Nitrate removal in riparian wetlands: interactions between surface flow and soils

Riparian wetlands containing springs are thought to be ineffective at removing nitrate because contact times between the upwelled ground water and the underlying microbially active soils are short. Tracer experiments using lithium bromide (LiBr) and nitrate (NO3-N) injected at the surface were used to quantify residence times and NO3-N removal in a riparian swale characteristic of New Zealand hill-country pasture. An experimental enclosure was used with collecting trays at the downstream end to measure flow and concentration, shallow wells to measure subsurface concentrations, and an array of logging conductivity probes to monitor tracer continuously. The majority of added tracer reached the outlet more slowly than could be explained by surface flow, but more quickly than could be explained by Darcy seepage flow. There was evidence from the wells of tracer diffusing vertically to a depth of at least 5 cm into the surface soil layer, which was permanently saturated and highly porous. During dry weather 24 +/- 9% of added NO3-N was removed over a distance of 1.5 m largely by denitrification. The net uptake length coefficient for this wetland (K = 0.08 +/- 0.03 m(-1)) is slightly higher than the range (K = 0.01-0.07 m(-1)) measured in a small stream channel infested with macrophytes. Nitrate removal is expected to decrease with increasing flow. Seepage flow is estimated to have removed only 7 +/- 4% of the added NO3-N and we hypothesize that vertical diffusion substantially increases NO3-N removal in this type of wetland. Riparian wetlands with springs and surface flows should not be dismissed as having low NO3-N removal potential without checking whether there is significant vertical mixing.     

Nuclear crisis relocation: Issues for a host community-the case of Greenfield,Massachusetts, USA

US civil defense planning for nuclear attack since 1974 has emphasized the doctrine of crisis relocation. Under this doctrine, some 150 million people would evacuate from urban areas and other probable targets to rural host communities. The population of the latter would stay put to assist the relocatees. Local communities would be responsible for the welfare of up to ten times their normal population for an indefinite period of time.This study examined certain implications of crisis relocation for the town of Greenfield, Massachusetts, USA, a typical host community. Various assumptions were articulated regarding the timing of events, the season of year, weather, and social behavior. Assumptions were favorable to the success of crisis relocation. Nevertheless, Greenfield would face impossible burdens in attempting to provide fallout protection, water, food, medical care, and civil order. Additional pressures would arise from adjoining communities which are functionally dependent upon Greenfield for normal goods and services, but which would receive their own allotment of relocatees. Crisis relocation is not taken seriously in Greenfield and virtually no preparations have been made to implement it.     

The case for international emission trade in the absence of cooperative climate policy

We evaluate the efficacy of international trade in carbon emission permits when countries are guided strictly by their national self-interest. To do so, we construct a calibrated general equilibrium model that jointly describes the world economy and the strategic incentives that guide the design of national abatement policies. Countries’ decisions about their participation in a trading system and about their initial permit endowment are made non-cooperatively; so a priori it is not clear that permit trade will induce participation in international abatement agreements or that participation will result in significant environmental gains. Despite this, we find that emission trade agreements can be effective; that smaller groupings pairing developing and developed-world partners often perform better than agreements with larger rosters; and that general equilibrium responses play an important role in shaping these outcomes.