Single-species versus mixed-species community: which one is better for shore stabilization. A case study of Chongming Island, China

There are five vegetation communities for shore stabilization on the southern coast of Chongming Island: a reed (Phragmites australis) community, a 4-yr-old Salix babylonica-Phragmites australis community (4Sb), an 8-yr-old S. babylonica-P. australis community (8Sb), a 4-yr-old Taxodium ascendens-Phragmites australis community (4Ta), and an 8-yr-old T. ascendens-P. australis community (8Ta). One major question is which is better for shore stabilization: the reed community (a single-species community) or 4Sb, 8Sb, 4Ta and 8Ta (mixed-species communities)? The soil stability index (K) and root length density (RLD) were selected as indicators for evaluating soil stability in response to water erosion. There are two main types of shore facing downward erosion and erosion scarp retreat along the southern coast of Chongming Island, and the erosion period may occur from March to August (scenario 1) or October to December (scenario 2). The assumed erosion period is scenario 1, and 4Sb is the most suitable plant community for preventing erosion scarp failure and mitigating shoreline retreat because it has the greatest K and RLD in the 20-50-cm deep soil layer among all of the vegetation communities within all intertidal zones. Additionally, 4Sb and 8Ta provide the best protection for reducing downward beach face erosion compared to the other vegetation types in the lower intertidal zone (LIT). At the middle intertidal zone (MIT) and higher intertidal zone (HIT), the reed community is optimal for protecting the shore face because it has the greatest K and RLD at 0-20-cm soil among the five vegetation communities in March-April and July-August within the MIT and HIT. Under scenario 2, 4Sb is still the most suitable type for reinforcing the scarp and preventing shoreline retreat. With respect to shore face downward erosion, 8Ta might provide the best protection for beach surfaces within the intertidal zones because it had the greatest K and RLD at 0-20-cm depth among the five vegetation types in November-December within the LIT, MIT and HIT.     

Atmospheric nitrogen-deposition may intensify phosphorus limitation of shallow epilithic periphyton in unproductive lakes

1. We tested whether increasing atmospheric nitrogen (N) deposition along a north–south gradient intensifies epilithic phosphorus (P) limitation in oligotrophic Swedish lakes from the north to the south. We examined the epilithic community at a shallow depth from seven northern and six southern Swedish lakes, and also compared the results with a lake located geographically between the two groups. We determined lake nutrient state, epilithic nutrient ratios and epilithic algal composition, as well as grazer N : P ratios, grazer-epilithon N : P imbalance, and N : P cycling ratios.
2. Epilithic communities appear to be generally more N-limited in the northern lakes and more P-limited in the southern lakes. Lake water total N (Tot-N) and epilithic N : P ratios were lower in northern than in southern lakes and the proportion of N₂-fixing cyanobacteria was higher in northern than in southern lakes.
3. Gastropod grazers had lower N : P imbalances and cycled less N relative to P in northern than in southern lakes.
4. Atmospheric N-deposition showed a strong positive correlation with lake water Tot-N and a much weaker positive correlation with epilithon N : P ratios. Atmospheric N-deposition also correlated negatively with the proportion of N₂-fixing cyanobacteria.
5. There are indications that increased atmospheric N-deposition towards the south might intensify P-limitation of epilithic algae and invertebrate grazers, although more studies are needed to show the strength and generality of our findings.     

Caesium-137 and lead-210 dating of recent sediments from Mondsee (Austria)

Mean annual sedimentation rates over the last 20–30 years were determined in the pre-alpine Mondsee (Upper Austria) using Cs-137 and Pb(Po)-210 profiles for sediment core dating and two natural sediment markers. Lower sedimentation rates of about 2–3 mm yr^–1 were observed in the central part of the lake near the shore at 18–20 m and in the southern part at 30 m depth. Higher sedimentation rates of 4–7 mm yr^–1 were found in the central part of the lake at 47 and 65 m and in the northern bay at 18 and 41 m depth. At both these sites the Pb-210 profiles were strongly disturbed in the upper zone of the sediment cores, whereas the Cs-137 pattern remained intact. The higher annual sediment accumulation rates can be explained only partly by deposition of allochthonous material discharged by the streams, enhanced eutrophication in these parts of the lake, erosion and sediment focusing by turbidity currents being also probable.     

