Increasing Water Depth Research Articles

Water depth rather than substrate heterogeneity affects the clonal performance of the stoloniferous submerged plant, Vallisneria spiralis L

Environmental heterogeneity profoundly influences the performance of clonal plants. To evaluate the effects of substrate patchiness and different water depths on clonal performance, we subjected the stoloniferous submerged plant Vallisneria spiralis L. to different patchy substrates and water depths. We measured several growth traits. We found that ramet number, leaf number, and stolon length decreased, and ramet height, spacer thickness, and biomass increased with increasing water depth. We saw no significant trait variations across different substrates. Furthermore, the trait allocation – the distribution of trait values in different patches of heterogeneous substrates – was consistent in most treatments. Clonal integration homogenized the effects of substrate patchiness via resource exchange through interconnected ramets. The ability to use water nutrients may enable submerged plants to alleviate the uneven distribution of soil nutrients in patchy substrates. Additionally, the simple root structure and weak root functions curtail submerged plants in obtaining sufficient nutrients from soil. Water depth rather than substrate heterogeneity determined the plant performance of V. spiralis.

Fast Water Waves in Stationary Surface Disk Arrays.

Traditionally, the phase and group velocities of water waves can be increased by increasing water depth but possess upper bounds, which are related to the gravitational acceleration and difficult to exceed. Here, we theoretically propose and experimentally demonstrate that when water is covered with a periodic array of stationary rigid disks, both the gravitational acceleration and reduced water depth can be effectively increased in the lowest frequency band. As a result, fast water waves can occur in the system, with both the phase and group velocities exceeding those in water without disks. Unusual effects, such as total reflection at oblique incidence and unidirectional transmission of water waves, are further realized.

Tellurium stable isotope composition in the surface layer of ferromanganese crusts from two seamounts in the Northwest Pacific Ocean

We present the first report of the concentrations and stable isotope compositions of Te in the surface layer of ferromanganese crusts collected from the slope of two seamounts in the Northwest Pacific Ocean, Takuyo-Daigo and Takuyo-Daisan, which cover water depths from 1000 to 5500 m. The Te concentration in the surface layer of the ferromanganese crusts sharply decreases with increasing depth at shallow regions, but this decrease becomes more gradual at deeper regions. The Te isotope composition exhibits two trends that become (1) lighter with increasing water depth at shallow depths and (2) heavier with increasing water depth at greater depths. These profiles are the same for the two seamounts and indicate two types of correlations between the concentration and isotope composition with water depth. The turning points are located at approximately 2000 m for Takuyo-Daigo and 3200 m for Takuyo-Daisan, which likely correspond to different oxygen minimum zones. Co-precipitation processes with Fe and oxidation involving Mn may be responsible for the variation of Te concentration and isotope composition with water depth. These processes are also related to a change of the dissolved oxygen concentration in ambient seawater. The Te isotope compositions in ferromanganese crusts may therefore serve as a potential proxy for changes of the oxygen minimum zone of paleoceans.

Paleoenvironment and chemostratigraphy heterogenity of the Cretaceous organic-rich shales

The Cretaceous Qingshankou Formation in the Songliao Basin is rich in shale oil resources, which has become one of the most important exploration targets of lacustrine shale oil in China. Based on X-ray fluorescence element analysis, X-ray diffraction analysis, total organic carbon, rock pyrolysis, scanning electron microscope and nitrogen adsorption, the Paleoenvironment was reconstructed by comprehensive utilization of integrated prediction error filter analysis of chemical stratigraphy, and its relationship with organic geochemistry, mineralogy and pore structure was discussed. The results indicated that the Qingshankou Formation was deposited in the environment with fresh water-brackish water, semi-deep/deep water and strong reduction. The evolution of Paleoenvironment during the deposition of Qingshankou Formation changed from bottom to top, with increasing water depth, decreasing salinity and oxygen content. Paleosalinity was positively correlated with total organic carbon, residual hydrocarbon and carbonate mineral content. From bottom to top, the contents of carbonate and chlorite decreased, while the contents of plagioclase and clay minerals increased slightly. The pores were dominated by intra-illite pores, intra-I/S mixed-layer pores and intra-pyrite pores. Some intra-plagioclase pores and calcite dissolution pores were developed, and the organic matter pores are slightly few. Nitrogen adsorption data showed that the dominate pore size was 40-53 nm. This study clarifies the Paleoenvironmental evolution of the Qingshankou Formation, and may shed lights on lacustrine shale oil accumulation and sweet-spotting. Cited as : Guan, M., Wu, S., Hou, L., Jiang, X., Ba, D., Hua, G. Paleoenvironment and chemostratigraphy heterogenity of the Cretaceous organic-rich shales. Advances in Geo-Energy Research, 2021, 5(4): 444-455, doi: 10.46690/ager.2021.04.09

