Overlying Water Body Research Articles

Distribution Patterns of Sediment Organic Carbon Stocks in Shallow Lakes and the Significance for Sustainable Lake Management: Chaohu Lake in Eastern China as a Case Study

Shallow lake sediments have huge potential for carbon storage, but they are vulnerable to various environmental changes and are highly susceptible to becoming a source of carbon emissions. Understanding the amount of sediment carbon storage can provide information about the potential of shallow lakes in mitigating climate change. In this study, sediment sampling was conducted at 12 study sites in Chaohu Lake, China, and sediment water content, grain size, bulk density, and sediments organic carbon (SOC) content were examined in five layers along the vertical direction, respectively, and the distribution and storage of SOC were estimated. The results showed that the surface sediments in the west lake area of Chaohu Lake would release 66,300 t of SOC to the overlying water body in the future. The sediments in the middle lake area and the east lake area will absorb another 15,900 t and 17,300 t of TOC from the water body in the future, respectively. Overall, the lake-wide sediments will release 33,100 t of SOC into the water body in the future. In addition, the results of the study also indicate that human activities are another major influence on the change in organic carbon stocks in lake sediments, and therefore, proactive measures for the restoration and protection of lake sediments are essential because increasing the SOC stocks in the sediments and maintaining the lakes in a sustainable manner can contribute to the crucial role they play in mitigating climate change.

Capping fiberbank sediments to reduce persistent organic pollutants (POPs) fluxes: A large-scale laboratory column experiment

Deposits of contaminated wood fiber waste (fiberbanks), originating from sawmills and pulp and paper industries, have been found in the aquatic environment in boreal countries. In-situ isolation capping has been proposed as a remediation solution because it has the potential to prevent dispersal of persistent organic pollutants (POPs) from this type of sediment. However, knowledge about the performance of such caps when placed on very soft (unconsolidated), gaseous organic rich sediment is scarce. We investigated the effectiveness of conventional in-situ capping to limit POPs fluxes to the water column from contaminated fibrous sediments that produce gas. A controlled, large-scale laboratory column (40 cm diameter, 2 m height) experiment was performed over 8 months to study changes in sediment-to-water fluxes of POPs and particle resuspension before and after capping the sediment with crushed stones (≥4 mm grain size). Two different cap thicknesses were tested (20 and 45 cm) on two types of fiberbank sediment with different fiber type composition. Results showed that capping fiberbank sediment with a 45 cm gravel cap reduced the sediment-to-water flux by 91–95% for p,p’-DDD, o,p’-DDD, by 39–82% for CB-101, CB-118, CB-138, CB-153, CB-180 and by 12–18% for HCB, whereas for less hydrophobic PCBs, capping was largely ineffective (i.e. CB-28 and CB-52). Although cap application caused particle resuspension, the long-term effect of the cap was reduced particle resuspension. On the other hand, substantial sediment consolidation released large volumes of contaminated pore water into the overlying water body. Importantly, both sediment types produced large amount of gas, observed as gas voids forming inside the sediment and gas ebullition events, which increased pore water advection and affected the structural integrity of the cap. This may limit the practical applicability of this method on fiberbank sediments.

Seismic analysis of a half-space containing a water-filled valley under 2D oblique incident waves by finite-infinite element method

This paper presents for the first time the seismic analysis of a half-space containing a water-filled valley under 2D oblique P- and SV-waves by the finite-infinite element (FE-IFE) method. The equivalent seismic forces for the Chi-Chi Earthquake on the near-field boundary are calculated based on the exact free-field response. The effect of water-filled valleys on the seismic response of the half-space is a problem not well treated previously, which is considered through the soil-liquid interface in this paper. The present analysis procedure including the soil-liquid coupling is verified against Luco et al. for a half-space with an empty semi-circular canyon. New findings of this paper include: (1) The horizontal acceleration is amplified on the “near” side (to incident waves) of the valley, which is higher for filled valleys under P-waves, but decayed by the filled valley under SV-waves. (2) The effect of overlying water body on vertical acceleration is less significant for SV- than for P-waves. (3) For SV-waves with overly critical angles, the horizontal acceleration is larger for the “far” than “near” side, and larger difference exists for deeper filled valleys, coupled by amplified vertical acceleration. Additional observations were made for the numerical analysis inside the text.

