Green roofs can potentially be used to tackle a variety of environmental problems, and can be used as development mitigation for the loss of ground-based habitats. Brown (biodiversity) roofs are a type of green roof designed to imitate brownfield habitat, but the best way of engineering these habitats requires more research. We tested the effects of altering organic matter content on the development of vegetation assemblages of experimental brown (biodiversity) roof mesocosms. Three mulch treatments were tested: (1) sandy loam, where 10 mm of sandy loam mulch (about 3% organic matter by dry weight) was added to 100 mm of recycled aggregate; (2) compost, where the mulch also contained some garden compost (about 6% organic matter by dry weight); and (3) no mulch, where no mulch was added. Mesocosms were seeded with a wildflower mix that included some Sedum acre, and vegetation development was investigated over a six-year period. Species richness, assemblage character, number of plants able to seed, and above-ground plant biomass were measured. Drought disturbance was an important control on plant assemblages in all mulch treatments, but there were significant treatment response interactions. The more productive compost treatment was associated with larger plant coverage and diversity before the occurrence of a sequence of drought disturbances, but was more strongly negatively affected by the disturbances than the two less productive treatments. We suggest that this was due to the over-production of plant biomass in the more productive treatment, which made the plants more vulnerable to the effects of drought disturbance, leading to a kind of 'boom-bust' assemblage dynamic. The 'ideal' amount of added organic matter for these green roof systems was very low, but other types of green roof that have a larger water holding capacity, and/or more drought resistant plant floras, will likely require more organic matter or fertiliser. Nonetheless, nutrient-supported productivity in green roof systems should be kept low in order to avoid boom-bust plant assemblage dynamics. Research into the best way of engineering green roof habitats should take place over a long enough multi-year time period to include the effects of temporally infrequent disturbances. (C) 2015 Elsevier B.V. All rights reserved.

Green roofs have the potential to address several of the environmental problems associated with urbanisation, and can be used as mitigation for habitats lost at ground level. Brown roofs (a type of green roof) can be used to mitigate for the loss of brownfield habitat, but the best way of designing these habitats remains unclear. This paper reports an experiment to test the effects of different types of recycled aggregate on the development of vegetation assemblages on brown roof mesocosms. Five recycled aggregates were tested: (1) crushed brick, (2) crushed demolition aggregate, (3) solid municipal waste incinerator bottom ash aggregate, (4) a 1:1 mix of 1 and 2, and (5) a 1:1 mix of 3 and 2. Each was seeded with a wild-flower mix that also included some Sedum acre and vegetation development was studied over a six-year period. Species richness, assemblage character, number of plants able to seed, and plant biomass were measured. Drought disturbance was the key factor controlling changes in plant assemblage, but effects varied with substrate treatment. All treatments supported a similar plant biomass, but treatments with a high proportion of crushed brick in the growth substrate supported richer assemblages, with more species able to seed, and a smaller amount of Sedum acre. Crushed brick, or recycled aggregates with a high proportion of crushed brick, are recommended as good growth substrate materials for encouraging brown roof plant diversity. This investigation demonstrates the importance of multi-year studies of green roof development for the generation of robust findings. (C) 2014 Elsevier B.V. All rights reserved.

Forced gradient tracer tests between two boreholes can be used to study contaminant transport processes at the small field scale or investigate the transport properties of an aquifer. Full depth tests, in which tracer samples are collected just from the discharge of the abstraction borehole, often give rise to breakthrough curves with multiple peaks that are usually attributed to different flow paths through the aquifer that can rarely be identified from the test results alone. Tests in selected levels of the aquifer, such as those between packer-isolated sections of the boreholes, are time consuming, expensive; and the identification of major transport pathways is not guaranteed. We present a method for simultaneously conducting multiple tracer tests covering the full depth of the boreholes, in which tracer sampling and monitoring is carried out by a novel multilevel sampling system allowing high frequency and cumulative sampling options. The method is applied to a tracer test using fluorescein conducted in the multilayered sandstone aquifer beneath the city of Birmingham, UK, producing six well-defined tracer breakthrough curves.

