Direct quantification of long-term rock nitrogen inputs to temperate forest ecosystems

Area of Science:

• Geochemistry
• Ecology
• Soil Science

Background:

• Sedimentary and metasedimentary rocks store significant amounts of fixed nitrogen (N).
• The contribution of rock nitrogen weathering to terrestrial ecosystems remains under-investigated.
• Temperate forests are crucial ecosystems where nutrient cycling is vital.

Purpose of the Study:

• To provide direct evidence and quantify rock nitrogen weathering inputs in temperate forest ecosystems.
• To compare rock nitrogen inputs with atmospheric nitrogen deposition.
• To investigate the role of biologically mediated weathering in nutrient release from rocks.

Main Methods:

• Utilized a mass balance model for element addition/depletion.
• Developed a procedure to quantify fixed nitrogen within rock minerals.
• Combined weathering fractions with regional denudation estimates.

Main Results:

• Quantified long-term nitrogen weathering from bedrock, ranging from 37% to 48% of initial content.
• Estimated rock nitrogen inputs at 1.6-10.7 kg/ha/yr, comparable to atmospheric inputs (4.5-7.0 kg/ha/yr).
• Observed greater nitrogen depletion than sodium, indicating biologically mediated weathering of essential nutrients.

Conclusions:

• Rock nitrogen weathering is a substantial source of nitrogen for temperate forest ecosystems.
• Biologically mediated weathering plays a key role in releasing essential nutrients from parent rock material.
• Regional tectonics, biological activity, and rock chemistry influence nitrogen input magnitudes.