Stable Water Levels Research Articles

A Method and Equipment for Continuously Testing the Permeability Coefficient of Rock and Soil Layers

The water pressure test and steady‐flow pumping test are still commonly used for measuring the permeability coefficient of rock and soil strata. Limited by the fact that the average value of the permeability coefficient could be obtained only by this testing method, the accuracy of the experimental results of the permeability coefficient for special rock and soil strata is not good. Therefore, a new on‐site testing method and equipment for continuously measuring the permeability coefficient of rock and soil strata is studied in this paper. The method is suitable for water pressure testing in borehole and the steady‐flow pumping test. The technical proposal is when the pumping test or water pressure test is carried out, the final water penetration will tend to be a stable value, and then, the high‐precision current meter probe will be placed at the bottom of the pumping test hole or water pressure test hole. For the pumping test, the current meter will be lifted uniformly from the bottom of the borehole testing section to the stable water level. Meanwhile, the flow rate of a differential zone of the tested section is continuously detected. For the water pressure test, the current meter will be lifted uniformly from the bottom of the borehole test section to the top of the borehole test section, and the flow rate of the differential section will be continuously detected. Through data analysis and processing, not only the average permeability coefficient of the detected sections can be obtained but also the permeability coefficient of the differential section of the rock and soil stratum can be calculated, respectively. Furthermore, the corresponding relationship between the permeability coefficient and the detected location can be obtained. In view of the abovementioned reasons, the leaking point, the specific position, and the leakage quantity of the detected section could be found out accurately, which will improve the accuracy of the testing results obviously.

Management of loss of offsite power avoiding reactor trip

A loss of offsite power event in a nuclear power plant resulting from the loss of connections to the electrical grid can be effectively managed without resulting in an unscheduled reactor trip. We have developed effective procedures for managing such house load operations that will maintain a stable steam generator water level using the auxiliary feedwater system. The procedures are based on a first-principle energy balance with the heat flux from the primary to the secondary side represented through an average primary system temperature. The reduced order model has been validated through actual simulations of steam generator dynamics with the MARS-KS code. With the help of the reduced order model, various scenarios or tracks involving judicious combinations of reactor power, reactor coolant flowrate and steam generator feedwater flowrate that could support stable house load operations are simulated and summarized as an operating procedure in a multi-path event tree structure.

Managed marshes can be good alternatives to natural marshes as breeding habitats for birds

Loss of natural tidal marshes has caused rapid population declines for many bird species, raising the question about whether managed marshes can be used for bird conservation. Although many studies have indicated that managed marshes can provide a complementary habitat for birds, it is unclear how the breeding habitats provided by managed marshes compare with those provided by natural marshes. We compared habitat conditions (vegetation and food) and breeding performance of a common reed specialist, the Oriental reed warbler (Acrocephalus orientalis), in natural and managed artificial reed marshes (about 2 km × 5 km) at Chongming Dongtan, an estuarine wetland in China. We found that vegetation was denser and warbler food resources were greater in managed than in natural marshes. The density of breeding territories, nest density, clutch size, egg size, and fledgling number per nest were greater in managed than in natural marshes. Breeding failure was reduced in managed marshes because of a reduced risk of nest predation. However, the high nest position on the reeds in the managed marshes increased the risk of nest destruction by strong wind. The better breeding performance in managed than in natural marshes could be attributed to the following factors: the high and stable water level in the managed marshes increased reed growth and arthropod reproduction and decreased access by terrestrial predators; dense vegetation helped conceal nests from predators; and human activities in the managed marshes deterred nest predators. The results suggest that managed marshes can provide quality breeding habitat for the Oriental reed warbler and probably for other marsh birds and can therefore help compensate for the loss of natural marshes. The preference of the Oriental reed warbler for managed marshes largely depends on the suitable habitat conditions. The current study highlights the importance of maintaining a relatively high and stable water level.