Modulational instability of two obliquely interacting waves with different carrier frequencies

The paper investigates the crossing sea state situation characterized by two obliquely interacting water wave systems having different carrier frequencies in finite depth domain. Nonlinear evolution equations are derived to study the instability properties of two obliquely interacting uniform wave trains for both unidirectional and bidirectional perturbations. It is found that the growth rate of modulational instability increases with the decrease in angle of interaction of the two wave systems and also with the increase in the ratio of the carrier wave numbers of the two wave systems. The growth rate of instability decreases with the increase in water depth, while it increases with the increase in wave steepness of the second wave system.

Evaluation of the Safe and Failure Zones of Mooring and Riser Systems in a CALM Oil Terminal

The mooring and riser system is the most critical part of an offshore oil terminal. Traditionally, these two parts are designed separately without considering the nonlinear interaction between them. Thus, the present paper aims to develop an integrated design process for riser systems with a lazy-S configuration and mooring systems in the offshore catenary anchor leg mooring (CALM) oil terminal. One of the important criteria considered in this integrated design is the offset diagram and safe operation zone (SAFOP) related to the mooring system and the riser, respectively. These two diagrams are obtained separately by different analyses; therefore, codes or standards are available separately for two components. In this methodology, the diagrams of both risers and mooring lines are incorporated into a single spiral, thus identifying the safe and failure zones of risers and the mooring lines of the oil terminal. This, in turn, leads to substantial benefits in terms of overall system response, cost reduction, and safety to the offshore oil terminal. To implement this process, three different riser lengths with the lazy-S configuration are considered at three different sea depths at the terminal installation site. For each condition, the integrated design of the mooring system and riser is executed according to the derived procedure. Then, coupled dynamic models, wherein both buoys and hoses are included, are developed using OrcaFlex. Results show that the criteria of the relevant regulations are not satisfied by reducing the length of the riser relative to the designed size. Further, as water depth increases, this type of riser configuration shows good coupled performance while interacting with the mooring system. In the cross offset mode, the maximum margin is created between the offset diagram and the SAFOP diagram, while the most critical dynamic response of the tanker and terminal system occurs in the near and far modes. Therefore, with this method, the best position for the riser direction with the tanker direction is 90° in the best case.

Method to optimize the volume of nitrogen gas injected into the trapped annulus to mitigate thermal-expanded pressure in oil and gas wells

