M. Deurer

Quantum dot transport in soil, plants, and insects.

Environmental risk assessment of nanomaterials requires information not only on their toxicity to non-target organisms, but also on their potential exposure pathways. Here we report on the transport and fate of quantum dots (QDs) in the total environment: from soils, through their uptake into plants, to their passage through insects following ingestion. Our QDs are nanoparticles with an average particle size of 6.5 nm. Breakthrough curves obtained with CdTe/mercaptopropionic acid QDs applied to columns of top soil from a New Zealand organic apple orchard, a Hastings silt loam, showed there to be preferential flow through the soils macropores. Yet the effluent recovery of QDs was just 60%, even after several pore volumes, indicating that about 40% of the influent QDs were filtered and retained by the soil column via some unknown exchange/adsorption/sequestration mechanism. Glycine-, mercaptosuccinic acid-, cysteine-, and amine-conjugated CdSe/ZnS QDs were visibly transported to a limited extent in the vasculature of ryegrass (Lolium perenne), onion (Allium cepa) and chrysanthemum (Chrysanthemum sp.) plants when cut stems were placed in aqueous QD solutions. However, they were not seen to be taken up at all by rooted whole plants of ryegrass, onion, or Arabidopsis thaliana placed in these solutions. Leafroller (Lepidoptera: Tortricidae) larvae fed with these QDs for two or four days, showed fluorescence along the entire gut, in their frass (larval feces), and, at a lower intensity, in their haemolymph. Fluorescent QDs were also observed and elevated cadmium levels detected inside the bodies of adult moths that had been fed QDs as larvae. These results suggest that exposure scenarios for QDs in the total environment could be quite complex and variable in each environmental domain.

Estimation of indirect nitrous oxide emissions from a shallow aquifer in Northern Germany.

Ground water is considered to be an important source for indirect N2O emissions. We investigated indirect N2O emissions from a shallow aquifer in Germany over a 1-yr period. Because N2O accumulated in considerable amounts in the surface ground water (mean, 52.86 microg N2O-N L(-1)) and corresponding fluxes were high (up to 34 microg N2O-N m(-2) h(-1)), it was hypothesized that significant indirect N2O emissions would occur via the vertical and the lateral emission pathway. Vertical N2O emissions were investigated by measuring N2O concentrations and calculating fluxes from the surface ground water to the unsaturated zone and at the soil surface. Lateral N2O fluxes were investigated by measuring ground water N2O and NO3- concentrations at five multilevel wells and at a waterworks well. Negligible amounts of N2O were emitted vertically into the unsaturated zone; most of it was convectively transported into the deeper autotrophic denitrification zone. Only a ground water level fall and rise triggered the emission of N2O (up to 3 microg N2O-N m(-2) h(-1)) into the unsaturated zone. Ground water-derived N2O was probably reduced during the upward diffusion, and soil surface emissions were governed by topsoil processes. Along the lateral pathway, N2O and NO3- concentrations decreased with increasing depth in the aquifer. Discharging ground water was almost free of N2O and NO3-, and indirect N2O emissions were small.

Spatial and temporal variability of N2O in the surface groundwater: a detailed analysis from a sandy aquifer in northern Germany

The knowledge of the spatial and temporal variability of N2O concentrations in surface groundwater is the first step towards upscaling of potential indirect N2O emissions from the scale of localized samples to aquifers. This study aimed to investigate the spatial and the temporal variability of N2O concentrations at different scales in the surface groundwater of a denitrifying aquifer in northern Germany. The spatial variability of N2O concentrations in the surface groundwater was analysed at the plot (200xa0×xa0200xa0m) and at the transect scale (12xa0m). Twenty plots that were distributed across an area of 11xa0km2 and 6 transects were sampled. Sixty per cent of the spatial variance of N2O was located at the plot scale and 68–79% was located at the transect scale. This indicates that small-scale processes governed the spatial variability of N2O in the surface groundwater. A spatial upscaling of N2O from the transect to the aquifer scale might be possible with an adequate number of samples that represent important boundary conditions for N2O accumulation in the catchment (topography, groundwater level, land use). For the investigation of the temporal variability, 4 multilevel wells were sampled monthly over a period of 13xa0months. In two periods, a multilevel well was additionally sampled in 2-day intervals over 8xa0days. At the annual scale, N2O concentrations in the surface groundwater were higher during the vegetation period (median 87xa0μg N2O-Nxa0l−1) and could change rapidly on the day scale whereas the concentrations were smaller in winter (median 21xa0μg N2O-Nxa0l−1). Groundwater recharge events seemed to be crucial for the day scale variability. Capture of the temporal variations for upscaling might be achieved with a process-based sampling strategy with weekly sampling intervals during the vegetation period, the additional sampling after groundwater recharge events and monthly sampling intervals in winter.

