Periods Of Tidal Inundation Research Articles

Geographic variability in headward erosion of marsh tidal creeks: Ecological and physical causes

AbstractExpansion of drainage networks through the headward erosion of tidal creeks is an eco‐geomorphologic response of salt marshes to accelerated sea‐level rise (SLR). This response can counter the negative impacts of an elevation deficit by increasing drainage and encouraging plant health, thereby reducing potential for submergence and marsh platform loss. In the wetlands of Cape Romain, SC, intense bioturbation near creek heads by the common marsh crab Sesarma reticulatum has been found to facilitate sediment erosion and rapid creek growth. This keystone grazer has been recently observed to have increasing influence on landscape evolution throughout the southeast US coast. Here, we compare measurements taken at Sapelo Island, GA, with those previously collected at Cape Romain, to confirm that eco‐geomorphic feedbacks facilitating creek growth at each location are similar, and to compare these processes under differing background conditions. We use sediment cores, precise elevation measurements and historical imagery to compare substrate properties, elevation within the tidal frame, creek growth rates and drainage morphology at both sites. Our results show identical processes; however, the higher elevation of the marsh at Sapelo Island leads to shallower and shorter periods of tidal inundation, explaining the greater soil strength and lower belowground biomass compared with the marsh at Cape Romain. The smaller tidal range at the site in Cape Romain compared with Sapelo Island translates to a proportionally shallower depth of tidal creeks, which therefore requires less erosion to produce headward creek extension. These effects are likely to have contributed to slower growth rates of tidal creeks at Sapelo Island during the past several decades of SLR. Our findings highlight the similarities in process but differences in rates in how marshes are responding to climate‐related stress.

Elevations of mangrove forests of Pohnpei, Micronesia

Mangrove surface elevation is the crux of mangrove vulnerability to sea level rise. Local topography influences critical periods of tidal inundation that govern distributions of mangrove species and dictates future distributions. This study surveyed ground surface elevations of the extensive mangroves of Pohnpei, Federated States of Micronesia, integrating four survey technologies to solve issues of canopy blocking satellite reception, dense aerial roots limiting line-of-sight, and remoteness from surveyed datums. The island-wide average elevation of the mangrove seaward edge was −0.57 ± 0.13 m relative to MSL, while the landward average elevation was 0.33 ± 0.12 m relative to MSL. The overall mangrove elevation range was thus estimated to be 0.90 m. Mangrove species Bruguiera gymnorrhiza, Rhizophora apiculata and Sonneratia alba had large, overlapping elevation ranges, while Rhizophora stylosa occurred low in the tide frame. These species are likely to be less vulnerable to rising sea level given their greater range of elevation occurrence and presumably flooding tolerance, and hence have the highest adaptive capacity to rising sea level. Some landward edge species had very narrow elevation ranges, increasing their vulnerability to sea-level rise, with adjacent potential upland migration areas limited due to steep topography and human development. Pohnpei mangroves occupied 74% of the mean tidal range, similar to surveys elsewhere in the Pacific. This study demonstrates how more extensive understanding of the elevation distributions of intertidal species can contribute to sea-level rise vulnerability assessments, to allow prioritised climate change adaptation. However, more work is needed in standardizing approaches for global comparisons.

Sea-level rise and refuge habitats for tidal marsh species: Can artificial islands save the California Ridgway's rail?

Terrestrial species living in intertidal habitats experience refuge limitation during periods of tidal inundation, which may be exacerbated by seasonal variation in vegetation structure, tidal cycles, and land-use change. Sea-level rise projections indicate the severity of refuge limitation may increase. Artificial habitats that provide escape cover during tidal inundation have been proposed as a temporary solution to alleviate these limitations. We tested for evidence of refuge habitat limitation in a population of endangered California Ridgway's rail (Rallus obsoletus obsoletus; hereafter California rail) through use of artificial floating island habitats provided during two winters. Previous studies demonstrated that California rail mortality was especially high during the winter and periods of increased tidal inundation, suggesting that tidal refuge habitat is critical to survival. In our study, California rail regularly used artificial islands during higher tides and daylight hours. When tide levels inundated the marsh plain, use of artificial islands was at least 300 times more frequent than would be expected if California rails used artificial habitats proportional to their availability (0.016%). Probability of use varied among islands, and low levels of use were observed at night. These patterns may result from anti-predator behaviors and heterogeneity in either rail density or availability of natural refuges. Endemic saltmarsh species are increasingly at risk from habitat change resulting from sea-level rise and development of adjacent uplands. Escape cover during tidal inundation may need to be supplemented if species are to survive. Artificial habitats may provide effective short-term mitigation for habitat change and sea-level rise in tidal marsh environments, particularly for conservation-reliant species such as California rails.

