedo which determines how much incoming radiation is reflected. Surface albedo, also affected by land cover changes driven by climate change (e.g., vegetation, ice, and water surfaces) lead to feedback mechanisms that either reinforce or balance warming. A declining sea ice cover, increasing water surfaces (wetlands), or the northward migration of the treeline due to vegetation succession lowers the surface albedo, which enhances warming in the Arctic.

Ice, water, and vegetation also interact with ground temperatures, and the so-called ground thermal regime, which directly influences the presence of permafrost. The relatively high heat capacity of water, for instance, enhances ground temperatures and therefore leads to permafrost thaw. Vegetation, in contrast, shields and insulates the ground from radiation. The northward migrating treeline and vegetation succession in general, caused by warming, might therefore balance and decelerate the progressing permafrost degradation in the Arctic. However, the increasing probability and severity of ecosystem disturbances resulting from climate change, such as wildfires and insect outbreaks, might again counteract this process.

These ecosystem dynamics also impact the uptake and release of carbon in the Arctic. Generally, wetlands contribute to the emissions of methane as they support anaerobic decomposition. Since methane is a potent greenhouse gas, its effect on climate change is of high relevance for the global climate. To which degree the negative feedback mechanism of enhanced carbon uptake by more vegetation can balance this process is still uncertain.

All processes interact

Wetland systems in the Arctic are affected by multiple environmental processes. This makes them vulnerable to climate change which in turn impacts local communities and ecosystems. The new scientific article in WIREs WATER structures these factors and elucidates the state-of-the-art research in this topic. As these processes all interact, directly or indirectly, the impact of the identified feedbacks goes beyond Arctic landscapes and needs to be considered for the whole planet.

Scientific article in the journal WIREs WATER

Kreplin, H., Santos Ferreira, C.S., Destouni, G., Keesstra, S., Salvati, L. and Kalantari, Z. (2021): Arctic wetlands system dynamics under climate warming. Wiley Interdisciplinary Reviews: Water, e21526.