Increasing Water Depth Research Articles

Centrifuge shaking table study on the hydrodynamic effects on a pile foundation bridge pier in soft soil under earthquakes

Previous investigations have shown that water-pier interaction has a considerable effect on the seismic response of bridge piers in deep water. However, most of those studies assumed that the foundation is rigid and there are few studies on the hydrodynamic effects on the piers considering soil-structure interaction under earthquakes. To investigate the hydrodynamic effects on bridge piers built on soft ground, series of centrifuge shaking table tests were conducted. In the tests, a pile foundation bridge pier was scaled down by a factor of 1:50. The height of the pier was 340 mm, and the length of the pile was 200 mm. The pile foundation pier was installed in soft soil contained in a laminar shear box. Three depths of water, i.e., no water, 150 mm and 300 mm, were considered. The dynamic responses of pier displacement, acceleration and bending moment of the pier and piles, hydrodynamic pressure on the pier, soil pressure on the pile and pore-water pressure in the soil were measured. The results show that the natural frequency of the pier decreases as the water depth increases, and the displacement of the pier with a water depth of 300mm is significantly reduced in comparison with that of no water. However, water increases the acceleration and bending moment of the pier and the pile. The results also show that as the water depth increases, the hydrodynamic pressure acting on the pier and the dynamic soil pressure exerted on the pile both increase under earthquakes.

Balancing carnivore conservation and sustainable hunting of a key prey species: A case study on the Florida panther and white‐tailed deer

Abstract Large carnivore restoration programs are often promoted as capable of providing ecosystem services. However, these programs rarely measure effects of successful restoration on other economically and ecologically important species. In South Florida, while the endangered Florida panther Puma concolor coryi population has increased in recent years due to conservation efforts, the population of its main prey, the white‐tailed deer Odocoileus virginianus, has declined in some regions. The extent to which panther predation has affected deer populations has been difficult to assess because several other factors have changed during this period, including hydrology and hunting regulations. We collected known‐fate survival data on 241 GPS‐collared adult deer (156 females and 85 males) from 2015 to 2018 in the Florida Panther National Wildlife Refuge and the Big Cypress National Preserve in Florida, USA, to assess effects of panther predation on the deer population, while also evaluating the impacts of hunting and hydrology. Predation was the primary cause of death (110 of 134 mortalities), and 87% of predation events were attributed to panthers, a much greater rate than reported by studies conducted before the panther genetic restoration effort initiated in 1995. One deer was legally harvested, and two were likely killed by poachers. Increasing water depth decreased female survival but had little impact on male survival, and drowning was never a cause of mortality. Females had greater survival probability than males, except during fawning season. From 2015 to 2018, annual survival rates increased from 0.61 (0.52–0.70) to 0.86 (0.79–0.91) for females, and from 0.45 (95% CI: 0.33–0.58) to 0.79 (0.69–0.86) for males. Synthesis and applications. High predation rates, coupled with previous evidence of low recruitment of deer in South Florida, suggest that it will be challenging to meet society's competing demands for large predator restoration and sustainable deer harvest. Deer hunting in the area must remain tightly controlled, for now, if it is to be sustainable, and managers should seek to mitigate effects of high waters and improve deer habitat quality to increase deer population viability. Future work should closely monitor the deer population to assess if management actions can increase vital rates and abundance in the context of high predation rates.

