HAL Id: insu-01309196
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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
2and Shreeram INAMDAR
21. 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 OHFreeze-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 dischargeHydrological 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