# The Influence of Hydrogeomorphology on Food Webs in Riverine Landscapes

## TL;DR

This study shows how the physical structure of rivers influences food chain length, with low flow variance and permanent flow promoting longer food chains.

## Contribution

The study reveals a direct link between reach-scale hydrogeomorphology and food chain length in river ecosystems.

## Key findings

- A curvilinear relationship exists between river physical heterogeneity and food chain length.
- Low flow variance and permanent flow increase food chain length, while overbank flood frequency does not.
- Ecosystem size does not affect food chain length.

## Abstract

A central tenet of river science is the interaction between flow and the physical habitat template—hydrogeomorphology—that governs biophysical structure and function. While studies have shown how this interplay shapes structural river ecosystem attributes, our knowledge of their influence on ecosystem function is limited. Using geomorphological, hydrological, and stable isotope ratio data for basal resources and primary and secondary consumers from 88 rivers, we test hypotheses on relationships between hydrogeomorphology and food chain length. A significant curvilinear relationship between the physical heterogeneity of a river reach and food chain length was found. Low flow variance was shown to have an additive influence on food chain length; longer food chain lengths occurred in reaches that experienced permanent flow but not the frequency of overbank floods. Ecosystem size had no effect on food chain length. The results of this study suggest reach‐scale hydrogeomorphology has a direct influence on ecological function—food chain length—in riverine landscapes. We suggest that the spatial heterogeneity of physical character is a primary driver of ecosystem function that provides a template upon which flow variability acts as a regulator of food chain length. Understanding biocomplexity, the interplay of spatial heterogeneity and temporal variability, is critical to predicting responses of riverine landscapes to natural and human‐derived disturbances.

Reach scale hydrogeomorphology was shown to have a direct effect on food chain length. Low flow variance was shown to have an additive influence on food chain length; longer flood chain lengths occurred in reaches that experienced permanent flow but not the frequency of overbank floods. Ecosystem size had no effect on food chain length.