ИСТИНА

Small urban rivers in Moscow are under strong anthropogenic pressure, they receive huge amounts of suspended sediments from eroding banks, road dust, wastewater and suspended matter from residential, industrial, transportation, natural areas. Suspended sediments transport macroelements, trace metals, rare earths elements and other chemicals. Estimates of sediment origin is crucial for river valley green development and water quality management. Aim of this study is to quantify the contributions of suspended sediment sources in small rivers of Moscow and to adapt sediment fingerprinting techniques to an urban environment. Study area of research are two contrasting catchments: the heavily urbanised Setun river catchment (190 km²) and the Chertanovka river catchment (34 km²) with contrast parts of land use zones in the watershed. We classify sources by land use zones: natural, transportation, residential, industrial. Regular monitoring is carried out in several control sites and includes: water discharge and level measurements, water sampling for suspended and dissolved forms of chemical elements, also water sampling for particle size distribution, collection of integrated sediment samples using sediment traps or bottom silt. Laboratory analyses include filtration of water samples and fractionation for PM1, PM1-10. Then total concentrations and fractions are measured by ICP-MS for 54 chemical elements. Grain-size distribution analyses are carried out using laser particle-size analyser «Analysette 22 NanoTec plus». To identify the most informative tracers a three-step tracer selection method was applied. For source apportionment was used two R based mixing and unmixing models: FingerPro, a linear probabilistic unmixing model with Monte-Carlo uncertainty analysis, and simmr - a Bayesian mixing model. Preliminary results for the Setun catchment show that suspended sediment mostly originate from natural zones (bank erosion) and transportation zones (road dust and surface soils), whereas contributions from residential and industrial soils are relatively small. For the PM1 fraction the transportation zone is the main source, while for PM1-10 natural zones prevail. Seasonal analysis demonstrates that during the winter period the transportation area (road dust and surface soils) is the dominant source, whereas bank material dominates during warm low-flow periods. The use of multiple models in the study and a broad set of tracers may increase the robustness of the obtained results. These study results provide the basis of concrete actions: cleaning road runoff and stabilise eroding banks, creating green buffer zones and provide rehabilitation actions of polluted urban river valleys in Moscow.