Wave and tidal flushing in a near-equatorial mesotidal atoll

Most of the atolls found worldwide are under microtidal regimes, and their circulation mechanisms are widely documented and well known. Here, we describe the flushing mechanisms of a small-sized mesotidal atoll, based on water-level, wave and current data obtained during two different periods (total of 60 d). Rocas is the only atoll in the South Atlantic Ocean and is built primarily of coralline algae. Two reef passages connect the atoll lagoon to the ocean. Synchronous current profilers were deployed at the two reef passages, one inside and one outside the atoll, to characterize the influence of tides and waves on the circulation. Results showed that wind waves drove a setup on the exposed side of the atoll and that currents were predominately downwind, causing outflow at both reef passages. Waves breaking on the windward side supplied water to the atoll causing the lagoon water level to rise above ocean water level, driving the outflow. However, unlike microtidal atolls, at Rocas Atoll the water level drops significantly below the reef rim during low tides. This causes the reef rim to act as a barrier to water pumping into the lagoon by waves, resulting in periodic activation of the wave pumping mechanism throughout a tidal cycle. As result, inflow occurs in the wider passage during 27% of each tidal cycle, starting at low tides and reversing direction during mid-flood tide when the water level exceeded approximately 1.6 m (while overtopping the atoll’s rim). Our findings show that tides play a direct role in driving circulation on a mesotidal atoll, not only by modulating wave setup but also by determining the duration of wave pumping into the lagoon.

     

Pacific sardine behaviour related to tidal current dynamics in Bahía Magdalena, México

The behaviour, distribution and abundance of the Pacific sardine Sardinops sagax , detected by acoustics, was studied in relation to the pelagic environmental conditions of water temperature, fluorescence and dissolved oxygen concentration induced by tidal currents in Bahía Magdalena, México (24°32' N; 112°01' W). Sampling was along an 18 km long transect covering an area inside the bay (mean depth 20 m), the main entrance to the bay (mean depth 35 m), and the continental shelf (mean depth 100 m). The main entrance to the bay was the most dynamic area along the hydrographic transect, where the Pacific sardines tended to aggregate, probably to feed on the phytoplankton accumulated during the receding tide. With the flood tide, a high-speed tidal current is generated, introducing cool water with low oxygen concentrations into the bay. During the ebb tide, a tidal wave is also formed, but the warm and relatively well oxygenated bay water mass is transported towards the open sea. Acoustic records showed that whatever the tidal current direction (inflow or outflow), no fish schools were detected within the area of more intense tidal current speeds (>120 cm s⁻¹). Visual observations of surface Pacific sardine schools during the flood tide indicate that sardines were out of the transducer signal detection range (<10 m depth), suggesting that Pacific sardines undergo vertical migration, probably to avoid the high water current speed with low dissolved oxygen content. This behaviour may have a relevant effect on the overall hydroacoustic estimation of small pelagic fish abundance in shallower pelagic environments such as this subtropical bay.     

Mangrove inundation and nutrient dynamics from a GIS perspective

A digital elevation model describing topography, tide elevation and inundation degree and frequency of a mangrove forest in North Brazil is discussed in relation to existing phosphate and physicochemical data in waters of an adjacent tidal creek. Due to smooth topography, an increase of 20 cm in tidal height above average neap tides increases flooded area from about 50 to 80%. Analysis of the relationship between microtopography, tidal height and flooding rate showed that in the upper 60 cm of the mangrove forest, increases of 20 cm in topographical height resulted in a doubling of the inundation frequency. This can be particularly relevant for the analysis of nutrient mobilization and vegetation structure of infrequently inundated wetlands. Throughout the year, low-tide phosphate in creek water was inversely proportional to the maximum area flooded during high tide, this correlation being higher during the dry season. Similarly, the inverse relationship between flooded areas and low-tide/high-tide pH ratios was highly significant during the dry season and the beginning of the rainy season. Although the high correlations obtained are based on data pairs obtained at high and low tide, it has to clarified whether the association between inundation degree and creek water pH is relevant for the stability of P compounds in sediment on the short scale of a tidal cycle.     

