Marinus L. Otte

Organism-induced accumulation of iron, zinc and arsenic in wetland soils

The aim of this study was to gain a better understanding of the impact of rhizosphere/burrow oxidation by wetland plants and burrowing invertebrates on the biogeochemistry of metals and metalloids in salt marsh ecosystems. It was hypothesised that salt marsh plants and burrowing invertebrates could considerably affect the retention capacity of wetlands for metals through oxidation of the rhizosphere/burrow wall. Various soil, plant and porewater samples were collected from areas dominated by the plant species Spartina townsendii and Atriplex portulacoides and by the lugworm Arenicola marina, and from corresponding nearby unvegetated/uninhabited sites at North Bull Island salt marsh, Dublin Bay, Ireland. Samples were analysed for total Fe, Zn and As. The organic matter content (LOI), bulk density, water content and dry/fresh weight ratio of rhizosphere, burrow wall and bulk soil was measured for each species. DCB-extractable Fe, Zn and As, associated with the iron plaque on the roots of the two plant species were also determined. The presence of vegetation and, to a lesser extent, burrowing organisms were shown to have a significant effect on the concentration and accumulation of heavy metals in salt marsh soils. Iron and arsenic concentrations were significantly higher in vegetated/inhabited soils compared to nearby unvegetated/uninhabited areas. Zinc showed the same trend but the difference was not statistically significant. The concentrations of Fe and As were also significantly higher in the rhizosphere soil around the plant roots and in the burrow walls of Arenicola compared to the bulk soil. For zinc, the same pattern was significant only for S. townsendii-dominated soils. Atriplex stands appeared to have the greatest potential for heavy metal accumulation with concentrations reaching 1238 micromol Fe g(-1), 4.9 micromol Zn g(-1) and 512 nmol As g(-1) in the rhizosphere. The Zn/Fe ratio for S. townsendii and the As/Fe ratios for both plant species also increased from the bulk soil towards the roots. Concentrations of Zn and As appeared to correlate with both Fe concentrations and LOI values. However, covariation was significant only with Fe, indicating that it is the oxidation of Fe, rather than the binding to organic matter, that drives the accumulation of Zn and As. The amount of each element present in the various compartments associated with the plants (the sum of the element concentrations in the rhizosphere, ironplaque and roots) in 1 litre of the top 20 cm of soil, amounted to 0.84 % for Fe, 3.6% for Zn and 2.8% for As for S. townsendii, and 12.5% for Fe, 19% for Zn and 18.3% for As for A. portulacoides. Densities of A. marina were never higher than 1 per litre of top soil so the small volume of burrow wall soil would therefore render that pool of negligible size compared to the rhizospheres of plants. It is likely that lugworms affect the movement of metals more importantly through bioturbation.

CONFLICTING PROCESSES IN THE WETLAND PLANT RHIZOSPHERE: METAL RETENTION OR MOBILIZATION?

Increasingly wetlands are used for treatment of metal-contaminated water or as a cover over metal-enriched mine tailings. Natural wetlands may also be contaminated with metals from anthropogenic sources. While wetland conditions tend to be favorable for immobilization of metals, wetland plants could influence metal mobility through redox and pH processes in the rhizosphere. Our current knowledge of these processes is reviewed, focusing on the question of whether the advantages of growing wetland plants in metal-contaminated sediments outweigh the disadvantages. Wetland plants alter the redox conditions, pH and organic matter content of sediments and so affect the chemical speciation and mobility of metals. Metals may be mobilized or immobilized, depending on the actual combination of factors, and it is extremely difficult to predict which effects plants will actually have on metal mobility under a given set of conditions. However, while the effects of plants can extend several tens of centimeters into the sediments, there are no reports suggesting large-scale mobilization of metals by wetland plants.

