Using ion-exchange resins to study soil response to experimental watershed acidification

Area of Science:

• Environmental Science
• Soil Science
• Ecosystem Ecology

Background:

• Ion-exchange resins (IER) present a potential alternative to traditional soil solution sampling methods.
• Understanding the comparative efficacy of IER versus ceramic cup tension lysimeters in forested ecosystems is crucial for accurate environmental monitoring.
• The Bear Brook Watershed in Maine (BBWM) provides a unique setting for long-term ecological studies with controlled atmospheric deposition treatments.

Purpose of the Study:

• To compare the effectiveness of ion-exchange resins (IER) and ceramic cup tension lysimeters in measuring ionic movement in forested soils.
• To evaluate how these methods reflect soil solution responses to experimental sulfur and nitrogen additions in a paired watershed study.
• To assess the agreement between IER and lysimeter data for various soil analytes and their interpretation of watershed biogeochemistry.

Main Methods:

• Deployment of both IER and ceramic cup tension lysimeters in paired forested watersheds at the Bear Brook Watershed in Maine (BBWM).
• Application of bi-monthly treatments of sulfur (S) and nitrogen (N) to one watershed over approximately 11 years.
• Analysis of soil solution samples collected by both methods to quantify ionic concentrations and compare results.

Main Results:

• Both IER and lysimeters indicated that S and N treatments mobilized base cations and aluminum (Al), increasing SO(4)-S and inorganic N in the treated watershed.
• Both techniques revealed similar patterns in ionic concentrations related to forest type (hardwoods vs. softwoods), reflecting differences in litter quality and aerosol interception.
• Correlation analysis showed significant agreement between IER and lysimeter data for several analytes (e.g., Na, Al, NO(3)-N), but not for NH(4)-N or Pb.

Conclusions:

• Ion-exchange resins (IER) offer a viable alternative to lysimeters for studying soil ionic dynamics in forested ecosystems, yielding similar interpretations of biogeochemical processes.
• Despite varying correlations for specific analytes, both methods successfully captured treatment effects and forest type influences on soil solution chemistry.
• The study supports the utility of IER as a complementary or alternative tool for watershed biogeochemical research, particularly in long-term monitoring programs.