Linking chemical extraction to microbial degradation of 14C-hexadecane in soil

Chemical extractions have been shown to measure the biodegradable fraction of aromatic contaminants in soil; however, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for cyclodextrin extractions to predict hexadecane biodegradation in soil. Soils were amended with 10 or 100 mg kg⁻¹ of a model alkane n-hexadecane and 100 Bq g⁻¹¹⁴C-n-hexadecane. Correlations between the extents of mineralisation and extractions of the ¹⁴C-contaminant were determined. Solvent shake extractions and aqueous CaCl₂ extractions were poor predictors of hexadecane bioaccessibility. However, the novel HP-α-CD shake extraction showed close correlation (r² = 0.90, n = 36, p < 0.05) to the mineralisation data. This novel extraction technique has the potential to be used to assess the biodegradable aliphatic hydrocarbon fraction in contaminated soils.     

The impact of synthetic pyrethroid and organophosphate sheep dip formulations on microbial activity in soil

Sheep dip formulations containing organophosphates (OPs) or synthetic pyrethroids (SPs) have been widely used in UK, and their spreading onto land has been identified as the most practical disposal method. In this study, the impact of two sheep dip formulations on the microbial activity of a soil was investigated over a 35-d incubation. Microbial utilisation of [1-(14)C] glucose, uptake of (14)C-activity into the microbial biomass and microbial numbers (CFUs g(-1) soil) were investigated. In control soils and soils amended with 0.01% sheep dip, after 7d a larger proportion of added glucose was allocated to microbial biomass rather than respired to CO(2). No clear temporal trends were found in soils amended with 0.1% and 1% sheep dips. Both sheep dip formulations at 0.1% and 1% concentrations resulted in a significant increase in CFUs g(-1) soil and [1-(14)C] glucose mineralisation rates, as well as a decline in microbial uptake of [1-(14)C] glucose, compared to control and 0.01% SP- or OP-amended soils. This study suggests that the growth, activity, physiological status and/or structure of soil microbial community may be affected by sheep dips.     

Assessing biodegradation potential of PAHs in complex multi-contaminant matrices

This study sought to extend validation of a cyclodextrin based extraction method for the assessment of PAH-biodegradation potential to complex multi-contaminant matrices. To this end, four reference materials (RMs) were produced by blending, in different proportions, soils impacted with diesel, lubricating oil and spent oxide. These reference materials had modest ∑PAH (16 US EPA) concentrations that ranged from 5.6 ± 0.5 to 44.4 ± 4.5 mg kg⁻¹. However, extractable petroleum hydrocarbon (EPH) concentrations were comparatively high (up to 2520 ± 204 mg kg⁻¹). To complement these RMs, two further soils from a municipal gas plant (MGP) with highly elevated concentration of PAHs ranging from 877 ± 52 to 2620 ± 344 mg kg⁻¹ were also tested. Results showed, regardless of matrix complexity, that PAH biodegradation within the four RM substrates, and two MGP soils correlated well with biodegradation predicted by hydroxypropyl-β-cyclodextrin (HPCD) extraction.     

Prediction of microbial accessibility of carbon-14-phenanthrene in soil in the presence of pyrene or benzo[a]pyrene using an aqueous cyclodextrin extraction technique

Traditionally, solvent extractions are routinely used in the assessment of contaminated land. However, vigorous solvent extractions only give total concentrations rather than that relating to the bioaccessible fraction. Recently, less harsh, aqueous-based extraction methods have been shown to be a better estimate of the microbial degradation of polycyclic aromatic hydrocarbons (PAHs). The aqueous-based hydroxypropyl-beta-cyclodextrin (HPCD) extraction technique was tested using 14C-PAHs in soils and compared against indigenous microbial mineralization (a measure of bioaccessibility) of 14C-phenanthrene in the presence of pyrene or benzo[a]pyrene (B[a]P) over a range of concentrations (0, 5, 10, or 50 mg kg(-1)) and aged for 0, 25, 50, and 100 d in four soils. At each time point, the total loss, extractability, and mineralization of 14C-phenanthrene was measured in each of the soils. The presence of the other PAHs had little effect on the behavior of 14C-phenanthrene in any of the soils. Comparisons between the amounts of 14C-phenanthrene extracted using HPCD and mineralized were made and showed that there was a correlation (1:1). This study demonstrates that HPCD extraction is able to predict the microbial accessibility fraction of 14C-phenanthrene in the presence of other PAHs in a range of soils, further supporting the applicability of this technique.     

