POSTER SESSION 4
10:30–12:30, Thursday, September 17
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
ABSTRACT 1137 | POSTER 240
ASSESSING THE IMPACT OF THE LOWER SESAN 2 DAM ON SPM AND POC CONCENTRATIONS IN THE 3S–MEKONG CONFLUENCE VIA HIGH-SPATIAL RESOLUTION SATELLITE IMAGERY
This study quantifies the impacts of the Lower Sesan 2 (LS2) dam on the quantity and biochemical quality of suspended particulate matter (SPM) including Particulate Organic Carbon (POC) at the 3S–Mekong confluence, a critical tributary system of the Mekong River.
We integrated high-spatial resolution, multi-sensor satellite imagery (Sentinel-2 MSI, Landsat 8/9 OLI) from 2014 to 2024, coupled with DINEOF gap-filling techniques to overcome monsoon cloud cover. To accurately retrieve POC, we calibrated and merged existing algorithms based on Optical Water Types (OWT). A Before-After Control-Impact (BACI) framework was employed across an upstream–reservoir–downstream continuum to isolate the dam’s net effects on SPM, POC, and Chlorophyll-a (Chl-a).
The LS2 reservoir induced a permanent net sediment trapping of 43.8%. Beyond physical depletion, the impoundment functioned as a seasonal ‘biogeochemical reactor’. During the dry season, increased water clarity and residence time stimulated localized primary production, enriching the particulate pool in labile algal carbon (net increases of 56.7% and 84.0% for POC:SPM and Chl-a:SPM ratios, respectively). Downstream, SPM concentrations showed no significant decrease, indicating a ‘hungry water’ effect. This geomorphological compensation resuspended inorganic bed sediments, diluting the reservoir’s autotrophic signature before it reached the Mekong mainstream.
The LS2 dam alters the particulate regime, shifting from intense biogeochemical alteration (autotrophy) within the reservoir to physical degradation (channel incision and bank erosion) downstream. Recognizing reservoirs as both sediment traps and biogeochemical reactors is essential to anticipating cumulative impacts on downstream ecosystems, including the Tonle Sap Lake and the Mekong Delta.
Charles Verpoorter, Laboratoire d’Océanologie et de Géosciences (LOG), [email protected], https://orcid.org/0000-0002-5134-4124
Julien Masson, Université Littoral Côte d’Opale, CNRS, Université Lille, IRD, Laboratoire d’Océanologie et de Géosciences (LOG), France, [email protected]
Cédric Jamet, Université Littoral Côte d’Opale, CNRS, Université Lille, IRD, Laboratoire d’Océanologie et de Géosciences (LOG), France, [email protected]
Poster Session | 1 | 2 | 3 | 4 | Schedule at a Glance
