The Potential of Myrtaceae Species for the Phytomanagement of Treated Municipal Wastewater.

The use of native plants in land application systems for treated municipal wastewater (TMW) can contribute to ecological restoration. However, research on the potential of native species to manage the nutrients and contaminants contained in TMW is scarce. At a 10-hectare field site irrigated with TMW at >4000 mm yr-1, we investigated the distribution of nutrients and trace elements in the soil-plant system, comparing the New Zealand native Myrtaceae species Leptosperum scoparium and Kunzea robusta with pasture. The results showed that plant growth did not correlate with TMW irrigation rates. L. scoparium and K. robusta had higher foliar trace element concentrations than pasture, but these were not correlated with TMW irrigation rates. The pasture accumulated more N and P (68 kg of N ha-1 yr-1 and 11 kg of P ha-1 yr-1) than the Myrtaceae species (0.6-17 kg of N ha-1 yr-1 and 0.06-1.8 kg of P ha-1 yr-1). Regular harvesting of the pasture would likely remove more N and P from the site than the Myrtaceae species. The results highlight the importance of adjusting TMW application rates to the soil-plant capacity, in which case, native plants could provide ecological or economic value to TMW-irrigated land.

Chemical Elements and the Quality of Manuka (Leptospermum scoparium) Honey.

Soil properties in the foraging range of honeybees influence honey composition. We aimed to determine relationships between the antimicrobial properties of New Zealand manuka (Leptospermum scoparium) honey and elemental concentrations in the honey, plants, and soils. We analyzed soils, plants, and fresh manuka honey samples from the Wairarapa region of New Zealand for the chemical elements and the antimicrobial activity of the honey as indicated by methylglyoxal (MGO) and dihydroxyacetone (DHA). There were significant negative correlations between honey MGO and the concentrations of Mn, Cu, Mg, S, Na, Ba, K, Zn, and Al. These elements may provide a low-cost means of assessing manuka honey quality. For individual elements, except for K, there were no correlations between the honeys, plants, and soils. Soil nitrate concentrations were negatively correlated with concentrations of MGO and DHA in the honey, which implies that soil fertility may be a determiner of manuka honey quality.

Risks and benefits of pasture irrigation using treated municipal effluent : a lysimeter case study, Canterbury, New Zealand.

Compared to discharge into waterways, land application of treated municipal effluent (TME) can reduce the need for both inorganic fertilizers and irrigation. However, TME irrigation may result in the accumulation of phosphorus (P) or trace elements in soil, and increased salinity and sodicity, which could damage soil structure and reduce infiltration. TME irrigation can also result in groundwater contamination through nitrate leaching or surface water contamination through runoff. This study aimed to evaluate the effects of increasing TME irrigation rates on quantity and quality of leachate and pasture growth in a lysimeter experiment using a Fluvial Recent soil and a Fragic Pallic soil. Pasture growth in the lysimeters was up to 2.5-fold higher in the TME treatments compared to the non-irrigated treatments. There were no signs of toxicity or accumulation of B, Al, Cd, Cu, Fe, Mn, As, and Zn. TME significantly increased the concentration of P and Na in the pasture. Nitrogen leaching from the lysimeters was negligible (< 1 kg/ha-1 equiv.) in all treatments, but mineral N accumulated in the soil profile of the highest application rate (1672 mm/yr). Although more P was added than removed in pasture, the rate of accumulation indicated that over a 50-year period, P will still be within the current New Zealand thresholds for grazed pastures. Sodium accumulated in the soil columns in all the TME treatments. The rate of accumulation was not proportional to the TME application rate, indicating that Na was moving down through the soil profile and leaching. Results indicate a low to moderate risk of sodicity in soil or toxicity in plants caused by Na.

Response of a Pioneering Species (Leptospermum scoparium J.R.Forst. & G.Forst.) to Heterogeneity in a Low-Fertility Soil.

Root foraging may increase plant nutrient acquisition at the cost of reducing the total volume of soil explored, thereby reducing the chance of the roots encountering additional patches. Patches in soil seldom contain just one nutrient: the patch may also have distinct textural, hydrological, and toxicological characteristics. We sought to determine the characteristics of root foraging by a pioneering species, Leptospermum scoparium, using pot trials and rhizobox experiments with patches of biosolids. The growth of L. scoparium was increased by <50 t/ha equiv. of biosolids but higher doses were inhibitory. Roots foraged patches of biosolids in a low-fertility soil. There was no evidence of chemotaxis, rather, the roots proliferated toward the patch of biosolids, following chemical gradients of nitrate. While the biosolids also contained high concentrations of other nutrients (P, K, and S), only significant chemical gradients of nitrate were found. Once the roots encountered a patch of biosolids, the growth of the plant increased to a level similar to plants growing in soil homogeneously mixed with biosolids or surface-applied biosolids. Our results indicate that roots forage nitrate, which is mobile in soil, and that gradients of nitrate may lead to patches containing other less mobile nutrients, such as phosphate or potassium.