Distribution Characteristics of Soil Phosphorus Forms and Phosphatase Activity at Different Altitudes in the Soil of Water-Level-Fluctuation Zone in Pengxi River, Three Gorges Reservoir

Phosphatases play important roles in converting organic phosphorus into inorganic phosphorus in soil. However, studies from this perspective on the water-level-fluctuation zone (WLFZ) of the Three Gorges Reservoir are limited. In this study, phosphatase activity and the forms of phosphorus were analyzed. Soil samples were collected in the river basin of the Penxi River in the WLFZ during a drying period. The correlation between phosphatase activity and phosphorus forms and the impacts of phosphatase activity on the phosphorus forms were analyzed. The results showed that the contents of H2O-Pi, NaHCO3-Pi, and NaOH-Pi in the soils of the WLFZ were higher than those in the soils by the river. In addition, a higher altitude resulted in higher contents of bio-enzymatically hydrolysable phosphorus and NaOH-Po. Furthermore, redundancy analysis (RDA) showed that the contents of organic matter and amorphous Fe and Mn were the main factors affecting soil organic phosphorus forms. The average activities of acid phosphomonoesterase (ACP), alkaline phosphomonoesterase (ALP), phosphodiesterase (PDE) (all in p-NP), and phytase (PAE) (in P) in the soils of the WLFZ were 1.40, 2.60, 0.44, and 11.43 μmol·(g·h)-1, respectively. Moreover, the activities of different phosphatases increased with altitude. Soil plant biomass and microbial biomass were important reasons for the difference in spatial distribution of phosphatase activity in the soil of the WLFZ. Phosphatase activities were significantly positively correlated with the contents of organic phosphorus forms but negatively correlated with the content of bioavailable phosphorus. A higher soil phosphatase activity and a lower content of bioavailable phosphorus were usually detected in soil samples taken at a higher altitude. In the early stage of flooding, phosphatase converted organic phosphorus into inorganic phosphorus at a relatively high rate, and the risk of phosphorus release to the overlying water body was also high. This study contributed to a comprehensive understanding of the geochemical cycle of soil phosphorus in the soil of the WLFZ.

A Case Study on Deformation Failure Characteristics of Overlying Strata and Critical Mining Upper Limit in Submarine Mining

Unlike land mining, the safety of seabed mining is seriously threatened by an overlying water body. In order to ensure the safety of subsea mining projects, it is of great importance to understand the failure characteristics and influencing factors of overlying strata deformation. Focusing on the Sanshandao Gold Mine, a typical submarine deposit in China, geomechanical model testing and numerical simulations were carried out. The results show that in the mining of a steeply dipping metal ore body, subsidence deformation mainly occurs on the hanging wall; the subsidence center is located on the surface of the hanging wall, and the uplift center is located on the upper surface of the ore body. The critical mining upper limit, which represents the minimum thickness of the reserved isolation pillar between the overlying seawater and the goaf, was determined to be 50 m in the Xinli mine; fault slip would occur if this critical value was exceeded. The dip angle and thickness of the ore body were negatively correlated with the vertical surface deformation. As the dip angle and thickness increased, the critical upper mining limit increased. When the fault was located in the footwall, the critical upper mining limit increased as the distance between the fault and the ore body increased, and the failure mode of the goaf was fault slip. When the fault was located in the hanging wall, the final failure mode of the goaf changed to a combined failure mode of overlying rock collapse as well as fault slip. These research results provide a theoretical basis for the selection of the reserved pillar height in the Xinli mining area, as well as a reference for safe mining practices under similar geological conditions.

