Calculating critical loads for acidification for five forested catchments in China using an extended steady state...

Area of Science:

• Environmental Chemistry
• Ecosystem Ecology
• Acid Deposition Research

Background:

• Critical load concept is key for acid deposition control.
• Base cation (BC) deposition's role in mitigating acidification is often overlooked in calculations.
• Ignoring BC deposition variability, particularly anthropogenic sources, leads to uncertainty and over-estimation.

Purpose of the Study:

• To apply an extended sulfur (S)-nitrogen (N)-BC function using the Steady State Mass Balance (SSMB) method.
• To calculate critical loads for five catchments in southern China considering variable S, N, and BC deposition.
• To assess the impact of changing BC deposition on critical load values.

Main Methods:

• Utilized an extended sulfur (S)-nitrogen (N)-BC function.
• Employed the Steady State Mass Balance (SSMB) method.
• Calculated critical loads for five southern China catchments under variable deposition scenarios.

Main Results:

• Ceiling of S deposition (CL(max)(S)) ranged from 4.5 to 10.8 keq ha(-1) yr(-1).
• Ceiling of N deposition (CL(max)(N)) ranged from 23.2 to 54.5 keq ha(-1) yr(-1).
• A 75% reduction in BC deposition decreased CL(max)(S) by 46%-86% and CL(max)(N) by 45%-81%.

Conclusions:

• Critical loads were not exceeded under current BC deposition in the studied catchments.
• A significant decrease in BC deposition (to 25% of current) would cause critical loads to be exceeded at most sites.
• Future BC deposition levels are crucial for critical load uncertainty, alongside ecosystem response to soil chemistry.