Shallow Bay Research Articles

Rapid drops of ocean temperatures in several shallow bays in Nova Scotia during a recent cold air outbreak

Abstract From February 3-5, 2023 Atlantic Canada experienced an extremecold Arctic air outbreak with high winds that set many local meteor-ological records, including wind chills as low as -47°C. The impacts of the cold air outbreak on ocean temperatures and ice formation are investigated using predictions from the Coastal Ice-Ocean Prediction System for the East Coast of Canada (CIOPS-E), developed by Environment and Climate Change Canada. Observations from moorings further inform the predictions. The analysis suggests that during the event, several shallow bays and coastal areas in Nova Scotia experienced significant, abrupt temperature decreases ranging from 1.0 to 3.9°C. Overall cooling estimated by the model was 2.3°C for nearshore locations where observations recorded an average temperature decrease of 3.0°C. On the other hand, at individual sites the difference between observed and modelled cooling was up to 2.4°C. This difference can be attributed partly to the fact that the model does not adequately resolve the coastline features of some of the nearshore mooring sites. In comparison, we also analyze another cold air outbreak that occurred on December 15-18, 2016, with wind chills as low as -37°C. The ocean temperatures changes associated with this earlier event saw decreases of 0.8 to 3.5°C, potentially contributing to an ongoing fish kill in St. Mary’s Bay (near the mouth of the Bay of Fundy) at the time. Keywords: Ocean temperature, Cold air outbreak, Ocean forecasting, Shallow bays, Nova Scotia

T4-Like Cyanophages of Lake Baikal: Genetic Diversity and Biogeography

The work deals with investigation of genetic diversity and biogeography of T4-like cyanophages from the shallow bay of the Posolsk Sor (Lake Baikal), based on analysis of the g20 marker gene. High diversity of g20 gene fragments and their uniqueness were revealed. The greatest similarity was noted with the previously obtained sequences from Lake Baikal and with those from freshwater ecosystems: oligotrophic Lake Green, Lake Round, oligomesotrophic Lake Ancy, and mesotrophic Lake Bourget. From the point of view of biogeography, it was determined that the phage sequences were similar to the previously obtained ones from different Lake Baikal ecotopes than to those from other ecosystems.

Response of hydrodynamic environment to land reclamation in Sanmen Bay, China over the last half-century

Sanmen Bay (SMB) is one of the important harbors in Zhejiang Province. It is a semi-enclosed shallow bay that has undergone large-scale land reclamation activities. Long-term reclamation has changed the hydrodynamic conditions of SMB, such as tide, residual current, tidal prism, water exchange capacity, and tidal asymmetry. In this study, three typical periods of numerical models, based on historical charts and remote sensing, were established to investigate the influence of reclamation activities on the hydrodynamic conditions of SMB from 1971 to 2020. These model results reveal that the amplitude and phase of M2, the main tidal components in SMB, decreased by ~0.1–0.3 m and ~ 5°–15°, respectively, over the last half-century. Additionally, under the influence of ~200 km2 reclamation, many hydrodynamic conditions in SMB also changed. This includes the reduction of a residual current and tidal prism, an increase in residence time, and a change in tidal asymmetry characteristics. The residence time in nearby Xiayangtu exhibited a downward trend from 2003 to 2020, because land reclamation squeezed, and thus, enhanced the residual current eddy. The water-exchange capacity of the bay became weaker with the reduction of tidal prism to one-third and an increase in residence time. The tidal asymmetry characteristic of SMB changed from half of flood dominant to fully flood dominant by the influence of shoreline and bathymetry, which raised the flood risk. Research on the response of the hydrodynamic environment to reclamation activities in SMB reminds the local government to reassess the impact of land reclamation on the hydrodynamic environment.

Wat is er gebeurd? Een interpretatie van de scheepsramp van de 18e-eeuwse koopvaarder Queen Anne

What happened? An interpretation of the shipping disaster of the 18th-century merchantman Queen AnneThis paper focuses on the depositional phase of the Queen Anne, a large, three-masted freighter that sank on the Zuiderzee (a shallow bay of the North Sea, in the north-western Netherlands) sometime between AD 1715 and 1720. This depositional phase entails the moments of a shipping disaster and should be taken into consideration in order to fully understand a wreck site. However, as information on most shipping disasters is solely recorded in historical sources and oral traditions, it can be hard to connect the disaster itself to specific a shipwreck, and vice versa. In the case of the Queen Anne, no information has been found in historical records on the ship’s sinking, and oral accounts have disappeared over time. Fortunately, the excavation of the shipwreck revealed several clues that may help to reconstruct the final moments of this vessel.

