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A. Sukenik et al.
boundary processes, thennal fluxes, thennal stratification, wind-induced water
motions, schooling-patchiness of biological populations, and more. In Lake
Kinneret, allochthonous nutrients are provided mainly by the Jordan River,
therefore the river mouth at the northern part of the lake is characterized by a
relatively higher chlorophyll concentration. The river is always of a lower salinity
and often colder than the lake surface water, leading to preferential flow patterns
of river water within the lake (Serruya 1975). The occurrence of two whole-lake
gyres affects the spatial distribution of various chemical and biological parameters
in the northern and in the southern parts of the lake, as described by Ostrovsky et
al. (1996) and Yacobi et al. (1993) for chlorophyll concentration.
In Lake Kinneret both surface and internal waves cause resuspension of
particles and their uneven distribution in littoral and sublittoral zones (Ostrovsky
et al. 1996; Ostrovsky and Yacobi 1999). Daily wind-produced internal seiches
are common from May through September. These seiches induce vertical
displacement of isothenns, which in tum, cause resuspension of bottom material
in the sublittoral zone. Most of the mixing of hypolimnetic nutrient-rich water
with epilimnetic water occurs in this zone. This creates favorable conditions for
enhanced productivity of planktonic community, which attracts planktivorous fish
to the nearshore zone (Ostrovsky et al. 1996). In addition, frequently observed
algal patches in Lake Kinneret (Pollingher and Bennan 1975; Yacobi et al. 1993;
Gitelson et al. 1994), are caused by western wind as phytoplankton communities
are built up on the downwind (eastern shore) or are carried by subsurface returned
currents and accumulated near the western shores. These patches can then drift
and disperse throughout the lake via wind-induced convection cells. In addition,
large loads of nutrients and suspended particles enter the north zone of the lake
during the winter with floods (Avnimelech 1980), are unevenly distributed by
currents (I. Ostrovsky and A. Nishri, unpubl. data), and support the patchiness
development of the plankton community.
The current routine monitoring program can hardly detect the patchy
distribution of any parameter or process in the Lake Kinneret ecosystem, since it is
based on only four fixed stations. Intensification of the traditional monitoring
scheme by adding stations and increasing sampling frequency could resolve this
problem but would require substantial capital investment in manpower,
equipment, and operational costs. On the other hand, ignoring the patchy structure
and processes would restrain our knowledge about the organization and
functioning of the ecosystem.
An innovative approach to increase spatial resolution of several in situ
measured limnological parameters (temperature, turbidity, salinity, and
chlorophyll) was recently implemented in the Lake Kinneret monitoring program
by operating an underwater-towed undulating monitoring system (U-TUMS). The
purpose of this operation was to monitor and study, with a moderate effort and
within a limited time schedule, spatial distribution of limnological parameters and
to identify processes that occur over a large portion of the waterbody.
A. Sukenik et al.
boundary processes, thennal fluxes, thennal stratification, wind-induced water
motions, schooling-patchiness of biological populations, and more. In Lake
Kinneret, allochthonous nutrients are provided mainly by the Jordan River,
therefore the river mouth at the northern part of the lake is characterized by a
relatively higher chlorophyll concentration. The river is always of a lower salinity
and often colder than the lake surface water, leading to preferential flow patterns
of river water within the lake (Serruya 1975). The occurrence of two whole-lake
gyres affects the spatial distribution of various chemical and biological parameters
in the northern and in the southern parts of the lake, as described by Ostrovsky et
al. (1996) and Yacobi et al. (1993) for chlorophyll concentration.
In Lake Kinneret both surface and internal waves cause resuspension of
particles and their uneven distribution in littoral and sublittoral zones (Ostrovsky
et al. 1996; Ostrovsky and Yacobi 1999). Daily wind-produced internal seiches
are common from May through September. These seiches induce vertical
displacement of isothenns, which in tum, cause resuspension of bottom material
in the sublittoral zone. Most of the mixing of hypolimnetic nutrient-rich water
with epilimnetic water occurs in this zone. This creates favorable conditions for
enhanced productivity of planktonic community, which attracts planktivorous fish
to the nearshore zone (Ostrovsky et al. 1996). In addition, frequently observed
algal patches in Lake Kinneret (Pollingher and Bennan 1975; Yacobi et al. 1993;
Gitelson et al. 1994), are caused by western wind as phytoplankton communities
are built up on the downwind (eastern shore) or are carried by subsurface returned
currents and accumulated near the western shores. These patches can then drift
and disperse throughout the lake via wind-induced convection cells. In addition,
large loads of nutrients and suspended particles enter the north zone of the lake
during the winter with floods (Avnimelech 1980), are unevenly distributed by
currents (I. Ostrovsky and A. Nishri, unpubl. data), and support the patchiness
development of the plankton community.
The current routine monitoring program can hardly detect the patchy
distribution of any parameter or process in the Lake Kinneret ecosystem, since it is
based on only four fixed stations. Intensification of the traditional monitoring
scheme by adding stations and increasing sampling frequency could resolve this
problem but would require substantial capital investment in manpower,
equipment, and operational costs. On the other hand, ignoring the patchy structure
and processes would restrain our knowledge about the organization and
functioning of the ecosystem.
An innovative approach to increase spatial resolution of several in situ
measured limnological parameters (temperature, turbidity, salinity, and
chlorophyll) was recently implemented in the Lake Kinneret monitoring program
by operating an underwater-towed undulating monitoring system (U-TUMS). The
purpose of this operation was to monitor and study, with a moderate effort and
within a limited time schedule, spatial distribution of limnological parameters and
to identify processes that occur over a large portion of the waterbody.