Wetlands & climate change

Wetlands are vulnerable to climate change

Climate change is expected to impact wetlands due to changes in temperature and the timing and amount of precipitation. Coastal wetlands will also be impacted by sea level rise and changes in water chemistry. Those changes can alter wetland conditions and processes, including the types of habitat they provide, and their ability to manage water quality and flooding.

Wetlands mitigate climate change

Wetlands are a key player in global greenhouse gas budgets. Wetlands can be a source of some greenhouse gases, especially when disturbed, but they are also an important sink for greenhouse gases, where carbon is stored and prevented from entering the atmosphere.

Wetlands and adaptation to climate change

Many wetlands will play a role in our ability to manage risks from climate change. Wetlands are dynamic systems that experience cycles of wet and dry phases on seasonal, annual, and decadal scales. Because of that natural variability, many wetlands may be able to persist and continue to provide ecosystem services despite climate change. These ecosystem services include:

Cleaning up polluted water.
Slowing and storing floodwaters and snow melt.
Recharging groundwater.
Supporting habitat for many different native plant and animal species.

As the climate changes, many of those services will be in greater need.

Wetlands are vulnerable to climate change

Because of their position where land and waters meet, wetlands are at risk of damage from climate change. Effects of climate change on wetlands may include:

Loss of carbon stored in soil
Changes in soil structure
More frequent drying or flooding
Changes in plant or animal communities
Saltwater intrusion to freshwater coastal wetlands
Changes in timing and amount of water available to wetlands fed by snow melt.¹

Most of the carbon stored in wetlands is in the soil, where carbon cycling and microbial processes take a long time to develop. For example, the organic soil in peatlands can take thousands of years to develop- it can take up to 250 years for just one inch of peat to accumulate.² Disturbance of those systems can result in loss of the carbon stored in those soils to the atmosphere.³ It is estimated that oxidation of disturbed organic soil contributes a substantial amount of CO2 to the atmosphere.¹Undisturbed wetlands store nearly twice as much carbon as wetlands disturbed by human activities.⁴ Warmer temperatures and changes in precipitation can also increase the loss of carbon stored in wetland soils.¹The combination of wetland disturbance from human activities and changes in climate may have greater impacts on wetland functions than either stressor would alone.¹

Wetlands that rarely dry out are expected to shift to more frequent drying in some areas, and wetlands that currently are frequently dry may be lost in some areas. In other areas where precipitation is expected to increase or the timing is expected to change, wetlands that occasionally dry out may become wetter.⁵

Wetlands in some areas may be at greater risk. For example, montane wetlands are expected to be affected by higher temperatures, less snow pack, and earlier snow melt, resulting in a loss of more seasonal wetlands and habitats suitable for amphibians and wetland invertebrates.⁶ In addition to changes in temperature and precipitation, coastal wetlands will be impacted by sea level rise. In the Puget Sound region, sea level was estimated to rise gradually by 15 to 54 inches.⁷ A more recent effort to estimate sea level rise along Washington's coast includes changes in land elevation to generate relative sea level rise projections for different carbon emissions scenarios and based on the probability of occurrence.⁸ For example, they estimated a 50 percent chance of sea level to rise 2.7 ft in Olympia under a high carbon emission scenario, with a range of 2.0 ft -3.4 ft most likely (83-17% chance).⁹This rise in sea level can result in saltwater intrusion to freshwater wetlands and water depths too deep for coastal wetland plants to survive. In areas where coastal wetlands are not able to move inland as the water rises, they may disappear.

The changes to wetlands that may happen with climate change can alter water quality, water quantity, and habitat functions.^{1, 10, 11} The response of individual wetlands to climate change will depend on:

Exposure to altered climate conditions.
Sensitivity to those changes.
Potential impacts from exposure and sensitivity.
Capacity to adapt.¹²

Wetlands mitigate effects of climate change

Coastal wetlands, undisturbed inland wetlands, and lakebeds are important carbon sinks.

Coastal wetlands sequester carbon efficiently and emit relatively little methane. They are estimated to sequester twice as much carbon in their soil than all tropical forests.¹³
Older freshwater wetlands sequester more carbon than they emit.
Forested wetlands sequester large amounts of carbon in tree biomass.
Younger freshwater wetlands and disturbed wetlands can emit carbon until they develop sufficiently to sequester carbon.

