Tree species effects on Cd and Zn mobility after afforestation of contaminated soils in the Campine region (northern Belgium)

This thesis was executed in the context of the historical metal pollution in the Campine (Kempen) region in north-eastern Belgium. Due to metal refining activities in the past, an extended area of about 700 km² is diffusely polluted with mainly cadmium (Cd) and zinc (Zn). The historical soil pollution is still causing human-toxicological and ecotoxicological risks, through metal leaching to groundwater and accumulation in the food chain. Moreover, the Campine region is characterized by poor sandy soils, aggravating the risks for metal dispersion in the environment. Conventional soil sanitation techniques are technically and financially inadequate to tackle the pollution problem, because of its spatial extent and the relatively moderate contamination levels. Hence, alternative remediation strategies, such as phytostabilization, are to be investigated. Sustainable phytostabilization projects require the metals to be stabilized in the soil and should thus aim at minimizing metal dispersion via both above- and below-ground pathways. As there is a clear tree species effect on metal uptake, on litter decomposition, on biogeochemical processes in the soil profile and on the water balance, the distribution and fluxes of metals in the forest-soil system will be tree species specific as well. Selecting appropriate tree species is thus crucial for achieving successful phytostabilization. The main objectives of this thesis were to assess the feasibility of phytostabilization by afforesting diffusely Cd and Zn contaminated sandy soils, and to determine the tree species effects on Cd and Zn cycling on these soils. Our study was carried out in ‘Waaltjesbos’, a young post-agricultural forest on a metal contaminated site on sandy soil. At the moment of our study, the trees were 10-15 years old. The six selected tree species were silver birch (Betula pendula), oak (Quercus robur and Q. petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula), Scots pine (Pinus sylvestris) and Douglas fir (Pseudotsuga menziesii). We showed that aspen translocates high amounts of Cd and Zn into its foliage, generating a significant accumulation of total Cd and Zn concentrations in the topsoil (0-5 cm), and this after only 10 years of tree growth. Moreover, accumulated metals in the leaves may pose a long-term risk to primary consumers and enter the food web. Given these risks of above-ground metal dispersion, aspen should be avoided when afforesting Cd and Zn contaminated sites. We also showed that Cd and Zn leaching at 50 cm depth was elevated under black locust, Scots pine and Douglas fir, compared to lower seepage fluxes under silver birch, oak and aspen. This pattern was significantly correlated with leaching of anions and base cations, and to a lesser extent to soil solution pH, at least at this young stage of forest development at a post-agricultural site. Due to former (agricultural) liming and fertilization processes, the base cation status of the soil and the solution pH were still relatively high. However, we expect both parameters to decrease with forest age, especially for species with slowly decomposing litter, implying that the effect of pH on Cd and Zn leaching will become relatively more important in the long term. In this respect, we recommend not to plant tree species that generate high anion, base cation or H+ fluxes when afforesting Cd and Zn contaminated lands, because these species pose a serious risk for metal leaching to deeper soil layers and potential contamination of the groundwater. In general, coniferous as well as N-fixing species should thus be avoided. Finally, contrary to what is often argued in literature about phytostabilization, we found that Cd and Zn leaching losses at our study site showed no resemblance with the downward soil water fluxes. This might imply that the impact of the biogeochemical processes in the soil (solution) on Cd and Zn leaching (complexation with anions, competition for sorption sites with base cations and protons) was relatively more important than the effect of evapotranspiration. Summarized, taking into account all the aforementioned recommendations, it seemed that silver birch and oak may be planted on Cd and Zn contaminated sandy soils. Aspen, black locust, Scots pine and Douglas fir, on the other hand, cause risks for above-ground or below-ground metal dispersion and should therefore be avoided. These conclusions were drawn from our study in a young forest (10 – 15 years). Consequently, it is unsure whether they can be extended to the long term. Further research in older forests is thus essential

Bacterial invasion potential in water is determined by nutrient availability and the indigenous community

In drinking water (DW) and the distribution systems, bacterial growth and biofilm formation have to be controlled both for limiting taste or odour development and preventing clogging or biocorrosion problems. After a contamination with undesired bacteria, factors like nutrient availability and temperature will influence the survival of these invaders. Understanding the conditions enabling invaders to proliferate is essential for a holistic approach towards microbial risk assessment in DW. Pseudomonas putida was used as a model invader because this easy-growing bacterium can use a wide range of substrates. Invasion experiments in oligo- to eutrophic waters showed the requirement of both a carbon and phosphate source for survival of P.putida in DW. Addition of C, N and P enabled P.putida to grow in DW from 5.80x10(4) to 1.84x10(8)cellsmL(-1) and survive for at least 12days. However, in surface water with similar nutrient concentrations, P.putida did not survive, indicating the concomitant importance of the present indigenous microbial community of the specific water sample. Either extensive carbon or phosphate limitation can be used in water treatment design in order to obtain a DW which is not susceptible for unwanted bacterial growth

Occurrence of transparent exopolymer particles (TEP) in drinking water systems

Numerous membrane fouling studies have been conducted to predict and prevent membrane fouling. It was only recently that a new parameter, TEP, was introduced in this research. The deposition of TEP on reverse osmosis (RO) membranes has already been imaged, correlations between ultrafiltration (UF) fouling and TEP concentrations have been reported. Furthermore, TEP deposition takes place in an early stage of aquatic biofilm formation, making TEP one of the accused in search for biofilm initiation factors. After literature reporting about TEP in marine, surface and wastewater, this is the very first research focusing on TEP through in drinking water. Every single treatment step in three completely different drinking water production plants was scored on TEP removal. It could be concluded that TEP concentrations were very dependent of the raw water source but in none of the installations, TEP was able to reach the final drinking water in significant concentrations. The combination of coagulation and sand filtration proved efficient in strongly reducing TEP levels, while the combination of UF and RO could provide a total TEP removal

