The concepts of system and mass balance

System and mass balance are foundational concepts in geography, particularly within the WJEC A-Level specification. A system is a set of interconnected components (stores, flows, inputs, and outputs) that function together as a whole. In geography, systems can be open (exchanging energy and matter with their surroundings, e.g., a drainage basin) or closed (exchanging only energy, e.g., the global carbon cycle). Understanding systems helps geographers analyse how natural and human environments operate, change, and maintain equilibrium.

Mass balance refers to the difference between inputs and outputs of a system over a given time period. It is expressed as: Inputs – Outputs = Change in Storage. A positive mass balance indicates net gain (e.g., a glacier accumulating more snow than it loses), while a negative mass balance indicates net loss (e.g., a glacier retreating). This concept is crucial for studying dynamic equilibrium, feedback mechanisms, and the impacts of environmental change, such as climate change on ice sheets or nutrient cycles in ecosystems.

Mastering system and mass balance allows students to apply quantitative thinking to geographical issues. These concepts link to topics like coastal sediment cells, the hydrological cycle, carbon and nitrogen cycles, and glacial systems. They also underpin understanding of sustainability, resource management, and the Earth's energy balance. By grasping these ideas, students can critically evaluate how human activities disrupt natural balances and how systems respond through feedback loops.