Exchange of nutrients across the sediment–water interface in intertidal ria systems (SW Europe)

Concentrations of nitrate, nitrite, ammonium, phosphate and silicate were determined in river water, tidal water that floods the intertidal sediment (flooding water) and pore water of those sediments in the Northern Galician Rias of Ortigueira and Viveiro (NW Iberian Peninsula). The field surveys were done in the productive seasons of spring and summer 2008. Short-sediment cores and tidal flooding water were sampled at the intertidal area during the first 20min that the tide inundates the sampling site. Nutrient fluxes of rivers (Lourido and Landro) flowing into the rias were in the order of H4SiO4>NO3−>NH4+>HPO4−2 Nutrients input from those rivers were low relative to the nutrient discharge of the entire coastal area. Striking changes of nutrient concentrations in flooding and pore waters of intertidal sediments were observed in the short periods of tidal inundation. Nutrient fluxes driven by molecular diffusion and tide-induced transport across the sediment–water interface were quantified and compared to the nutrient river contribution. Diffusive fluxes ranged from 9.3 to 13.7nmol·cm−2·d−1 for nitrate and nitrite, −1.32 to 30.1nmol·cm−2·d−1 for ammonium, −0.01 to 0.49nmol·cm−2·d−1 for phosphate, and −13.2 to 0.2nmol·cm−2·d−1 for silicate. Tide-induced transport always exceeded diffusive fluxes, with differences reaching up to four orders of magnitude for silicate. The overall results of this study emphasize the relevance of tidal water movement in promoting the sediment–water exchange of nutrients in intertidal sub-ecosystems.

Experiencing the salt marsh environment through the foot of Littoraria irrorata: Behavioral responses to thermal and desiccation stresses

Behavioral responses to environmental conditions can determine both the microclimate surrounding an organism, as well as how an organism experiences that microclimate. The salt marsh snail Littoraria irrorata (Say) employs two types of behaviors that potentially affect its likelihood of experiencing thermal and/or desiccation stress: 1) retracting its foot into its shell and 2) vertically migrating on the marsh grass Spartina alterniflora. One aim of our study was to determine how the use of retracting behaviors by L. irrorata modifies its ability to tolerate thermal and desiccation stresses, and the interactions between these stresses. A related goal was to elucidate whether the snails move vertically on the stalks of S. alterniflora to avoid thermal and/or desiccation stresses. In the laboratory, snails were kept in 10 biomimic (~ potential body) temperature (25–45 °C in 5 °C increments) and vapor density (VD) deficit (~ 3 g/m 3 and ~ 17 g/m 3) treatments to determine how they use retracting behaviors to avoid thermal and desiccation stresses. Performance measurements of water loss, body temperature, and mortality were made in relation to behavioral responses, with independent measures from 1.5 to 9 h. In the South Carolina salt marsh, snails' movements and retracting behaviors were monitored and compared to their body temperatures and microclimate conditions. Measurements were made in the high and low marsh (characterized by the height of S. alterniflora) as a function of height in the canopy. We found that the snails used retracting behaviors to shift their ability to tolerate thermal and desiccation stresses by changing their capacity for evaporative cooling through mantle exposure. L. irrorata consistently responded to emersion, or potential desiccation stress, by retracting into its shell, and continued to avoid water loss even under high thermal stress. Both field and laboratory experiments indicated that the snails' behavioral avoidance of thermal stress was severely limited by simultaneous avoidance of desiccation stress. Furthermore, snail movement was largely restricted to periods of tidal inundation in the low marsh and did not reflect behavioral avoidance of abiotic stresses. The use of retracting behaviors by L. irrorata to manipulate its tolerance to temperature and humidity levels exemplifies the importance of behavior as a functional trait that determines its climate space. Viewing behavior at a mechanistic level provides a more accurate picture of how organisms experience their environment and how these impacts translate to interactions at the community level.