Community Structure and Microbial Function Responses of Biofilms Colonizing on Microplastics with Vertical Distribution in Urban Water

Microplastics have received increasing attention worldwide due to their carrier effects. In the aquatic environment, microplastics always show a vertical distribution, which thereby may change the structure and function of the attached microbial communities. However, few studies have focused on this alteration. In this study, the structural changes and functional expression responses of the attached bacterial communities to microplastics under vertical distribution were investigated in the field combined with high-throughput sequencing technology. Polyethylene terephthalate (PET) and polyvinyl chloride (PVC) were selected as the target microplastics, which were frequently detected in the aqueous environment. The results showed that the α-diversity of bacterial communities attached to PET microplastics was much higher than that of those attached to PVC microplastics. The abundance and diversity of the bacterial communities attached to PET and PVC both increased with the increase in water depth. The α-diversity index of bacteria attached to the two typical microplastics was significantly higher in deep water (90 cm) than that in water 30 cm and 60 cm deep. The Cyanobacteria, Proteobacteria, Planctomycetes, and Verrucomicrobia were the dominant phyla in the attached bacterial communities. In addition, the deep water distinctly altered the bacteria community attached to different microplastics. The results of functional prediction showed that the functional expression of pyrimidine metabolism, amino sugar and nucleotide sugar metabolism, starch and sucrose metabolism, and aminoacyl-tRNA biosynthesis were positively correlated with water depth. In addition, the functional responses of the bacterial communities attached to microplastics were also increased, especially in deep water. Further, the bacterial functions of those attached to PET were significantly higher than that of those attached to PVC. This suggests that both the microplastic polymer and the water depth could affect the structure and function of the attached bacterial communities and that the water depth was more important, which may be related to the difference in the vertical distribution of light and turbidity. The results of this study provide a new insight into the microbial response to and environmental risk of microplastic pollution.

Improved Planktonic, Benthic Foraminiferal and Nannofossil Biostratigraphy Aids the Interpretation of the Evolution at Hole U1468A: IODP Expedition 359, the Maldives

Extended shallow carbonate platform, pelagic, and drift deposits were drilled during International Ocean Discovery Program (IODP) Expedition 359 in the Inner Sea of the Maldives. These sediments yield rich and well-diversified benthic, planktonic foraminiferal and nannofossil assemblages spanning from the early Oligocene to the Recent. We present here the shore-based revised integrated biostratigraphy of these microfossil groups at IODP Hole 359-U1468A together with the paleobathymetric reconstruction. Our data suggests the presence of a late Oligocene carbonate platform, marked by the shallowest water depths of the entire sequence of around 80 m. This carbonate platform sequence occurred from around 29 Ma, the extrapolated minimum age estimate, at least up to 27.5 Ma and possibly up to 25.4 Ma. Up the sequence, similar carbonate production conditions occurred until 22.5 Ma across the Oligocene–Miocene transition, equated at 23.04 Ma, with increased water depths >120 m. Notably, in the time interval approximately from 24 to 21.5 Ma, orbitally induced sapropel layers indicate a change of open to restricted circulation. However, at around 22.5 Ma, pelagic deposition at a distal slope occurred with sedimentation rates of 3 cm/years. This initially occurred in water depths of >350 m but gradually reached deposition in water depths of >500 m, which persisted from 21.12 Ma until approximately the extrapolated age of 12.8 Ma. Sedimentation rates gradually increased to 10.5 cm/1000 years at around 450 m below sea floor, marking the initiation of the drift sequence as identified in seismic lines with an age estimate of 12.8 Ma. The initiation of the drift sequence is also marked by a drastic decrease in the preservation of benthic and planktonic foraminifera from good to very poor at around 12.8 Ma. The drift sequence essentially continued to the present day but was interrupted by two events: the deposition of distinct shallow water benthic shoals and a large hiatus. From 12.8 Ma, a shallowing upward bathymetry is suggested by the occurrence of shallow benthic foraminiferal assemblages that close to around 11.93 Ma reached a maximum water depth of 80 m. This shoal then prograded into the basin and persisted at least until 9.89 Ma. Basin conditions with water depths exceeding 500 m were re-established in the upper part of the sedimentary succession after a hiatus spanning approximately from 9.83 Ma to 2.39 Ma, implying that renewed open ocean conditions occurred in the Pliocene–Pleistocene part of the sedimentary record.

Effect of Water Depth on Limb and Back Kinematics in Horses Walking on a Water Treadmill.

