Tidal Influence Research Articles

Large‐Scale Scour in Response to Tidal Dominance in Estuaries

AbstractChannel beds in estuaries and deltas often exhibit a local depth maximum close to the river mouth. There are two known mechanisms of large‐scale (i.e., >10 river widths along‐channel) channel bed scours: width constriction and draw‐down during river discharge extremes, both creating flow acceleration. Here, we study a potential third mechanism: tidal scour. We use a 1D‐morphodynamic model to reproduce tidal dynamics and scours in estuaries that are in morphologic equilibrium. A morphologic equilibrium is reached when the net (seaward) sediment transport matches the upstream supply along the entire reach. The residual (river) current and river‐tide interactions create seaward transport. Herein, river‐tide interactions represent the seaward advection of tide‐induced suspended sediment by the river flow. Tidal asymmetry typically creates landward transport. Scours form when tidal flow is amplified through funneling of tidal energy. Scours simultaneously reduce the residual (river) current and the river‐tide interaction contribution to sediment transport, thereby maintaining morphologic equilibrium. When tidal influence is relatively large, and when channel convergence is strong, an equilibrium is only obtained with a scouring profile. We propose a predictor dependent on the width convergence, quantified as SB, and on the ratio between the specific peak tidal discharge at the mouth and the specific river discharge at the landward boundary (qtide/qriver). Scours develop if (qtide/qriver)/SB exceeds 0.3. Scour conditions were found to occur globally across a range of scales, which allows its prediction in estuaries under future changes.

Deciphering Star Cluster Evolution by Shape Morphology

Abstract We analyze the morphological evolution of open clusters and provide shape parameters for 265 open clusters. The results show that the overall shape of sample clusters becomes more elliptical as they grow older, while their core remains circular or slightly trending to circular. There is a negative correlation of the ellipticities with the number of members of the sample clusters. A significant negative correlation between the overall ellipticities and masses is also detected for the sample clusters with log(age/year) ≥8, suggesting that the overall shapes of the clusters are possibly influenced by the number of members and masses, in addition to the external forces and the surrounding environment. For most young sample clusters, the radial stratification degree of the short-axis direction is greater than that of the long, implying that the radial stratification degree in the two directions within the young sample cluster may be unevenly affected by an internal evolutionary process. Older sample clusters exhibit lower stratification in the tangential direction, which possibly means those clusters may continue to survive for a long time at a low level of stratification. Our analysis shows that the overall shape of the sample clusters may be more susceptible to the influence of Galactic tides toward the Galactic center than the shear forces embedded in Galactic differential rotation. By analyzing the distribution of the ages and number of members of star clusters, we suggest that NGC 6791 may originate from superclusters.

Sequence stratigraphic framework of the Upper Eocene–Oligocene succession, northwest Birket Qarun, Fayum-Egypt

The Upper Eocene–Oligocene sequence exposed northwest Birket Qarun; Fayum district covers two rock units, Qasr El-Sagha (Temple and Dir Abu Lifa members) and Gebel Qatrani formations were re-evaluated by sequence stratigraphy. Six depositional sequences were recognized based on facies geometry, and sedimentological aspects. The first sequence (Temple Member) was accumulated under marginal intertidal flat environment indicating highstand deposits. The second (the lower Dir Abu Lifa Member) displays a regressive sedimentary facies starting with progradational delta front environment reflecting lowstand deposits followed upward by a lagoonal environment indicating transgressive/highstand deposits. The third (the top of the Dir Abu Lifa Member) was accumulated under a low sinuosity stream reflecting lowstand deposits. The fourth which constitutes the topmost of Dir Abu Lifa Member initiating near-shore shallow marine points to transgressive sediments, followed upward by fluvial sediments reflecting highstand deposits. The fifth (the Lower of Gebel Qatrani Formation) accumulated as point-bar deposits demonstrating lowstand deposits. The last occupies the main of Gebel Qatrani Formation initiates with restricted riverine marking lowstand deposits, followed upward by several fining upward cycles that were accumulated in fluvial and flood plain conditions with evidence of tidal influence on sedimentation near its top denoting transgressive deposits. Several minor transgressive episodes accompanied by tidal influence on sedimentation are noticed near the top, which may reflect gradual subsidence of the Oligocene alluvial plain. The area is subjected to relative sea-level changes that show a similarity with the global sea level. The base-level fluctuations are mainly controlled by the regional tectonic setting.

