Estimated N2O and CO2 Emissions as Influenced by Agricultural Practices in Canada

The Denitrification-Decompostion (DNDC) model was used to estimate the impact of change in management practices on N₂O emissions in seven major soil regions in Canada, for the period 1970 to 2029. Conversion of cultivated land to permanent grassland would result in the greatest reduction in N₂O emissions, particularly in eastern Canada wherethe model estimated about 60% less N₂O emissions for thisconversion. About 33% less N₂O emissions were predicted for a changefrom conventional tillage to no-tillage in western Canada, however, a slight increase in N₂O emissions was predicted for eastern Canada. GreaterN₂O emissions in eastern Canada associated with the adoption of no-tillage were attributed to higher soil moisture causing denitrification, whereas the lower emissions in western Canada were attributed to less decomposition of soil organic matter in no-till versus conventional tilled soil. Elimination of summer fallow in a crop rotation resulted in a 9% decrease in N₂O emissions, with substantial emissions occurringduring the wetter fallow years when N had accumulated. Increasing N-fertilizer application rates by 50% increased average emissions by 32%,while a 50% decrease of N-fertilizer application decreased emissions by16%. In general, a small increase in N₂O emissions was predicted when N-fertilizer was applied in the fall rather than in the spring. Previous research on CO₂ emissions with the CENTURY model (Smith et al.,2001) allowed the quantification of the combined change in N₂O andCO₂ emissions in CO₂ equivalents for a wide range of managementpractices in the seven major soil regions in Canada. The management practices that have the greatest potential to reduce the combined N₂O andCO₂ emissions are conversion from conventional tillage to permanent grassland, reduced tillage, and reduction of summer fallow. The estimated net greenhouse gas (GHG) emission reduction when changing from cultivated land to permanent grassland ranged from 0.97 (Brown Chernozem) to 4.24 MgCO₂ equiv. ha^–1 y^–1 (BlackChernozem) for the seven soil regions examined. When changing from conventional tillage to no-tillage the net GHG emission reduction ranged from 0.33 (Brown Chernozem) to 0.80 Mg CO₂ equiv. ha^–1 y^–1 (Dark GrayLuvisol). Elimination of fallow in the crop rotation lead to an estimated net GHG emission reduction of 0.43 (Brown Chernozem) to 0.80 Mg CO₂ equiv.ha^–1 y^–1 (Dark Brown Chernozem). The addition of 50% more or 50% less N-fertilizer both resulted in slight increases in combined CO₂ and N₂O emissions. There was a tradeoff in GHG flux with greaterN₂O emissions and a comparable increase in carbon storage when 50% more N-fertilizer was added. The results from this work indicate that conversion of cultivated land to grassland, the conversion from conventional tillage to no-tillage, and the reduction of summerallow in crop rotations could substantially increase C sequestration and decrease net GHG emissions. Based on these results a simple scaling-up scenario to derive the possible impacts on Canada's Kyoto commitment has been calculated.     

Transport over a narrow shelf: Exuma Cays, Bahamas

Current meter and temperature data were collected over a 402-day period from an outer shelf and a tidal channel study site in the Exuma Cays, Bahamas. The shelf width is less than 2 km, and floods and ebbs through a nearby tidal channel extend across the entire shelf and reduce coherence of wind forcing and along-shelf flow. The data are used in perturbation analyses to investigate the across-shelf turbulent transport of heat and momentum over seasonal time scales. Data show a net landward transport of both heat and momentum over the course of the study, but the perturbation products contain distinct seasonal cycles. In fall and winter months, across-shelf heat and momentum fluxes are landward, while during spring and summer months fluxes are seaward. Comparison of shelf-water temperature with the temperature of bank water leaving on the ebb suggests that seasonal cycles of across-shelf heat and momentum in shelf waters are influenced by the seasonal export of relatively warm and cool water from Great Bahama Bank.Responsible Editor: Iris Grabemann     