Two mechanisms of aquatic and terrestrial habitat change along an Alaskan Arctic coastline

Arctic habitats at the interface between land and sea are particularly vulnerable to climate change. The northern Teshekpuk Lake Special Area (N-TLSA), a coastal plain ecosystem along the Beaufort Sea in northern Alaska, provides habitat for migratory waterbirds, caribou, and potentially, denning polar bears. The 60-km coastline of N-TLSA is experiencing increasing rates of coastline erosion and storm surge flooding far inland resulting in lake drainage and conversion of freshwater lakes to estuaries. These physical mechanisms are affecting upland tundra as well. To better understand how these processes are affecting habitat, we analyzed long-term observational records coupled with recent short-term monitoring. Nearly the entire coastline has accelerating rates of erosion ranging from 6 m/year from 1955 to 1979 and most recently peaking at 17 m/year from 2007 to 2009, yet an intensive monitoring site along a higher bluff (3–6 masl) suggested high interannual variability. The frequency and magnitude of storm events appears to be increasing along this coastline and these patterns correspond to a greater number of lake tapping and flooding events since 2000. For the entire N-TLSA, we estimate that 6% of the landscape consists of salt-burned tundra, while 41% is prone to storm surge flooding. This offset may indicate the relative frequency of low-magnitude flood events along the coastal fringe. Monitoring of coastline lakes confirms that moderate westerly storms create extensive flooding, while easterly storms have negligible effects on lakes and low-lying tundra. This study of two interacting physical mechanisms, coastal erosion and storm surge flooding, provides an important example of the complexities and data needs for predicting habitat change and biological responses along Arctic land–ocean interfaces.     

巢湖崩岸湖滨基质-水文-生物一体化修复

湖滨带生态修复不是简单的水生植物移种,还必须提供其适于生存的基质、水文等外部物理条件。基质作为水生植被的载体,既需要适宜的柔度,也要求一定的刚度。在巢湖崩岸湖滨综合调查的基础上,系统分析了崩岸湖滨带生态退化的成因,研发了基质、水文、生物一体化修复技术,解决了水生植物在恢复生长时期受基质流失和水力切割影响的问题,为水生植物营造了适宜的水生环境。通过西北岸万年埠湖滨的示范工程建设,取得了良好的治理效果,为巢湖崩岸湖滨的生态修复提供一种生态型的、可工程化实施的技术方法。     

Hazards of living on the edge of water: The case of Minnesota Point,Duluth, Minnesota

Based on a systematic sample survey among the residents of Minnesota Point, a fresh-water spit/baymouth bar on the southwest shore of Lake Superior, this study tests a number of hypotheses related to the perceived causes of lake level fluctuation and shore property hazards. The study found that, despite significant differences in property setting and the nature of flood and erosion hazards between the lakeside and the bayside of the spit, the majority of the respondents perceived that their property hazards were induced primarily by the manipulation of lake levels by the International Joint Commission (IJC). Consequently, one in every two respondents would like to lower the lake level by amounts ranging from 30 cm to more than 1 m. The study points out the physical limitations of controlling water levels and recommends that greater attention should be given to shoreline management, which could proivde guidelines for protecting existing coastal structures and for developing minimum standards for future encroachment of the remaining unused sections of the shoreline.Formly of the Department of Geography, University of Minnesota, Duluth, Minnesota 55812.     

Population structure of lakeshore willows and ice-push events in subarctic Québec, Canada

The effects of ice-push on shoreline population age structure of Salix planifolia was investigated at Clearwater Lake, a large lake (1270 km²) located in the eastern Canadian subarctic. Twenty-three willow stands located along a gradient of exposure to ice features were studied along the shoreline of a large island. Stand characteristics are significantly correlated with the degree of shore exposure. Drift-ice action maintains continuously vegetation free substrata furthering willow colonization in shoreline habitat. Well-rooted shrubs withstand disturbance through vegetative regenetation, that is profuse basal sprouting in response to ice-scouring and breakage of stems. Age structure of basal shoots is highly correlated with ice-scar dates. The rapid turnover of stem metapopulations frequently damaged by ice allows the shrubs to live older than usually. During recent decades, drift-ice activity contributed to maintain a fast changing shore zone, favourable for the development of shrub populations. High frequency and magnitude of ice-push events were caused by periodic high spring water levels.     