Mapping benthic sediment types and composition in a turbid Jamaican bay using hydroacoustic data and different spatially explicit interpolation techniques

Hydroacoustic sensors are better suited for mapping shallow turbid coastal waters, but surveys must take place along transects, necessitating the interpolation of processed, large, spatially dependent hydroacoustic datasets to produce continuous maps. The aim of this study was to evaluate the performance of interpolation techniques that can handle data obtained from a hydroacoustic survey (covering 23 km2) conducted in 2016 in a shallow bay in southwestern Jamaica. Independent data or a 5-fold cross validation were used to compare the accuracies of continuous maps of benthic sediment percentage composition and submerged aquatic vegetation cover (SAV), interpolated from the survey data using random forest (RF) regression (RFr), RFr kriging (RFrk) and Ensemble Machine Learning (EML) with rotated/oblique coordinates. Categorical/thematic maps of sediment types interpolated using RF (RFc) and EML classifiers and a spatial Markov chain model with indicator kriging predictor/simulation (Mc-IK) were also compared. RFr, RFc, RFrk and EML covariates included coordinates and auxiliary data. The following maps were more accurate than corresponding interpolated maps: EML - mud, sand, silt, clay and SAV; RFr - loss on ignition [LOI]; RFrk - calcium carbonate; Mc-IK – sediment types with 3 and 4 classes. The Mc-IK maps were also the most suitable maps for assessing spatial and quantitative changes. The predominant substrate type in the bay was muddy sand covering 15.7 km2. The highest percentage composition of mud, silt, clay, and organic matter [LOI] was found close to the mouth of the Black River where sandy mud was found, indicating a high input of terrigenous sediment. Calcium carbonate composition showed an opposite spatial trend and was positively associated with higher SAV percentage cover. The bay is now part of a protected area, as such, these maps will be used as a baseline to gauge the impact of increased protection/management on benthic dynamics.

Thermal habitat fragmentation in stratified lakes induces resource waves that brook charr track across seasons

The spatial configuration of thermal habitats constrains the thermoregulatory performance of ectotherms. Thermal landscapes also vary through time, which is particularly relevant in seasonal environments such as temperate lakes. Indeed, elevated temperatures in the epilimnion of dimictic lakes during summer could substantially reduce the use of this habitat by cold‐stenothermic fish during the stratified period. The main objective of this study was to evaluate whether thermal habitat fragmentation in stratified lakes modulates accessibility to resources that brook charr, Salvelinus fontinalis, which is a mobile consumer, can track across seasons. More specifically, we hypothesize that reduced access to the littoral habitat during summer enhances foraging opportunities in this habitat during winter. We used an automatic acoustic telemetry system offering full coverage of the lake to continuously record brook charr locations across seasons, and we estimated zoobenthos abundances in the littoral habitat using image processing and semi‐automatic classification. While brook charr concentrate in the metalimnion of the pelagic habitat in summer, most individuals in winter shift to a shallow bay that is unexploited in summer due to thermal constraints. In this habitat, zoobenthos abundance is more than twice as high at the end of the summer compared to littoral habitats close to the thermal refuge in the pelagic habitat. Surprisingly, brook charr showed strong within‐lake site fidelity between two consecutive summers, which suggests that spatial memory could be a key driver of seasonal habitat use in this lacustrine population. Overall, our results suggest that thermal barriers create fragmentation between littoral and pelagic habitats that in turn produces resource opportunities that brook charr can track across seasons.