Water treadmill (WT) exercise is frequently used for training/rehabilitation of horses. There is limited study into the effect of water depth on limb/back kinematics warranting investigation. The objective was to determine the effect of walking in different water depths, at the same speed, on limb/back kinematics measured simultaneously in a group of horses. Six horses (age:15 ± 6.5 years) completed a standardized WT exercise session (19 minutes duration; speed:1.6 m/s; water depths: 0.0/7.5/21.0/32.0/47.0 cm). Ten waterproof light-emitting-diode tea-light-markers and reflective-spheres were affixed to the skin at predetermined locations; inertial-measurement-units were fixed to the poll/withers/left and right tubera coxae (TC)/sacrum to determine range-of-motion (ROM) changes of these locations. Univariable-mixed-effects-linear-regression-analyses were carried out, with a significance value of P ≤ .05. At maximum carpal/tarsal flexion during swing, regression analyses showed a clear and consistent nonlinear increase in carpal and tarsal flexion at increasing water depths (P < 0.0001 for both variables). As water depth increased there was a significant increase in thoracic spine flexion-extension ROM (P < 0.0001 at all thoracic sites) and increased dorsoventral and mediolateral ROM of the sacrum/left and right TC (P < 0.001 for all variables) as water depth increased. Results suggest that horses responded to an increase in water depth until a threshold depth was reached when the biomechanical response levelled off, and there was increased pelvic roll. In conclusion, changes in limb kinematics brought about by relatively modest increases in water depth at walking speed of 1.6 m/s are sufficient to induce significant changes in back/pelvic movement highlighting key issues with relevance for WT program design.

Cosmopolitism, rareness and endemism in deep-sea marine nematodes

Nematodes represent the most abundant benthic metazoan of all seas and oceans, and their relative importance increases with increasing water depth. Understanding the biodiversity patterns of this dominant phylum could be a critical step towards our comprehension of the evolutionary patterns across the largest biome of the biosphere. For instance, it has been assumed for a long time that nematodes are ubiquitous across depths, latitudes and biogeographic regions, but there is still little scientific evidence for this lack of endemism. The present study is based on a meta-analysis of nematode biodiversity data collected from 246 deep-sea sites of the Atlantic Ocean and Mediterranean Sea. We explored the cosmopolitanism, rareness and potential endemism of nematode genera in deep-sea sediments. The results of this analysis indicate that only one-third of nematode families are widely distributed and could potentially be cosmopolitan, whereas 94% of the nematode genera are linked to specific habitats or bathymetric ranges. Singleton nematode genera (i.e. genera presenting as a single individual only in one specific habitat) increased in importance with increasing water depth. We conclude that rareness and endemism may be a far more common feature than previously thought in deep-sea nematode assemblages and hypothesise that the deep ocean interior could be a huge reservoir of endemic nematode species.

Characteristics of Plant Community and Its Relationship with Groundwater Depth of the Desert Riparian Zone in the Lower Reaches of the Ugan River, Northwest China

The vegetation in the desert riparian zone represents a critical barrier in the maintenance of the ecosystem’s balance. However, in recent years, the vegetation degradation of the riparian zone has seriously hindered economic development and ecological environment conservation. Based on a field investigation and literature, the mechanisms of vegetation degradation in the lower reaches of the Ugan River are discussed in this study through the analysis of plant coverage, diversity, substitution rate, distribution pattern, grey correlation analysis, and the relationship with groundwater depth. The results showed that the vegetation coverage in this region is relatively low when the water depth exceeds 4 m. Furthermore, the Shannon–Wiener index, the Simpson index, and the Pielou index all decreased with increases in water depth. Woody plants are the main species maintaining the ecological balance of the region with an aggregation distribution pattern. The degradation of vegetation is the result of the lack of water sources and the intense water consumption caused by human activities (especially agricultural). To promote ecological balance and vegetation restoration, the relative optimal water depth range should be maintained within 2 to 5 m as well as proper control of human activities. In addition, the degraded vegetation can gradually be restored using point and surface (i.e., flowering in the center and spreading to the surrounding areas). The results can provide a scientific basis for vegetation restoration and ecological conservation in the lower reaches of China’s Ugan River.

