Journal of Conference Abstracts

Heavy Metals in the Water Medium

S. Mazukhina (sharov@alphais.inep.ksc.ru) & A. Moiseenko (tatyana@alphais.inep.ksc.ru)

Institute of North Industrial Ecology Problems,Kola Science Centre,
Russian Academy of Science, 14 Fersman Str., Apatity, Murmansk Region, 184200, Russia.

The future forecast of water quality is an important issue in limnology. Water quality is determined by a set of parameters, and its physico-chemical properties. Anthropogenic eutrophication, resulting from organic oxidation and subsequent accumulation at the bottom of the lake, is responsible for anoxic conditions. Imandra Lake is one of the water bodies to be considered. The aim of this work is to investigate the behaviour of heavy metals under anoxic conditions by a method of physico-chemical modeling. This method is based on the principle of free energy minimisation in the calculation of heterogeneous equilibrium. Thermodynamic equilibrium is established between aqueous species, gases, and minerals. To obtain this aim, we have investigated the system Al-Fe-Mg-Mn-Ca-Ni-Sr-Na-K-C-N-Si-Cl-S-H-O (at temperature 25 °C, at a constant composition at a depth of 2 m; Imandra Lake mirrow). Anoxic conditions were obtained by titrating the organic composition (C_org) from 10^-4 to 10^-2 mol L^-1. Results of modeling indicate qualitative and quantitative changes in the ionic composition, phases, gases, and energy potential, in relation to oxidation-reduction conditions. pH, and water medium.

The increase in C_org causes a decrease in energy potential of the system, resulting in higher concentrations of H₂CO₃ and HCO₃^- in solution, a decrease in pH , and an increase in the quantity Fe(OH)₂⁺, Mn⁺², HSO₄^-, MnHCO₃⁺, CaHCO₃⁺, MgHCO₃⁺, NaHCO₃, Fe(OH)⁺², Mn(OH)⁺. Such minerals as gibbsite, goethite, pyrolusite, and kaolinite are formed. Redox transition in this system occurs at n(C_org)= 10^-3.65 mol L^-1. The Eh potential changes from positive to negative values; the set of minerals changes. The formation of pyrite and NiS₂ suggests a change in conditions from acidic to reproductive.

When n(Corg)=0.001 mol L^-1, the energy potential of the system is at a minimum. The quantity of MgSO₄, K₂SO₄, KSO₄-, NaSO₄^- , CaSO₄, HSO₄^-, HSO₃^-, SO₄^-2 decreases, and such gases as H₂S, CH₄, CO, H₂ are produced. Thus, a new gas regime results, new quality conditions of the system results. New energy levels of the system are obtained by further increases in C_org.

Effects of Chronic N Amendment on DOC and
DON Production in Forest Soils

William H. McDowell¹ (bill.mcdowell@unh.edu), William S. Curie² (wcurrie@lupine.mbl.edu),
John D. Aber³ (john.aber@unh.edu) & Yuriko Yano¹ (yy@christa.unh.edu)

¹ Department of Natural Resources, University of New Hampshire, Durham, New Hampshire 03824, U.S.A.

² Ecosystems Centre, Marine Biological Laboratory, Woods Hole, Massachusetts 02541, U.S.A.

³ Complex Systems Research Centre, University of New Hampshire, Durham, New Hampshire 03824, U.S.A.

Chronic N deposition has been hypothesized to affect DOC production in forest soils due to the carbon demand exerted by microbial immobilization of inorganic N. We tested this hypothesis in field experiments at the Harvard Forest, Petersham, Massachusetts, USA. In forest plots (hardwood and conifer), we found no consistent changes in DOC dynamics associated with elevated N inputs. During four years of sampling soil solution collected beneath the forest floor in zero-tension lysimeters, DOC concentrations varied seasonally and with rainfall, but were unaffected by inorganic N levels. DON concentrations also followed the seasonal pattern shown by DOC, but did show an effect of fertilisation with inorganic N. In the high-N pine plots, where N retention capacity has been saturated, we observed a progressive increase in DON concentrations over time, with concentrations as high as 20-40 mg L^-1. The organic chemistry of soil solution thus appears to undergo progressive, qualitative changes as a result of N saturation at this site. In contrast to our field results, laboratory experiments with sieved soils from the N-amended plots showed that DOC production declined sharply with high rates of N application. This inconsistency suggests that tree root exudates may be a major source of DOC in intact forest soils.