The Value of Wetlands in Protecting Southeast Louisiana from Hurricane Storm Surges

by Andrew Walnum

Wetlands are recognized as important habitats not only for their benefits of maintaining biodiversity, water purification, erosion control, and carbon sequestration, but also their ability to reduce the impacts of storm surges. Hurricanes pose a particular threat coastal areas as can be seen during Katrina and other devastating hurricanes. Wetland restoration in areas along the Gulf Coast seems to be a logical way to help reduce the devastating impacts of surges and floods from ocean storms. However, there has never been a full analysis combining the hydrological and economic impacts of increasing wetland areas along the Gulf Coast. The authors of this study used models to look at the effects of increasing wetlands on property damage in Southeast Louisiana, near New Orleans. Their study finds that an increase in 10% vegetation cover per square meter saves $99-$133 in property damage per unit area and only a 1% increase saves $24-$43.

Barbier and colleagues used storm simulations across a transect along with estimates of analysis of the economic impact of a storm surge. The transect was chosen using numerical models and the (ADCIRC) unstructured grid hydrodynamic model to predict the direction, intensity, and duration of storm surges. Twelve locations along the transect were collected using ADCIRC and were sub-sampled to create 100 points from sea to land. Next, the wetland-water ratio and bottom roughness along the transect was collected. The wetland-water ratio (WL) was based on a scale of 0-1 with 0 being open water and 1 representing solid marsh. Bottom roughness (WR) is the value of friction caused by vegetation with 0.002 being no vegetation and 0.045 being dense vegetation. Reducing surge power was then measured as the maximum amount of attenuation over each of the 11 transects between the 12 locations. Each one of the 11 transects was 6,000 meters long and the WL and WR along each transect was averaged. The authors were next able to change the WL and WR values to observe changes in storm surge attenuation. Changes in storm surge frequency and duration can vary greatly but the authors used expected damage function approach to find the marginal values of WL and WR on damage to surrounding human-inhabited areas.

The authors found a direct correlation between both increasing wetland-water continuity and vegetative roughness on storm surge attenuation. More and wetlands and vegetation decrease the intensity of incoming waves from storms. Increasing the wetland-water ration by only 1% reduced storm surge intensity by 8.4% to 11.2% and 1% increase in wetland roughness decreased storm surge by 15.4% to 28.1%. This reduction in storm surge also has an effect on the amount of money saved from damage reduction. A 10% increase in wetland-water continuity saves $99-$133 dollars per unit area and a 1% increase saves $24-$43 per unit area. If an increase in wetland continuity is expanded along the transect, the results are even more positive. An increase in wetland-water along the full length of a 6,000 meter transect results in saving $592,000 to $792,100 for the average sub-planning units in local parishes surrounding the wetlands. An increase in bottom roughness from vegetation accounts for $141,000 to $258,000 saved for the average sub-planning unit.

Although used for only one transect, the study helps illustrate the need for wetland protection in the future. Wetlands provide a large array of environmental services but there most important benefit may be the protection of coastal property. However, restoration is expensive and even with a large scale project along the Gulf Coast, there would continue to be a decrease in the number of wetlands over time. As more information on the economic benefits of maintaining wetlands comes out, it may prove to be more beneficial in the long-run to spend money on restoration to protect damage by storm surges.

Barbier EB, Georgiou IY, Enchelmeyer B, Reed DJ (2013) The Value of Wetlands in Protecting Southeast Louisiana from Hurricane Storm Surges. PLoS ONE 8(3)

The Value of Wetlands in Protecting Southeast Louisiana from Hurricane Storm Surges

by Andrew Walnum

Wetlands are recognized as important habitats not only for their benefits of maintaining biodiversity, water purification, erosion control, and carbon sequestration, but also their ability to reduce the impacts of storm surges. Hurricanes pose a particular threat coastal areas as can be seen during Katrina and other devastating hurricanes. Wetland restoration in areas along the Gulf Coast seems to be a logical way to help reduce the devastating impacts of surges and floods from ocean storms. However, there has never been a full analysis combining the hydrological and economic impacts of increasing wetland areas along the Gulf Coast. The authors of this study used models to look at the effects of increasing wetlands on property damage in Southeast Louisiana, near New Orleans. Their study finds that an increase in 10% vegetation cover per square meter saves $99-$133 in property damage per unit area and only a 1% increase saves $24-$43. Continue reading

