Analyzing Particle-Associated Pollutant Transport to Identify In-Stream Sediment Processes during a High Flow Event

Abstract

Urban areas are a leading source of polycyclic aromatic hydrocarbons (PAHs) that result from combustion processes and are emitted into rivers, especially during rain events and with particle wash-off from urban surfaces. In-stream transport of suspended particles and attached PAHs is linked strongly to sediment turnover processes. This study aimed to identify particle exchange processes that contribute to the transport of suspended particles during flood events. An urban high-flow signal was tracked in high temporal resolution at two sampling sites in the Ammer River (South-western Germany). Samples were analyzed for turbidity, total suspended solids concentrations (TSS), particle-size distribution, organic carbon, and PAH. Maximum discharge and the highest TSS occurred nearly simultaneously at the upstream sampling site, whereas a temporally shifted course was observed for downstream. The total load of particles was similar, yet a decrease of PAH mass (~28%) and an increase of the particulate organic carbon (POC) content (~3.5%-points) occurred. Coarser particles (≥26 µm) dominated at the beginning of the event at both sampling sites. The signal of remobilized riverbed sediment increases downstream and leads to well-established, robust linear correlations between TSS and PAHs. This study highlights that riverbed sediment acts as intermediate storage for contaminated particles from upstream sources that shape, together with the fresh urban input, the “particle signature” of suspensions moving through catchments during high discharge conditions.

Storm Event–Driven Occurrence and Transport of Dissolved and Sorbed Organic Micropollutants and Associated Effects in the Ammer River, Southwestern Germany

“…The SPM fluxes in the Ammer River followed the hydrographs at AS1 and AS2 and were at maximum 7.10 and 2.93 kg dry weight s –1 (after 1.5 and 3.4 h, respectively; Supplemental Data, Table S3). Glaser et al (2020) found a broader discharge function at AS2 and a particle loss of approximately 13% between both sampling sites. Again, the target compounds detected in the SPM extracts from AS1 and AS2 can be subdivided into 3 groups in terms of the mass flux dynamics associated with SPM, similar to the compounds detected in the water extracts.…”

“…Further research would be necessary on whether these pollutants were transported into the Ammer River by particles flushed in during the storm event or whether they originated from mobilized riverbed sediment. For polycyclic aromatic hydrocarbons, it was shown that they rather stemmed from remobilized river sediment during the same event (Glaser et al 2020), but the sources could be entirely different for the pesticides, consumer products, and pharmaceuticals we investigated.…”

“…Given the available amount of 250‐mL sample for determining the SPM concentration (Glaser et al 2020) and the high uncertainty resulting from subtracting 2 relatively large gravimetric values, we omitted data for compound concentrations in SPM extracts of water sample with SPM concentration <50 mg dry weight L –1 (AS1_12, AS2_1, AS2_2, AS2_3, and AS2_12; Supplemental Data, Table S2) because no reliable and robust results were obtained.…”

“…This empirical correlation only accounts for hydrophobic compounds that are not ionized and was only applied to compounds that were shown to predominantly partition to the organic carbon of SPM. The organic carbon content ( f OC ) was derived from the amount of sampled SPM, the dissolved organic carbon (DOC), which refers to organic carbon after 0.45‐µm filtration, and the total organic carbon concentration; these data were obtained from replicate samples as reported in Glaser et al (2020; Supplemental Data, Table S2). The K OW values of target compounds detected in water and SPM extracts are provided in the Supplemental Data, Table S10.…”

“…All samples were kept cool at 4°C and processed within the next 48 h. At AS1 and AS2, discharges were derived from measured water levels (using online probes from UIT) and pre-established rating curves. Discharges (Q) of 15-min intervals (Supplemental Data, Table S1) and amounts of SPM (Supplemental Data, Table S2) have been reported by Glaser et al (2020). The SPM amounts were derived by filtering (250 mL of replicate samples, 1.5-µm cellulose membrane) according to the German industrial standard Deutsche Industrienorm 38409-2 (1987).…”