Variability in water chemistry in the Lower Mekong Basin: Considerations for fish life history reconstruction

Spatial and temporal variation of nine elements (Ba, Ca, Cu, Mg, Mn, Na, Se, Sr, and Zn) and some additional environmental parameters (salinity, water levels, and conductivity) were examined over two 2,000 km along the length of the main Mekong River channel from Luang Prabang in Northern Lao PDR to the Mekong Delta in Vietnam. Longitudinal profiles of some dissolved elemental concentrations varied significantly along the river channel. For example, Sr concentration in marine water was up to 83 times higher than in fresh water. By contrast, Ba concentration was around 4 times higher in fresh water than in marine water, but was significantly influenced by inflows from major tributaries in Cambodia (dilution effects). We found dissolved Ba was elevated in low salinity. Furthermore, Sr concentration was more variable than Ba, especially in the Mekong Delta due to different tidal influences in each of the Delta branches. Selenium was only present along the coast and one river branch in the delta. The variation in water chemistry of the Mekong main channel identified through this study provides information that can be used in the interpretation of regional fish movements using otolith chemistry, including across the freshwater, estuarine and marine interface. Accurate interpretation is essential given the Lower Mekong Basin has a high biodiversity that is under threat from rapid development, and substantial knowledge gaps exist on the life history requirements of numerous fish species.

Reuse and recycle: Integrating aquaculture and agricultural systems to increase production and reduce nutrient pollution

Integrated agriculture and aquaculture systems (IAAS) allow nutrients, energy, and water to flow throughout the components of the system, increasing the efficiency with which inputs are converted to food. Yet effectively designing an IAAS requires understanding how nutrients accumulate and alter the system's productivity. Here we developed a mechanistic model for nitrogen transport and utilization and parameterized it using the IAAS in He'eia, Hawai'i. Of note, we modeled tidal influence, which extends existing IAAS models that often assume aquaculture in tank enclosures. We simulated the impact of nitrogen loading from three possible land use scenarios across agriculture and development priorities on the productivity of the fishpond downstream. We projected that organic nitrogen and nitrate concentrations parallel the successive increases in nitrogen loading across management strategies. Autotroph and fish densities were predicted to follow similar trends in response to increased nitrogen availability, causing fish harvests to increase from the current land use (25 kg/ha) to the restored agriculture (35 kg/ha) and urban (50 kg/ha) alternatives. While fish harvests were predicted to be highest in the urban scenario, modeled caloric production in the restored scenario from agriculture and aquaculture would sustain 235 people (4.3 people/ha) in the He'eia IAAS, 16 and 125 times more than the current or urban land uses, respectively. Restoring diversified agriculture was also predicted to retain a larger proportion of nitrogen inputs (0.43) than urbanizing the region (0.30), which would reduce nitrogen export to the adjacent Kāne'ohe Bay. Several state variables were notably sensitive to tidal flux rates, highlighting the importance of incorporating tidal dynamics into a coastal IAAS model. This model provides valuable insights for the management of existing coastal IAAS and design of new IAAS in coastal regions to improve the sustainability of future food systems.

Exploring the potential for internal tides to reshape the continental shelf edge seafloor

Studies in the literature have argued anecdotally that strong near-bottom flow induced by internal tides could transport sediment and modify shelf-edge topography over the long term. To explore this argument, this study quantitatively investigates the topographic influence of internal tides using an idealized quasi-two-dimensional model that represents modern-day conditions at the shelf edge of the Mid-Atlantic Bight off the U.S. northeast coast. Observed temporal evolution of the internal tide amplitude and phases at the Mid-Atlantic Bight shelf edge over a 2-month period is used in conjunction with the model. We i) investigate two sources of semi-diurnal internal tides at the shelf edge, locally generated internal tides (LIT) and incident internal tides (IIT), and ii) consider transport of both suspended and bedload sediment. Model results indicate that LIT alone are inadequate to induce sediment transport, but a combination of tides, LIT and IIT can mobilize sediment at the shelf edge. Modeled sediment transport exhibits a tendency to compensate for changes in shelf-edge curvature and sea level from present-day conditions. However, the present-day shelf-edge profile does not represent a stable condition, as the sediment transport is stronger for the modern configuration than for other hypothetical shelf-edge geometries. Projecting short-term topographic change induced by the combined internal tides over longer timespans (with several major assumptions) indicates that, within the covered parameter range, the shelf-edge seafloor change induced by combined tides and internal tides over 10,000 years has an upper bound of 1–2 m. Sensitivity simulations show that although rates of bed change are affected by bottom roughness, shelf-edge curvature and sea level, the order of magnitude of the seafloor change remains unchanged across the parameter space considered here. This order of magnitude of modeled sediment transport and bed change suggests that it is unlikely for internal tides alone to have significantly shaped the edge of the Mid-Atlantic Bight continental shelf, at least for the conditions considered here. However, whether internal tides have interacted with other oceanographic processes and modified the shelf edge topography and what oceanic processes have shaped the shelf edge topography are questions that remain to be answered.

