ENVIRONMENTAL AUDITING: Risk Assessment in the Face of Controversy: Tree Clearing and Salinization in North Queensland

/ Several lines of evidence were followed to assess the risk of salinization after tree clearing in the upper Burdekin River basin in north Queensland. Conceptual, biophysical process-based approaches (pedological interpretation, event tree analysis, one-dimensional water balance modeling, and Boolean spatial analysis) were compared to empirical methods and field evidence. The convergence of all lines of conceptual reasoning to the conclusion that there exists a risk of salinization in north Queensland, consistent with field evidence of naturally occurring waterlogging and salinity, strengthens the argument against tree clearing.     

Gaseous nitrogen losses from a forest site in the North Tyrolean Limestone Alps

Microorganisms are responsible for the mineralisation of organic nitrogen in soils. NH ⁺₄ can be further oxidised to NO₃ ⁻ during nitrification and NO₃ ⁻ can be reduced to gaseous nitrogen compounds during denitrification. During both processes, nitrous oxide (N₂O), which is known as greenhouse gas, can be lost from the ecosystem.

The aim of this study was to quantify N₂O emissions and the internal microbial N cycle including net N mineralisation and net nitrification in a montane forest ecosystem in the North Tyrolean Limestone Alps during an 18-month measurement period and to estimate the importance of these fluxes in comparison with other components of the N cycle. Gas samples were taken every 2 weeks using the closed chamber method. Additionally, CO₂ emission rates were measured to estimate soil respiration activity. Net mineralisation and net nitrification rates were determined by the buried bag method every month. Ion exchange resin bags were used to determine the N availability in the root zone.

Mean N₂O emission rate was 0.9 kg N ha⁻a⁻, which corresponds to 5 % of the N deposited in the forest ecosystem. The main influencing factors were air and soil temperature and NO ⁻₃ accumulated on the ion exchange resin bags. In the course of net ammonification, 14 kg NH ⁺₄ −N ha⁻ were produced per year. About the same amount of NO ⁻₃ −N was formed during nitrification, indicating a rather complete nitrification going on at the site. NO ^t-₃ concentrations found on the ion exchange resin bags were about 3 times as high as NO ^t-₃ produced during net nitrification, indicating substantial NO ^t-₃ immobilisation. The results of this study indicate significant nitrification activities taking place at the Mühleggerköpfl.

     

Characterization and phosphate stabilization of dusts from the vitrification of MSW combustion residues

The use of soluble PO₄³⁻ as a heavy metal chemical stabilization agent was evaluated for a dust generated from melting or vitrification of municipal solid waste combustion residues. Vitrification dusts contain high concentrations of volatile elements such as Cl, Na, K, S, Pb, and Zn. These elements are present in the dusts largely as simple salts (e.g. PbCl₂, ZnSO₄) which are highly leachable. At an experimental dose of 0.4 moles of soluble PO₄³⁻ per kg of residue, the pH-dependent leaching (pH 5,7,9) showed that the treatment was able to reduce equilibrium concentrations by factors of 3 to 100 for many metals; particularly Cd, Cu, Pb and Zn. Bulk and surface spectroscopies showed that the insoluble reaction products are tertiary metal phosphate [e.g. Zn₃(PO₄)₂] and apatite [e.g. Pb₅(PO₄)₃Cl] family minerals. Geochemical thermodynamic equilibrium modeling showed that apatite family and tertiary metal phosphate phases act as controlling solids for the equilibrium concentrations of Ca²⁺, Zn²⁺, Pb²⁺, Cu²⁺, and Cd²⁺ in the leachates during pH-dependent leaching. Both end members and ideal solid solutions were seen to be controlling solids. Soluble phosphate effectively converted soluble metal salts into insoluble metal phosphate phases despite the relatively low doses and dry mixing conditions that were used. Soluble phosphate is an effective stabilization agent for divalent heavy metals in melting dusts where leachable metals are present in high concentrations.