Establishment and growth of two willow species in a riparian zone impacted by mine tailings

Mobilisation of Cd, Mn, and Zn in floodplains by action of plants and its consequences for spreading historical contamination and fluvial geochemistry

Cadmium, Mn, and Zn are mobilised by plants commonly growing in floodplains, most notably willows (Salix) and alder (Alnus). These plants accumulate unwanted elements (Cd) or excessive element concentrations (Mn, Zn) in their foliage, thus introducing them into the food web and enriching them in floodplain surface by litterfall. In floodplain of the Litavka River in Czechia, contaminated by historical mining activities, up to 100 mg kg^-1 Cd and up to several thousand mg kg^-1 Mn and Zn are present in willow leaves in autumn, probably close maxima for sustainable plant growth. Willows and alders show seasonal growth of their foliar Mn and Zn. The willow leaves showed Cd/Zn larger than contaminated fluvisol of the Litavka River. Senesced willow leaves thus contribute to spread of risk elements from historically contaminated floodplains back to river water even without the bank erosion. Alders and willows alter geochemical cycles of Cd, Mn, and Zn in fluvial systems and increase Cd/Zn and Mn/Fe concentration ratios and Cd and Mn concentrations in fluvially transported particles relative to global geochemical averages as well as relative to floodplain sediments. Willows, in particular Salix fragilis L., S. aurita L, and S. cinerea L are particularly important "plant pumps". Other common floodplain plants, such as bird cherry (Prunus padus L.) and herbaceous plants (common nettle, Urtica dioica L. and grasses, Poaceae) do not contribute to those phenomena.

Phytoremediation efficacy of native vegetation for nutrients and heavy metals on soils amended with poultry litter and fertilizer

Poultry litter on agricultural lands could introduce nitrogen (N), phosphorus (P), heavy metals in soil and ground water. Native vegetations were identified to assess efficacy for phytoremediation of nutrients and metals from soil and water. Objective was to measure capability of multi-year native species to remove metals, nutrients, and prevent Nitrate-N leaching below the rooting zone. Treatments were distributed in four replicates with/without fertilization. Suction lysimeters were installed at 30, 60, and 90-cm depths in 3 of 4 replicates. Species were identified, recorded, five specified cuttings sampled. Plant, soil, water samples were prepared and analyzed by spectroscopy. Nitrate-N extraction, nitrates in water samples were determined using flow injection analysis. Fertilized plots (NVM) had 39% more biomass yield than unfertilized plots (NVN). In plants, nutrient and metal concentrations varied significantly with 14% increase in Zn, 36% and 26% in K and Mg over NVN for first and second year. Uneven between NVM and NVN, topsoil had higher values for most nutrients and metals. Largest P and (NO3-)-N in plant and water were observed from NVM. Cultivation of native vegetation appears to be an effective approach for remediation of excess nitrates-N, P, heavy metals from surface and sub-surface zones of the soil.

The Clean Water Act and biosolids: A 45-year chronological review of biosolids land application research in Colorado

The 1972 U.S. Clean Water Act set forth the generation of biosolids. In Colorado, biosolids land application research began in 1976 and continues today. Pastureland research suggested that sewage effluent could effectively be land applied to benefit aboveground plant growth and to polish water prior to reaching receiving waters. Forest wildfire-affected ecosystems can also benefit from biosolids applications; application rates of up to 80 Mg ha^-1 can lead to greater plant establishment, soil microbial activity, and nutrient turnover and reduced nutrient and heavy metal concentrations in runoff below livestock and USEPA drinking water standards. Long-term (24-yr) observations in oil shale-mined lands showed that biosolids (up to 224 Mg ha^-1 ) can have a positive effect on microbial-mediated nutrient cycling and, in turn, on aboveground plant community structure. Biosolids applications of up to 40 Mg ha^-1 in high-elevation shrubland ecosystems, dominated by Mo-containing shale deposits, can aid in reducing imbalances between Mo and Cu in soils and plants; excessive plant Mo, when consumed by ruminants, can lead to molybdenosis. Biosolids and lime applications (both at 224 Mg ha^-1 ) have been shown to improve long-term reclamation success on acid-generating, heavy metal-containing fluvial mine tailings. Thirty years of grazing land research, focused on soil and aboveground plant benefits, illustrate that soil health and plant productivity can be improved to the greatest extent at biosolids application rates close to 10 Mg ha^-1 . Finally, 40 yr of dryland agroecosystem research (a) have helped identify biosolids N fertilizer equivalency (∼8 kg N Mg^-1 ) and thus dryland winter wheat application rates (e.g., 4.5-6.7 dry Mg ha^-1 ); (b) have identified first-year mineralization rates of 25-32%; (c) dispute the "time bomb" theory by showing that plant metal uptake follows an exponential rise to a maximum; (d) showcase economic return to producers via increased wheat grain protein content; (e) suggest that biosolids-borne proteins and their degradation products are labile C and N sources; (f) have led to long-term tracking of micronutrients and heavy metals in soils and revealed that plants-soil concentrations will not lead to groundwater degradation and that plants are safe for human consumption; and (g) have shown that biosolids provide Zn, helping to overcome soil deficiencies and enhancing Zn biofortification in wheat grain. This latter point is important because ∼2 billion people globally suffer from Zn deficiencies. Forty-five years of research in Colorado have proven that biosolids can enhance environmental quality, improve soil health, and produce healthy food products.