The simplified methods of evaluating detention storage volume for small catchment

Massive land development reduces the plant-cover area and increases the impervious area of watershed, which induces downstream flooding. A detention pond stores runoff from watershed and releases the stored runoff slowly to reduce the flood threat in the downstream area. While the runoff hydrograph is irregular, several researches verify that the runoff hydrograph can be represented by simple geometrical-shaped (such as triangular or trapezoidal) hydrographs. This study collects and develops simplified detention volume design models. The study also develops a suitable hydrological condition and the calculation method of detention volume for various models. A real world case is used to demonstrate the calculation procedure used in the detention pond design. The case shows that the combination of triangular inflow and triangular outflow produces a maximum detention volume, which implies a large reduction of peak flow needs greater detention volume. The combination of trapezoidal inflow and triangular outflow produces a second large detention volume. It implies a long duration of inflow hydrograph (IH) needs greater detention volume. A combination of triangular inflow and trapezoidal outflow results in a minimum detention volume, which indicates that either the storm water drains completely before the permissible outflow occurs, or storm water is kept from entering the detention pond before the inflow rate reaches the permissible outflow. In either case, the detention pond has more space to accommodate the flood inflow so as to reduce the rate of peak outflow.     

红树林生长带与潮汐水位关系的研究

根据海南东寨港林市村,廉江车扳镇那肋村,深圳锦锈中华等３个实验点１０条横断面红树林潮滩高程水准测量,林市村潮汐水位观测,潮汐特征水位及浸淹频率分布计算,参照有关港点潮汐实测或预测报资料,确定红树林外边界为平均海面或稍上,内边界（或林内最大高程）为回归潮平均高高潮位（或大潮平均高潮位）对国内外有关报道进行了评述,指出国内许多红树林文献中使用的“高潮位”,“中潮位”“低潮位”用潮汐学术语表述应为“回归     

Tidal cycling and parental behavior of the cichlid fish,Biotodoma cupido

Synopsis Parental behavior of the substrate-brooding cichlid, Biotodoma cupido, was studied in a small creek entering the lower Essequibo River, Guyana, where the freshwaters are affected by semi-diurnal tides. Physico-chemical variables of the tidal cycle were associated with the parental behavior of B. cupido. During late ebb and early flood tides, while off-spring were nest dependent, parents displayed intense aggression toward brood predators, mainly characins. At low tide, when the concentration of dissolved oxygen decreased to about 4 mg 1^–1 and that of free carbon dioxide increased to 28 mg 1^–1, parents entered a state of somnolence and brood predators vanished. Early flood tide brought an immediate and dramatic reversal of hypoxic and hypercarbic conditions and an associated renewal of aggressive and predatory activity. At very low tide, parents orally transferred the brood to a secondary nest depression in deeper water. The significance of water-level fluctuation to the evolution of this behavior, as well as that of parent-brood itineracy and the related phenomena of oral incubation and movable nests, is discussed.     

Reversing cavitation in tracheids of Pinus sylvestris L. under negative water potentials

Xylem cavitation is a frequent event, but since resistance to flow does not generally increase in vivo, reversal must also occur even under negative potentials. We demonstrated that this can occur in excised wood. Our results suggest that refilling of cavitated tracheids at negative water potentials may result from a change in equilibrium between gas concentrations, water potential and surface tension at the embolism interface. Excised branch-wood specimens from small trees of Pinus sylvestris were dried on the bench to a range of relative water contents and then rehydrated in a permeability apparatus using ultra-filtered, de-aerated water as permeant. Water inflow and outflow were measured gravimetrically by recording the gain or loss from two reservoirs held on balances. Flow was induced through the specimen by holding the balances at different levels, while an overall negative water potential could be imposed by raising the specimen above the inflow/outflow reservoirs. Changes in water content of the specimen were calculated as the difference between inflow and outflow. The time-course data for both relative water content and permeability were fitted to an exponential function to give initial and final estimates and a time constant. Rehydration occurred at all imposed water potentials, but the speed of recovery was affected at lower potentials. Where drying of the specimen was more protracted, permeability was initially lower but also recovered during permeation. Both flow and de-aeration were necessary for complete rehydration. A model requiring new information on gas concentrations and transport coefficients is suggested.     

