Physical Integrity – What Have We Altered?
The physical integrity of the Great Lakes ecosystem is driven by the movement
of water across and through the land, in streams and rivers, and in the lakes
themselves. While it too is a critical process, the vertical movement of water in
the open lakes, and the thermal stratification that limits mixing during the
summer months, are beyond the scope of this paper. Suffice it to say that
human population pressure has not widely altered the seasonal stratification of
the open lakes, nor limited the mixing of the layers when stratification breaks
down in the fall. Population pressure and resource consumption can, however,
be linked to significant alterations in how water, energy, and materials have
historically moved through the basin. Just recently we have begun to recognize
the ecological consequences of the hydrological alterations brought about by
water uses, diversions, and physical modifications to the land and waters of the
Great Lakes.