Establishment of willows using the novel DeValix technique: ecological restoration mats designed for phytotechnologies

Successful willow (Salix spp., hybrids and cultivars) establishment is a major determinant of their effectiveness when grown for phytotechnologies. Vertically-planted hardwood cuttings have been shown to produce adequate willow growth and survival, although site conditions at phytoremediation installations can make vertical planting methods unsuitable. The DeValix willow mat restoration technique was designed and tested as an alternative horizontal planting method that can be installed by hand in a variety of environmental applications. The DeValix technique was evaluated by testing five willow clones ("Millbrook"; "Sherburne"; "SX61"; "SX67"; "Tully Champion") grown at two phytoremediation sites (Ontonagon, MI; Manitowoc, WI) for the 2019 growing season. Differences in survival and growth were tested among sites, genotypes, and their interactions. Stem height, diameter, and number of stems per mat were compared to identify clones with greater establishment success and higher phytoremediation potential. Results demonstrated significant effects of site (p < 0.0001) and clone (p < 0.0001) on shoot number. Additionally, the site × clone interaction significantly affected stem height (p = 0.0045) and diameter (p = 0.0166). Stem density ranged from 95,000 to 212,000 stems per hectare, indicating the DeValix technique is a viable establishment method for environmental applications, including phytoremediation and shoreline stabilization.

Variation of tolerance and accumulation to excess iron in 24 willow clones: Implications for phytoextraction

Willows (Salix spp.) are characterized by having large biomass, high tolerance to flooding, and strong metal accumulation ability, exhibiting great promise in the phytoremediation of iron (Fe) from contaminated sites. In this study, the variation of Fe tolerance and accumulation in 24 willow clones was investigated with two levels of Fe(II)-EDTA, 0.025 mM (control) and 2.0 mM (treatment) by hydroponic system for 21 days in a greenhouse. Visual symptoms of Fe toxicity were observed in the leaves and roots of Fe sensitive clones. Clonal comparisons showed a great variation in Fe tolerance, and the high levels of Fe reduced biomass productions of most clones. Tolerance indexes (TIs) varied about five-fold based on shoot dry biomass and about six-fold based on root dry biomass among clones. Clones also exhibited a wide variation in Fe concentrations (mg g^-1 DW), ranged from 0.80 to 3.41 in leaves, from 5.40 to 10.51 in stems, and from 3.25 to 17.10 in roots under Fe treatments among clones. Large differences varied in the transport of Fe from roots to aerial parts among clones. The results highlighted the selection of Salix clones with high resistance to Fe toxicity and high Fe accumulation to improve phytoremediation efficacy.

Phytoremediation of cadmium and lead-polluted watersheds

Abandoned hard rock mines and the resulting acid mine drainage (AMD) are a source of vast, environmental degradation that are toxic threats to plants, animals, and humans. Cadmium (Cd) and lead (Pb) are metal contaminants often found in AMD. In our mine outwash water samples, Cd and Pb concentrations were 300 and 40 times greater than EPA Aquatic Life Use water quality standards, respectively. We tested the phytoremediation characteristics, accumulation and tolerance of Cd and Pb contamination, for annual aboveground biomass harvest of three montane willows native to the Rocky Mountains: Salix drummondiana, S. monticola, and S. planifolia. We found S. monticola best suited for Pb remediation based on greater growth and tolerance in response to the low Pb treatment compared to the high Pb treatment. Salix monticola stems also contained higher Pb concentrations in control treatment compared to S. planifolia. We found S. planifolia and S. drummondiana best suited for Cd remediation. Salix drummondiana accumulated higher concentrations of Cd in stems than both S. monticola and S. planifolia. Salix planifolia accumulated nearly 2.5 times greater concentrations of Cd in stems in control treatment than did S. drummondiana. Salix planifolia also contained more total Cd in stems than did S. monticola in Cd treatments. Based on our results, S. drummondiana and S. planifolia could aid in reduction of Cd in watersheds, and S. monticola is better suited than is S. planifolia for aboveground accumulation and tolerance of Pb pollution.

Actinorhizal Alder Phytostabilization Alters Microbial Community Dynamics in Gold Mine Waste Rock from Northern Quebec: A Greenhouse Study

Phytotechnologies are rapidly replacing conventional ex-situ remediation techniques as they have the added benefit of restoring aesthetic value, important in the reclamation of mine sites. Alders are pioneer species that can tolerate and proliferate in nutrient-poor, contaminated environments, largely due to symbiotic root associations with the N2-fixing bacteria, Frankia and ectomycorrhizal (ECM) fungi. In this study, we investigated the growth of two Frankia-inoculated (actinorhizal) alder species, A. crispa and A. glutinosa, in gold mine waste rock from northern Quebec. Alder species had similar survival rates and positively impacted soil quality and physico-chemical properties in similar ways, restoring soil pH to neutrality and reducing extractable metals up to two-fold, while not hyperaccumulating them into above-ground plant biomass. A. glutinosa outperformed A. crispa in terms of growth, as estimated by the seedling volume index (SVI), and root length. Pyrosequencing of the bacterial 16S rRNA gene for bacteria and the ribosomal internal transcribed spacer (ITS) region for fungi provided a comprehensive, direct characterization of microbial communities in gold mine waste rock and fine tailings. Plant- and treatment-specific shifts in soil microbial community compositions were observed in planted mine residues. Shannon diversity and the abundance of microbes involved in key ecosystem processes such as contaminant degradation (Sphingomonas, Sphingobium and Pseudomonas), metal sequestration (Brevundimonas and Caulobacter) and N2-fixation (Azotobacter, Mesorhizobium, Rhizobium and Pseudomonas) increased over time, i.e., as plants established in mine waste rock. Acetate mineralization and most probable number (MPN) assays showed that revegetation positively stimulated both bulk and rhizosphere communities, increasing microbial density (biomass increase of 2 orders of magnitude) and mineralization (five-fold). Genomic techniques proved useful in investigating tripartite (plant-bacteria-fungi) interactions during phytostabilization, contributing to our knowledge in this field of study.