# 13 years-long, high frequency monitoring of stream water DOC concentrations in a temperate headwater catchment: controlling factors and implications for DOC sources and DOC transfer processes

Guillaume Humbert, Anne Jaffrézic, Ophélie Fovet, Gérard Gruau, Patrick Durand

► To cite this version:

Guillaume Humbert, Anne Jaffrézic, Ophélie Fovet, Gérard Gruau, Patrick Durand. 13 years-long, high frequency monitoring of stream water DOC concentrations in a temperate headwater catchment: controlling factors and implications for DOC sources and DOC transfer processes. AGU Fall Meeting 2014, Dec 2014, San Francisco, United States. 2014. hal-04163185

HAL Id: hal-04163185

https://hal.science/hal-04163185

Submitted on 17 Jul 2023

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

INRA
SCIENCE & IMPACT

<figure><img src="image_3.png" /></figure>

AGRO
CAMPUS
OUEST

<figure><img src="image_4.png" /></figure>

Response time in Agro-Hydro Systems

<figure><img src="image_5.png" /></figure>

ORE
AgrHyS

<figure><img src="image_6.png" /></figure>

http://www6.inra.fr/ore_agrhys_eng/

# 13 years-long, high frequency monitoring of stream water DOC concentrations in a temperate headwater catchment : controlling factors and implications for DOC sources and DOC transfer processes

Guillaume Humbert*<fnref n="1" />,<fnref n="2" />, Anne Jaffrézic<fnref n="1" />,<fnref n="2" />, Ophélie Fovet<fnref n="1" />,<fnref n="2" />, Gérard Gruau<fnref n="3" />, Patrick Durand<fnref n="1" />,<fnref n="2" />

## Context

### ☐ At landscape scale, groundwater table connects soils to stream:

Organo-mineral horizons of wetland soils are unlimited sources of stream dissolved organic carbon (DOC) [1] [2]

In storm events, upland DOC contribution is temporally limited, decreasing from 30% of the stream DOC flux at the beginning of the high flow period to <10% later in this period [3]

### ☐ Dry season controls DOC production:

By microbial-derived DOC accumulation in soils [4]

By increasing stream water DOC concentrations of the next hydrological period [5]

## Study site: Kervidy-Naizin catchment

☐ This catchment belongs to the French Environment Research Observatory (ERO) AgrHyS. Part of the French catchment network on critical zone (http://rnbv.ipgp.fr/)

☐ 5 km<fnref n="2" /> lowland headwater catchment dominated by agricultural activities

☐ Meteorology, hydrology of groundwater, stream water and chemistry monitored since 2001. Data available at: http://www6.inra.fr/ore_agrhys_eng/Data/Naizin-Morbihan

<figure><img src="image_7.png" /><figcaption>**Fig. 1.** Localisation and topographic map of the catchment.</figcaption></figure>

<figure><img src="image_8.png" /><figcaption>**Fig. 2.** Average water table depth along two transects depending on the season in the hydrological year</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>**Fig. 3.** Variations of temperatures, rainfall, discharge, water table levels and DOC concentrations over the study period.</figcaption></figure>

## Objectives

☐ To confirm the conceptual model suggested from one year-long study

☐ To identify hydro-climatic controllers and linked processes of discharge weighted mean DOC concentrations:

* at annual scale

* at hydrological season scales

## Methods

☐ Season D: dry season of continuous days of low water table levels (<-0.3 m) in the riparian wetland soils (Fig. 2)

<figure><img src="image_10.png" /><figcaption>**Fig. 4.** Conceptual scheme of mobilisation of DOC pool-sources along the hydrological year.</figcaption></figure>

☐ Season A: Progressive rewetting of the uppermost soil layers of the riparian wetland soils (Fig. 2 and 4a)

☐ Season B: Hillslope waterwater table rising and holding high (Fig. 2 and 4b)

☐ Season C: Drowdawn of the hillslope water-table, with decreasing connection between topsoils and the stream (Fig. 4c)

☐ Stormflows and baseflows are separated using hourly discharge data.

☐ Partial least square regressions (PLSR) combined to linear regressions (SLR and MLR)

## Results & Discussion

### INTRA-ANNUAL VARIATIONS

☐ Quick decreases in DOC concentrations in A are consistent with a first **limited** DOC source (Fig. 5).

☐ Intra-annual dynamics controlled by initial concentrations and water runoff.

