Does lake eutrophication support biological invasions in rivers? A study on Dreissena polymorpha (Bivalvia) in lake–river ecotones

The zebra mussel (Dreissena polymorpha) has all traits required to effectively colonize the aquatic environment and consequently reduce the diversity of native bivalves. We hypothesized that the zebra mussel chooses lake outlets characterized by medium current velocity and good food conditions. Here, we analyzed differences between bivalve abundances in lake outlets with varying environmental conditions such as the Carlson Index (trophy status), depth, width, current velocity, bed vegetation coverage, and type of bottom substrate. The results showed that the zebra mussel inhabits outlets that provide food (high trophy outlets) and have a mineral bed and a medium current velocity (ca. 0.2–0.3 m/s). The following main factors seem to be favorable for colonizing such outlets: (1) easy access to high amounts of food due to the increased density of the suspension drifting from the lake and (2) easy transport of the zebra mussel larvae from the lake to the downstream. The zebra mussel larvae drifting with the current may colonize the downstream. An increase in lake trophy may indirectly cause an increase in biological invasions in rivers.     

Meteorology and species composition of plant communities, birds and fishes before and after initial impoundment of Miharu Dam Reservoir, Japan

The immediate impact of damming appears most notably at the first filling of water, when the dam blocks the river and a lake suddenly forms. In this review, the changes in meteorology, plant communities, birds and fishes surrounding initial impoundment of Miharu Dam, constructed in an Asian Monsoon region, are summarised based on previous papers and subsequent field research. Although wind and temperature changes were investigated, land and lake wind occur due to the different thermal properties between the land and lake, and this type of wind often occurs at large lakes such as Glen Canyon Dam Reservoir or Lake Biwa. The size of Miharu Dam Reservoir (ponding area 2.9 km²) was insufficient to cause land–lake air differentials. Therefore, wind direction and air temperature were unaffected. Mountain winds weakened at the lake centre and near the dam body. Changes in vegetation were especially diverse at the drawdown zone (the slopes above and below the normal water level). On slopes above this zone, trees died and species composition changed due to submergence. Within the drawdown zone, the pre-existing plant community disappeared, and flood-resistant plants such as Salix subfragilis increased. The natatorial bird population continued to grow for 4 years after dam reservoir emergence and stabilised thereafter. Every year, the majority of natatorial birds utilising the dam reservoir as a resting area were ducks, but populations of diving ducks fluctuated depending on water level and iced area. After impoundment, the fish populations increased. As in most dam reservoirs in Japan, populations of invasive fish species such as Micropterus salmoides and Lepomis macrochirus increased. However, spawning grounds dried up during low-water-level seasons, suggesting that regulating water levels may help reduce invasive species.     

The effect of the impoundment of Lake Kainji, Nigeria, on the indigenous species of mormyrid fishes

SUMMARY. Changes in the numbers and species composition of mormyrid fishes since the impoundment of the Niger (Lake Kainji) are analysed. An initial decline after impoundment appears to have been reversed and these fish are now increasing. The increase is, however, restricted to a few species only; many forms common in the river are still declining or have disappeared altogether. Marked seasonal variations in abundance are described and possible explanations discussed.     

Synopsis of scientific results of the sarec sponsored project on the ecology of Lake Kariba

A summary of current research on Lake Kariba is given. Lake Kariba is now a phosphorus limited oligotrophic lake, dependent on annual nutrient input for the maintenance of production. Nitrogen fixation by cyanobacteria has become an important source of nitrogen in the dry season and that fish harvesting is an important phosphorus sink. An up to date plankton composition list has been produced and plankton biomass determined. Diving studies indicate large biomass of bivalves. The aquatic vegetation displays both longitudinal as well as depth gradients, related to light regimes. Only preliminary data are available on mud/water interactions, but the available data indicate considerable fluxes in the river mouth stations and shallow protected littoral areas. The role of predatory birds and crocodiles in the fishery economy of the lake is evaluated and indicates no major conflict between these predators and human fishing interests. The research also draws attention to pesticides in Lake Kariba as indicated by work on fish eating birds and crocodile research. Since the publication of ‘Lake Kariba’ by Balon & Coche (1975) the research project, THE ECOLOGY OF LAKE KARIBA, being undertaken by the University Lake Kariba Research Station constitutes the first multidisciplinary study of the lake, 30 years after the Zambezi river was impounded at Kariba Gorge. It could have offered a unique opportunity of comparing the lake now with what it was soon after impoundment.     

