Biogeochemical patterns in a river network along a land use gradient

The Bode catchment (Germany) shows strong land use gradients from forested parts of the National Park (23 % of total land cover) to agricultural (70 %) and urbanised areas (7 %). It is part of the Terrestrial Environmental Observatories of the German Helmholtz association. We performed a biogeochemical analysis of the entire river network. Surface water was sampled at 21 headwaters and at ten downstream sites, before (in early spring) and during the growing season (in late summer). Many parameters showed lower concentrations in headwaters than in downstream reaches, among them nutrients (ammonium, nitrate and phosphorus), dissolved copper and seston dry mass. Nitrate and phosphorus concentrations were positively related to the proportion of agricultural area within the catchment. Punctual anthropogenic loads affected some parameters such as chloride and arsenic. Chlorophyll a concentration and total phosphorus in surface waters were positively related. The concentration of dissolved organic carbon (DOC) was higher in summer than in spring, whereas the molecular size of DOC was lower in summer. The specific UV absorption at 254 nm, indicating the content of humic substances, was higher in headwaters than in downstream reaches and was positively related to the proportion of forest within the catchment. CO₂ oversaturation of the water was higher downstream compared with headwaters and was higher in summer than in spring. It was correlated negatively with oxygen saturation and positively with DOC concentration but negatively with DOC quality (molecular size and humic content). A principle component analysis clearly separated the effects of site (44 %) and season (15 %), demonstrating the strong effect of land use on biogeochemical parameters.     

Biochar and earthworm effects on soil nitrous oxide and carbon dioxide emissions

Biochar is the product of pyrolysis produced from feedstock of biological origin. Due to its aromatic structure and long residence time, biochar may enable long-term carbon sequestration. At the same time, biochar has the potential to improve soil fertility and reduce greenhouse gas (GHG) emissions from soils. However, the effect of biochar application on GHG fluxes from soil must be investigated before recommendations for field-scale biochar application can be made. A laboratory experiment was designed to measure carbon dioxide (CO) and nitrous oxide (NO) emissions from two Irish soils with the addition of two different biochars, along with endogeic (soil-feeding) earthworms and ammonium sulfate, to assist in the overall evaluation of biochar as a GHG-mitigation tool. A significant reduction in NO emissions was observed from both low and high organic matter soils when biochars were applied at rates of 4% (w/w). Earthworms significantly increased NO fluxes in low and high organic matter soils more than 12.6-fold and 7.8-fold, respectively. The large increase in soil NO emissions in the presence of earthworms was significantly reduced by the addition of both biochars. biochar reduced the large earthworm emissions by 91 and 95% in the low organic matter soil and by 56 and 61% in the high organic matter soil (with and without N fertilization), respectively. With peanut hull biochar, the earthworm emissions reduction was 80 and 70% in the low organic matter soil, and only 20 and 10% in the high organic matter soil (with and without N fertilization), respectively. In high organic matter soil, both biochars reduced CO efflux in the absence of earthworms. However, soil CO efflux increased when peanut hull biochar was applied in the presence of earthworms. This study demonstrated that biochar can potentially reduce earthworm-enhanced soil NO and CO emissions. Hence, biochar application combined with endogeic earthworm activity did not reveal unknown risks for GHG emissions at the pot scale, but field-scale experiments are required to confirm this.     

Effects of limestone addition and sintering on heavy metal leaching from hazardous waste incineration slag

Hazardous waste incineration (HWI) in rotary kilns and the disposal of the residual slag on landfills play an important role in German waste treatment. In order to save disposal costs the elution behaviour of HWI-slag should be further optimised. Quality-improved slag may be disposed off on cheaper landfill sites still applying to landfill regulations. In a new process-integrated approach hazardous waste is mixed with limestone, which initiates chemical reactions with heavy metals in the rotary kiln yielding new compounds of different solubility. In this work HWI-slag/limestone mixtures are thermally treated and then examined by elution tests. Experimental data indicate that the heavy metals pertinent to landfill class assignment of a HWI-slag share a solubility minimum at a CaO-content of about 15%. Such improved HWI-slags are allowed to be disposed off on cheaper landfill sites. Furthermore, a new combination of thermodynamic calculation methods is applied to predict heavy metal solubility for different process conditions. Used models hold the opportunity to explain the tendencies of heavy metal leaching and propose plausible chemical reactions. With it, a new tool to examine the impact of temperature treatment and slag composition on heavy metal elution from HWI-slag is presented.     

The use of navigation systems in naturalistic driving

Objective: In this study, we assessed the use of portable navigation systems in everyday driving by applying in-vehicle naturalistic driving.

Method: Experienced users of navigation systems, 7 females and 14 males, were provided with a specially equipped vehicle for approximately 1 month. Their trips were recorded using 4 cameras, Global Positioning System (GPS) data, and other sensor data. The drivers’ navigation system use data were coded from the video recordings, which showed how often and for how long the system was activated and how often and for how long a driver operated the system.

Results: The system was activated for 23% of trips, predominantly on longer and unique trips. Analyses of the percentage of time for which the speed limit was exceeded showed no evidence of differences between trips for which the navigation system was used or not used. On trips for which the navigation system was activated, participants spent about 5% of trip time interacting with the device. About 40% of interacting behavior took place in the first 10% of the trip time, and about 35% took place while the car was standing still or moving at a very low speed; that is, 0–10 km/h.

Conclusion: These results shed light on how and when drivers use navigation systems. They suggest that although drivers regulate their use of such systems to some extent, they often perform risky tasks while driving.     

Mercury in compact fluorescent lamps (CFLs): European legislation introduces an avoidable analytical bias

European legislation has set a limit of 5 mg Hg per compact fluorescent lamp (CFL). Compliance with this regulation is tested with a method given in a European law from 2002 (“EU method”). According to the EU method, the arc tube has to be placed inside a fume cupboard and cut into segments. These pieces are collected and washed with HNO₃, which is finally analyzed for Hg. In this study, we investigated the losses of Hg via the gas phase, which are ignored by the EU method, using a semiquantitative radiochemical neutron activation analysis (RNAA) technique developed at the TRIGA Mark II reactor in Vienna (Austria). Depending on the product, the losses range as high as approximately 2 % at 20 °C. At higher ambient temperatures (hot summer days), the losses may increase by a factor of 4. Quality products generally suffer lower emission via the gas phase than cheap products, which is probably due to amalgam or other techniques that retain the Hg from broken CFLs. In any case, the EU method introduces a small but avoidable systematic error into the analysis and, in contrast to recommended practices, underestimates the Hg content of the CFL in question. Having technical alternatives at hand, we urge European lawmakers to adjust the law accordingly.