Regional analysis of soil-atmosphere nitrous oxide emissions in the Northern Atlantic Zone of Costa Rica

Regional analysis of greenhouse gas emissions is becoming increasingly impo rtant in answering questions related to environmental change, and typically employs a Geographic Information System (GIS) linked with a process-based simulation model. For the Northern Atlantic Zone (NAZ) in Costa Rica (281 6 49 ha), a regional analysis of soil-atmosphere nitrous oxide fluxes from th e dominant land-use types forest, cattle pastures, and banana plantations w as performed with both deterministic and stochastic variable representation s. The stochastic representation accounted for soil and land management var iability across nongeoreferenced fields within 1572 georeferenced land unit s in 13 relevant classes. Per class, frequency distributions of held-scale fluxes were simulated with a process-based model and Monte Carlo methods. S tochastic incorporation of both soil and land use variability resulted in a real (i.e. land unit-scale) fluxes that were 14-22% lower than estimates ba sed on averaged inputs. Soil heterogeneity was dominant. In addition, spatial flux patterns for current (1992) land use and two alte rnative land-use scenarios were evaluated using stochastic inputs. With cur rent management, the regional nitrous oxide-N flux (standard deviation in p arentheses) from agricultural land was 0.43 (0.13) Gg y(-1). Replacing natu ral grasses with mixtures of grasses and N-fixing species on relevant soil types and introducing different forms of banana plantation management (alte rnative I) increased the regional nux by 51% to 0.65 (0.22) Gg y(-1) When a ll natural grasses were replaced by fertilized improved species and allowin g different forms of banana plantation management (alternative II), the reg ional flux increased by 126% to 0.97 (0.68) Gg y(-1). Using the revised IPCC methodology, the 1992 nitrous oxide emission from ag riculture in the NAZ was estimated to be 0.32 Gg y(-1). Due to formidable d ata requirements, regional analysis may not easily be used to produce count ry-level estimates. However, regional analysis does provide a valuable benc hmark against which the more straightforward IPCC methodology can be evalua ted.