The effect of lake morphology on aquatic vegetation development and changes under the influence of eutrophication

Data on aquatic and emergent vegetation, morphology and water quality from 274 Polish lowland lakes surveyed in the years 1996–2009 were used to validate the preliminary typology of Polish lakes based on macrophytes and to indicate the environmental parameters which most significantly determine the vegetation patterns in lakes under various morphological conditions. In highly alkaline lowland lakes representing non-disturbed conditions the key determinants influencing the vegetation patterns were mean depth and the shape of the littoral. Three morphological lake types were distinguished: shallow (<3.5 m), deep, and additionally, within the latter, deep ribbon-shaped, with a clearly elongated base and steep bed slopes. The lake types varied in their vegetation patterns developed under non-disturbed conditions. In the shallow lakes, the share of the phytolittoral in the total lake area (%phytol) was the highest (40–100%, 72.3% on average) and the maximum colonisation depth (C_max) the lowest (3.2 m as the maximum) compared to the lakes from both deep types. In the ribbon-shaped deep lakes, %phytol and the plant coverage (%cover) were the lowest, the proportion of submerged vegetation was extraordinarily high (over 90%) and the emergent vegetation was extremely sparsely developed (<6%) compared to the lakes of the two other types.The alterations of aquatic vegetation resulting from the eutrophication process in distinguished morphological lake types were explored. Within the macrophyte variables tested, three groups of indicators were distinguished: (a) metrics performing best in selected lake types, i.e. the type-specific indicators (abundance metrics, %Pota), (b) metrics performing equally well in all the lake types, considered as the universal indicators (e.g. S_Chara, %Subm and %Emerg) and (c) metrics performing poorly in all the lake types, with generally limited applicability (most of the metrics on syntaxonomic richness). In the shallow lakes, %cover and %phytol performed notably better than in deep lakes, whereas C_max worked best in deep lakes and showed the strongest response in the deep regular-shaped lakes. Moreover, in deep regular-shaped lakes the number of communities of stoneworts and submerged plants (S_Chara and S_Subm), and in deep ribbon-shaped lakes the proportion of area inhabited by vascular plant communities (%Pota) performed exceptionally better than in the other two lake types. The most universal metrics, performing equally well in all the lake types, were the proportions of submerged (%Subm) and emergent (%Emerg) vegetation in the total phytolittoral area.     

The plant biodiversity of the Wadi Allaqi Biosphere Reserve (Egypt): impact of Lake Nasser on a desert wadi ecosystem

A data set comprising 95 stands of desert vegetation, collected from the Wadi Allaqi Biosphere Reserve and its environs within the South-Eastern Desert of Egypt during 1985–90, was analysed using multivariate procedures (two-way indicator species analysis: TWINSPAN; detrended correspondence analysis: DCA; canonical correspondence analysis: CCA), to produce a classification of plant communities in the area, and to examine the relationships of these plant communities to natural and man-induced features of the physical environment of the area (in particular, the influence of Lake Nasser, a major impoundment of the River Nile formed in 1964). The vegetation classification produced groupings broader, in both floristic and ecological terms, than those found by earlier studies of this area. In total 78 plant species were recorded from four phytogeographic elements. Four principal vegetation groups were identified, of which one is new to the area, and is the result of major environmental changes affecting the downstream part of the Wadi Allaqi system, following periodic flooding of the wadi by Lake Nasser during the past 30 years. This community was indicated by Tamarix nilotica. There was a strongly-zoned (downstream–upstream) pattern to the vegetation within this lower part of Wadi Allaqi, which appears to be a function of the probability of flooding by the lake. The remaining three vegetation groups occur higher in the wadi basin. Groundwater-dependence appeared to be important in defining a group indicated by Acacia tortilis, as well as the Tamarix nilotica group. The two remaining groups, characterized respectively by Acacia ehrenbergiana and Cullen plicatum, represent vegetation groups which are precipitation-dependent, and which tolerate drier conditions within the Allaqi system.     