Early microhabitat use by age 0 year brook charr Salvelinus fontinalis in lakes

The early habitat use of age 0 year brook charr Salvelinus fontinalis in three north temperate lakes which differ in terms of shoreline physical habitat is described. In the two lakes, which contained abundant shoreline woody debris and inundated vegetation, brook charr were observed in extremely close proximity with these habitat features, near shore and near the surface. Fish were absent from open areas away from shore unless in close proximity with fallen floating logs near the surface, extending offshore. In a third lake that had no woody debris or inundated shoreline vegetation, brook charr were observed exclusively in close proximity with the shoreline itself, and near the surface. In all three lakes, fish were most closely associated with the shoreline and with woody debris and inundated vegetation (when present) shortly after emergence, and significantly farther from shore and deeper in the water column thereafter.     

Last glacial maximum biomes reconstructed from pollen and plant macrofossil data from northern Eurasia

Pollen and plant macrofossil data from northern Eurasia were used to reconstruct the vegetation of the last glacial maximum (LGM: 18,000 ± 2000 ¹⁴C yr bp ) using an objective quantitative method for interpreting pollen data in terms of the biomes they represent ( Prentice et al., 1996 ). The results confirm previous qualitative vegetation reconstructions at the LGM but provide a more comprehensive analysis of the data. Tundra dominated a large area of northern Eurasia (north of 57°N) to the west, south and east of the Scandinavian ice sheet at the LGM. Steppe‐like vegetation was reconstructed in the latitudinal band from western Ukraine, where temperate deciduous forests grow today, to western Siberia, where taiga and cold deciduous forests grow today. The reconstruction shows that steppe graded into tundra in Siberia, which is not the case today. Taiga grew on the northern coast of the Sea of Azov, about 1500 km south of its present limit in European Russia. In contrast, taiga was reconstructed only slightly south of its southern limit today in south‐western Siberia. Broadleaved trees were confined to small refuges, e.g. on the eastern coast of the Black Sea, where cool mixed forest was reconstructed from the LGM data. Cool conifer forests in western Georgia were reconstructed as growing more than 1000 m lower than they grow today. The few scattered sites with LGM data from the Tien‐Shan Mountains and from northern Mongolia yielded biome reconstructions of steppe and taiga, which are the biomes growing there today.     

Primary succession of subarctic vegetation and soil on the fast‐rising coast of eastern Hudson Bay,Canada

Aim The objectives of the study are: (1) to evaluate the dynamics of the maritime tree line and forest limit of white spruce, Picea glauca, within the dual framework of primary succession induced by the rapid post‐glacial land emergence on the eastern coast of Hudson Bay and the impacts of recent and past climate changes; and (2) to determine the time lapse between land emergence and seedling, tree, and forest establishment in the context of the primary chronosequence occurring on rising, well‐drained sandy beaches and terraces. Location The study area was located on the eastern coast of Hudson Bay (56°20′ N, 76°32′ W) in northern Québec, Canada. Methods We evaluated the colonization dynamics of white spruce as seedlings, tree‐line trees and primary‐forest trees at eight sites distributed along a 200‐km latitudinal gradient based on a mean land emergence rate of 1.2 m century^?1. A 30‐m wide by 140–300‐m long quadrat was positioned at random at the centre of each site. The elevation above sea level, position and age of all individuals of spruce present in the quadrat areas were determined, and the soils of each chronosequence were described. Results The main stages of primary succession along the emerging coast were common to all the sites, regardless of latitude, but occurred at different elevations above sea level (a.s.l.). White spruce seedlings colonized near‐shore beaches 2 m a.s.l., whereas the tree line and forest limit tended to form only at about 3–4 m and 4–8 m a.s.l., corresponding approximately to 180–825 years and 310–1615 years after land emersion, respectively. White spruce establishment at the tree line occurred about 50 years ago. Climatic conditions at this time were probably more favourable to tree colonization than when the species established at the forest limit. Soil formation was influenced primarily by distance from the seashore and elevation above sea level, with podzolization being accelerated by white spruce cover. Main conclusions The current tree‐line and forest‐limit positions on the rising coast of eastern Hudson Bay correspond to ecological limits established during the course of primary succession within a context of changing climatic conditions. The recent establishment of trees at the tree line and forest limit at relatively old coastal sites is associated with warmer conditions over the last 100 years. Although white spruce was present nearby, coastal sites were devoid of trees before the 20th century.     

