Stormwater impact on urban waterways in a cold climate: variations in sediment metal concentrations due to untreated snowmelt discharge

• Purpose: Stormwater discharges include contaminated sediments that accumulate in the receiving water body. It is thus important to investigate sediment and pollutant processes and pathways from the catchment to, and within, the receiving water. These processes may be influenced by seasonal changes. The objective of this study was to investigate the stormwater impact on receiving waters in the Luleå area, Northern Sweden; seasonal changes in contamination loads in the receiving waters due to snowmelt; and factors influencing the pollutant pathways in the receiving waters.Materials and methods: In front of three storm sewer outlets in Luleå, samples of bottom sediment (surface layer 0-2 cm) were collected from the connecting ditches and the downstream water body in autumn and spring (before and after the snow season 2009/2010). The characteristics of the receiving waters differed in geomorphology and vegetation. The sediment was analyzed for loss-on-ignition (LOI), grain size, and bulk concentrations of SiO 2, Al 2O 3, CaO, Fe 2O 3, MnO, Na 2O, P 2O 5, TiO 2, As, Cd, Co, Cr, Cu, Hg, Ni, Pb, S, V, and Zn. The sediment contamination was compared to concentrations at a reference point in Luleå where the bottom sediment was not affected by stormwater discharges and with Swedish environmental quality guidelines. Pearson's correlation and a principal component analysis were used to further evaluate the results.Results and discussion: Relative to the reference point, elevated trace metal concentrations were detected in sediments at all three sampling stations. At two of the stations, seasonal variations in ditch sediment grain size, LOI, and contaminant concentrations were observed, originating from stormwater sediment. Snowmelt runoff caused an increased proportion of fine-grained sediment fractions (<0.063 mm) in spring, mainly due to changes in runoff intensity and high sediment loads in the snowmelt runoff. The retention of metals appeared to be due to low turbulence in the water and the presence of organic material.Conclusions: Stormwater discharge affected the contaminant concentrations in the bottom sediments. The observed seasonal variation of contaminants indicated that relatively high amounts of contaminants are discharged during snowmelt and then reallocated within the receiving water body, either directly or after some temporal retention, depending on the characteristics of the receiving water. A calm water column and the presence of organic material in the receiving water body were crucial for the retention of metals.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Samhällsbyggnadsteknik -- Vattenteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Civil Engineering -- Water Engineering (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geokemi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geochemistry (hsv//eng)

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Tillförlitlighets- och kvalitetsteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Reliability and Maintenance (hsv//eng)

Nyckelord

VA-teknik

Urban Water Engineering

Applied Geology

Tillämpad geologi

Kvalitetsteknik

Quality Technology & Management

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