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The catastrophic decrease of Prespa Lake level -result of natural or anthropogenic reason? Природна или антропогенна е причината за катастрофалното понижаване на нивото на Преспанското езеро?

Authors:

Abstract

In South-eastern Albania, in bordering area with North Macedonia and Greece, Prespa and Ohrid Lakes constitute a common hydraulic system. Prespa Lake has no surface flow and the outflow of the Lake is realized only through karst underground conduits into Ohrid Lake. During some decades Prespa Lake has suffered extremely worrying water level decline of about 8.5 m, which is seriously influenced by nat- ural climatic changes as well as by uncontrolled an- thropogenic impact. As a result of insufficient scien- tific collaboration the hydrology and hydrogeology of this wide and complicated watershed is not fully investigated. This paper will try to shortly analyze the problem and should bring some important field observation helping the discussion.
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СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 80, кн. 3, 2019, с. 215–217
REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 80, part 3, 2019, p. 215–217
Национална конференция с международно участие „ГЕОНАУКИ 2019“
National Conference with international participation “GEOSCIENCES 2019”
The catastrophic decrease of Prespa Lake level – result of natural
or anthropogenic reason?
Природна или антропогенна е причината за катастрофалното
понижаване на нивото на Преспанското езеро?
Romeo Eftimi
Ромео Евтими
Atelier 4, Rr. Rreshit Çollaku, pll. Eurokol, nr. 43, Tirana, Albania; Е-mail: eftimiromeo@gmail.com
Keywords: karst aquifers, Prespa Lake, environmental impact, climatic changes, Albania.
Introduction
In South-eastern Albania, in bordering area with
North Macedonia and Greece, Prespa and Ohrid
Lakes constitute a common hydraulic system. Prespa
Lake has no surface flow and the outflow of the lake
is realized only through karst underground conduits
into Ohrid Lake. During some decades Prespa Lake
has suffered extremely worrying water level decline
of about 8.5 m, which is seriously influenced by nat-
ural climatic changes as well as by uncontrolled an-
thropogenic impact. As a result of insufficient scien-
tific collaboration the hydrology and hydrogeology
of this wide and complicated watershed is not fully
investigated. This paper will try to shortly analyze
the problem and should bring some important field
observation helping the discussion.
Geology
Mali Thate-Galichitsa Mountain consists mainly of
Upper Triassic–Lower Jurassic massive limestone
with highest peak 2287 m above sea level (Fig. 1).
During the Pliocene–Quaternary the study area em-
braced strong and progressive general uplifting, while
the depression areas suffered mainly subsidence and
partially uplifting (Aliaj, 2012). Most significant re-
sult of this tectonic style is the formation of big Mali
Thate-Galichica Mountain horst. On both sides of the
horst big graben structures are placed: Prespa Lake
graben to the east, and Ohrid Lake and Korcha plain
grabens to the west. Some regional faults with N-S ori-
entation are developed along the eastern and western
edges of Mali Thate-Galichitsa horst. The Pliocene
deposits represented by clay, sandstone and conglom-
erate fill most of the bottom of Prespa Lake and some
small outcrops are developed along the lakeside.
Hydrogeology
Main hydrogeological features of the area are shown
on Fig. 1. The elevation and the surface of Ohrid
Lake are respectively 694 m asl and 348 km2, while
those of Prespa Lake are respectively 849 m asl and
274 km2. Small Prespa Lake surface is 47.4 km2 and
the water level is 1 to 3 m higher than that of Big
Prespa and a natural sandy dam with a sluice gate
separates them. Ohrid and Prespa Lakes are sepa-
rated by the karst massive of Mali Thate-Galichica
Mountain characterised by dense presence of karst
phenomena like karst plateaus, dead valleys, sink-
holes and caves. As the Prespa Lake water level is
about 155 m higher than that of Ohrid Lake, big karst
water quantities flow through Mali Thate-Galichitsa
karst massive to the Ohrid lakeside recharging many
karst springs in the bordering area between Albania
and North Macedonia. Main water recharges are the
big springs of St. Naum average discharge 7.5 m3/s
and that of Tushemisht with 2.5 m3/s. There are
also two other groups of springs, Biljana near Ohrid
with an average discharge between 1 and 2 m3/s and
a group of springs, with total discharge of about
0.5 m3/s, issues in Devoll River Valley in Albanian
territory, near the villages Golloborda, Manchurisht
and Proger, in Devoll River Valley (Fig. 1).