Invertebrate Responses to Large- and Small-Scale Drivers in Coastal Phragmites australis Beds in the Northern Baltic Sea

Phragmites australis is a common helophyte, covering much of the sheltered and shallow soft bottoms along the coasts of the Baltic Sea. Despite the expansion of P. australis over the past decades, there is little information on aquatic macroinvertebrates within P. australis beds. In this study, we examined the effect of large-scale (wave exposure, nutrients) and small-scale (distance from the seaward edge, live and dead stalk density, epiphyte and rhizome biomass) drivers on the density, taxa richness, diversity, and community structure of epifauna and infauna in monospecific P. australis beds around the Åland Islands and the Archipelago Sea. We found that higher wave exposure and nutrient levels generally supported higher epi- and infauna abundance and taxa richness. The effects on Shannon–Wiener diversity were less evident apart from an increase of the infauna diversity in the Archipelago Sea with increasing nutrient levels. On a local scale, the distance from the seaward edge, live and dead stalk density, and epiphyte biomass had varying effects on both epi- and infauna communities in the different regions. Rhizome biomass had no effect on either the epi- or infauna abundance, taxa richness, or diversity. Furthermore, according to existing studies, other habitats, e.g., Zostera marina meadows, Fucus vesiculosus belts, and vegetated soft-bottomed shallow bays, are generally characterized by more abundant fauna, except for the infauna, which had a higher density in P. australis beds than in vegetated soft-bottomed shallow bays. P. australis are a widespread, expanding, and understudied habitat with an important role in supporting coastal biodiversity.

Anthropogenic activities decrease functional richness over time, but not other functional aspects of the fish community in a tropical bay

Functional diversity can be used to help understanding the processes shaping biological communities and the effects of human disturbances on the ecosystem's services. Untangling these biological processes is crucial to apply effective policies aiming the biodiversity conservation. Temporal changes (1983–1985, 1999–2001 and 2017–2019) in five functional indices (functional richness, divergence, evenness, specialization and originality) of the fish communities in two zones (inner and outer) of shallow areas in a tropical bay heavily human-impacted in recent decades were evaluated. The tested hypothesis was that functional indices decrease over time, because of the environmental degradation. A substantial decrease in species richness and abundance in the more recent periods (1999–2002 and 2017–2019) compared to 1983–1985 was observed. However, the functional structure remained relatively stable, with the exception of functional richness that showed a significant decrease over time. The apparent stability in the other functional indices may be due to the presence of dominant and functionally redundant species over time that compensates for the loss of species while maintaining similar functions. It was also discovered that decreases in fish richness in shallow bay areas result in losses in functional richness, with resident fish and benthivorous species being the most affected by environmental degradation. By employing a comprehensive approach that integrates the use of functional indices and taxonomic diversity to assess temporal changes in the fish community, it provides a broader understanding of ecological processes. Such insights could prove invaluable in guiding the implementation of conservation strategies.

Role of macroalgal forests within Mediterranean shallow bays in blue carbon storage

Although seaweeds rank among the most productive vegetated habitats globally, their inclusion within Blue Carbon frameworks is at its onset, partially because they usually grow in rocky substrates and their organic carbon (Corg) is mostly exported and stored beyond their habitat and thus, demonstrating its long-term storage is challenging. Here, we studied the sedimentary Corg storage in macroalgal forests dominated by Gongolaria barbata and in adjacent seagrass Cymodocea nodosa mixed with Caulerpa prolifera algae meadows, and bare sand habitats in Mediterranean shallow coastal embayments. We characterized the biogeochemistry of top 30 cm sedimentary deposits, including sediment grain-size, organic matter and Corg contents, Corg burial rates and the provenance of sedimentary Corg throughout stable carbon isotopes (δ13Corg) and pyrolysis analyses. Sediment Corg stocks and burial rates (since 1950) in G. barbata forests (mean ± SE, 3.5 ± 0.2 kg Corg m−2 accumulated at 15.5 ± 1.6 g Corg m−2 y−1) fall within the range of those reported for traditional Blue Carbon Ecosystems. Although the main species contributing to sedimentary Corg stocks in all vegetated habitats examined was C. nodosa (36 ± 2 %), macroalgae contributed 49 % (19 ± 2 % by G. barbata and 30 ± 3 % by C. prolifera) based on isotope mixing model results. Analytical pyrolysis confirmed the presence of macroalgae-derived compounds in the sediments, including N-compounds and α-tocopherol linked to G. barbata and C. prolifera, respectively. The sedimentary Corg burial rate linked to macroalgae within the macroalgal forests examined ranged from 5.4 to 9.5 g Corg m−2 y−1 (7.4 ± 2 g Corg m−2 y−1). This study provides empirical evidence for the long-term (∼70 years) sequestration of macroalgae-derived Corg within and beyond seaweed forests in Mediterranean shallow coastal embayments and thereby, supports the inclusion of macroalgae in Blue Carbon frameworks.

