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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.

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.
Roger Flower University College London, UK
Mohammed Ramdani Institut Scientifique, Rabat, Morocco
Mejdeddine Kraïem Faculté des Sciences, Tunis University, Tunisia
Adel Fathi University of El Minia, Egypt
Hilary Birks Bergen University, Norway
Hani Abdelzaher University of El Minia, Egypt
Peter Appleby Liverpool University, UK
Cheddeli Ben Hamza Faculté des Sciences, Tunis University, Tunisia
John Birks Bergen University, Norway
Najat Elkhiati Faculté des Sciences, Casablanca, Morocco
Simon Patrick University College London, UK
Sylvia Peglar Bergen University, Norway
Andrew Peters Lancaster University, UK
Anne Bjune Bergen University, Norway
Ian Boomer Newcastle University, UK
Joan Lees
Simon Dobinson University College London, UK

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

Palaeolimnological responses of nine North African lakes in the CASSARINA Project to recent environmental changes and human impact detected by plant macrofossil, pollen, and faunal analyses

Recent ecosystem dynamics in nine North African lakes in the CASSARINA Project

Terrestrial pollen record of recent land-use changes around nine North African lakes in the CASSARINA Project

Zooplankton (Cladocera, Ostracoda), Chironomidae and other benthic faunal remains in sediment cores from nine North African wetland lakes: the CASSARINA Project

Open water zooplankton communities in North African wetland lakes: the CASSARINA Project

Radiometrically determined dates and sedimentation rates for recent sediments in nine North African wetland lakes (the CASSARINA Project)

UCL project write-up