Urban Metabolism: filling gaps in analysis

Urban metabolism, Ecological Footprints and Material Flow Analysis

Town planning is often a collection of disparate disciplines which are grouped together as much by the expedient of cost, as for any recognition that each section is actually related to the other.

For instance water supply and waste water may or may not be under the same management in a town or city. Sometimes they are even given out to entirely separate organisations by sub-contract. If you haven't thought they are related then at the very least there is a cause and effect relationship as every time you turn on a tap almost all of that water will end up nearly directly into waste water. Especially if you're:

• having a shower
• washing your hands
• doing the dishes (even in a dish washer)
• flusing your toilet (yes, it fills up from the tap)
• preparing or cooking food some pasta or noodles for instance

If you have trouble imagining this, put the plug into your sink, don't flush your toilet and block up your shower hole for a day. Imagine how it would be after a week. I think you can quickly see how important these things are.

Looking around in nature you'll find animals and plants all living together. Forests don't look dirty even though there's no taps, no one takes away the garbage or has a toilet. Mainly this is because the population density of the creatures which live in the forest is within the 'carrying capacity' of the environment. Carrying capacity is part of the method called "Ecological foot printing" which works out how much land is needed to provide for and assimilate the waste products of a city (or the urban footprint). Its a really interesting and revealing look out how much space our city really takes up.

We may think that our city sprawls over some dozens of square kilometers and we may be concerned about the impact of that on the environment. Wackernagel & Rees however in their book "Our Ecological Footprint: Reducing Human Impact on the Earth" show us that it extends to require much more than we actually see.

Knowing and understanding this is important in grasping our influence on the environment, but it doesn't really help us find ways to reduce it ... other than just saying "gosh, maybe we should use less"

What has this got to do with metabolism?

Consider for a moment two things one is your own body and the other is a large group of single cell algae living in a lake (say, here in Finland), both humans and algae are independent organisms which are alive. People however are made up of many different cells, while the algae are just clusters of exactly the same cell.

But the density of cells that makes up your body is enormous compared to what we would consider to be the most dense algal bloom in the lake.

In the small area of your body are millions of cells all living in just the same manner as the bunch of Algae on the lake. The algae could not ever hope to have the same density of population (a measure of success in some ways) because they have individual metabolisms confined to their own cells, your body on the other hand has an integrated metabolism which exists over and above the metabolism of any given cell in your body.

Key in this is that you have a circulatory system to carry nutrients and oxygen to the most inner parts of your body, and also to carry out waste.

Since the Algae do not have this they would start to die in their own waste products If one single system (such as your kidneys) were to stop working. I'm sure you would find your own body producing wastes well above what the cells can tolerate. If you've ever experience a power outage in your city, or had some water break down in your building you see pretty quickly that the same things seem to apply there too.

However it is exactly how our early cities, in medieval periods were built and operated. The European cities were quit filthy, often riddled with disease and the stink of garbage because there were no utilities such as waste disposal. In fact its not hard to imagine what it would be like to live in this manner now, as all you have to do is visit any large city in the developing world where budget is not spent on this sort of infrastructure.

So it is not just a loose metaphor to compare the metabolism of a city to that of your own body. At a different scale a city is indeed a collection of cells, each household can be thought of as a cell. Each apartment in a block, each home, each building is connected together by a network of pipes and wires which bring in water, energy, communication and dispose of wastes generated by those cells.

Without that we would be living in the wastes we produce ... sort of like these places.

Urban metabolism vs Material Flow

Material Flow analysis is a tool for understanding and tracking the flow of stuff and energy into and out of an ecosystem / city / environment. This is handy stuff, but in many ways its just inventory. It can be surprising to learn just how much and of what goes in and out.

Consider a basic analysis of water in the house, some 140 liters of water is needed by each person per day in the house, and you then need to dispose of about the same amount (yes, we keep very little of what water we put into our mouths). A curious researcher may extend this to wonder about energy, and wonder how much energy is used by our community. What Materials Flow doesn't provide is a basis for logically relating these informations.

For example if we consider the metabolism of water But it doesn't just end there, getting water to you requires energy, as does removing waste water. Processing waste water is even more costly than the process of carting it away. In fact in a typical urban situation the cost of waste water removal and processing is about 75% of the costs.

Yes that's right. To give a concrete example from a large Australian east coast city in 2005:

• disposal of sewage accounted for 78% of the electricity usage of
• while supply and treatment only required 22%.