Some investigations conducted with environ-
mental isotope techniques supported by IAEA–Vi-
enna have demonstrated that Tushemisht Spring at
about 52–54%, and St. Naum Spring at about 42–
46% are recharged by Prespa Lake (Anovski et al.,
1991; Eftimi, Zoto, 1997; Kolaneci, 2003; Matz-
inger at al., 2006).
However, the most significant and curious karst
phenomenon of the area is Zaver swallow hole,
which is located in Prespa lakeside between Small
216
Gorica and Gollomboch villages (in Albanian terri-
tory), where an intensive loss of the lake water into
the karst basin could be seen (Fig. 1). Taking into
consideration the difference of water levels in both
lakes of 155 m in average and the distance of 17 km
between the two lakes in the direction Zaver swal-
low hole – Tushemisht and St. Naum, the maximum
hydraulic gradient of karst water flow is 0.0091.
Catastrophic decrease of Prespa Lake level
Lake Prespa is an important natural, ecological and
economical water resource in a region suffering wa-
ter shortage. According to Kolaneci (2003) during
the period 1963–2002 Prespa lake level is lowered
8.79 m, with a decreasing level trend of 21.7 cm/
year, while the decreasing trend of the precipitation
for the same period is 7.8 mm (Fig. 1). According
to Popovska and Bonacci (2007) during the period
1951–2000 Prespa Lake level is lowered 7.79 m,
with the decreasing trend of 10.9 cm/year, and the
precipitation decreasing trend, for the same period,
of 3.16 mm/year. Both investigations take into con-
sideration different time periods.
Many balance calculations of Prespa-Ohrid basin
performed by different authors and institutions of
three neighboring countries result in big discrepan-
cies (Pano, 1984; Kolaneci, 2003; Popovska, Bonac-
ci, 2007). This is the result of missing collaboration
and coordination regarding exchange of documen-
tations between the three countries and systematic
measurements of important water points (springs,
rivers etc) as well as regarding the measurements of
the climatic elements at high elevation areas of the
karst basin and lack of data of snow fall and evapo-
ration. Mostly, the conclusions of the investigators
about the Prespa Lake level decline are based only
on the data of “own country”. In the specialized tech-
nical literature (Hollis, Stevenson, 1997; Kolaneci,
2003; Matzinger at al., 2006; Popovska, Bonacci,
2007) different opinions are expressed about the
Prespa Lake level decrease which could be summa-
rized as (a) geological (tectonic and karst widening
of underground channels connecting both lakes),
(b) anthropogenic (intensive use of lake water for ir-
rigation) and (c) less recognized climate changes.
The widening of the tectonic-karst pathways
transmitting the water from Prespa Lake to Ohrid
Lake presuppose at least the increase of the dis-
charge of the big karst springs of Tushemisht and St
Naum, which is not supported by some non system-
atic measurements of the discharge of the springs.
The anthropogenic impact on Prespa Lake level
is related to the increased use of the Prespa Lake
water for irrigation or for other purposes. Often the
increased use of Prespa Lake is related mainly to
the “intensive” use of the lake Small Prespa for ir-
rigation in Albanian territory. In 1976 the Devoll
River in Albanian territory was diverted to flow to
Small Prespa Lake and during the period 1976–1996
the River input was about 30–70 million m3/year
with the intention to be used for irrigation of Ko-
rça plain during the summer. As the constructed
sedimentation basins of Devoll River didn’t func-
tioned normally about 40 000 m3, of fine grained
sediments are deposited every year in Small Prespa
Lake, which in total reach about 800 000 m3. The
huge quantities of sediments changed completely
the littoral zone and in the Albanian territory the
beautiful Small Prespa was transformed into a wet-
Fig. 1. a, recharge of Lake Ohrid Lake from Lake Prespa. The black arrows show the proven underground connection; b, Zaver
swallow hole, where the Lake Prespa waters disappear to re-emerge at the Lake Ohrid coastal line; c, detail of road (or dam) of
Zaver swallow hole at the lowest historical level during 2002–2005.
217
land making impossible to further host the Devoll
River water. It is obvious that the lake water used
for irrigation cannot be the reason for the decrease
of Big Prespa Lake level. The maximal volume of
Prespa Lake in 1961 was 4.23 km3 which has so far
decreased by about 1.1 km3 (Popovska, Bonacci,
2007). The used for irrigation water quantity is rela-
tively small comparing with the total volume of Big
Prespa Lake and moreover the used for irrigation
water mostly was supplied by Devoll River belong-
ing to another watershed.
