This introductory article of the special GAP issue gives an overview on gen
eral limnological characteristics of the prealpine Lakes Zurich and Lucerne
and the alpine Lake Cadagno and reports on the specific situation of prima
ry production parameters during the international GAP Workshop in mid Septe
mber 1999. Furthermore, it describes methods used for water analysis and fi
eldwork in these lakes. A comparison of data related to primary production
in the three lakes in September 1999 during stratification shows that (i) p
hytoplankton community structure varied considerably between the lakes. The
dominating algae were Planktothrix rubescens in Lake Zurich, various chrys
ophytes and diatoms in Lake Lucerne, and Echinocoleum elegans in Lake Cadag
no, (ii) the euphotic zone in Lake Lucerne was considerably deeper (app. 15
m) than in the other two lakes (app. 10 m), (iii) chlorophyll a standing c
rop was highest in mesotrophic Lake Zurich (August: 121 mg m(-2)), followed
by oligotrophic Lake Lucerne (August: 75, September: 34 mg m(-2)) and meso
trophic Lake Cadagno (August: 33, September: 25 and 14 mg m(-2)), and (iv)
areal primary production was highest in Lake Zurich (August: 105, September
: 124 mg C m(-2) h(-1)), followed by Lake Cadagno (August: 102, September:
52 mg C m(-2) h(-1)) and Lake Lucerne (August: 90, September: 52 Mg C m(-2)
h(-1)). Physiological parameters, determined in situ from P versus I relat
ionships, showed a lower initial slope a in Lake Lucerne (August: 0.03, Sep
tember: 0.02 mg C mg(-1) chi a h(-1) mu mol(-1) m(2) s) than in the other t
wo lakes (Lake Zurich in August: 0.05, in September: 0.11; Lake Cadagno in
August: 0.05, in September: 0.11 and 0.28 mg C mg-1 chl a h(-1) mu mol(-1)
m(2) s). Lake Zurich showed the lowest AN(max) (August: 2.6, September: 3.2
mg C mg(-1) chi a h(-1), as compared to 5.9 - 7.4 mg C mg(-1) chi a h(-1)
in the Lakes Lucerne and Cadagno), while in Lake Cadagno the highest inhibi
tory effects of C-assimilation were found (highest slopes of inhibition bet
a ,0.007-0.011, as compared to 0.0003-0.0026 in the other two lakes), due t
o a higher UV-exposure in this alpine lake.