Field study of Haplochromis burtoni: habitats and co-habitant

Synopsis This report describes the natural habitat of the cichlid fish Haplochromis burtoni along the Burundi coast of Lake Tanganyika in central Africa. Parameters of the physical environment as well as more general biological factors are described qualitatively and quantitatively. Temporary shore pools, a previously undescribed habitat, are examined in detail. These pools, appear to play an important role in the life cycle of Haplochromis burtoni and other mouthbrooding cichlids by providing, for a large part of each year, a protected area 0 which is particularly suited for reproduction, possibly at the cost of high predation. As a result of circaannual changes in the lake level, the shore pools are alternately isolated from and rejoined with the lake, allowing a regular exchange of fauna.     

Variations in the periphytic community structure and dynamics of Lake Nahuel Huapi (Patagonia,Argentina)

Little is known about periphyton community in Patagonia and the influence that urban development has on a particular water body. Lake Nahuel Huapi is located in a National Park with little industrial or agricultural activity in the basin, but it is influenced by urban discharges from San Carlos de Bariloche, a town of 80000 inhabitants located on its south shore. Variations in structure and dynamics of the periphyton community in Lake Nahuel Huapi were studied during 1 year, to examine the influence of urban discharges on this community. Periphyton samples were collected on the shoreline of the lake and evaluated for biomass (as chlorophyll a concentration) and cell density of the main algal groups, at sites with and without urban influence. Results indicated the major influence of pollution from urban sources on periphyton at the most impacted sites, as well as the effect of different local events at each site (degree of contamination, type of coast, wind exposure, etc.). Higher biomass and cell densities at contaminated sites were evident, but the variation of main algal groups through the year was similar in all the sites. Periphyton in Lake Nahuel Huapi proved to be an important bioindicator of urban impacts on this water body.     

Small fish communities in two regions of the Liangzi Lake, China, with or without submersed macrophytes

Small fish communities were compared between the vegetated and vegetation-free regions of the Liangzi Lake, a shallow lake along the middle reach of the Yangtze River, China. Fish were sampled using 10 × 10 m² block nets and poisoning. Three samples were taken from either the near shore area or lake centre of each region. A total of 19 fish species were collected; all species occurred in the vegetated region but only 12 occurred in the vegetation-free region. The dominant small fish were Carassius auratus auratus in the vegetated region and Ctenogobius giurinus in the vegetation-free region. Diversity, density and biomass of small fishes were significantly higher in the vegetated region than in the vegetation-free region in both near shore and lake centre areas. In the vegetated region, density and biomass of small fishes was significantly higher, while species diversity significantly lower in the near shore area than in the lake centre. In the vegetation-free region, density of small fishes was significantly higher in the near shore area than in the lake centre area, but species diversity or biomass was unaffected by location.     

Biomass seasonality of Caulerpa taxifolia in the Mediterranean Sea

The biomass of the introduced and invasive alga Caulerpa taxifolia was measured monthly over one year at four different sites along the French Mediterranean coast at depths of 5 and 20 m in a sheltered and an exposed area. At the 5 m depth, C. taxifolia mean biomass ranged from 203 to 518 g dry wt. m⁻², while at the 20 m depth, it ranged from 62 to 466 g dry wt. m⁻². The study clearly shows that a major characteristic of C. taxifolia is its perennial life cycle with relatively high biomass values throughout the year, in different biotopes. This could be a factor in the broad ecological impact of C. taxifolia.     

