Comparing biotic drivers of litter breakdown across stream compartments

Area of Science:

• Ecology
• Environmental Science
• Biogeochemistry

Background:

• Litter breakdown is crucial for organic carbon cycling and energy transfer.
• Research has primarily focused on microbial and macroinvertebrate breakdown in the benthic zone (BZ), neglecting the hyporheic zone (HZ).
• Understanding litter decomposition in the HZ is vital due to its role as a bioreactor.

Purpose of the Study:

• To investigate litter breakdown rates and mediating factors in both benthic and hyporheic zones.
• To explore the relationship between litter decomposition and the community structure of streambed organisms.
• To assess the efficiency of litter processing across different streambed compartments and biota.

Main Methods:

• Deployed standardized bioassays (cotton strips, tea bags) in 30 UK streams.
• Modeled litter breakdown as a response to streambed compartment and biological features (Prokaryota, Protozoa, Eumetazoa invertebrates).
• Analyzed the influence of biotic group biomass, invertebrate diversity, and prokaryotic metabolic diversity on breakdown rates.

Main Results:

• Litter breakdown was significantly faster in the BZ than the HZ (5x for cotton strips, 1.5x for tea leaves).
• Differences in breakdown rates between zones were mediated by benthic and hyporheic biological characteristics.
• Biomass of biotic groups, Eumetazoa diversity, and Prokaryota metabolic diversity positively predicted breakdown rates.

Conclusions:

• Litter decomposition is partitioned across streambed compartments and biota.
• The study highlights the importance of Prokaryota, Protozoa, and Eumetazoa invertebrates in litter breakdown.
• A novel multimetric bioassay effectively disentangled the contributions of different organisms to organic matter decomposition.