Control of Endogenous Phosphorus Release at the Sediment–Water Interface by Lanthanum-Modified Fly Ash

This study optimizes the modification and granulation of fly ash to make it more stable at the sediment–water interface. Through laboratory simulations, the modified fly ash pellets were optimally granulated to cover the sediment–water interface, and its control effect and mechanism were evaluated. The results showed that the phosphorus adsorption effect of lanthanum-modified fly ash was 34% and 40% higher compared with those of acid-modified and alkali-modified fly ash, respectively, with the phosphorus adsorption effect reaching 85%. The best dosing ratio was about 0.3 g/L. Adsorption was affected by pH and was more effective under weak alkalinity, close to the Langmuir adsorption model, which was consistent with the unimolecular layer adsorption characteristics and the presence of chemisorption and physical adsorption. The saturation adsorption amount of phosphate by lanthanum-modified fly ash was 8.89 mg/g. The optimized granulation conditions for lanthanum-modified fly ash pellets were a fly ash/montmorillonite ratio of 7:3, a roasting temperature of 900 °C, a roasting time of 4 h, and a particle size of 3 mm. After 20 days, the orthophosphate removal rate was more than 60% higher than that of the control group, with a total phosphorus removal rate of 43%. After covering for 60 days, active phosphorus in the surface layer of the sediment was gradually transformed into a stable phosphorus form, with calcium phosphorus accounting for 70% of the total inorganic phosphorus. The ability of the sediment to release phosphorus to the overlying water body was also significantly weakened. Meanwhile, the total phosphorus removal rate in the overlying water at the sediment–water interface reached more than 40%, and orthophosphate removal reached more than 60%, indicating an obvious phosphorus control effect. Transmission electron microscopy analysis showed that lanthanum was present at locations enriched with elemental phosphorus and was adsorbed onto the material surface. Therefore, lanthanum-modified fly ash pellets are a promising in situ phosphorus control agent with good endogenous phosphorus pollution control abilities in eutrophic water bodies.

Water Inrush Hazard in Shijingshan Tunnel during Construction, Zhuhai, Guangdong, China

This short communication reports a water inrush hazard during the construction of the Shijingshan Tunnel in Zhuhai, Guangdong, China. On 15 July 2021, a water inrush accident occurred at the construction site 1.16 km away from the tunnel entrance, resulting in 14 casualties. The purpose of this study is to investigate and discuss the water inrush process in this atypical case. The principal causes of this tunneling accident include the special geological conditions at the construction site, high hydraulic conductivity at the part that connects the underground water system and the overlying water body (the Jida Reservoir), and the impact of heavy rainfall. Moreover, four significant suggestions are proposed to prevent the possible occurrence of water inrush disaster: (1) assessing the risk level in areas prone to water inrush; (2) getting a comprehensive geological prediction based on borehole data and artificial intelligent methods; (3) establishing a monitoring system during the tunneling process; (4) strengthening the self-protection skills of construction workers.

Effect of water flow on the release flux of dense non-aqueous phase liquids from the riverbed–take dichloromethane as an example

This research is intended to study the effect of water flow on the release flux of DNAPLs, which have been deposited on the riverbed surface after sudden water pollution accidents. Those contaminants will slowly diffuse from the riverbed into the overlying water body through hydrodynamic action, causing ongoing and serious water pollution. By taking dichloromethane as a typical contaminant, the release form under different hydrodynamic conditions was observed through flume experiments, and the response relationship between the release flux and hydrodynamic factors was analyzed, with an emphasis on parameterizing the release rate. The results suggested that stronger water disturbance significantly enhanced the release of contaminants. And the relationship between the release flux and hydrodynamic factors generally followed an exponential distribution (R2 > 0.94). Besides, the mathematical relationships between the release flux and the average flow velocity, shear force and turbulent intensity were established as follows: and Thus, this study has offered a solution to solve the source term quantification problem of the differential equation of convective diffusion, which can provide the basis for further developing the mathematical models of this kind of pollutants.

