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Lecture 9

GGRA03H3 - Lecture 9.docx

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University of Toronto Scarborough
Andre Sorensen

GGRA03H3 – Week 9 – Urban Ecosystems, Pollution Urban Ecosystems - During the last 15 years, new understandings of cities as complex ecosystems have developed o Cities are now seen as complex systems with their own metabolic processes o They have huge inputs and outputs that are structured by metabolic processes of production, delivery, consumption, and waste emission. o Inputs and outputs can be measured and can be influenced by public policy - It is critical to understand the nature of the inputs and outputs. Urban Metabolism - The concept of Urban Metabolism is a model that describes the flow and transformation of materials and energy within cities. - Energy, goods, water, food, and materials are imported by cities, transformed (metabolized), and other products and wastes are exported. - Urban Metabolism describes the full set of the technical and socio-economic processes that occur in cities, including the production of energy and disposal of wastes Political Ecology Perspective on Water - Political ecology starts with the assumption that cities include multiple metabolic processes - Processes of socio-environmental change are never neutral, but are mediated by politics and power, with particular arrangements providing benefits for some, and costs for others. th - Rapid urbanization in the 20 century meant a huge growth of demand for water, and expansion of the water frontier of many cities. - This has led to growing conflicts over water and waste-water in rich and poor countries. Water Inputs and Outputs - Water is one of the most important urban inputs - Polluted water is one of the main urban outputs th - One of the key achievements of the 19 century ‘sanitary revolution’ was the development of public water supply and wastewater removal infrastructure o Sewage Systems - Initially just pipes to dump the water downstream, later primary treatment, secondary treatment, tertiary treatment systems were added. o Primary – Screen filters, settling ponds o Secondary – Active digesting of nutrients with bacteria, aeration. o Tertiary – treatment for toxic wastes, heavy metals, pharmaceuticals, etc. Current Water Challenges - Are partly a consequence of dominant sewer technology - Combined sanitary and stormwater sewer systems used one set of pipes for all wastewater in cities - Works well in dry weather, but heavy rain events routinely overload the system and water is released into streams, rivers, lakes o When snow melts, it creates large bodies of water that flows into streams, rivers, etc. - Millions of gallons of untreated waste into water bodies. - Gradually, cities are rebuilding systems to separate sanitary and storm sewers. - And storage for stormwater surges. Key Concept 1 - Cities are now seen as ecosystems, with inputs, metabolic processes, outputs o They have huge inputs and outputs, that are structured by metabolic processes of production, delivery, consumption, and waste emission o Inputs and outputs can be measured and can be influenced by public policy. o In 20 century, a big issue was water supply and waste water management, in terms of quantity and quality. o Now key policy issues relate to managing flows through cities, how inputs are transformed and quality of outputs. Current Water Challenges 2 - Point-source and non point-source - Point sources are those where there is a clear point of discharge o E.g. Factories, sewers, etc. with a pipe that discharges liquid wastes - These are relatively easy to monitor, and there has been considerable progress in cleanup. - Non point-source pollution is everything else, including pesticides and fertilizers on lawns, dog feces, and pollution on roads (antifreeze, brake fluid, gasoline, tire rubber), particulate pollution that settles from air o Cigarette butts are also an example Current Water Challenges 3 - Non-point source pollutants include wastes dumped into sewer systems where the source cannot be identified - What besides human wastes get dumped into sewers? - Use of municipal sewage sludge for fertilizer spread rapidly since the 1990s (as alternative to landfill and incineration) - But includes volatiles, organic solids, nutrients, disease-causing pathogenic organisms (bacteria, viruses, etc.), heavy metals and inorganic ions, and toxic organic chemicals - Problems with drugs – 70-90% not metabolized, endocrine disruptors. Rain as Pollution - Why would rain runoff be considered pollution? - Problems of hard surfaces in cities, and greatly increased storm water surges. - Overloaded treatment plants, flooding of urban rivers and creeks - Toxic chemicals on roads o Gasoline, antifreeze, salt, etc.  Get washed into sewers with rains or nearby creeks - Major investments are made to reduce storm water surges o Retention ponds, buffers along streams, green roofs, disconnect downspouts, soakaways. Key Concept 2 - Water pollution is a major concern for urban ecology o In most of the developed countries, the focus of policy has shifted from point- source pollution (fairly successfully regulated) to non-point source emissions o Non point-source pollution includes pesticides, herbicides, dog shit,
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