Advanced Approach for Synoptic Monitoring of a Lake Ecosystem
169
The U-TUMS is towed behind the boat along a chosen transect across the lake.
The on-board computer operates the vehicle's steering mechanism and causes the
vehicle to undulate from near-surface to near-bottom (in our case the maximum
diving depth was restricted to 27 m due to the limited length of the cable). The
computer also collects data from sensors and position information of the vehicle
within the waterbody and presents it in real time. The collected data is then
analyzed to produce a two-dimensional view (vertical by horizontal) of the UTUMS transect. Subsequently, several such two-dimensional transects can be
combined to produce a three-dimensional distribution pattern for a given
parameter. The horizontal (areal) variability of each parameter is then extracted
and presented for a given water depth layer to reflect spatial variations.
3 Application of U-TUMS for Limnological Studies in Lake
Kinneret
3.1 Spatial Limnological Heterogeneity of a Stratified Lake
A typical large-scale survey consisted of several west/east transects positioned 2
km apart from each other during the summer time, when Lake Kinneret is strongly
stratified, clearly demonstrated spatial variability within the thermal structure (Fig.
3a). The upper, warmer water layer, the epilimnion, is distinctly separated from
the deeper, cool water layer, the hypolimnion, by a relatively thin water layer, the
metalimnetic layer (see position of 19 to 21°C isotherms, Fig. 3a). During the
sampling time (ca 1 h for a single west to east transect), the vertical distance
between metalimnetic isotherms varied with the location. These variations are
attributed to the presence of second vertical modes of internal waves. The entire
transect reveals that the metalimnion was tilted, being deeper in the western zone
of the transect. The thermocline tilting is attributed to the first mode of Kelvin
internal wave, first noted by Serruya (1975) and further investigated by Antenucci
et al. (2000). The rapid performance of the U-TUMS, that covered a single west to
east transect (ca 10 km) within 1 h, allowed the identification of the thermal
signature of internal seiches due to their relatively longer cycle (Antenucci et al.
2000). The highest water temperature was detected in surface water (Fig. 3a). The
location of 25 and 26°C isotherms within the epilimnion indicated that the eastern
area was notably warmer than the western part of the lake. This phenomenon
could be attributed to higher heat absorption in the eastern area relative to the
western part, presumably due to higher proportion of resuspended material, and/or
due to the development of a denser algal population in the eastern side of the lake.
Another possible explanation is that of wind-induced west to east horizontal
transport of surface water. In the winter as the lake is fully mixed, temperatures
along the water column at particular geographical location were nearly identical
(Fig. 3c). Nonetheless, sampling with the U-TUMS discovered lateral temperature
169
The U-TUMS is towed behind the boat along a chosen transect across the lake.
The on-board computer operates the vehicle's steering mechanism and causes the
vehicle to undulate from near-surface to near-bottom (in our case the maximum
diving depth was restricted to 27 m due to the limited length of the cable). The
computer also collects data from sensors and position information of the vehicle
within the waterbody and presents it in real time. The collected data is then
analyzed to produce a two-dimensional view (vertical by horizontal) of the UTUMS transect. Subsequently, several such two-dimensional transects can be
combined to produce a three-dimensional distribution pattern for a given
parameter. The horizontal (areal) variability of each parameter is then extracted
and presented for a given water depth layer to reflect spatial variations.
3 Application of U-TUMS for Limnological Studies in Lake
Kinneret
3.1 Spatial Limnological Heterogeneity of a Stratified Lake
A typical large-scale survey consisted of several west/east transects positioned 2
km apart from each other during the summer time, when Lake Kinneret is strongly
stratified, clearly demonstrated spatial variability within the thermal structure (Fig.
3a). The upper, warmer water layer, the epilimnion, is distinctly separated from
the deeper, cool water layer, the hypolimnion, by a relatively thin water layer, the
metalimnetic layer (see position of 19 to 21°C isotherms, Fig. 3a). During the
sampling time (ca 1 h for a single west to east transect), the vertical distance
between metalimnetic isotherms varied with the location. These variations are
attributed to the presence of second vertical modes of internal waves. The entire
transect reveals that the metalimnion was tilted, being deeper in the western zone
of the transect. The thermocline tilting is attributed to the first mode of Kelvin
internal wave, first noted by Serruya (1975) and further investigated by Antenucci
et al. (2000). The rapid performance of the U-TUMS, that covered a single west to
east transect (ca 10 km) within 1 h, allowed the identification of the thermal
signature of internal seiches due to their relatively longer cycle (Antenucci et al.
2000). The highest water temperature was detected in surface water (Fig. 3a). The
location of 25 and 26°C isotherms within the epilimnion indicated that the eastern
area was notably warmer than the western part of the lake. This phenomenon
could be attributed to higher heat absorption in the eastern area relative to the
western part, presumably due to higher proportion of resuspended material, and/or
due to the development of a denser algal population in the eastern side of the lake.
Another possible explanation is that of wind-induced west to east horizontal
transport of surface water. In the winter as the lake is fully mixed, temperatures
along the water column at particular geographical location were nearly identical
(Fig. 3c). Nonetheless, sampling with the U-TUMS discovered lateral temperature