Fire transforms effects of terrestrial subsidies on aquatic ecosystem structure and function

Area of Science:

• Ecology
• Environmental Science
• Biogeochemistry

Background:

• Wildfires are increasing due to climate change, impacting terrestrial ecosystems.
• The effects of fire on terrestrial organic matter subsidies in aquatic ecosystems remain poorly understood.
• Understanding these impacts is crucial for predicting ecosystem responses to global change.

Purpose of the Study:

• To investigate the effects of burned versus unburned terrestrial detritus on freshwater pond ecosystem functions.
• To determine how fire alters the chemical composition of detritus and its subsequent impact on aquatic systems.
• To assess the consequences of fire-induced detritus changes on carbon cycling, metabolism, and trophic transfer.

Main Methods:

• A gradient design experiment using freshwater pond mesocosms.
• Addition of varying amounts of burned and unburned plant detritus.
• Monitoring of dissolved organic carbon (DOC), ecosystem metabolism, greenhouse gases (CO2, CH4), and trophic transfer over 89 days.

Main Results:

• Terrestrial subsidies exhibited time- and mass-dependent, non-linear impacts on ecosystem functions.
• Burning increased detritus nutrient content, leading to lower DOC and CO2, and higher DO in mesocosms through Day 59.
• Fire magnified detritus effects on metabolism, stimulating photosynthesis and respiration, but also induced hypoxia and destabilized metabolism at high loads.
• Fire altered trophic transfer, reducing the incorporation of terrestrial detritus into aquatic food webs.

Conclusions:

• Fire chemically transforms plant detritus, altering its role in aquatic carbon processing and storage.
• Wildfires can induce shifts in ecosystem functions that bridge aquatic and terrestrial habitats.
• These findings highlight the significant, yet underappreciated, influence of fire on freshwater ecosystem dynamics.