Abstract
PurposeSuspended particulate matter (SPM) plays a crucial role in the transport of natural and anthropogenic substances. However, obtaining a representative sample and a substantial amount of SPM in rivers, where the flux and quantity of SPM are highly episodic, can be a challenging task. To collect a sufficient quantity of SPM for detailed sedimentological and geochemical analysis, a time-integrated mass flux sampler (TIMS) was used for the sampling in a medium size river (the Sava River, Croatia).Materials and methodsSampling was conducted in August and October 2014, and February and May 2015 under different discharge conditions. The SPM collected by TIMS was characterized with respect to its particle size distribution (PSD), mineral content, and geochemical composition.Results and discussionPSD analysis identified silt as a dominant size fraction in all samples except in May 2015 when sand prevailed; subsequent chemical dispersion of samples revealed flocculation as the main factor responsible for the resulting PSD. The mineralogical composition of the SPM was quite constant (quartz, calcite, dolomite, feldspar, illite/muscovite, kaolinite), but the contribution of particular mineral varied depending on the sampling period. In May 2015, unusually high calcite content was determined. Though the dominant source is still uncertain, a portion of calcite is likely detrital in origin. Geochemical analyses of collected material revealed significant anthropogenic input of ecotoxic elements (Ni, As, Cr, Pb, Bi, Cd, Zn, Sb) primarily associated with the fine fraction of the Sava River SPM.ConclusionsA considerable amount of the SPM was collected by TIMS, both during high and low river discharge. Sedimentological analyses of the Sava River SPM suggested the input of material from various sources during different river regimes. Geochemical composition of the SPM followed its sedimentological characteristics—preferential adsorption of trace elements to fine-grained clay mineral particles was documented. Some processes inside TIMS were observed during this investigation—the suspended material captured inside the sampler underwent additional changes. The flocculation of the colloidal material instigated by algal bloom was observed.
Highlights
The global contribution of river-derived sediments comprises up to 95% of the material entering the world oceans, and the suspended particulate matter (SPM) accounts for most of the riverine sediment load (Syvitski 2003)
The Sava River is a transboundary watercourse flowing through Slovenia and Croatia, alongside the northern border of Bosnia and Herzegovina, and through Serbia, where it flows into the Danube River at Belgrade (Fig. 1)
Due to the extreme conditions, the Sava River overflowed its banks several times resulting in catastrophic floods in the lower reaches of the river
Summary
The global contribution of river-derived sediments comprises up to 95% of the material entering the world oceans, and the suspended particulate matter (SPM) accounts for most of the riverine sediment load (Syvitski 2003). Horowitz (1991) indicated that more than 90% of the flux of trace elements is associated with fine particles transported in suspension, which highlights the importance of the SPM in the transport of many natural and anthropogenic substances. In fine sediment dominated rivers, the upper size limit is not so definite. The flocculated material can account for more than 90% of the total volume of the sediment carried in suspension (Droppo and Ongley 1994) and is characterized by highly complex structures, composed of small inorganic particles, organic matter, and pore water (Droppo 2001, 2005)
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