Influence of fresh water discharge on nutrient distribution in a macrotidal lagoon,West Sussex,UK

Results of nitrate and phosphate concentrations measured using hand-held ‘Hach’ monitors are presented, both over individual tidal cycles and over longer term deployments at Pagham Harbour, West Sussex, UK. This macrotidal lagoon (offshore tidal range 3.0 m neaps–6.5 m springs) is a site of key importance as a nature reserve and a home for several rare species of plants and animals. In particular, the effects of fresh water-salt water stratification over 4 tidal cycles at two tidal-fresh water boundaries is presented. It is shown that obtaining periodic vertical profile measurements during individual tidal cycles helps to quantify the transport mechanisms of nutrients from the tidal limits into the main body of the lagoon. Of key interest is the interaction between sediment-bound nutrients with the surrounding water in which the sediment is suspended during parts of the tidal cycle. Synthesis of these results with existing knowledge about sediment-water-nutrient interactions reveals how it is possible for nutrients to become trapped at the muddy tidal limits of the lagoon. In certain cases it is shown that nutrient-rich water from fresh water streams only gradually mixes with the denser, salt water of the incoming tide. Whilst a degree of salinity-induced stratification may be expected during the flood tide, these observations suggest that the water column is stratified with respect to both N and P, even well into the ebb tide. Thus at sites where stratification is important, there is a tendency for nutrients to remain preferentially near the water surface, and thus come into contact with fine, less mobile sediments near the surface of inter-tidal zones, which are themselves, in general, accreting. Since the overlying water is generally slow-moving during high water, it is postulated that saline-induced vertical stratification of estuarine water is an important mechanism in promoting nutrient build-up in muddy inter-tidal areas of this kind.     

Assessment of Upper Taylor Slough water quality and implications for ecosystem management in Everglades National Park

This study addresses water quality conditions across several distinct hydrologic regimes in the Upper Taylor Slough (UTS) region of Everglades National Park and briefly considers implications for long-term water quality management. Due to upstream changes in water delivery and construction of a detention area, Taylor Slough has experienced a significant change in hydrology over a 27-year period, progressing from direct discharge at varying amounts to sheet flow via groundwater conditions. Cumulative flow and rainfall relationships at the inflow and outflow of UTS demonstrate distinct break points. These changes in water delivery and subsequent upstream water management have resulted in a change in water quality conditions within the UTS region. Since 1986, total phosphorus (TP) flow-weighted mean concentrations exiting UTS have significantly decreased from 10 µg/L in the late 1980s to 4 µg/L or less since 2010. Based on analysis of surface water ion ratios, saltwater intrusion is unlikely and rather hyporheic exchange could be occurring between the inflow and outflow of the UTS region. Based on the analysis of existing water quality data, the UTS region is a resilient oligotrophic wetland system retaining strong assimilation capacity in the face of major management changes. While TP concentrations remain extremely low, restoration is not complete for Taylor Slough and adjacent coastal basins will inevitably bring additional nutrient loading. Management of the Slough should recognize this and consider what water quality condition is best for long-term sustainability of Taylor Slough’s ecology.     

