The potential for carbon dioxide removal by enhanced rock weathering in the tropics: An evaluation of Costa Rica.

Tropical environments show great potential to sequester CO2 by enhanced rock weathering (ERW) of powdered mafic rocks applied to agricultural fields. This study seeks to assess carbon dioxide reduction (CDR) potential in the humid tropics (1) by experimental weathering of mafic rock powders in conditions simulating humid tropical soils, and (2) from weathering rates determined from a Holocene tropical soil chronosequence where parent material is andesitic sediments. Experimentally determined weathering rates by leaching of basaltic andesites from Costa Rica (Arenal and Barva) for 50 t ha-1 applications indicate potential sequestration of 2.4 to 4.5 t CO2 ha-1 yr-1, whereas the USGS basalt standard BHVO-1 yields a rate of 11.9 t ha-1 yr-1 (influenced by more mafic composition and finer particle size). The chronosequence indicates a rate of 1.7 t CO2 ha-1 yr-1. The weathering experiment consisted of 0.6 mm of powdered rock applied atop 12 mm of Ultisol at 35 °C. To simulate a tropical soil solution, 100-mL aliquots of a dilute solution of oxalic acid in carbonated DI water were rained onto soils over a 14-day period to simulate soil moisture in the humid tropics. Solutions were collected and analyzed by ICPMS for concentrations of leached cations. A potential ERW scenario for Costa Rica was assessed assuming that one-half of lowland agricultural kaolinitic soils (mainly Ultisols, common crop and pasture soils, excluding protected areas) were to receive 50 t ha-1 of annual or biennial applications of powdered mafic rock. With an experimentally determined humid tropical CDR rate for basaltic andesite (3.5 t ha-1 yr-1) and allowances for carbon costs (e.g. emissions from processing and delivery) that reduce CDR to a net 3.2 t ha-1 yr-1, potential annual CDR of this tropical nation is ∼2-4 million tons, amounting to ∼25-50 % of annual CO2 emissions (mainly from transportation in Costa Rica).

Urbanization Affects Composition but Not Richness of Flower Visitors in the Yungas of Argentina.

Urban areas represent a spatially small impact in relation to other land-uses such as livestock and agriculture, but they undergo rapid changes. Such changes involve their size, shape, interconnectivity, and composition of natural patches. Habitat loss generated by urbanization affects the diversity and abundance of bees and other flower visitors in many sites. In general, the presence of urban areas represents a strict boundary to flower visitors and restricts their movement between natural and suburban habitat patches. The aim of this work is to evaluate how the flower visitor assemblage change along an urban-natural gradient in northwest Argentina. We established five areas in the Yungas ecoregion and sampled three sites with different degrees of urbanization (urban, suburban, and natural), at each area, reaching 15 sites. At each site, we sampled flower visitors during 5-min observation periods done over flowering plants. We found 197 morphospecies of flower-visiting insects along the gradient and an invariant richness, abundance, and Shannon diversity. The assemblage presented the same taxonomic group distributions in the three categories established. However, in urban sites, solitary bees and bees with soil borrowing nesting type predominate, while eusocial and cavity nesting bees were the main flower visitors in suburban sites. Our results suggest that the cities of northwestern Argentina are not a strict boundary for flower visitors; however, urbanization seems to be selecting and favoring certain flower-visitor species traits.