Contaminant southwest of England has resulted in metal concentrations

Contaminant fluxes from point and diffuse sources from
abandoned mines in the River Tamar catchment, UK by Krongkaew Mighanetara, Charlotte B.
Braungardt, John S. Rieuwerts, Fethi Azizi

of mining activities in the southwest of England has resulted in metal
concentrations that exceeds the environmental quality standards, even though
mining has stopped since the 1990s. Concentrations of Cu, Pb and Zn have not
decreased by the late 1970s, a century after the peak of Cu mining and it seems
that it will not reduce if steps are not taken. This study focussed on
quantifying the fluxes of the concentrations of the mining-related contaminants
in the River Tamar catchment. Contamination in this area is largely due to
adits or drainage channels that carry run-off and leachate from the
contaminated soil and waste piles directly into the river. These waste piles,
that are situated directly on the bank river, are considered as the greatest
potential impact as diffuse contamination. By addressing on 25 adits (single-point
source) and streams (combination of diffuse and point source)  in this area (figure 1), the authors focussed
on the dominant contributors of contamination in the catchment area. Temporal
variations in water discharge are indicated with seasonal flow changes, with
a  relative higher discharge during
autumn and winter and a relative lower discharge during spring and summer
(figure 3). The enrichment of SO4, Cu, Zn, Ni and Co was highest during
the onset of the wet season (October), although their dissolved concentration
in the Tamar decreased (figure 2). This was probably a result of dilution
effects. The highest metal concentrations in streams and adits were observed
for Fe, Mn, Cu, As and Zn, which is consistent with the geological setting and
the dominant mineral ores in this mining district. Furthermore, the highest
dissolved metal concentrations occurred in waters with lowest pH values and
highest conductivity and sulphate concentrations. Seven specific sources (sample
2, 13, 14, 16, 17, 21 and 25) accounted for more than 75% each of the total
(dissolved and particulate) annual Fe, Mn, Cu, Zn, As, Ni, Co, Pb and Cd flux
determined in the 25 adits and streams. The signal strength for each
metal differed between these dominant sources, according to the source
mineralogy and pathways involved. Further, a trend towards higher dissolved element
fluxes during periods of higher flow was observed in most streams within the mining
area, irrespective of their average flow rate. According to this study, the
estuary received approximately 440 t Fe, 81 t Mn, 16 t Cu, 14 t Zn, 6.3 t Ni,
5.6 t As, 4.2 t Co and 260 kg Pb in dissolved and suspended form from its
catchment during the study period. This continued input in combination with the
re-working of the fine-grained sediment results in high levels of
contaminants in sediments throughout the estuary.

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