Methods
Study area
The Pepital River watershed is located between latitude 2° 20′ and 2° 23′ S and longitude 44°
20′ and 44° 30′ W, in the municipality of Alcântara, Maranhão state, Brazil (Figure 1). This
watershed is part of the Great Basin of the Atlantic and flows directly into the Atlantic
Ocean. The study area is situated in the Amazon region. The soil type is low fertility Ultisol;
the annual average precipitation is 2,000 mm with a distinct dry season from June to
December and mean temperature of 25ºC. The original vegetation, typical of Eastern Amazon
forests, features large trees and a well-defined understory [12]. It varies from non-flooded
riparian forests (headwaters) to flooded forest and mangroves in the delta.