Effect of heavy metals on salt march biota
Department of Chemistry and Environmental Science
Doctor of Philosophy
Malhotra, Sanjay V.
Arbuscular mycorrhizal fungi
Environmental restoration of disturbed, degraded and potentially contaminated wetland sites aims for the persistent and sustainable re-establishment of biological communities and important wetland functions. An ecologically informed restoration strategy presupposes some understanding of these system processes, but also of potential impacts on contaminants in the environment for risk assessment, long-term management, and potential cost-effective mitigative measures. In this study, potential effects of moderate heavy metal contamination in sediments of the urban salt marsh Harrier Meadow, NJ, were evaluated on growth performance of the common salt marsh plant S. patens and associated arbuscular mycorrhizal fungi (AMF) colonizing its roots. Growth performance as well as uptake of heavy metals into roots and translocation from below- into above-ground parts was studied as a function of basic environmental conditions such as pH and redox potential, absence or presence of AMF, as well as additional contamination with nickel (Ni) at selected times during the first growing season, and after the third growing season.
The experimental setup in the greenhouse with soil cores containing S. patens from Harrier Meadow resulted in consistent environmental conditions in cores within and between treatments, with values for most physicochemical parameters being not significantly different at comparable depths. Concentrations and spectra of total hydrolysable amino acids (THAA) in the organic material analyzed after the third growing season as measure for organic matter quality and thus metabolic processes were similar in cores of all treatments and thus indicated no significant biotic environmental differences that might have developed in time as a function of treatments. Measures for AMF were similar on plants from all treatments even though small, statistically significant differences were obtained for percent root length colonized, and arbuscular or vesicular colonization. Since none of the treatments eliminated AMF, these differences could not be related to treatment effects, but were suggested to be the result of potential shifts in AMF community structure, that, however, were not analyzed within the scope of the thesis.
Plant growth performance assessment based on leaf nitrogen (N) content, stable isotope ratios (δC), carboxylation efficiency (CE), CO2 saturated photosynthetic capacity (Amax), estimations of optimal transfer efficiency of open photosynthesis II (PSII) reaction centers (Fv/Fm), sprout numbers, and shoot and root biomass generally showed seasonal variation in these characteristics only. However, additional variation was displayed for parameters such as Amax, Fv/Fm, and shoot and root biomass where significant effects of Ni amendment were found during "reproduction". These effects were no longer significant at the end of the growing season, and were not obtained when Ni amendment was combined with AMF suppression.
Sediment of Harrier Meadow was found to be moderately contaminated with heavy metals (Cd, Cr, Cu, Ni, Zn). Calculations using MineQL+, a data driven, chemical equilibrium modeling program suggested that, under suboxic and anoxic conditions found in all cores, only Cd, and under anoxic conditions, Ni would not form precipitates, while Cd, Cr, Cu, Pb and Zn would mainly form precipitates. 70-95% of the total concentration of the dissolved forms of all heavy metals could also be adsorbed to organic compounds. None of the heavy metals nor the additional Ni application resulted in uptake or translocation values typical for hyperaccumulating plants, but rather values in the typical range found for many agricultural plants. Since all values in plant tissues were above the critical deficiency contents and below the critical toxicity contents, effects on plant growth performance should not be expected. Ni amendment did not increase uptake and translocation in most cases although effects of Ni amendment were displayed for root uptake of certain heavy metals (i.e., Cu, Pb, Zn and Fe) at the depth of 7.5 cm.
These results demonstrate that moderate heavy metal contamination found in sediments of Harrier Meadow did not affect growth performance of the common salt marsh plant S. patens and associated arbuscular mycorrhizal fungi (AMF) colonizing its roots during key points of the growing season. Although considerable uptake of all heavy metals into or adsorption to roots was encountered, translocation from below- into aboveground parts of S. patens was not significant, and always below regulatory action limits (maximum limit levels for vegetative leaves of Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn are 0.2, 2.30, 73.3, 425.50, 500, 67.90, 0.3 and 99.40 mg.kg-1). Thus, the risks associated with the restoration of moderately contaminated salt marshes with S. patens, i.e., the potential of S. patens to act as a conduit for the movement of toxic metals into the food web, are minimal and thus of low public health concern.
njit-etd2005-136 (211 pages ~ 14,295 KB pdf)
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Created September 8, 2008