STUDYING SIMULATION FUZZY BASED-PID CONTROLLER TO CONTROL WATER LEVELS IN MARINE BOILERS

On ships, boilers are used for many purposes: Supplying steam to the main steam turbine to drive the propeller to create thrust, drive generators, drive pumps and winches. Also, it has a role to drive trouble equipment, provide steam for heating lubricants, fuel, steam supply for air conditioning systems for crew members ... With so many important uses, ensuring good operation of the boiler is a matter of primary concern for operators. In the operation of the boiler, controlling the water levels ensures not only good steam generation but also operator safety as well as the boiler itself. Automatic control of the water supply process is an important part of the boiler control system. This system has the function of maintaining a stable water level in the boiler. Currently, fuzzy control theory, whose mathematical tool is the fuzzy set theory of L.A Zadeh is being developed strongly. Different from the old control technique that relies purely on the absolute accuracy of the information that many applications cannot, the fuzzy control can handle unclear information. Information that their accuracy is only recognized by their relations with each other and can only be described in the control language. Fuzzy control allows copying personal information processing and control methods to solve complex control problems. The paper focuses on research to use fuzzy control theory combined with traditional PID controller to achieve optimal quality control for the process of adjusting the boiler water level. Construct a fuzzy controller to adjust parameters of the PID water level controller to optimize the process of adjusting the boiler water level. Simulation of water level control of fuzzy PID control on Matlab-Simulink software.

Evolution of a landslide-dammed lake on the southeastern Tibetan Plateau and its influence on river longitudinal profiles

Landslide damming of valleys may have a significant effect on the evolution of fluvial landscapes. The southeastern Tibetan Plateau is highly prone to landslide damming due to its deeply incised valleys and young, active geology. Here we present a sedimentological investigation of a landslide-dammed lake in the upper reach of Lulang River on the eastern Himalayan syntaxis. Detailed interpretation of lacustrine varve, lakeshore, and subaqueous delta sediment shows that Lulang landslide-dammed lake (LLDL) had a surface elevation of 3360 m a.s.l., an area of 3.3 × 106 m2, and a volume of 6.5 × 107 m3. Radiocarbon dating of six organic clay lacustrine samples demonstrate that LLDL formed before 24.2 ka cal. BP and persisted for at least 8.8 ka. Sediment infill reached full capacity soon after 15.4 ka cal. BP and fluvial conditions then prevailed. Sedimentary evidence and morphological analysis of cross sections along the LLDL outlet channel revealed a larger, earlier lake with a total volume of 4.3 × 109 m3 and water surface elevation at 3570 m a.s.l. that failed catastrophically; the resulting outburst flood drained 98.5% of the impounded lake. The remnant lake maintained a relatively stable water level of 3360 m a.s.l. for its lifetime of at least 8.8 ka. Long profile and steepness index analysis indicate that the location of the catastrophic dam failure and subsequent long-term blockage is associated with a knickpoint. The origin of the knickpoint may have been polygenetic, however, the landslide damming seems to have increased its distinctiveness and persistence. The relatively wide valley and low channel slope characteristic of reaches upstream of LLDL is likely to have resulted from glacial activity, rather than backwater aggradation which had only a local influence.

Temporal and Spatial Variation of Mercury in the Water of the Ruxi River Estuary, a Typical Tributary of the Three Gorges Reservoir Area

Four typical estuaries located in the Ruxi River, a tributary of the Yangtze River, were selected to investigate the possibility of mercury pollution in tributary estuaries from the Three Gorges reservoir water storage. Water samples were collected during the water storage period (September to October), the flooding period (November to December), the water withdrawal period (February to March), and the drying period (May to June) to determine the levels of mercury species including total mercury (THg), particulate mercury (PHg), dissolved mercury (DHg), reactive mercury (RHg), total methylmercury (TMeHg) and dissolved methylmercury (DMeHg). The results showed that the concentration of THg and TMeHg in the estuary of the Ruxi River was comparable with that of other reservoirs or natural waters in China. There was a significant difference in the concentration of DHg and TMeHg in the water at different depths, because DHg and TMeHg might be derived from the release of sediment to the overlying water. Comparing the concentrations of different mercury species in the four estuaries during the same period, it was found that the difference of water flow direction during the water storage period could lead to an uneven concentration distribution of THg and PHg in the estuary areas. During the water withdrawal period, the particles in the estuary water could adsorb and carry a large amount of PHg, resulting in higher THg concentration in the water in comparison with other periods. The concentration of TMeHg in the flooding and the drying periods was higher than in the other two periods, indicating that the stable water level might be conducive to the accumulation of methylmercury in the water, and the severe disturbance of the water level could significantly reduce the concentration of TMeHg in the water.

