The Nature and Distribution of Particulate Matter in the Mandovi Estuary, Central West Coast of India

Abstract

Systematic seasonal variations of suspended particulate matter (SPM) along a 44-km transect of the Mandovi estuary reveal that the concentrations of SPM are low at river-end stations, increase generally seaward, and are highest at sea-end stations of the estuary. An estuarine turbidity maximum (ETM) occurs at sea-end stations during June-September when river discharge is high and also in February-May when river discharge is low. These are the two windiest times of year, the former associated with the southwest monsoon and the latter characterized by a persistent sea breeze. The salinity vs. SPM plot shows that high SPM is a seaward deposit and skewed landward. Suspended matter comprised of floccules, fecal pellets, and aggregates that consist of clay and biogenic particles occur everywhere in the estuary. Diatoms are the most common and are of marine type at the sea-end and freshwaterdominated at river-end stations of the estuary. SPM is characterized by kaolinite-and smectite-rich clay mineral suites at the river-and sea-end stations, respectively. Smectite concentrations increase seawards with the increase in SPM content and are not influenced by salinity. Winddriven waves and currents and biogeochemical processes at the mouth of estuary likely play an important role in the formation of ETM in resuspension and transformation of SPM into floccules and aggregates and in their upkeep or removal.

Biofilm origin of clay-coated sand grains

“…The textural characteristics of the sediments are consistent with biofilms produced by diatoms (Higgins et al, 2003), as reported in studies of both modern (natural) estuaries (Kessarkar et al, 2010;Tolhurst et al, 2003) and laboratory-based experiments Paterson, 1989). Our study found textures that are consistent with reported diatom trails and linkages (Fig.…”

“…Biofilm (EPS) bound aggregates of clay particles and freshwater diatoms on sand grains have been reported in marine sediment 27 km from the nearest river mouth, implying that biofilm attachments remain effective during transport from the inner estuary clay coat factory into the marine realm (Kessarkar et al, 2010). A marginal marine, primary origin of claycoated grains has been suggested within the continental slope (sediment gravity flows) and basin plain sediments of the Atoka Formation, Arkoma basin, central USA (Bloch et al, 2002;Houseknecht and Ross, 1992) and west of Shetland, UK (Sullivan et al, 1999).…”

“…Biofilms in intertidal sediments have been reported to form an adhesive coat on sand grains that acts as a binding agent capable of forming aggregates of diatoms, organics, and clay minerals (Kessarkar et al, 2010) and that is also responsible for fine particle entrapment in sand-dominated estuarine tidal flats (Garwood et al, 2015). In the presence of common divalent cations, such as Mg 2+ and Ca 2+ , that are present in estuarine waters, EPS biofilm fractions become water insoluble, tightly bound to sand grain surfaces, and resistant to degradation, increasing with depth in the top few millimeters of the sediment column (Stal, 2003;De Winder et al, 1999).…”

Temporal and spatial variability of trace metals in suspended matter of the Mandovi estuary, central west coast of India

“…4). Two processes appear to control SPM and metal concentrations: (a) the increase of SPM towards downstream can be attributed to the development of estuarine turbidity maximum (ETM) that results in resuspension of bottom sediments (Kessarkar et al 2010). …”

Estudo biogeoquímico do fósforo no complexo estuarino-lagunar de Cananéia-Iguape (SP): influência do Valo Grande e fluxo bêntico

“…Quando são parcialmente misturados (fluxo da maré maior ou igual à entrada de água doce), apresentam maior eficiência de retenção, atuando também como armadilhas para os sedimentos costeiros. A eficiência de um estuário na retenção de sedimentos depende das suas taxas de sedimentação e da energia disponível para o transporte (Kessarkar et al, 2010).…”