EDNA as a tool for non-invasive monitoring of the fauna of a turbid, well-mixed system, the Elbe estuary in Germany.

The Elbe is one of the longest European rivers and features a large, turbid and well-mixed estuary, which runs through the inner city of Hamburg. The Elbe has been closely monitored using classical catch techniques in the past. Here we tested a COI-based eDNA approach for assessing the biodiversity within the Elbe. We sampled three stations in the Elbe, included low and high tide events, as well as two adjoining lakes to compare the recovered faunas. To analyze the data, we employed two different pipelines: the automated mBRAVE pipeline utilizing the BOLD database and one including NCBI BLAST. The number of OTUs with species or higher-level identifications were similar between both approaches with 352 OTUs and 355 OTUs for BLAST and mBRAVE, respectively, however, BLAST searches recovered another 942 unidentified metazoan OTUs. Many taxa were well represented; however, fish species were poorly represented, especially in the Elbe estuary samples. This could be a result of the universal COI primers, which also yielded high read numbers for non-metazoan OTUs, and small-bodies taxa like Rotifera, which might have been sampled together with the eDNA. Our results show a strong tidal influence on the recovered taxa. During low tide, downstream stations resembled sites further upstream, but the former showed a very different OTU composition during high tide and early tide. Such differences might be due to varying impacts of upstream-originating eDNA during tide cycles. Such factors need to be considered when routinely employing eDNA for monitoring programs.

Effects of tidal influence on the structure and function of prokaryotic communities in the sediments of a pristine Brazilian mangrove

Abstract. Mangrove forests are ecosystems that constitute a large portion of the world's coastline and span tidal zones below, between, and above the waterline, and the ecosystem as a whole is defined by the health of these tidal microhabitats. However, we are only beginning to understand tidal-zone microbial biodiversity and the role of these microbiomes in nutrient cycling. While extensive research has characterized microbiomes in pristine vs. anthropogenically impacted mangroves, these have, largely, overlooked differences in tidal microhabitats (sublittoral, intertidal, and supralittoral). Unfortunately, the small number of studies that have sought to characterize mangrove tidal zones have occurred in impacted biomes, making interpretation of the results difficult. Here, we characterized prokaryotic populations and their involvement in nutrient cycling across the tidal zones of a pristine mangrove within a Brazilian Environmental Protection Area of the Atlantic Forest. We hypothesized that the tidal zones in pristine mangroves are distinct microhabitats, which we defined as distinct regions that present spatial variations in the water regime and other environmental factors, and as such, these are composed of different prokaryotic communities with distinct functional profiles. Samples were collected in triplicate from zones below, between, and above the tidal waterline. Using 16S ribosomal RNA (rRNA) gene amplicon sequencing, we found distinct prokaryotic communities with significantly diverse nutrient-cycling functions, as well as specific taxa with varying contributions to functional abundances between zones. Where previous research from anthropogenically impacted mangroves found the intertidal zone to have high prokaryotic diversity and be functionally enriched in nitrogen cycling, we find that the intertidal zone from pristine mangroves has the lowest diversity and no functional enrichment, relative to the other tidal zones. The main bacterial phyla in all samples were Firmicutes, Proteobacteria, and Chloroflexi while the main archaeal phyla were Crenarchaeota and Thaumarchaeota. Our results differ slightly from other studies where Proteobacteria is the main phyla in mangrove sediments and Firmicutes makes up only a small percentage of the communities. Salinity and organic matter were the most relevant environmental factors influencing these communities. Bacillaceae was the most abundant family at each tidal zone and showed potential to drive a large proportion of the cycling of carbon, nitrogen, phosphorus, and sulfur. Our findings suggest that some aspects of mangrove tidal zonation may be compromised by human activity, especially in the intertidal zone.

