Behaviour of suspended particulate matter (SPM) and selected trace metals during the 2002 summer flood in the River Elbe (Germany) at Magdeburg monitoring station

Abstract

In August 2002, in the worst flooding in more than 100 years, the River Elbe destroyed built-up areas and caused widespread erosion and the relocation of soils and river sediments. To assess the pollutants entering the water, surveys of dissolved constituents and suspended particulate matter (SPM) were carried out daily during the flood at a monitoring station near Magdeburg. The sampling point is part of the network of the International Commission for the Protection of the Elbe (ICPE). The results were compared with those of previous flood studies which used the same sampling strategy. Unlike past floods, the 2002 flood was characterised by the transport of relatively fine suspended material with a low mass concentration. Owing to different input sources, the maxima of dry weight and of particle number concentration occurred at different times. Hg, Fe, Mn, Zn, Cu, Ni and Cr showed a maximum concentration concurrent with the dry weight of the SPM, whereas the maximum concentrations of As, Pb, and Cd coincided with the particle number concentration peak. The concentration of particulate matter decreased rapidly, unlike the concentrations of dissolved substances such as DOC and trace metals, as well as the values of UV extinction, all of which remained high for a longer period. Comparing the results of the 2002 flood with the winter floods in 1995, 1999 and 2000, revealed increased values of As and Pb as well as higher concentrations of dissolved compounds.

Nitrite consumption and associated isotope changes during a river flood event

“…This scenario is supported by SPM values: the high runoff initially results in a peak of SPM from groyne fields, which is eluted directly before the discharge peak (Baborowski et al, 2004). The decrease of δ 15 N SPM from ∼ 8 ‰ to < 6 ‰ during increasing discharge also indicates the input of terrestrial organic material due to leaching.…”

“…It is a substrate for phytoplankton assimilation or denitrifi-cation, but it is also clearly correlated to discharge, dilution, and to leaching from agricultural soils. This is reflected in the complex changes of nitrate concentration over the course of the flood event, which is in this context comparable to previous river floods (Baborowski et al, 2004). During the flood, nitrate concentration first decreases with rising discharge, then rises and peaks with peak discharge, decreasing again with lower discharge until the end of the flood event.…”

“…The high C / N ratio during the SPM peak and minimum of nitrate (10 compared to 7.5 before the peak) further suggests that terrestrial organic matter contributes to the riverine signal at this time. Afterwards, the C / N ratio decreases, probably because water masses from tributaries and upstream regions contribute to the pool, as it has been observed during a previous flood event in the Elbe River (Baborowski et al, 2004). At the same time, assimilation by phytoplankton is low, probably due to high turbidity, short residence times, dilution of active cells, and decreased light availability (Deutsch et al, 2009;Voss et al, 2006).…”

“…After this minimum, i.e. after 10 June, the input from tributaries and upstream regions gained in importance (Baborowski et al, 2004). Nitrate concentration increased with discharge, which can be attributed to terrestrial soil nitrate that is leached from the catchment area.…”

Chemical variability of water and sediment over time and along a mountain river subjected to natural and human impact

“…An increase of some other metals during high water flow and flood was also found in mountain streams (Abesser et al, 2006;Hardie et al, 2007). In such periods, additional sources of metals may be atmospheric precipitation or re-suspension of river sediments, which often act as 'secondary' sources of pollution (Baborowski et al, 2004;Wilber and Hunter, 2007). The contents of Cr and Ni were also dependent on the Biała Tarnowska River flow, indicating diffuse contamination as a dominant source.…”