The plankton community of an acid blackwater South Carolina power plant impoundment

Robinson Impoundment, an acid blackwater system in the South Carolina sandhills, serves as a cooling pond for a 854 MW power plant. It is divided by a causeway into an upper and lower impoundment. The upper impoundment is narrow, shallow, exhibits higher flow, and much more periphytic and rooted aquatic macrophyte vegetation. The lower impoundment is wide and deep with many sandy shoreline areas and little macrophyte vegetation.The zooplankton and phytoplankton communities of both the lower and upper impoundment were investigated over a three-year period (1980–1982) in an effort to determine power plant discharge effects on the plankton. Primary productivity rates were low, characteristic of an oligotrophic system. The phytoplankton community was dominated by the Bacillariophyceae and Chlorophyceae in cell density and the Chlorophyceae in species richness. The zooplankton community was dominated numerically by copepods, rotifers, and cladocerans, respectively. Principal zooplankton species includedDiaptomus mississippiensis, Bosmina longirostris, Diaphanosoma brachyurum, Keratella americana, K. cochlearis, Pompholyx sulcata, andConochiloides coenobasis. The rotifers were dominant in species richness, while crustacean zooplankton species richness was usually quite low. Statistical analyses performed using phytoplankton and zooplankton population variables indicated that in most cases upper impoundment densities were significantly lower (p < 0.05) than lower impoundment densities which were likely a function of the lotic upper impoundment habitat. No significant differences were found between the discharge area and the rest of the lower impoundment stations suggesting that localized power plant discharge effects did not occur during the study. Peak midsummer thermal discharge (36.0 ° C) may have caused temporary reductions inD. mississippiensis and several rotifers. Thermal stimulation during summer may have caused population increases for the filter-feeding cladocerans,B. longirostris andD. brachyurum.     

Holocene environments in the central Sahara

Palynological investigations of corings in the sebkhas of Taoudenni (N-Mali) and Segedim (N-Niger), archaeological excavations in the Acacus Mts. (SW-Libya) and charcoal records in the central Ténéré (Niger) give evidence for a northward shift of the desert-savanna boundary to 22°–20° N during the middle Holocene. Between Niger and S-Libya there was a ecological gradient from the sudanian, sahelian and saharan savannas to a denser saharan desert vegetation. After a transition phase between 6000 and 4000 BP the saharan desert vegetation was finally established in the Taoudenni and Segedim region and this degraded from ca. 2000 BP to its present condition.During the middle Holocene the central Sahara had a monsoonal summer rain climate with an effective rainfall of 250–300 mm per year near the desert-savanna boundary (ca. 22° N). Interaction between the monsoon and the atlantic cyclones also allowed rainfall in other periods of the year.     

Successional patterns of aquatic macrophytes in Jebba Lake, Nigeria

Macrophyte succession in Jebba Lake, Nigeria, was observed through the first four years after impoundment. Two distinct serai phases, a floating fern phase and a draw-down flora phase could be recognized. The floristic composition of the macrophyte vegetation was also investigated to check earlier predictions (Obot & Mbagwu, 1986) on the probable structure of the macrophyte flora. The failure of obligate floating macrophytes such as Pistia, Azolla and Salvinia to establish in the lake as predicted is discussed. However, rooted emergent macrophytes were observed to be more successful than would be expected from the predictions.     

