Free and underfit-scavenger river dynamics dominate the large Amazonian Pacaya-Samiria wetland structure

Abstract

The Peruvian Amazon is known for harboring the greatest biodiversity on the planet, with a world record for biodiversity per unit area. Previous studies suggested that the high ecological value depends on correlations between ecosystem functionality and seasonal inundation control vegetation patches. However, the knowledge on how river morphodynamics and its complex erosion-depositional processes influence the aquatic mosaic and fishing activity in the region is still incipient. This study examines the hydrogeomorphology of the Peruvian tropical wetland of Pacaya Samiria, located in Western Amazonia, and its role in the distribution of aquatic habitats. By using remote sensing techniques, the hydrogeomorphological connectivity that bounds the Pacaya Samiria National Reserve is characterized by ancient to modern river processes. Additionally, river signatures developed by the Ucayali, Marañon, Huallaga, Pacaya, and Samiria Rivers overlap with fish extraction and dominant vegetation to describe how geomorphology is associated with the spatial distribution of fishing zones. Results indicated that paleochannels regulate wetland drainage within the Ucamara Depression, supporting stational water stagnation, vegetation cover, and formation of carbon rich detritus, relevant aspects to understand fish traits. Moreover, the Ucayali River dominates river dynamics in the Pacaya Samiria wetland, thus playing a pivotal role in shaping the complexity of streams and lakes. Furthermore, underfit-scavenger meandering rivers are observed in areas where paleochannels from large rivers are found. A geomorphological characterization of drainage patterns in freshwater environments, such as Amazonian wetlands, is crucial to develop sound management strategies. This methodological approach is expected to support decision-making in conservation actions in Amazonian environments based on understanding wetland connectivity and hydrogeomorphological behavior and their influence on commercial fisheries.

Hydrogeomorphology of Asymmetric Meandering Channels: Experiments and Field Evidence

“…As discussed by Rojas et al. (2023), paleochannels are abundant along the river floodplain, and the paleochannels belong to different stages (ages) of the river evolution, which induce a heterogeneous distribution of soils and vegetation patterns. As discussed by Motta et al.…”

“…Instead of only relying solely on studying in-channel processes (which might be filtered out at field scale), more research is needed to include out of the channel processes to describe how the geology-driven (incision, horizontal and vertical soil heterogeneity and regional slopes imposed by tectonics), and the morphology-driven (paleochannels inducing hydrology-based connectivity, specially at high flows) controls produce US-and DS-skewed bends. As discussed by Rojas et al (2023), paleochannels are abundant along the river floodplain, and the paleochannels belong to different stages (ages) of the river evolution, which induce a heterogeneous distribution of soils and vegetation patterns. As discussed by Motta et al (2012Motta et al ( , 2014, horizontal and vertical heterogeneity of soil distribution modulate planform patterns of meandering rivers, a feature also shown by Zhao et al (2022).…”

High-resolution modeling of meander neck cutoffs: laboratory and field scales

“…The second process is the reduction of sinuosity with intermittent, longterm occurrence of channel cutoffs, where the flow bypasses the meander loop by a shorter path with the subsequent formation of an abandoned reach (Camporeale et al, 2008). An example of the effect of such processes is illustrated by the reconstruction of the scrollbars and paleochannel of different ages distributed along the floodplain (following Rojas et al (2023)'s methodology) of the Ucayali River shown in Figure 1. Notice the change in local sinuosity from 2.24 to 1.75 in the region where a cutoff occurred in 2014-2015 (determined from the satellite images from 2006 to 2017, when the bend was finally abandoned).…”

“…A conceptual model for long-term neck cutoff evolution (Richards and Konsoer, 2020), considers four main stages: 1) the active meander stage occurs before the cutoff development; 2) neck cutoff stage is characterized by the deevelopment of a shorter path while the old bend remains active; 3) the lacustrine stage involves the plugging of the input and output of the old bend; 4) the terrestrialized stage marks the filling of the oxbow lake with sediment. Depending on local hydrogeomorphic conditions, some of the abandoned channels remain connected or not the main channel Rojas et al (2023). Accelerated erosion and increased sediment supply have been noted downstream of cutoffs (Howard and Knutson, 1984;Zinger et al, 2011).…”

“…Based on these field studies, identified precursors to cutoff include channel widening, bar development, and slope steepening. The geometric schemes also neglect paleo-channels, which influence surficial lithology and later can serve for inference of paleo-ecology and paleo-climate, and are therefore helpful in long-term reproduction or prediction of river evolution and sediment budgets (Todd and Went, 1991;Sylvia and Galloway, 2006;Davidson and North, 2009;Constantine et al, 2014;Rojas et al, 2023). A physically-based model was proposed by Asahi et al (2013) based on numerical models flow, bed evolution, and bank erosion; however, it still ignored the complex hydrodynamic and sediment deposition processes that happen during the cutoff stage [stage 2 described before (Richards and Konsoer, 2020)].…”