The characteristic levels of heavy metals (Cd, Cr, Cu, Pb, Ni and Zn) of soil profiles of automobile mechanic waste dumps were studied. The concentration of heavy metals decreased with the depth of the profile and lateral distance from the dumpsites. The levels found in this study exceeded background concentrations and limits for agricultural and residential purposes. The distribution pattern of heavy metals in the soil profiles were in the following order Pb > Zn > Cu > Cd > Ni > Cr. The mechanic waste dumps represent potential sources of heavy metal pollution to environment. The elevated levels of heavy metals in these soil profiles constitute a serious threat to both surface and groundwater.

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Monitoring of the forms of N in water and sediment, and investigations of N cycling in Lake Wingra, a small, eutrophic, hardwater lake in southern Wisconsin, were conducted. Nitrification in the waters appeared to be by heterotrophs, while autotrophic nitrification dominated in the sediments. Rapid turnover of 15N‐NH4+ occurred in the waters, but not in the sediments, while 15N‐NO3− turnover was slow in the waters. In the sediments, denitrification and immobilization of 15N‐NO3− was rapid. About 80% of the added 15N‐NO3− was denitrified, the remainder being immobilized. Detrital‐15N was slowly mineralized in the sediments. Sediment‐water interchange occurred at a significant rate. About 40 µg NH4+‐N/liter sediment/day was formed from organic‐N, and subsequently released to the overlying water. Estimates of the overall average N content in various compartments indicated that about 50% of the “available” N was in the water, 20% in the macrophytes, and 30% in the sediments, while over 97% of the total N in the lake (to 30 cm sediment depth) was as sediment organic N. Consideration of seasonal changes in the NH4+‐N content of the sediments gave an average release rate of NH4+‐N of 7 to 29 mg m−2 day−1. This would supply from 3 to 14 metric tons of N to the lake water yearly. This is about the same order of magnitude as all external N inputs. Thus, even if the controllable point sources of N were eliminated, the biomass N in the lake water would not be significantly decreased.

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