Basics of qualitative research: Grounded theory procedures and techniques

The term ''urban stream syndrome'' describes the consistently observed ecological degra- dation of streams draining urban land. This paper reviews recent literature to describe symptoms of the syndrome, explores mechanisms driving the syndrome, and identifies appropriate goals and methods for ecological restoration of urban streams. Symptoms of the urban stream syndrome include a flashier hy- drograph, elevated concentrations of nutrients and contaminants, altered channel morphology, and reduced biotic richness, with increased dominance of tolerant species. More research is needed before generaliza- tions can be made about urban effects on stream ecosystem processes, but reduced nutrient uptake has been consistently reported. The mechanisms driving the syndrome are complex and interactive, but most impacts can be ascribed to a few major large-scale sources, primarily urban stormwater runoff delivered to streams by hydraulically efficient drainage systems. Other stressors, such as combined or sanitary sewer overflows, wastewater treatment plant effluents, and legacy pollutants (long-lived pollutants from earlier land uses) can obscure the effects of stormwater runoff. Most research on urban impacts to streams has concentrated on correlations between instream ecological metrics and total catchment imperviousness. Recent research shows that some of the variance in such relationships can be explained by the distance between the stream reach and urban land, or by the hydraulic efficiency of stormwater drainage. The mech- anisms behind such patterns require experimentation at the catchment scale to identify the best management approaches to conservation and restoration of streams in urban catchments. Remediation of stormwater impacts is most likely to be achieved through widespread application of innovative approaches to drainage design. Because humans dominate urban ecosystems, research on urban stream ecology will require a broadening of stream ecological research to integrate with social, behavioral, and economic research.

https://www.jstor.org/stable/10.1899/04-028.1

The urban stream syndrome: current knowledge and the search for a cure

Membranes have an increasingly important role in alleviating water scarcity and the pollution of aquatic environments. Promising molecular-level design approaches are reviewed for membrane materials, focusing on how these materials address the urgent requirements of water treatment applications.

Materials for next-generation desalination and water purification membranes

As photovoltaic penetration of the power grid increases, accurate predictions of return on investment require accurate prediction of decreased power output over time. Degradation rates must be known in order to predict power delivery. This article reviews degradation rates of flat-plate terrestrial modules and systems reported in published literature from field testing throughout the last 40 years. Nearly 2000 degradation rates, measured on individual modules or entire systems, have been assembled from the literature, showing a median value of 0·5%/year. The review consists of three parts: a brief historical outline, an analytical summary of degradation rates, and a detailed bibliography partitioned by technology. Copyright © 2011 John Wiley & Sons, Ltd.

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Photovoltaic Degradation Rates—an Analytical Review

In the last few decades, pharmaceuticals, credited with saving millions of lives, have emerged as a new class of environmental contaminant. These compounds can have both chronic and acute harmful effects on natural flora and fauna. The presence of pharmaceutical contaminants in ground waters, surface waters (lakes, rivers, and streams), sea water, wastewater treatment plants (influents and effluents), soils, and sludges has been well doccumented. A range of methods including oxidation, photolysis, UV-degradation, nanofiltration, reverse osmosis, and adsorption has been used for their remediation from aqueous systems. Many methods have been commercially limited by toxic sludge generation, incomplete removal, high capital and operating costs, and the need for skilled operating and maintenance personnel. Adsorption technologies are a low-cost alternative, easily used in developing countries where there is a dearth of advanced technologies, skilled personnel, and available capital, and adsorption appears to be the most broadly feasible pharmaceutical removal method. Adsorption remediation methods are easily integrated with wastewater treatment plants (WWTPs). Herein, we have reviewed the literature (1990-2018) illustrating the rising environmental pharmaceutical contamination concerns as well as remediation efforts emphasizing adsorption.

Pharmaceuticals of Emerging Concern in Aquatic Systems: Chemistry, Occurrence, Effects, and Removal Methods.

This paper describes a life cycle costing module that has been developed as part of the Model for Urban Stormwater Improvement Conceptualisation (MUSIC). MUSIC is a pollutant export computer model that is used by stormwater managers during the conceptual design stage of projects to determine appropriate treatment options. The life cycle costing module allows users to enter size-related details of a proposed treatment measure (eg. the area of a stormwater treatment pond) to estimate the measure’s approximate life cycle cost, as well as “cost elements” that make up this cost (eg. total acquisition cost, typical annual maintenance cost, etc.).