Paleoenvironmental variations during the Late Cambrian: Implications from Zn isotopes, I/(Ca+Mg) ratios, and other elemental proxies

The Upper Cambrian at the Martin Point section (∼110 m-thick) in western Newfoundland is a part of the Cow Head Group and partially spans the coeval Tuckers Cove and the Martin Point members of the Shallow Bay and Green Point formations, respectively. These units comprise alternating shale, minor conglomerate beds, and limestone rhythmites of a toe-of-slope apron. Earlier studies of the C-isotope profile, based on the lime mudstone interbeds, documented global negative δ13Ccarb shifts (from old to young: NL1, NL2, HERB) correlated with the lowermost Proconodontus posterocostatus, Proconodontus muelleri and base of Eoconodontus notchpeakensis conodont zones, respectively (post-Steptoean Positive Carbon Isotope Excursion NL1 and NL2 and Hellnmaria-Red Tops Boundary-HERB). Samples were extracted from the most preserved spots of micritic to near-micritic grain size (≤4 μm−10 μm). Fabric retention confirms petrographic preservation and insignificant correlations (R2 ≤ 0.1) of diagenetic proxies (e.g., Sr) with their environmental counterparts support the preservation of at least near-primary geochemical signatures. The paleoenvironmental proxies (TOC, Zn, P, Cu, Al/Ti, Mn, Fe, V, Mo) support dominant dysoxic conditions. The δ66Zn values (0.09–0.73 ‰ JMC Lyon) and (I/(Ca + Mg)) ratios (0.02–0.48 μmol/mol) vary consistently throughout the studied events. The minor decreases in δ66Zn values seem to denote inhibition of bioproductivity in a dysoxic water column, consistent with warm and humid climate during general transgressive settings and shoaling of organic-rich water into the shallow environment. The low I/(Ca + Mg) ratios (<0.5 μmol/mol) reinforce this interpretation, suggesting general dysoxic settings throughout the entire section.

Dietary reconstruction and influencing factors of oysters cultured in a typical estuarine bay of South China

Blue carbon can be transferred from primary producers to primary consumers through oyster filter feeding. Understanding the carbon (food) sources is crucial for understanding coastal food webs and management of oyster aquaculture ecosystems. In the present study, Bayesian stable isotope mixing models (MixSIAR) were used to identify and quantify food composition within a cultured oyster ecosystem at six sites along a salinity gradient in the estuarine bay of Zhenhai (ZHB). The carbon stable isotope (δ13C) signatures of oyster Crassostrea hongkongensis ranged from −22.06 to −27.27‰, with significant spatial differences (p < 0.001), indicating variations in food resources along the salinity gradient. The primary food source for cultured oysters was suspended particle organic matter across ZHB (55.7–90.6%), with sedimentary organic matter contributing more in the mid-estuary (28.9–44.3%). Partial least squares regression (PLSR) was used to explore the effects of habitat environment and human disturbance on spatial variation in oyster diets. The results indicated that dissolved oxygen, sediment particle size, elevation, and mangrove-related landscape indices were the main factors influencing oyster diet in ZHB. The findings provide insights into the dietary composition of cultured oysters and the underlying factors in a typical shallow bay in southern China, with particular emphasis on the role of terrestrial landscape features. In addition, the findings validate PLSR as a reasonable tool for predicting the food composition of consumers in estuarine bays.