The role of mangroves in coastal flood protection: The importance of channelization

The historical, present, and projected future risk of coastal flooding necessitates measures to protect coastal communities and environments, including using natural defences such as mangroves. Estimates of extent of flood protection provided by mangrove forests range widely, probably because of differences in growth characteristic of trees combined with variations in local geomorphology in each case study site. Here we use a Delft3D model of a mangrove forest in Tauranga, Aotearoa New Zealand, with vegetation flow resistance parameterized by frontal area, as a basis of idealized scenarios designed to explore and generalize the impact of channels, vegetation density, and forest slope on long wave (surge/tide) attenuation. Previous models often parameterise the frictional effect of mangroves with high bottom friction, which we show using theoretical arguments, becomes increasingly problematic with larger amplitude flood events. However, the contorted forms of the shrubby Avicenna mangroves at the field site necessitate new ways to quantify vegetation density more accurately for modelling. Nevertheless, modelling experiments show that vegetation distribution and channelization have a greater impact on flood attenuation than vegetation density, with large events resulting in less attenuation than smaller events due to the increased hydraulic efficiency associated with increased water depth. Additionally, a forest with sloping topography reduces the rate at which long wave attenuation occurs. Implications are that mangroves can only be effective coastal flood protection if the larger scale (forest-scale) distribution of vegetation also contributes to reducing the landward flow of water.

A random displacement model of sediment transport in ice-covered alluvial channel flows.

There is a need for developing efficient models to simulate the sediment transport phenomenon in ice-covered alluvial channel flows, which is essential in enriching the theory of riverbed evolution. This study establishes a random displacement model parameterized with the time-averaged streamwise velocity U(z), the sediment settling velocity ωs(z), and the turbulent diffusion coefficient Dz(z) to calculate the suspended sediment concentration and the longitudinal dispersion coefficient for ice-covered alluvial channels. The proposed model is first validated to determine if it could be used to predict the sediment concentration profiles by comparing to limited experiments published in the literature. Results show that the simulations agree well with the measurements except for the underestimated concentration near the ice cover boundary. Once validated, the random displacement model is applied to explore the variation law of the suspended sediment concentration and the longitudinal dispersion with different sediment particle release modes. The sediment concentration and the stable value of the longitudinal dispersion coefficient for a given flow condition in the dynamic equilibrium state are not affected by the change of the particle release mode. The Fickian time required for the longitudinal dispersion coefficient converging to a constant, however, has a close relationship with the particle release mode and increases as the water depth increases.

Predicting failure pressure of the corroded offshore pipelines using an efficient finite element based algorithm and machine learning techniques

This paper aims to predict the failure pressure of corroded offshore pipelines, employing different machine learning techniques. To this end, an efficient finite element based algorithm is programmed to numerically estimate the failure pressure of offshore pipelines, subjected to internal corrosion. In this process, since the computational effort of such numerical assessment is very high, the application of reliable machine learning methods is used as an alternative solution. Thus, 1815 realizations of four variables are generated, and each one is keyed into the numerical model of a sample pipeline. Thereafter, the machine learning models are constructed based on the results of the numerical analyses, and their performance are compared with each other. The results indicate that Gaussian Process Regression (GPR) and MultiLayer Perceptron (MLP) have the best performance among all the chosen models. Considering the testing dataset, the squared correlation coefficient and Root Mean Squared Error (RMSE) values of GPR and MLP models are 0.535, 0.545 and 0.993 and 0.992, respectively. Moreover, the Maximum Von-Mises Stress (MVMS) of the pipeline increases as the water depth grows at low levels of Internal Pressure (IP). Inversely, increase in water depth leads to reduction in the MVMS values at high IP levels.

