Evolution of the source of storm particulate organic matter exported along forested nested catchment. ? Impact of granulometry and climate

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Evolution of the source of storm particulate organic matter exported along forested nested catchment. ?

Impact of granulometry and climate

Laurent Jeanneau, Richard Rowland, Shreeram Inamdar

To cite this version:

Laurent Jeanneau, Richard Rowland, Shreeram Inamdar. Evolution of the source of storm particulate organic matter exported along forested nested catchment. ? Impact of granulometry and climate. Eu-ropean Geosciences Union General Assembly 2016, Apr 2016, Vienne, Austria. Geophysical Research Abstracts, 18, pp.EGU2016-6097, 2016. �insu-01309196�

Laurent JEANNEAU

1

, Richard D. ROWLAND

2

and Shreeram INAMDAR

2

1_{. Géosciences Rennes, CNRS-Université de Rennes 1, France;} 2_{. Plant and Soil Sciences, University of Delaware, Newark, DE, USA}

Discussions and message to carry back

• In the 12Ha catchment, the POM mainly derived from litter, wetland A and forest O horizons. Their relative contributions changed along the particles size continuum and from one event to another. • At the scale of the headwater catchment, the sources of POM changed with an increasing proportion of stream bed-derived POM downstream. Going downstream seems to decrease the differences along the particles size continuum.

• The composition of POC changed along the particle size continuum: different fractions from different sources.

• Investigation at the molecular scale using THM-GC-MS seems to provide fruitful data to determine the sources of POM transferred along nested catchments.

Investigation at the molecular scale

Thermally assisted hydrolysis and methylation

_{Macromolecules lysis}

Step 1: Thermochemolysis

Step 2: Gas chromatography

Separation

Step 3: Mass spectrometry

Identification

O H O H CO₂H CO₂H OH HO O HO OH OH

Freeze-dried POM

0 10 20 30 40 0 40 80 120 May 1, 2014 April 21, 2015 July 1, 2015 Sept 30, 2015 Rain fall (mm) Total Rainfall Max hourly I Med hourly I 0 50 100 150 200 0 2 4 6 Max runoff Max discharge

Hydrological data

Hourly In tensity (mm/ hr ) Ma x Disc har ge (L/ s) Ma x Turbidity _(UT) Ma x Suspended Ma tt er (g /L)

No

da

ta

Ma x Runoff (mm/ hr )

Sampling area

Fair Hill Watershed site

• Piedmont region of Maryland, USA • Cold-temperate climate

• Annual rainfall: 1007 (2014), 1165 (2015) mm • Elevations from 48 to 116 m (89 ± 14 m; mean ±

SD)

• Slopes from 0 to 35% (7.4 ± 5.0 %; mean ± SD)

Nested catchment 12 and 79 Ha Sampling of deposited sediment during 4 storm events

Sampling of potential end-members

Outlet of the 12 Ha catchment

Deposited sediment sampler 0 25 50 75 100 Fine (<250µm) Medium Coarse (>1mm) May 01, 2014 Apr 21, 2015 Jul 01, 2015 Sep 30, 2015 May 01, 2014 Apr 21, 2015 Jul 01, 2015 Sep 30, 2015 12 Ha 79 Ha

Distribution of particles size

End-members

Wetland

Stream bank A & B Stream bed

Upland A

Forest O & Litter

Results of the molecular analysis

Event 1 Event 2 Event 3 Event 4

1. First PCA treatment based on the distribution of the type of molecules

Individuals: End-members

Variables: % of fatty acids (FA), carbohydrates (CAR), phenols (PHE) among the analyzed compounds and the sum of the area per gram of analyzed sample.

2. Second PCA treatment based on the distribution of plant-derived markers

Individuals: End-members Variables: Relative proportion of the eight most abundant PHE and

plant-derived FA. 1C 1M 1F 2C 2M 2F 3C 3M 3F 4F 4M 4C C M F 1C 1M 1F 2C 2M 2F 3C 3M 3F 4F 4M C M F Sec ond co mponen t (26.4 %) First component (66.7 %) A B O Li Forest floor Upland A Wetland Stream Bank Stream bed nX n: event number

X: C, coarse; M, medium; F: fine

Orange: 12 Ha catchment Blue: 79 Ha catchment 1C 1M 1F 2C 2M 2F 3C 3M 3F 4F 4M 4C C M F 1C 1M 1F 2C 2M 2F 3C 3M 3F 4F 4M C M F Sec ond co mponen t (32.2 %) First component (40.0 %) nX n: event number

X: C, coarse; M, medium; F: fine

Forest floor Upland A Wetland Stream Bank Stream bed Orange: 12 Ha catchment Blue: 79 Ha catchment A B O Li

Differentiation between the potential end-members. Specific areas are

increased by spatial heterogeneity.

The composition of POM changed along: (1) the catchment (differentiation

between the samples from the 12 Ha and the 79 Ha catchments), (2) the size continuum from coarse to fine fractions

and (3) the year.

The 12 Ha catchment POM derived mainly from a combination of Litter, Forest O and Wetland A horizons. The

contribution of stream bed increased downstream. % CAR % FA % PHE [Sq] FA PHE

Context and question

Particulate Organic Matter (POM) plays a key-role

toward biodiversity, ecotoxicology and within the

C cycle. POM exported within the fluvial

suspended matter load during storm events may

represent up to 80% of its annual load.

1. Where does this POM come from?

2. Is it homogeneous along the particle size

continuum?

3. How its source may change down a continuum

of catchment drainage locations?

4. Is there a seasonal effect?

Acknowledgments

This work benefits from NSF and USDA funding (grant numbers IIA-1330238 and 2015-37020-23585, respectively). Contact: laurent.jeanneau@univ-rennes1.fr 12 Ha 0 100 200 300 400 500 0 2 4 6 8 _{Susp Sed} Turbidity 12 Ha