Recent Trends In Laurentian Great Lakes Ice Cover

A 39-winter (1963–2001) record of annual maximum ice concentration (AMIC), the maximum fraction of lake surface area covered by ice each year, is analyzed for each Great Lake. Lake Erie has the largest median AMIC (94%) followed by Lakes Superior (80%), Huron(63%), Michigan (33%), and Ontario (21%). The frequency distributionof AMICs is negatively skewed for Lakes Superior and Erie and positively skewed for Lakes Michigan and Ontario. Temporal and spatial patterns of typical and extreme AMICs is presented within the context of long-term average air temperatures and lake bathymetry. The variation of spatially averaged ice concentration with discrete depth ranges are discussed for each lake for the upper and lower end of the typical range of AMIC values. In general, ice concentration decreases with increasing depth ranges for a given winter. A decrease in the gradient of ice concentration with depths was also observed with an increase in the AMIC from winter 1983 to winter 1984. A temporal trend in the AMICs supports the hypothesis of three ice cover regimes over the past 39 winters. Approximately 44% of the highest quartile (10 highest) AMICs for the Great Lakes occurred during the 6-winter period:1977–1982 providing evidence of a higher ice cover regime during thisperiod relative to the 14 winters before them (1963–1976) and the 19 winters after them (1983–2001). Winter 1998 established new low AMIC extremes,and the AMIC averaged over the 1998–2001 winters is the lowest for theperiod of record on four of the five Great Lakes. These recent trends taken together are noteworthy as they may be harbingers of a period of even lower AMICs in the 21st Century.     

Normalization of metal concentrations in estuarine sediments from the Gulf of Mexico

Metal concentrations were examined in sediments from 497 sites within the estuaries of the Gulf of Mexico by the United States Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP). Data were normalized for extant concentrations of aluminum to isolate natural factors from anthropogenic ones. The normalization was based on the hypothesis that metal concentrations vary consistently with the concentration of aluminum, unless metals are of anthropogenic origin. Strong linear correlations (>75% variation explained) were observed between Al and Cr, Cu, Pb, Ni, and Zn. Moderate correlations (50–75% variation explained) were observed between Al and As or Ag. Weak but significant correlations (30–40% variation explained) were observed between Al and Hg or Cd. Based on these results, the spatial extent of contamination was examined. About 39% of sites with contamination by at least one metal occurred near population centers, industrial discharge sites, or military bases. The remainder of the observed contamination represented a dispersed pattern, including the lower Mississippi River (7%) and numerous agricultural watersheds (54%), suggesting that the contamination might be from nonpoint sources.     

Artisanal and Small-Scale Gold Mining in Senegal: Livelihoods,Customary Authority,and Formalization

In Sub-Saharan Africa, efforts to formalize the artisanal and small-scale gold mining (ASGM) sector under legal frameworks and to improve its environmental and health practices have largely failed as a result of top-down policy measures that make change complicated and burdensome for low-resource miners. Using evidence from a case study of the ASGM sector within areas of Senegal, this article demonstrates that ASGM has become an important source of income for many traditionally agricultural rural populations. The findings point toward the embedded nature of ASGM within customary management structures in Senegal, and demonstrate that customary authority is an important component of ASGM operations and development, and should be recognized and integrated into innovative formalization policies and better practices initiatives.     

Manufactured home building regulations and the February 2, 2007 Florida tornadoes

The Department of Housing and Urban Development (HUD) and the state of Florida implemented new wind load and tie-down regulations for manufactured homes following Hurricane Andrew. This article examines the effect of the new regulations on the likelihood that occupants of mobile homes would survive a tornado. On February 2, 2007, three tornadoes struck central Florida, resulting in 21 deaths in Lake County, all in manufactured homes. The deaths occurred almost exclusively in homes rated as leveled by the county tax appraiser. Manufactured homes built to the new regulations, however, were significantly less likely to be leveled. Regression analysis finds that manufactured homes built to the post-Andrew requirements were 79% less likely to be leveled than homes built prior to the HUD Code in 1976, and 68% less likely to be leveled than homes built after 1976 but before the 1994 wind load regulations. Construction of all manufactured homes in the tornado paths to the wind load and tie-down requirements could have reduced fatalities by 70%.