Behavioral regulation of genetic caste determination in a Pogonomyrmex population with dependent lineages

The fate of a social insect colony is partially determined by its ability to allocate individuals to the caste most appropriate for the requirements for growth, maintenance, and reproduction. In pairs of dependent lineages of Pogonomyrmex barbatus, the allocation of individuals to the queen or worker caste is constrained by genotype, a system known as genetic caste determination (GCD). In mature GCD colonies, interlineage female eggs develop into sterile workers, while intralineage eggs become reproductively capable queens. Although the population-level consequences of this system have been intensively studied, the proximate mechanisms for GCD remain unknown. To elucidate these mechanisms, we brought newly mated queens into the laboratory and allowed them to establish colonies, nearly half of which unexpectedly produced virgin queens only seven months after colony founding. We genotyped eggs, workers, and the virgin queens from these colonies. Our results showed that queens in young colonies produce both interlineage and intralineage eggs, demonstrating that queens of GCD colonies indiscriminately use sperm of at least two lineages to fertilize their eggs. Intralineage eggs were more frequent in colonies producing virgin queens. These findings suggest that intralineage eggs are predetermined to become queens and that workers may cull these eggs when colonies are not producing queens. Virgin queens produced by young GCD colonies were smaller than field-caught virgin queens, and often had developmental problems. Hence, they are probably nonfunctional and represent an intense resource drain for developing colonies, not a contribution to colony fitness.     

Do honey bees tune error in their dances in nectar-foraging and house-hunting?

The "tuned-error" hypothesis states that natural selection has tuned the divergence angle in the dances of the honey bee to produce an optimal scatter of recruits across a resource. Weidenmüller and Seeley (Behav Ecol Sociobiol 46:190–199, 1999) supported this hypothesis by finding smaller divergence angles in dances indicating potential home sites, which are always point sources, than in dances indicating food sources, which often occur in patches. This study tested for the same effect, but controlled for variables, e.g., substrate and context, that may have confounded those results. When performed on the same substrate, divergence angle does not differ between dances for the two resources. Furthermore, dances performed for food within an observation hive exhibit significantly greater divergence angle when performed on comb (as Weidenmüller and Seeley measured food dances) than on hardware cloth (as they measured home-site dances on a swarm). These findings suggest that the angular variance in direction indication in dances is more likely an artifact of physical constraints, rather than an adaptive modification of a behavior that a bee could perform more precisely.     

Grazing management effects on sediment, phosphorus, and pathogen loading of streams in cool-season grass pastures

Erosion and runoff from pastures may lead to degradation of surface water. A 2-yr grazing study was conducted to quantify the effects of grazing management on sediment, phosphorus (P), and pathogen loading of streams in cool-season grass pastures. Six adjoining 12.1-ha pastures bisected by a stream in central Iowa were divided into three treatments: continuous stocking with unrestricted stream access (CSU), continuous stocking with restricted stream access (CSR), and rotational stocking (RS). Rainfall simulations on stream banks resulted in greater ( < 0.10) proportions of applied precipitation and amounts of sediment and P transported in runoff from bare sites than from vegetated sites across grazing treatments. Similar differences were observed comparing vegetated sites in CSU and RS pastures with vegetated sites in CSR pastures. Bovine enterovirus was shed by an average of 24.3% of cows during the study period and was collected in the runoff of 8.3 and 16.7% of runoff simulations on bare sites in CSU pastures in June and October of 2008, respectively, and from 8.3% of runoff simulations on vegetated sites in CSU pastures in April 2009. Fecal pathogens (bovine coronavirus [BCV], bovine rotavirus group A, and O157:H7) shed or detected in runoff were almost nonexistent; only BCV was detected in feces of one cow in August of 2008. Erosion of cut-banks was the greatest contributor of sediment and P loading to the stream; contributions from surface runoff and grazing animals were considerably less and were minimized by grazing management practices that reduced congregation of cattle by pasture streams.     

