Urbanization affects stream ecosystem function by altering hydrology, chemistry, and biotic richness.

Area of Science:

• Ecology
• Environmental Science
• Stream Ecology

Background:

• Catchment urbanization significantly alters stream ecosystem attributes, including organic matter decomposition.
• Changes in land use patterns associated with urbanization can disrupt crucial ecosystem functions.

Purpose of the Study:

• To investigate the effects of varying catchment urbanization levels on leaf-litter decomposition rates.
• To identify key physical, chemical, and biological factors influencing decomposition dynamics in urban-influenced streams.

Main Methods:

• A litter-bag technique was employed to measure mass loss, fungal biomass, and macroinvertebrate biomass for two leaf species (red maple and sweetgum).
• Studies were conducted across 18 tributaries with land use ranging from 0% to 93% urban, corresponding to 0% to 66% total impervious area (TIA).
• Principal-components analysis and stepwise regression were used to analyze intercorrelated variables and identify key drivers of decomposition.

Main Results:

• Leaf litter decomposition rates initially increased with impervious catchment area up to 30-40% TIA, then declined.
• Fungal biomass peaked in streams with intermediate TIA levels.
• Snail biomass, invertebrate richness, flow regime, and nutrient/metal content were strongly correlated with litter breakdown rates.

Conclusions:

• Stream ecosystem function, specifically organic matter decomposition, exhibits a nonlinear response to catchment urbanization.
• Invertebrate communities, particularly snails, play a significant role in regulating decomposition rates.
• Protecting stream health requires managing urban land use to mitigate negative impacts on ecosystem processes.