Selecting methods [part 1]

For the next several posts I will talk about the process of method selection.

Method selection is tricky in general, but it seems particularly challenging when studying a complex socio-ecological system like a city, and a resource (P in my case) that is affected both by biophysical and by sociopolitical factors. I think it gets even more complicated because the methods you use also depend on the skill sets you have, collaborators and facilities you have access to, and what you want to learn.  Obviously methods, first and foremost, need to be appropriate to answer the research questions.

In my case, I felt that the questions that interested me about the importance of local context on urban P cycling and the role of urban agriculture could require both natural science and social science methods. I wanted (and still want) to measure the flow of P in the urban ecosystem (natural science), and I wanted to understand the context that may be influencing the flow of P (social science). The division wasn’t that clear after all.

In order to carry out my research I selected the flowing strategies:

 Case study comparison

I selected 6 cities, in fact 2 clusters of 3 cities, to be able to compare P cycling, UA, and P recycling between and within the clusters, getting a better idea of the importance of local context. Although case studies are used both in natural and social sciences, it seems that the literature on case studies, when you are involving people in the system (and cities do have a lot of people in them!) as a method is more developed in the social sciences ( I used this book as a guide).

 Substance Flow Analysis

In order to compare P in the case studies I decided to use Substance Flow Analysis (SFA is used in both Industrial Ecology but also in Ecosystem Ecology, here are some papers that do it for N and P here, here, here, here, and a summary of the use of urban metabolism and SFA are here and here).  It’s a method I am familiar with, as I used it in my master’s degree. I decided to do SFA on the food system of a city (not the city as a whole) to match my research questions and minimize unnecessary data collections (more on that in another post).

Basically for SFA of P you need to know:

  1. The boundaries of your system (physical, temporal, and theoretical)
  2. The amount of organic material and fertilizer (entering the city, being moved around in the city, and exiting the city as waste, pollution, or as a productive output)
  3. The amount of P in each one of these flows

In order to get these data you could

  1. Look at the peer-reviewed literature and official city, organizations, or company documentation
  2. Collect secondary data by asking stakeholders (people that participate in the food and waste system of the city) through surveys and interviews about what they know about the flow of these materials and P concentrations
  3. Collect primary data by going around and collecting your own data with field measurements and lab tests (both flow of material and the concentration of P).

 Local Context

In order to examine the effect of “local context” it seems that you first have to define what local context is in the framework of your questions (more on a post about what am I really measuring).  I see three broad ways to look at it.

  1. Literature review on studies where their explicitly interviewed people about why they do what they do.
  2. Review of “larger scale” official data about the city as a whole. For example, temperature, socio-demographic data or survey data on practices carried out by cities or other organizations.
  3. Collect your own interview and survey data about motivations, barriers, and facilitators.

I think it’s important to note that these methods are not mutually exclusive and that in order to triangulate bias (jargon word that means trying to better understand a system or event from more than one perspective) you need to use more than one method.  It also important to note that not all these methods measure the same thing, and that taking into consideration limited financial and time resources excludes some of these methods from being  “fully” carried out.


New York City (left) and Montreal (right), two of my case studies cities, on a cloudy day. They have some similar local context (both islands), but are also different. Looking at P cycling and UA will be exciting in both cases!


Research questions

So now we (well me at least) think the subject matter is very interesting. But what research questions are interesting and answerable within the context of a PhD?


I will not go into detail about my specific questions, but I thought I could at least give an overview of the process of getting from a general idea to something that ends up in a paper. There are great books that give suggestions about how to write a dissertation and go about choosing a question (e.g. here). Here is my personal experience.

I think I started out with something I thought was a research question, but really was a career research focus. My advisor was amazingly helpful at making me come down to more reasonable questions that might work within my time-frame and build towards that larger career research goal. Some of the things that help me focus my questions were:

  1. Trying to tease apart a larger research question into smaller sub-questions
  2. Thinking of each sub-question and an associated method(s) to answer it
  3. How much time would it to carry-out those methods to legitimately answer the question.
  4. Start over (one of the sub-questions is now really a “large” question I have to widdle down)

In order to prepare my thesis proposal I went through the list above more than once. Each time doing more reading on methods to be sure I was selecting appropriate ones to answer my questions.

I felt like I had a good and feasible plan when I defended my proposal in front of a committee of professors. Still, as I now delve more deeply in to my chapter on agriculture and cities, I find myself having to narrow my questions even more, and having to change my methods to better answer those questions within reasonable time delays.

What is phosphorus sustainability?

Let me start out by saying that P sustainability is simple and complicated at the same time. I will start with a “simple” idea and work through some of the key complexities. There is much more to be said so if you are interested follow some of the links or google it. (At some point this year a book is going to come out about all this, which a co-authored a couple of chapter in, and I will put the link up as well).

