Influence Of Drying Conditions Research Articles

Multi-year eddy-covariance measurements at a pre-alpine humid grassland site: Dataset overview, drought responses, and effects of land management

Impacts of drought events on terrestrial ecosystems have been studied extensively in the last decades in light of the long-term human-induced global warming trend and the recent occurrence of severe heat waves and droughts across the globe. The 2003 European summer heat wave sparked high attention towards such events in Switzerland, where ecosystems were largely affected again by summer dry periods in 2015 and 2018. With a newly applied processing scheme of calculating fluxes of net ecosystem exchange of CO2, latent and sensible heat from eddy-covariance measurements, the impact of droughts on GPP and exchange of energy between land and atmosphere are investigated at a managed grassland site in Switzerland. The rate of primary production is considerably reduced under the influence of dry conditions. This effect is further intensified by grassland management. Evapotranspiration, on the other hand, seems to be unaffected by the lack of precipitation at the site.

The influence of sample drying and storage conditions on methylmercury determination in soils and sediments

The separate influences of drying and storage conditions on methylmercury (MeHg) concentrations in soil and sediment samples were investigated. Concentrations of MeHg and total Hg were determined in various soil and sediment samples that had been stored or dried under differing conditions. The influence of drying conditions (oven-drying (40 °C) versus freeze-drying) on MeHg concentrations in marine sediments, river sediments, soils, and paddy field soils was investigated (n = 43). The ratio of the MeHg concentration in oven-dried sub-samples divided by the concentration in freeze-dried sub-samples ranged from 0 to 336%. In order to confirm the production of MeHg during storage in some samples, Hg2+ was added at 15 mg kg−1 to a paddy soil, and the sample was then stored at 30 °C. The concentrations of MeHg at 1-h, 1-day, 4-days and 7-days after Hg2+ spiking were 2.0 ± 0.1, 13.8 ± 1.0, 36.0 ± 5.0, and 24.9 ± 1.6 μg kg−1 (n = 3), respectively. The concentration of MeHg at 4-days after Hg spiking and sterilizing (121 °C, 30 min) was 1.8 μg kg−1, similar to the original value. These results indicate that bacterial Hg methylation and MeHg demethylation occurred within days in the soil. In addition, tests of the stability of MeHg in wet and dry samples during storage were also performed. Overall, our results indicate that the best way to preserve MeHg in soil and sediment samples is to freeze the samples immediately after collection, followed subsequently by freeze-drying, grinding, homogenization, and storage of the dry material in cool, dark conditions until analysis.

Driving forces of effluent nutrient variability in field scale bioretention

Nutrient exports from urbanized watersheds have been identified as a major contributor to surface water degradation worldwide. As efforts to implement stormwater treatment controls, such as bioretention, become increasingly common, understanding how the functionality of these systems varies based on environmental conditions is critical. Quantifying this variability and its causes will aid in developing more robust models and watershed restoration plans which incorporate the uncertainty of bioretention function. This study investigated effluent nutrient concentrations from ten bioretention areas in North Carolina, USA. Nitrogen species were found to have higher variability than phosphorus species, with changes in effluent concentrations being significantly influenced by environmental conditions. In particular, effluent concentrations of total nitrogen (TN) and nitrate (NO3-N) were strongly correlated to antecedent rainfall depth and temperature. As antecedent rainfall depth increased, NO3-N and TN concentrations decreased. These trends have been noted in other laboratory-based studies and are logical based on the influence of dry conditions on microbial communities. Increases in ambient temperature were shown to increase effluent TN and NO3-N concentrations in conventionally drained systems. However, a negative correlation was found between temperature and effluent NO3-N concentrations in systems with an internal water storage (IWS) layer, suggesting increased denitrifying microbe activity. These results show that variability in effluent nutrient concentrations can be explained by environmental conditions, and that the effects of these conditions may differ based on system design.