Ecosystem activity
Vegetation activity as captured by NDVI from MODIS and LANDSAT images
showed divergent temporal trends for croplands, native vegetation and
wetlands (Table 2 and Figure 9). The long-term analysis of the whole El
Morro catchment based on MODIS data revealed a decreasing greenness
across the forests > grassland/pasture >
cropland (all differences being significant with p<0.01, Table
2). An increased vegetation activity with time, and likely water
transpiration, was observed comparing the second decade (2011-2020) with
the first (2000-2010) with average greenings of 5.5 and 3.5 % for
forests and grasslands/pastures, respectively. In the same temporal
comparison, croplands and sediment deposits experienced a -1.1 and -6.7
% drops, respectively (Table 2). The catchment as whole, displayed a
small decadal greenness increase of 1.3% as the previous contrasting
trends compensated out, particularly between the dominant components of
grassland/pastures vs. croplands (Table 2).
With the higher spatial resolution of LANDSAT imagery, we targeted
vegetation types and change trajectories more precisely focusing on the
shorter period that encompassed the last erosion episode and our field
observations (Figure 9). Forest sustained the highest greenness
throughout the whole period while croplands the most temporally
variable. Pre existing wetlands and new wetlands emerging in croplands,
displayed a sustained and stable greenness raise (Figure 9). Deposits
landed on croplands in 2015 showed a sharp greenness decline followed by
a steady recovery that was still not completed but close to wetlands and
croplands four years later. The single dried wetland location (site B),
had a high greenness that matched that of forests until one year after
the new incisions drained the area. After that time its greenness
dropped steadily for three consecutive years approaching levels that are
close to those in the recovering sediment deposits (Figure 9).