Watershed land use as a determinant of metal concentrations in freshwater systems

Abstract

Concentrations of Fe, Mn, Cu, dissolved organic matter (DOM), and pH were synthesized from 30 publications to determine the factors regulating concentrations and behavior of metals in freshwater systems. Results from the review suggest that contrasting watershed land use can directly (erosion and runoff) and indirectly (in-lake processes including metal-DOM-pH interactions) affect the metal concentrations in freshwater systems. Among the watershed land uses considered here, concentrations of Fe, Mn, and Cu were observed in the following order: arctic lakes < forested < agricultural < urbanized < mined. A drastic difference in mean metal concentrations has been observed when undisturbed or low impact watersheds (arctic and forested) were changed by agricultural, urban, and mining developments. Relationships between metal concentrations and pH revealed that metals precipitate at high pH (pH > 5). Additionally, at pH < 5, metal concentrations were significantly correlated with DOM due to metal-DOM complexation. High ratios of metal: DOM occur only at low DOM concentrations. Collectively, two general conclusions can be drawn from this review. First, lakes, rivers, and streams with urbanized watersheds are the most susceptible to increased concentrations of metals. Secondly, these results also suggest that regardless of high or low DOM in the water column, pH would affect metal concentrations in freshwater systems. Nonetheless, free metal ions would be higher in freshwater systems with acidic water and low DOM.

Urbanization Effects on Watershed Hydrology and In-Stream Processes in the Southern United States

“…Specifically, Fe, Mn and Cu were consistently high in urban watersheds [Fe (12-58 g/L), Mn (0.20-30 g/L) and Cu (0.4-15 g/L)], with only streams draining mining areas having higher concentrations (Das et al 2009) [109]. Additionally, metal concentrations were inversely correlated with pH indicating that at low pH levels, metal solubility increases and metal particles become more mobile.…”

“…In a review of 135 observations from a wide range of aquatic ecosystems, watershed land use was shown to directly (erosion and runoff) and indirectly (pH driven metal-DOM interactions) affect metal concentrations in freshwaters [109]. Specifically, Fe, Mn and Cu were consistently high in urban watersheds [Fe (12-58 g/L), Mn (0.20-30 g/L) and Cu (0.4-15 g/L)], with only streams draining mining areas having higher concentrations (Das et al 2009) [109].…”

Influence of land use on total suspended solid and dissolved ion concentrations: Baton Rouge, Louisiana area

“…This study's results appear to be similar to the Christian et al (2011) study in that urbanization tends to decrease iron concentrations. By contrast Paul & Meyer (2001) observed that urbanization increases iron concentrations; this was also true for most of the 30 studies included in Das et al (2009). Maybe in this area water acidity is more important than land use.…”

“…Maybe in this area water acidity is more important than land use. Das et al (2009) noted that increases in acidity tends to increase iron concentrations in lakes, so maybe this is happening to the set of streams in the study area. In this area both of these landscapes are largely tree covered-forest landscapes, which in this case is pine and hardwood mix forest (Smith, 1999).…”

“…Forest landscapes will tend to have more acidic soil for water to infiltrate through (Jobbagy & Jackson, 2003), which in turn yields a greater solubility of metals, for example iron (Crivineanu et al, 2012). Das et al (2009) noted that soil, geology, topography and vegetation can also influence iron and manganese concentrations in addition to land use. Rural forested landscapes have significantly higher concentrations of total organic carbon IU for industrial and utilities; LDR for low density residential; MHDR for medium and high density residential; P for Park, UD for undeveloped.…”