Managed floodplain inundation maintains ecological function in lowland rivers.

Area of Science:

• Riverine ecology
• Environmental science
• Hydrology

Background:

• Anthropogenic activities disrupt riverine ecosystems, affecting carbon dynamics, diversity, and ecological function.
• Managed environmental flows are proposed as a tool to restore these functions.
• Empirical data quantifying these interactions are scarce.

Purpose of the Study:

• To quantify the impact of a managed environmental flow event on carbon, nutrient, and invertebrate dynamics in a river-floodplain system.
• To assess the persistence of floodplain-derived carbon in riverine food webs.
• To evaluate the role of floodplain forests in riverine ecosystem restoration.

Main Methods:

• Measurement of dissolved organic carbon (DOC), seston carbon, total nitrogen (TN), chlorophyll-a (chl-a), and total phosphorus during a managed flow event.
• Stable isotope analysis to trace carbon incorporation into riverine food webs.
• Comparison of outcomes between a major and a subsequent smaller flow event.

Main Results:

• Significant increases in DOC, seston carbon, TN, and chl-a downstream of the inundated floodplain forest.
• Peak yields from the floodplain: DOC (~100 t d⁻¹), seston carbon (~50 t d⁻¹), TN (~5 t d⁻¹), chl-a (~0.1 t d⁻¹), and total phosphorus (~0.4 t d⁻¹).
• Allochthonous carbon was rapidly assimilated by riverine food webs, persisting for up to four months.
• The floodplain acted as a carbon and nutrient sink during a subsequent smaller flow event.

Conclusions:

• Managed environmental flows inundating floodplain forests can significantly enhance riverine carbon and nutrient loads.
• Floodplain-derived carbon is readily incorporated into riverine food webs, supporting ecological function.
• The findings support the River Wave Concept, highlighting the importance of forest-floodplain connectivity for river health.