Is in-stream processing an important control on spatial changes in carbon fluxes in headwater catchments?

Area of Science:

• Environmental Science
• Hydrology
• Biogeochemistry

Background:

• Headwater streams are crucial in regional carbon budgets, yet their small-scale spatial dynamics are not fully understood.
• Upland catchments with organic-rich soils present unique challenges for carbon cycling research.

Purpose of the Study:

• To quantify spatial variations in dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and carbon dioxide (CO2) fluxes within a Scottish headwater stream.
• To determine the influence of in-stream processes and atmospheric exchange on carbon dynamics over a 2.7 km stretch.

Main Methods:

• Measured concentrations of DOC, DIC, and CO2 at various points along the stream.
• Utilized chloride as a conservative tracer to account for diffuse water inputs.
• Calculated instantaneous carbon fluxes and estimated gains/losses within the stream system.

Main Results:

• DOC concentrations peaked in peat-dominated areas before declining downstream.
• DIC and CO2 concentrations showed significant increases through peat areas, influenced by tributary inputs, before declining.
• Substantial removal of DOC (11.6-17.6%) and significant losses of DIC (over nine times the outlet flux) occurred in-stream, alongside CO2 outgassing.

Conclusions:

• In-stream processing of DOC and DIC, along with CO2 outgassing, are key drivers of spatial carbon flux variability in these upland streams.
• Headwater streams in organic-rich catchments play a significant role in processing and transporting carbon.