Concentration of zinc in water and bottom sediments in small water reservoirs located in rural areas

Depending on its concentration in the environment, zinc can be either an important bio-element for development of living organisms, or a toxic heavy metal. Small water reservoirs are especially sensitive to contamination, as because of their location in the lowest point of the catchment they tend to receive contaminants from its whole area. The purpose of this work was to assess changes in concentration of zinc in surface, supra-bottom and interstitial water, and in the upper layer of sediment, in five small water reservoirs located in rural areas. The reservoirs G1 and G2 were located in a golf course, water body SW was in a village, very close to farmyards, water body P1 was in the middle of a crop field, and water body P2 was on fallow land. For this research, samples were collected once a month, during three vegetation seasons. The water reservoirs contained an elevated average concentration of zinc in water from 0.026 to 0.063 mg dm–3). The average concentration of zinc in the sediments (from 25.8 to 118.2 mg kg–1) classified the examined reservoirs into the geochemical purity class 1. The highest content of zinc was in the village pond. Highly significant correlations were determined between the content of organic matter and zinc in the bottom sediment in the investigated reservoirs. At the same organic matter content, the zinc concentration in the bottom sediments of the rural pond was find-fold higher than in the other reservoirs. The concentration of zinc in water and the factor of its accumulation in the sediment showed a clear seasonal character of changes. In the spring season, concentration of zinc in interstitial water was lower than in the water depth, whereas in the vegetation season, the zinc concentration was observed to rise in all layers, up to over ten-fold in the interstitial water. In the sediment, the zinc accumulation factor changed in a reverse manner, i.e. it reached thee highest values during spring but fell the lowest in autumn.