Limnology

Unit 5- Biological relations

5.1 Influence of physical and chemical conditions on living organisms in inland waters
Shoreline
The greater the length of the shore line the greater the biological productivity. Increased irregularity of shore line results in
1) greater contact of water with land
2) increased areas of protected bays and covers
3) increased areas of shallow water for growths of rooted vegetation
4) greater diversification of bottom and margin conditions
5) reduction of the amount of exposed, wave-swept shoal and
6) increased opportunity for extensive, close superposition of the photosynthetic zone upon the decomposition zone. These and other possible results combine in various ways to increase the production of animals and plants.
Relation of photosynthetic and decomposition zones
The form of basin of a lake determines, among other things, the relative amounts of shallower waters. Within limits and under strictly comparable conditions, the grater the areas of shallow water the greater the biological productivity. Their exposed nature usually results in
a. the absence of rooted plants
b. the absence of organic bottom deposits and
c. the absence of any permanent animal population save those whose burrowing habits make occupancy of position in such a habitat possible.
Nevertheless, a fairly substantial but largely concealed population may be present, although of all the shallow water faunas it is usually the smallest one.
In contrast to conditions described above, the steeper the slope of the basin, or the greater the exposure of shoals, or both, the greater the removal of the decomposition zone to the profundal depths of deeper lakes
A deeper lake with steep basin slope thus tends to automatically and continuously rob itself of its stores of organic matter. Lakes of the third order, because of shallow depth and continuous circulation except during the ice cover period, retain all organic accumulations in available position, the essential decomposition products either remaining immediately beneath the plant beds or else being constantly the tribute by the water.
Slope and the deeper decomposition zone
Form of basin also involves the slope of deeper portions of the basin. Upon the nature of this slope depends, to a large extent, the character of the bottom. The influence of gravity, aided by water movements in pulling to the lowermost bottom the various materials which settle through, is much more effective on a declivitous slope. Some basin slopes are so abrupt that very little of the loose, settling materials can remain on the steep sides. Thus the decomposition zones of such a lake are restricted to (1) those of the shallow, protected shoals (if any are presently), and (2) those at the bottoms of the deepest regions, separated by steep sides which maintain little or no decomposition deposits.