Trapped annular pressure caused by thermal-expand liquid greatly threatens well integrity, so its mitigation is very necessary and essential. Nitrogen gas has been proved as an effective and low-cost mitigation measure for thermal-expanded annular pressure, but few methods are available to design the injection volume while this is vital for its mitigation reliability. Hence, this paper aims to develop a design method of the optimal injection volume of nitrogen gas to mitigate trapped annular pressure. The design method is based on volume consistency law and volume compensation effect. The proposed design method takes annular pressure increment and optimal injection volume as mitigation aim. A solving process is proposed according to volume increment and error iteration. An index is defined to evaluate mitigation efficiency. The results indicate the mitigation would fail once the injection volume is lower than the optimal injection volume, but over-surplus injection volume reduces mitigation efficiency. Optimal injection volume increases as production time and rate increase. The mitigation efficiency decreases and optimal injection volume increases as water depth increases. The optimal volume increases as the geothermal gradient increases. More nitrogen gas is needed as the mitigation aim of annular pressure increment decreases. The optimal injection volume increases as the expand-compress ratio increase while mitigation efficiency changes little. This design method can be applied in deep-water and HPHT wells. Detailed production data should be obtained and the geothermal temperature should be measured accurately. The extra injection volume is recommended to overcome the unexpected change of production plan and error of geothermal temperature measurement. The mitigation aim should consider the change of well barriers’ strengths. The expand-compress ratio of annular liquid should be adjusted to prevent too large optimal injection volume. Compared with field experience or qualitative analysis, this method can provide an optimal injection volume as reference for the mitigation of thermal-expanded annular pressure, which can enhance the long-term reliability of mitigation by injecting nitrogen gas, thus promoting the popularization.

Erratum to: Analysis of differences in nutrients chemistry in seamount seawaters in the Kocebu and M5 seamounts in Western Pacific Ocean

Comprehensive surveys were conducted in the Kocebu deep seamount and the M4 shallow seamount in the Western Pacific Ocean in March 2018 and May 2019, respectively. The distributions of nutrients in euphotic zone of the two seamount-areas were revealed, and the causative controlling factors were analyzed. Results show that the vertical distribution of nutrients in the two seamount-areas accorded with the general law of the oligotrophic ocean. The concentrations of NO3-N, PO4-P, and SiO3-Si generally increased gradually with the increase of water depth, and they were extremely low in water layers within 100 m. The area of high NO2-N concentration well agreed with the Deep Chlorophyll Maximum Layer. On the other hand, the distribution of water masses and phytoplankton and hydrological conditions in the two seamount-areas were different, resulting in lower concentrations of NO3-N, PO4-P, and SiO3-Si in the water layers below 100 m in the Kocebu seamount area than those in the M4 seamount area. In addition, NO2-N was affected by the distribution of phytoplankton, and distributed mainly in the water layers of 150 and 100 m. There was upwelling in the euphotic zone of M4 seamount area, causing accumulations of nutrients and phytoplankton around the seamount, forming a “seamount effect”; however, no such an effect was found in Kocebu seamount area. Affected by the composition of biological community and the “seamount effect”, the nitrogen limitation in the M4 seamount area was not significant, and the dissolved inorganic nitrogen (DIN):PO4-P and SiO3-Si:DIN were closer to the Redfield ratios.

The Shoreline Deformation in Convex Beach due to Sea Level Rise

Sea level rise (SLR) is become more serious on a global scale and has become one of the main reasons causes shoreline changes, and erosion, even on an extreme scale can cause the sinking of coastal areas and islands. It was recorded that many big cities were damaged by SLR. The Bruun rule is the most widely used method for predicting the horizontal translation of the shoreline associated with a given rise in sea level. In this study, however, the change in the average shoreline at the convex beach, which is more vulnerable to erosion due to sea level rise, is investigated. The increase in water depth by sea level rise causes a change in the wave crestline, ultimately leading to a linearization of the shoreline. In general, it is assumed that the annual average shoreline is parallel to the annual mean wave crestline. Moreover, assuming that the equilibrium depth contour is formed according to the crestline, the retreat of the shoreline is predicted. The shoreline change is indirectly predicted through the wave crestline deformation obtained from a wave model and this method is applied to the convex beach. Our result showed that for a convex beach with a length of 1 km has open ends with free littoral drift at both ends, the sea level rise of 1 m cause the erosion of 10 m in the protruding area, and the sea level rise of 2 m causes erosion of 23 m. However, if the convex beach is blocked at both ends, sea level rise of 1 m causes the erosion of 6.3 m in the convex area, but the shoreline advance of 3.8 m at both ends, and if the sea level rise of 2 m occurs, the erosion of 14.3 m can occur in the convex area and shoreline advance of 8.6 m can occur at both ends.