Application of iron [Fe(0)]-rich substrate as a novel capping material for efficient simultaneous remediation of contaminated sediments and the overlying water body

Release of contaminants from sediments has been one of the main pollution sources causing eutrophication and malodorous black of ponds. In this study, an iron-rich substrate (IRS) was developed based on iron‑carbon micro-electrolysis and applied for simultaneous sediments and overlying water remediation. IRS obtained high ammonia and phosphate adsorption capacities (Langmuir isotherm) of 13.02 and 18.12 mg·kg−1, respectively. In the 90-day long-term remediation, IRS reduced NH4+-N, PO43−-P, organic-N, organic-P, TN and TP in overlying water by 48.6%, 97.9%, 34.2%, 67.1%, 53.2% and 90.4%, respectively. In sediments, IRS reduced NO3−-N, NH4+-N and organic-N by 98.5%, 26.5% and 6.3%, respectively. The unstable P-compounds (i.e., organic-P, Ca-bounded-P and labile-P) were effectively transferred (20.1%, 54.3% and 98.2%, respectively) into inert P-compounds (i.e., Fe-bounded-P and residual-P). Meanwhile, flux rates of nitrogen and phosphorus from sediments to overlying water were reduced from 7.02 to 4.92 mg·m−2·d−1 (by 29.9%) and from 7.42 to 2.21 mg·m−2·d−1 (by 70.2%), respectively. Due to micro-electrolysis, Fe2+/Fe3+/[H] were in-situ generated from IRS and NO3−-N was effectively reduced. Additionally, the generation of O2· was promoted by Fe2+/[H] and strengthened the NH4+-N, organic-N/P oxidation. Fe3+ enhanced the immobilization of PO43− (e.g., as FePO4·H2O and FenPO4(OH)3n-3). The released Fe2+/Fe3+ from IRS were finally stabilized as poorly reactive sheet silicate (PRS)-Fe and magnetite-Fe in the sediments and hardly showed side effect to sediments and water body. The developed IRS obtained advantages of high efficiency, ecologically safe and cost-effective in contaminated sediments and overlying water remediation.

Assessment of metal pollution in the Anzali Wetland sediments using chemical partitioning method and pollution indices

Metal pollution in aquatic ecosystems is of immense importance. Under various environment circumstances, the metal contents of sediments can enter into the overlying water body leading to severe toxicity. This study aims to determine metal concentrations in sediments of Anzali International Wetland in Iran. Chemical partitioning method is used to determine the portion of anthropogenic pollution and the mobility potential of each metal. The intensity of metal pollution in sediments of the wetland is assessed using three reliable indices. The results of chemical partitioning reveal that cadmium bear the highest risk of being released into the aquatic environment and high amount of manganese in sulfide bond phase implies the initiation of redox state in aquatic environment of the Anzali Wetland. The results of chemical partitioning studies show that Pb, Cd, Mn and As have the highest anthropogenic portion. Cluster analysis also confirms the results of chemical partitioning and indicates that the mentioned metals can be originated from anthropogenic sources. Sediment pollution indices, including, Igeo, IPOLL, and m-ERM-Q reveal that metals are in the range of low to moderate pollution and also show that the highest metal pollution is in the eastern and central parts of the wetland. This can be ascribed to rivers which are the recipient of industrial, agricultural and municipal wastewaters and flow into these parts of the wetland.

Assessment of the Mutagenicity of Sediments from Yangtze River Estuary Using Salmonella Typhimurium/Microsome Assay.

Sediments in estuaries are of important environmental concern because they may act as pollution sinks and sources to the overlying water body. These sediments can be accumulated by benthic organisms. This study assessed the mutagenic potential of sediment extracts from the Yangtze River estuary by using the Ames fluctuation assay with the Salmonella typhimurium his (−) strain TA98 (frameshift mutagen indicator) and TA100 (baseshift mutagen indicator). Most of the sediment samples were mutagenic to the strain TA98, regardless of the presence or absence of exogenous metabolic activation (S9 induction by β-naphthoflavone/phenobarbital). However, none of the samples were mutagenic to the strain TA100. Thus, the mutagenicity pattern was mainly frameshift mutation, and the responsible toxicants were both direct (without S9 mix) and indirect (with S9 mix) mutagens. The mutagenicity of the sediment extracts increased when S9 was added. Chemical analysis showed a poor correlation between the content of priority polycyclic aromatic hydrocarbons and the detected mutagenicity in each sample. The concept of effect-directed analysis was used to analyze possible compounds responsible for the detected mutagenic effects. With regard to the mutagenicity of sediment fractions, non-polar compounds as well as weakly and moderately polar compounds played a main role. Further investigations should be conducted to identify the responsible components.