With only 67KWh consumed per property in water supply yet 255KWh per property in waste water treatment per year.
Part of the reason for this is the linear flow of water, and part of it is related to our historical use of gravity to supply water, thus assisting the costs. Dams are a major supply of water in countries like Australia.

This may be different in countries like Finland which rely more on ground water (which must be pumped up from the ground). Perhaps there the water supply costs would be higher as gravity is not really being employed to assist.

Either way it follows the pattern in the figure to the left of drawing water from the source, treating it and providing it for use. Then after use waste water is treated (thank god we've started doing that, many places still dispose of sewage raw) and then disposed of into the environment again.



Putting a metabolism spin onto this view, lets consider the city as something like a tree. A collection of cells, depending on water from the roots and a system of pipes (xylem) to transport the water to where its needed like the leaves (households and properties).

In this way we get a model rather like this one on the left.

It seems similar until you realize that plants go to great lengths to stop water loss at the leaves. They have mechanisms to prevent it (such as closing the stomata). As well water is reused in their metabolism as a normal practice. Plants are actually so effective with their metabolism of water that if they have CAM metabolism they can get by on almost no water inputs at all.

This is where making using a model for analysis which makes comparisons to natural systems brings its other advantages over simple scientific analysis. It facilitates comparison with already working and proven successful systems.

Putting metabolism to use

Could we reuse water?

Sure, what would stop you from saving the shower water to water your plants (why put good high quality treated drinking water onto the plants), or your could save it to use to flush your toilet.

If you did more than one load of washing at a time then rinse water could be reused to mix with detergent in the next wash cycle ...

all this stuff has been and is done by people who live in places where water is in short supply. Heck if you've ever stayed in a cottage or gone camping where you have to draw water from a well I'm sure you've learned to be frugal with it.

As well municipalities are now starting to treat waste water to higher qualities and using it themselves and distributing it to other users for non-drinking purposes (like watering local parks / golf courses / washing roads and dust control on dirt roads.

Metabolically on site water reuse is different to the reuse of water collected by the town and redistributed.

Water reused on site like the washing water requires far less energy, remember the costs of waste water disposal above. But rather than simply dispose of it we can still put it to use.

I've represented this in the diagram to the left.

This not only makes greater use of the water resources we have, but reduces greatly the impacts on the environment of disposing of the wastes.

Following practices like this we can transform our cities into much cleaner places for us just like our kidneys transform the concentrations of waste products in our blood increasing our bodys ability to tolerate the dense cellular population.

multicellular organisms

I think one of the key observations in biology is to discover how complex single cell organisms actually are. Protists in particular are quite complex creatures with distinct observable behavior and complex morphology.

As humans we're clearly multi-cellular organisms, but an interesting view on this is that as humans we are complex members of an even more complex society.

Just as our bodies are composed of organs, which are in turn composed by cells (all of which share a common DNA) our society is composed of organizations and bodies (which essentially consist of rules and definitions) and bound into corporeal form by the law and a common factor of humans (us) to be the 'agents' which carry out the functions of the organization.

If this seems a bit 'far fetched' reflect for a moment on the fact that we regularly describe organisations using vocabulary which comes from nearly the same set as that which we use to describe organisms. Even the nature of the words are similar:

organisation <=> organism

However as the organizations and bodies do not (as yet) think for themselves they rely on us to do their thinking, and so it is valuable if we can think as an organism not as a cell when working within the organisational roles we have.

This viewpoint is one such viewpoint which is facilitated by Urban Metabolism and lends itself nicely to examine (for instance) the operations of a city.

If you're finding it hard to comprehend this try looking at a wonderful new tool like Google Maps, pick a city which you know, and zoom in until you start to see blocks beginning to be separated by streets. It doesn't take much of a leap of imagination to begin seeing streets as vessels of transportation and if you could see the reticulated water and sewage system overlaid on that map then you'd clearly see this as a vascular system.

Viewed this way its easy to see how the organisation of a city can resemble the organisation of a complex multicellular organisation / ism.


Brisbane City at Night
slowing down our time scale shows the cars on the road as like streams though a vascular system (in this case the road). Like all models one of the purposes for representation is to facilitate our understanding of things (not just to have fun), because we (as humans) seem to have a lot of problems understanding what it is that we can't see.

Just look at recent biological history, before we had microscopes and understood that there were micro-organisms we invented all manner of concepts to explain their effects. Without the right way of looking at things we struggle to understand what may from another perspective appear obvious.

Because water (and sustainable use of water) is my personal topic of interest I see great benefits in examining the cities use of water from this perspective.

