Temporal sedimentary record of thallium pollution in an urban lake: An emerging thallium pollution source from copper metallurgy

The impact of the urban effluents of Mytilene (Lesvos island, Greece) on the receiving coastal marine environment, was evaluated by studying the quality of the city effluents (BOD5, COD, SS, heavy metals) and the marine sediments (grain size, organic matter, heavy metals). It was found that the urban effluents of Mytilene contain high organic matter and suspended particle load because of septage discharge into the sewerage network. Furthermore, although the city does not host important industrial activity, its effluents contain appreciable metal load, which is mainly associated with the particulate phase. The city effluents are discharged into the coastal marine environment and their colloidal and particulate matter after flocculation settles to the bottom, where is incorporated into the sediments. Over the years, the accumulation of organic matter and metals into the harbour mud has created a non-point pollution source in the relatively non-polluted coastal marine environment of the island. Copper and Zn were the metals which presented the higher enrichment in the sediments of the inner harbour of Mytilene.

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Distribution of nitrifying bacteria in a shallow stream

Water Science & Technology ◽

10.2166/wst.1997.0660 ◽

1997 ◽

Vol 36 (8-9) ◽

pp. 161-166 ◽

Cited By ~ 1

Author(s):

Ivana Jancarkova ◽

Tove A. Larsen ◽

Willi Gujer

Keyword(s):

Field Experiments ◽

Heterotrophic Bacteria ◽

Pollution Source ◽

Nitrifying Bacteria ◽

Channel Water ◽

River Bed ◽

Hydraulic Conditions ◽

Major Floods ◽

Shallow Stream ◽

Stream Bed

A project investigating the dynamics of self-purification processes in a shallow stream is carried out. Effects of the concentration gradient due to the distance to the pollution source, of hydraulic conditions in the river bed and of storm floods on the distribution of nitrifying bacteria were studied with the help of laboratory and field experiments. Nitrifiers density on the surface of the stream bed increased rapidly up to a distance of 300 m from the WWTP indicating possible competition of the nitrifiers with the heterotrophic bacteria close to the WWTP. Afterwards a slight decrease in the downstream direction was observed. In vertical profiles, higher bacterial densities were found at sites with rapid infiltration of channel water to the stream bed than at sites with no exchange between channel water and stream bed water or where stream bed water exfiltrated. A major flood event scoured the nitrifiers nearly totally from the surface of the river bed. Major floods belong so to the most dominant processes controlling self-purification in shallow streams. Minor floods, however, don't scour bacteria in the depth of the stream bed that could then be important for the self-purification processes.

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