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Vigdis Vandvik 55 58 33 32 |
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CASSARINA
ChAnge, Stress, Sustainability, and Aquatic ecosystem Resilience In
North African wetland lakes during the 20th century
The CASSARINA project highlighted the heavy human impacts on fragile
aquatic ecosystems and water resources in arid countries. Poor ecological
planning and lack of appropriate control of water-use projects are failing
to conserve water resources and the biodiversity they support.
The AIMS of the project were
1. To monitor water quality, zooplankton, phytoplankton, vegetation,
and fish diversity, growth rates, and pesticide content in 3 contrasting
lakes in each North African country.
2. To reconstruct changes over the last 100 years in the lakes' ecosystems using multiproxy palaeolimnological methods. Proxies used from the sediment records were diatoms, micro- and macro-invertebrates, plant macrofossils, pollen, radionuclide dating, and sediment chemistry, including heavy metals and persistent organic residues.
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CASSARINA was an EU-INCO Project (1997-1999)
led by Roger Flower (University College London) and a team of scientists
from Morocco, Tunisia, Egypt, Norway, and UK. |
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Sampling Lake Burullus |
Sampling Megene Chitane |
Of the 9 lakes, 3 were inland lakes, 1 had a remote connection to the
sea (Ichkeul), and 5 were lagoons.
Mean values of water chemistry variables for each CASSARINA lake and
minimum variance dendrogram that groups similar lakes. T.D.S. = total
dissolved solids.
All the nine lakes had undergone substantial ecosystem changes during the last 100 years, at an increasing rate over recent decades. Freshwater availability has generally decreased during the latter part of the 20th century at the Moroccan and Tunisian sites but the Nile Delta sites have experienced a freshening trend during this period.
The 3 Nile Delta lakes used to have a natural balance between brackish and more fresh-water conditions depending on the seasonal Nile flood. The inflow of fresh water drained slowly, eventually allowing sea water to penetrate once more. All have become fresher and more eutrophic due to year-round fresh-water input, increased agricultural fertilisation, and increased human population since the early 20th century, accelerated after the closure of the Aswan High Dam in 1964. All are being reduced by land reclamation and are overgrown in varying degrees by water hyacinth.
Lake Edku
Its salinity has been reduced by fresh-water overload from the Nile drains.
Fish quality is reduced by eutrophication and the spread of water hyacinth
and Azolla filiculoides on the water surface. Its size is being rapidly
reduced by land reclamation.
Changes in the biota of Lake Edku during the 20th century were recorded
from a core of the lake sediments. A saline phase with the marine foraminifer
Quinqueloculina seminulum, the bivalve Pholas dactylus, and the marine
plant Zostera was followed by less saline conditions as control of the
Nile flood and year-round fresh-water supply increased. Fresh-water molluscs
expanded in the 1940s and increased enormously after the closure of the
Aswan High Dam in 1964. Water weeds also increased, including indicators
of eutrophication such as Ceratophyllum (hornwort), Lemna (duckweed),
and Eichhornia (water hyacinth), and reedswamps grew up dominated by
Typha (cattail). Meanwhile, molluscs and foraminifera typical of brackish
lagoon conditions decreased as the water became fresher. Azolla nilotica thrived in the brackish and saline conditions early in the century, but
became extinct after about 1920 when nutrient levels began to increase.
Azolla filiculoides was introduced to the delta as a green fertilizer
(it fixes atmospheric nitrogen) and it spread across the lake in the
1990s. Occasional recent records of A. nilotica and Quinqueloculina are
probably reworked by fishermen's punt-poles. 
Azolla
nilotica (left),
a floating water fern, became extinct in the Nile Delta during the
last century. The latest record of megaspores in
lake sediments was from Lake Burullus at about 1965. (H.H. Birks (2003)
The recent extinction of Azolla nilotica in the Nile Delta, Egypt.
Acta Palaeobotanica 42, 203-213).
Nitella opaca oospores (right) of this macro-alga
were recorded in the sediments of Megene Chitane but living plants were
never found during
monitoring and it is assumed to be already extinct in this, its only
North African locality.
Lake Manzalla
This huge shallow lake is suffering from land reclamation, industrial
and nutrient pollution, and overgrowth by water hyacinth (right). Formerly
saline or brackish, its salinity is reduced by year-round freshwater
inflow and poor drainage to the sea, and fis
h catches are reduced. Extensive emergent reed beds, mainly of Phragmites, help to localise pollution, but also prevent the circulation of saline water.
Lake Burullus
Lake Burullus retains some marine influence and is still mildly saline.
Fishermen using feluccas still make good fish catches.
Cores of lake sediment deposited over the last century were taken from each lake to reconstruct palaeolimnological changes.The results are published in volume 35 number 3-4 of Aquatic Ecology (2001). The following articles are available electronically.
North African wetland lakes: characterization of nine sites included in the CASSARINA Project
Recent ecosystem dynamics in nine North African lakes in the CASSARINA Project
Open water zooplankton communities in North African wetland lakes: the CASSARINA Project