Hydro-Morphological Disturbance and Suitability for Temporary Agriculture of Riverine Islands in a Tropical Wandering River

Fluvial islands define fundamental interfaces between the aquatic and terrestrial environment in river corridors, have unique environmental value, and represent a place of interest for human communities worldwide. Temporary agriculture occurs in many riverine islands in tropical regions of the planet, but this has received little attention so far. By integrating remote sensing, field and laboratory investigations, hydrological and hydraulic analysis, we quantified controls on their agricultural suitability in terms of fluvial disturbance, morphological stability, soils characteristics, and selection of flood-resistant crops. A highly dynamic foothill reach of the wandering Huallaga River (Peruvian Amazon) where temporary agriculture is practiced by local farmers is used as a case study. Islands show rapid turnover rates, with their number and total area tripling in the 1986-2019 period, in association with recent river corridor widening. Simulated disturbance-free windows of opportunity can be long enough (up to 230 days, for plantain) to cultivate on the most elevated portions of the largest islands, about 3 m above the thalweg. A gradient of increasing agricultural suitability paralleled that of decreasing fluvial disturbance from the most recently developed island (e.g., organic matter 0.2%-1.2%) to the more stable one (0.1%-2.6%) to the established floodplain (0.5%-3.5%). While the floodplain is more suitable for farming, we quantified how suitable islands are for temporary food production. Our results are generalized through a conceptual model for fluvial islands' agricultural suitability, thus filling an important knowledge gap about the characteristics of those highly sensitive environments within floodplains still moderately affected by human activities.

Automated summary

The study evaluates the agricultural suitability of riverine islands by integrating various research methods, revealing the potential for temporary agriculture on these islands and exploring the differences in agricultural suitability among different islands.