With the characterisations of potentially habitable planetary atmospheres on the horizon, the search for biosignatures is set to become a major area of research in the coming decades. To understand the atmospheric characteristics that might indicate alien life we must understand the abiotic characteristics of a planet and how life interacts with its environment. In the field of biogeochemistry, sophisticated models of life-environment coupled systems demonstrate that many assumptions specific to Earth-based life, e.g. specific ATP maintenance costs, are unnecessary to accurately model a biosphere. We explore a simple model of a single-species microbial biosphere that produces 𝐶𝐻 4 as a byproduct of the microbes' energy extraction -known as a type I biosignature. We demonstrate that although significantly changing the biological parameters has a large impact on the biosphere's total population, such changes have only a minimal impact on the strength of the resulting biosignature, while the biosphere is limited by 𝐻 2 availability. We extend the model to include more accurate microbial energy harvesting and show that adjusting microbe parameters can lead to a regime change where the biosphere becomes limited by energy availability and no longer fully exploits the available 𝐻 2 , impacting the strength of the resulting biosignature. We demonstrate that, for a nutrient limited biosphere, identifying the limiting nutrient, understanding the abiotic processes that control its abundance, and determining the biospheres ability to exploit it, are more fundamental for making type I biosignature predictions than the details of the population dynamics of the biosphere.