Influence of Seawards Water and Sediment Conditions on the Turbidity Maximum Zone in Yangtze Estuary

On the combined influence of runoff and tide, seawards sediment forms the turbidity maximum zone (TMZ) nearby the sandbar of Yangtze estuary. The water and sediment transport of the sandbar has important theoretical and practical significance for ecosystem, waterway regulation, and so on. According to the situation of seawards water and sediment variation, and based on the ECOMSED simulation of flow and suspended sediment dynamic process, the relation of the seawards water and sediment and the TMZ, and the law of water and sediment motion after the Three Gorges Project are discussed. It enhances the comprehension of suspended sediment concentration (SSC) variation law of the TMZ always seawards discharge. As the lower seawards sediment concentration, the SSC of the TMZ center is gradually decreasing with the increasing discharge. As the sediment concentration is higher than some critical value, the SSC of the TMZ center is gradually increasing with the increasing discharge.

Depositional and sequence stratigraphic model of transgressive shelf sandstone: The Late Cretaceous Tocito Sandstone, San Juan Bain, New Mexico, U.S.A.

ABSTRACT There has long been debate about the origin of long, linear, isolated shallow marine sandstones. In the 1980s these were routinely interpreted as wave- or tide-modulated shelf sandstones. With the advent of sequence stratigraphy, many of these sandstones were reinterpreted as top-truncated forced-regressive to lowstand delta or shoreface, inviting the question regarding whether the concept of a shelf sandstones remain a viable depositional model. More recent syntheses demonstrate that shelf sands tend to be derived by reworking of underlying sediment through transgressive erosion and show varying levels of detachment and reworking into discrete ridges and bars by wave and tidal processes as they become more evolved. The Late Cretaceous Tocito Sandstone in the Western Interior Seaway, which overlies the regressive Gallup Formation, is a candidate for a transgressive shelf sandstone. In this study, we present detailed facies analysis, based on sedimentological sections measured from well-exposed outcrops of the Tocito Sandstone and its related stratigraphic units in northwest New Mexico, USA. With high-resolution sequence stratigraphic control, facies analysis, detrital-zircon anatomy, and petrographic analysis are integrated to investigate the sequence stratigraphic evolution and depositional processes of the Tocito Sandstone. Detrital zircons indicate that the Tocito, Torrivio, and Gallup deposits are derived from different source areas, and therefore imply separate sequence stratigraphic origins. The Tocito Sandstone is interpreted to have been deposited as shelf sand ridges in retrogradational estuarine to drowned-barrier-system environments with tidal and wave influence, characterized by intense bioturbation. The Tocito was deposited in an overall transgressive systems tract and sourced from reworking of the underlying Torrivio and Gallup units through processes of transgressive erosion.

Effect of turbulent structures on the riverbank erosion due to tidal influence: A case study from the Rupnarayan River, eastern India

For understanding the sediment removal mechanism from the bank face, field measurements of the dominating turbulent flow structures under the influence of flood and ebb tide were carried out at the middle reach 98 km upstream of the mouth of Rupnarayan River, India where the bank erosion activity was highly dynamic. Measurement of the three-dimensional temporal variation of velocity was carried out using a 16-MHz Micro-ADV during the transition period of flood to ebb tide. Results from the present field study depict that during the transition of the onset of the ebb tide, the velocity field showed reduced values that gradually acquired negative values at the near bank region. This manifested the existence of an anti-clock circulation during flood tide and clock-wise circulation during ebb tide at the near bank flow field. It was also pertinent that the velocity gradient during ebb tide was greater as compared to the velocity gradient during flood tide. Accordingly, the turbulent bursting analysis revealed that the ejection and sweep events were prominent during ebb tide resulting in the dislodgement of sediment from the bank face at a larger rate. Further, the similarity of the wavelet patterns revealed that a good correlation existed between the stream-wise and transverse velocity component during ebb tide that enhanced the erosion process during the ebb tide event.