Carbon,phosphorus and nitrogen budgets of the littoral Equisetum belt in an oligotrophic lake

Stores and flows of carbon, phosphorus and nitrogen in a littoral Equisetum stand were studied in 1978–1980 in the oligotrophic, mesohumic lake Pääjärvi, southern Finland. The major carbon and nutrient stores were sediment and Equisetum. The seasonal cycle of the macrophyte vegetation had a profound influence on the whole littoral ecosystem. In spring, when only dead remains of Equisetum were present above ground, there were few differences in nutrient, chlorophyll a and zooplankton concentrations between the littoral and the open lake; phytoplankton and epiphytes were the major producers.In early June, when new shoots of Equisetum reached the water surface, water exchange between the littoral and the open lake started to diminish, and the characteristic features of a closed macrophyte zone gradually developed: by August the P, Chl a and zooplankton concentrations in the littoral were 5–10 times those in the open lake. From late June until autumn Equisetum was overwhelmingly dominant both in biomass and in production.The measured total primary production and respiration values indicated a high rate of internal cycling of carbon and nutrients. The daily P requirements of plant growth exceeded the total P stored in the water by a factor of 2–4, and also exceeded the release of nutrients in excretion. High N:P ratios in the water (total 10–64, inorganic 18–171) suggested that P was probably always the limiting nutrient.The P content of the annual production of Equisetum in Pääjärvi was 2.3% of the mean annual P load, and 5.3% of the mean total P storage in the water volume of the lake.     

Response of fringing vegetation to flooding and discharge of hypersaline water at Lake Austin,Western Australia

Patterns and dynamics of the salt marsh vegetation that surrounds many of the salt lake systems of arid/semi-arid Australia are poorly known. Lake Austin is a very large salt lake with extensive areas of fringing salt marsh; it is located in the arid Yilgarn Region of Western Australia. In this study, the changes in this vegetation over a 4-year period (1998–2002), during which both a major flooding event and addition of hypersaline groundwater from a nearby mining operation occurred, are reported. The monitoring program, based on Before-After-Control-Impact (BACI) principles, was designed to detect impacts of discharging hypersaline water into the lake; however, the flooding event, the result of above average rainfall in early 2000, complicated the results. The rains of 2000 and subsequent inundation of the vegetation immediately fringing the lake bed and major inlet channels resulted in dramatic changes to the species composition of annual and short-lived species and growth of perennial species. Flooding resulted in substantial death and damage to perennial shrubs (particularly Halosarcia fimbriata) due most likely to a combination of several weeks/months of inundation and smothering by macroalgae and Ruppia, with smaller plants and those closer to the lake bed impacted upon to a greater degree. Seed germination and recruitment of new Halosarcia plants was substantial as floodwaters receded with the majority of these seedlings surviving some 2 years after flooding despite the severe drought that followed the flood. Growth rates of seedlings differed substantially and were linked to subtle differences in micro-topography. Recruitment following flooding was also demonstrated in in vitro experiments involving inundated soil cores, provided water was relatively non-saline (conductivity <30 mS cm⁻¹). A conceptual model is proposed to explain changes in fringing vegetation in response to frequency, depth, period and salinity of flooding in relation to micro-topography. Despite the profound effect of flooding, impacts of discharge were identified, with changes in topsoil pH and salinity greater in areas closer to the discharge than those further away. Impacts on vegetation characteristics were not detected. Guest Editors: J. John & B. Timms Salt Lake Research: Biodiversity and Conservation—Selected papers from the 9th Conference of the International Society for Salt Lake Research     

The macrophytic community of an acidic lake in adirondack (New York,U.S.A.): A new depth record for aquatic angiosperms

