Multi-element composition of soils of seasonal wetlands across North Dakota, USA

The main goal of this study was to assess if the soils of wetlands of different condition varied in terms of element composition. The rationale was that compared to wetlands of good condition, wetlands of poor condition-which in the region have typically been disturbed by agricultural activities, are lower in biodiversity and have fewer native species-would have been altered in their physical and chemical soil characteristics. This in turn would have altered the element composition of the soils. The concentrations of about 50 elements in the topsoil of 43 seasonal wetlands of varying condition, as measured by plant community based assessments, across North Dakota were determined. Organic matter content of the soils increased as condition increased, and it was the most important variable explaining 40 % of variation in the concentrations of elements. This can be partly explained by binding of elements to organic matter (S, Se) and for most other elements (that bind mostly to the inorganic fraction) by displacement by organic matter. The biogeochemistry of S is further implicated in the distribution of Ca, most likely via formation of insoluble gypsum (calcium sulfate).

Multi-Elements in Waters and Sediments of Shallow Lakes: Relationships with Water, Sediment, and Watershed Characteristics

We measured concentrations of multiple elements, including rare earth elements, in waters and sediments of 38 shallow lakes of varying turbidity and macrophyte cover in the Prairie Parkland (PP) and Laurentian Mixed Forest (LMF) provinces of Minnesota. PP shallow lakes had higher element concentrations in waters and sediments compared to LMF sites. Redundancy analysis indicated that a combination of site- and watershed-scale features explained a large proportion of among-lake variability in element concentrations in lake water and sediments. Percent woodland cover in watersheds, turbidity, open water area, and macrophyte cover collectively explained 65.2 % of variation in element concentrations in lake waters. Sediment fraction smaller than 63 µm, percent woodland in watersheds, open water area, and sediment organic matter collectively explained 64.2 % of variation in element concentrations in lake sediments. In contrast to earlier work on shallow lakes, our results showed the extent to which multiple elements in shallow lake waters and sediments were influenced by a combination of variables including sediment characteristics, lake morphology, and percent land cover in watersheds. These results are informative because they help illustrate the extent of functional connectivity between shallow lakes and adjacent lands within these lake watersheds.

Macrophytes in shallow lakes: relationships with water, sediment and watershed characteristics

We examined macrophyte-environment relationships in shallow lakes located within the Prairie Parkland and Laurentian Mixed Forest provinces of Minnesota. Environmental variables included land cover within lake watersheds, and within-lake, water and sediment characteristics. CCA indicated that sediment fraction smaller than 63 μm (f<63), open water area, turbidity, and percent woodland and agricultural cover in watersheds were significant environmental variables explaining 36.6% of variation in macrophyte cover. When Province was added to the analysis as a spatial covariate, these environmental variables explained 30.8% of the variation in macrophyte cover. CCA also indicated that pH, f<63, percent woodland cover in watersheds, open water area, emergent vegetation area, and organic matter content were significant environmental variables explaining 43.5% of the variation in macrophyte biomass. When Province was added to the analysis as a spatial covariate, these environmental variables explained 39.1% of the variation in macrophyte biomass. The f<63 was the most important environmental variable explaining variation for both measures of macrophyte abundance (cover and biomass) when Province was added as a spatial covariate to the models. Percent woodland in watersheds, turbidity, open water area, and Ca+Mg explained 34.5% of the variation in macrophyte community composition. Most species showed a negative relationship with turbidity and open water area except for Potamogeton richardsonii, Stuckenia pectinata, and filamentous algae. Our study further demonstrates the extent to which macrophyte abundance and community composition are related to site- and watershed-scale variables including lake morphology, water and sediment characteristics, and percent land cover of adjacent uplands.

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 area's 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.

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.

Phyto (in)stabilization of elements

The effects of plants (corn, soybean, and sunflower) and fertilizer on mobility of more than 60 elements were assessed in a greenhouse experiment. Unplanted columns with the same soil served as controls. Half the columns received fertilizer and all columns were watered at the same rate. At the end of the experiment, the columns were watered to mimic a rainstorm event such that water drained from the bases of the columns, which was collected and analyzed for element content. Soil from between the roots of the plants was also collected and the water-extractable fraction determined. It was expected that (1) more mobile elements, as measured by water extraction, would be leached from the soils at a higher rate compared to less mobile elements, (2) plants would immobilize most elements, but that some would be immobilized, and (3) that this would depend on plant species. The results led to the following conclusions: plants cause metal mobility to vary over a wide range for a specific soil and do mobilize some elements (e.g., Th) while immobilizing others (e.g., U). The effects depended on plant species for some elements. Water-extractable fractions of elements do not predict mobility.

