In an urban ecosystem justice model for metabolic justice, it will be necessary to completely re-think the idea of waste.  Guidance for how to do so can be gained through observance of cyclical non-human and regenerative pre-industrial human societies.  In cyclical ecosystems, “waste” means something fundamentally different than it does in a system with linear throughputs.  Rather than falling at one end of the input/output dichotomy, cyclical waste represents the by-products produced by organisms, i.e. oxygen, carbon dioxide, sweat, urine, feces, dead leaves, corpses, etc.  These are either rapidly taken up by other living things in the ecosystem, broken down in to minerals that re-enter the planet’s biogeochemical cycles, or buried so as to become part of Earth’s geological layers.  In terrestrial ecosystems, much of this material ultimately ends up becoming incorporated into in the planet’s organic soil horizon – the complex interface of minerals, organic molecules, moisture, air, and living organisms that create the basis of land-based food chains.  As soils increase in depth, so does the fertility and overall productivity of an ecosystem, along with its capacity to retain moisture, buffer climate changes, filter water, sequester carbon, support biodiversity, resist erosion, etc.  In this regard, “wastes” are not undesirable materials to be rapidly expelled but rather resources to be used for building greater ecological resilience.  Regenerative human societies that practiced sustainable agriculture in the same lands for prolonged periods understood this principle, and incorporated that knowledge into their cultures.  For instance, ancient Amazonian cultures were able to build highly fertile soils through the organic wastes, charcoal, and pottery shards discarded in their middens (Balee, 2006).