The submerged vegetation of Silver Lake (Herkimer County, NY, U.S.A.) was extensively surveyed to help to determine the effects of low pH on aquatic biota. This extra-ordinarily clear lake (Secchi disk > 18 m, the maximum depth of the lake), was low in conductivity (27 μS cm^?1), pH (4.8) chlorophyllα (0.11 μg l[^?1), and total phosphorus (<1 μg 1^?1).The vegetation was dominated, in terms of percentage of the total plant community, by Utricularia spp. (47%), Sphagnum spp. (23%), and Eriocaulon septangulare With. (17%). Distinct depth zonation was evident, with U. geminiscapa Benj. extending to the deepest part of the lake (18 m). This represents a new maximum depth penetration for aquatic angiosperms. The mechanisms by which angiosperms are limited in depth-distribution are discussed. It is concluded that single factor theories, those which ascribe the maximum depth of penetration to a single variable (e.g., light, temperature, hydrostatic pressure), are all deficient, and that the actual limitation is brought about by a combination of factors.     

Delineation of vegetation shaded ox-bow lakes in Ganges flood plain,India

Floating vegetation cover over the ox-bow lake withstands against its sharp delineation. A good many spectral indices are successfully used for water body delineation. But how far these are applicable in vegetation-shaded ox-bow lakes is a research question. The study also aimed that if the existing indices are not satisfactory and how a new index could be endorsed for resolving the problem. The study additionally monitored the ox-bow lake and vegetation cover area from 1991 to 2021 based on Landsat satellite images.Normalized differences water index (NDWI), Modified NDWI (MNDWI), Re-modified NDWI (RmNDWI), and Normalized Difference Vegetation Index (NDVI) spectral indices were used for delineating ox-bow lakes and multiple accuracy test measures revealed that these are not highly satisfactory. Vegetation inclusive aggregated water index (ViAWI) was built by coupling mentioned spectral indices with the vegetation index and the ensemble map was found more accurate.Monitoring the ox-bow lake area clearly showed that these declined in the last 30 years irrespective of the historical drainage modification legacy of the major rivers to which the ox-bow lakes belonged. Aquatic vegetation cover within ox-bow lakes changed dynamically.The endorsed ViAWI would be a good approach for resolving wetland delineation shaded with floating vegetation and it could be used in other regional units worldwide. Quantitative information regarding ox-bow lake and vegetation cover within ox-bow lakes would be valuable data support for adopting ox-bow lake conservation and restoration planning.     

Spatial patterns in aquatic vegetation composition and environmental covariates along chains of lakes in the Kokemäenjoki watershed (S. Finland)

The diversity and community structure of macrophyte vegetation was studied in 50 boreal lakes forming several upper reaches of lake chains around Lammi, southern Finland. Water chemical parameters and morphometry of the basins were included in a multivariate analysis. Floating-leaved vegetation was the dominant growth form, followed by emergent plants. In downstream lakes, the dominance of floating-leaved macrophytes declined, and emergent species increased in abundance. Species richness was highest in larger lakes, with a wider range of littoral habitats than smaller lakes. Electrical conductivity (range 18–151 mS cm⁻¹, 25 °C) of the water correlated well with patterns in diversity among lakes, but this was not the case for nutrient concentrations. As a whole, morphometrical characteristics of lake basins showed better correlations with vegetation structure than any of the measured chemical parameters. The macrophyte vegetation of neighbouring lake chains differed considerably, depending on the surrounding landscape properties, water quality of the lakes and immigration history of plant species.     

Distribution of freshwater snails in the river Niger basin in Mali with special reference to the intermediate hosts of schistosomes

