Horizons in Earth Science Research. Volume 18 opens with a chapter discussing the influence of canyons at the nearshore of river mouths on water dynamics and sediment transport, seawater intrusion into estuaries, and erosion-accumulative processes. The mouths of the rivers Congo and St. Lawrence are studied as examples of the effect of canyons of different genesis on estuary formation. Next, the authors use numerical examples to demonstrate qualitatively and quantitatively the variability of the Odum - Pianka ecosystem under different conditions. An analysis of stability shows that the Odum - Pianka ecosystem has two steady states.