Rhythmic swimming activity in Anguilla anguilla glass eels: Synchronisation to water current reversal under laboratory conditions

Synchronisation of swimming activity to water current reversal every 6.2 h was tested in the European glass eel (Anguilla anguilla L.). When presented with a change in water current direction, glass eels exhibited rhythmic patterns of activity with a period close to the tidal one. Glass eels began to swim with the current and then alternated between positive and negative rheotaxis after each change in the water current direction. Results are discussed in relation to the flood tidal transport theory. Following synchronisation to current reversal, glass eels subjected to constant conditions displayed a weak rhythmic activity suggesting that locomotor behaviour might, in the wild, synchronise to several environmental cues related to the tide. Results obtained with different densities also suggest that social cues might improve the synchronisation.     

Theoretical analysis of systematic errors introduced by a pedicel-girdling technique used to estimate separately the xylem and phloem flows.

The water budget of fruits was analysed by means of a biophysical model of fruit growth, built and calibrated recently for peaches [Prunus persica (L.) Batsch]. This analysis was applied to the evaluation of systematic errors introduced by a pedicel-girdling method (with the observations being treated by means of a subtractive technique) used to separate the contributions of xylem and phloem flow to the total water inflow to the fruit. The flows were considered as solution transport through composite membranes and were calculated by means of equations drawn from non-equilibrium thermodynamics. The total inflow of water was simulated as dependent on the water status in the tree. The hourly time step was used for the simulation. The flows obtained by simulation of the pedicel-girdled fruit were compared with those found by simulation of the intact-pedicel fruit. The error introduced by the pedicel-girdling technique was evaluated theoretically and was shown to vary during the day, ranging from very small (relative error of 3-7%) at the period when the rate of fruit growth is maximal to 100% when the fruit volume does not change. The vascular flows obtained from the "girdling experiments" are discussed in relation to the possible theoretically estimated errors.     

Circulation changes depending on manifestations in soft tissue tensioning in the leg lengthening process

Surgical intervention was found to intensify circulation in the limb and redistribute the blood flow. Leg lengthening led to arterial inflow limitation due to the magisterial artery strain. The changes were accompanied both by increase of functioning capillaries in number and increase of venous outflow dependence on blood inflow. The decreased after surgery oxygen tension in m. gastrocnemius did not change throughout distraction. The increase of functioning capillaries in number in resting contributed to maintenance of tissue oxygenation in the initial period of distraction, and in case of maximal tissue tensioning hydrostatic pressure increased in the capillaries due to arterial pressure rise. Restoration of the circulation parameters in the fixation period started with an increase of circulation volumetric rate in vessels with preservation of the rest mechanisms of the tissue oxygenation maintenance.     

Plankton relationships under small water level fluctuations in a subtropical reservoir

In reservoirs, variations in water level may affect plankton biomass and species composition. Studies on the effect of water-level fluctuations are scarce and restricted to Europe and Australia. In the Río Tercero Reservoir (Argentina), the management policies of a nuclear-power plant require a minimum depth of 650 m. During periods of excessive rainfall, however, the input is such that the excess passes over the spillway, thus causing a high turnover of water. Phytoplankton, zooplankton, and physicochemical variables were monitored over 2 years at three sampling stations during a period with annual precipitation higher than the historical annual mean. Different hydrological situations occurred based on precipitation, spillway outflow, and water-renewal rate. At high renewal rates, phyto- and zoo-plankton diversities peaked. During high outflow periods phytoplankton biomass peaked through the contribution of Ceratium hirundinella. Once the spillway outflow ceased, stable conditions (low renewal rates) were achieved, thus allowing the onset of biological interactions. Maximum phytoplankton density (mainly Actinocyclus normanii) was reached at such times, and efficient grazers (Daphnia laevis) with long life cycles dominated in terms of biomass. The structure and dynamics of the plankton community could be altered by changes in hydrological conditions (renewal rate and spillway outflow) that act to compromise the apparent stability imposed by steady water levels. These variables must be considered to identify disturbance conditions and improve knowledge of reservoir environments, so as to implement appropriate management practices.     