Phenotypic responses of a submerged macrophyte (Vallisneria natans) to low light combined with water depth

Adaptations to low light and water depth stresses are crucial for the survival of submerged macrophytes. To determine the phenotypic responses of Vallisneria natans to such stresses, we combined a field investigation, a light control experiment and an in situ response experiment to evaluate adaptive variations in fresh weight and morphological and physiological characteristics. In the field investigation and the light control experiment, water depth and light intensity were the main environmental factors affecting the fresh weight and morphological characteristics of V. natans. Fresh weight and leaf length were the most significant responding variables, and they were positively correlated with water depth and negatively correlated with underwater light intensity, although the root length and leaf number exhibited no variation. The leaf length elongated more rapidly at sites with intermediate water depth and low light intensity, and the allometric slopes were steeper. Furthermore, the in situ response experiment results showed a unimodal distribution of the chlorophyll-a concentrations of V. natans along with increasing water depths (from 0.5 m to 8.5 m). The turning point of the chlorophyll-a concentration occurred at 5.5 m, which is almost the maximum water depth at which V. natans occurs in Lake Erhai. Overall, our results evidenced that light availability is an important driving factor that controls the status of V. natans by affecting not only its morphology and physiology but also its biomass allocation and ramet production. An alternative resource allocation pattern of V. natans could be a shift between light acquisition and clonal reproduction.

Development of a Tsunami-tide Interaction Model with Simulation of Tsunami Wave Propagation to Korea Coasts

Kim, K.O.; Jung, K.T., and Ha, T.M., 2021. Development of a tsunami-tide interaction model with simulation of tsunami wave propagation to Korea coasts. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 91–95. Coconut Creek (Florida), ISSN 0749-0208. Simulation studies of historic and prognostic tsunamis have been performed with a focus on tsunami-tide interactions. A modeling system based on the 3D POM (Princeton Ocean Model) has been developed that is composed of a global tsunami model and a regional multinesting tide/tsunami/tsunami-tide interaction model covering the Northwest Pacific region. Propagations of two historic tsunamis, the 2010 Chilean and 2011 Tohoku tsunamis, were simulated to estimate the effects of tsunami-tide interactions by comparing the results from tsunami-only and tsunami simulations with tide simulations. Calculations show that tsunami waves are significantly transformed after traveling a long distance and subsequently affected by the tidal phase. As prognostic tsunami propagation, the Nankai Trough earthquake-induced tsunami wave in Japan was investigated. A series of calculations were performed with a systematic shift of the tsunami occurrence time. The effects of tsunami-tide interactions were examined in terms of local tidal phase changes, focusing on the changes in the first tsunami heights and occurrence times arriving at the selected tidal stations in Korea. The tsunami-tide interaction mostly results in a positive change in the tsunami first peak heights with a maximum change near low tide probably due to the interaction between the tsunami-induced current and tidal current. The water depth increase near high tide advances the arrival of the tsunami first peaks, whereas the water depth decrease near low tide delays the arrival of the tsunami first peaks.

Determination of the effect of water depth on the yield of a solar still using an automatic feedwater system.

Herein, the water depth in a pyramidal solar still was kept constant using an automatic feedwater system through an auxiliary tank. Six water depths ranging from 5 to 50 mm were investigated. All variables were measured continuously but were logged automatically every hour. Increasing the water depth increased the water volume, thereby increasing the thermal capacity of the solar still. Therefore, increasing water depth increases the nocturnal yield but decreases the diurnal yield. Over the whole day, lower water depths resulted in higher accumulated yields. These accumulated yields increased by 37% by decreasing the water depth by 90% from 50 mm. The desalination system can work without human intervention, improving its sustainability. Moreover, the automatic feedwater system facilitates the end-user operation processes and succeeds in maintaining a constant optimal water depth in the solar still.

