Seasonal and spatial variations in major and trace elements in a regulated boreal river (Esse River) affected by acid sulphate soils

Abstract

In coastal areas of Finland, extensive artificial drainage of Holocene sulphide-bearing marine and lacustrine sediments has resulted in development of acid sulphate (AS) soils (pH 2.5-4.5) over an estimated area of approximately 3000 km 2 . During heavy rains and snow melting, these soils are flushed resulting in discharge of acidic and metal-rich waters that strongly affect small streams. However, the total and precise effects in the important and large rivers are not well understood. In this study, the impact of AS soil occurrence and hydrological changes on water quality was determined in an important regulated boreal river (Esse River) having a catchment area of 2054 km 2 partially covered with AS soil (39 km 2 ). Water samples, collected at five sites along the river during four carefully selected events, were analysed for pH, total organic carbon, conductivity and the following elements/anions: Al, Ba, Br, Ca, Cd, Cl À , Co, Cr, Cu, Fe, K, La, Mg, Mn, Na, Ni, NO À 3 , Rb, Sc, Si, SO 2À 4 , Sr, Th, Y and Zn. There is a clear spatial correlation between AS soil occurrence and elevated element concentrations in the river water, especially when the conditions change from dry/warm (summer) to wet/cool (autumn). During the rains in autumn these soils are extensively flushed and concentrations of Co, La, Zn, Y, Mn and Al are increased between three and nine times towards the outlet. The buffering capacity of the river was, however, high enough to prevent a detrimental drop in pH. Another intriguing feature is substantially elevated concentrations of several potentially toxic metals (Cr, Cd, Cu) in the middle reaches in winter when the river is ice-covered. Since no external source for this was found, we suggest an internal source operating by an as yet unknown mechanism. During baseflow in summer, the concentrations of several solutes reach minimum concentrations.

Hydrochemistry of rivers in an acid sulphate soil hotspot area in western Finland

“…During summer, in addition to low flow conditions, abundant algal growth causing carbon dioxide uptake during photosynthesis can force the pH to higher values. As a consequence of this, in line with Lahermo et al (1996), Roos and Åström (2005) and Åström and Spiro (2005), the AS soils have a smaller effect on pH than on many other elements (see above) in river waters. This is controversial, since the general belief is that AS soils affect, in particular, the pH of the waters.…”

“…have low pH and high metal concentration (Palko and Yli-Halla 1993, Weppling 1993, Edén et al 1999, the impact on the larger and biologically important rivers has not been adequately investigated. A few studies focusing on a single river exist (Åström and Åström 1997, Edén et al 1999, Åström 2001b, Roos and Åström 2005, but studies covering and comparing several rivers at the same time are rare (Weppling 1993). The aim of this study was to investigate the hydrochemistry of all the rivers in this area and to rank them from the least to the most affected by this environmentally unfriendly soil type.…”

Influence of anthropogenic inputs and a high-magnitude flood event on metal contamination pattern in surface bottom sediments from the Deba River urban catchment

“…According to Taylor and Owens (2009), many previous anthropogenic sources dominate the contaminant load in urbanised river catchments. Nevertheless, the presence of metals and suspended particulate matter in aquatic environments may also have a natural origin, such as geological weathering, soil erosion and landslides (Roos and Åström, 2005;Göransson et al, 2009;Nystrand et al, 2012). Additionally, sediment sources, which are a direct result of human activities, also include the construction of urban infrastructures such as railway lines, road and channel networks, tunnels, and dams, among others.…”

Assessment of heavy metal pollutants accumulation in the Tisza river sediments

“…The studies of heavy metal pollution in sediments and soils have increased in recent years (Li and Thornton, 2001;Smolders et al, 2002;Bird et al, 2003;Veeresh et al, 2003;Relić et al, 2005;Roos and Åströ m, 2005;Sysalova and Szakova, 2006;Bacon and Davidson, 2008). Heavy metals are regarded as serious pollutants of aquatic ecosystems, because of their environmental persistence (Armitage et al, 2007), toxicity, and ability to be incorporated into food chains (Fö rstner and Wittman, 1983).…”