Petrogenesis of orthopyroxene- and amphibole-bearing andesites, Mustique, Grenadine Islands, Lesser Antilles Arc: Isotope, trace element and physical constraints

Abstract On the island of Mustique, fresh and propylitized olivine–plagioclase–clinopyroxene basalt, plagioclase–clinopyroxene–orthopyroxene and plagioclase–clinopyroxene–amphibole andesite lavas and minor intrusions are interbedded with Oligocene pyroclastic and epiclastic rocks. Chemical data show that two isotopically identical, but chemically different, suites of lava are present: (i) the OPXS (⁸⁷Sr/⁸⁶Sr 0.70403–0.70454; ¹⁴³Nd/¹⁴⁴Nd 0.512952–0.512986; δ¹⁸O_cpx 5.49 and 5.61), comprising basalts and orthopyroxene‐bearing andesites; and (ii) the AMPHS (⁸⁷Sr/⁸⁶Sr 0.70401–0.70457; ¹⁴³Nd/¹⁴⁴Nd 0.512981–0.513037; δ¹⁸O_cpx 5.54), made up of basalts and amphibole‐bearing andesites. The OPXS has higher contents of TiO₂, P₂O₅, light rare earth elements, Sm, Pb, Th, U, Zr, Y and Nb, and higher La/Yb ratios than the AMPHS. The isotopic data suggest that both suites formed from melts derived from the same subduction‐modified depleted mantle source as the volcanic rocks of nearby St Vincent and Bequia, and the northern islands of the Lesser Antilles Arc. The immobile trace element contents, and La/Yb ratios, of the OPXS are indicative of ～10% partial melting of the source, whereas those of the AMPHS are indicative of ～25% partial melting. The within‐suite chemical variation of the OPXS is consistent with ～45% fractional crystallization of its intratelluric mineral assemblages, and that of the AMPHS is consistent with the removal of ～65% of its intratelluric assemblages. Experimental evidence suggests that both suites of basalt crystallized at pressures <8 kbar from melts containing 1–2 wt% water. After extensive fractional crystallization, the andesites crystallized at pressures between approximately 5 and 2 kbar. The OPXS magmas appear to have lost more of their water content than the AMPHS magmas. Thus, the OPXS andesites formed from melts with an estimated water content of 2–3 wt%, whereas the AMPHS andesites formed from melts containing at least 4.5 wt% water.     

Revolution or evolution? New Zealand agriculture since 1984

Agriculture was the primary target of moves to deregulate the New Zealand economy in 1984. Within twelve-months all production subsidies had been removed, including those for fertiliser and other inputs, as well as funding for drought relief, floods and other natural weather disasters. Whereas at the start of 1984, subsidies were estimated to represent as much as 33% of farm income, by 2003 this had fallen to less than 2% with most of this spent on agricultural research. The anticipated shift of thousands of people off the land did not appear to occur, and by conventional measures at least New Zealand agriculture in 2003 is a major success story. At the core of the changes imposed on agriculture was a commitment to remove all state or government distortions from the system and to fully expose the agricultural sector to market forces. This included wide-ranging and fundamental changes in the broad institutional context within which agriculture must operate. All this was achieved at great social cost and with a significant impact on the environment. In many respects New Zealand agriculture is now very different from that in 1984. Some sectors, such as dairying, have grown and become increasingly industrialised. On the other hand, sheep farming, particularly for wool has struggled to maintain its market share, while other enterprises have emerged as significant sources of income, including horticulture, viticulture and fruit. It is argued here that the trends evident in New Zealand agriculture since 1984 pre-existed the reform period and that the apparent success of the reforms evident at a national scale have not addressed or removed the fundamental problems which face New Zealand agriculture, just as they do modern agricultural systems elsewhere. This revised version was published online in July 2006 with corrections to the Cover Date.     