Effect of Soil Surface Slope on Water Distribution Uniformity for Stationary Sprinkler Systems

The research included studying the effect of the slope of soil surface on water distribution uniformity of stationary sprinkler systems. 30 tests were conducted to obtain the pattern of water distribution along the radius of the wetting circle, where the sprinkler at the center, using 6 different sprinklers heads. In addition, different slopes of the surface were considered to study the wetting pattern, obtained by calculating the vertical deflection from the sprinkler head riser. 420 patterns of field water distribution were found for five slopes of the ground surface at seven different spacing, using rectangular and triangular arrangement of six sprinkler heads. It has been concluded that both of the uniformity coefficient CU and the distribution coefficient DU decrease with the increase of the soil surface slope, (87.5% and 89% of the cases respectively). In addition, The mean percentages of maximum decrease in UC and DU due to the gradient increase from 0% to 20% for all sprinkler heads was 3.17% and 6%, respectively.and the pattern of the water distribution does not change with the change of the soil surface slope, but rather the depth of water decreases and the range of the spraying increases as the negative slope decreases, and vice versa, the rate of water depth increases and the range of spraying decreases as the positive slope increases. Two equations were concluded to calculate the uniformity coefficient CU (or the distribution coefficient DU) for the distribution of water spray over lands with different slopes as a function of the slope and the uniformity coefficient CU (or the distribution coefficient DU) for the distribution of the water spray on flat surfaces with coefficients of determination of 0.98 and 0.977, respectively.

Wading through water: effects of water depth and speed on the drag and kinematics of walking Chilean flamingos, Phoenicopterus chilensis.

Wading behaviours, in which an animal walks while partially submerged in water, are present in a variety of taxa including amphibians, reptiles, mammals and birds. Despite the ubiquity of wading behaviours, few data are available to evaluate how animals adjust their locomotion to accommodate changes in water depth. Because drag from water might impose additional locomotor costs, wading animals might be expected to raise their feet above the water up to a certain point until such behaviours lead to awkward steps and are abandoned. To test for such mechanisms, we measured drag on models of the limbs of Chilean flamingos (Phoenicopterus chilensis) and measured their limb and body kinematics as they walked and waded through increasing depths of water in a zoo enclosure. Substantial drag was incurred by models of both open- and closed-toed feet, suggesting that flamingos could avoid some locomotor costs by stepping over water, rather than through it, during wading. Step height was highest while wading through intermediate water depths and while wading at a faster speed. Stride length increased with increasing water depth and velocity, and the limb joints generally flexed more while moving through intermediate water depths. However, movements of the head and neck were not strongly correlated with water depth or velocity. Our results show a wide range of kinematic changes that occur to allow wading birds to walk through different water depths, and have implications for better understanding the locomotor strategies employed by semi-aquatic species.

Reassessment of the age and depositional environment of the Kırkgeçit Formation based on larger benthic foraminifera, NW Elazığ, Eastern Turkey

The middle-upper Eocene Kırkgeçit Formation, the fossil content of which is the subject of this study, is deposited in a back-arc basin controlled by block-faulting. The Kırkgeçit basin is interpreted as being formed under an extensional regime related to convergence between the Anatolian plate in the north and the Arabian plate in the south. The aim of this study is to reassess the age and depositional environment of the Kırkgeçit Formation by using detailed biometric analysis data obtained from the reticulate Nummulites and determinations of other larger benthic foraminifera (LBF) in the unit. For this purpose, two sections were measured from the latest Bartonian-Priabonian aged unit. Biometric data of the Nummulites hormoensis and Nummulites fabianii from the Kırkgeçit Formation exposures in the northwest of Elazığ has been presented for the first time. In general, Nummulites fabianii has robust test with thick walls, while Nummulites hormoensis has elongated test with thinner walls in relation to the increase of water depth. The change in embryon size of these reticulate Nummulites has been considered an important indicator for evolution and biostratigraphy. Nummulites hormoensis marks latest Bartonian to early Priabonian (SBZ 18) while Nummulites fabianii is a marker for middle-late Priabonian (SBZ 19-20). The Kırkgeçit Formation in the study area was previously dated as late Lutetian-Priabonian based on LBF of it. However, by considering the LBF determined in this study, the latest Bartonian-Priabonian age was assigned to unit. Based on the paleontological and sedimentological features, the Kırkgeçit Formation has been interpreted as a unit deposited on the inner and middle parts of a shallow ramp.