Estimating Life Cycle Costs of Stormwater Treatment Measures

Green roofs can be used to reduce the volume of polluted stormwater that is generated by cities. Modelling rainfall retention is critical, but green roof water balance models often rely on the physical properties of substrates. In these models, substrate water holding capacity (WHC) determines the depth of water which can be stored before runoff is generated; whereas, the permanent wilting point (PWP) limits evapotranspiration. The WHC and PWP, as well as plant available water (PAW; where PAW = WHC − PWP), as determined from laboratory tests, may not truly reflect how substrates perform on green roofs. We therefore ran a simulated rainfall experiment on green roof modules to (i) compare the rainfall retention of vegetated and non-vegetated substrates with different WHC and PAW, and (ii) relate retention to substrate storage capacity, as calculated from laboratory measures of WHC and PAW. We found that the PAW of a substrate is a better indicator of evapotranspiration and retention when compared with WHC. However, we also found that substrates always retained less water than their calculated storage capacity would suggest, most likely being due to their high permeability. Our results indicate that using laboratory-derived measures of WHC and PAW in green roof models may be over-estimating both evapotranspiration and rainfall retention.

Laboratory Tests of Substrate Physical Properties May Not Represent the Retention Capacity of Green Roof Substrates In Situ

This paper tests a simple two-parameter regression model, based on rainfall intensity, for calculating event loads of total suspended solids, total phosphorus, and total nitrogen from urban catchments. It also examines the sensitivity of the model to its two parameters and to the rainfall time step. This was done by using large data sets collected at six urban catchments in temperate Melbourne. It was found that the two-parameter model typically explains approximately 90% of the variation in event loads at a site. The model also predicts the within-event behavior of pollutants when the flow lag time is taken into account, with R2 correlations greater than 0.6 in most cases for both loads and concentrations at a six minute time step. Despite its acknowledged correlation with flow, rainfall intensity over short time steps is shown to be the primary driver of pollutant mobilization, and provides a practical means of predicting pollutant loads by using readily available data.

Testing and Sensitivity of a Simple Method for Predicting Urban Pollutant Loads

Reliable estimation of evapotranspiration is important for many hydrological applications, including agriculture, climatology, and assessment of stormwater control measures. An automated chamber system was constructed to measure field evapotranspiration. The system consists of six chambers, sampled consecutively by means of a dynamic closed-chamber design, and is fully automated to allow replicable long-term measurements. However, the use of such a system is subject to measurement errors due to vapor adsorption along the sampling tubes and inappropriate internal ventilation. Because these issues are rarely addressed in the literature on flux chambers, a laboratory calibration was performed to estimate errors in evapotranspiration rates measured by the system. The effects of the sampling tube length and air mixing were investigated. A correction factor for evapotranspiration rates relative to the tube length was established. Appropriate air mixing induced by small fans ensured that the measured rates were representative of the internal conditions of the chambers. With appropriate internal ventilation and correction factors, the relative error of measurements was less than 5% for high evapotranspiration rates.

Automated Chamber System to Measure Field Evapotranspiration Rates

A key feature of biofiltration systems, or 'raingardens', is the modification of the local water balance through the enhancement of the infiltration and evapotranspiration fluxes. Thus, widespread implementation of raingardens has the potential to bring the catchment water balance closer to its pre-development state. However, the magnitude of these effects is still unclear, partly because of uncertainties in the water budget of individual raingardens. Since July 2011, two raingardens have been monitored in a residential area 40 km east of Melbourne, Australia, with the aim to determine the volume and fate of infiltrated water. The two sites differ in terms of topography and surrounding vegetation, with one bordered by short lawn grass and the other featuring a mix of clovers and tall grass. We measured the soil moisture profile at different distances from the raingardens to i) determine the lateral influence of the biofiltration system on soil moisture and ii) infer the enhancement of evapotranspiration due to the increased soil moisture. During the wet season, the results suggest an absence of water stress for surrounding vegetation even in the absence of a raingarden, meaning that nearly all the infiltrated water seeped to recharge groundwater. The total evapotranspiration flux of the raingarden itself is thus very small, limited by the raingarden area. However, in drier conditions, the system may enhance the evapotranspiration rates of its surroundings, particularly where nearby vegetation has high transpirational demand.

Tim D. Fletcher

Papers

Estimating Life Cycle Costs of Stormwater Treatment Measures

Laboratory Tests of Substrate Physical Properties May Not Represent the Retention Capacity of Green Roof Substrates In Situ

Testing and Sensitivity of a Simple Method for Predicting Urban Pollutant Loads

Automated Chamber System to Measure Field Evapotranspiration Rates

Water retention by raingardens: Implications for local-scale soil moisture and water fluxes