Another anthropogenic impact on the decline of
Prespa Lake level could be also the use of lake wa-
ter for the massive irrigation of Resen plain located
north to the Lake in the territory of North Macedo-
nia, or the use of Small Prespa water for irrigation
in Greek territory but no published data exist about
these activities.
Zaver swallow hole as a testimony
of the climatic changes
For a better understanding of the climate changes let
us describe in more detail the Zaver swallow hole
(Fig. 1) This is the biggest and most important swal-
low hole where the water of Prespa Lake disappears
to reappear in the big karst springs along the Ohrid
lakeside. The configuration of Zaver swallow hole at
high water level is like an prolongation of the lake
about 600 m in length finishing in a natural verti-
cal Upper Triasic limestone wall about 25 m high of
Mali Thate Mountain. At the foot of the limestone
wall is located Zaver swallow hole and a big cave
not yet well investigated is developed close to it. In
the memory of the local people is transmitted the de-
scription of a “road” connecting two sides of the Lake
prolongation finishing to Zaver swallow hole but no
one has seen it untill the years 2002–2005. At this
time interval the Lake reached the lowest known lev-
el of about 844.5 m asl and the road emerged with all
its mystery. The road is about 200 m long; it is con-
structed like a dam whose carriage way is in average
about 2.5 to 3.0 m wide, while its height varies from
about 0.5 m in both extremes of the road to about
3 m in the central, deepest part of the water flowing
to Zaver swallow hole. The road is constructed with
stones of different dimensions, from about 15–20 cm
to big blocks more than 70–80 cm thrown without
order and actually no signs of any former pavement
could be seen on the road. The used building stones
are taken from the local sandstone-conglomerate
Plio cene deposits outcropping along the lakeside
near Zaver swallow hole and consist of igneous, met-
amorphic and carbonate rocks (Fig. 1c).
The presence of the road suggests some ques-
tions. When and why is constructed this “road”? Is
there an ancient “road” or an ancient “dam”? Why
it was necessary to construct this “road”? About the
time of the construction of the road there is no any
testimony; the local people say that “the road is very
old and no one knows when it was constructed”. The
stone road is shorter and more convenient compared
with the former existing road passing on limestone
rocks and quite near to Zaver swallow hole. At the
actual situation the stone road is not convenient and
is not used by the local population. The water level
on both sides of the road is different; the level of the
Prespa Lake is about 0.8 m higher that of flowing wa-
ter to Zaver swallow hole. Maybe the road is a dam
constructed to keep Lake level at higher elevation so
important for the fishing activity of the local people.
The construction of such a road (or dam) is jus-
tified only if for a long time (at least some tens of
years or more) in the past Lake Prespa level has
suffered by climatic shortages similar to the ac-
tual ones. An important investigation undertaken
to explain the past climatic variability determining
the sediment isotope and geochemical record from
Lake Prespa over the Last Glacial cycle found very
low lake levels occured around 1000 years ago and
a rapid reversal is established in the last 500 years
(Leng et al., 2013). This period could be the age of
the road of Zaver swallow hole as well.
Conclusions
The existence of the ancient road of Zaver swal-
low hole testifies that the main reason of the cata-
strophic decline of Prespa Lake water level are the
permanent cyclic climate shortages on which nowa-
days overlap seriously the dangerous anthropogenic
impacts as well.
