Exploring Scenarios of Agricultural Intensification and Urbanization in a Environmentally Sensitive Watershed in Southern Brazil.

The Arroio Marrecas (Duck´s Creek) watershed, located in the Caxias do Sul municipality in the highlands of Rio Grande do Sul State, is a major drinking water source for 0.5 million inhabitants. The watershed comprises a unique mosaic of fragments of humid temperate forests (Brazilian pine) and grasslands. Due to the proximity of a major city, this region is undergoing a trend of agricultural intensification and urbanization (especially in the form of hobby farms).

This study assessed historical and current land uses with census and remote sense data, and investigated future states with the CLUE-S (Conversion of Land Use and Effects-Small regional extent) model. Scenarios were explicitly established by quantitative analysis of past changes, taking into account driving forces, land suitability, and neighborhood aspects–which include legal constraints on land use currently in place in Brazil and a zoning regulation issue by the municipality–in a multiscale approach, as proposed by CLUE-S developers.

A status quo scenario with minimal enforcement indicated that additional decrease of land under grasslands on suitable soils is very likely to occur by exapnsion of intensive agricultural systems such as horticulture and plantation forestry, wich pose potential threats to water quality and availability in the watershed.  On the other hand, a conservation-based scenario, with enforcement of existing legislation and active agricultural extension to ensure best management practices work showed little change in current land use patterns, from which environmental benefits could be inferred.

Our results explicitly depict the challenge faced by local authorities to assure long term water availability and quality in the Arroio Marrecas, and point to site-specific actions. Additional studies will link the established scenarios with water and soil models.