Effects of Water Depth on the Growth of the Submerged Macrophytes Vallisneria natans and Hydrilla verticillata: Implications for Water Level Management

Water level is one of the most important factors affecting the growth of submerged macrophytes in aquatic ecosystems. The rosette plant Vallisneria natans and the erect plant Hydrilla verticillata are two common submerged macrophytes in lakes of the middle and lower reaches of the Yangtze River, China. How water level fluctuations affect their growth and competition is still unknown. In this study, three water depths (50 cm, 150 cm, and 250 cm) were established to explore the responses in growth and competitive patterns of the two plant species to water depth under mixed planting conditions. The results show that, compared with shallow water conditions (50 cm), the growth of both submerged macrophytes was severely suppressed in deep water depth (250 cm), while only V. natans was inhibited under intermediate water depth (150 cm). Moreover, the ratio of biomass of V. natans to H. verticillata gradually increased with increasing water depth, indicating that deep water enhanced the competitive advantage of V. natans over H.verticillata. Morphological adaptation of the two submerged macrophytes to water depth was different. With increasing water depth, H. verticillata increased its height, at the cost of reduced plant numbers to adapt to poor light conditions. A similar strategy was also observed in V. natans, when water depth increased from 50 cm to 150 cm. However, both the plant height and number were reduced at deep water depth (250 cm). Our study suggests that water level reduction in lake restoration efforts could increase the total biomass of submerged macrophytes, but the domination of key plants, such as V. natans, may decrease.

Carbon and nitrogen isotope evidence for widespread presence of anoxic intermediate waters before and during the Permian-Triassic mass extinction

Abstract The largest mass extinction since the advent of animals occurred during the Permian-Triassic (P-Tr) transition, ca. 252 Ma, and is commonly attributed to the eruption of the Siberian Traps large igneous province. However, the direct killing mechanism is still debated. In this study, we investigated marine redox conditions of the intermediate water column that most organisms inhabit with special attention to the time interval before the onset of the mass extinction. The carbon isotope composition of carbonate and organic carbon (δ13Ccarb and δ13Corg) as well as the nitrogen isotope composition of bulk nitrogen (δ15N) were analyzed in four P-Tr boundary sequences (Zhongli, Jianshi, Ganxi, and Chaotian sections), which record a transect from a shallow water carbonate platform to a deep water, lower ramp slope in South China. δ13Ccarb shows a distinct negative shift in all sections and displays a clear, 2–4‰, decreasing gradient accompanying an increase in water depth both before and after the mass extinction. A distinct negative shift in δ15N is observed in the shallow water Zhongli section, whereas a minor negative shift is present in the three deeper water sections. Before the mass extinction, the δ15N values from shallow water sections are higher than those from deeper waters. The low δ15N values close to 0‰ in deeper water sections suggest that microbial nitrogen fixation was the predominant source of biologically available nitrogen before the onset of the mass extinction. Thus, the water depth- dependent gradient in δ13Ccarb and δ15N suggests that an oxygen-deficient intermediate water column was already present before the mass extinction. The uniform δ15N values around 0‰ accompanying the onset of the mass extinction reveal that anoxic intermediate waters expanded into shallow waters. Meanwhile, the distinct positive shift in δ13Corg observed in upper ramp slope sections, i.e., the Jianshi and Ganxi sections, suggests that a euxinic photic zone was at least episodically present in the earliest Triassic. The temporal coincidence between the expansion of intermediate water column anoxia and the onset of the P-Tr mass extinction supports the hypothesis that marine anoxia was a direct killing mechanism.