Ureolysis-driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport. In this study urea hydrolysis and calcite precipitation rates for the model bacterium Sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite (up to 50gL−1). We conducted microcosm experiments in oxic artificial and anoxic natural groundwaters (collected from the Permo-Triassic sandstone aquifer at Birmingham, UK) that were inoculated with aerobically grown S. pasteurii. The rate constants for urea hydrolysis, kurea, ranged between 0.06 and 3.29d−1 and were only affected by inoculum density. Higher Ca2+ concentration (50–500mMCa2+) as well as differences in fO2 did not inhibit the ureolytic activity of S. pasteurii and did not significantly impact kurea. These results demonstrate that S. pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters, especially if indigenous communities lack ureolytic activity. Urea hydrolysis by indigenous groundwater communities was investigated in anoxic, natural groundwaters amended with urea and CaCl2. A notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients (with best results from blackstrap molasses). Furthermore, there was a considerable lag time (12–20days) before ureolysis and calcite precipitation began. Calculated ureolysis rate constants, kurea, ranged between 0.03 and 0.05d−1 and were similar to kurea values produced by S. pasteurii at low inoculum densities. Overall, this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface, and thus can be used to induce calcite precipitation in these environments. The time required for urea hydrolysis to begin is almost instantaneous if an inoculum of S. pasteurii is included, while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active.

Production of manufactured nanoparticles (mNPs) is likely to increase significantly in the near future. To investigate mNP mobility in sandstone groundwaters, column experiments have been completed on intact continental redbed sandstone. SiO2 mNP breakthrough concentrations decrease as ionic strength increases, with reversibility indicating secondary minimum attachment: a maximum retention capacity is observed. In contrast, initial metal oxide mNP breakthrough concentrations in deionized water gradually fall as clogging occurs, mobility being in the order (Si >) Ti, Sb > Ce, Ag: no detectable breakthrough occurs for artificial groundwater solutions, even after many 100s of pore volumes. These results suggest that most particles have limited mobility, consistent with measured zeta potentials, but that remobilization can occur if conditions change. A small proportion of particles appear to be more mobile, and this is confirmed by the presence of small amounts of mNPs in wellwaters.

A mathematical model describing the steady state flows in a forced gradient tracer test between an injection and pumping borehole in a multilayered sandstone aquifer has been developed that includes the effect of vertically variable background heads. A second model describing the recovery of tracer from a layer in which there are discharges due to vertical flow in the injection borehole is also presented. Application of the models to field tracer test data indicates that the observed recoveries, which are not proportional to the abstraction rate in each layer, are consistent with the hydraulic behavior of the aquifer when natural vertical head gradients are taken into account. Investigation with the models illustrates that the vertical distribution of tracer recovery depends strongly upon the background heads and that tracer tests conducted in the same aquifer, but at different times, may interrogate different aquifer layers. It is also shown generally that for a given abstraction rate the vertical distribution of tracer recovery in small‐scale tracer tests is controlled largely by the transmissivity distribution but that as the spatial scale of the test increases, the distribution of recovery becomes proportional to the discharges from the injection borehole because of vertical flows within it, which may be natural or induced by pumping in the monitoring borehole. Uncertainties inherent in the design of forced gradient tracer tests in multilayered aquifers and the problems of applying the results of such tests to natural gradient contaminant migration are discussed.

Despite the presence of gas in river beds being a well known phenomenon, its potential feedbacks on the hydraulic and thermal dynamics of the hyporheic zone has not been widely studied. This paper explores hypotheses that the presence of accumulated gas impacts the hydraulic and thermal dynamics of a river bed due to changes in specific storage, hydraulic conductivity, effective porosity, and thermal diffusivity. The hypotheses are tested using data analysis and modelling for a study site on the urban River Tame, Birmingham, UK. Gas, predominantly attributed to microbial denitrification, was observed in the river bed up to around 14% by volume, and to at least 0.8m depth below river bed. Numerical modelling indicates that, by altering the relative hydraulic conductivity distribution, the gas in the river bed leads to an increase of groundwater discharge from the river banks (relative to river bed) by a factor of approximately 2 during river low flow periods. The increased compressible storage of the gas phase in the river bed leads to an increase in the simulated volume of river water invading the river bed within the centre of the channel during storm events. The exchange volume can be more than 30% greater in comparison to that for water saturated conditions. Furthermore, the presence of gas also reduces the water-filled porosity, and so the possible depth of such invading flows may also increase markedly, by more than a factor of 2 in the observed case. Observed diurnal temperature variations within the gaseous river bed at 0.1 and 0.5m depth are, respectively, around 1.5 and 6 times larger than those predicted for saturated sediments. Annual temperature fluctuations are seen to be enhanced by around 4 to 20% compared to literature values for saturated sediments. The presence of gas may thus alter the bulk thermal properties to such a degree that the use of heat tracer techniques becomes subject to a much greater degree of uncertainty. Although the likely magnitude of thermal and hydraulic changes due to the presence of gas for this site have been demonstrated, further research is needed into the origins of the gas and its spatial and temporal variability to enable quantification of the significance of these changes for chemical attenuation and hyporheic zone biology.