Effect of rising atmospheric CO2 on sediment and water 15N interactions in experimental riparian wetland

The experiment was conducted to ascertain net production and consumption rates of 15NH4+ and 15NO3− for water and sediment in a wetland. This was done using 15N isotope pool dilution methodology under ambient and elevated atmospheric CO2 concentrations in experimental riparian wetlands to obtain the gross N transformation rates. The 15N budget for sediment was also estimated. The results suggested that the differences in high proportion of 15N concentration in the overlying water body under elevated CO2 could be attributed to the low production and high consumption rates of 15NH4+ in sediment. The elevated CO2 effect on production and consumption of NH4+ decreased by 144 % (P = 0.014) and increased by 153 % (P = 0.009), respectively. Thereby, 15NH4+ production rates are negatively related with 15NO3− consumption rates and this accounted for the decreases in net 15NO3− consumption under CO2 enrichment in the wetland sediment by 11 % (P = 0.528). Therefore, 15NO3− production and consumption rates may strongly depend on NH4+ production. Inorganic 15N and total 15N exported from sediment to overlying water body by the effect of CO2 were 41 % (P = 0.071) and 18 % (P = 0.000), respectively. Therefore, low net 15NH4+ production and high 15NH4+ consumption rates under elevated CO2 may partly explain the significant reduction of N from the sediment.

Estimation of Nitrogen and Phosphorus Release Rates at Sediment-Water Interface of Nansi Lake, China

At present, Nansi Lake restoration is maily focused on reducing extraneous pollution, however, it is unclear about the endogenous pollution. In this study, twelve intact sediment cores were collected from four sub-lakes (Nanyang Lake, Dushan Lake, Zhaoyang Lake and Weishan Lake) in Nansi Lake, and the fluxes of NH4+-N, PO43--P, NO3--N, TN and TP at sediment-water interface were calculated based on static incubation of sediment cores with a laboratory-scale benthic chamber. The incubation results showed fluxes of PO43--P, NO3--N, TN and TP in Nanyang Lake were the highest and as follows: 2.73, 7.55, 44.43 and 3.06 mg/m2.d, respectivly, and the flux of NH4+-N in Nanyang Lake, Dushan Lake and Zhaoyang Lake had little difference ranged from 8.99 to 10.19 mg/m2.d. This study indicated that during the sampling period sediment acted as a source of nitrogen as well as phosphorus to the overlying water body in Nansi Lake.

What is bioturbation? The need for a precise definition for fauna in aquatic sciences

The term 'bioturbation' is frequently used to describe how living organisms affect the substratum in which they live. A closer look at the aquatic science literature reveals, however, an inconsistent usage of the term with increasing perplexity in recent years. Faunal disturbance has often been referred to as particle reworking, while water movement (if considered) is re ferred to as bioirrigation in many cases. For consistency, we therefore propose that, for contemporary aquatic scientific disciplines, faunal bioturbation in aquatic environments includes all transport processes carried out by animals that directly or indirectly affect sediment matrices. These pro- cesses include both particle reworking and burrow ventilation. With this definition, bioturbation acts as an 'umbrella' term that covers all transport processes and their physical effects on the sub- stratum. Particle reworking occurs through burrow construction and maintenance, as well as ingestion and defecation, and causes biomixing of the substratum. Organic matter and microor- ganisms are thus displaced vertically and laterally within the sediment matrix. Particle reworking animals can be categorized as biodiffusors, upward conveyors, downward conveyors and regen- erators depending on their behaviour, life style and feeding type. Burrow ventilation occurs when animals flush their open- or blind-ended burrows with overlying water for respiratory and feeding purposes, and it causes advective or diffusive bioirrigation ex change of solutes between the sedi- ment pore water and the overlying water body. Many bioturbating species perform reworking and ventilation simultaneously. We also propose that the effects of bioturbation on other organisms and associated processes (e.g. microbial driven biogeochemical transformations) are considered within the conceptual framework of ecosystem engineering.