Spring Invertebrate Communities in a Restored Wetland

by Andrew Walnum

The goal of every restoration project is to restore degraded ecosystems as closely as possible to their pre-disturbed functions. For wetlands, restoring the hydrological function of the area is usually what restoration ecologists aim to achieve, often at a rate which quickly makes changes to the hydrology and chemistry of the landscape. Although ecological restoration is an important growing field, very little is known about the inter-habitat effects of restoration. Freshwater springs regularly form along wetland ecosystems but there have been no studies to find how restoration might affect these habitats. Illmonen et al.(2013) looks at the effects of restoring wetland on these non-target ecosystems by looking at macroinvertebrate diversity. Because these habitats are geographically scattered the authors believed that recovery time for these springs may be slow due to poor dispersing mechanisms for macroinvertebrates, although more cosmopolitan species may take over quickly. Continue reading

Challenges of Ecological Restoration: Lessons from Forests in Northern Europe

by Andrew Walnum

The degradation of ecosystems around the world continues to occur and an increasingly rapid rate. As a relatively new field of ecology, ecological restoration sometimes struggles to find ways to combat the challenges faced by restoring disturbed ecosystems on a local and global scale. At the latest Convention on Biological Diversity (CBD, 2010 in Nagoya, Japan), restoring ecosystems was recognized as one of the most important tools for preventing future loss of bio diversity. Although this field has grown rapidly since the 1980s, many developed countries, especially in Northern Europe, are just starting recognize its importance. Several challenges are needed to be overcome in order to protect biodiversity on a large scale. This study uses northern forests in Europe as an example on what can and needs to be done in order to ensure long-term environmental and biodiversity preservation to reach goals set forth by the CBD. Continue reading

Ecological Restoration for the 21st Century

Ecological restoration is a relatively new and evolving field that developed in the 1980s and focuses on restoring land that has been degraded or destroyed by human activities. This study and practice is gaining popularity by governments, private businesses, and community organizations that recognize the importance of having healthy ecosystems for intrinsic, practical, and economic benefits.  However, in order for any ecological restoration project to work there must be a firm set of goals in place so that practitioners can plan and act accordingly to achieve ecosystem health. The Society for Ecological Restoration International Primer on Ecological Restoration (Primer for short) defined and detailed these goals in a section called “The Nine Attributes of Ecological Restoration” which places these attributes into four separate groups. Shackelford et al. (2013) attempts to build upon these goals as well as add a new group “The Human Element.” With a large increase in the amount of information about rebuilding ecosystems and restoring their health, changes to the nine attributes are needed for repairing environmental damage done to habitats by humans. –Andrew Walnum

Shackelford, N., Hobbs, R. J., Burgar, J. M., Erickson, T. E., Fontaine, J. B., Laliberté, E., Ramalho, C. E., Perring, M. P. and Standish, R. J. (2013), Primed for Change: Developing Ecological Restoration for the 21st Century. Restoration Ecology, 21: 297–304.

                  Shackelford and her colleagues found new ways to define ecological restoration goals and important categories by consulting with professors, practitioners, students, and post-doctorates versed in the study. These volunteers were placed into small individual groups for a literature review and discussion on articles pertaining to restoration ecology. Then, a larger group discussion was held with the participants to talk about key points that arose from reviewing the literature. The main points of the discussion groups were recorded in order to find what the experts or students felt were important to the field of ecological restoration.
                  The results from the discussions raise new thoughts on what the nine attributes of ecological restoration should be. Before, the list was as follows: 1. The restored ecosystem contains a characteristic assemblage of the species that occur in the reference ecosystem and that provide appropriate community structure. 2. The restored ecosystem consists of indigenous species to the greatest practicable extent. In restored cultural ecosystems, allowances can be made for exotic domesticated species and for noninvasive ruderal and segetal species that presumably co-evolved with them. Ruderals are plants that colonize disturbed sites, whereas segetals typically grow intermixed with crop species. 3. All functional groups necessary for the continued development and/or stability of the restored ecosystem are represented or, if they are not, the missing groups have the potential to colonize by natural means. 4. The physical environment of the restored ecosystem is capable of sustaining reproducing populations of the species necessary for its continued stability or development along the desired trajectory. 5. The restored ecosystem apparently functions normally for its ecological stage of development, and signs of dysfunction are absent. 6. The restored ecosystem is suitably integrated into a larger ecological matrix or landscape, with which it interacts through abiotic and biotic flows and exchanges. 7. Potential threats to the health and integrity of the restored ecosystem from the surrounding landscape have been eliminated or reduced as much as possible. 8. The restored ecosystem is sufficiently resilient to endure the normal periodic stress events in the local environment that serve to maintain the integrity of the ecosystem. 9. The restored ecosystem is self-sustaining to the same degree as its reference ecosystem, and has the potential to persist indefinitely under existing environmental conditions. Nevertheless, aspects of its biodiversity, structure, and functioning may change as part of normal ecosystem development, and may fluctuate in response to normal periodic stress and occasional disturbance events of greater consequence. As in any intact ecosystem, the species composition and other attributes of a restored ecosystem may evolve as environmental conditions change.
                  All of these attributes are meant to describe what a practitioner of restoration ecology should strive for when restoring an ecosystem. These nine attributes fit into the categories of species composition, ecosystem function, landscape context, or ecosystem sustainability. The authors also talk about the importance of fifth category, the human element. Humans play an integral part in shaping ecosystems and their involvement should be taken into account during restoration. The paper argues that in some cases restoration should be set to include permanent human involvement as can be seen in places like Europe where grasslands have been maintained for centuries by grazing animals or mowing. Social and cultural values must also be taken into account, especially in urban areas or areas that are considered important or sacred to a group of people.