The transport and fate of colloidal particles is coming under increasing scrutiny, largely because of the expected rapid expansion in the production of manufactured nanoparticles and because of possible interactions of natural and manufactured nanoparticles with pollutants. Risk assessments of engineered nanoparticles may only be carried out if means exist to quantify the processes that control the fate of the particles as they interact with materials in the environment. For aqueous systems, there are several analytical methods available that may be utilised to classify and quantify a colloidal suspension but where the particles are of a generally uniform nature, and in sufficient number, the turbidity of the fluid provides an accurate measurement of concentration. In order to investigate the transport of manufactured nanoparticles through small saturated rock columns, a simple and inexpensive laser nephelometer was developed which incorporates a low volume flow-through cell in order to provide a continuous record of the elution of particles from the column. The design, construction and evaluation of the device are presented together with example data. Although designed specifically for the laboratory study of colloid transport through columns, the device may be readily adapted for other purposes in the field or laboratory wherever an inexpensive and robust continuous means of turbidity measurement is required.

The measurement of water level or pressure is often a key requirement in the study of hydrogeological, hydrological and soil science processes. Modern microelectronics can provide a range of solutions for the automated monitoring of water levels in boreholes, rivers as well as more specialised applications such as tensiometry. The advantages of stand-alone monitoring systems when compared to manual measurement approaches are well understood, especially when the point of measurement is remote or the frequency of perturbation is rapid. For this reason the combination of a pressure transducer and logging system within a single package has been widely adopted in commercially available systems. However, although the price of these devices continues to fall, they may still represent a significant cost for researchers on limited budgets. We therefore present a design for a simple, inexpensive (∼£30) but versatile pressure monitoring system which can interface to low-cost (£50–£70) data-loggers. We demonstrate how the design may be adapted for a range of field applications which include: river level measurements, tensiometers, permeameters and in situ river-bed piezometers. The performance of the system is assessed and for each application the specific design and examples of resulting data are described.

This paper summarises research based in the city of Birmingham, UK, into the ecological and hydrological performance of extensive green roofs designed to act as mitigation for the loss of brownfield habitat. It focuses particularly on possible trade-offs between design elements that maximise biodiversity potential, and design elements that maximise rainfall run-off management potential.

A prototype flow meter has been developed, based upon the heat perturbation principle, to monitor groundwater specific discharge in soft sediments. The device is designed for use in spatially intensive, long-term monitoring campaigns in remote or inconvenient locations, and is cheap, robust and capable of being logged automatically. The results of the laboratory tests indicate that the heat perturbation principle is suitable for determining the magnitude of specific discharge to a degree of accuracy that would be useful in practical applications in dynamic groundwater systems with rapidly changing flows of approximately 1md−1 or more and that the groundwater flow direction can generally be determined to a high level of precision. The accuracy and reliability of the estimates of specific discharge have been shown to depend strongly upon the geometrical precision of manufacture and the quality of the temperature monitoring system. These factors become most significant in the estimation of lower flows and further investigation is required to determine the detection limit of the device. Specific discharge estimates have been shown to be insensitive to dispersivity values appropriate to the scale of the device. Unlike the majority of heat perturbation devices, calibration is unnecessary.

Increasing water demand in urban areas is focusing attention on the possibilities of the re-use of urban wastewaters, waters that often contain human and animal (including avian) viruses. In urban red-bed sandstone aquifers in the UK, which are predominantly matrix flow systems, evidence from well and piezometer monitoring shows that viable human viruses can be transported to depths of at least 80 m. The aim of the studies described here is therefore to determine the processes controlling the virus transport as a basis for risk assessment. Laboratory column experiments show that virus breakthrough is severely attenuated in synthetic groundwater solutions, some viruses remaining effectively irreversibly attached to the rock: attenuation capacity is only slowly reduced as more viruses are eluted. However, addition of silica colloids (which when injected by themselves are also severely attenuated) to the virus solutions, results in breakthrough of the injected virus particles and release of previously attached virus particles. Forced-gradient tracer field experiments suggest that (severely attenuated) virus breakthrough occurs, but only through specific pathways. Current fieldwork is aimed at determining the location, and hence the hydraulic and geochemical characteristics of these pathways. It appears, therefore, that virus attenuation is reduced by the presence of other colloidal matter, low ionic strength, and continuous virus loading, and that conditions for transport occur only in specific pathways. Future laboratory work will be aimed at further quantifying these processes and relating them to the petrographic and geochemical properties of the various sandstone (hydro)lithofacies which the field experiments indicate are important. This will provide the understanding necessary for a process-based risk assessment procedure.