Snail surveys were carried out in various parts of Mali. All areas surveyed are part of the Niger basin being either affluents or irrigation schemes fed by this river. The snail species present varied greatly between areas. The following potential hosts of schistosomes were recorded: Biomphalaria pfeifferi, Bulinus truncatus, B. globosus, B. umbilicatus, B. forskalii and B. senegalensis. In the large irrigation schemes, i.e. ‘Office du Niger’ and Baguinéda, only B. pfeifferi and B. truncatus appear to be intermediate hosts. Snail distribution appeared to some extent to be focal and high snail densities appeared to be associated with human water contact activities, which apparently create favourable biotopes for the snails. This is probably due to an alteration of the vegetation and an increase of the trophic status of the site by contamination with food remnants and other debris. The larger irrigation canals or lakes in these schemes play an important role in the transmission of human schistosomes and transmission appears to be very focal in these habitats. Infected snails are almost exclusively found in well-defined human water contact sites (WCS). Local infection rates with schistosomes were often high (i.e. up to 27% in B. pfeifferi). In urban areas (i.e. Bamako), transmission patterns are more variable. In Bamako schistosome-infected B. truncatus were found in the Niger river. A number of smaller semi-permanent or permanent streams are very important transmission sites, and schistosome infections were recorded from B. pfeifferi, B. truncatus and B. globosus. Schistosome infection rates in B. pfeifferi were often high (up to 30%). In a new lake at Sélingué, B. truncatus was found to be widely distributed only about a year and a half after the dam was constructed, and in some sites schistosome infections were recorded.     

Diversity and Above-Ground Biomass Patterns of Vascular Flora Induced by Flooding in the Drawdown Area of China's Three Gorges Reservoir

Hydrological alternation can dramatically influence riparian environments and shape riparian vegetation zonation. However, it was difficult to predict the status in the drawdown area of the Three Gorges Reservoir (TGR), because the hydrological regime created by the dam involves both short periods of summer flooding and long-term winter impoundment for half a year. In order to examine the effects of hydrological alternation on plant diversity and biomass in the drawdown area of TGR, twelve sites distributed along the length of the drawdown area of TGR were chosen to explore the lateral pattern of plant diversity and above-ground biomass at the ends of growing seasons in 2009 and 2010. We recorded 175 vascular plant species in 2009 and 127 in 2010, indicating that a significant loss of vascular flora in the drawdown area of TGR resulted from the new hydrological regimes. Cynodon dactylon and Cyperus rotundus had high tolerance to short periods of summer flooding and long-term winter flooding. Almost half of the remnant species were annuals. Species richness, Shannon-Wiener Index and above-ground biomass of vegetation exhibited an increasing pattern along the elevation gradient, being greater at higher elevations subjected to lower submergence stress. Plant diversity, above-ground biomass and species distribution were significantly influenced by the duration of submergence relative to elevation in both summer and previous winter. Several million tonnes of vegetation would be accumulated on the drawdown area of TGR in every summer and some adverse environmental problems may be introduced when it was submerged in winter. We conclude that vascular flora biodiversity in the drawdown area of TGR has dramatically declined after the impoundment to full capacity. The new hydrological condition, characterized by long-term winter flooding and short periods of summer flooding, determined vegetation biodiversity and above-ground biomass patterns along the elevation gradient in the drawdown area.     

The importance of drawdown and sediment removal for the restoration of the eutrophied shallow Lake Kraenepoel (Belgium)

Lake Kraenepoel (Belgium) is a shallow lake (22 ha), divided in two basins since 1957 by a shallow dike. The lake was used for fish farming until World War II and was drawn down about every 5 years to harvest fish. Despite its dense historical carp population, it had clear water and a rich Littorelletea vegetation. During the course of the 20th century, the lake became eutrophic and the Littorelletea vegetation degraded. The northern basin, which was still drawn down about every decade after 1957, retained its clear water and had a dense submerged macrophyte vegetation. The southern basin, which was never drawn down after 1957 and which received direct surface water inputs, had become a turbid shallow lake with phytoplankton blooms in summer. In 2000, efforts were taken to restore the lake: the entire lake was drawn down, the fish community was biomanipulated, nutrient-rich surface water inputs were diverted from the southern basin and sediments were removed (only in the northern basin). Fish biomanipulation and sediment removal were successful in the northern basin, as nutrient levels declined and the Littorelletea vegetation recovered. In the southern basin, sediment analyses indicated that drawdown resulted in sediments with a lower water and organic matter content and water column turbidity decreased after the drawdown. But pH in the southern basin declined to <4, probably because sulphides in the sediment were oxidized during drawdown and sediment desiccation. In contrast, desiccated sediments were removed from the northern basin and pH did not decline below 6 after restoration. In spite of the still high dissolved nutrient concentrations, phytoplankton biomass declined significantly in the southern basin, probably due to acidification. However, no Littorelletea species colonised the lake bottom in the southern basin. Thus, lake drawdown may be a useful management technique to promote clear water conditions in shallow lakes. However, acidification due to sulphide oxidation may be an undesirable outcome and should be considered in drawdown and sediment desiccation manipulations.     