Deposition characteristics of debris flows in a lateral flume considering upstream entrainment

The sediment deposited by debris flows in rivers is a common cause of mountain disasters. The deposition characteristics of debris flows are strongly affected by the entrainment during the transportation process and the water depth in the river channel, but how is poorly understood. Here, the effects of the released flow volume, flow density, bed sediment and water depth on the deposition process of debris flows are investigated for a total of 22 different tests. Detailed topographic surveys of deposit lobes are conducted using a 3D laser scanner with high precision. The slopes of lobes are largely determined by the flow density and bed-sediment composition. However, the effect of released flow volume on the lobe slope is relatively limited. The lobe areas projected onto the horizontal plane display dumbbell or trapezoidal shapes depending on deposit volume, and the cross sections along the lateral flume present a Gaussian distribution for flows after bed-sediment entrainment. The lobe area is reduced and lobe height is enhanced with an increase of water depth, contributing to a steeper deposit. Partial, submersed or complete blockages occur, depending on the debris-flow volume and water depth. This study improves understanding of the deposition features and may aid future hazard assessments of debris flows.

Exploration of Decadal Tidal Evolution in Response to Morphological and Sedimentary Changes in the Yangtze Estuary

AbstractEstuarine tidal dynamics are influenced by changes in morphology and friction. In this work, we quantified changes in tidal damping in the Yangtze Estuary and explored the impact of morphology and friction using a numerical model. In‐depth analyses of tidal data reveal a strong reduction in tidal damping from 1990 to 2010, followed by a slightly enhanced damping from 2010 to 2020 in the South Branch. The reduced tidal damping in the South Branch from 1990 to 2010 is controlled by sediment decline which induces an increase in water depth (erosion), thereby strongly amplifying tides. However, the effective bottom roughness (Manning coefficient) is increased by 60%, which is probably related to the 80% decrease in the suspended sediment concentration (SSC). Such an effect may enhance tidal damping, which counteracts the contribution of water depth increase on amplifying tides by 75%. From 2010 to 2020, the tides in the South Branch became more damped, suggesting a dominance of the decrease in SSC over the morphological changes. In the mouth zone, tidal dissipation is enhanced from 1997 to 2010, which is mainly caused by an overall increase in effective bottom roughness. Local structures dominate the increase in effective bottom roughness; however, fluid mud formation may contribute to a decrease after 2010. Overall, we argue that estuarine morphological and sedimentary changes in response to riverine sediment decline and local engineering works control the tidal evolution in the Yangtze Estuary, which is important for evaluation of human activities and estuarine management.

Population structure and resource change of Larimichthys polyactis in spring in Zhoushan fishery spawning ground protection area, China

We investigated population structure, resource density changes of Larimichthys polyactis and its relationship with environmental factors in spring, based on the survey data of bottom trawl in adjacent sea areas of Zhoushan fishery spawning ground protection area from 2014 to 2019. The results showed that the relationship between body length and body weight of Larimichthys polyactis was W=0.44×10-4×L2.78, and parameter b was less than 3, which indicated that L. polyactis had negative allometric growth in recent years. There was a negative correlation between fullness and body length, with body becoming slender. From 2014 to 2019, body length and weight of L. polyactis were the highest in 2014 and the lowest in 2019. Since 2014, population size of L. polyactis in Zhoushan fishery spawning ground protection area and adjacent sea area had gradually decreased, indicating that the miniaturization of L. polyactis had not altered in recent years. From the perspective of the annual change of resource density, resource density of L. polyactis was higher than that before the establishment of the reserve, indicating that the management and protection of the reserve area played a protective role in the recovery of L. polyactis resources. The fitting results of GAM model showed that water depth and bottom water temperature were the environmental factors closely related to the density distribution of L. polyactis resources. With increasing water depth, the resources showed a fluctuating upward trend and were the highest near the water depth of 60 m. In the range of 12-16 ℃ water temperature, the resources increased with the increases of bottom water temperature. When water temperature was above 16 ℃, resources decreased with the increases of bottom water temperature.