Nutrient and pesticide remediation using a two-stage bioreactor-adsorptive system under two hydraulic retention times.

Nutrients and pesticides in agricultural runoff contribute to the degradation of water resources. Nitrates and phosphates can be remediated through the use of treatment systems such as woodchip bioreactors and adsorbent aggregate filters; however, concerns remain over potential effects of pesticides on nutrient removal efficiency in these systems. To test this, we designed laboratory-scale woodchip bioreactors equipped with secondary adsorbent aggregate filters and investigated the capacity of these systems to remediate nutrients when operated under two hydraulic retention times (HRT) and in the presence of commonly used pesticides. The woodchip bioreactors effectively removed over 99% of nitrate per day when operated under a 72 h hydraulic retention time, with the secondary expanded shale aggregate filters consistently reducing phosphate concentrations by 80-87%. Treatment efficacy of both systems was maintained in the presence of the insecticide chlorpyrifos. Reducing HRT in the bioreactors to 21 min decreased nitrate removal efficiency; however, the insecticides bifenthrin, chlorpyrifos, and the herbicide oxyfluorfen were reduced by 76%, 63%, and 31%, respectively. Cultivation approaches led to the isolation of 45 different species from the woodchip bioreactors operated under a 21 min HRT, with Bacillus species being the most prevalent throughout the treatment. By contrast, pesticide application decreased the number and diversity of Bacillus isolates and enriched for Pseudomonas and Exiguobacterium species. Woodchip bioreactors and adsorbent aggregate filters provide effective treatment platforms to remediate agrochemicals, where they maintain treatment efficacy in the presence of pesticides and can be modulated through HRT management to achieve environmental and operational water quality goals.

Spatial and temporal distribution of trunk-injected imidacloprid in apple tree canopies.

BACKGROUND: Pesticide use in orchards creates drift-driven pesticide losses which contaminate the environment. Trunk injection of pesticides as a target-precise delivery system could greatly reduce pesticide losses. However, pesticide efficiency after trunk injection is associated with the underinvestigated spatial and temporal distribution of the pesticide within the tree crown. This study quantified the spatial and temporal distribution of trunk-injected imidacloprid within apple crowns after trunk injection using one, two, four or eight injection ports per tree. RESULTS: The spatial uniformity of imidacloprid distribution in apple crowns significantly increased with more injection ports. Four ports allowed uniform spatial distribution of imidacloprid in the crown. Uniform and non-uniform spatial distributions were established early and lasted throughout the experiment. The temporal distribution of imidacloprid was significantly non-uniform. Upper and lower crown positions did not significantly differ in compound concentration. Crown concentration patterns indicated that imidacloprid transport in the trunk occurred through radial diffusion and vertical uptake with a spiral pattern. CONCLUSION: By showing where and when a trunk-injected compound is distributed in the apple tree canopy, this study addresses a key knowledge gap in terms of explaining the efficiency of the compound in the crown. These findings allow the improvement of target-precise pesticide delivery for more sustainable tree-based agriculture.

Spatial and temporal distribution of trunk-injected (14) C-imidacloprid in Fraxinus trees.

BACKGROUND: Since the discovery of Agrilus planipennis Fairmaire (emerald ash borer) in 2002, researchers have tested several methods of chemical control. Soil drench or trunk injection products containing imidacloprid are commonly used to control adults. However, efficacy can be highly variable and may be due to uneven translocation of systemic insecticides. The purpose of this study was to determine whether sectored xylem anatomy might influence imidacloprid distribution in tree crowns. RESULTS: Imidacloprid equivalent concentrations were higher in leaves from branches in the plane of the injection point (0°) than in leaves from branches on the opposite side of the injection point (180°). Leaves from branches 90° to the right of injection points had higher imidacloprid equivalent concentrations than leaves from branches 90° to the left of injection points. Leaves and shoots had higher imidacloprid equivalent concentrations than roots and trunk cores, indicating that imidacloprid moves primarily through the xylem. CONCLUSION: Imidacloprid equivalent concentration in leaves varied over time and in relation to injection points. It is concluded that ash trees have sectored 'zigzag' xylem architecture patterns consistent with sectored flow distribution. This could lead to variable distribution of imidacloprid in tree crowns and therefore to variable control of A. planipennis.

Carbon sequestration potential of extensive green roofs.

Two studies were conducted with the objective of quantifying the carbon storage potential of extensive green roofs. The first was performed on eight roofs in Michigan and four roofs in Maryland, ranging from 1 to 6 years in age. All 12 green roofs were composed primarily of Sedum species, and substrate depths ranged from 2.5 to 12.7 cm. Aboveground plant material was harvested in the fall of 2006. On average, these roofs stored 162 g C x m(-2) in aboveground biomass. The second study was conducted on a roof in East Lansing, MI. Twenty plots were established on 21 April 2007 with a substrate depth of 6.0 cm. In addition to a substrate only control, the other plots were sown with a single species of Sedum (S. acre, S. album, S. kamtshaticum, or S. spurium). Species and substrate depth represent typical extensive green roofs in the United States. Plant material and substrate were harvested seven times across two growing seasons. Results at the end of the second year showed that aboveground plant material storage varied by species, ranging from 64 g C x m(-2) (S. acre) to 239 g C x m(-2) (S. album), with an average of 168 g C x m(-2). Belowground biomass ranged from 37 g C x m(-2) (S. acre) to 185 g C x m(-2) (S. kamtschaticum) and averaged 107 g C x m(-2). Substrate carbon content averaged 913 g C x m(-2), with no species effect, which represents a sequestration rate of 100 g C x m(-2) over the 2 years of this study. The entire extensive green roof system sequestered 375 g C x m(-2) in above- and belowground biomass and substrate organic matter.