Niche differentiation of ammonia-oxidizing archaea and related autotrophic carbon fixation potential in the water column of the South China Sea

SummaryThe significant primary production by ammonia-oxidizing archaea (AOA) in the ocean was reported, but the carbon fixation process of AOA and its community composition along the water depth remain unclear. Here, we investigated the abundance, community composition, and potential carbon fixation of AOA in water columns of the South China Sea. Higher abundances of the amoA and accA genes of AOA were found below the euphotic zone. Similarly, higher carbon fixation potential of AOA, evaluated by the ratios of amoA to accA gene, was also observed below euphotic zone and the ratios increased with increasing water depth. The vertical niche differentiation of AOA was further evidenced, with the dominant genus shifting from Nitrosopelagicus in the epipelagic zone to uncultured genus in the meso- and bathypelagic zones. Our findings highlight the higher carbon fixation potential of AOA in deep water and the significance of AOA to the ocean carbon budget.

Satellite-derived bathymetry based on machine learning models and an updated quasi-analytical algorithm approach.

Retrieving the water depth by satellite is a rapid and effective method for obtaining underwater terrain. In the optical shallow waters, the bottom signal has a great impact on the radiation from the water which related to water depth. In the optical shallow waters, the spatial distribution characteristic of water quality parameters derived by the updated quasi analysis algorithm (UQAA) is highly correlated with the bottom brightness. Because the bottom reflection signal is strongly correlated with the spatial distribution of water depth, the derived water quality parameters may helpful and applicable for optical remote sensing based satellite derived bathymetry. Therefore, the influence on bathymetry retrieval of the UQAA IOPs is worth discussing. In this article, different machine learning algorithms using a UQAA were tested and remote sensing reflectance at water depth in situ points and their detection accuracy were evaluated by using Worldwiew-2 multispectral remote sensing images and laser measurement data. A backpropagation (BP) neural network, extreme value learning machine (ELM), random forest (RF), Adaboost, and support vector regression (SVR) machine models were utilized to compute the water depth retrieval of Ganquan Island in the South China Sea. According to the obtained results, bathymetry using the UQAA and remote sensing reflectance is better than that computed using only remote sensing reflectance, in which the overall improvements in the root mean square error (RMSE) were 1 cm to 5 cm and the overall improvement in the mean relative error (MRE) was 1% to 5%. The results showed that the results of the UQAA could be used as a main water depth estimation eigenvalue to increase water depth estimation accuracy.

External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

Explosive volcanic eruptions can inject sulfur dioxide (SO2) into the stratosphere to form aerosol particles that modify Earth’s radiation balance and drive surface cooling. Eruptions involving interactions with shallow layers (≤500 m) of surface water and ice modify the eruption dynamics that govern the delivery of SO2 to the stratosphere. External surface water controls the evolution of explosive eruptions in two ways that are poorly understood: 1) by modulating the hydrostatic pressure within the conduit and at the vent, and 2) through the ingestion and mixing of external water, which governs fine ash production and eruption column buoyancy flux. To make progress, we couple one-dimensional models of conduit flow and atmospheric column rise through a novel “magma-water interaction” model that simulates the occurrence, extent and consequences of water entrainment depending on the depth of a surface water layer. We explore the effects of hydrostatic pressure on magma ascent in the conduit and gas decompression at the vent, and the conditions for which water entrainment drives fine ash production by quench fragmentation, eruption column collapse, or outright failure of the jet to breach the water surface. We show that the efficiency of water entrainment into the jet is the predominant control on jet behavior. For an increase in water depth of 50–100 m, the critical magma mass eruption rate required for eruption columns to reach the tropopause increases by an order of magnitude. Finally, we estimate that enhanced emission of fine ash leads to up to a 2-fold increase in the mass flux of particles &lt; 125 μm to spreading umbrella clouds, together with up to a 10-fold increase in water mass flux, conditions that can enhance the removal of SO2 via chemical scavenging and ash sedimentation. On average, compared to purely magmatic eruptions, we suggest that hydrovolcanic eruptions will be characterized by reduced climate forcing. Our results suggest one possible mechanism for volcano-climate feedback: temporal changes with climate in surface distributions of water and ice may modify the relative global frequency or dominance of hydrovolcanic eruption processes, modulating, in turn, global patterns in volcano-climate forcing.