Influence of ocean tides and ice shelves on ocean–ice interactions and dense shelf water formation in the D’Urville Sea, Antarctica

The D’Urville Sea, East Antarctica, is a major source of Dense Shelf Water (DSW), a precursor of Antarctic Bottom Water (AABW). AABW is a key water mass involved in the worldwide ocean circulation and long-term climate variability. The properties of AABW in global climate models suffer from several biases, making climate projections uncertain. These models are potentially omitting or misrepresenting important mechanisms involved in the formation of DSW, such as tides and ocean–ice shelf interactions. Recent studies pointed out that tides and ice shelves significantly influence the coastal seas of Antarctica, where AABW originates from. Yet, the implications of these two processes in the formation and evolution of DSW are poorly understood, in particular in the D’Urville Sea. Using a series of NEMO-LIM numerical simulations, we assess the sensitivity of dense water formation in the D’Urville Sea to the representation of tides and ocean–ice shelf interactions during the years 2010–2015. We show that the ice shelves off Adélie Land are highly sensitive to tidal forcing, with a significant basal melt increase in the presence of tides. Ice shelf basal melt freshens and cools the ocean over significant portions of the coastal seas at the depth of the ice shelf draft. An opposite warming and increase in salinity are found in the upper layers. The influence of ice shelf basal melt on the ocean is largely increased in the presence of tides. However, the production of sea ice is found to be mostly unaffected by these two processes. Water mass transport out of polynyas and ice shelf cavities are then investigated, together with their sensitivity to tides and ocean–ice shelf interactions. Ice shelf basal melt impacts the volume of dense waters in two ways: (1) Dense Shelf Water and Modified Shelf Water are consumed to form water masses of intermediate density inside the ice shelf cavities, and (2) the freshening of the ocean subsurface makes its transformation into dense water by sea ice formation more difficult. These results suggest that ice shelf basal melt variability can explain part of the observed changes of dense water properties, and may also affect the production of dense water in a future climate.

Young soils of a temperate barrier island under the impact of formation and resetting by tides and wind

The island Spiekeroog (Germany) at the southern North Sea coast exhibits an island tail (Ostplate) of which large parts formed after 1860 by gradual eastward deposition of marine sediments. This study aimed to (i) provide a first overview of soils on the Ostplate, (ii) verify whether soil formation stages in different landscape elements (dune chain, dune slacks, saltmarsh, pioneer zone) are linked to the island’s gradual development and (iii) to assess the impact of tides and winds on soil formation. Standard physicochemical properties of dune -and dune slack topsoils and 19 pedons (i.a. pH, total organic carbon (TOC), total inorganic carbon (TIC), total nitrogen (TN), and mean weight diameter (MWD) of water stable aggregates) were analyzed. Soils of the dune slacks, the saltmarsh and the pioneer zone classified as Gleysols which showed no trend towards differences along the Ostplate. The dune chain exhibited Protic Arenosols that were initially acidified in lee positions (min. pH = 5.1). Carbon (C) and nitrogen (N) isotopes (δ13C, δ15N) signatures of saltmarsh sediments were used as a proxy for the tidal influence on soil formation. In addition, sulfur (S) isotope (δ34S) signatures revealed insights on sulfur sources in the saltmarsh. The δ13C signatures of organic matter (OM) decreased and TOC/TN -and TOC/total sulfur (TS) ratios increased with increasing elevation and decreasing flooding frequency. At higher flooding frequency, δ15N resembled the dominant input of OM from the southern North Sea, at a lower interaction level, mixing of a wider range of sources was indicated. S isotopes indicated dissolved sulfate and reduced species as sulfur sources. It was concluded that an ongoing impact of wind-induced sand movement at the dunes, and flooding-induced sediment movement in the saltmarsh and the pioneer zone, repealed any potential disparities in soil formation stages, which might have existed along the Ostplate.

Basin-fill development from marine to intermontane settings: Lithostratigraphy, Sedimentology and Paleogeography of the Malacatos-Vilcabamba basin in the southern Ecuadorian Andes

