Deposition and transport of functionalized carbon nanotubes in water-saturated sand columns

Knowledge of the fate and transport of functionalized carbon nanotubes (CNTs) in porous media is crucial to understand their environmental impacts. In this study, laboratory column and modeling experiments were conducted to mechanistically compare the retention and transport of two types of functionalized CNTs (i.e., single-walled nanotubes and multi-walled nanotubes) in acid-cleaned, baked, and natural sand under unfavorable conditions. The CNTs were highly mobile in the acid-cleaned sand columns but showed little transport in the both natural and baked sand columns. In addition, the retention of the CNTs in the both baked and natural sand was strong and almost irreversible even after reverse, high-velocity, or surfactant flow flushing. Both experimental and modeling results showed that pH is one of the factors dominating CNT retention and transport in natural and baked sand. Retention of the functionalized CNTs in the natural and baked sand columns reduced dramatically when the system pH increased. Our results suggest that the retention and transport of the functionalized CNTs in natural sand porous media were mainly controlled by strong surface deposition through the electrostatic and/or hydrogen-bonding attractions between surface function groups of the CNTs and metal oxyhydroxide impurities on the sand surfaces

Anthropogenic Renourishment Feedback on Shorebirds: a Multispecies Bayesian Perspective

In this paper the realized niche of the Snowy Plover (Charadrius alexandrinus), a primarily resident Florida shorebird, is described as a function of the scenopoetic and bionomic variables at the nest-, landscape-, and regional-scale. We identified some possible geomorphological controls that influence nest-site selection and survival using data collected along the Florida Gulf coast. In particular we focused on the effects of beach replenishment interventions on the Snowy Plover (SP), and on the migratory Piping Plover	(PP)	(Charadrius	melodus )	and	Red	Knot	(RK)	(Calidris	canutus ).	Additionally, we investigated the potential differences between the SP breeding and wintering distributions using only regional-scale physiognomic variables and the recorded occur- rences. To quantify the relationship between past renourishment projects and shorebird species we used a Monte Carlo procedure to sample from the posterior distribution of the binomial probabilities that a region is not a nesting or a wintering ground conditional on the occurrence of a beach replenishment intervention in the same and the previous year. The results indicate that it was 2.3, 3.1, and 0.8 times more likely that a region was not a wintering ground following a year with a renourishment intervention for the SP, PP and RK respectively. For the SP it was 2.5. times more likely that a region was not a breeding ground after a renourishment event. Through a maximum entropy principle model we observed small differences in the habitat use of the SP during the breeding and the wintering season. However the habitats where RK was observed appeared quite different. While ecological niche models at the macro-scale are useful for determining habitat suitability ranges, the characterization of the species’ local niche is fundamentally important for adopting concrete multi-species management scenarios. Maintaining and creating optimal suitable habitats for SP characterized by sparse low vegetation in the foredunes areas, and uneven/low-slope beach surfaces, is the proposed conservation scenario to convert anthropic beach restorations and SP populations into a positive feedback without impacting other threatened shorebird species

Methods of using carbon nanotubes as filter media to remove aqueous heavy metals

Although carbon nanotubes (CNTs) are well known to have a strong affinity to various heavy metals in aqueous solution, little research has been dedicated to exploit their use in fixed-bed water treatment systems (e.g., trickling filters). In this work, batch sorption and fixed-bed experiments were conducted to examine the ability of functionalized multi-walled CNTs as filter media to remove two heavy metal ions (Pb2+ and Cu2+) from infiltrating water. Batch sorption experiments confirmed the strong sorption affinity of the CNTs for Pb2+ and Cu2+ in both single and dual metal solution systems. In addition, sonication-promoted dispersion of the CNT particles enhanced their heavy metal sorption capacity by 23.9–32.2%. For column experiments, laboratory-scale fixed-bed columns were packed with CNTs and natural quartz sand by three different packing: layered, mixed, and deposited. While all the three packing methods enhanced the fixed-bed filtering efficiency of Pb2+ and Cu2+ from single and dual metal systems, the CNT-deposited packing method was superior. Although the amount of the CNTs added into the fixed-bed columns was only 0.006% (w/w) of the sand, they significantly improved the fixed-bed’s filtering efficiency of Pb2+ and Cu2+ by 55–75% and 31–57%, respectively. Findings from this study demonstrate that functionalized multi-walled CNTs, together with natural sand, can be used to effectively and safely remove heavy metals from water