Methodology for studying exchanges between salt marshes and coastal marine waters

The salt marshes of the Mont St. Michel bay represent a complex system in continuous change, mostly due to the frequent exchanges with the coastal waters through tidal processes. In such ecosystems, water is an important element insofar as it represents the common vector of flows between and among several ecosystem compartments. The purpose of the approach discussed here is to estimate the volume of water coming in and out and to determine the variations of the water quality according to time and nutrients concentrations. The estimation of the water fluxes is dependent on the channel calibration downstream of the watershed. Among the different methods examined, the continuous integrals calibration appears as the best one because the water level changes very quickly.Up to now, estimations of nutrients exchanges in wetlands have been based on rigorously regular field sampling, in consideration of the fact that exchanges occurred mainly during annual spring tides or during spring tides of each cycle of the year. According to our results, it seems that every tide, and portion of a tide, of a monthly and seasonal cycle has some importance and variability, which suggests that all parts of a tide should be considered in estimations of exchanges between wetlands and coastal waters.Corresponding Editor: W. Mitsch     

The influence of tidal forcing on groundwater flow and nutrient exchange in a salt marsh-dominated estuary

Data from salt marshes in the U.S. Southeast show that long-term variations in mean water level (MWL) correlate strongly with salt marsh productivity and porewater salinity. Here we used numerical models of tidally-driven groundwater flow to assess the effect of variations in tidal amplitude and MWL on porewater exchange between salt marshes and tidal creeks. We modeled homogeneous and layered stratigraphy and compared flat and sloped topography for the marsh surface. Results are consistent with field observations and showed that increases in tidal amplitude increased groundwater flushing, particularly when increasing the tidal amplitude caused the marsh platform to be inundated at high tide. Increases in MWL caused groundwater flushing to increase if that rise caused greater areas of the marsh to be inundated at high tide. Once the marsh was fully inundated at high tide, further increases in MWL caused groundwater flushing to decrease. Results suggest that small increases in MWL associated with sea level rise could increase nutrient export significantly in marshes with elevations that are equilibrated near mean high water, but rising sea level could decrease the export of nutrients to, and thus fertility in, estuaries adjacent to marshes that are equilibrated lower in the tidal frame. Likewise, macrotidal estuaries are predicted to be subject to much larger groundwater and nutrient exchange than similar microtidal estuaries. We speculate that the early stages of rising relative sea level may significantly impact water quality in estuaries that are not river-dominated by raising the discharge of nutrients from coastal wetlands.     

Field measurements and modeling of groundwater flow and biogeochemistry at Moses Hammock, a backbarrier island on the Georgia coast

A combination of field measurements, laboratory experiments and model simulations were used to characterize the groundwater biogeochemical dynamics along a shallow monitoring well transect on a coastal hammock. A switch in the redox status of the dissolved inorganic nitrogen (DIN) pool in the well at the upland/saltmarsh interface occurred over the spring-neap tidal transition: the DIN pool was dominated by nitrate during spring tide and by ammonium during neap tide. A density-dependent reaction-transport model was used to investigate the relative importance of individual processes to the observed N redox-switch. The observed N redox-switch was evaluated with regard to the roles of nitrification, denitrification, dissimilatory nitrate reduction to ammonium (DNRA), ammonium adsorption, and variations in inflowing water geochemistry between spring and neap tides. Transport was driven by measured pressure heads and process parameterizations were derived from field observations, targeted laboratory experiments, and the literature. Modeling results suggest that the variation in inflow water chemistry was the dominant driver of DIN dynamics and highlight the importance of spring-neap tide variations in the high marsh, which influences groundwater biogeochemistry at the marsh-upland transition.     