Defining bottlenose dolphin (Tursiops truncatus) stocks based on environmental,physical, and behavioral characteristics

The population structure of bottlenose dolphins, Tursiops truncatus, along the U.S. Atlantic coast has recently been redefined from one homogenous population into five coastal stocks. Local studies indicate even finer structure, primarily based on isolation of dolphins inhabiting estuaries. We identified population structuring of non‐estuarine coastal bottlenose dolphins during a study in New Jersey, the northern range along the Atlantic Coast. Using photo‐identification and distribution survey results, an analysis identified two major clusters of individuals significantly separated by five variables (distance from shoreline, group size, occurrence of the barnacle Xenobalanus globicipitis, avoidance behavior, and individual coloration). Sightings assigned to cluster 1 occurred in nearshore shallow waters (0–1.9 km, x?= 3.5 m), and those assigned to cluster 2 occurred further offshore in deeper waters (1.9–6 km, x?= 9.5 m). Only eight of 194 individuals (4%) were identified in both regions. Collectively, this suggests an occurrence of two stocks that are spatially, physically, and behaviorally distinguishable over a small distance. These results indicate that complexity in Tursiops population structure is not limited to latitudinal gradients or barriers created by estuarine habitats, but also by partitioning of habitat as a function of distance from shore and depth over small distances.     

Adaptive significance of facultative paedomorphosis in Triturus alpestris (Amphibia, Caudata): resource partitioning in an alpine lake

1. Facultative paedomorphosis is a polymorphism that has important evolutionary implications in promoting morphological differentiation and variation in habitat use. It occurs in several urodele species throughout the world. Several hypotheses based on life-history theory have been proposed to explain the wide range of habitats in which facultative paedomorphosis occurs, suggesting multifactorial causes.
2. In harsh habitats, such as mountain lakes, paedomorphosis might promote niche partitioning between morphs. This hypothesis was tested by comparing micro-habitat use and diet of two coexisting morphs in an alpine lake.
3. Paedomorphs occupied all microhabitats in the lake while metamorphs occurred only along the shoreline or at the water surface. Paedomorphic newts were frequent in deep water, where they foraged mainly on plankton. Plankton was poorly exploited by metamorphic newts, which fed mainly on terrestrial insects. Difference between morphs in microhabitat use, and consequently in the diet, were consistent in both sexes and in juveniles.
4. In adults, the mass and energy value of stomach contents did not differ between morphs, suggesting a similar food availability in the habitats occupied.
5. This study indicates habitat partitioning between morphs involving dietary differences. Specific benefits and costs of each ontogenetic pathway may allow their coexistence in this deep and fishless lake. Paedomorphosis benefits individual newts by making new food resources available and presumably reducing competition at the shore of the lake. However, the proximate causes of such an ontogenetic switch remain unclear.     

Climate,plant response and development of dunes on barrier beaches along the U.S. east coast

In recent years, the U.S. National Park Service has taken responsibility for eight National Seashores along the East and Gulf Coasts and has been supporting research aimed at an understanding of natural processes, human effects, and management techniques that will accomplish various goals related to public use. The importance of developing management approaches, including dune stabilization, consistent with goals of individual Seashores and in keeping with natural dune dynamics, has become increasingly clear. Current studies underway deal with variations in dune ecology along the coast and in the response of dune species to environmental variables. While certain basic processes (such as dune building or migration, inlet formation, littoral transport, and overwash) occur all along the coast, they do not do so with the same importance or frequency. The relative significance of such processes depends on the general climatic and oceanic conditions of any given area. Prevailing winds, shoreline orientation, average wave energies, sea level change, storm frequency, off shore profiles, shore configuration, and tidal range are important environmental factors which determine the relative importance of dune building, overwash, or various combinations of the two. Added to the climatic factors are the response of dune strand species to environmental forces and the distribution of adapted species along the coast. The behavior of plants adapted to dune building, overwash, or both, can be a significant factor in the development of shoreline morphology.Presented at the Seventh International Biometeorological Congress, 17 – 23 August, 1975, College Park, Maryland, USA.     

Floating mats: their occurrence and influence on shoreline distribution of emergent vegetation