In order to investigate the natural attenuation potential in the hyporheic zone, a study of the relationship between the hydraulic conditions and the chemical reactions within the hyporheic zone is being undertaken. To understand the process interactions, the groundwater-surface water flow exchanges within the hyporheic zone will be controlled by careful groundwater extraction from the aquifer beneath the river. A field experimental site has now been established on the River Tame – Birmingham aquifer system, in an urban environment regionally contaminated by VOCs and heavy metals. The site comprises a single bank-side extraction well (now operational) that will be used for a long-term pumping test, during which hydraulic and chemical conditions within the hyporheic zone will be carefully monitored. A dense riverbed monitoring network comprising multilevel sampling points and piezometers for head measurements within the riverbed has been established along the adjacent 200 m long reach. A major water quality sampling round has recently been undertaken with analytical data pending, and preliminary data show a c.15 cm thick surface water-groundwater mixing zone with some evidence of locally deeper mixing zones with greater temporal variability. Spatial variability in hydraulic heads and hydraulic conductivities is also evident. An optimum extraction rate between 100 and 150 m/d is suggested from preliminary simulations investigating the sensitivity of hydraulic gradient to various hydraulic conductivities and extraction rates. The long-term extraction test is expected to begin in early 2008. By inducing a decrease in hydraulic gradients, it will increase the residence time within the hyporheic zone and may therefore enhance the attenuation potential.

The development of cost-effective approaches to monitor groundwater–surface-water exchange processes and contaminant fate within the hyporheic zone fundamentally underpins implementation of legislation such as the European Community Water Framework Directive, which requires integrated management of groundwater and surface water. Cost-effective mini drive-point piezometers (MDPs) and multilevel samplers (MLSs) are presented that use cheap construction materials, involve simple fabrication and installation procedures, and have a proven durability with low vulnerability to flood events and vandalism. They have been used across a range of hydro(geo)logical settings in the UK and proven to be effective in discerning flow exchange, geochemical trends, and contaminant transport and attenuation over monitored depths of 0.25 to 2 m at a resolution as low as 0.05 m. Example depth profiles, cross-river transects and river-reach longitudinal profiles from the River Tame catchment (West Midlands, UK) illustrate the value of MDP–MLS approaches in establishing surface-water–groundwater mixing zone depths, contaminant natural attenuation as a result of biotic activity within the hyporheic zone, and estimates of contaminant flux exchanges between groundwater and surface water. The MDP–MLS approaches allow discernment of contaminated groundwater plume discharges that may go undetected, or at best poorly resolved, if reliance was solely placed on conventional riverside monitoring wells and/or surface-water sampling. The MDP–MLS approaches described also have potential to be used in the investigation of shallow sediment aquifers, lake shorelines and wetland features.

Urban waste waters will often contain viruses, including human (and, topically, avian) viruses. Use of waste water in artificial recharge therefore requires a risk assessment of virus hazard, and establishing the knowledge needed for this in an example sandstone aquifer is the aim of the present SWITCH project (WP3.2). Presently there is some limited evidence that, even in predominantly matrix flow aquifers such as the Birmingham sandstone aquifer, viable human viruses can be transported to depths of at least 40 m. Horizontal transport distances are (even) less certain, but laboratory studies suggest survival times of < 2 years. To gain the knowledge necessary to develop rules for operation of AR schemes, a four-stranded approach is proposed: (i) field experimentation on a borehole array using bacteriophage as surrogates for human viruses; (ii) laboratory experimentation on intact cores; (iii) monitoring of virus concentrations at multi-level piezometers and pumping wells; and (iv) modelling. Work to date has concentrated on establishing the basic design of the field experiments, and has included hydraulic testing and checking for virus presence in the groundwaters of the test site.

In the last two years the city of Birmingham has witnessed the first steps in the development of a network of green roofs that are designed to mimic brownfield habitat (brown roofs) and compensate for its loss during redevelopment. As part of the SWITCH programme, a test array has been established at the University of Birmingham (UoB) that has undergone extensive monitoring since May 2007. This research is testing the potential of brown roof mesocosms, constructed from different mixtures of recycled aggregate, as habitat for brownfield plant and animal species, whilst fulfilling important roles in the sustainable management of urban water. In addition to this site, two, part SWITCH-funded (in association with landfill tax funding from SITA trust), demonstration brown roofs on the International Convention Centre (ICC) and Birmingham Volunteer Studies Council (BVSC) buildings were completed in August 2007. These roofs build on the design concepts used in the UoB design, but their large scale will allow the investigation of the importance of additional habitat resources, and provide an opportunity for the general public to see and appreciate ‘real’ brown roofs in action. This document describes: (1) the construction, monitoring and development of these brown roofs in their initial establishment phase, (2) reports the initial findings of the UoB research on the effect of substrate type on vegetation development, run-off quality and storm-water attenuation, and (3) describes the initial steps taken to enable the public and practitioners to gain first-hand experience of the make-up and benefits of green roofs.