AMAZON WATERSHEDS

Work in small watersheds has a long and distinguished history in ecology in addressing questions about how land use alters ecosystem biogeochemistry and the movement of material from land into streams and rivers. We work at the interface between hydrology and biogeochemistry. I work with hydrologists and biogeochemists to combine hydrometric measurements with chemical measurements to identify the specific flowpaths that water takes as it moves in watersheds.

We work in forest and pasture watersheds at Fazenda Rancho Grande in Rondônia and in watersheds Fazenda Tanguro, a large soybean farm in Mato Grosso. These experiments show that surficial flowpaths such as overland flow increase dramatically following deforestation. They indicate large sinks for dissolved nitrogen in deep soils and at the interface between soils and ground waters in forest. They also show that deforestation decreases nitrate concentrations in soil solution and a leads to a dramatic "homogenization" of flowpath nitrogen chemistry. We developed end member mixing models to use stream chemistry to identify flowpath sources to stream water, and we combine these with measurements of water levels and flows during events to develop a dynamic picture of how water moves and key biogeochemical transformations within flowpaths.

Small forest stream at Fazenda Tanguro in Mato Grosso.

Shelby Hayhoe and Rich McHorney sample water in a Tanguro pasture stream.

Vania Neu filters a water sample in a forest headwater stream.