Sustainability is so malleable and ubiquitous a concept that it invites immediate skepticism. It enjoys a degree of political traction, and invokes a sense of urgency which sometimes obscures the extent to which sustainability, and its underlying pillars, are analyzed and understood as products of social, as well as ecological, dynamics. Why is a shared vision of sustainability so elusive, especially given that it is so widely invoked? The concept of sustainability has three dimensions—metaphor, meaning, and model. As a metaphor, sustainability conjures up images of healthy environments, wise and equitable use of resources, socially cohesive communities, and persistent economies. Sustainability, however, must move beyond metaphor and towards clear definition, or meaning, in order to set goals and ultimately assess whether or not those goals have been met. It is for this reason that situating sustainability is crucial. It is only when the motivations and corresponding goals are articulated, and the spatial and temporal scales determined, that sustainability is situated and, with a shared vision of sustainability, action can be taken. Models of sustainability represent a specific situation and establish the domain of the topic under consideration in a specified set of circumstances or a demarcated spatial area.
Sustainability is not solely a scientific concept. It draws on ecological concepts and processes but incorporates social perceptions and values. Sustainability consists of three pillars popularly referred to as the 3 E's: economy, environment, and equity. We adopt a broader conception of these pillars as human well-being, ecological integrity, and equity and translate them into the corresponding theoretical realms of ecosystem services, resilience, and environmental justice, respectively. To operationalize sustainability, two things must occur. First, it must be situated in time, place and motivation. Second, indices or benchmarks must be established so that progress towards specified goals can be measured. Despite the need for measurables, sustainability is not a fixed state or something achievable per se; rather it is more usefully thought of as a trajectory along which the balancing of tradeoffs and synergies among goals results in making systems relatively more sustainable. We will employ the three theoretical realms and provide an example of situating sustainability within the context of enhancing the water quality of the Chesapeake Bay to sustain aquatic life and important fisheries as a case study.