Spatial distribution and flux of terrigenic He dissolved in the sediment pore water of Lake Van (Turkey)

In this study, the largest ever carried out to measure noble gases in the pore water of unconsolidated sediments in lakes, the emission of terrigenic He through the sediment column of Lake Van was successfully mapped on the local scale. The main input of He to the water body occurs at the borders of a deep basin within the lake, which is probably the remains of a collapsed caldera. The 3 He / 4 He ratio identifies the He injected into the sedimentary column of Lake Van as a mixture of He released from a mantle source and radiogenic He of crustal origin ( 3 He / 4 He ∼ 2.6 - 4.1 × 10 - 6 ) . During passage through the pore space, terrigenic He seems to be further enriched in radiogenic He that is most likely produced in the sediment column. In fact, two distinct trends in isotopic composition can be distinguished in the He injected from the lake basement into the sediments. One of these characterizes samples from the shallow water, the other characterizes samples from the deep basin. However, both of these trends are related to the same source of terrigenic He. The He fluxes determined seem to be characteristic of each sampling location and might be considered as a proxy for the fluid permeability of the deep sediment column. These new findings provide insight into the process of fluid transport within the sediments and into the process of formation of the lake basin. Moreover, the isotopic signature of the He that emanates into the water column of Lake Van is strongly affected by the mixing conditions prevailing in the overlying water body. This fact misled previous studies to interpret the terrigenic He in Lake Van as being solely of mantle origin ( 3 He / 4 He ∼ 10 - 5 ) .

Phosphorus availability in sediments from a tidal river receiving runoff water from agricultural fields

Eutrophication of surface water is a worldwide concern. Sediments may play an important role in buffering phosphorus (P) concentration in the overlying water column. However, information on the spatial variation of sediment P availability as affected by agricultural water discharge and hydrological conditions is limited. In this study river sediments were sampled in spring, summer, fall and winter, respectively from seven locations along a main tributary (Ten Mile Creek, TMC), which receives surface runoff water from agricultural lands and discharges into the Indian River Lagoon, south Florida, USA, and analyzed for P availability. Simultaneously, hydrological variables were measured on the spot and river water samples were collected for analyses of water quality. The results demonstrated that available P in the sediments of TMC as measured by several commonly used extraction procedures had a large spatial variation. The downstream locations had a greater amount of available P in the sediments than the upstream locations, which is attributable to the settlement of finer particles due to slower water flow and increased influence from salt water in the downstream locations where the fresh river water gradually mixed with salt water from the Indian River Lagoon. Phosphorus availability in the sediments appeared to be related to P sorption by iron and aluminum oxides and the competition for adsorbing sites between SO42− and PO43−. This spatial variation of P availability agrees with the elevation of chlorophyll a (Chla) in overlying water body in the downstream locations of TMC, indicating that the internal P source plays an important role in triggering an algal boom in surface water systems.

Practice and adaptable conditions classification of aquifer-protective mining in longwall coalface for shallow seam with thin bedrock

A set of adaptable conditions classification of aquifer-protective mining in the longwall coalface for shallow coal seams with thin bedrock was put forward to deal with the conflict between water protection and high efficiency for the mining field in west China. This classification was suitable for shallow coal seams with different thickness and was beneficial to the local environmental protection. Using the 3-Universal Distinct Element Code (3DEC) numerical software, the height of the fractured zones for shallow coal seams with thin bedrock was calculated and analyzed, and its predicting formula was achieved. Meanwhile, according to the lithology and the weathering degree of the shallow coal seam, the thickness of the protective layer was determined as 10 m and the overlying water body of loose water-bearing sand for shallow coal seams with thin bedrock was divided into three types, namely, weak, medium and strong. Based on these, the necessary bedrock thickness of the longwall coalface for shallow coal seams with thin bedrock was confined according to the different mining height and water yield nature of the overlying loose water-bearing sand. Combined with the present mining status, a set of new methods of adaptable conditions classification of aquifer-protective mining technology in the longwall coalface for shallow coal seams with thin bedrock was put forward.