Distribution, sources, and ecological risk assessment of HCHs and DDTs in water from a typical coal mining subsidence area in Huainan, China.

Coal mining subsidence areas are a special and widespread ecosystem in China and many developing countries in the world. However, limited research has focused on HCHs and DDTs in coal mining subsidence areas. Investigating the concentration, distribution, and sources of HCHs and DDTs at the Yangzhuang coal mining subsidence area in Huainan, China, is the object of this study. Water samples from different depths were collected from this region to detect and analyze HCHs and DDTs using gas chromatography-mass spectrometry. The result showed that the concentrations of HCHs and DDTs increased with increasing water depth, and the average concentrations of HCHs and DDTs in the top (T-layer), middle (M-layer), and bottom (B-layer) layers were 152, 169, and 182ng∙L-1, respectively. Spatial distribution of HCH and DDT concentrations in the study area revealed that the concentrations gradually decreased in the direction of water flow, and the highest concentration was observed at the entrance of the Nihe River. The T-layer was easily influenced by environmental and human activities, while the M-layer and B-layer were mainly influenced by sediment. Using principal component analysis and diagnostic ratios, we found that HCHs and DDTs in the study area mainly originated due to natural and human activities (such as pesticide use). Hexachlorocyclohexanes (HCHs) were mainly derived from lindane, and dichlorodiphenyltrichloroethanes (DDTs) mainly originated due to the recent agricultural use of dicofol; both of these are directly related to agricultural activities. Based on a comparison of reported concentrations of HCHs and DDTs in the rivers and lakes throughout China, we found that the overall ecological risk of HCHs and DDTs in the study area was elevated. The results are important for further understanding the transfer characteristics of HCHs and DDTs as well as the ecological health of the water in coal mining subsidence areas.

A large-scale study of microplastic abundance in sediment cores from the UK continental shelf and slope

To inform risk assessments, reliable, time efficient and affordable quantification methods are required for creating a microplastic (MP) pollution baseline in the world's oceans. To facilitate this, MP abundance was investigated in sediments of three contrasting areas of the UK continental shelf: North West of Jones Bank, the Canyons in the Celtic Sea and Dogger Bank in the North Sea, utilising the Nile Red tagging method to assess its time efficiency and cost. Average MP abundance in the top 10 cm was 1050–2700 MP kg−1. MP abundance decreased with increasing sediment depth and increased with increasing water depth. The findings emphasise the extent of MP pollution and illustrate the value of Nile Red for large scale mapping at relatively low cost.

Synthesis and application of a temperature sensitive poly(N-vinylcaprolactam-co-N,N-diethyl acrylamide) for low-temperature rheology control of water-based drilling fluid

During deepwater drilling operation, the wellbore temperature decreases with the increase of water depth, and increases rapidly with the increase of formation depth. Temperature sensitive polymers can change the molecular conformation with temperature, and then change its hydrophobicity, to adjust the network structure between solid particles and polymer in drilling fluid. In this paper, a novel temperature sensitive copolymer poly(N-vinylcaprolactam-co-N,N-diethyl acrylamide) (PNVDE) was synthesized. Its molecular structure, molecular weight and molecular weight distribution were characterized. The effects of salinity, pH value and copolymer concentrations on lower critical solution temperature (LCST) were studied. Based on the temperature sensitive property of the copolymer, the ability to control the low-temperature rheology of water-based drilling fluid (WBDF) was studied. The results showed that PNVDE can effectively control the rheology of deepwater WBDF in the range of 4~ 60 ℃. At the same time, the experiments of temperature and salt resistance showed that the copolymer has strong ability of temperature resistance and salt resistance, and can withstand the temperature alternation of drilling fluid. The synergistic effect of PNVDE and bentonite made the rheology of deepwater drilling fluid stable, which can be explained by “SASA Hydrogen Bond Network”.

