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Measurement of dissolved and particulate organic carbon (DOC & POC) flux in streams after fire

Erdozain, M.1, de-Miguel, S.1,2

1 Forest Science and Technology Centre of Catalonia (CTFC)

2 Department of Agricultural and Forest Sciences and Engineering, University of Lleida

Last updated: 29/09/2026

Recommended citation:

Erdozain, M. & de-Miguel, S. 2026. Measurement of dissolved and particulate organic carbon (DOC & POC) flux in streams after fire. In: Pere Casals, Davide Ascoli, Lena Vilà-Vilardell, Imma Oliveras, Madoka Krick (eds.) 2026. Methods handbook for characterizing fire use behavior, assessing fire effects, and monitoring soil and vegetation responses at the stand level. FIRE-ADAPT project (number 101086416), deliverable D1.1

Indicator

Fire severity: Ecosystem carbon losses

Brief introduction

Wildfires alter soil structure, vegetation cover, and hydrological pathways, often increasing the mobilization of organic carbon into streams (Raoelison et al., 2023). Carbon enters watercourses through two main pathways:

  • Dissolved Organic Carbon (DOC): leached from ash, charred litter, and hydrophobic soils, especially during the first post-fire precipitation events.
  • Particulate Organic Carbon (POC): transported as suspended sediments, including ash, char fragments, and eroded soil particles.

Measuring DOC and POC provides insight into post-fire biogeochemical responses, carbon export, and water quality impacts. This protocol describes standardized field and laboratory procedures to quantify DOC and POC in streams draining burned areas.

Method specifications

Method type

Soft

Hard

Method timing

Before
fire

During
fire

After fire 
(short-term)

After fire
(mid-term)

After fire
(long-term)

Field skills

Low

Medium

Hard

Lab skills

Low

Medium

Hard

Material cost

Low

Medium

Hard

Time cost

Low

Medium

Hard

Calculation expertise

Low

Medium

Hard

Equipment

Field:

  • Pre-cleaned HDPE or amber glass bottles (60–250 mL)
  • 0.45 µm syringe filters (pre-rinsed) for DOC
  • Pre-combusted GF/F filters (0.7 µm) for POC
  • Syringes (50–100 mL)
  • Cooler with ice packs
  • Field meter (temperature, conductivity, turbidity) [optional]
  • Waders, permanent markers, labels
  • Portable vacuum pump [optional]

 

Laboratory:

  • TOC analyzer (for DOC)
  • Drying oven (60 °C)
  • Muffle furnace (450 °C) for filter combustion
  • Analytical balance (precision 0.1 mg)
  • Filtration manifold (optional)

Experimental design

Sampling sites: 

  • Downstream of burned area: Select at least one sampling site located downstream of the burned catchment, ensuring that it receives the drainage from the fire-affected area. This may require the use of GIS tools, high-resolution DEMs, and stream network layers to delineate the burned catchment and identify the main drainage outlet.
  • Coverage of large fires: For large or spatially heterogeneous fires, several sampling points can be established along the stream network (e.g., headwaters, mid-reach, downstream) to assess how DOC and POC signals accumulate, transform, or dissipate along the flow path.
  • Upstream–downstream comparison: Where possible, include at least one upstream site located above the burned area to serve as an internal control, allowing direct comparison between pre-fire (or unburned) and post-fire influenced sections within the same stream.
  • Reference (unburned) catchments: Ideally, select additional streams in nearby catchments that have not been burned, but are comparable in terms of stream order/size, geology, and general land cover. These reference sites provide a baseline against which to interpret post-fire changes in DOC and POC in the burned catchments.

 

Temporal design:

  • Baseflow sampling (monthly or seasonal): Conduct regular sampling during stable, low-flow conditions (e.g., monthly or seasonally). This provides a baseline for DOC and POC concentrations and helps detect longer-term post-fire trends once the immediate disturbance has passed.
  • Event-based sampling (rainfall and first flush): Sample during or immediately after rainfall events, especially the first significant storms following the fire. These events mobilize ash, char, and dissolved compounds, often producing the highest DOC and POC pulses and representing the main period of carbon export.

 

Replication: 3 replicate samples per site per date. Make sure samples are collected in running water (riffles ideally); avoid backwaters, stagnant pools, or areas with visible contamination (e.g., animal activity).

Methodology

Field sampling

  1. Rinse sample bottles three times with stream water.
  2. Collect water mid-stream, mid-depth, upstream from the sampling person.
  3. For DOC:
    • Filter immediately through a 0.45 µm syringe filter into a clean bottle.
    • Keep samples cool and dark.
  4. For POC:
    • Collect unfiltered water in a separate bottle.
    • Keep cool until filtration (within 24 h).
  5. Record metadata: site, date, time, water temperature, turbidity, recent rainfall.

Filtration and preservation

DOC samples:

  1. Store filtered samples at 4 °C.
  2. Analyze within 7 days or acidify to pH < 2 with HCl for longer storage.

POC samples:

  1. Pre-combust GF/F filters at 450 °C for 4 h.
  2. Filter a known volume of stream water (typically 1–5 L, depending on suspended sediment concentration), continuing until the filter flow becomes noticeably restricted.
  3. Dry filters at 60 °C for 24 h and store in petri dishes.

Laboratory analysis

DOC:

  1. Analyze using a TOC analyzer (high-temperature combustion or UV-persulfate oxidation).
  2. Report concentrations in mgC L⁻¹.

POC:

  1. Weigh dried filters (W₁).
  2. Combust filters at 450 °C for 4 h.
  3. Re-weigh (W₂).

Calculations

Concentrations

DOC (mgC L⁻¹): directly from TOC analyzer

\mathrm{POC}\,(mgC \, L^{-1}) = \frac{(W_1-W_2)*0.45}{V}

\begin{array}{l} \textbf{Where:} \\[0.5em] \mathrm{POC} = \text{Particulate organic carbon} \\ W_1 = \text{Weight of dry filter} \\ W_2 = \text{Weight of dry filter after combustion} \\ V = \text{Filtered volume} \end{array}

Carbon flux (optional)

If discharge (Q) is available:

\mathrm{Cflux}\,(gC \, day^{-1})= C \times Q \times 86.4
\begin{array}{l} \textbf{Where:} \\[0.5em] \mathrm{Cflux} = \text{Carbon flux} \\ Q = \text{Discharge}\,(L \, s^{-1}) \end{array}

Relation with other methods

NA

Data templates

NA

Further information

Raoelison, O. D., Valenca, R., Lee, A., Karim, S., Webster, J. P., Poulin, B. A., & Mohanty, S. K. (2023). Wildfire impacts on surface water quality parameters: Cause of data variability and reporting needs. Environmental Pollution, 317, 120713.