Magdi Ali

Concentrations of Ca, Mg, K, Na, Cu, Zn, Al, Fe and Mn were measured in soils and in Tamarix nilotica from Wadi Allaqi on the shore of Lake Nasser in the Eastern Desert of Egypt. All of the elements were concentrated in the leaves of Tamarix relative to the stems and roots. Leaf?:?soil concentration ratios, used as an indicator of

Multivariate analysis of data from a 1997 survey of submerged vegetation at 3 locations on the River Nile in Upper Egypt showed that hydrochemical factors (total oxidised nitrogen, sulphate and sodium) were the most important environmental variables explaining the distribution and the abundance of submerged plant species. The kinetic energy of waves produced by tourist ship wash (measured using an

ABSTRACT Multivariate analysis of data from a 1997 survey of submerged vegetation at 3 locations on the River Nile in Upper Egypt showed that hydrochemical factors (total oxidised nitrogen, sulphate and sodium) were the most important environmental variables explaining the distribution and the abundance of submerged plant species. The kinetic energy of waves produced by tourist ship wash (measured using an index incorporating measured wave height at shore, depth of sampling site and distance between ship channel and sampling site) was next in importance, and explained more of the variation in submerged plant abundance and distribution than did river flow rate. Classification using TWINSPAN identified 5 major groups of sites characterised by differing plant community composition (and having significant inter-group differences in wave index and flow rate). Ship wave effects are likely to be an important factor contributing to differences observed in hydrosoil texture and organic matter content at different depths at one study location (Aswan) heavily used by ship traffic. Coarse sand and gravel fragments with low organic matter content, were predominant in the shallow water zone, most heavily impacted by ship waves; while finer sand with high organic matter content formed the hydrosoil in deeper water. Such variation in sediment characteristics is also likely to influence macrophyte growth. The environmental disturbance effects of ship traffic in the Nile in Upper Egypt currently appear to play a significant role in the ecology of the river's submerged vegetation. Given the long-term trend towards tourism use of the Nile for cruise holidays, it is likely that ship traffic intensity will increase over the next decade, adding to the impacts on aquatic vegetation.

ABSTRACT The first-ever extensive macrophyte survey of Zambian rivers and associated floodplain waterbodies, conducted during 2006 – 2012, collected 271 samples from 228 sites, mainly located in five freshwater ecoregions of the world primarily represented in Zambia. The results supported the hypothesis that variation in macrophyte community structure (measured as species composition and diversity) in southern tropical African river systems, using Zambia as a case study area, is driven primarily by geographical variation in water physico-chemical conditions. In total 335 macrophyte taxa were recorded, and a chronological cumulative species records curve for the dataset showed no sign of asymptoting: clearly many additional macrophyte species remain to be found in Zambian rivers. Emergent macrophytes were predominant (236 taxa), together with 26 floating and 73 submerged taxa. Several species were rare in a regional or international context, including two IUCN Red Data List species: Aponogeton rehmanii and Nymphaea divaricata. Ordination and classification analysis of the data found little evidence for temporal change in vegetation, at repeatedly-sampled sites, but strong evidence for the existence of seven groups of samples from geographically-varied study sites. These supported differing sets of vegetation (with eight species assemblages present in the sample-groups) and showed substantial inter-group differences in both macrophyte alpha-diversity, and geographically-varying physico-chemical parameters. The evidence suggested that the main environmental drivers of macrophyte community composition and diversity were altitude, stream order, shade, pH, alkalinity, NO3-N, and underwater light availability, while PO4-P showed slightly lower, but still significant variation between sample-groups.

The paper reports on the flora along the banks of Lake Nubia and the long-term changes that have taken place since the formation of the Aswan High Dam (AHD) Lake about 40 years ago. Both aquatic and shoreline vegetation were studied in 15 transects located across the lake, from Debeira (337.5 km south of the Aswan High Dam), to the Dal Cataract (500 km south of AHD). Water temperature, pH, dissolved oxygen, total dissolved solids, electric conductivity and turbidity were measured in the field. Water and hydrosoil samples were collected and analysed for phosphates, nitrates, sulphates, carbonates, bi-carbonates, calcium, magnesium, and silicates. The shoreline was classified into four moisture segments depending on the period of inundation, namely: wet (frequently inundated and recently exposed); moist (periodically inundated); semi-dry (rarely inundated); and dry (never inundated). Plants characterising each segment have been identified. Factors affecting the distribution of aquatic macrophytes in Lake Nubia were analysed using canonical correspondence analysis. Temporal and spatial variations of the shoreline vegetation were revealed.

QUATIC macrophytes are important to managers of captive fisheries in inland waters. Construction of the Aswan High Dam created a lake, which extends for 480 km; 300 km within the Egyptian borders (Lake Nasser). We investigated the impact of composition, structure, and distribution of aquatic macrophytes on the production and diversity of fish in Lake Nasser. Macrophytes, fish, and water were sampled from four stations in Lake Nasser (Kalabsha, Garf Hussein, Kurusku and Tushka) representing different bottom habitats, either in texture or in steepness, of the lake, which are important to submerged plants distribution and abundance, and hence their associated fish. At each site, submerged macrophytes were collected from shallow and deep water, down to the depth limit of plants colonisation. The plants were identified and the mean dry weight standing crop was calculated for each species. Fish were sampled using both trammel and floating-gill nets. For each fishing method, total weight of the catch, total weight of each species and number of individuals per species were determined. A one-litre surface-water sample was collected from each station and temperature, dissolved oxygen, pH, electrical conductivity, Secchi disc transparency, carbonate, and bicarbonate were measured. Three macrophyte communities were detected: a) Myriophyllum spicatum; b) Myriophyllum spicatum-Potamogeton schweinfurthii; and c) Myriophyllum spicatum-Najas horrida-Najas marina. Thirteen fish species were recorded. Oreochromis niloticus dominated the trammel-net catch in all regions and the floating gill-net catch at Garf Hussein. O. niloticus dominated the littoral semi-pelagic zone (>10 m depth), while Lates niloticus was co-dominant. The lateral pelagic zone (<10 m depth) is dominated by L. niloticus and O. niloticus in the northern sector and Hydrocynus forskalii, Sarotherodon galilaeus and Tilapia zillii in the southern sector. CCA indicates that temperature, dissolved oxygen, transparency, carbonates and bicarbonates are the most important water variables influencing the distribution of macrophytes and their associated in fish in the littoral semi-pelagic, while water pH, bicarbonate, and carbonates are the most influential variables in the lateral pelagic zone. PCA indicates that the three submerged macrophyte communities recognized and fish characterizing each of them are A