The Calcium, Magnesium, Potassium, and Sodium Budgets for a Small Forested Ecosystem

Area of Science:

• Ecosystem analysis
• Biogeochemistry
• Environmental science

Background:

• Hubbard Brook Experimental Forest ecosystems are characterized by northern hardwoods, humid continental climate, and acid metamorphic rock.
• Understanding cation balance is crucial for assessing ecosystem health and geochemical processes.

Purpose of the Study:

• To investigate the balance of calcium (Ca⁺⁺), magnesium (Mg⁺⁺), potassium (K⁺), and sodium (Na⁺) in six watersheds.
• To quantify cation input via precipitation and output via streamwater runoff.
• To estimate geochemical weathering rates based on cation budgets.

Main Methods:

• Weekly sampling of precipitation and stream water from June 1963 to May 1965.
• Cation analysis using atomic absorption spectrophotometry.
• Calculation of cation budgets based on input (precipitation) and output (runoff) volumes and concentrations.

Main Results:

• Precipitation and runoff volumes varied between years, with peak runoff in April.
• Cation concentrations in precipitation were variable but generally low; dry fallout contribution was negligible.
• Streamwater cation concentrations were low and relatively constant, with significant inverse relationships for Na⁺ and discharge in some watersheds.

Conclusions:

• Net losses of Ca⁺⁺, Mg⁺⁺, and Na⁺ were observed, indicating significant geochemical weathering.
• The K⁺ budget appeared to be near balance, suggesting minimal net loss or gain.
• These findings provide conservative estimates of weathering rates in the northern hardwood ecosystem.