                  The authors go on to add improvements to the original four categories. For species composition, they suggest recognizing that animals and plants are dynamic and that “indigenous” or “native” species can have large ranges. Also, using historical references for species composition may not be practical but rather looking at current, similar ecosystems to gain a better perspective about what species need to be a part of the restored habitat. When looking at ecosystem function, the authors argue that rapid climate change must be taken into account as the historical ecosystem did not have to face to same stresses or benefits that global climate change might raise. In addition, the economic or social services that a restored ecosystem can provide should also be taken into account. Using more trait-based measurements of ecosystem stability is also a new suggestion. They also explain the difference between resistance and resilience. Whereas resistance refers to an ecosystem being able to remain even through a large disturbance resilience is how an ecosystem is able to handle smaller disturbance over a long time period. For landscape context, it is important to understand the permeability of the landscape or how species and genes can spread through an environment. Knowing key areas that might allow invasive species, predators, or disease to enter can be taken into account and the ecosystem can be planned to minimize negative effects. Overall, the revision of ecological restoration goals can allow for further improvements to restoring an ecosystem that might not have been taken into consideration before. 

July 2012 Greenland Melt Extent Enhanced by Low-Level Liquid Clouds

Increased glacier melting due to global warming can have serious global consequences. Run-off from this rise in melting contributes to sea-level rise around the world which puts communities or even whole countries at risk of permanent flooding in the future. In July of 2012 the Greenland ice-sheet (GIS) experienced an enhanced period of melting that had not been observed in past years. Using various methods to record the melting and local temperature it was determined that low-level liquid clouds were the main factor causing the decrease in the ice-sheet (Bennartz 2013). These clouds were of a particular thickness that allowed them to trap heat while allowing in enough solar radiation to heat the surface of the glaciers. These clouds are part of a positive feed-back loop in which global warming has already contributed to ice melt in the arctic, putting more water into the atmosphere which contributes to the low-level liquid clouds. These clouds then further enhance the melting contributing to more of these types of clouds. Using multi-channel microwave measurements, the researchers were able to determine that these clouds can cover up to 20-50% of the arctic (Bennartz 2013). –Andrew Walnum 

Bennartz, R., Shupe, M., Turner, D., Walden, V., Steffen, K., Cox, C., Kulie, M., Miller, N., Pettersen, C., 2013. July 2012 Greenland melt extent enhanced by low-level liquid clouds. Nature 496, 83-86.

                  R. Bennartz and his colleagues used many different methods for observing melting and the low-level liquid clouds. Ground-based data were collected using “infrared, microwave, radar and lidar remote sensing observation” as part of the ‘Integrated characterization of energy, clouds, atmospheric state, and precipitation at Summit’(ICECAPS). These data were then compiled to plot the amount of ice melt for the Greenland icesheet. Based on cloud data the researchers were able to develop a model to explain the effects of low-level liquid clouds.
                  The results revealed that on days when low-level liquid clouds were present temperatures were able to rise to or above 0 oC. Melting occurred on days when clouds were absent the GIS did not experience surface temperatures above melting temperature. Using a model which takes into account temperature, specific heat, height, air density, infrared flux, and time, the researchers were able to conclude that it was in fact low-level liquid clouds contributing to the rise in temperature and ice clouds. However, the low-level liquid clouds do not always contribute to rising temperatures. The thickness of the clouds determines how much solar radiation is reflected or trapped. When the clouds are thin enough they allow more solar radiation to pass through to the earth while still radiating the heat downwards. When this occurs, surface temperatures are essentially the same temperatures as the clouds.

                  The helps give important insight into future models of climate change in the arctic. The results from this paper show how important low-level liquid clouds are to surface energy balance (the amount of infrared energy that hits the GIS’ surface and is retained or reflected.) Modern climate models do not take into account how changes in the atmosphere will contribute to cloud cover which inhibits the models from recognizing feedback loops that might further contribute glacier and ice-sheet melting in Greenland.