Jose Romero

Seasonal water quality of shallow and eutrophic Lake Pamvotis, Greece: implications for restoration

Lake Pamvotis is a moderately sized (22 km2) shallow (zavg=4 m) lake with a polymictic stratification regime located in northwest Greece. The lake has undergone cultural eutrophication over the past 40 years and is currently eutrophic (annual averages of FRP=0.07 mg P l-1, TP=0.11 mg P l-1, NH4+=0.25 mg N l-1, NO3−=0.56 mg N l-1). FRP and NH4+ levels are correlated to external loading from streams during the winter and spring, and to internal loading during multi-day periods of summer stratification. Algal blooms occurred in summer (July–August green algae, August–September blue-green algae), autumn (October blue-green algae and diatoms), and winter (February diatoms), but not in the spring (March–June). The phytoplankton underwent brief periods of N- and P-limitation, though persistent low transparency (secchi depth of 60–80 cm) also suggests periods of light limitation. Rotifers counts were highest from mid-summer to early autumn whereas copepods were high in the spring and cladocerans were low in the summer. Removal of industrial and sewage point sources a decade ago resulted in a decrease in FRP. A phosphorus mass balance identified further reductions in external loading from the predominately agricultural catchment will decrease FRP levels further. The commercial fishery and lake hatchery also provides opportunities to control algal biomass through biomanipulation measures.

Understanding the factors contributing to the rise in water temperature in a stratified lake with long-term simulations

Water temperatures in lakes may undergo long-term changes following alteration to the catchment (inflows), the meteorological conditions, or to the lake itself (e. g. changes to lake level). It has been predicted that changes to climatic conditions will result in changes to lake temperature and ecosystem functioning (MAGNUSON et al. 1990, DESTASIO et al. 1996). Models have predicted that the changes to the hypolimnion will be of greater magnitude than surface-water temperatures (STEFAN et al. 1993). Lake Kinneret is the only freshwater lake in Israel and provides over 30% of the countrys drinking water. Over the past decade, population growth and greater water usage per capita have increased the demand on this vital resource. Several periods of reduced precipitation have caused a marked decrease in inflows and as a consequence, the lake level has reached record lows. An observed increase in water temperature has occurred in Lake Kinneret over the last decade. The increase in temperature coincided with large surfacelevel fluctuations, with an overall decline in lake level. I t is not apparent, however, if this is the reason for the increase in water temperature. In the present study, through the use of model simulations, the main factors driving the increase in water temperature are examined and an attempt is made to determine if the decline in lake level, meteorological conditions or inflows are responsible.