Taxon-related pollen source areas for lake basins in the southern Alps: an empirical approach

The pollen/vegetation relationship in broadleaved forests dominated by Castanea sativa was analysed using an empirical approach. The pollen content of surface sediments of three lake basins of different sizes (6.3, 22.2, and 101.2 ha) in Ticino (southern Switzerland) was used for a comparison with the surrounding vegetation. We surveyed the vegetation around the two small lakes, Lago di Origlio and Lago di Muzzano, and estimated the relative crown coverage of tree species. The regional vegetation outside the lake catchment (ca. >1 km) was determined with the data from the first Swiss National Forest Inventory. For the third large lake, basin of Ponte Tresa, we used only this latter approach for comparison with pollen data. We compare uncorrected and corrected pollen percentages with vegetational data that were processed with distance-weighting functions. To assess the degree of correspondence between pollen and vegetation data we define a ratio pollen/vegetation, which allows a comparison at the taxon level. The best fit between total pollen load and vegetation is reached for a distance from the lake shore of ca. 300 m for Lago di Origlio (150×350 m in size) and of ca. 600 m for Lago di Muzzano (300×750 m in size). Beside these general patterns, our analysis reveals taxon-specific pollen dispersal patterns that are in agreement with results from previous studies in northern Europe. Ratios of species with local (proximal) and long-distance (distal) pollen dispersal provide evidence that pollen dispersal mechanisms can influence the size of the taxon-related pollen source area, from small (100–400 m) to large (>5 km) for the same lake. The proportion of distal species increases with increasing lake size, highlighting the predominance of atmospheric pollen transport. We conclude that the large species-related differences in pollen source areas have to be taken into account when the provenance at a site is estimated and discussed.     

The southern limit of the Mediterranean vegetation in the Sahara during the Holocene

Holocene records from the southern Sahara in Niger allow a reconstruction of the vegetation history and inform us about the former extension of the Mediterranean. Both pollen and charcoal analyses evidenced the direct contact of Sudanian and Saharan savannas during the middle Holocene at about 19°N, whereas at 20°N the transition from the Saharan savanna to the desert was found. In southwestern Libya (26°N) a combination of a Saharan desert vegetation and a semi‐desert Artemisia shrub on the plateaus demonstrated the contact with Mediterranean influenced formations. Regular ash and charcoal layers in middle‐Holocene sediments of the northern Niger prove an early interference of man with the vegetation development. One has to imagine that, in combination with the cattle‐keeping and the later metal production, man could have changed the former northern Sudanian vegetation into the present Sahelian savanna system from the middle Holocene on.     

Assessing the potential for recovery of lakeshore vegetation: species richness of sediment propagule banks

To assess the potential and develop appropriate techniques for the recolonization of lakeshore vegetation at sites where it had been completely lost, a pilot project was launched at Lake Kasumigaura, Japan. We investigated the species composition and density of the soil seed banks (propagule banks) of lake sediments at nine sites (total area, 65,200 m²) where lake sediments were spread thinly (∼10 cm) on the surfaces of artificial littoral zones. These zones were constructed in front of concrete levees and had microtopographic variations. In total, 180 species, including six endangered or vulnerable species and 12 native submerged plants that had disappeared from the aboveground vegetation of the lake, were recorded during the first year of restoration. The distribution of each restored species at the sites suggested the importance of microtopographic variation for recolonizing species-rich lakeshore vegetation. Furthermore, the origin of the source sediment affected the species composition of the established vegetation.