Quantification of pumping rate of Chironomus plumosus larvae in natural burrows

This paper investigates and compares experimentally determined water velocity field above natural macrozoobenthos burrows generated by Chironomus Plumosus larva during their bio-irrigation activity. All experiments were carried out using particle image velocimetry and performed in mesocosms filled with sediment burrowed by larvae, and the water velocity fields near the inlets and outlets of the U-shaped burrows were measured. From water velocity data the average volumetric flow rates between 54.6 and 61.1 mm3/s were calculated. Assuming an average burrow diameter of 2.25 mm, the volumetric flow rates suggest the average flow velocities through burrows during the pumping period between 13.7 and 15.4 mm/s. Two additional interesting phenomena could also be shown by analyzing the flow field generated by the larva. The analysis of the amount of tracers used for visualizations revealed that some of the tracer particles added to the water must have been consumed along their path from the inlet toward the outlet, hinting clearly to the so-called filter-feeding action of C. plumosus. The second phenomenon is due to the form of motion C. plumosus generates. By careful flow visualizations it was found that unlike other organisms such as Urechis caupo that use peristaltic body contractions, C. plumosus worms its body sinusoidally catapulting the fluid far into the overlying water body. This action is of ecological advantage for it avoids generating short oxygen circuits for their respiration and filter feeding.

Episodic high intensity mixing events in a subterranean estuary: Effects of tropical cyclones

Hydrostatic balances between fresh and saline groundwater and saline surface water control the physical and chemical framework of subterranean estuaries, but they are responsive to high frequency (waves and tides), low frequency (seasonal recharge patterns), and episodic (storm) events. In this study, we document a salinity and pressure perturbation to the subterranean estuary in east‐central Florida during and after the passage of Tropical Storm Tammy on 04 Oct 2005–05 Oct 2005 and Hurricane Wilma on 24 Oct 2005. These storms reversed hydraulic gradients, forced lagoon water into the aquifer, and shifted the outflow face landward. Salinity at 1.5 m and 2.5 m below a common datum converged on similar values intermediate between fresh and lagoon water salinities. The outflow face reestablished pre‐storm conditions after 80 days at 15 m offshore, but more than 160 days at 30 m offshore, confirming that both the flow field and fluid sources control the position of the subterranean estuary. Episodic, high intensity events could influence the biogeochemical setting of the subterranean estuary and the overlying water body by altering redox conditions in the subterranean estuary during the landward migration of the dispersive mixing zone, increasing short‐term discharge of potentially contaminated groundwater, and/or changing pore fluid residence time within the seepage face and along the mixing zone‐seepage face front.

SPIEL—a model for phosphorus diagenesis and its application to lake restoration

The internal phosphorus (P) cycle of a lake can delay the effects of external P load reduction. Thus, some in-lake measures are used to speed up the recovery process by influencing the P retention in the sediment. The P retention is determined by the quantity and composition of settling seston and the P diagenesis. Existing diagenetic models do not include all important processes of the P diagenesis, or the control parameters of in-lake measures as input variables. Therefore, a deterministic P diagenetic model (SPIEL) has been developed for lake sediments of eutrophic lakes, to predict the development of the P release after an in-lake measure has been carried out. This tool helps to analyse the complex biological and chemical processes in the sediment, and to determine the appropriate measure for a lake. The model is structured in modules, reflecting the control variables of the measures and their effects on the steering factors of the P diagenesis. The main module calculates the P cycle within the sediment; other sub modules can be added to calculate the aerobic layer thickness, the iron–sulphur cycle, the P sorption capacity of aluminium, the change in porosity, or the P concentration in the overlying water body. Thus, it is possible to create measure-specific models by combining different modules, for example, for oxidation with oxygen or nitrate, precipitation with iron or aluminium, capping, hypolimnetic withdrawal and measure combinations. The model has been calibrated and verified for Lake Sempach, Switzerland. Scenarios have been calculated to show the effects of different in-lake measures on the P retention. The model results indicate that the most suitable measures for Lake Sempach regarding the P retention would be a P precipitation with aluminium or iron. Aluminium has the advantage of a longer lasting effect on the P release than iron.