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Article
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This paper deals with hydrological analyses of Lakes Ohrid and Prespa. The watersheds and the lakes themselves are shared by three countries: Albania, Greece and Macedonia. As a result of insufficient interstate scientific cooperation and inexistence of data exchange, the lakes and their watersheds are not fully investigated regarding hydrology and hydrogeology. This paper represents a first attempt at a complete hydrological analysis based on data from the Macedonian side. This is not considered to be a particular deficiency, because over 60% of the lakes' watersheds and the lakes themselves belong to Macedonia, where a great number of reliable and long-term data series of hydrometeorological observations exist. The Prespa lakes do not have surface outflow and are connected with Lake Ohrid by underground karst conduits. Because of this, from the hydrological point of view, the lakes and their watersheds cannot be analysed separately. The changes of the regime of the air temperature and the rainfall distribution have been investigated in this report. An increase of the maximum and decrease of the minimum annual air temperatures, as well as a decrease of annual precipitation sums has been determined. Also, a statistically significant descending trend of water level in both lakes has been confirmed, with a statement that the water level decrease in Lake Prespa is extremely alarming. From 1985 to 1995 the water level in Lake Prespa has dropped by more than 5 m. The main reasons for this cannot be identified easily because there are no data on water use quantities from all three countries. As the lakes represent unique natural, ecological and economical water resources in a region suffering water shortage, we plead for a strengthening of international support in activities on salvation of both lakes. A prerequisite for this is the water balance calculation and common cooperation in sustainable water resources management of the lakes. Copyright
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Lake Mikri Prespa is 47 km2 in area, with amaximum depth of 8.4 m and a normal water level ataround 850 m above sea level. It collects water froma granitic and karstic catchment of 189 km2 whichincludes snowy mountains rising to over 2000 m. Themain flat land is the sedimentary plain to the eastand the sandy isthmus that separates Mikri Prespa fromthe much larger Megali Prespa into which the formernormally drains. Rainfall averages around 750 mmbecause the 600 mm to 700 mm falling on the plains isaugmented by heavier falls including much snow on themountains. There is rainfall each month with anautumnal maximum. River inputs to the lake and thelake level itself peak in the spring with thesnowmelt. Mikri Prespa normally rises by about a metreto flood the surrounding wet meadows landward of thereed fringe. The annual cycle of water levelfluctuation is superimposed on infrequent upwardsurges in the level of Mikri and Megali Prespa becauseof particularly wet and snowy winters and, in recentyears, the steady decline of the level of MegaliPrespa because of tectonic activity.There has been considerable human modification of thehydrology of the area with the diversion of the AgiosGermanos torrent from Mikri to Megali Prespa, thecreation of a canal in Albania which can input orwithdraw water from the lake, the culverting of thecanal linking Mikri and Megali Prespa, and thecreation of an irrigation scheme taking water directlyfrom Mikri Prespa and from the Agios Germanosstream.The lake water is base rich because of the limestonein the catchment. Whilst concern has been expressed atthe eutrophication of the lake, recent studies haveproved that there has been no significant change innutrient status this century and the lake is noteutrophic. There has been a significant increase inturbidity but this may be the result of sedimentdisturbance by an introduced fish species.The lake and its supporting hydrological system willneed careful monitoring if it is to be effectivelymanaged. A particularly high priority is thedevelopment and implementation of a water levelmanagement plan for the lake.
Neotectonic of Albania
  • Sh Aliaj
Aliaj, Sh. 2012. Neotectonic of Albania. Tirana, KLEAN, 292 p. (in Albanian).
Study of the hydrologic relationship between Ohrid and Prespa lakes
  • T Anovski
  • B Andonovski
  • B Minceva
Anovski, T., B. Andonovski, B. Minceva. 1991. Study of the hydrologic relationship between Ohrid and Prespa lakes. -In: Proceedings of an IAEA International Symposium. March 11-15, 1991, Vienna, IAEA-SM-319, p. 62.
Towards Integrated Conservation and Sustainable Development of Transboundry Macro and Micro Prespa Lakes
  • R Eftimi
  • J Zoto
Eftimi, R., J. Zoto. 1997. Isotope study of the connection of Ohrid and Prespa Lakes. -In: Proceedings of International Symposium "Towards Integrated Conservation and Sustainable Development of Transboundry Macro and Micro Prespa Lakes". October 24-26, 1997, Korcha, Albania, 32-37.
IAEA Regional project RER/8/008 Study of Prespa Lake using nuclear and related techniques
  • M Kolaneci
Kolaneci, M. 2003. IAEA Regional project RER/8/008 Study of Prespa Lake using nuclear and related techniques.
Understanding past climatic and hydrological variability in the Mediterranean from Lake Prespa sediment isotope and geochemical record over the Last Glacial cycle
  • M J Leng
  • B Wagner
  • A Bohem
  • K Panagiotopoulos
  • C H Vane
  • A Snelling
  • C Haidon
  • E Woodly
  • H Vogel
  • G Zancheta
  • I Baneschi
Leng, M. J, B. Wagner, A. Bohem, K. Panagiotopoulos, C. H. Vane, A. Snelling, C. Haidon, E. Woodly, H. Vogel, G. Zancheta, I. Baneschi. 2013. Understanding past climatic and hydrological variability in the Mediterranean from Lake Prespa sediment isotope and geochemical record over the Last Glacial cycle. -Quaternary Sci. Rev., 66, 123-136.
Hydrology of Albania. Tirana, Institute of Hydrometeorology, Academy of Science
  • N Pano
Pano, N. 1984. Hydrology of Albania. Tirana, Institute of Hydrometeorology, Academy of Science, 441 p. (in Albanian).