Marek Kruk (email@example.com)
Department of Ecology, Agricultural University, 10-957 Olsztyn, Poland.
Accumulation of Mn, Zn, Cu, Pb and Cd in four compartments of a wetland/lake complex in northeastern Poland, was determined with ecosystem input-output budgets, and chemical analyses using inverse voltammetry. The following wetland types were used in this study: (1) a wetland with a declining lake, (2) a wetland with a transitional mire, and (3) two drained peatlands with meadows in forested and agricultural surroundings. These ecosystems document general long-term tendencies of postglacial landscape transformations: terrestrialisation of lakes, and impact of forest and agricultural activities on drainage of wetlands, and afforestation. The two-year study (monthly data collection) included assessment of microelement concentrations in several types of water fluxes, which were compared to metal inputs from the atmosphere and upland portions of the surrounding watersheds.
Concentrations of microelements were typically higher in atmospheric deposition than in stream water, spring or artificial drain waters. Mean concentrations of Zn in rain averaged 56.7 mg L-1 and in terrestrial water bodies 2.4 to 3.7 mg L-1. Concentrations of Pb were 2.5 and 0.12 - 0.35 mg L-1, and concentrations of Cd were 0.61 and 0.01 - 0.04 mg L-1, in rainfall and terrestrial water bodies, respectively. Smaller differences were observed for Cu: 2.84 mg L-1 in deposition and a range from 1.09 to 2.46 mg L-1 in streams. An inverse trend was observed for Mn: 15.3 mg L-1 and 28.4 to 76.6 mg L-1, respectively.
Trace metals accumulation rates were higher in the wetland with a declining lake (Zn - 0.51, Cu - 0.13, Pb - 0.04, Cd - 0.012 and Mn - 0.16 kg ha-1 year-1) and lowest in the forest meadow (Cu - 0.008, Pb - 0.015 kg ha-1 year-1) and agricultural meadow (0.25 Zn and 0.0008 Cd kg ha-1 year-1; Table 1). However, accumulation rates, expressed in relative values - % of inflow, were variable among the different ecosystem types. The level of relative accumulation of Zn and Pb and net loss of Mn increased with every wetland-meadow stage. The accumulated portion of the inflowing Zn increased from 55 % in the wetland with a lake to 87 % in the agricultural meadow, and removed part of inflowing Pb load from 44 to 92 % respectively. On the other side, net loss of Mn increased from near 0 in the declining lake to 134 % of inflow in mid-field meadow. The behaviour of Cu and Cd were also contrasting. The level of relative accumulation rate of Cu reached almost 50 % in the mid-field meadow, while in forest ecosystems they were 20-30 %. Removal rates of Cd were high (approx. 80-95 % of inflow) in all studied areas (Table 1).
The rates of accumulation expressed in relative values, i.e. % of inflow, clearly indicate considerable changes in Zn, Pb, Mn and also Cu cycling in wetlands influenced by human activity. These ecosystems developed accumulative properties for Zn, Pb and Cu, while considerably increased leaching of Mn. It should be noted that the above process is not observable in absolute values (kg ha-1 year-1). The most likely factor controlling the amount of retained metals seems to be the amount of water throughflow.
Table 1. Accumulation of trace metals in wetland-meadow stages of landscape long-term changes (NE Poland). Values are in kg ha-1 yr-1, italicised values in parentheses express accumulation in % of inflow).
|Wetland-meadow stages of landscape change||Mn||Zn||Cu||Pb||Cd|
|Wetland with declining lake||0.16||0.51||0.132||0.040||0.0117|
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