Periods of Extreme Shallow Depth Hinder but Do Not Stop Long-Term Improvements of Water Quality in Lake Apopka, Florida (USA)

We recently documented that during times of extreme shallow depth, there are severe effects on the water quality of one of the largest shallow lakes in the southeastern USA—Lake Apopka. During those times, total phosphorus (TP), total nitrogen (TN), chlorophyll-a (Chl-a) and toxic cyanobacteria blooms increase, and Secchi transparency (SD) declines. The lake recovers when water levels rise in subsequent years. In this paper, we determined whether extreme shallow depth events, particularly when they re-occur frequently, can stop the long-term recovery of a shallow eutrophic lake undergoing nutrient reduction programs. Apopka is an ideal location for this case study because the State of Florida has spent over 200 million USD in order to reduce the inputs of P to the lake, to build large filter marshes to treat the water, and to remove large quantities of benthivorous fish that contribute to internal P loading. We obtained data from 1985 to 2018, a period that had relatively stable water levels for nearly 15 years, and then three successive periods of extreme shallow depth, and we examined the long-term trends in TP, TN, Chl-a, and SD. There were significant decreasing trends in all of these water quality variables, and even though water quality deteriorated during periods of extreme shallow depth, and reduced the slope of the long-term trends, it did not stop the recovery. However, in the future, if climate change leads to more frequent shallow depth events, which in lakes such as Apopka, result in the concentration of water and nutrients, it is unclear whether the resilience we document here will continue, vs. the lake not responding to further nutrient input reductions.

Using a new database of plant macrofossils of the Czech and Slovak Republics to compare past and present distribution of hypothetically relict fen mosses

Modern databases containing large amounts of botanical data are a promising source of new results based on large data analyses. We used a new database of plant macrofossils of the Czech and Slovak Republics to compare the recent distributions of putative relict species of fen bryophytes with their past distributions since the late glacial. All the species studied occur in late-glacial sediments, but mostly in regions where they are recently recorded (19–21st centuries). There are specific regions rich in putative relict species of fen bryophytes both in late glacial / early Holocene times and recently. In some cases the target species were, however, found outside the recent distribution range where environmental conditions are no longer suitable for their occurrence. We further found that the total number of the glacial and early-Holocene records greatly exceeds the total number of records for the middle Holocene, when succession to woodlands or bogs resulted in a reduction in species of bryophytes that are specific to open rich fens. The observed patterns may imply a relict status of the target species. We especially documented a substantial decline in the abundance of species requiring a high and stable water level (Drepanocladus trifarius, Meesia triquetra and Scorpidium scorpioides), both throughout the Holocene and during the most recent transformations of the landscape. In contrast, those species that tolerate transient decreases in water level persisted into recent times at more localities (Calliergon giganteum, Hamatocaulis vernicosus, Paludella squarrosa). Macrofossil data cannot, however, provide a quantitative analysis of the distribution of a species, because the number of recent data usually greatly exceeds the number of fossil records. The reason is that the area sampled in palaeoecological research is very small as it is time-consuming and expensive; cores or excavations usually are of only a few square centimetres. Despite this shortcoming, macrofossil data are an important, but not the only, source of evidence for the identification of the relict status of a species.

Why has Phragmites australis persisted in the increasingly saline Gippsland Lakes? A test of three competing hypotheses

Common reed Phragmites australis is the dominant vascular plant species of the shorelines of the Gippsland Lakes, south-eastern Australia. Although substantial declines have been reported for over 50 years, with increasing salinity posited as the cause, P. australis still occurs around the Gippsland Lakes, including in environments with near-oceanic salinities. The occurrence of P. australis in highly saline environments cannot be explained in terms of either seasonal variations in surface water salinity or a freshwater subsidy provided by intrusions of non-saline groundwater into the root zone. An experimental growth trial with plants of different provenance showed that P. australis grew vigorously even at 8–16PSU (with maximum aboveground biomass at 2–4PSU). There was some evidence that specimens from saltier sites were more salt tolerant than those from fresher sites. The selection of salt-tolerant strains is the most likely explanation for the occurrence of P. australis in saline sites. However, anthropogenic salinisation is unlikely to be the only factor involved in the historical loss of reed beds, and lower and more stable water levels following the permanent opening of the Gippsland Lakes to the ocean in 1889 are probably also contributing factors.