Analysis on distribution characteristics of velocities over depth in a coastal area

Based on the continuous Acoustic Doppler Current Profiler (ADCP) data at two stations in the Strait of Georgia, Canada, spatiotemporal variation characteristics of the eastern and northern velocity component over depth was analyzed, and dominant tidal components M2, K1 and O1at each layer were extracted through tidal current harmonic analysis. Main results are: (1) The vertical flow velocity in the study area has significant stratification, and the flow velocity generally decreases with the increase of water depth. Analysis of standard deviation of the flow in direction of east–west (u) and north–south​ (v) components shows that the standard deviation of u component at station 1 varied from 76.24 cm/s to 10.12 cm/s at depth of 20 m or more, while the standard deviation of v component varied from 99.65 cm/s to 11.6 cm/s. The standard deviation of component u at station 2 varied from 51.73 cm/s to 9.68 cm/s. While the standard deviation of component v changes from 93.56 cm/s to 11.39 cm/s, and the standard deviation below 20 m does not change significantly. It indicates that the velocity variation over depth is bounded at 20 m, the above gradient is relatively large, and the below gradient is relatively small; (2) Tidal pattern coefficient F of station 1 is 1.06, and that of station 2 is 1.15, both are 0.5<F≤2.0, thus, this area was dominated by the irregular semi-diurnal tide. The averaged value of the shallow water tide influence coefficient G is 0.084 and 0.063 at station 1 and 2, respectively, both are greater than 0.04. This indicates that the shallow water tide is significant in tidal currents; (3) The tidal current ellipse of the two stations is a reciprocating flow as a whole. The flow is dominated by M2 component, followed by K1 and O1. The surface tidal ellipse is larger than other layers. This research can provide theoretical basis and reference significance for the evaluation and utilization of tidal current energy.

Scale dependence of drilling predation in the Holocene of the northern Adriatic Sea across benthic habitats and nutrient regimes

AbstractPredation has strongly shaped past and modern marine ecosystems, but the scale dependency of patterns in drilling predation, the most widely used proxy for predator–prey interactions in the fossil record, is a matter of debate. To assess the effects of spatial and taxonomic scale on temporal trends in the drilling frequencies (DFs), we analyzed Holocene molluscan assemblages of different benthic habitats and nutrient regimes from the northern Adriatic shelf in a sequence-stratigraphic context. Although it has been postulated that low predation pressures facilitated the development of high-biomass epifaunal communities in the eastern, relatively oligotrophic portion of the northern Adriatic shelf, DFs reaching up to 30%–40% in the studied assemblage show that drilling predation levels are comparable to those typical of late Cenozoic ecosystems. DFs tend to increase from the transgressive systems tract (TST) into the highstand systems tract (HST) at the local scale, reflecting an increase in water depth by 20–40 m and a shift from infralittoral to circalittoral habitats over the past 10,000 years. As transgressive deposits are thicker at shallower locations and highstand deposits are thicker at deeper locations, a regional increase in DFs from TST to HST is evident only when these differences are accounted for. The increase in DF toward the HST can be recognized at the level of total assemblages, classes, and few abundant and widespread families, but it disappears at the level of genera and species because of their specific environmental requirements, leading to uneven or patchy distribution in space and time.