<figure><img src="image_11.png" /><figcaption>**Fig. 5.** 13 years of DOC concentrations dynamics</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>**Fig. 6.** DOC concentrations dynamics for 2 years</figcaption></figure>

☐ Increase in DOC concentrations between the end of season A and the onset of season B is consistent with the **connection to the stream of an** upland DOC source.

☐ Decrease of the concentrations to the same value of ca. 2-3 mg C.l⁻<fnref n="1" /> in season B is coherent with the **existence of** two pools, a limited one and a quasi-infinite one.

<figure><img src="image_13.png" /><figcaption>**Fig. 7.** Examples of changes in daily DOC concentrations dynamics within seasons A (left panel) and B (right panel)</figcaption></figure>

### INTER-ANNUAL VARIATIONS

☐ No significant long-term trend (Fig. 8)

☐ Year-to-year resilience with respect to the response of DOC to climatic variations (Fig. 3)

<figure><img src="image_14.png" /><figcaption>**Fig. 8.** Inter-annual variability of annual mean DOC concentrations (black dots).</figcaption></figure>

### PLSR – MLR RESULTS

☐ **Drought intensity** controls the **accumulation** of the DOC into the pool-sources.

☐ **Wetness of seasons A and B** controls the **depletion** of the DOC pool-sources.

<figure><img src="image_15.png" /><figcaption>**Fig. 9.** Mean annual DOC concentrations modelled by multiple linear regressions.</figcaption></figure>

## Conclusion

☐ Intra-annual stream water DOC concentrations in A are controlled by annual DOC concentration:

☐ Water table fluctuations control the variations in mean annual DOC concentration:

* DOC accumulation in dry season

* DOC transfers and DOC sources depletion during the first wet seasons

☐ Two alternating antagonist processes (accumulation and exportation) and **predominance** of an unlimited DOC pool-source explain the year-to-year resilience with respect to the response of DOC to climatic variations.

[1] Morel. et al., 2009. Sources of dissolved organic carbon during stormflow in a headwater agricultural catchment. Hydrol. Process., 23: 2888–2901.

[2] Lambert et al., 2013. Hydrologically driven seasonal changes in the water and sedimentary mechanisms of dissolved organic carbon in a small lowland catchment, Water Resour. Res., 49, 5792–5803

[3] Lambert et al., 2014. DOC sources and DOC transport pathways in a small headwater catchment as revealed by carbon isotope fluctuation during storm events, Biogeosciences, 11, 3043–3056

[4] West et al., 1992. Microbial activity and survival in soils dried at different rates. Aust. J. Soil Res., 30, 209–222

[5] Mehring et al., 2013. Interannual drought length governs dissolved organic carbon dynamics in blackwater rivers of the western upper Suwannee River basin, JGR-Biogeosciences, 118, 1636–1645

[1] Morel. et al., 2009. Sources of dissolved organic carbon during stormflow in a headwater agricultural catchment. Hydrol. Process., 23: 2888–2901.

[2] Lambert et al., 2013. Hydrologically driven seasonal changes in the water and sedimentary mechanisms of dissolved organic carbon in a small lowland catchment, Water Resour. Res., 49, 5792–5803

[3] Lambert et al., 2014. DOC sources and DOC transport pathways in a small headwater catchment as revealed by carbon isotope fluctuation during storm events, Biogeosciences, 11, 3043–3056

[4] West et al., 1992. Microbial activity and survival in soils dried at different rates. Aust. J. Soil Res., 30, 209–222

[5] Mehring et al., 2013. Interannual drought length governs dissolved organic carbon dynamics in blackwater rivers of the western upper Suwannee River basin, JGR-Biogeosciences, 118, 1636–1645

<figure><img src="image_16.png" /></figure>

INRA
SCIENCE & IMPACT

Voir publication dans

UMR 1069 Sols, Agro-hydrosystèmes, Spatialisation
http://www6.rennes.inra.fr/umrsas_eng/

65 rue de St Brieuc,
35042 Cedex Rennes
FRANCE

* guillaume.humbert@rennes.inra.fr

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

<footnote n="1">¹ INRA, UMR 1069, Soil Agro and hydroSystem, F-35000 Rennes, France</footnote>

<footnote n="2">² Agrocampus Ouest, Soil Agro and hydroSystem, F-35000 Rennes, France</footnote>

<footnote n="3">³ OSUR, UMR 6118 Géosciences Rennes, Campus de Beaulieu, 35042 Rennes Cedex, France</footnote>