BIOGENIC STRUCTURES OF UNIONIFORM BIVALVES IN WET-INTERDUNE DEPOSITS (LATE MIOCENE–EARLY PLIOCENE, ARGENTINA)

Abstract Environmental changes within a Neogene coastal dune system are recorded by endobenthic unioniform bivalves that lived in muddy or sandy interdune pond sediments. These bivalves were suspension-filter feeders that formed dense, almost monospecific communities in the wet-interdune deposits of the continental intervals of the Rio Negro Formation (late Miocene–early Pliocene). Activity of unioniform bivalves appears to be related to sediment type; resting and locomotion traces dominate in the muddy heterolithic facies, whereas equilibrium/escape structures prevail in the sand-dominated heterolithic facies. These traces characterize two scenarios of the wet-interdune development. First, during high and/or relatively stable water levels, bivalves colonized the muddy bottom and produced resting and locomotion traces. When water level dropped due to desiccation, biogenic structures were impacted by the formation of mud cracks and subsequently covered by sand delivered by migrating dunes. Second, in spite...

A new early Holocene shoreline displacement record for Blekinge, southern Sweden, and implications for underwater archaeology

We present evidence of a submerged early Holocene landscape off the Blekinge coastline in the Baltic Sea, dating to the Yoldia Sea and Initial Littorina Sea Stages when the water level was lower than at present. 14C dated wood remains obtained by surveillance diving and new archaeological findings in combination with bathymetric analyses and interpolations between other sites across the Baltic Sea were used for refinement of the shoreline displacement history of the region. The new results reveal a Yoldia Sea lowstand level at 20 m b.s.l., a subsequent Ancylus Lake highstand at 3 m a.s.l., and then a period of relatively stable water level at about 4 m b.s.l. during the Initial Littorina Sea Stage, several metres lower than previously concluded. The refined shoreline displacement record was used for palaeo‐reconstructions of the study area during four key periods, the Yoldia Sea lowstand phase, the Ancylus Lake transgression phase, the Ancylus Lake highstand phase and the Initial Littorina Sea lowstand phase, using elevation data and map algebra functions. A flow accumulation algorithm was used for reconstruction of the now submerged prehistoric river network in order to identify areas of high archaeological potential. Our revised shoreline displacement record, and especially its lowstand period during the Initial Littorina Sea Stage around 9500–8500 cal. a BP, raises future demands not only for specific archaeological shallow‐water surveys down to 4 m b.s.l. in the area, but also for a renewed cultural heritage management strategy. The results of this study fill an important gap in the early Holocene part of the shoreline displacement history of Blekinge, contributing to its completion since the deglaciation, which is unique for the Baltic Sea.

Can water-level management reduce malaria mosquito abundance around large dams in sub-Saharan Africa?

BackgroundWater level management has been suggested as a potential tool to reduce malaria around large reservoirs. However, no field-based test has been conducted to assess the effect of water level management on mosquito larval abundance in African settings. The objective of the present study is to evaluate the effects of water level drawdown rates on mosquito larval abundance.MethodsTwelve experimental dams were constructed on the foreshore of the Koka Dam in Ethiopia. These were grouped into four daily water drawdown treatments, each with three replicates: no water-level drawdown (Group 1; Control), 10 mm.d-1 (Group 2), 15 mm.d-1 (Group 3) and 20 mm.d-1 (Group 4). Larval sampling was conducted weekly for a period of 6 weeks each in the main malaria transmission season (October to November 2013) and subsequent dry season (February to March 2014). Larval densities were compared among treatments over time using repeated measures Analysis of Variance (ANOVA).ResultsA total of 284 Anopheles mosquito larvae were collected from the experimental dams during the study period. Most (63.4%; n = 180) were collected during the main malaria transmission season while the remaining (36.6%; n = 104) were collected during the dry season. Larvae comprised four Anopheles species, dominated by Anopheles arabiensis (48.1% of total larval samples; n = 136) and An. pharoensis (33.2%; n = 94). Mean larval density was highest in control treatment dams with stable water levels throughout the study, and decreased significantly (P < 0.05) with increasing water drawdown rates in both seasons. During the main transmission season, anopheline larval density was generally lower by 30%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, compared with the control dams (Group 1). In the dry season, larval density was reduced by 45%, 70% and 84% in Groups 2, Group 3 and Group 4, respectively, when compared to the control dams.ConclusionIncreased water drawdown rates were associated with lower mosquito larval abundance. Water level management could thus serve as a potential control measure for malaria vectors around reservoirs by regulating the persistence of shallow shoreline breeding habitats. Dam operators and water resource managers should consider incorporating water level management as a malaria control mechanism into routine dam operations to manage the risk of malaria transmission to human populations around reservoirs.

