Chapter 24

Discuss the relative merits of making a compartment model of a nutrient cycle very coarse (with only a few compartments) versus making it very fine (with many compartments)

Shallow lakes may have two alternate stable states depending on nutrient influx, one dominated by phytoplankton in turbid water and another dominated by macrophytes in clear water. Discuss how you might determine the critical nutrient loading that would trigger a transition between these states. Would you expect the transition from phytoplankton to macrophytes to occur at the same nutrient loading as the opposite transition? Janse (1997) discusses this problem.

The idea of one cause-one effect is left over from the nineteenth century when physics dominated science The whole notion of causality is under question in the ecosystem framework. Does it make sense to say that high primary production causes a rich organic soil and a rich organic soil causes high production? This kind of reasoning leads up a blind alley. Discuss.

Pacific salmon grow to adult size in the ocean and move into freshwater streams and lakes to spawn and die. In the process they transport nutrients from ocean ecosystems to freshwater ecosystems. These returning salmon are eaten by bears and other predators, bringing some of these nutrients into the terrestrial ecosystem. Discuss how you might measure the impacts of this nutrient transport system both for aquatic and for terrestrial ecosystems within the geographic range of Pacific salmon. Helfield and Naiman (2006) discuss this issue.

Soils in Australia contain very low amounts of phosphorus, from $10\mathrm{\%}-50\mathrm{\%}$ the amount in North American soils (Keith 1997 ). Would you predict that eucalypts growing in Australian soils would be phosphorus limited? What adaptations might plants evolve to achieve high nutrient use efficiency when growing on soils of low nutrient content?

A key question in restoration ecology is how long it will take for an ecosystem to recover from some disturbance caused by humans. Discuss how we might find out what the time frame is for ecological recovery from acid rain.