The turnover time from a wetland being a carbon emitter to a carbon sink can take 61 to 14,000 years.¹⁴Globally wetlands store up to 700 billion tons of carbon, mostly in peat soils,³ with 96 million tons sequestered per year.¹⁵ U.S. wetlands are estimated to store 11.52 billion tons of carbon, approximately 1 percent of the global soil carbon.⁴ Wetlands in the western United States are estimated to have soil carbon densities of over 200 million tons per hectare.⁴ While coastal wetlands are the focus of “blue carbon” markets, freshwater wetlands have a similar density of soil carbon, and cover a much larger area than coastal wetlands. This makes them an important resource for carbon marketing (i.e., “teal carbon”).⁴

Chart compares mean organic carbon density in U.S. wetland soils and locations where various soils occur. — Wetlands act as carbon sinks. The chart shows that wetland soils in the US have a density of 300 million tons of carbon per hectare. [Citation 4, Figure 3a]

Wetlands and adaptation to climate change

Adaptation is about enabling a response, promoting resilience, and creating resistance to the effects of climate change.¹⁶ Wetlands provide ecosystem services that will contribute to our ability to adapt to climate change. Three of the most commonly cited wetland ecosystem services are:

Their role in the hydrologic cycle.
Their ability to improve water quality.
The habitat they provide for Washington’s fish, wildlife, and native plants.

Wetlands in the hydrologic cycle

Climate change is expected to result in changes to the hydrologic cycle including altered precipitation and snow melt patterns. Wetlands can offset changes in precipitation and snow melt by storing water and reducing the effects of drought and severe storms. The cumulative presence of wetlands and lakes in a watershed can reduce flood flows during big storm events.¹³ Wetlands are also a source of surface and groundwater recharge in drying landscapes. They help keep waters flowing in streams, which helps offset the effects of summer droughts on salmon and other species. Even a small percent of peatland in a watershed can produce up to half of the stream flow.¹³ Coastal wetlands can protect against storm surges that can affect areas farther inland on the coast than in the past because of higher sea levels.

Wetlands and water quality

Climate change can increase storm intensity, resulting in increased stormwater runoff, which carries contaminants harmful to water quality, salmon, and other wildlife. Wetlands are often referred to as a “kidney” in the landscape. Through cycles of wetting and drying, combined with the bacteria and plants that live in wetlands, they can sequester, alter, and / or assimilate contaminants such as excess nutrients, heavy metals, and petroleum products.¹⁷ Their role in water quality management will contribute to our ability to adapt to climate change.

Wetlands and habitat

Wetlands provide a refuge from the effects of climate change. Wetlands are among the most productive ecosystems in the world.² They are used by more than two-thirds of terrestrial vertebrate species in Washington and Oregon, including 65 percent of mammals and 72 percent of birds.¹⁸ They are also key habitats for salmon development and amphibian reproduction.

Oregon spotted frog in a wetland habitat. — Wetlands can provide amphibians refuge from heat and drought.

Wetlands can reduce the effects drought and heat have on wildlife by providing a source of water or moist, cool microclimates. As the climate changes, wetlands also provide a corridor or stepping stone on the landscape that may help species move to better areas.¹⁹

In coastal areas, eelgrass beds can reduce the effects of ocean acidification, resulting in areas that may be able to support species like oysters and clams²⁰ that have already been impacted by changes in water chemistry.²¹

Wetland buffer sign saying not to disturb the natural area. — Protecting wetland buffers from disturbance will help them persist in the face of climate change.

Impacts on buffers

Changes in temperature and precipitation can affect upland plant communities. This can affect forested buffers around wetlands because some trees may experience higher mortality as a result of climate change. Species once uncommon in an area may be encountered more frequently as their ranges shift with climate change. Current research indicates that moisture availability and impacts from land use change and altered disturbance regimes are more important to vegetation communities than changes in temperature.²²

¹ Moomaw, W. R., Chmura, G. L., Davies, G. T., Finlayson, C. M., Middleton, B. A., Natali, S. M., . . . Sutton-Grier, A. E. (2018). Wetlands in a changing climate: science, policy and management. Wetlands, 38(2), 183-205).

² Sheldon, D., Hruby, T., Johnson, P., Harper, K., McMillan, A., Stanley, S. and Stockdale, E. (2005). Freshwater Wetlands in Washington State. Volume 1: A Synthesis of the Science. (Publication #05-06-006). Washington Department of Ecology, Olympia, WA.

³ Bridgham, S. D., Megonigal, J. P., Keller, J. K., Bliss, N. B. and Trettin, C. (2006). The carbon balance of North American wetlands. Wetlands, 26(4), 889-916.

⁴ Nahlik, A. M. and Fennessy, M.S. (2016). Carbon storage in US wetlands. Nature Communications, 7 (13835).

⁵ Halabisky, M. (2017). Reconstructing the Past and Modeling the Future of Wetland Dynamics Under Climate Change (Doctoral dissertation). University of Washington, Seattle, WA.

⁶ Ryan, M. E., Palen, W. J., Adams, M. J. and Rochefort, R. M. (2014). Amphibians in the climate vise: loss and restoration of resilience of montane wetland ecosystems in the western US. Frontiers in Ecology and the Environment, 12(4), 232-240.

