1. Du Rietz, G. E.: 1949, Svensk Bot. Tidsk. 43, 274.
2. Glooschenko, W. A., Capobianco, J. A., Mayer, T., and Gregory, M.: 1977, Canada Center for Inland Waters Unpublished Report.
3. Goodman, G. T. and Roberts, T. M.: 1971, Nature 231, 287.
4. Ellison, G., Newham, J., Pinchin, M. J., and Thompson, I.: 1976, Environ, Pollut. 11, 167.
5. Information Report 0-X-215;J. K. Jeglum,1974