R. Brian E. Shutes

The impacts of urban discharges on the hydrology and water quality of an urban watercourse

Abstract This paper presents the findings of a study which has investigated the effects of urban discharges upon the hydrology and water quality of a small urban watercourse located in north London. A variety of hydrological variables and water quality parameters were monitored at a site downstream of two surface water outfalls (SWOs) and two combined sewer overflows (CSOs). Precipitation volume was found to be highly correlated with the total storm discharge ( r 2 = 0.91) and the duration of storm flow ( r 2 = 0.93). Precipitation intensity displayed a 0.67 level of correlation with peak discharge volume. Aqueous loadings of biochemical oxygen demand (BOD), nitrate, chloride, total ammonia, suspended solids and total and dissolved zinc, copper, cadmium and lead, increased during the five monitored storm events. The highest increases in pollutant loadings compared with dry weather values were associated with BOD and suspended solids.

CONSTRUCTED WETLAND CONTROL OF BOD LEVELS IN AIRPORT RUNOFF

A surface water treatment system consisting of an aeration reservoir and pond (holding capacities 45,000 and 19,000 m3) and a network of 12 horizontal subsurface flow gravel-filled constructed wetland cells of different sizes (total surface area 2.08 ha) and planted with Phragmites australis, was commissioned at Heathrow Airport, London, United Kingdom, in the winter of 2002. Ongoing monitoring of the treatment system has shown significant reductions in the biochemical oxygen demand (BOD5) throughout the system with levels decreasing by up to 76.7% across the constructed wetland cells following high anti- and de-icing fluid applications. However, continued exposure to BOD5 concentrations exceeding the design target has resulted in anaerobic conditions in the wetland. The addition of nutrients to the treatment system has resulted in improved removal efficiency for elevated BOD5 loadings in the aerated reservoir from 25.5% to 47.5%, The addition of different nutrient dosing regimes to complementary pilot-scale planted and unplanted vertical flow columns showed average but statistically insignificant BOD5 removal percentage increases from 61.9 ± 21.1% to 70.8 ± 26.5%, respectively, in planted columns over a 7-day period. There is an overall improvement in the performance of the system, but operational reviews are continuing.

Planting woody crops on dredged contaminated sediment provides both positive and negative effects in terms of remediation.

There is currently a requirement for studies focusing on the long-term sustainability of phytoremediation technologies. Trace element uptake by Salix, Populus and Alnus species planted in dredged contaminated canal sediment and concentrations in sediment and pore waters were investigated, eight years after a phytoremediation trial was initiated in NW England. Soil biological activity was also measured using invertebrate and microbial assays to determine soil quality improvements. Zinc was the dominant trace metal in foliage and woody stems, and the most mobile trace element in sediment pore water (~14 mg l(-1)). Biological activity had improved; earthworm numbers had increased from 5 to 24, and the QBS index (an index of microarthropod groups in soil) had increased from 70 to 88. It is concluded that biological conditions had improved and natural processes appear to be enhancing soil quality, but there remains a potential risk of trace element transfer to the wider environment.

Environmental factors influencing the prevalence of respiratory diseases and allergies among schoolchildren in Chiang Mai, Thailand

Air quality has seriously deteriorated as a consequence of population growth and urbanisation and respiratory diseases increased among residents of urban areas in Chiang Mai Province, Thailand. An International Study of Asthma and Allergies in Childhood (ISAAC) study was conducted among children attending schools located in the selected sites to assess the potential impacts of air pollution on health. The results showed that the prevalence of asthma was similar in all of the schools (approximately 5%; p = 1.000) but that the prevalence of rhinitis [24.3% (CI = 19.4–30.1) vs. 15.7% (CI = 10.3–23.0); p = 0.029] and atopic dermatitis [12.5% (CI = 9.1–16.8) vs. 7.2% (CI = 3.7–12.6); p = 0.093)] was higher in the urban schools, which were exposed to more pollution. Logistic regression analysis identified factors that may be involved, including air pollution, some components of the diet and contact with animals.