Apart from the nutrients arriving in rainfall, the.: ther major source for most ecosystems is the gradual degradation of underlying rocks (weathering), which replenishes elements removed by plants and by water percolating through the soil. The water movement through the soil also leaches away unbound nutrients and takes them from one ecosystem to another, of ten from a terrestrial ecosystem to an aquatic one. Knowledge of the quantities and flow rates of ecosystems helps :IS to manage them efficiently {81. If we wish to crop the ecosystem at any given trophic level (e.g., hay at the first trophic level or sheep at the second trophic level),