Anthropogenic control of coupled changes in organic and inorganic carbon burial in karst landscape: Sediment evidence from two lakes of subtropical China

Hydrological regulation and land uses are known to alter lake organic carbon stock, while inorganic carbon cycling in karst landscapes may as well be shifted due to its rapid kinetic rate. To date, the synchronous pattern in the variations of sediment organic carbon (TOC) and inorganic carbon (TIC) burial in karst lakes largely remains to be quantified along the gradient of catchment development. Two karst lakes with contrasting nutrient level and water depth from Southwest China, both of which were converted to medium-sized reservoirs in ∼1985, were selected for sediment multi-proxy analyses on the temporal and spatial variation of carbon burial in the last ∼80 years. While hydrological fluctuations were well recorded by the sediment variation of particle size, the gradual decrease in median grain size showed a trend of increasing water depth that is consistent with the damming events for both lakes. Meanwhile, the nutrient variables revealed an acceleration of eutrophication since ∼2000 when a rapid expansion of catchment croplands was documented for both lakes. While diatom assemblage showed a significant response to hydro-climatic fluctuation and nutrients at both lakes, algal production (i.e. chlorophyll and cyanobacterial pigments) significantly increased with eutrophication at both lakes. The TIC content in the mesotrophic Taiping Lake and the TOC content in the eutrophic lake of Sanjiaohai both showed a significant increase with agricultural expansion, however, the contents of TOC in Taiping and of TIC in Sanjiaohai remained relatively stable over time. While a significant increase in the sediment flux with decreasing bulk sediment C:N ratios suggests elevated autochthonous input, the temporal change of TIC and TOC flux showed a significant synchrony at both lakes. Meanwhile, the sediment content and flux of TIC is significantly higher than those of TOC in Taiping Lake with a higher rate of carbon turnover, but lower than those of TOC in Sanjiaohai. Thus, the accumulation of TIC was disproportionally promoted in deep lakes while the burial of TOC is more favorable in eutrophic and shallow lakes. Overall, our sediment evidence highlights that agricultural expansion and hydrological regulation could interact in altering the sediment stock of TIC and TOC, and their synchronous variation in Karst landscapes.

Mechanism of Faster CH4 Bubble Growth Under Surface Waves in Muddy Aquatic Sediments: Effects of Wave Amplitude, Period, and Water Depth

Methane (CH4) transport from organic-rich fine-grained (muddy) shallow aquatic sediments to water column is mediated dominantly by discrete bubbles, which is an important natural source of greenhouse CH4. The lifespan of these bubbles within the sediment comprises two successive stages: growth from nucleation up to a mature size and then buoyant ascent toward the sediment–water interface. Bubbles often experience an oscillating overburden load due to the passage of winds and/or storm-induced short period surface waves or long-period tides, which can potentially affect both stages of the bubble’s lifespan. However, little is known about the wave effects over bubble growth phase. In the present work, this subject is investigated using a numerical single-bubble mechanical/solute transport model, which quantifies the effects of different parameters (amplitude and period) of the wave loading and of the water depth, over the bubble growth pattern in sediments and its specific characteristics. It was found that bubbles induce early sediment fracturing in the presence of waves, attributed to the low overburden load appearing at wave troughs. Bubbles at shallow depth rapidly grow at wave troughs by inducing multiple intense fracturing events. However, this ability decreases with an increasing water depth because of a slower solute influx. In the presence of waves, bubbles mature in shorter time, whose contrast to the no wave case is controlled by the ratio of wave amplitude to equilibrium water depth. Due to the higher frequency of occurrence of wave troughs for shorter-period waves, bubble growth is accelerated compared with the case of longer-period waves. Overall, our modeling suggests that the fastest bubble growth can be predicted for higher amplitude, short-period waves traveling in shallow water. We further infer that accelerated bubble growth, along with subsequent wave-induced ascent can sufficiently shorten the bubble’s total lifespan in sediment, which explains the observed episodic in situ ebullitions correlated with wind- or storm-induced waves.