Náttúrufræðingurinn - 1970, Blaðsíða 54

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NÁTTÚRUFRÆÐINGURINN
localities (Fig. )). These investigations included temperature, pH, dissolved
oxygen, alkalinity, phospliate, nitrate, nitrite, ammonia and reactive silicate.
Tlie results (Table 1) show several interesting fcatures:
(a) Great temperature contrasts (about 16°C) exist between the cold and
warm springs discharging into the lake.
(b) The alkalinity and pH values of tlie inflowing water (stations 1, 13. 14
and 8) were relatively high and increased further in the lake itself in tlte
direction of flow, reaching a maximum at tlie outflow (station 10). These changes
can be attributed to phytoplankton production in the lake.
(c) Tlie oxygen concentrations increased in direction of flow in much the
same way as pH. The spring water was 7—15% undersaturated with respect to
oxygen, while the lake water was supersaturated by as much as 15—25%. The
high saturation values in the middle oí the lake and near the outflow region
indicate an active phytoplankton production.
(d) Very higli silicate concentrations, exceeding 1000 pg-at/L, were observed
in the water emerging lrom tlie warm springs, while in the cold springs the
concentrations were smaller by a factor of three. The concentration of silicate
as well as other nutrients decreased in the direction of flow, presumably clue
to the uptake of silicon and other nutrients by diatoms in the lake.
(e) The phosphate and nitrate concentrations of the inflowing spring water
were also relatively high, while in the lake they were almost depleted. Thus
the emerging spring water represents an important source of nutrients. An
additional nutrient supply is undoubtedly provided by the great number of
birds on the lake.
These results suggest a number of interesting problems to be pursued
further, sucli as the water and nutrient budgets, the removal of silica by diatoms,
the distribution of trace elements and organic constituents and the primary
production in different parts of the lake in spring and summer. These
studies would require repeated sampling and analyses of chemical constituents
as well as discharge measurements. If it can be assumed that dissolved silica is
a conservative property in winter, i.e. that it is then changed by mixing pro-
cesses only, and the outflow into Laxá and the inflow from Grænilækur arc
known, tlien it should be possible by measuring simultaneously the chemical
composition of the outflowing water and the various inílowing waters to
compute the runoff and the nutrient input of the warin and cold springs
respectively. An estimate of the net removal of silicate and other nutrienls in
spring and summer might conceivably be derived by similar methods and
could be compared with estimates of the plant production, e.g. the well-
known C14-technicjue.