Lake ecosystems

A 2500 year old reed-fringed lake with rich birdlife protected as a nature reserve and a deep, thermally-stratified gravel quarry lake with impressive physico-chemical vertical gradients, harbouring a typical plankton community, are investigated in this two-day course. 

Shallow lakes differ from deep lakes in many ways. Shallow lakes normally have larger catchments and thus higher nutrient inputs. Furthermore, introduced nutrients concentrate in a smaller water volume compared to deep lakes. Larger quantities of nutrients are released from the sediment in shallow lakes, predominantly by bioturbation, and always affect the productive zone. In deep lakes in contrast stable thermal stratification in summer prevents recycling of nutrients mineralized in the hypolimnion and thus limits production. Deep lakes also have a large hypolimnetic oxygen reserve. In effect, deep lakes are less susceptible to eutrophication, and anaerobic conditions occur less frequently.

These fundamental differences are reinforced for the two lakes studied here by special circumstances. Both lakes are surrounded by agriculturally used land, which is more or less flat level near the deep lake but is sloping towards the shallow lake. This situation increases nutrient inputs and the tendency for eutrophication of the shallow lake. A small stream likewise surrounded by sloping agricultural fields flows through the lake and does not only transport water-soluble nitrate into the lake, but also significant amounts of sediment from soil erosion with much absorbed phosphate, which has thus long since lost its growth-limiting role in this lake. 

Two-day course: On the first day, the natural, non-stratified, eutrophic lake (partly nature reserve) is investigated. A deep, stratified, mesotrophic lake which is also treated in the one-day course is contrasted to this lake on the second day. The methods are the same as in the one-day course.

Alternative or supplementary topics include day courses of physic-chemical gradients or productivity measurements in different lakes and depths using the light and dark bottle method in connection with chlorophyll analyses.

Most of the chemical analyses can be carried out alternatively by wet chemistry/photometry at XLAB’s chemistry lab (higher time requirement)

Duration: 2 days. Longer programs, topical excursions or a combination with stream ecology courses are possible.
Season: April to November
Travel expenses: € 8 per person or use of own vehicles
Maximal number of participants: 23 with organized travel, 24 with own vehicles