Appropriate experimental ecosystem warming methods by ecosystem, objective, and practicality

The temperature of the Earth is rising, and is highly likely to continue to do so for the foreseeable future. The study of the effects of sustained heating on the ecosystems of the world is necessary so that we might predict and respond to coming changes on both large and small spatial scales. To this end, ecosystem warming studies have been performed for more than 20 years using a variety of methods. These warming methods fall into two general categories: active and passive. Active warming methods include heat-resistance cables, infrared (IR) lamps and active field chambers. Passive warming methods include nighttime warming and passive field chambers. An extensive literature review was performed and all ecosystem warming study sites were compiled into a master list. These studies were divided by latitude and precipitation, as well as the method type used and response variables investigated. The goals of this study were to identify: (1) the most generally applicable, inexpensive and effective heating methods; and (2) areas of the world that are understudied or have been studied using only limited warming methods. It was found that the most generally applicable method, and the one that is most true to climate change predictions, is IR heating lamp installation. The least expensive method is passive chambers. The extreme lower and upper latitudes have been investigated least with ecosystem warming methods, and for the upper-mid-latitudes (60–80°) there have been limited studies published using methods other than passive chambers. Ecosystem warming method limitations and recommendations are discussed.     

Comment on the comment by Amthor et al. on “Appropriate experimental ecosystem warming methods” by Aronson and McNulty

In a recent comment on the paper by Aronson and McNulty (2009) about “Appropriate experimental ecosystem warming methods by ecosystem, objective, and practicality”, Amthor et al. (2010) state that infrared lamps do not warm open-field plots by the mechanism expected with global warming. While this statement is correct, in the aftermath of their comment, confusion exists about how warming with infrared heaters can be related to global warming. This comment illustrates how infrared heating at “constant temperature rise” relates in a quantitative way to anticipated global warming. Amthor et al. (2010) also state that changes in vapor pressure gradient from leaf to atmosphere are an issue with infrared heating, but this problem can be minimized with supplemental irrigations in controlled amounts. Therefore, “constant temperature rise” infrared warming experiments with supplemental irrigations are a viable T-FACE (temperature free-air controlled enhancement) that can be used in combination with CO₂-FACE to produce conditions more representative of future open-fields than can be done with chambers with their many known artifacts.     

Combining landslide and contaminant risk: a preliminary assessment

Background, aim, and scope

The aim of this paper is to highlight a not yet recognized hazard for mass failure (landslides) of contaminated soils into rivers and to provide an understanding of important interactions of such events. A first effort to investigate the problem is made focusing on the south eastern part of the Göta Älv river valley, in Sweden, by combining geographical information on potentially contaminated sites with slope stability levels on maps. The objectives of this study were to: (1) Review current Swedish risk assessment methodologies for contaminated areas and landslides, and analyze their capability to quantify the risk of contaminated areas being subject to landslides. (2) Investigate the presence of contaminated areas at landslide risk along the Göta Älv river valley. (3) Provide an overview of the national methods for landslide risk analysis and for environmental risk classification, followed by a comparison between the methods and the results from the superposition of the two methods for the study site. (4) Make a first attempt to conceptualize the release and transport mechanisms.

Materials and methods

Environmental risk assessment data of the study site was combined with data on slope stability levels. Conceptual issues of the release and transport scenario were identified and a first conceptual model was created.

Results

Of 31 potentially contaminated sites, eight had moderate to high probability for landslide, and of these eight sites, five were classified as having a high or very high environmental risk. These findings had not been revealed when the data had only been considered separately. The ‘actual’ risk could hence be even higher than the highest environmental risk class actually suggests. By visualizing results from the landslide risk analysis with the results from the environmental risk classification of contaminated sites, a better understanding of the potential hazard involved is obtained.

Discussion

The release mechanisms as a result of a landslide into surface water were conceptualized using two time scales: the instantaneous and the long-term release. It is clear that the Swedish method for landslide risk assessment and for environmental risk assessment of contaminated soil considers hazard events that are characterized by different time scales. The method for landslide risk assessment addresses events that are rapid (occurring over minutes) with instantaneous impact and consequences. Measurements are made within a short time after the event (days to months). The environmental risk assessment is done with respect to events that are slowly evolving (over years or decades) and any possible consequence materializes after a long period of time.

Conclusions

The combined data provided a more solid basis for decisions; however, inherent difficulties when combining data based on different methods were revealed. Separate assessment methodologies executed by different authorities may lead to incorrect assessments and inappropriate protective measures.

Recommendations and perspectives

The effects and the consequences of landslides in areas with contaminated soil need to be further investigated. The climate change expected to occur over the next hundred years will increase the probability of slope failures, such as landslides, in many parts of the world where the precipitation is predicted to increase (e.g., in Scandinavia). This will accentuate the need for methods and models to assess the impact of such events. In order to achieve established environmental quality objectives there is an urgent need for models and assessment principles (criteria) for contaminated areas that are at risk of experiencing slope failure. Knowledge of the governing processes that control the release and transport of substances under a variety of conditions, taking into account characteristic spatial and temporal scales, is required.     

Greenhouse gas flux from cropland and restored wetlands in the Prairie Pothole Region

It has been well documented that restored wetlands in the Prairie Pothole Region of North America do store carbon. However, the net benefit of carbon sequestration in wetlands in terms of a reduction in global warming forcing has often been questioned because of potentially greater emissions of greenhouse gases (GHGs) such as nitrous oxide (N₂O) and methane (CH₄). We compared gas emissions (N₂O, CH₄, carbon dioxide [CO₂]) and soil moisture and temperature from eight cropland and eight restored grassland wetlands in the Prairie Pothole Region from May to October, 2003, to better understand the atmospheric carbon mitigation potential of restored wetlands. Results show that carbon dioxide contributed the most (90%) to net-GHG flux, followed by CH₄ (9%) and N₂O (1%). Fluxes of N₂O, CH₄, CO₂, and their combined global warming potential (CO₂ equivalents) did not significantly differ between cropland and grassland wetlands. The seasonal pattern in flux was similar in cropland and grassland wetlands with peak emissions of N₂O and CH₄ occurring when soil water-filled pore space (WFPS) was 40-60% and >60%, respectively; negative CH₄ fluxes were observed when WFPS approached 40%. Negative CH₄ fluxes from grassland wetlands occurred earlier in the season and were more pronounced than those from cropland sites because WFPS declined more rapidly in grassland wetlands; this decline was likely due to higher infiltration and evapotranspiration rates associated with grasslands. Our results suggest that restoring cropland wetlands does not result in greater emissions of N₂O and CH₄, and therefore would not offset potential soil carbon sequestration. These findings, however, are limited to a small sample of seasonal wetlands with relatively short hydroperiods. A more comprehensive assessment of the GHG mitigation potential of restored wetlands should include a diversity of wetland types and land-use practices and consider the impact of variable climatic cycles that affect wetland hydrology.