# 11. The sizes of buffers and other stabilizing stocks, relative to their flows Consider a huge bathtub with slow in- and outflows. Now think about a small one with very fast flows. That's the **difference between a lake and a river**. You hear about catastrophic river floods 'much more often than catastrophic lake floods, because stocks that are big, relative to their flows, are more stable than small ones. In chemistry and other fields, a big, stabilizing stock is known as a Buffer.
The **stabilizing power of buffers** is why you keep **money in the bank** rather than living from the flow of change through your pocket. It's why stores hold **inventory** instead of calling for new stock just as customers carry the old stock out the door. It's why we need to maintain more than the minimum breeding population of an endangered species. Soils in the eastern U.S. are more sensitive to acid rain than soils in the west, because they haven't got big buffers of **calcium** to neutralize acid.
Often you can stabilize a system by increasing the capacity of a buffer. But if a buffer is **too big, the system becomes inflexible. It reacts too slowly.** And big buffers of some sorts, such as water reservoirs or inventories, **cost a lot to build or maintain**. Businesses invented **just-in-time inventories**, because they figured that vulnerability to occasional fluctuations or screw-ups is cheaper than certain, constant inventory costs--and because small-to-vanishing inventories allow more flexible response to shifting demand. It's quite likely that many businesses making small-inventory decisions in their own rational best interests add up to a **much more unstable economy**.
There's **leverage, sometimes magical, in changing the size of buffers**. But buffers are usually physical entities, **not easy to change**. The acid absorption capacity of eastern soils is not a leverage point for alleviating acid rain damage. The storage capacity of a dam is literally cast in concrete. So I have put buffers at the **less influential end of the list of leverage points**.