Analysis on influencing factors and simulation of sediment release by density current: the case of Xiaolangdi Reservoir

Density current venting by bottom outlets is the main form of sediment release from large reservoirs during sediment retention periods. Taking Xiaolangdi Reservoir as a case study, this study analyzed influencing factors of sediment release by density currents and proposed a semi-empirical formula to simulate the density current release process. The results show that the amount of incoming water and sediment, length of backwater, and sedimentation volume upstream of backwater zones are the main factors influencing sediment discharge. However, the importance of influencing factors varies slightly for different sediment supply areas. The semi-empirical formula provides a good simulation of the actual sediment release process under a relatively stable water level, and thus, it can extend scientific and technical support necessary for reservoir operation.

Effects of reservoirs water level variations on fish recruitment

ABSTRACT The construction of hydroelectric power plants has many social and environmental impacts. Among them, the impacts on fish communities, which habitats are drastically modified by dams, with consequences across the ecosystem. This study aimed to assess the influence of water level (WL) variations in the reservoirs of the Itá and Machadinho hydroelectric plants on the recruitment of fish species from the upper Uruguay River in southern Brazil. The data analyzed resulted from the WL variation produced exclusively by the hydroelectric plants generation and were collected between the years 2001 and 2012. The results showed significant correlations between the abundance of juvenile fish and the hydrological parameters only for some reproductive guilds. The species that spawn in nests showed, in general, a clear preference for the stability in the WL of the reservoirs, while the species that spawn in macrophytes or that release demersal eggs showed no significant correlation between the abundance of juvenile fish and hydrological parameters. A divergence of results between the two reservoirs was observed between the species that release semi-dense eggs; a positive correlation with a more stable WL was only observed in the Machadinho reservoir. This result can be driven by a wider range of WL variation in Machadinho reservoir.

Flora of karst lakes in the Pustynsky State Nature Reserve (Nizhny Novgorod oblast)

Pustynsky State Natural Reserve of Regional Importance (area 19,730 hectares) was established by decree of the administration of Nizhny Novgorod oblast on September 16, 2013. It is located in the Tyoshe-Seryozhinsky karst area of the Oka-Sura karst region or Seryozhe-Panskoy karst lake district. Its creation is justified by the need to protect the rare species of living organisms, diverse types of vegetation, unique landscapes and plant communities that are concentrated in this territory. Despite the fact that in 1934 on the shore of the Great Lake in the Staraya Pustyn village the biological station of the State University of Nizhny Novgorod was founded, local flora of the karst lakes which are linked into a single system by the channel of the River Seryozha, remains insufficiently studied. In 2014 and 2015 the authors conducted a study of the flora of the Pustynsky lake-river complex. The collection of material for study of the taxonomic composition of the flora of the reservoirs and the collection of herbarium material were carried out by the route method from a rowing boat and, in part, by traversing along the shore. Taxonomic, ecological (including the spectrum of life forms of plants) and ecobiomorphological analysis of the flora, including the analysis of the ratio of its latitudinal and longitude elements, was carried out in cameral conditions. The taxonomic analysis of flora showed 162 species of vascular plants from 61 genera and 42 families, 6 of these species – Najas minor All., N. major All., Trapa natans L., Potamogeton praelongus Wulf., P. trichoides Cham. et Schlecht. and Carex bohemica Schreb, being included in the List of Rare and Protected Species on the Territory of Nizhny Novgorod oblast. On the basis of the annotated list of plant species, taxonomic, geographic, ecological-coenotic and ecobiomorphological analysis of the flora of the water reservoirs was made. We confirmed that the flora of the lake-river complex is traditional for this territory. Poaceae, Cyperaceae, Potamogetonaceae, Polygonaceae and Asteraceae belong to the dominant families and Potamogeton L., Carex L., Juncus L. and Salix L. belong to the dominant genera of the Pustynsky lake-river system. The level of the hybrid component of the flora is extremely low, which is typical for the watershed lakes. We found that a 6.5 km stretch of the Seryozha River accounts for about 30% of species of the vascular plants belonging to the flora in the Volga River basin. The high species richness of the flora of this territory is due, primarily, to the specific features of the shoreline, forming a broad range of habitats and the relatively stable water level regime despite the strong fluctuation in the level of anthropogenic pressure. We found that boreal and plurizonal elements dominate zonally but Holarctic and Eurasian species – regionally. The predominance of species typical for the ecotone zones of lakes (hygrophytes, hydrophytes and mesophytes) is an integral feature of the ecological-coenotic diversity which is characteristic of the Volga River basin. According to the Raunkiaer classification of life forms, hemicryptophytes are the most numerous group and the hamephytes are the least numerous one. A biomorphological analysis shows the predominance of vegetative mobile, clearly polycentric and vegetative immobile monocentric ecobiomorphs.