What is stress to a wetland plant

Abstract The definitions of the term ‘stress’ and its applications are reviewed in relation to wetland plants. Three views on the use of the term stress prevail; (1) that it should not be used at all; (2) that it defines any situation which leads to a decrease from optimum performance; and (3) that it should only apply to extreme conditions, outside the normal range of the organism. It is argued here that View 3 should be accepted only; i.e. that stress should only be regarded to be arising from changes in environmental conditions outside the normal range encountered by plants. Conditions normally encountered by wetland plants, such as waterlogged, anaerobic soils and salinity, are not stressful to such plants, but only to non-adapted dryland plants. Stress occurs only when plants are exposed to environmental conditions outside the range they are normally exposed to due to natural or anthropogenic changes. Such conditions are found in agriculture—when plants are grown in places they would not naturally grow, in rapidly changing environments—for example when hydrology is changed due to subsidence or engineering works, and under conditions of environmental pollution. The actual stress imposed on wetland plants may be secondary to the factor thought to cause the stress. Very few studies exist showing direct stress on wetland plants.

UPTAKE AND TRANSLOCATION OF TI FROM NANOPARTICLES IN CROPS AND WETLAND PLANTS

Bioavailability of engineered metal nanoparticles affects uptake in plants, impacts on ecosystems, and phytoremediation. We studied uptake and translocation of Ti in plants when the main source of this metal was TiO2 nanoparticles. Two crops (Phaseolus vulgaris (bean) and Triticum aestivum (wheat)), a wetland species (Rumex crispus, curly dock), and the floating aquatic plant (Elodea canadensis, Canadian waterweed), were grown in nutrient solutions with TiO2 nanoparticles (0, 6, 18 mmol Ti L−1 for P. vulgaris, T. aestivum, and R. crispus; and 0 and 12 mmol Ti L−1 for E. canadensis). Also examined in E. canadensis was the influence of TiO2 nanoparticles upon the uptake of Fe, Mn, and Mg, and the influence of P on Ti uptake. For the rooted plants, exposure to TiO2 nanoparticles did not affect biomass production, but significantly increased root Ti sorption and uptake. R. crispus showed translocation of Ti into the shoots. E. canadensis also showed significant uptake of Ti, P in the nutrient solution significantly decreased Ti uptake, and the uptake patterns of Mn and Mg were altered. Ti from nano-Ti was bioavailable to plants, thus showing the potential for cycling in ecosystems and for phytoremediation, particularly where water is the main carrier.

Analysis of Dimethylsulphoniopropionate (DMSP), Betaines and other organic solutes in plant tissue extracts using HPLC

An HPLC method using a cation-exchange column and UV detection for the simultaneous determination of dimethylsulphoniopropionate (DMSP), glycinebetaine, prolinebetaine, proline and arginine in plant tissue extracts is described. Recoveries of DMSP and glycinebetaine in either 5% perchloric acid, or methanol:chloroform:water (12:5:1) extracts of sugarcane leaf tissue were 94.0–95.4%. Proline was resolved in the 5% perchloric acid extract (recovery was 93.8%), whereas in the methanol:chloroform: water extract quantification of proline was not possible due to interference by unidentified compounds. Retention times of DMSP and arginine were increased when the pH of the mobile phase was decreased from 4.6 to 3.5, and the adjustment of the pH of the mobile phase was shown to be necessary in order to resolve DMSP in extracts from sugarcane leaves. The quantification of DMSP in sugarcane leaves using the HPLC method was compared with an indirect GC method, and the values obtained using GC were 1.14–1.65-fold higher. This discrepancy remains to be resolved. The detection limit for DMSP using the HPLC technique was about 2 µmol/g dry weight, while for the GC method it was 0.04 µmol/g dry weight. Copyright

Biogeochemistry of Metals in the Rhizosphere of Wetland Plants — An Explanation for “Innate” Metal Tolerance?

Publisher Summary Wetland plant rhizospheres are often aerobic and oxidized, while bulk soil is anaerobic and chemically reduced. As a result, metals tend to be immobile in the bulk soil but are mobilized by plant-induced changes in the rhizosphere. This leads to enrichment of metals near the roots and enhanced availability for uptake by plants. The apparent metal tolerance of wetland plants compared to dryland plants, without the development of separate metal-tolerant ecotypes, is because of the relatively high exposure of plant roots to metals under the soil conditions prevailing in wetlands. To live in the anaerobic soil conditions, wetland plants have developed root morphology different from that of dryland plants. Many species have porous roots for the supply of oxygen for root respiration, often forming a specialized tissue known as aerenchyma or air tissue. This supply of oxygen is thought to be more than sufficient for root respiration, and excess oxygen may leak into the rhizosphere.