A detailed lithostratigraphic and sedimentologic study was performed in the southern Andes of Ecuador along the Malacatos-Vilcabamba intermontane basin, a thrust-controlled inverted basin developed during the middle Miocene. We defined twenty-three sedimentological facies grouped into seven facies associations and three different depositional systems (deltaic, tidal flat and alluvial fan) for the entire basin fill. The 500–1100 m thick Malacatos-Vilcabamba basin fill currently lies at about 1470 m above current sea level. It is unconformably underlain by a metamorphic and volcanic basement and usually exhibits some evidence of synsedimentary deformation and synchronous volcanism. Long-term patterns of basin sedimentation suggest a basal fining-upward sequence of marginal-marine lithofacies that gradually passes upward into a coarsening-upward sequence (conglomeratic) typical of a continental setting. The history of basin-filling was initiated in the middle to late Miocene (15-10 Ma) as a lowland basin. Proximal facies within a deltaic system under tidal influence were preserved as the San José and San Francisco Formations, while a flat tidal system alternating between arid and humid climatic episodes was preserved as the Santo Domingo Formation. During the subsequent continental sedimentation, which occurred in the late Miocene (9-5 Ma), the prior basin-fill was partially deformed and uplifted. This episode of basin inversion is primarily evidenced by the arrival of thick alluvial successions (conglomerates) composing the Cerro Mandango Formation. Compressive tectonics continues throughout the Pliocene with alluvial sedimentation (Suro Unit) and the gradual inversion of the basin-bounding normal faults into thrusting systems that currently predominates at basin borders. An insight into the connection via marine incursions between the Miocene basins and either the Pacific Ocean or the eastern Oriente basin, is provided herein as a discussion based on the data collected and a local paleogeographic model.

Mid-late Holocene evolutionary history and climate reconstruction of Vellayani lake, south India

The lake sediments received wide attention for archiving paleoclimate and paleo sea-level variability during the late Quaternary period. It has also been extensively used to disentangle the interrelationships existing among the regional and the global climate systems. In the present study, the applicability of lake sediments has been the major impetus to delineate the mid-late Holocene climate and sea level variability using a ∼10 m sediment core retrieved from a protected freshwater lake-the Vellayani lake, southern Kerala, southwest India. The sediment core was investigated using multiproxy approach and was chronologically supported by AMS radiocarbon dates. The results show monsoon intensification and a high sea level during 6430−4390 cal yr BP led to the formation of a coastal lagoon system in the area. Climatically, a marginal reduction in monsoon during 4390−2600 cal yr BP interspersed by an intensified phase during 3800−2600 cal yr BP was observed while concurrently, a sea regression during4390−2600 cal yr BP restricted sea water influence in the study area. Proxies indicated a significant monsoon reduction during 2600−1000 cal yr BP followed by monsoon intensification post-1000 cal yr BP. After 2600 cal yr BP, a thick pile of alluvial sediments was deposited by the Karamana River which might have hindered the tidal influence and later the basin was transformed into a freshwater lake. The present lake configuration was attained after 440 cal yr BP. Further, comparison of paleoclimate reconstructed from the present study with the global records revealed a teleconnection of Indian monsoon with the global climate system.

Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by the Venus Express radio science experiment VeRa

The Venus Express radio science experiment VeRa provided more than 900 neutral atmospheric profiles between the years 2006 and 2014. About 800 of these could be used for an analysis of the radio signal absorption at X-Band (wavelength: 3.6 cm), which is mainly caused by sulfuric acid vapor within the Venus atmosphere. The absorptivity profiles were converted into sulfuric acid vapor profiles. The combined measurements from the entire Venus Express mission reveal a distinct latitudinal H2SO4(g) variation. A latitudinal gradient can be observed at the topside of the H2SO4(g) layer, which is located approx. 4 km higher at equatorial latitudes compared to polar latitudes. Regions of enhanced sulfuric acid vapor abundance were found at equatorial and polar latitudes. The highest H2SO4(g) values at equatorial latitudes show mean maximal values of more than 12 ppm at around 47 km altitude. At polar latitudes mean maximal values were found at around 43 km altitude and ranged from 9 to 12 ppm. Both latitudinal regions of increased sulfuric acid vapor abundance are clearly separated by a low abundance region located at mid-latitudes with values of 5 to 7 ppm.A simplified two-dimensional transport model was developed to study the formation processes of sulfuric acid vapor accumulation at equatorial and polar latitudes. It turned out that the H2SO4(g) accumulation observed at high latitudes can be explained by precipitation of H2SO4(l) droplets that evaporate into gaseous sulfuric acid upon entering lower (warmer) altitudes. The influence of wind transport on this formation process was minor. In contrast, the H2SO4(g) accumulation observed at equatorial latitudes could be reproduced in the model by oppositely directed mass transport (upward winds and sedimentation) as well as by simplified evaporation and condensation processes. The low H2SO4(g) abundance observed at mid-latitudes was reproduced by downward winds in the model calculations.The VeRa observations were additionally used to estimate the abundance of SO2 above the cloud bottom. A latitudinal dependence was found with highest values of 90 ± 60 ppm at equatorial latitudes, compared to 150 ± 50 ppm and 160 ± 50 ppm at southern and northern polar latitudes, respectively.Both the equatorial and polar regions displayed show large variability of the H2SO4(g) and SO2 abundances from observation to observation. A weak tidal influence is also visible in the sulfuric acid vapor abundance in the equatorial region. The northern polar H2SO4(g) abundance, as well as the southern and northern SO2 abundances, exhibit distinct long-term variations.