⁷ Mauger, G. S., Casola, J. H., Morgan, H. A., Strauch, R. L., Jones, B., Curry, B., Busch Isaksen, T. M., Whitely Binder, L., Krosby, M. B. and Snover, A. K. (2015). State of Knowledge: Climate Change in Puget Sound. Report prepared for the Puget Sound Partnership and the National Oceanic and Atmospheric Administration. Climate Impacts Group, University of Washington, Seattle.

⁸ Miller, I.M., Morgan, H., Mauger, G., Newton, T., Weldon, R., Schmidt, D., Welch, M., Grossman, E. (2018). Projected Sea Level Rise for Washington State – A 2018 Assessment. A collaboration of Washington Sea Grant, University of Washington Climate Impacts Group, Oregon State University, University of Washington, and US Geological Survey. Prepared for the Washington Coastal Resilience Project.

⁹ Raymond, C., Conway-Cranos, L., Morgan, H., Faghin, N., Spilsbury Pucci, D., Krienitz, J., Miller,I.,
Grossman, E. and Mauger, G. (2018). Sea level rise considerations for nearshore restoration projects in Puget Sound. A report prepared for the Washington Coastal Resilience Project.

¹⁰ Erwin, K. L. (2009). Wetlands and global climate change: the role of wetland restoration in a changing world. Wetland Ecology and Management, 17(1), 71-84.

¹¹ Corcoran, R. M., Lovvorn, J. R. and Heglund, P. J. (2009). Long-term change in limnology and invertebrates in Alaskan boreal wetlands. Hydrobiologia, 620(1), 77-89.

¹² Glick, P., Stein, B. A. and Edelson, N. A., editors. (2011). Scanning the Conservation Horizon: A Guide to Climate Change Vulnerability Assessment. National Wildlife Federation, Washington, D.C.

¹³ Davies, G. T. (2016). Wetlands and Climate Change: A Summary of Current Wetland Scientific Findings. Hot Topics Webinar Series. Association of State Wetland Managers. November 15, 2016.

¹⁴ Neubauer, S. (2014). On the challenges of modeling the net radiative forcing of wetlands: reconsidering Mitsch et al. 2013. Landscape Ecology, 29(4), 571-577.

¹⁵ Bridgham, S., Moore, T., Richardson, C. and Roulet, N. (2014). Errors in greenhouse forcing and soil carbon sequestration estimates in freshwater wetlands: a comment on Mitsch et al. (2013). Landscape Ecology, 29(9), 1481-1485.

¹⁶ Millar, C. I., Stephenson, N. L. and Stephens, S. L. (2007). Climate change and forests of the future: managing in the face of uncertainty. Ecological Applications, 17(8), 2145-2151.

¹⁷ U.S. EPA (2015). Connectivity of Streams and Wetlands to Downstream Waters: A Review and Synthesis of the Scientific Evidence. (EPA/600/R-14/475F). U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC.

¹⁸ Kauffman, J. B., Mahrt, M., Mahrt, L. A. and Edge, W. D. (2001). Wildlife of riparian habitats. In D. H. Johnson and T. A. O'Neil (ed.), Wildlife-Habitat Relationships in Oregon and Washington (Chapter 14 pp. 361-388). Corvallis, OR: Oregon State University Press.

¹⁹ ASWM (2015). Wetlands and Climate Change: Considerations for Wetland Program Managers. Association of State Wetland Managers.

²⁰ Jones, N. (2016). How growing sea plants can help slow ocean acidification. Yale Environment 360. Yale School of Forestry and Environmental Studies, June 6, 2017.

²¹ Barton, A., Waldbusser, G. G., Feely, R. A., Weisberg, S. B., Newton, J. A., Hales, B., Cudd, S., Eudeline, B., Langdon, C. J., Jefferds, I., King, T., Suhrbier, A. and McLaughlin, K. (2015). Impacts of Coastal Acidification on the Pacific Northwest Shellfish Industry and Adaptation Strategies Implemented in Response. Oceanography, 28(2), 146-159.

²² Franklin, J., Serra-Diaz, J. M., Syphard, A. D. and Regan, H. M. (2016). Global change and terrestrial plant community dynamics. Proceedings of the National Academy of Sciences, 113(14), 3725-3734.

Contact information

Amy Yahnke
Senior Ecologist
amy.yahnke@ecy.wa.gov
360-688-4263

Wetlands & climate change

Wetlands are vulnerable to climate change

Wetlands mitigate climate change

Wetlands and adaptation to climate change

Wetlands are vulnerable to climate change

Wetlands mitigate effects of climate change

Wetlands and adaptation to climate change

Wetlands in the hydrologic cycle

Wetlands and water quality

Wetlands and habitat

Impacts on buffers

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