SEAFLOOR MORPHOLOGY OF THE OB RIVER GULF, KARA SEA

The article presents the results of an extensive study of the bottom topography of the Ob River Gulf in the Kara Sea, which is a follow-up to the long-term studies of the authors. It refines the existing ideas and aims at solving a fundamental problem of reconstructing the conditions for the formation of bottom topography in the shallow bays of the Kara Sea in the Late Pleistocene and Holocene. The work aims to create a regional characteristic of the geomorphologic structure of the Ob River Gulf bottom. The initial data on the bottom topography were taken from marine navigational maps and sounding boards at a scale of 1:50 000 - 1:100 000. We processed and interpreted the collected cartographic material to create a detailed DEM of the bottom and a bathymetric map at a scale of 1:200 000 with an isobaths interval of 1 m. In addition to bathymetric data, the compilation of a geomorphologic map engaged a large amount of literature and stock materials on geomorphology, geology, and geocryology of the region. The original morphogenetic legend was elaborated with due account of current ideas regarding the conditions for the formation of periglacial plains relief at the regressive stage of the Kara Sea shelf evolution. It was found that the relict fluvial relief prevails within the gulf and was partly modified by subaqueous processes during post-LGM transgression and the current epoch. We have indicated the most critical features of the structure and pattern of the flooded pravalley of the Ob River, as well as the total ancient erosion network. The selected individual forms and relief elements take into account the scale of objects and the degree of their generalization on the map and give an idea of the development of relief-forming processes both at the subaerial stage and under subaqueous conditions, including specific features of modern dynamics of the coastal and bottom relief.

Responses of phytoplankton and periphyton community structure to an anthropic eutrophication gradient in tropical high-altitude Lake Titicaca

Eutrophication is a global environmental problem in aquatic ecosystems, mainly caused by increased nutrient loads (nitrogen and phosphorus). Phytoplankton and periphyton responses to the nutrients increase and temporal variation may be related to mutual seeding and/or variable environmental constraints. Each of these communities may be useful for characterizing and monitoring eutrophication processes. However, little information exists about the simultaneous responses or interactions between such communities during eutrophication, even less in high-altitude tropical lakes such as Lake Titicaca. Here, we first established a eutrophication gradient with stable isotopes (δ15N and δ13C) and physicochemical variables in a shallow bay of Lake Titicaca. Later, we analyzed the shifts in taxonomic and morphological forms of phytoplankton and periphyton colonizing the underwater stems of totora (Schoenoplectus californicus ssp. tatora), an emergent aquatic macrophyte, along the eutrophication gradient. There is a clear turnover (groups, genera, and morphological forms) in phytoplankton and periphyton and decreased biodiversity along the eutrophication gradient. Gomphonema genus relative abundance increase with eutrophication in both communities, while Achnanthidium abundance decreases. However, other genera behave differently in each community, allowing for the identification of specific bioindicators of eutrophication for phytoplankton (Oscillatoria, Spirogyra, and Euglena) and periphyton (Oedogonium, Stigeoclonium, and Characium). They share genus composition with some taxa showing similar behaviors, thus interactions between phytoplankton and periphyton may exist. We also believe that each compartment can act as a seeding reservoir for the other, though remaining independent to some extent.

Size-ftactioned photoautotrophic production in a shallow Bay.

CO2 assimilation measurements werecarried out in Concepción Bay (36"40'S, 73"0rW), toevalúatesizefractioned and total primary production in HC incubations. The P-I curve shows an assimilation nuinber of 3.82 mgC (mgChl-a)-1 h~1 and an a valué of 0.0076 (mgC(mgChl — a)'1 h~‘)/uE m-2 s-1, both parameters were used to estimate primary production in the water column using the Hermán &amp; Platt model (1983). Integrated production was calculated as 0.97 gC m-2 d-1, four times higher than previous estimations reponed off the Chilean coast. At low irradiance (1= 109 uE m~2 s" ’). picoplankton and nanoplankton were responsible for 9.5% and 12.5% of the non-normalized production. whereas the net phytoplankton accounted for 64.6% of the photosynthetic assimilation.The chlorophyll normalized photosynthetic rate (productivity Índex) was higher for smaller than larger fractions, size dependant relationship with ecological significance at low light irradiances.