The impact of soil carbon management and environmental conditions on N mineralization

Soil carbon (C) management is identified as a key element of sustainable agriculture, and an increase in nitrogen (N) mineralization rates is expected with an increase in soil C. However, any practical recommendation for using soil C management to substitute the application of synthetic N fertilizer needs to account simultaneously for other important agronomic variables and environmental conditions. For this purpose we investigated the simultaneous impact of soil C management, environmental conditions, and soil structure on N mineralization in two apple orchard systems in Havelock North, New Zealand. One system is an organic orchard using regular compost applications and the other is a neighboring integrated orchard with no external inputs of organic matter. The soil type, texture, and climate are identical in both orchards. We selected different temperatures (10°C, 15°C, and 20°C) and soil moistures (−30, −100, and −300xa0kPa) as the environmental conditions for N mineralization. Simultaneously, the hot-water extractable C (HWC) contents were measured and served as the indicator for the soil C management of the orchards. To analyze the impact of soil structure, the N mineralization of undisturbed cores was compared with that of disturbed samples. The net N mineralization of the soil in the organic orchard was on average six times higher than that in the integrated orchard. At the same time, in the organic orchard the HWC contents at the beginning of the N mineralization experiment were about two times higher than in the integrated orchard. In a multiple regression as a practical recommendation for the orchards of our case study, we could explain 84% of the variability of N mineralization rates using HWC and environmental conditions as the independent variables. The HWC content was the most significant variable in the multiple regression model and showed that soil C management has a more prominent role than the environmental conditions. Soil C management such as regular compost applications which increase the soil’s HWC contents can also be used to manage N mineralization. The significant difference between the undisturbed and disturbed samples showed the soil structure can have an effect on N mineralization.

Carbon Sequestration in Kiwifruit Orchard Soils at Depth to Mitigate Carbon Emissions

Management practices designed to increase carbon sequestration via perennial tree crops are potential tools to mitigate the consequences of climate change. Changes in orchard management could enable growers to meet eco-verification market demands for products with a low carbon footprint and potentially exploit the emerging business opportunity in carbon storage, while enhancing the delivery of ecosystem services that depend on soil carbon stocks. However, there is no standard methodology to verify any potential claims of carbon storage by perennial vine crops. We developed a robust methodology to quantify carbon storage in kiwifruit orchards. Soil carbon stocks (SCS) were determined in six depth increments to 1 m deep in two adjacent kiwifruit blocks, which had been established 10 (“young”) and 25 (“old”) years earlier. We used a space-for-time analysis. Our key results were the young and old kiwifruit block stored about 139 and 145 t C/ha to 1 m depth. Between 80–90 percent of the SCS were stored in the top 0.5 m, and 89–95 percent in the top 0.7 m; there was no significant difference between the SCS in row and alley to a depth of 0.5 m; a CV of 5–15 percent indicates that 4–10 cores are needed for 80 percent confidence in the estimated SCS; we recommend separating each core into the depths 0–0.1, 0.1–0.3, 0.3–0.5, and 0.5–1 m to allow the assessment of SCS dynamics; we detected a weak spatial pattern of the SCS only for the old kiwifruit block with a range of about 3 m. A sampling bay along a vine row should have a maximum length of 3 m. We then assessed SCS in more than sixty kiwifruit orchards throughout New Zealand. They stored on average 174.9 ± 3 t C ha−1 to 1 m depth. On average, 51 percent of the SCS down to 1 m depth were stored in the top 0.3 m, which is the standard depth according to the Kyoto protocol. About 72 percent of the SCS to 1 m depth were captured when increasing the sampling depth to 0.5 m. These results underscore the necessity to analyze SCS in an orchard to at least 0.5 m deep. Using the same methodology to 1 m deep, we determined SCS in two wine grape vineyards on shallow, stony alluvial soils. We found a difference between vineyard and adjacent pasture SCS of nearly 16 t/ha. As the vines are 25 years old, this equates to carbon sequestration rates of 640 kg ha−1 yr−1. Our results of the space-for-time analysis also showed that all sequestration had occurred below 0.5 m. Therefore, we decided to sample C to a greater depth. In a 30-year old kiwifruit orchard and an adjacent pasture, SCS was measured to 9 m deep. In the kiwifruit orchard, we found a sequestration rate of 6.3 tons of C per hectare per year greater than in the adjacent pasture that was the antecedent land use.

Quantum Dot Uptake in the New Zealand Environment

The use of quantum dots (QDs) for different applications such as biomarkers has increased in the past decade. Here we report on the uptake of fluorescent QDs into agricultural soil, and transport following their ingestion by the larvae of some common lepidopteran insects. Some QDs were leached through soil but their emission was quenched due to geo-effect. In contrast, fluorescence was still seen in leafroller larvae fed with these QDs and in their frass. Abbreviations: QD, quantum dot; NPs, Nanoparticles; Cys, cysteine; Gly, glycine; MPA, mercaptopropionic acid; MSA, mercaptosuccinic acid; AM, 2-aminoethanethiol; Na2EDTA, ethylenediaminetetraacetic acid disodium salt; PV, pore volume