Influence of flooding on accumulation of nutrients and heavy metals in the delta of the river Nemunas in Lithuania

Abstract

Accumulation of heavy metals in the flooded polders were 20 to 40 % larger than in non-flooded ones. Distribution of Pb in soils along the river delta corresponded to the character of the sediment deposition. Closer to the river's mouth the amount of sediments as well as Pb decreased. This showed that water is cleaning itself on account of soil pollution. To preserve existing self- purification capacity of nutrient and heavy metals it was not purposeful to reconstruct a flooded polder to a non-flooded one. Reeds, energy crops or natural wetlands should be established on swampy meadows of flooded polders. Studies in the river Nemunas delta were conducted in order to evaluate the nutrient and heavy metal input to the flooded and non-flooded polders and to propose environmentally friendly farming methods. This article analyses nutrient and heavy metal accumulation in the river Nemunas delta area in the years of 1992-2000 and leaching of these compounds to various soil layers. The analysis of nutrient accumulation showed that the soil amounts of N increased (mg kg(-1)) about 50, P2O5 40-100, K2O - 20-30 correspondingly. In the soil layer 20-50 cm. of the non-flooded polders N the content was 4-5 times less than in flooded polders. Comparing non-flooded polders with flooded ones showed the difference in the P2O5 content of soils. Flooding of meadows most of all influenced K2O. The content of K2O increased after the flood on average 20 and 54 % in mineral soils and in peat soils respectively. After the flood 1.4-1.8 times more of K2O appeared in the soil of a flooded polder than in a nonflooded one. Retention of nutrients during flooding of a valley were positive, both for soil fertilisation and for improvement of water quality.