Fluid and aero-acoustic analysis of internal bays: Geometric length-to-depth effects

Weapon bays are essential for any bomber, Next Generation Fighter Aircraft, and unmanned combat air vehicles (UCAVs). As flow approaches the leading edge of such cavity, it separates and forms a shear layer. The structure of bays and residing stores thus become prone to intense acoustic and aerodynamic loading– a major design concern. Cavity flow shows significant dependence on its shape. This makes flow actuation possible by only changing the geometric variable of length-to-depth (L/D) ratio. This study compares two bays with an L/D ratio of 5 (deep) and 10 (shallow) in terms of acoustics and affiliated aerodynamic drag. A transient RANS formulation obtained overall sound pressure levels (OASPL) on bay ceilings. An integral-based method was also used to predict far-field noise propagation due to flow fields of both cavities. It is argued that at Mach 0.6, the character of bays changes remarkably when its L/D is altered. Deeper bays show a smoother pressure profile and significantly less drag while operating in shear mode. Shallow bays, on the other hand, show bluff body type drag with uneven pressure distribution, having the potential of causing downwash on residing stores. At the same time, acoustic loads on the ceiling and acoustic signatures in the far-field are comparable for both cavities.

A novel method of identifying estuary high-nutrient zones for water quality management

Coastal shallow waters are highly vulnerable to pollution, often leading to the development of intricate eutrophication zones. However, accurately determining these areas poses a significant challenge due to the complex interplay of estuarine hydrodynamics and nutrient transformation. To address such issue, a novel method was proposed to identify high-nutrient zones through calculating the continuous zonation of released tracers when their instantaneous concentrations declined to 1/e of their initial values. The method was well tested using idealized estuary models with varying shape parameters, water depths and river discharges. The results consistently revealed that the boundaries of high-nutrient zones fell within the mixed zone, characterized by salinity levels of 10– 20 psu. In Shenzhen Bay, a typical shallow bay, distinct differences were observed in the concentrations of dissolved inorganic nitrogen (DIN) and PO43−. Both the 20 psu isohaline and the proposed method effectively identified the partition boundary of high DIN and PO43− in 2001–2010, but only the newly proposed method demonstrated accuracy in delineating the actual high-nutrient zone during the continuous nutrient reduction period from 2010 to 2020. This study provides a practical and feasible approach that can serve as an auxiliary decision-making tool for managing estuarine water environments, and it has potential to facilitate the implementation of timely and effective measures for pollution control.

Redox conditions across the Upper Cambrian of eastern Laurentia: Implications from geochemical proxies

The lower part of the Martin Point section (∼ 110 m - rhythmites) spans the uppermost Shallow Bay and lowermost Green Point formations (uppermost Franconian–lowermost Trempealeauan) of the Cow Head Group (western Newfoundland, Canada). It records two post-SPICE (Steptoean Positive Carbon Isotope Excursion) events marked by negative δ13Ccarb excursions (NL1 and NL2) that were also documented in South China. The petrographic and chemical screening of the investigated carbonate samples proves the preservation of at least near-primary geochemical signatures. The proxies of weathering (e.g., Mn, Fe, Al, and ∑REE), bioproductivity (e.g., δ13Corg, TOC, P, Ni, Zn, and Cu), and paleoredox (e.g., Cr, Th/U, Ce/Ce*) have been utilized to reconstruct the paleoenvironmental conditions during the post-SPICE events. The TOC, P, Ni, Cu, Cr, ∑REE, Mn, Fe, and U Ca-normalized profiles exhibit a positive pulse at the base of NL2 (upper negative δ13Ccarb excursion), followed by a drop. This might have resulted from shoaling organic-rich anoxic waters into an oxygenated shallow environment during transgression, which led to a negative shift in the δ13Ccarb and a decrease in TOC contents as well as an increase in the δ13Corg. The correlated enrichment in Zn and δ15Norg values and the Ce/Ce* around unity are consistent with the shoaling scenario. A similar scenario seems to be consistent with NL1 (lower negative δ13Ccarb excursion) although the lower resolution of correlated proxy variations makes the interpretations based on a few points and to be therefore taken with caution.

Effects of tidal cycles on the variability of microbial communities in a semiclosed bay