1. A study was conducted on the northern shore of Lake Victoria (Uganda) to determine the factors controlling the occurrence of floating root mats and the influence of the floating mats on the distribution of emergent vegetation. 2. Environmental conditions within 78 bays in the study area were characterised using bay size, wave exposure, water depth, littoral slope, sediment characteristics and water level fluctuations. Emergent plants that form floating root mats occur along the shores of these bays. The way in which commonly occurring shoreline vegetation was distributed across a wave‐exposure gradient was compared with their distribution across a water level fluctuation gradient. 3. Results suggested that wind–wave action and water level fluctuations are important factors determining the occurrence of floating mats. Mat‐forming plants occur in the most sheltered locations along the shore and in waterbodies with modest water level fluctuations. 4. The ability to form mats facilitated the lakeward expansion of emergent plants. Plants forming floating root mats had a larger depth range than non‐mat forming plants. 5. The initiation mechanisms for the floating mats of emergent vegetation in Lake Victoria appear to be: (i) invasion of mats of free‐floating plants by emergent vegetation; and (ii) detachment of emergent plants from the lake bed following flooding. 6. The formation of floating mats comes with a cost and benefit to emergent plants. The cost is increased vulnerability to damage by water level fluctuations or wind–wave action, leading to reduced horizontal distribution. The benefit is that deep flooding is avoided, thus increasing vertical distribution. The net effect may be to lead to dominance of mat‐forming plants in low‐energy environments and non‐mat‐forming plants in high‐energy environments.     

Insect drift and the case of Mayrinia curvidens (Mayr) (Hemiptera: Pentatomidae) drift on the southern atlantic coast of Brazil

Insect drift on shore of lakes and seas is a relatively common phenomenon although apparently not frequently reported in the literature. Here we review the worldwide occurrence of insect drift with emphasis on Heteroptera, and speculate on possible causes to explain such phenomenon. The dramatic drift of millions of specimens of the pentatomid Mayrinia curvidens (Mayr) on the shore of the southern coast of the Atlantic ocean in Brazil is reported for the first time. This drift, previously observed to occur in the mid 70s on the coast of Paraná state with minor intensity (A.R. Panizzi, unpublished) was again observed on January 2006 along the Atlantic coast of Paraná (latitude 25 masculine 45 S), where an estimated population of 16 to 18 million of dead specimens of the bug were observed forming a windrow for at least 15 km along the ocean shore. The circumstances of such event are analyzed in detail considering meteorological data and the possible build up of populations of the bug on cultivated and non-cultivated host plants along the coast of the states of Paraná and Santa Catarina.     

Abundance and distribution of Neomysis mercedis and a major predator, longfin smelt (Spirinchus thaleichthys) in Lake Washington

Seasonal variations in the horizontal and depth distributions of Neomysis mercedis and longfin smelt (Spirinchus thaleichthys) were examined using night-time mid-water trawl and Bongo net samples collected in Lake Washington from July 1989 to February 1992. Mysid density varied spatially, seasonally and yearly. For example, during summer, and fall (odd years), mysid abundance was highest in the northern, and lowest in the southern sections of the lake, except in December 1991 when they were uniformly distributed. In fall (November 1990), mysid density was highest in the central basin of the lake. Furthermore, in winter of even years, highest mysid density occurred in the southern region of the lake, but in the central region in winter (February) of odd year. Longfin smelt horizontal distribution also varied seasonally. For example, density of the 1988 YC smelt (1+) was highest in the northern area of Lake Washington in summer but highest in the southern area in fall. During winter, distribution seemed random. The abundance of the 1990 YC smelt (YoY) was also highest in the northern section of the lake in summer, but highest in the southern section in fall; density remained high in the southern section in winter. But, by late spring when they were more than one year old, the distribution had changed such that highest abundance occurred in the northern and mid-section of the lake. By winter when they were about two years old and about to begin spawning, density had become highest again in the southern section. These suggest extensive movement of mysids and smelt from one area to another, perhaps driven by wind-induced water currents in the lake. Depth distribution patterns of mysids and smelt are discussed. Smelt were captured mainly in the shallow strata (8 m) of the lake during all seasons except during winter when they predominated at 50 m. Mysids were also mainly caught in the shallow strata of the lake during all seasons, although a significant proportion occurred at greater depths (> 30 m). The abundance of both species was positively correlated in spring and summer but negatively correlated in fall. A poor correlation was observed in winter. Negative correlation in fall was primarily due to the occurrence of mysids and smelt in different areas of the lake whereas poor correlation in winter was particularly due to their occurrence at different depths. Because of considerable overlap in the distribution of both species in the lake, mysids face a high risk of predation by smelt. This piece of information is consistent with the hypothesis that smelt control mysid abundance in Lake Washington. This revised version was published online in July 2006 with corrections to the Cover Date.