Dynamics of dissolved and biogenic silica in the freshwater reaches of a macrotidal estuary (The Scheldt, Belgium)

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1 UNIVERSITE LIBRE DE BRUXELLES Faculté des scieces Départemet des Scieces de la Terre et de l Eviroemet Laboratoire d Océaographie Chimique et Géochimie des Eaux Dyamics of dissolved ad biogeic silica i the freshwater reaches of a macrotidal estuary (The Scheldt, Belgium) Vicet Carboel Marie Lioard,3 Koeraad Muylaert, Lei Chou Results published i: Biogeochemistry (9) 96:9 7 : Laboratoire d Océaographie Chimique et Géochimie des Eaux, Faculté des Scieces, Uiversité Libre de Bruxelles, Campus de la Plaie, CP 8, Boulevard du Triomphe, B-5 Brussels, Belgium : Protistology ad Aquatic Ecology, Biology Departmet, Ghet Uiversity, Krijgslaa 8-S8, B-9 Ghet, Belgium 3 (preset address): Départemet de Biologie, Uiversité Laval, Pavillo exadre-vacho, 5, av. de la Médecie, Québec(Québec), GV A6 Caada (preset address): K.U. Leuve, Campus Kortrijk, Biology Departmet, E. Sabbelaa 53, B-85 Kortrijk, Belgium

2 Objectives lad/rivers tidal river DSi estuary Ivestigatio of the DSi ad dyamics i the Scheldt tidal river ad i its tributaries: quatificatio of the sources, siks ad processes affectig silica the relatio betwee dyamics ad those of the phytoplakto ad of the SPM mass-balaces to estimate the retetio impact o the trasport of silica to the coastal zoe diatoms dissolutio diatom frustules + phytoliths Water colum Sedimets diatom uptake livig diatom mortality dead burial sedimetatio resuspesio et DSi cosumed DSiretetio (%) DSi iputs et silica deposited silica retetio (%) DSi + iputs

3 Samplig Measured parameters: UK NORTH SEA F NL B Dissolved silica (DSi) Particulate biogeic silica () Suspeded particulate matter (SPM) (brackish) estuary Scheldt Scheldt Upper River Durme Deder tidal river NL B Rupel Nete Zee Kleie Nete chlorophyll a + pigmets chlorophyll a associated with diatoms (DiatChla) multiple regressio versus SPM ad DiatChla: livig diatoms "detrital": empty frustules phytoliths

4 (Si, ) (Si, ) (Si 3, 3 ) (Si, ) Model : Ŝi (½) -. + k. Miimisig Σ(Si - Ŝi ) : ( ) ( ) ( ) ( ) ) ( Si Si Methodology for determiatio (Ŝi -Si )/ Si < % validatio o pure lithogeic/biogeic phases, ad o mixtures precisio ( with LSi) :.3 µmol o filter

5 Cocetratios DSi (µmol L - ) (µmol L - ) DiatChla (µg L - ) (chlorophyll a due to diatoms) Scheldt Upper River Scheldt Deder Rupel Nete Zee Kleie Nete oe year oe year 3 Scheldt Upper River 3 Deder Tributaries at tidal limits 3 Zee 3 DSi: oly little seasoal variatios, DiatChla: low cocetratios 3 3 Kleie Nete

6 Cocetratios DSi (µmol L - ) (µmol L - ) DiatChla (µg L - ) Scheldt Upper River Scheldt Deder Rupel Nete Zee Kleie Nete oe year 3 3 km km Tidal river DSi: summer cosumptio : summer productio ad depositio parallelism - DiatChla i summer 3 km 9

7 Cocetratios 3 DSi (µmol L - ) (µmol L - ) DiatChla (µg L - ) km oe year compariso versus DiatChla ad SPM fractio of the associated with livig diatoms: fractio of associated with livig diatoms (%) (M)A M J J A S O N km km km 9 mostly associated with livig diatoms livig 3 3 km km 9 with particulate orgaic carbo (ot associated with livig diatoms) + Si cotet i plat detritus (max %) maximum cotributio of phytoliths to : cotributio to pool (%) (M)A M J J A S O N mior cotributio of phytoliths km km km 9 phytoliths dead

8 Silica mass-balace direct calculatio of the fluxes usig freshwater discharge Silica mass-balace for May to October 3 (i Mmol): Ghet Upper Scheldt river Zoe a Scheldt b Hemiksem Temse Durme Dedermode Deder Rupel Zoe Nete Zee Kleie Nete Zoe Zoe a b DSi DSi uptake: 7 6 (8.) Diatom growth i Zoe a, but hardly ay mortality or depositio 3.8 (.).9 - Iverse i Zoe b liv Diatom mortality: (.).8 - Importat diatom growth i Zoe, as well as mortality ad depositio det depositio (or resuspesio): Importace of det (ot associated to livig diatoms) Ghet Deder Dedermode (lateral iput cotributio) Temse Tributaries of the Rupel Hemiksem

9 Overall fuctioig ad impact DSi retetio % of iputs: May-Oct. 8 % Aual % timig effects i the coastal zoe i summer i autum (due to the water residece time i the estuary) after the coastal diatom bloom reduced impact o the coastal zoe dyamics liked to that of DSi the trasport of couterbalaces the impact of DSi cosumptio o the trasport of silica % detrital : May-Oct % (flux weighted averages) Aual 67 % mior cotributio of phytoliths Total silica retetio % of iputs: May-Oct.3 % Aual 6 % lower compared to DSi cosumptio small impact o the trasport of silica to the coastal zoe