Intensive human land-use cover
The selected stream sites covered a wide range in percentages of agriculture, pasture, urbanization and afforestation, from nearly pristine (natural forest in Amazonia and grasslands in Uruguay) to highly altered areas (e.g., streams with high cover of land-use; Figure 1b,c). The intensive cover of each land-use was quantified based on percentage of the total upstream catchment of each stream site. To do so, each catchment area was delimited using geographical information system (GIS) databases with flow direction and digital elevation, running on QGIS (v. 3.6). The upstream percentages of agriculture, pasture, urbanization, and afforestation were visually assessed using satellite images and digital topographic maps from Google Earth (http://earth.google.com). The cover of each land-use was estimated at a resolution of 30m pixel in the upstream catchment, during the sampling periods (see, Figure 1 b and c).
In addition to the cover of the single land-uses, we created an index of intensive land-use cover (ILUC), which synthesizes the four land-uses (i.e., agriculture, pasture, urbanization, and afforestation) into a single combined land-use intensity measure. In this index, each land-use was standardized relative to its mean cover across all stream sites in each region. The ILUC index was then estimated by summing all standardized land-use types. This ILUC index is analogous to the land-use intensity index developed by Blüthgen et al. (2012), which has been commonly used in recent studies, as it provides a robust estimate of the impact of land-use intensity on biodiversity and ecosystem functioning (Allan et al., 2015; Gossner et al., 2016). The ILUC index is robust and positively correlated with agriculture, pasture and urbanization, thereby reflecting the simultaneous intensity in the cover of these land-uses (Figure S2). The ILUC can be considered ‘low’ when the catchment is occupied by a low percentage of agriculture, pasture, and urbanization (i.e., low land-use degradation). Conversely, ILUC is considered ‘high’ and ‘very high’ when these land-uses occupy more than 40% and 90% of the total catchment, respectively.