Effect of glucose feeding on net transport of plasma free fatty acids

The effect of a single glucose feeding upon the net inflow and outflow transport of plasma free fatty acids (FFA) has been studied in 75 unanesthetized rats. The animals were fasted for 22 +/- 2 hr; then 50 rats were refed 2 ml of 50% glucose by gastric intubation. At 0, 10-15, and 30-35 min after glucose refeeding, the rats were injected with palmitate-1-(14)C complexed to rat serum. The tracer dose included (131)I-labeled albumin. Plasma FFA concentration, (131)I concentration, and FFA-(14)C were measured at five time intervals after injection of the tracer dose. From these data the irreversible disposal rate, or net outflow transport, and the net inflow transport of plasma FFA were calculated. Estimations were based upon a special case of a general solution for measuring net inflow and outflow transport of a circulating metabolite. The general solution is independent of the number of compartments, how they are interconnected, the number of nonradioactive inflows, and where the inflows enter the system. Net inflow = net outflow transport = 7.6 micro eq/min in the fasted state and 3.5 micro eq/min in the new steady state that is reached 30-40 min after glucose refeeding. A very slight imbalance between the rates of net inflow and outflow transport could account for the rapid fall in plasma FFA concentration that results from a single glucose feeding. Theoretical and practical problems associated with studying inflow and outflow transport by means of the technique using a single injection of racer are discussed.     

Effects of Natural and Anthropogenic Change on Habitat Use and Movement of Endangered Salt Marsh Harvest Mice

The northern salt marsh harvest mouse (Reithrodontomys raviventris halicoetes) is an endangered species endemic to the San Francisco Bay Estuary. Using a conservation behavior perspective, we examined how salt marsh harvest mice cope with both natural (daily tidal fluctuations) and anthropogenic (modification of tidal regime) changes in natural tidal wetlands and human-created diked wetlands, and investigated the role of behavioral flexibility in utilizing a human-created environment in the Suisun Marsh. We used radio telemetry to determine refuge use at high tide, space use, and movement rates to investigate possible differences in movement behavior in tidal versus diked wetlands. We found that the vast majority of the time salt marsh harvest mice remain in vegetation above the water during high tides. We also found no difference in space used by mice during high tide as compared to before or after high tide in either tidal or diked wetlands. We found no detectable difference in diurnal or nocturnal movement rates in tidal wetlands. However, we did find that diurnal movement rates for mice in diked wetlands were lower than nocturnal movement rates, especially during the new moon. This change in movement behavior in a relatively novel human-created habitat indicates that behavioral flexibility may facilitate the use of human-created environments by salt marsh harvest mice.     

Effect of trimecaine, ajmaline, stenopril and chloracizine on fluctuations in K+ currents in rat liver mitochondria

Antianginal hypotensive preparations chloracyzin and stenopryl, antiarrhythmic aimalin as well as local anesthetic and antiarrhythmic trimekaine hydrochloride were studied for their effect on the K+ inflow and outflow rate in the rat liver mitochondria during Sr2+-induced vibrations. In spite of differences in the chemical structure and pharmacological effect, all these substances are shown to uniformly suppress ion flow vibrations in mitochondria, inhibiting K+ outflow. It is found that the inhibition of the K+ outflow rate depends on the concentration of the preparations. Activity of the studied substances as to inhibition of K+ outflow from mitochondria correlates with their pharmacologic activity.     

Hysteresis Can Grant Fitness in Stochastically Varying Environment

Although the existence of multiple stable phenotypes of living organisms enables random switching between phenotypes as well as non-random history dependent switching called hysteresis, only random switching has been considered in prior experimental and theoretical models of adaptation to variable environments. This work considers the possibility that hysteresis may also evolve together with random phenotype switching to maximize population growth. In addition to allowing the possibility that switching rates between different phenotypes may depend not only on a continuous environmental input variable, but also on the phenotype itself, the present work considers an opportunity cost of the switching events. This opportunity cost arises as a result of a lag phase experimentally observed after phenotype switching and stochastic behavior of the environmental input. It is shown that stochastic environmental variation results in maximal asymptotic growth rate when organisms display hysteresis for sufficiently slowly varying environmental input. At the same time, sinusoidal input does not cause evolution of memory suggesting that the connection between the lag phase, stochastic environmental variation and evolution of hysteresis is a result of a stochastic resonance type phenomenon.