fertilizers and pesticides, making it unhealthy in the lower
reaches as a source of water.
In the diagram (Fig. 9.4) opposite, the river water temperature
varies from +17°C (63°F) at the surface to +13°C (55°F) at the bot-
tom. Where the ground under the wooded area on one side of the river
is cooler than the river water, a positive temperature gradient exists
from river to ground. On the opposite side, in the absence of trees, the
ground is warmer and attracts a negative gradient from river to
ground. The diagram shows nutrients being removed from the
warmer bank and deposited on the opposite, cooler bank.
Where the tree cover cools the river, it flows faster with a lami-
nar structure, removing sediment and deepening its bed.
The rivers are the arteries of Gaia. If they are not allowed to oper-
ate as natural conveyors of energy and nutrients to the land through
which they flow, the fertility of the land gravely suffers. If we were
really to take care of our rivers, protecting their banks from over-
heating, and allowing them to flow sinuously as they will, rather
than make them follow straight lines, we would be taking important
steps to give back to Nature her own power.
- THE HYDROLOGICAL CYCLE