Multi-element accumulation near Rumex crispus roots under wetland and dryland conditions

Rumex crispus was grown under wet and dry conditions in two-chamber columns such that the roots were confined to one chamber by a 21 mum nylon mesh, thus creating a soil-root interface ('rhizoplane'). Element concentrations at 3 mm intervals below the 'rhizoplane' were measured. The hypothesis was that metals accumulate near plant roots more under wetland than dryland conditions. Patterns in element distribution were different between the treatments. Under dryland conditions Al, Ba, Cu, Cr, Fe, K, La, Mg, Na, Sr, V, Y and Zn accumulated in soil closest to the roots, above the 'rhizoplane' only. Under wetland conditions Al, Fe, Cr, K, V and Zn accumulated above as well as 3 mm below the 'rhizoplane' whereas La, Sr and Y accumulated 3 mm below the 'rhizoplane' only. Plants on average produced 1.5 times more biomass and element uptake was 2.5 times greater under wetland compared to dryland conditions.

Influence of Typha latifolia and fertilization on metal mobility in two different Pb-Zn mine tailings types

Storing metal-rich mine waste (tailings) under submerged and reduced conditions can prevent the release of metals to the water column, but introduction of wetland plants on these sediments may alter the reducing environment through root oxygen diffusion or organic matter accumulation. Fertilization of these wetlands can enhance plant growth, but also may either strengthen reducing conditions via microbial stimulation, or increase the redox potential (Eh) through increased root radial oxygen loss. This long-term study (2.25 years) investigated the porewater As, Fe, and Zn concentrations of waterlogged Pb-Zn tailings from two Irish mines, Silvermines and Tara mines, with addition of Typha latifolia, fertilizer, or both treatments combined. In both tailings types, the fertilized plants showed significantly increased total biomass production, but the plants grew greater biomass in Tara tailings relative to Silvermines tailings even without fertilization. In Tara mines tailings, the addition of plants increased Eh and mobilized Zn; the addition of fertilizer enhanced reducing conditions and increased porewater concentrations of As and soluble sulfides; and the combination of treatments on these tailings resulted in complex interactions. In Silvermines tailings, there were negligible effects of the treatments. For effective sequestration of metals in these tailings, Silvermines would require only water cover, but Tara mines tailings would require either both treatments or neither because each treatment individually would increase solubility of As or Zn. These results show also the necessity of evaluating treatment effects specific to individual tailings, that long-term studies (years) are crucial for tailings equilibration and valid experimental conclusions, and that passive accumulation of organic matter may take decades.

Long-term effects of submergence and wetland vegetation on metals in a 90-year old abandoned Pb-Zn mine tailings pond

A Pb-Zn tailings pond, abandoned for approximately 90 years, has been naturally colonized by Glyceria fluitans and is an excellent example of long-term metal retention in tailings ponds under various water cover and vegetation conditions. Shallow/intermittently flooded areas (dry zone) were unvegetated and low in organic matter (OM) content. Permanently flooded areas were either unvegetated with low OM, contained dead vegetation and high OM, or living plants and high OM. It was expected that either water cover or high OM would result in enhanced reducing conditions and lower metal mobility, but live plants would increase metal mobility due to root radial oxygen loss. The flooded low OM tailings showed higher As and Fe mobility compared with dry low OM tailings. In the permanently flooded areas without live vegetation, the high OM content decreased Zn mobility and caused extremely high concentrations of acid-volatile sulfides (AVS). In areas with high OM, living plants significantly increased Zn mobility and decreased concentrations of AVS, indicating root induced sediment oxidation or decreased sulfate-reduction. This is the first study reporting the ability of wetland plants to affect the metal mobility and AVS in long-term (decades), unmanaged tailings ponds.

Silver staining nucleolar organiser region (AgNOR) study in melanocytic skin tumours

Silver staining nucleolar organiser regions (AgNORs) were studied in 35 cases of melanocytic skin tumours. In the 23 cases of benign melanocytic naevi AgNORs per nucleus were between 1.06 and 3.43 with a mean of 2.05. In the 12 cases of malignant melanoma the AgNORs ranged from 4.26 to 10.66 (mean 7.43). Since statistically significant difference in AgNOR counts between benign and malignant melanocytic skin tumours was noted, this technique may serve as a useful adjunct to routine histopathology.