Occurrence of transparent exopolymer particles (TEP) through drinking water treatment plants

Numerous membrane fouling studies have been conducted to predict and prevent membrane fouling. It was only recently that a new parameter, TEP, was introduced in this research. The deposition of TEP on reverse osmosis (RO) membranes has already been imaged, correlations between ultrafiltration (UF) fouling and TEP concentrations have been reported. Furthermore, TEP deposition takes place in an early stage of biofilms formation, making TEP one of the accused in search for biofilm initiation factors. After literature reporting about TEP in marine, surface and wastewater, this is the first research focusing on TEP through in drinking water. Each treatment step in three completely different drinking water production plants was evaluated on TEP removal and it could be concluded that a limited restfraction or no TEP could reach the drinking water. Coagulation + sand filtration proved efficient in strongly reducing TEP levels, UF + RO can provide a total TEP removal

From Combat Veterans to Criminals: Posttraumatic Stress Disorder and Criminal Justice Involvement

Posttraumatic stress disorder (PTSD) is currently known as the silent killer among combat veterans who have served in Operation Iraqi Freedom, Operation Enduring Freedom, and Operation New Dawn. Many combat veterans do not know or understand that they may be suffering from mental illness/disorders such as PTSD and turn to maladaptive behavior, resulting in criminal justice involvement (CJI). The goal of this study was to assess a relationship between PTSD and CJI among combat veterans. This study used cognitive behavior theory to understand the relationship between PTSD, CJI, and combat. This study used a predictive correlational design and statistical analysis of retrospective archival data (N=146) provided by the Department of Veteran Affairs to find the correlation between PTSD, CJI, and combat. The 5 research questions were: Does PTSD positively predict CJI in combat veterans? Does criminal history pre combat positively predict CJI in combat veterans who have PTSD? Does combat trauma experience positively predict CJI in combat veterans with PTSD? Does deployment length positively predict PTSD in combat veterans? And do multiple deployments positively predict PTSD in combat veterans? This study determined that PTSD did not significantly predict CJI and that criminal history did not predict PTSD. However, this study did predict that multiple deployments and length of deployment does predict PTSD in combat veterans. This study provides a way to bring change to how veterans are treated in the criminal justice system. This is important for many reasons, such as the positive social change it will have on the veteran community through providing insight on the changes that need to be made in PTSD awareness education and possible change in assessment and treatment of PTSD

Impact of mechanized harvesting on compaction of sandy and clayey forest soils : results of a meta-analysis

Nowadays, harvest operations are predominantly performed fully mechanized using heavy tractors or forestry machines. The resulting soil compaction may negatively affect the soil ecosystem. We wanted to draw general conclusions concerning the impact of mechanized harvesting on forest soil bulk density and the influencing factors. Therefore, we combined the data of several studies using a meta-analysis approach. The impact decreased from the surface towards deeper soil layers. At 0-10 cm depth, the impact on clayey soils was highest although not significantly different from the impact on sandy soils. Higher initial bulk densities, i.e., on already compacted forest soils, generally led to smaller extra increases of bulk density after machine traffic. For sandy soils, the impact was also significantly smaller when machines were lighter. No significant relationship was observed between the compaction degree and traffic intensity. We observed clear compaction on both clayey and sandy soils, especially in case of low initial soil compaction degrees and heavy machines. The compacted initial state of many forest soils, the long recovery period, and the generally high impact of the first passes that is frequently mentioned in literature all count in favour of designated skid trails and an adjustment of the machine type to the job

Bacterial exchange in household washing machines

Household washing machines (WMs) launder soiled clothes and textiles, but do not sterilize them. We investigated the microbial exchange occurring in five household WMs. Samples from a new cotton T-shirt were laundered together with a normal laundry load. Analyses were performed on the influent water and the ingoing cotton samples, as well as the greywater and the washed cotton samples. The number of living bacteria was generally not lower in the WM effluent water as compared to the influent water. The laundering process caused a microbial exchange of influent water bacteria, skin-, and clothes related bacteria and biofilm-related bacteria in the WM. A variety of biofilm-producing bacteria were enriched in the effluent after laundering, although their presence in the cotton sample was low. Nearly all bacterial genera detected on the initial cotton sample were still present in the washed cotton samples. A selection for typical skin- and clothes related microbial species occurred in the cotton samples after laundering. Accordingly, malodour-causing microbial species might be further distributed to other clothes. The bacteria on the ingoing textiles contributed for a large part to the microbiome found in the textiles after laundering

Soil inorganic N leaching in edges of different forest types subject to high N deposition loads

We report on soil leaching of dissolved inorganic nitrogen (DIN) along transects across exposed edges of four coniferous and four deciduous forest stands. In a 64-m edge zone, DIN leaching below the main rooting zone was enhanced relative to the interior (at 128 m from the edge) by 21 and 14 kg N ha-1 y-1 in the coniferous and deciduous forest stands, respectively. However, the patterns of DIN leaching did not univocally reflect those of DIN throughfall deposition. DIN leaching in the first 20 m of the edges was lower than at 32–64 m from the edge (17 vs. 36 kg N ha-1 y-1 and 15 vs. 24 kg N ha-1 y-1 in the coniferous and deciduous forests, respectively). Nitrogen stocks in the mineral topsoil (0–30 cm) were, on average, 943 kg N ha-1 higher at the outer edges than in the interior, indicating that N retention in the soil is probably one of the processes involved in the relatively low DIN leaching in the outer edges. We suggest that a complex of edge effects on biogeochemical processes occurs at the forest edges as a result of the interaction between microclimate, tree dynamics (growth and litterfall), and atmospheric deposition of N and base cations