Web-cam’s potential for collaborative activities in the Earth sciences

We report here our experiences from using easily acquired web-cam components for collaborative ventures in the Earth sciences. We have used a variety of hardware and different software. We demonstrate from various locations in the U.S.A. the feasibility of using web-cam in multitudinous activities, relevant for conducting research and knowledge dissemination. We summarize the quality of the connections from the various combinations of communicating parties. Today, web-cams can be utilized as an economical and viable means of point-to-point communication in the Earth science community. Greater bandwidth is sorely needed for activities such as multi-party conferencing on the present internet network. We propose that web-cam can be readily deployed as a web-service for facilitating collaborative research over the GRID infrastructure, using the middleware Narada-Brokering. Web-cam will play an important role in the emerging field of geoinformatics.     

Sulfur isotope fractionation during growth of sulfate-reducing bacteria on various carbon sources

Stable sulfur isotope fractionation during microbial sulfate reduction is a potential tool to estimate sulfate reduction rates at field sites. However, little is known about the influence of the utilized carbon source on the magnitude of sulfur isotope fractionation. To investigate this effect, both a pure culture (strain PRTOL1) and enrichment cultures from a petroleum hydrocarbon (PHC)-contaminated aquifer were used and grown in batch cultures on various carbon sources with an initial sulfate concentration of 1 mmol/L. As sole carbon sources the PHC components naphthalene, 1,3,5-trimethylbenzene, and heating oil (enrichment culture) and the organic acids acetate, pyruvate, benzoate, and 3-phenylpropionate (enrichment culture and PRTOL1) were used. Sulfate reduction rates of all cultures ranged from 6 ± 1 nmol cm⁻³ d⁻¹ (enrichment culture grown on 1,3,5-trimethylbenzene) to 280 ± 6 nmol cm⁻³ d⁻¹ (enrichment culture grown on pyruvate). Cell-specific sulfate reduction rates ranged from 1.1 × 10⁻¹⁴ mol cell⁻¹ d⁻¹ (PRTOL1 grown on pyruvate) to 1.5 × 10⁻¹³ mol cell⁻¹ d⁻¹ (PRTOL1 grown on acetate). Sulfur isotope enrichment factors (ε) for the enrichment culture ranged from 16.1‰ (3-phenylpropionate) to 34.5‰ (1,3,5-trimethylbenzene) and for PRTOL1 from 30.0‰ (benzoate) to 36.0‰ (pyruvate). Cultures of PRTOL1 always showed higher ε values than the enrichment culture when grown on the same carbon source due to culture-specific properties. Higher ε values were obtained when the enrichment culture was grown on PHC components than on organic acids. No relationship between ε values and cell-specific sulfate reduction rate existed when all data were combined. When comparing the magnitude of ε values determined in this laboratory study with ε values measured at contaminated and uncontaminated field sites, it becomes evident that a multitude of factors influences ε values at field sites and complicates their interpretation. The results of this study help us assess some of the general parameters that govern the magnitude of ε in sulfate-reducing environments.     

Urban land transformation for pro-poor economies

The transformation of land into a setting for clustering local economies can become an important cornerstone of poverty policy. This transformation has several functional aspects, which in turn have important institutional and political aspects. Underlying both the functional and institutional factors is the role of local government and local democracy. Such a conceptualization puts to center stage several paradoxes: A terrain that seems “slum-like” turns out to be highly productive and employment generating. Complex tenure forms and mixed land use seen as “unplanned” turn out to be pre-requisites for economic development. There are institutional paradoxes that contrast efforts at “transparency” and managerial “best practices”. Here, the messiness of local bureaucracies in municipal government turns out to be critical for poor groups to influence interventions in their favor. Influencing the public process may be more effective in stealth-like ways rather taking a more visible approach. Most fundamentally these issues remind us that the potential of cities to reinforce or reduce poverty moved far beyond projects and programs and the normative frameworks used by planners and administrators. Instead, it is the transformative process of turning land into economic settings that might be at the center stage. This is a stage where poor groups are the central actors who stealth-like draw on complex alliances across ethnic and class lines to shapes cities in their interests.     