Cadmium and associated metals in soils and sediments of wetlands across the Northern Plains, USA

Cadmium, present locally in naturally high concentrations in the Northern Plains of the United States, is of concern because of its toxicity, carcinogenic properties, and potential for trophic transfer. Reports of natural concentrations in soils are dominated by dryland soils with agricultural land uses, but much less is known about cadmium in wetlands. Four wetland categories - prairie potholes, shallow lakes, riparian wetlands, and river sediments - were sampled comprising more than 300 wetlands across four states, the majority in North Dakota. Cd, Zn, P, and other elements were analyzed by ICP-MS, in addition to pH and organic matter (as loss-on-ignition). The overall cadmium content was similar to the general concentrations in the areas soils, but distinct patterns occurred within categories. Cd in wetland soils is associated with underlying geology and hydrology, but also strongly with concentrations of P and Zn, suggesting a link with agricultural land use surrounding the wetlands.

The wetland grass Glyceria fluitans for revegetation of metal mine tailings

Revegetation under wetland rather than dryland conditions provides an alternative to traditional methods of rehabilitation of metal mine tailings. The wetland plant Glyceria fluitans (floating sweetgrass) was found growing in a lead/zine mine-tailings pond. The potential of this species for revegetation of mine tailings under wetland conditions had not previously been investigated. In two outdoor experiments. G. fluitans of non-contaminated origin grew successfully on alkaline tailings containing elevated metal concentrations (230 μmol g−1 Zn, 11 μmol g−1 Pb). Growth of G. fluitans was significantly enhanced on tailings treated with NPK fertilizer (700 kg ha−1), but the plants grew well even without fertilizer, indicating a low nutrient requirement. Glyceria fluitans did not survive on saline (MgSO4) tailings originating from another mine that contained much higher lead (34 μmol g−1) and iron (2584 μmol g−1) concentrations. The ability of G. fluitans to tolerate many of the adverse conditions associated with mine tailings favors its use for revegetation purposes.

ZINC TOLERANCE, UPTAKE, AND ACCUMULATION IN THE WETLAND PLANTS ERIOPHORUM ANGUSTIFOLIUM, JUNCUS EFFUSUS, AND JUNCUS ARTICULATUS

Metal tolerance in plants is thought to evolve following exposure to elevated metal levels in the soil. However, there are examples of species that appear to have developed constitutive metal tolerance without apparent exposure to metals. In previous studies, populations from contaminated and non-contaminated sites of the wetland plants Typha latifolia, Phragmites australis, and Glyceria fluitans were found to be equally tolerant to high concentrations of metals. In this study, zinc uptake and growth responses of populations of Eriophorum angustifolium, Juncus effusus, and Juncus articulatus from zinc-contaminated and non-contaminated sites were compared as part of a research project investigating metal tolerance in wetland plants. The populations were grown hydroponically in zinc-amended nutrient solutions. Juncus articulatus could not grow in the presence of elevated zinc concentrations, and no growth differences between populations were observed. Both populations of Juncus effusus from contaminated and non-contaminated sites grew well in moderately elevated zinc concentrations, but growth was inhibited at the higher treatment levels. Growth of Eriophorum angustifolium was inhibited less than growth of Juncus effusus at the higher zinc treatment levels. Both populations were able to tolerate concentrations of zinc of up to 100 μmol L−1. The findings for Juncus effusus and Eriophorum angustifolium support the theory that wetland plants tend to be tolerant to exposure to high levels of metals, but the results for Juncus articulatus suggest that this is not a general rule.

RETENTION OF METALS AND LONGEVITY OF A WETLAND RECEIVING MINE LEACHATE

Data on metal concentrations in soil and porewater of a marsh receiving leachate from an abandoned lead-zinc mine in Ireland were used to estimate the retention and accumulation of metals by the marsh. Iron concentrations did not vary according to a consistent pattern throughout the marsh. Levels of Zn, As, Pb and Cd decreased with increasing distance from the mine site. The marsh was estimated to retain 95 % of Zn and 65 % of As from porewater. Up to 30 % of the estimated total capacity of the marsh to retain metals had been used so far. Longevity of the marsh is estimated to be in the order of several centuries. Additional