BL1006 Lecture 10 Notes: Standing Waters

Lakes form in various ways due to geological action, glacial activity, river activity and by other means:

Tectonic Lakes: Formed by large-scale geological action, such as Rift Valley Lakes (e.g., East African Rift Valley lakes, Lake Baikal, Lough Ness), Volcanic lakes (e.g., Lake Taupo, New Zealand) and Tectonically uplifted lakes (e.g., Lakes Aral and Caspian).
Glacial Action: Ice scour lakes and Glacial moraine lakes.
Other ways: Solution lakes, river activity, shoreline lakes, beaver and human-made reservoirs.

Lentic organisms are classified by:

Size: Net plankton (>200 µm), Microplankton (20-200 µm), Nanoplankton (2-20 µm), Picoplankton (0.2 - 2 µm), Femtoplankton (0.02-0.2 µm).
Location: Littoral zone, Limnetic zone, Benthic zone, Photic and aphotic (profundal) zones.
Trophic Level: Heterotrophic decomposers (microbes), Primary producers (plants), Primary consumers (small animals), Secondary consumers (large animals).
Euphotic (or photic) zone: depth at which approximately 1% of the light available for photosynthesis remains.
Littoral zone: euphotic zone extends to the bottom.
Limnetic zone: the bottom lies below the euphotic depth.

Primary producers include phytoplankton, macrophytes and periphyton.
Zooplankton are dominated by planktonic crustaceans & rotifers

(a) Light: Controls the depth to which plants and algae can grow; measured using 'secchi depth'.
(b) Heat: Strong temperature gradients (stratification) develop due to varying water densities. Thermal stratification involves the Epilimnion, Metalimnion (thermocline), and Hypolimnion.
(c) Nutrients: Phosphorous (P) and nitrogen (N) are limiting nutrients affecting primary productivity. Lake trophy classifications: Eutrophic (nutrient-rich), Mesotrophic (medium nutrients), Oligotrophic (nutrient-poor).
(d) Wind: Influences lake littoral zones; creates depositing and eroding shores.