Spatial variability of biotic and abiotic tree establishment constraints across a treeline ecotone in the Alaska range

Throughout interior Alaska (U.S.A.), a gradual warming trend in mean monthly temperatures occurred over the last few decades (approximatlely 2-4 degrees C). The accompanying increases in woody vegetation at many alpine treeline (hereafter treeline) locations provided an opportunity to examine how biotic and abiotic local site conditions interact to control tree establishment patterns during warming. We devised a landscape ecological approach to investigate these relationships at an undisturbed treeline in the Alaska Range. We identified treeline changes between 1953 (aerial photography) and 2005 (satellite imagery) in a geographic information system (GIS) and linked them with corresponding local site conditions derived from digital terrain data, ancillary climate data, and distance to 1953 trees. Logistic regressions enabled us to rank the importance of local site conditions in controlling tree establishment. We discovered a spatial transition in the importance of tree establishment controls. The biotic variable (proximity to 1953 trees) was the most important tree establishment predictor below the upper tree limit, providing evidence of response lags with the abiotic setting and suggesting that tree establishment is rarely in equilibrium with the physical environment or responding directly to warming. Elevation and winter sun exposure were important predictors of tree establishment at the upper tree limit, but proximity to trees persisted as an important tertiary predictor, indicating that tree establishment may achieve equilibrium with the physical environment. However, even here, influences from the biotic variable may obscure unequivocal correlations with the abiotic setting (including temperature). Future treeline expansion will likely be patchy and challenging to predict without considering the spatial variability of influences from biotic and abiotic local site conditions.     

Scientists’ warning to humanity on the freshwater biodiversity crisis

Freshwater ecosystems provide irreplaceable services for both nature and society. The quality and quantity of freshwater affect biogeochemical processes and ecological dynamics that determine biodiversity, ecosystem productivity, and human health and welfare at local, regional and global scales. Freshwater ecosystems and their associated riparian habitats are amongst the most biologically diverse on Earth, and have inestimable economic, health, cultural, scientific and educational values. Yet human impacts to lakes, rivers, streams, wetlands and groundwater are dramatically reducing biodiversity and robbing critical natural resources and services from current and future generations. Freshwater biodiversity is declining rapidly on every continent and in every major river basin on Earth, and this degradation is occurring more rapidly than in terrestrial ecosystems. Currently, about one third of all global freshwater discharges pass through human agricultural, industrial or urban infrastructure. About one fifth of the Earth’s arable land is now already equipped for irrigation, including all the most productive lands, and this proportion is projected to surpass one third by midcentury to feed the rapidly expanding populations of humans and commensal species, especially poultry and ruminant livestock. Less than one fifth of the world’s preindustrial freshwater wetlands remain, and this proportion is projected to decline to under one tenth by midcentury, with imminent threats from water transfer megaprojects in Brazil and India, and coastal wetland drainage megaprojects in China. The Living Planet Index for freshwater vertebrate populations has declined to just one third that of 1970, and is projected to sink below one fifth by midcentury. A linear model of global economic expansion yields the chilling prediction that human utilization of critical freshwater resources will approach one half of the Earth’s total capacity by midcentury. Although the magnitude and growth of the human freshwater footprint are greater than is generally understood by policy makers, the news media, or the general public, slowing and reversing dramatic losses of freshwater species and ecosystems is still possible. We recommend a set of urgent policy actions that promote clean water, conserve watershed services, and restore freshwater ecosystems and their vital services. Effective management of freshwater resources and ecosystems must be ranked amongst humanity’s highest priorities.Electronic supplementary materialThe online version of this article (10.1007/s13280-020-01318-8) contains supplementary material, which is available to authorized users.