Importance of saltmarsh to fish species of a large south-eastern Australian estuary during a spring tide cycle

The dietary compositions of fish species over saltmarsh in a large south-eastern Australian estuary (Brisbane Water) were explored to ascertain the importance of this habitat type to the fish community of that estuary. Following tidal inundation, 12 fish species (<120 mm total length) were obtained using fyke nets, with Ambassis jacksoniensis being particularly abundant. The stomachs of all fish contained undigested prey, implying that they fed while on the saltmarsh. Three species (A. jacksoniensis, Atherinosoma microstoma and Redigobius macrostoma) fed nearly exclusively on the crab zoeae that were released in high numbers by saltmarsh crabs. The diets of these three species significantly differed from those of the other species, which comprised mainly foraminiferans, copepods, crabs, polychaetes, terrestrial insects and/or detritus. Substantial partitioning of food resources also occurred between the other nine species. With increasing body size, A. jacksoniensis fed more on benthic prey (polychaetes and copepods) and less on crab zoeae. This study highlights the importance of saltmarsh as providing both protection and food resources for fish species during even short periods of tidal inundation by its provision of a superabundant food source (crab zoeae) and other prey, and underscores the need for recognition of saltmarsh in management plans for fish.

Nekton utilization of intertidal salt marsh creeks: Tidal influences in natural Spartina, invasive Phragmites, and marshes treated for Phragmites removal

Intertidal creeks provide an extensive and direct interface with the marsh surface during periods of tidal inundation, and as such they represent a critically important corridor between the marsh surface and subtidal habitats. However, invasion by Phragmites can potentially alter this intertidal creek function. Habitat restoration was conducted in the oligohaline Alloway Creek watershed of Delaware Bay, USA, to ameliorate the deleterious effects of Phragmites invasion and restore marshes to pre-invasion form and function. Intertidal creeks in three marsh habitat types (natural Spartina-dominated, sites treated for Phragmites removal and now dominated by Spartina, and invasive Phragmites-dominated) were sampled during summer 2004 with seines during ebb and flood tides to determine juvenile nekton habitat and tidal utilization patterns and identify possible effects of marsh restoration efforts on intertidal nekton. Total nekton abundance was greater at Spartina and Treated marshes than Phragmites marshes. The overall nekton assemblage did not vary between habitat types, but the nekton assemblage did vary between tide stages, with low tide stages dominated by resident nekton (primarily Fundulus heteroclitus) and high tide stages consisting of a mix of transient and resident species (e.g., Anchoa mitchilli, Morone americana, Anguilla rostrata, Morone saxatilis). The effect of marsh restoration efforts on intertidal creek nekton was inconsistent, but most metrics examined indicated that restoration efforts had little effect in intertidal creek habitats, likely because the intertidal assemblage in all creek types was greatly influenced by many species moving from subtidal habitats and primarily a single (but abundant) species, F. heteroclitus, moving from the marsh surface.

Biotic resistance to green crab, Carcinus maenas, in California bays

The distribution of the introduced European green crab, Carcinus maenas, was investigated in the central California embayments of Bodega Bay Harbor (BBH), Tomales Bay, and Bolinas Lagoon using baited traps and snorkel surveys. Adult green crabs were very spatially limited in all three embayments and occurred primarily in warm, shallow areas that lacked large native Cancer spp. crabs. The green crabs that were found in closest proximity to populations of Cancer spp. exhibited high levels of limb damage and loss; damage was strongly correlated with low ratios of intertidal area: edge, indicative of narrow areas of intertidal that are more easily accessed by large Cancer spp. moving up to forage during periods of tidal inundation. Up to 70% of the green crabs tethered in areas of BBH that are utilized by Cancer spp. experienced limb loss, while those tethered in the marsh, where there are no Cancer spp., were undamaged. The results suggest that the potential distribution of green crabs in the northeastern Pacific will be far less than has been predicted, and that their impacts may be largely attenuated through predation by and competition with native crab species.