Potential Use of Biosolids to Reforest Degraded Areas with New Zealand Native Vegetation.

Biosolids could potentially be used for reforestation of degraded soils in New Zealand with native vegetation. Many native plant species of New Zealand thrive in low-fertility soils, and there is scant knowledge about their nutrient requirements. Therefore, it is unclear whether they will respond positively to the addition of biosolids. We used a pot trial to determine the responses of 11 native plant species to biosolids addition (10% w/w, ∼90 Mg hm) on two distinct degraded soils, Lismore stony silt loam and a Kaikoura sand. We also intended to prove that the soil microbial activity improves with the addition of biosolids, depending on the plant species. All species grew better in Lismore stony silt loam than the Kaikoura sand. All species in the Lismore stony silt loam responded positively to biosolids. The response to biosolids addition in the Kaikoura sand was variable, with four species showing no improvement in growth when biosolids were added. The nutrient status (N, P, S, Cu, and Zn) of all species improved when the two soils were amended with biosolids. However, some plant species, especially Sol. ex Gaertn. and Raoul, showed concerning concentrations of Cd (up to 2.4 mg kg). Dehydrogenase activity of soils (indicator of soil microbial activity) increased in biosolids-amended soils, with a strong species effect. Future work should involve field trials to determine the effect of biosolids addition on the establishment of native plant communities.

The Use of Field and Mesocosm Experiments to Quantify Effects of Physical and Chemical Stressors in Mining-Contaminated Streams.

Identifying causal relationships between acid mine drainage (AMD) and ecological responses in the field is challenging. In addition to the direct toxicological effects of elevated metals and reduced pH, mining activities influence aquatic organisms indirectly through physical alterations of habitat. The primary goal of this research was to quantify the relative importance of physical (metal-oxide deposition) and chemical (elevated metal concentrations) stressors on benthic macroinvertebrate communities. Mesocosm experiments conducted with natural assemblages of benthic macroinvertebrates established concentration-response relationships between metals and community structure. Field experiments quantified effects of metal-oxide contaminated substrate and showed significant differences in sensitivity among taxa. To predict the recovery of dominant taxa in the field, we integrated our measures of metal tolerance and substrate tolerance with estimates of drift propensity obtained from the literature. Our estimates of recovery were consistent with patterns observed at downstream recovery sites in the NFCC, which were dominated by caddisflies and baetid mayflies. We conclude that mesocosm and small-scale field experiments, particularly those conducted with natural communities, provide an ecologically realistic complement to laboratory toxicity tests. These experiments also control for the confounding variables associated with field-based approaches, thereby supporting causal relationships between AMD stressors and responses.

Heavy-Metal Phytostabilizing Potential of Agrostis castellana Boiss. & Reuter.

The soils of many abandoned mine sites in the central region of Spain are heavily polluted with a number of different metals. Having frequently found Agrostis castellana growing at these old mine sites, this study was designed to assess its remediation capacity for this type of setting. In an initial field study, plant specimens were collected from 4 abandoned mine sites to determine pollutant concentrations in their roots and shoots. This was followed by a 4-year bioassay in a controlled environment in which soils collected from the mines were used to set up microcosms. Maximum root concentrations of the most polluting elements present in the bioassay were 3625 mg kg(-1) Zn, 2793 mg kg(-1) Cu, 13042 mg kg(-1) Pb, 49 mg kg(-1) Cd and 957 mg kg(-1) As. These concentrations represent root bioaccumulation indices of over 1 and usually >2. In contrast, indices of transfer to above-ground phytomass were always < 1, indicating this species is a good candidate for use as a phytostabilizer. However, the high metal concentrations that could reach the above-ground mass of this plant determines a need for close monitoring and avoiding the use of areas under restoration for hunting or grazing.

Assessment of field portable X-ray fluorescence spectrometry for the in situ determination of heavy metals in soils and plants.

In soil pollution studies, large numbers of soil samples collected at random need to be processed and analyzed to determine their heavy metal contents. This study was designed to assess the use of a field portable X-ray fluorescence (FPXRF) spectrometry system for the in situ determination of heavy metal levels in both soil and plant samples. First, we optimised the method using 84 reference soil standards and soil samples from known polluted sites. The optimised method was then used to determine heavy metals at three abandoned mine sites and two sealed landfills in central Spain. Given that knowledge of heavy metal levels in plants is important for the ecotoxicological study of these sites, the FPXRF device was also used to determine heavy metals in plants. Our results indicate the acceptable to high quality of the data provided by the system especially for soil samples. The cost-benefits and sustainability of this instrument in relation to other techniques were also examined. The use of the FPXRF system for the study of potentially polluted sites was found to save on costs, time and materials. Results indicate its suitable use for the preliminary screening of heavy-metal polluted sites.