Shallow sediment-water plays an important role in transforming organic matter in estuaries. As a shallow bay often flanks a large estuary, the estuarine water enters the shallow bay during flood tides and exits during ebb tides. The inundation between flood and ebb tides in the shallow bay serves as an incubation of the bay water and sediment. However, little is known about the effects of tidal cycles on microbial diversity and biogeochemical processes. In Tangjiawan Bay, which is a small bay located on the west side of the Pearl River estuary, we examined changes in microbial diversity and environmental factors by collecting surface water samples between floods and ebbs. Using high-throughput sequencing targeting 16S and 18S rRNA genes, the results indicated that between floods and ebbs, the community composition of bacteria and eukaryotes differed significantly, the alpha diversity of bacteria and eukaryotes differed significantly, with floods harboring higher diversity. The analysis of RDA suggested that salinity and TOC were important in explaining community variation in both bacteria and eukaryotes. Moreover, the co-occurrence networks between bacteria and eukaryotes showed higher negative relationships in ebbs (83.87%) than in floods (64.29%), suggesting increased interactions between bacteria and eukaryotes during ebbs as the water was incubated in the bay. These findings demonstrated the dynamics of biogeochemical processes of nutrients and plankton communities in the shallow bay and tidal cycles are a dominant driving force in regulating variability in phytoplankton and bacterial community and the sediment-water interface exchange. The results indicate that we should not overlook at the importance of shallow water column fringing the shore lines.

Projecting future wave attenuation by vegetation from native and invasive saltmarsh species in the United States

Saltmarshes are naturally found along gently sloped coastlines of temperate zones including low-energy intertidal estuaries, shallow bays, and on the landward side of barrier islands. Often referred to as one of the most productive, dynamic, and valuable ecosystems on Earth, saltmarshes have been increasingly used as natural and nature-based features (NNBFs) for coastal defense. In preserved conditions, low-lying, regularly flooded marshes in the United States are naturally dominated by a single native species, Spartina alterniflora. However, over the last century the invasive Common Reed (i.e., Phragmites australis), which is directly associated with decreases in plant biodiversity and disruption of natural biochemical cycles, has become the dominant marsh species in North America. Our study quantified the influence of Phragmites australis invasion on future wave attenuation by vegetation when compared to native Spartina alterniflora marshes. We combined the coupled ADCIRC+SWAN with the point-based landscape model SLAMM and field-work-based explicit representation of vegetation to develop a series of modeling simulations based on a combination of low and high-intensity storms, SLR projections, and marsh migration scenarios. Wave attenuation by different marsh species was investigated using average vegetation characteristics (stem height, density, and diameter) for both Phragmites australis-dominated and Spartina alterniflora-dominated bay-wide modeling scenarios. Results are presented as spatially distributed differences in wave attenuation and average wave attenuation curves. Our results show that under current SLR conditions Phragmites australis-dominated marshes can provide significantly more wave attenuation than native Spartina alterniflora marshes during extreme hurricane events. On the contrary, under high-frequency and low-intensity storm events, Spartina alterniflora-dominated marshes are slightly more efficient than invasive Phragmites australis marshes. With the addition of SLR and the increase in the incoming wave heights Phragmites australis marshes can support more wave attenuation than Spartina alterniflora.

Changes in Diversity of Silica-Scaled Chrysophytes during Lake-River-Reservoir Transition (Baikal-Angara-Irkutsk Reservoir).

Hydroelectric dams create new ecosystems such as reservoirs. Several hydroelectric dams forming shallow reservoirs were built on the Angara River flowing out of Lake Baikal. The first of them in downstream Angara is Irkutsk Reservoir, with several shallow bays. Since silica-scaled chrysophytes are effective bioindicators for aquatic ecosystems, this paper aimed to determine their distribution, taxonomic structure and species richness in South Baikal and Irkutsk Reservoir, which have different environmental parameters. Thirty-one species were found using scanning and transmission electron microscopy. Only seven of them inhabited South Baikal in June 2023 at 3.66-4.51 °C and pH 7.80-8.24, with Chrysosphaerella baicalensis, Spiniferomonas trioralis f. cuspidata and Mallomonas alpina being prevalent. Only one species (M. alpina) was dominant in Irkutsk Reservoir at all stations at a water temperature of 5.33-11.55 °C and pH 8.10-8.52, alongside three other abundant species, Synura cf. glabra, Mallomonas acaroides and M. crassisquama. The maximum number of species (23) was found in a shallow bay of the reservoir at maximal values of temperature (11.5 °C) and pH (8.57) and minimal values of phosphate and nitrate concentrations during the study. The enrichment of Irkutsk Reservoir in species of silica-scaled chrysophytes was due both to cosmopolitan widespread and polyzonal species as well as to rare boreal, arctic-boreal, and unknown, possibly new species.