BIOTIC AND ABIOTIC FACTORS INFLUENCING GROWTH AND SURVIVAL OF WILD AND CULTURED INDIVIDUALS OF THE SOFTSHELL CLAM (MYA ARENARIA L.) IN EASTERN MAINE

A series of intertidal field experiments was conducted from 1986–2003 in eastern Maine to examine biotic and abiotic factors influencing the growth and survival of wild and cultured individuals of the softshell clam, Mya arenaria L. Separate experiments examined: (1) the efficacy of transferring sublegal wild clams (<50.8 mm SL) from areas near the high intertidal zone where shell growth was slow to areas where growth was predicted to be faster; (2) effects of tidal height on wild and cultured clam growth; (3) effects of spatial variation on cultured clam growth; (4) dispersion and growth of cultured juveniles in small experimental units; (5) effects of the naticid gastropod, Euspira heros Say, predation on survival of wild and cultured clams and (6) the species composition of large, crustacean predators that forage intertidally during periods of tidal inundation. Protective netting (4.2 mm aperture) increased recovery rate of transferred clams by 120% and resulted in a 3-fold enhancement of wild recruits. Effects of tidal height on wild clam growth revealed complex behaviors in >0 y-class individuals. Clams growing near the upper intertidal take >8 y to attain a legal size of 50.8 mm SL, whereas animals near the mid intertidal generally take 4.5–6.5 y. Unexpectedly, clams initially 38–54 mm SL and growing near the extreme low tide mark at a mud flat in Eastport, Maine, added, on average, <2 mm of new shell in a year, which was 8–10 mm SL less than animals at higher shore levels. It is hypothesized that biological disturbance by moon snails, that consumed >90% of clams at the low shore levels, contributed to this slow growth. In another field trial from 1986–1987, moon snails and other consumers were allowed access to clams ranging in size from 15–51 mm. E. heros preyed on clams over the entire size range and attacked clams between 31–40 mm at a rate that was nearly double what had been expected. Mean snail size was estimated to range from 10–52 mm shell height (SH), based on a laboratory study that yielded information about the linear relationship between snail size and its borehole diameter. In an experiment from June to September 1993, moon snails consumed >70% of juvenile clams (ca. 10 mm SL) within a month after planting at each of three tidal heights. Snail sizes ranged from 15–20 mm SD with larger individuals occurring near the upper intertidal zone. Green crabs, Carcinus maenas (L.) also prey heavily on softshell clam populations, but most studies that use shell damage to assign a predator have assumed that all crushing and chipping predation is because of this invasive species. An intertidal trapping study demonstrated that both green crabs and rock crabs, Cancer irroratus Say, are present during periods of tidal inundation, with the latter species accounting for ca. 40% of large crustacean numbers.

The importance of high-resolution monitoring in erosion and deposition dynamics studies: examples from estuarine and fluvial systems

