Wetlands in a changing climate: science, policy and management, Moomaw et al. 2018

This article emphasizes the global importance of protecting and restoring wetlands in the context of climate change and outlines policy strategies for wetland protection and restoration.

Wetlands play a major though under-appreciated role in climate change mitigation and adaptation. Wetlands enhance local resilience to climate change by providing: “flood storage, buffering of storm damage, protecting water quality by filtering pollutants and sediment out of runoff generated by severe storm events, groundwater recharge and provision of water supply during drought, provision of wildlife refuges and corridors and maintenance of biodiversity” [Moomaw 2018: 192], as well as “direct harvests of fish, animals, and plants” [Moomaw 2018: 188]. Furthermore, wetlands/peatlands store massive amounts of carbon, drawing it out of the atmosphere.  

Peatlands and vegetated coastal wetlands are among the most carbon rich sinks on the planet sequestering approximately as much carbon as do global forest ecosystems [Moormaw 2018: 183].

Wetland conditions are critical for C accumulation and storage since decomposition in these systems is limited by a lack of oxygen due to water saturation. Therefore, when plant productivity exceeds decomposition there is an accumulation of soil C. This process eventually develops deep peat deposits, which may accumulate for thousands of years [Moomaw 2018: 187].

By the same token wetlands can become major GHG sources when damaged or destroyed by land use change, fire or climate change.

Altering wetlands can increase the vulnerability of the organic C pool by weakening the self-regulating feedbacks that exist in many peatland systems. Land use change that affects wetland hydrology has had substantial impacts on wetland structure and function. Draining wetlands decreases CO2 uptake and increases rates of microbial decomposition and CO2 release. Soil C is also lost by peat extraction, drainage and other disturbance. The hydrologic changes can be so large that they result in massive losses of C to the atmosphere, such as occurred during the fires in tropical peatlands in Southeast Asia [Moomaw 2018: 187].

Many land-use practices in or near wetlands reduce wetlands’ resilience to any further stress, such as hotter, drier weather wrought by climate change.

Unfortunately, many of the world’s freshwater wetlands are already stressed by increased land-use pressure, so that additional hydrological alteration can contribute to an overall decrease in resilience to climate change. Human alteration is commonplace throughout river corridors, challenging management as the impacts of upstream alterations accumulate along the waterway. As demands for river resources increase, such problems are expected to worsen. Flowing water is compromised by river re-engineering practices, even though moving water generally improves oxygenation and plant health. Also, upriver freshwater extraction in tidal freshwater wetlands coupled with sea level rise can cause the salinification of surface and ground water, with accompanying stress and even the collapse of tidal vegetation in the freshwater reaches of estuaries [Moomaw 2018: 188].

On the other hand, wetland resilience can be bolstered through proper land management.

The effects of climate changes on wetland C storage will be determined largely by the extent to which the wetlands have been modified through land-use change [Moomaw 2018: 187].

One opportunity to decrease the amount of saltmarsh loss that is likely to occur with sea level rise is to actively plan for future inland marsh migration now [Moomaw 2018: 191].

The authors express concern that wetlands are overlooked in policy discussions on climate change, noting that climate scientists tend to sideline the role of wetlands, while wetlands science and management have often failed to acknowledge the outsized role of wetlands as a carbon sink. Thus:

To play a more effective role in climate change mitigation and adaptation/resiliency, wetland scientists need to clearly communicate the significance of wetlands to the wellbeing of society and the economy. Communicating with policy makers and the public requires aligning wetland science and specific climate mitigation and adaptation/resiliency ecosystem services with the concerns and mindset of the audience [Moomaw 2018: 198].

A handful of policy structures at international, national and subnational levels aim to better account for and protect wetlands. For example, the International Panel on Climate Change (IPCC) has since 2013 provided guidance (through the Wetlands Supplement) to countries about including wetlands in national GHG inventories, thus moving “closer to requiring countries to account for the substantial emissions from these ecosystems when they are disturbed or destroyed” [193]. The 1975 Ramsar Agreement establishes an international framework for wetland management, but lacks adequate guidance on how to best protect wetlands from the stressors of climate change. At the local level, decisions about wetlands are often made by land managers.

Thinking globally and acting locally, wetland managers can incorporate carbon management and climate resiliency science into project-level work (including developing a body of climate-related Best Management Practices), whether or not governing policies and regulations exist. As noted earlier in this article, avoidance of impacts to wetlands, and associated carbon stocks and processes, is likely to be the most effective management practice for preventing increases in GHG emissions from wetlands, protecting climate resiliency functions, and protecting traditional wetland ecosystem services, and it is therefore important for managers to understand the underlying science [Moomaw 2018: 197].