Influence of Tide and Runoff on Saltwater Intrusion in the Qiantang River Estuary, China

Qiantang River Estuary, as one of main fresh water resources for urban zone, has been threatened by salt water intrusion. Due to the combined influence of tide and runoff, the mechanism of saltwater intrusion is extremely complex. In view of this, research on the variation characteristics of chlorinity along Qiantang River Estuary is conducted based on chlorinity data. Further, analysis on effects that tide and upstream runoff exerting on chlorinity at intake is carried out to ensure urban water security. The chlorinity and tide data was obtained synchronously from automatic real-time monitoring systems at Zhakou, Qibao, Cangqian, Yanguan and Ganpu stations with sampling interval of 5 minutes. Results show that chlorinity Yanguan and Ganpu are mainly influenced by tide with period of 12.4 h; chlorinity at other stations are affected by runoff obviously. The peak chlorinity values at all observed stations increase with increase of tide ranges. The increase of upstream runoff enables to reduce the peak chlorinity. It is feasible to extract water under average tide and average runoff.

A Hooghly head‐scratcher

A Hooghly head‐scratcher

Numerical modeling of the influence of tides on cross-shore sediment dynamics of dissipative beaches under moderate wave conditions

The influence of tides on cross-shore sediment dynamics of a longshore-uniform beach is studied by means of a 1D numerical model (XBeach). The model is modified to include longshore tidal currents induced by water level gradients. The effect of tides on cross-shore sediment dynamics is quantified by analyzing the change in suspended sediment concentration, sediment advection velocity, and sediment transport. The effect of tides is decoupled into its two main components, i.e., water level fluctuations and tidal currents. Water level fluctuations modulate wave orbital velocities, wave-averaged currents and sediment advection velocity, therefore affecting both resuspension of sediments and cross-shore sediment transport. Tidal currents favor tidally-averaged sediment resuspension due to the increase in applied shear stress on the bed. The effects of water level fluctuations and tidal currents on sediment dynamics vary in the cross-shore direction: tidal currents increase sediment resuspension in deeper water depth, while water level fluctuations control the changes observed in shallow waters. In shallow waters, tidal amplitude is a good indicator of the influence of longshore propagating tides on the cross-shore sediment dynamics of a uniform beach, while in deeper waters, tidal wavelength also plays an important role. The model predictions are able to capture the trends observed in field measurements.

Changes to spotted turtle (Clemmys guttata) habitat selection in response to a salt marsh restoration

Development of coastal New England has led to the replacement of up to 37% of salt marshes with degraded freshwater wetlands, primarily through tidal restrictions. Removing these restrictions to restore salt marsh ecology would improve water quality, increase flood and storm protection, nutrient filtration, erosion control, and carbon sequestration. However, such restorations replace functional freshwater wetlands and could potentially impact freshwater species. Freshwater-dependent wildlife species such as the spotted turtle (Clemmys guttata), may be especially vulnerable to rapid changes in habitat resulting from tidal reintroduction due to their high site fidelity and limited ability to disperse quickly. Conservation of genetically and physically isolated spotted turtle populations as well as the restoration of salt marshes to mitigate climate change impacts are both high priorities on Nantucket Island. These two priorities conflicted in a project to restore tidal hydrology to an impounded freshwater marsh known to host a robust spotted turtle population. We evaluated changes to spotted turtle home range size and location and habitat use in response to salt marsh restoration over eight years. Home range size did not change but the location of home ranges shifted into bordering wetlands landward of the tidal salt water influence. Spotted turtles selected remaining freshwater marshes and shrub swamps while avoiding developed land and areas of establishing salt marsh within areas that had previously been high quality habitat. This study suggests prioritizing conservation of wetlands adjacent to planned salt marsh restoration to provide habitat for freshwater species to migrate.