Erosion and deposition processes lie at the centre of geomorphological explanation, but progress in understanding has been limited by a lack of appropriate high-resolution monitoring methodologies which permit detection of erosion and deposition dynamics. This paper presents a case for monitoring erosion and deposition at high temporal resolutions, and uses hypothetical approaches supported by example erosion and deposition events and analyses drawn from estuarine and fluvial systems. The paper first presents testable hypotheses to demonstrate the complexity of possible event combinations, sequences and juxtapositions for the erosion driving forces which underpin the need for high-resolution monitoring. Second, it summarises recent improvements to the Photo-Electronic Erosion Pin (PEEP) automatic erosion and deposition monitoring system, including the novel concept of Thermal Consonance Timing (TCT), which is particularly promising because it helps to define the timing of nocturnal events and through the entire hydrograph. Third, example results are discussed from high-resolution monitoring of bank erosion at a tidal site at Burringham on the River Trent in northern England. Tidal banks are revealed to be much more dynamic than previous conventional monitoring has indicated. A key result is that, because the high-resolution approach allows erosional and depositional activity to be assigned to specific periods of tidal inundation, it becomes possible for the first time routinely to produce ‘event-based’ erosion (36 mm h −1) and deposition rates (4.5 and 8.4 mm h −1). Such rate determinations are potentially very useful in the field validation of sedimentological and geomorphological models, including grain settling and resuspension theory. Fourth, through a longer term of aggregated daily data, a striking 2-week cycle of deposition and erosion emerges which correlates most strongly with spring-neap tidal cycling, but is moderated by wind stress effects. Sediment was deposited on the bank relatively quickly, over 4–5 days, but then removed by erosion rather slowly, over 9–10 days. Fifth, the dangers of low-resolution monitoring are illustrated by comparing the daily PEEP data set with a series resampled at a lower (14-day) frequency, to simulate the information generated by conventional resurvey methodologies. The low-frequency series failed adequately to represent the cyclicity, mean, range, variability and trend of bank elevation changes, and without this dynamics information, rate and process definition is very difficult, largely because of self-concealing activity. Sixth, a useful advance is illustrated by the fluvial erosion sequence for the River Wharfe (N. England). This shows how TCT can generate rare and important results with the definition of the precise time of an erosion event within the hydrograph: bank retreat here occurred very quickly, after initial inundation, and within 4 h of the flow peak-information which can be used to define thresholds for entrainment (e.g. critical shear stresses). Such high-resolution monitoring helps to unravel some of the erosional effects of complex sequences, combinations and juxtapositions of similar or different forcing events. Finally, high-resolution approaches have been adopted worldwide for fluvial, estuarine, mudflat and canal systems, but considerable potential exists for their development and use in these and other contexts (e.g. gully, hillslope, beach and dune environments), to improve understanding and modelling of geomorphological processes more widely.

Contamination of saltmarsh sediments and biota by CCA treated wood walkways

Sediments, marsh grasses, and ribbed mussels were collected under two CCA wood walkways (15 and 3 years old) and 1, 3, and 10 m out, in the high, middle and low marshes. These sediments, and samples from reference sites, were analyzed for Cu, Cr, and As by atomic absorption spectrophotometry. Metal concentrations were highly elevated under the walkways and up to 10 m away. Dispersal of contaminants near the old walkway was greatest in the low marsh, less in the middle, and least in the high marsh, corresponding to periods of tidal inundation. Accumulation under the walkway was generally greatest in the low marsh. Contamination was much higher in sediments under the new walkway than the old one, but metals had not dispersed as far. Accumulation patterns in plants were similar, but the contamination did not disperse as far and was not greater under the new vs the old walkway, despite differences in sediment concentrations. In mussels, bioaccumulation was seldom statistically significant, due largely to small sample sizes.

The cyclic development of a macrotidal mudflat on varying timescales

The development of a mudflat at Peterstone Wentlooge on the north shore of the Severn Estuary, UK, was observed over a two year period on a multi-timescale basis. The mudflat is located in an area with a macrotidal regime, strong tidal currents, exposure to short period wind waves and high turbidity. The mudflat consists of two Holocene sediment layers: relict clay extending over the entire width of the intertidal, overlaid by modern sediment located between the salt marsh edge and mean sea level. A combination of episodic and periodic mudflat development was observed on decadal, seasonal, spring-neap and tidal timescales. There was a clear seasonal development of the modern layer in terms of bed level, morphology and composition, with accretion during spring and summer and with erosion during autumn and winter. This periodic development was superimposed on a longer-term trend of continual erosion of the relict clay when its surface was exposed. The mean seasonal variation in bed level of the modern layer was in the order of 10 cm and was due to the presence or absence of short period waves. On the spring–neap and tidal timescales the development of the mudflat, due to tidally driven processes, was frequently modulated by episodic wave events. Variations of bed level during tidal inundation were observed autonomously and compared well with manual observations taken during exposure on a daily basis. Bed level variations of 1 cm were observed during single periods of tidal inundation and daily through measurements taken during mudflat exposure.