Sensitivity analysis and parameter estimation for an approximate analytical model of canal-aquifer interaction applied in the C-111 basin

The goal of this study was to better characterize parameters influencing the exchange of surface water in south Florida’s C-111 canal and Biscayne aquifer using the analytical model STWT1. A three-step model evaluation framework was implemented as follows: (1) qualitative parameter ranking by comparing two Morris method sampling strategies, (2) quantitative variance-based sensitivity analysis using Sobol’s method, and (3) estimation of parameter posterior probability distributions and statistics using the Generalized Likelihood Uncertainty Estimator (GLUE) methodology. Results indicated that the original Morris random sampling method underestimated total parameter effects compared to the improved global Morris sampling strategy. However, parameter rankings from the two sampling methods were similar. For the STWT1 model, only four out of the six parameters analyzed were important for predicting water table response to canal stage and recharge fluctuations. Morris ranking in order of decreasing importance resulted in specific yield (ASY), aquifer saturated thickness (AB), horizontal hydraulic conductivity (AKX), canal leakance (XAA), vertical hydraulic conductivity (AKZ), and half-width of canal (XZERO). Sobol’s sensitivity indices for the four most critical parameters revealed that summation of first-order parameter effects was 1.0, indicating that STWT1 behaved as an additive model or negligible parameter interactions. We estimated parameter values of 0.07 to 0.14 for ASY, 11,000 to 14,300 m d-1 for AKX, 13.4 to 18.3 m for AB, and 99.8 to 279 m for XAA. The estimated values were within the range of values estimated using more complex methods at nearby sites. The Nash-Sutcliffe coefficient of efficiency and root mean square error for estimated parameters ranged from 0.66 to 0.95 and from 4 to 7 cm, respectively. This study demonstrates a simple and inexpensive way to characterize hydrogeological parameters controlling groundwater-surface interactions in any region with aquifers that are highly permeable without using standard pumping tests or canal drawdown experiments. Hydrogeological parameters estimated using this approach could be used as starting values in large-scale numerical simulations

A spatiotemporal natural-human database to evaluate road development impacts in an Amazon trinational frontier

Road construction and paving bring socio-economic benefits to receiving regions but can also be drivers of deforestation and land cover change. Road infrastructure often increases migration and illegal economic activities, which in turn affect local hydrology, wildlife, vegetation structure and dynamics, and biodiversity. To evaluate the full breadth of impacts from a coupled natural-human systems perspective, information is needed over a sufficient timespan to include pre- and post-road paving conditions. In addition, the spatial scale should be appropriate to link local human activities and biophysical system components, while also allowing for upscaling to the regional scale. A database was developed for the tri-national frontier in the Southwestern Amazon, where the Inter-Oceanic Highway was constructed through an area of high biological value and cultural diversity. Extensive socio-economic surveys and botanical field work are combined with remote sensing and reanalysis data to provide a rich and unique database, suitable for coupled natural-human systems research

Opportunities for improving irrigation efficiency with quantitative models, soil water sensors and wireless technology

Increasingly serious shortages of water make it imperative to improve the efficiency of irrigation in agriculture, horticulture and in the maintenance of urban landscapes. The main aim of the current review is to identify ways of meeting this objective. After reviewing current irrigation practices, discussion is centred on the sensitivity of crops to water deficit, the finding that growth of many crops is unaffected by considerable lowering of soil water content and, on this basis, the creation of improved means of irrigation scheduling. Subsequently, attention is focused on irrigation problems associated with spatial variability in soil water and the often slow infiltration of water into soil, especially the subsoil. As monitoring of soil water is important for estimating irrigation requirements, the attributes of the two main types of soil water sensors and their most appropriate uses are described. Attention is also drawn to the contribution of wireless technology to the transmission of sensor outputs. Rapid progress is being made in transmitting sensor data, obtained from different depths down the soil profile across irrigated areas, to a PC that processes the data and on this basis automatically commands irrigation equipment to deliver amounts of water, according to need, across the field. To help interpret sensor outputs, and for many other reasons, principles of water processes in the soil–plant system are incorporated into simulation models that are calibrated and tested in field experiments. Finally, it is emphasized that the relative importance of the factors discussed in this review to any particular situation varies enormously