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.