Nitrogen Stable Isotopes of Macrophytes Assess Stormwater Nitrogen Inputs to an Urbanized Estuary

The ¹⁵N composition of seagrass and benthic macroalgae from shallow waters of Sarasota Bay was measured to determine if stable N isotopes can be used to trace stormwater N into macrophyte production within an urbanized estuary. Results show isotopically enriched macroalgae at the landward stations near creeks and bayous in the central Bay and in the southern portion of the Bay. A known sewage outfall at Whitaker Bayou resulted in δ ¹⁵NO₃ values from 0 to +9‰. Isotopically enriched NH₄ values in Phillippi Creek (+10 to +17‰) were similar to the stormwater ¹⁵NH₄ values from the watershed (+7 to +18‰). Enriched N sources supported a significant portion of macroalgae N demands in the southern reaches of the Bay while isotopically depleted N sources (i.e., atmospheric deposition and/or fertilizers) appear to be more important for macroalgae in the northern portion of the Bay. Macroalgae were typically more enriched than seagrass and appear to be better indicators of anthropogenic loadings near creeks and bayous that receive large volumes of stormwater and other anthropogenic N sources. Historically, studies have used enriched ¹⁵N in macrophytes to infer wastewater influences. This study shows that stormwater N inputs need to be considered in nitrogen budgets for aquatic systems that show anthropogenic ¹⁵N enrichment.     

What if negative emission technologies fail at scale? Implications of the Paris Agreement for big emitting nations

A cumulative emissions approach is increasingly used to inform mitigation policy. However, there are different interpretations of what ‘2°C’ implies. Here it is argued that cost-optimization models, commonly used to inform policy, typically underplay the urgency of 2°C mitigation. The alignment within many scenarios of optimistic assumptions on negative emissions technologies (NETs), with implausibly early peak emission dates and incremental short-term mitigation, delivers outcomes commensurate with 2°C commitments. In contrast, considering equity and socio-technical barriers to change, suggests a more challenging short-term agenda. To understand these different interpretations, short-term CO₂ trends of the largest CO₂ emitters, are assessed in relation to a constrained CO₂ budget, coupled with a ‘what if’ assumption that negative emissions technologies fail at scale. The outcomes raise profound questions around high-level framings of mitigation policy. The article concludes that applying even weak equity criteria, challenges the feasibility of maintaining a 50% chance of avoiding 2°C without urgent mitigation efforts in the short-term. This highlights a need for greater engagement with: (1) the equity dimension of the Paris Agreement, (2) the sensitivity of constrained carbon budgets to short-term trends and (3) the climate risks for society posed by an almost ubiquitous inclusion of NETs within 2°C scenarios.

POLICY RELEVANCE

Since the Paris meeting, there is increased awareness that most policy ‘solutions’ commensurate with 2°C include widespread deployment of negative emissions technologies (NETs). Yet much less is understood about that option’s feasibility, compared with near-term efforts to curb energy demand. Moreover, the many different ways in which key information is synthesized for policy makers, clouds the ability of policy makers to make informed decisions. This article presents an alternative approach to consider what the Paris Agreement implies, if NETs are unable to deliver more carbon sinks than sources. It illustrates the scale of the climate challenge for policy makers, particularly if the Agreement’s aim to address ‘equity’ is accounted for. Here it is argued that much more attention needs to be paid to what CO₂ reductions can be achieved in the short-term, rather than taking a risk that could render the Paris Agreement’s policy goals unachievable.     

Modeling of Plume Capture by Continuous, Low-Permeability Barriers

Modeling was performed to simulate ground water flow through reactive barriers of lower hydraulic conductivity than the surrounding aquifer to determine the plume capture widths. As a plume approaches such a barrier, it spreads laterally. Therefore, to intercept an entire plume, the barrier must be wider than the upgradient width of the undisturbed plume. The results indicate that, for practical values of barrier thickness and plume width, hydraulic conductivities ten-fold less than that of the aquifer can be accommodated by making the width of the barrier approximately 20% greater than the upgradient width of the plume. Barrier hydraulic conductivities one-hundred-fold less than that of the aquifer may require barrier widths up to twice the width of the upgradient plume for plumes 100 feet wide (33 m) and as little as 1.1 times for plumes 1000 feet wide (325 m). The results presented here lend support to the view that novel emplacement methods that create zones of slightly lower hydraulic conductivity than the native aquifer may be viable alternatives to the excavation-and-backfill approaches which have thus far been used for installing permeable reactive barriers.