Multicellular organisms are composed of single cells, which bear great resemblance to eukaryotic organisms. However significantly they can exist in much greater densities than single cell organisms are able to. For example, in our own bodies there are something like more than 50 trillion cells (that's 50 million million folks). This is concentrated in quite a dense area and if it were not for some complex specialisation of roles and development of systems then they would simply not be able to survive in this density.

Now look at human development, as we begun to develop the world around us (to be more suitable) we added structures and created environments to shelter us and look nice.

We wanted gardens and cover from the rain, dry place for bedding (away from pests and parasites) as well us being social creatures we kept living together in communities much like this example.

But just like the problems which a single cell organism faces this all starts to fall apart when population densities grow. Without a system of planning, a method of waterprovision and proper waste disposal we move quickly to areas which look more like this:

Which are no longer nice, no longer separate us from disease and parasites and in fact open us up to problems.

Its easy to forget that Europe was much like this in the period before the Industrial revolution. Its easy to take for granted all the adaptations and changes we have made as a society to enable us to live together in larger and larger groups (could anyone have imagined the population of London being over 7 million people (that's nearly 5 thousand people per square kilometer). Without our sophisticated systems of water provision and waste disposal we would not be able to be living in such a way.

This brings me back to my diagram of a tree (representing plants).

Much like a city a plant is a complex multicellular organism which depends on the environment for its water supply. It gathers water through the roots and channels it through vessels to the sites of metabolic activity, but unlike a city a plant is very particular on how it manages its water. Water out of the system is mainly losses through expiration losses metabolism of water in the Criric Acid cycle.

Both the City and the plant use water and depend on it for the existence, but the tree however is not only more frugal with its water, but has a much greater diversity of mechanisms for reducing water losses and coping with reductions in supply of water.

So, what has this got to do with administration of a city?

Firstly it has to do with choice. A main purpose of science is to study the world in order to be able to make accurate predictions; like "will that bridge collapse if 30 people walk across together". Much of science and our engineering knowledge has come from observations of nature in just this sort of way. By making an analogy (or building a model) with a natural system we can look to see what works in nature and what doesn't.

For example if a plant places all its dependence on water from what it obtains via the roots what happens if one year there isn't enough water in the environment?

Well, some plants will die, some plants will diminish their growth, perhaps only some parts dying.

If such a thing happens to a city (not having enough water) what will reaction of the city metabolism be?

Is it acceptable for parts of the city to die? Remember, that's people we're talking about now, not just cells.

Such a thing can happen and has happened many times in human history. In recent memory the cities have been towns and they could either ship in more water (essentially extending their root system successfully) or they could diminish in size and perhaps even vanish off the map (with the people moving away). If the city is substantially large, and has importance to the broader community then other solutions must be found. These can be expensive.

Such an example can be found in South East Queensland with the 'drought' of 2002/2003 when the city of the Gold Coast came within very close margins to having a failure of the city water supply (IE the dam nearly dried up). The response was to extend pipelines to other dams in the region and undertake an expensive water grid upgrade in order to source more water. As well restrictions were placed on the use of water by the residents.

Essentially in metabolic terms the reaction was control metabolic activity (with economic consequences) and attempt to extend the 'root system'.

The first strategy is not something which is by any vision sustainable, and the second worked in the short term until the water supply started to dry up in more of the region meaning that other 'organisms' could not lend a hand any more.

At this point two strategy's were considered:

1. obtain more water
2. recycle more water

Strategy 1 would be essentially attempting to further extend the root systems, and the approach of generating water by obtaining water from the ocean. While this is a plentiful supply of water it brings with it a problem: salt. The resulting "desalination" plant proposal has to this point in time (some 5 years after its mooting) failed to contribute to the water supply, cost many millions of dollars and will ultimately result in increasing the energy needs of the city by a very large and significant factor. Hey, this has a metabolic equivalent too!

Strategy 2 seems to be attractive, but there are a number of legislational issues which encumber this (in place for good reasons such as human health).

A quick look around the plant kingdom suggests a few other methods for solving the problems after all Mangroves (once so common on the Gold Coast) live in salty water and and Bromeliads still common in the rainforest (and hey, who can forget such a prominent example of a Promelaid, the Big Pineapple, if you've visited the sunshine coast) provide excellent examples of what a plant can with less water as well as how to get more when there is nothing available to the roots.

Summary

Hopefully I've been able to provide an example of how urban metabolism can be used not only as a metaphor for the logical grouping of city needs and wastes for analysis (such as material flow analysis, which is something which perhaps also stems from Wolmans works). Gradually I hope that I have been able to share a little of the concepts and advantages confered by the metabolic viewpoint for systems planning.