A preliminary study of the geochemistry of methylamines in a salt marsh

Concentrations of three aliphatic amines namely, methylamine, dimethylamine and trimethylamine were monitored in different vegetation zones of an inter-tidal salt marsh over a period encompassing two spring tides in March/April 1992. The analytes were abundant in both the pore-waters and sediments of the marsh, but there was considerable temporal variability in their concentrations. Maximum observed levels were higher than in any previous field studies, particularly for monomethylamine. The methylamines were depleted in pore-waters and sediments during periods of tidal inundation, which supports their suggested role in the osmotic strategies of the flora and fauna of estuarine environments.

Variations of Mn, Fe and S concentrations in sediment pore waters of Ria Formosa at different time scales

Intertidal sediments of Ria Formosa have been surveyed at different time scales. Pore water of short sediment cores was collected bimonthly at five stations, from May 1993 to June 1994, around low-tide. One location was studied intensively every 1.5 hour, during a 6-hour air-exposure period, and during 20 minutes (1, 5, 10 and 20 minutes) immediately after tidal water had inundated the sampling site. Determinations of vertical profiles of pH, Eh, water content, O2, total dissolved Mn (Mndiss), total dissolved Fe (Fediss) and inorganic sulphur [(HS−)t] were carried out in all samples. The results obtained indicate that daily variations of Mndiss, Fediss and (HS−)t concentrations appear to be superimposed to the seasonal ones. Probably, the renewal of the pore water at periods of tidal inundation causes advective transport of manganese and exchange of iron, between the pore water and the solid fraction of the sediment that masks seasonal fluctuations induced by temperature and organic matter input variations.

Buoyancy of Avicennia marina Propagules in South-Eastern Australia

Buoyancy of propagules of Avicennia marina (Forsk.) Vierh. was observed in the laboratory and in the field. Under constant exposure to seawater in the laboratory, propagules that shed their pericarp sank while those that retained their pericarp floated. The time taken for propagules to shed their pericarps varied greatly between trees in a population and between populations. However, more propagules lost their pericarps and sank faster in 10% seawater than in full seawater. Propagules that had sunk in 10% seawater refloated after several days' immersion. In the field, propagules placed at three tidal levels and exposed to differing periods of tidal inundation all lost their pericarps and sank within 24 h with no differences detected between tidal levels. Field observations were also made where brackish and seawater sites could be compared. Propagules shed their pericarps faster and sank earlier at the brackish site, although after 24 h more than 80% of propagules had sunk at all sites. After 48 h propagules in the brackish site began to refloat. These observations suggest that most A. marina. propagules strand and establish near the parent tree populations and only a few are dispersed more widely.

Influence of location in a salt marsh on survivorship of ribbed mussels

To assess how predation on ribbed mussels Geukensia dernissa varied with tidal elevation and distance into the salt marsh, identical mussel clumps were introduced into locations differing in elevation and distance from open water in salt marshes at 2 geographically separate areas. Mussel mortality was greater at lower tidal elevations. At similar tidal elevations, mussels on the marsh interior showed less mortality than those on the marsh edge. Mortality was most likely due to predahon by blue crabs Callinectes sapidus. Blue crabs and other aquatic predators forage in the salt marsh only during periods of tidal inundation and thus their feeding time decreases from low to high levels. At similar tidal elevations, their access to the marsh intenor may be impeded by dense marsh grasses.

PREDATOR-INDUCED SHELL DIMORPHISM IN THE ACORN BARNACLE CHTHAMALUS ANISOPOMA.

Field experiments were conducted in order to determine the nature of shell dimorphism in the acorn barnacle Chthamalus anisopoma and the adaptive significance of the atypical form. The typical morph has the conical shape which is characteristic of acorn barnacles, while the atypical morph appears bent over, with the rim of its aperture oriented perpendicular to its base. The experiments showed that: 1) the bent-over morphology is an environmentally-induced developmental response to the presence of a carnivorous gastropod (Acanthina angelica) and 2) that "bents" are more resistant than "conics" to specialized predation by this snail. The results also showed that predation by A. angelica is patchy and heaviest in the near vicinity of cracks and crevices, which it uses as refuges during periods of tidal inundation. Because predation is patchy and bents are less fecund and grow slower than conics, the conditional developmental strategy is likely to be favored over strict genetical control of shell morphology.