Bank instability along a weir pool of the River Murray

ABSTRACTRiver banks are an important transition zone between aquatic and terrestrial environments. This ecotone is highly vulnerable to natural and anthropogenic disturbances. Bank erosion is a common occurrence along the River Murray. Morphological features reflecting river bank instability form a near-continuous pattern along large tracts of the river. This study investigates the character and extent of bank instability along the Torrumbarry Weir Pool. Over 90% of the bank length in this weir pool was assessed as being actively eroding. Notch development was the dominant instability mechanism and it promoted other forms of bank instability. Erosion notches result from stable water levels and inherent soil instability of the river banks along the weir pool. The character and extent of river bank erosion recorded along this section of the River Murray is an artefact of flow regulation and not a reflection of the natural occurrence of bank erosion in river networks. Water level management in the upstream weir pool has significant implications for the management of river banks along regulated reaches of the River Murray.

Comparing DNA enrichment of proliferating cells following administration of different stable isotopes of heavy water

Deuterated water (2H2O) is a label commonly used for safe quantitative measurement of deuterium enrichment into DNA of proliferating cells. More recently, it has been used for labeling proteins and other biomolecules. Our in vitro - in vivo research reports important stable isotopic labeling enrichment differences into the DNA nucleosides and their isotopologues (e.g. deoxyadenosine (dA) M + 1, dA M + 2, dA M + 3), as well as tumor cell proliferation effects for various forms of commercially available stable heavy water (2H2O, H218O, and 2H218O). Using an in vitro mouse thymus tumor cell line, we determined that H218O provides superior DNA labeling enrichment quantitation, as measured by GC-positive chemical ionization (PCI)-MS/MS. In addition, at higher but physiologically relevant doses, both 2H218O and 2H2O down modulated mouse thymus tumor cell proliferation, whereas H218O water had no observable effects on cell proliferation. The in vivo labeling studies, where normal mouse bone marrow cells (i.e. high turnover) were evaluated post labeling, demonstrated DNA enrichments concordant with measurements from the in vitro studies. Our research also reports a headspace-GC-NCI-MS method, which rapidly and quantitatively measures stable heavy water levels in total body water.

Relations between vegetation and water level in groundwater dependent terrestrial ecosystems (GWDTEs)

Alkaline wetlands and fens are groundwater dependent, terrestrial ecosystems (GWDTEs) existing throughout the temperate zone. They contain a large number of protected and endangered plant species and their ecological status is threatened by insufficient groundwater quality and quantity. However, management and conservation of fens are constrained by limited knowledge on the relations between vegetation and measurable hydrological conditions. This study investigates the relations between vegetation and water level dynamics in groundwater dependent wetlands in Denmark.A total of 35 wetland sites across Denmark were included in the study. The sites represent a continuum of wetlands with respect to vegetation and hydrological conditions. Water level was measured continuously using pressure transducers at each site. Metrics expressing different hydrological characteristics, such as mean water level and low and high water level periods, were calculated based on the water level time series. A complete plant species list was recorded in plots covering 78.5m2 at each site. Community metrics such as total number of species and the number of bryophytes were generated from the species lists and Ellenberg Indicator scores of moisture, pH and nutrients were calculated for each site.The water level correlates with the number of typical fen species of vascular plants, whereas bryophytes are closer connected to the stable water level conditions provided by groundwater seepage. The water level variability is proved to be a significant limiting factor for species diversity in wetlands, which should be considered along with the fertility in order to access the habitat quality. The study provides new insight in the water level preferences for GWDTEs which is highly needed in the management and assessment of anthropogenic damage to these ecosystems.

