Interactions between Light Situation, Depth of Mixing and Phytoplankton Growth during the Spring Period of Full Circulation
✍ Scribed by Dipl.-Biol. Heidemarie Horn; Dipl.-Phys. Lothar Paul
- Publisher
- John Wiley and Sons
- Year
- 1984
- Tongue
- English
- Weight
- 861 KB
- Volume
- 69
- Category
- Article
- ISSN
- 1434-2944
No coin nor oath required. For personal study only.
✦ Synopsis
Investigations lasting several years at the artificial Lake Saidenbach have shown that, due to the poor light situation expressed in terms of average daily radiation (RILEY 1957), mean daily exposure (REYNOLDS 1973), extinction depth and the ratio zmix,/zeu, no mass development of the phytoplankton should actually occur during the spring complete circulation. I n practice, however, the period of complete circulation of the water in spring is not only a prerequisite for, but often also the factor causing, the mass development (usually Asterionella formosa). The poor light situation and the fact that the vertical phytoplankton profile shows significant differences between the plankton concentrations a t different depths indicate that the spring complete circulation does not represent a complete recirculation, and thus mixing, of the water down to the bottom but involves only episodic and local partial recirculations interspersed with periods of relatively slight turbulence. The actual mixing depth during this period of complete circulation is therefore obviously less than the mean depth of the water concerned, which is commonly assumed t o equal. This permits the algae in the upper layers to grow. Respiratory losses of the phytoplankton at greater depths probably remain slight due to their adaptation to low light intensities in winter. Contents 1973, LUND 1964, FOGG 1965 and others). A s a rule, the onset of the spring circulation induces the spring growth of the phytoplankton, and it,s end is associated with the 34'