Ocean colour and distribution of suspended particulates in the St. Lawrence Estuary.

Distribution of total suspended particulate matter (SPM) in the St Lawrence estuary was investigated based on spaceborne ocean colour measurements. Biogeooptical models were constructed and validated with in situ biogeochemical and optical data obtained during spring of 2000 and 2001. The resulting remote sensing reflectance (Rrs) model was applied to derive SPM maps during spring and fall of two years with different river discharge (i.e., 'low' in 2001, 'high' in 2000). Uncertainty of SPM estimates was quantified and SPM budgets were computed for different estuarine regions. The average relative error of SPM calculations was 36.6% with a range between 9.6 and 89.6%. The largest bias of SPM estimates (error >100%) was associated with the interference of chromophoric dissolved organic matter. For the 'high' river discharge year, SPM concentration was higher throughout the estuary during spring (average: 6.1 g m-3). Conversely, SPM levels during a 'low' river discharge year were higher during fall (average: 4.1 g m-3). Highest concentrations of SPM along the estuary (i.e., up to 21 g m-3) were detected nearby the maximum turbidity zone and a frontal system located in the vicinity of the Outardes delta in the lower estuary. Field and satellite data suggest different responses of SPM distributions to changes on river discharge (e.g., bank erosion, clay deflocculation) depending on the period of the year.