Convergence and impoverishment of fen communities in a eutrophicated agricultural landscape of the Czech Republic

AbstractQuestionsOn‐going rapid loss of fen biodiversity in Central Europe is well known, but rigorous testing of this is complicated. We compared historical and present‐day vegetation plot records from a cultural landscape rich in fishponds, where recent eutrophication and water table manipulations threaten the unique fen diversity. We assess species composition change over the last 50 yr.LocationTřeboň Basin, Czech Republic.MethodsFirst, we revisited historical vegetation plots to collect present‐day data and then identified the most similar present‐day record (the present‐day counterpart) because no permanent plots were available. Second, we inferred water level, pH and conductivity (a proxy of mineral richness) using a training set of present‐day field measurements, and calculated Ellenberg indicator values. Then we applied modified TWINSPAN classification, CCA, PERMANOVA, PERMDISP and RMANOVA in order to test changes in the species composition, β‐diversity and environmental conditions between the historical records and their present‐day counterparts.ResultsFen vegetation has persisted on half of the sites. Out of four vegetation types, poor fens and especially flooded fens were over‐represented in the present‐day subset, while rich fens and quaking fens were under‐represented. Overall species composition differed between historical plots and their present‐day counterparts, even within individual vegetation types. Historical rich fens showed significantly higher β‐diversity than their present‐day counterparts, which predominantly represent flooded fens. Inferred water level and its fluctuation, Ellenberg moisture and nutrient values have increased, while inferred pH, conductivity and Ellenberg light value have decreased.ConclusionsThe historically wide array of fen vegetation has turned into a homogeneous and floristically depauperate set of acidic yet productive flooded fens with a high water level. Rich and quaking fens that were both low in nutrient availability and had a stable water level near the moss layer experienced a large and substantial reduction and have become rare in the landscape. Eutrophication combined with a lack of management has resulted in fen species persisting only in flooded fens. However, fluctuating water levels and high nutrient availability in flooded fens favour productive Sphagnum fens over the other vegetation types, and, importantly, do not support some endangered fen species.

Analysis of soil seed bank patterns in an oxbow system of a disconnected floodplain

Soil seed banks have a high potential for vegetation re-establishment in restoration projects. We studied the soil seed bank in an oxbow system of a disconnected floodplain of the Danube River in Southern Germany. The aim of the study was to analyze if floodplain target species were still present in the seed bank after more than 150 years of embankment and disconnection from fluvial dynamics. In this context we investigated seed density, seed bank species richness and species composition in four broad habitat types with and without water-level fluctuations during the time of embankment (permanent water, fluctuating water, reed bed, hardwood floodplain forest). In addition, the similarity between seed bank and above-ground vegetation in these habitat types was studied in order to predict the success of future restoration measures. In total, 124 vascular plant species were determined in the seed bank samples. More than 50 % (66 species) were target species typical for floodplain habitats and 26 of these target species were lost or very rare in the above-ground vegetation. The four habitat types differed significantly in mean seed density and mean species richness. Mean species richness and the number of target species in the seed bank as well as the mean seed density were greatest in the habitats with fluctuating water level whereas mean seed density was much lower in the parts with more or less stable conditions like permanently standing water and hardwood floodplain forest. Sørensen similarity between seed bank and above-ground vegetation was very low in habitats with more or less stable water levels and desirable floodplain target species were very rare or completely absent. Our results indicate that the soil seed bank can be an important seed reservoir for the ecological restoration of floodplain plant communities especially for habitats with unstable environmental conditions during the period of disconnection. Restoration of water level dynamics is important to maintain the seed bank of populations of floodplain target species.