Phosphorus, as an essential resource and a pollutant, has been “on the map” for a while (for certain interest and research groups in agriculture and ecology). I would say that in our “modern” time, Dr. Dana Cordell has been a pivotal figure in bringing the current problems with P management to light and has been the impetus for bringing many actors to converge on the idea of sustainable P management.

Her 2009 paper “The story of phosphorus: Global food security and food for thought” (here) was my first real exposure to a whole-system perspective on P management. This article gave me a subject (P) with which I could integrate both my knowledge in ecology and environmental science, and my desire to do solution-oriented research in urban environments.

In her PhD thesis Cordell (2010) defines P sustainability as “all the world’s farmers have access to sufficient phosphorus in the short and long term to grow enough food to feed a growing world population, while ensuring farmer livelihoods and minimising detrimental environmental and social impacts’’

I believe her’s is a nice overarching definition, explicitly putting human well-being at the forefront, and acknowledging the necessity for a “healthy” environment which we ultimately depend on. Still, there is quite a gap between the idea of sustainable P management and the right research questions to facilitate effective management strategies and actual implementation by decision-makers. I think a big part of our knowledge gap stems from the reality that specific P management problems and solutions are complex and depend on what scale (both geographical and temporal) you decide to explore.

In my research I am interested in looking at the regional scale but this implies looking at some cross-scalar issues. Any one location is dependent on some lower scale properties, for example soil type is very important in determining P requirements, and larger scale properties, for example the price of mined-P fertilizer in any location is dependent on global trade and national policies. I could go on about this complexity, but to keep it brief I would say the understanding the context, whether it be biophysical or social in nature, is one of the key areas we need to research in order to make more sustainable P management a reality. Also, I would like to point out increasing P sustainability by increasing efficiency and recycling in the food system does not make P-mining obsolete (for example here). There will always be some losses of P that must be replaced and there are places in the world, notably sub-Saharan Africa, where more P fertilizer is currently needed but  don’t have physical or economic access.

I will allow myself one more point: there is no “magic bullet” to sustainable P management. I think it will require us to use many tools in our arsenal to change how we manage food production, food consumption and waste.  We also need to think about P at the same time as we think of other important sustainability issues.

p sustainability

Side note: I don’t think we need to get into the issue of peak P to talk about P sustainability. Yes, the numbers have changed since the “initial” Cordell et al. 2009 publication (here and here) and there are numerous papers debating the validity of the idea (here, here), but in my mind (and of others) the issues remain largely the same even without looming peak production (here).

Background before questions and before methods

Before I delve into the exciting journey of selecting and carrying out some data collection methods, I thought it would be helpful to start with some background to explain why I do the research I do.

Why phosphorus?


P is an essential resource for all living things (from plants to humans) and it is not substitutable.  Human management of P resources has become problematic. Unlike “natural” ecosystems, which recycle the majority of their P, humans use P in a one-way flow from mines to the ocean.

The major use for P is in agricultural production, which if fine in itself as plants need P, but along each step of the food chain we incur significant losses.

The problem with P management in our food system double sided: it is in limited supply but there is also too much P is some places. We need concentrated P to apply as fertilizer. We mine high-P deposits to make fertilizers, but these high-grade mined reserves are finite and they are also geopolitically concentrated. We are thus faced with both physical and economic scarcity of a non-substitutable resource that is key to food security. On the other hand, looses of P from mining, from agricultural fields, from food processing, and from wastewater treatment plants can accumulate in water bodies downstream.  Such a high concentration of nutrients in a water body allows for algal blooms, which can be toxic, and can lead to hypoxic zones (too little oxygen) where nothing can live.

We can change the way we manage P though. We can decrease our use of non-renewable P and decrease pollution by increasing efficiency and recycling through the food system. There is great research going on around the world in many fields to make P management more sustainable.  There are a few networks of scientists, practitioners, and decision-makers trying to bring some of these research efforts together including the Sustainable Phosphorus Initiative based at Arizona State University, Global P Research Initiative from University Technology Sydney in Australia and other partners, the Dutch Nutrient Platform, and Global TraPs from Zurich, Switzerland.

Why cities?

Cities are a key step in the movement of P across the global food landscape. They concentrate the demand for food and thus P. Cities also concentrate the production of high P waste, through the waste of food but also human waste (we excrete 98% of the P we eat), contributing to pollution downstream. I think there is great potential for cities to recycle their high-P waste, thus contributing to urban food security by decreasing dependence (and price fluctuations) on mined-P resources.  Urban and peri-urban agriculture (info here) may play a role in more sustainable urban P management, along with other practices and behaviors, but we need more information.

In order to improve how we manage P we need to look at how humans and ecosystems have cycled P in the past and how P is cycled today, in addition to thinking about the future. P management is complex because it is linked to the management of many other resources (including nitrogen, carbon, water, and land just to name a few).  P management is also complex because we must look at the global picture while considering local variability which arises from different ecological and social contexts and different needs. It’s simply fascinating! Next I will try and delve in to what I mean when I say I am working on “sustainable phosphorus management”.