A new Geologic Time Scale, with special reference to Precambrian and Neogene

A Geologic Time Scale (GTS2004) is presented that integrates currently available stratigraphic and geochronologic information. Key features of the new scale are outlined, how it was constructed, and how it can be further improved. The accompanying International Stratigraphic Chart, issued under auspices of the International Commission on Stratigraphy (ICS), shows the current chronostratigraphic scale and ages with estimates of uncertainty for all stage boundaries. Special reference is made to the Precambrian part of the time scale, which is coming of age in terms of detail, and to the Neogene portion, which has attained an ultra-high-precision absolute-age calibration.     

Kimberlite metasomatism at Murowa and Sese pipes, Zimbabwe

Metasomatism accompanying kimberlite emplacement is a worldwide phenomenon, although infrequently described or recognised. At the Cambrian-aged Murowa and Sese kimberlite clusters located within the Archean Zimbabwe Craton just north of the boundary with the Limpopo Mobile Zone in southern central Zimbabwe, the metasomatism is intense and well exposed and the processes can be readily studied. Dykes, sills and the root zones of pipes are exposed at the current erosion level. Kimberlite lithologies present are hypabyssal macrocrystic kimberlite (“HMK”), HMK breccia, and tuffisitic kimberlite breccia (“TKB”) including minor lithic tuffisitic kimberlite breccia (“LTKB”). Country rocks are 2.6 Ga Chibi and Zimbabwe granite batholiths emplaced into 2.6–2.9 Ga or earlier Archean tonalitic gneiss and greenstones. During initial metasomatism, the granites become spotted with green chlorite, needles of alkaline amphiboles (winchite, riebeckite, arfvedsonite) and pyroxenes (aegirine–augite) with minor carbonate and felts of talc. Oligoclase feldspar becomes converted to albite, extensively altered, dusted and reddened with hematite, whereas K-feldspar remains unaffected. The granites become converted to syenite through removal of quartz. More intense metasomatism at Murowa and Sese results in veins of green metasomatite which cut and disrupt the granite. Progressive disruption entrains granite blocks, breaking down the granite still further, spalling off needle-like granite slivers, and so giving rise to LTKB. This process of disruption and entrainment appears to be the manner of initial development of the pipe structure. The chemistry of the metasomatite is intermediate between granite and kimberlite. Compared to granite country rock it has markedly higher Mg, Cr, Ni, CO₂ and H₂O+, higher Ca, Mn, Nb, Sr, P, Fe³⁺/Fe²⁺ ratio, U, Co, and Cu, approximately equal TiO₂, K₂O, Na₂O, La, Ta, Rb, Zr, Zn and resultant lower SiO₂, Al₂O₃, Ga and Y. The metasomatite Na₂O/K₂O ratio is slightly higher than that of the granite. The metasomatic process is broadly analogous to fenitisation of granitic wall rock accompanying carbonatite complex emplacement. The metasomatism at Murowa and Sese was caused by fluids from the rising but confined proto-kimberlite melt penetrating into cracks and matrix of granite country rock and reacting with it. These fluids were CO₂-rich, hydrous, oxidising, enhanced in ultramafic elements and carried low levels of Na.     

Field and petrological evidence for a Late Palaeozoic (Upper Carboniferous–Permian) age of the Erfaulet orthogneiss (Gran Paradiso,western Alps)

In the Gran Paradiso massif (western Alps), the boundary between the Erfaulet orthogneiss and the overlying metasediments (Money Complex) is interpreted as a Late Palaeozoic intrusive contact. Major arguments in favour of this hypothesis are: (i) the obliquity of the sedimentary layering with respect to the contact; (ii) the presence of aplitic dykes within the Money Complex; (iii) the lack of a mylonitic zone; and (iv) rare relics of an early generation of garnet in the Money metasediments, interpreted as evidence of the contact metamorphism of the Erfaulet granite. To cite this article: B. Le Bayon, M. Ballèvre, C. R. Geoscience 336 (2004).