Anu Reinart

Relation between underwater irradiance and quantum irradiance in dependence on water transparency at different depths in the water bodies

The ratio between underwater quantum irradiance (q) and irradiance (E) for Jerlovs [1976] oceanic and coastal water types and for 11 Estonian and Finnish lakes was studied. This ratio was found to depend on the depth in the water body and the transparency of the water. The ratio q/E for the photosynthetically active radiation (PAR) region of the spectrum may differ from its value in air by up to 24%. The results of the present paper can be used to convert the underwater radiation data from units of W m−2 to μmol s−1 m−2 (or vice versa) and to estimate the errors caused by applying the “air” value of q/E instead of its real value in the water.

Modeling ice dynamics in Lake Peipsi

Lake Peipsi is the fourth largest lake in Europe, bordering on Estonia and Russia. It covers an area ~f 3555 km2, with an average depth of 8m and maxlmum depth of 15.3 m. The lake consists ofthree main parts: the largest, Lake Peipsi sensu stricto in the north; smaller Lake Pihkva in the south; and Lake Lãmmijãrv connecting the other two (Fig. l). The lake has over 200 inflowing rivers, brooks and ditches, and only one outflow, the River ofNarva. The lake is covered by ice every winter. In general, freezing begins in Lake Lãmmijãrv and Lake Pihkva in the beginning of November because they are shallower than Lake Peipsi. The latter starts to freeze from the eoast toward the eentre at the end of November. The iee thiekness typieally inereases until Mareh and is on average 50-60 em and at maximum 80 em, as measured at Hydrologieal Station Mustvee (Fig. l) l 00 m off the eoast. In January 2002 the iee