Sink For Phosphorus Research Articles

Phosphorus sorption kinetics and sorption capacity in agricultural drainage ditch sediments in reclaimed land, Kasaoka Bay, Japan

Equilibrium analysis is essential to evaluate sorption capacity and to determine whether sediment acts as a source or sink of phosphorus (P). This study was carried out to determine whether or not the sediment in drainage ditches acts as a source or sink of P, evaluate phosphorus sorption kinetics, and determine the potential P sorption by using the Langmuir isotherm sorption model. Surface sediment (0–10 cm) and the overlying water were collected from three drainage ditches for the experiments. Results showed that the drainage ditch that was the most contaminated with P had the highest sediment zero-equilibrium phosphorus concentration (EPC0). Because sediment EPC0 of the three ditches was higher than water P concentration, they acted as a sink of P across the sediment interface. The kinetic sorption of sediments consisted of two stages that were quick and slow, regardless of the sampling sites. The amounts of P sorbed to sediments at equilibrium (Qe) ranged from 50.8 to 77.5 mg kg−1. Phosphorus sorption capacity (Qmax) of sediments ranged from 447.0–493.8 mg kg−1 with the constant related to binding energy (K) (0.140–0.171 L mg−1). The results from this study indicate the importance of ditch sediment in controlling P dynamics in discharge from agricultural farms.

Empirical decryption of point source and nonpoint source loading in the context of a total phosphorus TMDL

ABSTRACTLehman JT. 2016. Empirical decryption of point source and nonpoint source loading in the context of a total phosphorus TMDL. Lake Reserv Manage. 32:259–269.A graphical and linear regression method was used to distinguish among point sources, nonpoint sources, and in-channel sinks of nitrogen, phosphorus, and other nutrients, relying on the observation that point-source loads and nonpoint-source loads are not correlated. Point-source loads from wastewater outfalls did not change proportionally with streamflow, whereas landscape erosion did. Point sources and sinks could be deduced from changes in the intercept of linear regressions of in-stream loads of nutrients at different points along the stream channel, whereas deviations of the slope from 1.0 revealed nonpoint source loading or diversions. The method demonstrates (1) how total phosphorus and total nitrogen released from a wastewater treatment facility is sequestered within macrophyte beds downstream from the outfall, and (2) how reductions in nonpoint source loading of total phosphorus coincident with a lawn fertilizer ordinance can be quantified. A related application of the method was used to quantify reduced internal loading and increased retention of dissolved phosphorus, total phosphorus, and silica in a polymictic impoundment after it was subjected to artificial mixing to prevent anoxia. The results revealed conceptual flaws in a total maximum daily load model for the watershed and provided information to improve the model. Regulatory restrictions on point-source discharges are ineffective when point-source nutrients are sequestered upstream of a lake that exhibits nuisance algal blooms and when most of the external nutrient loading to the lake of concern derives from runoff and other nonpoint sources across the landscape.

Vivianite is a key sink for phosphorus in sediments of the Landsort Deep, an intermittently anoxic deep basin in the Baltic Sea

Phosphorus (P) is an essential nutrient for marine organisms. Its burial in hypoxic and anoxic marine basins is still incompletely understood. Recent studies suggest that P can be sequestered in sediments of such basins as reduced iron (Fe)-P but the exact phase and the underlying mechanisms that lead to its formation are unknown. In this study, we investigated sediments from the deepest basin in the Baltic Sea, the Landsort Deep (site M0063), that were retrieved during the Integrated Ocean Drilling Project (IODP) Baltic Sea Paleoenvironment Expedition 347. The record comprises the whole brackish/marine Littorina Sea stage including past intervals of extensive hypoxia in the Baltic Sea that occurred during the Holocene Thermal Maximum (HTMHI) and the Medieval Climate Anomaly (MCA1HI and MCA2HI). Various redox proxies (e.g. the presence of laminations and high Mo contents) suggest almost permanent bottom water hypoxia during the Littorina Sea stage in the Landsort Deep. The bottom waters were likely even seasonally anoxic or sulfidic during the MCA1HI and MCA2HI, and permanently sulfidic during the HTMHI. With the use of micro-analysis of sieved minerals (SEM-EDS, XRD and synchrotron-based XAS), we show that Mn- and Mg-rich vivianite crystals are present at various depths in the Littorina Sea sediments. We also have indications for vivianite in the MCA1HI, MCA2HI and HTMHI deposits. The formation of vivianite thus likely explains the high Fe-bound P fraction throughout the whole Littorina Sea stage. Shuttling of Fe and Mn from the shelves into the basin and high inputs of P in settling organic matter are likely key drivers for vivianite formation. Our study shows that vivianite can likely form in near-surface sediments under a broad range of bottom water redox conditions, varying from hypoxic and anoxic to sulfidic.

Variations of Nutrients in Gross Rainfall, Stemflow, and Throughfall Within Revegetated Desert Ecosystems

Revegetation in arid desert ecosystems is emerging as a practical strategy to cease sand dune encroachment and combat desertification worldwide. The revegetation is expected to affect the spatial distribution of rainfall to the ground within vegetation communities. However, the impact of revegetation on the temporal distribution of dry and/or wet dust fall trapped by shrub canopies via stemflow and throughfall remains a topic of concern for shrub “fertile islands.” This study investigated whether xerophytic shrub community acts as a sink of various cations (Na+, K+, Ca2+, and Mg2+), inorganic anions (Cl− and SO4 2−), total nitrogen, and total phosphorus to the revegetated desert ecosystems. Gross rainfall, the stemflow, and throughfall of two codominated xerophytic shrubs (Caragana korshinskii and Artemisia ordosica) were volumetrically measured after natural rainfall events, and their samples were chemically analyzed in the laboratory. Results showed that ions had higher concentrations in stemflow than in throughfall, followed by gross rainfall. Ion concentrations in stemflow and throughfall strongly depends on the first flush effect, rainfall depth, and the antecedent dry period before a rainfall event occurring. Concentrations of most of the ions in stemflow and throughfall collected after the first rainfall event of a year were obviously higher than other rainfall events for both shrub species, suggesting a first flush effect. Ion concentrations generally decreased with the increasing depth of gross rainfall, stemflow, and throughfall, while increased with prolonged antecedent dry period. Based on nutrient input by stemflow and throughfall at the community scale, we conclude that chemical enrichment of stemflow and throughfall plays an important role in forming the shrub fertile islands and contributes significantly to a sustainable succession of the revegetated desert ecosystems.

Sediment–water interaction in phosphorus cycling as affected by trophic states in a Chinese shallow lake (Lake Donghu)

Lake sediment substantially accumulates nutrients, while little is known regarding the conditions under which it tends to be a sink or source of phosphorus. It is postulated that the above functions were largely dependent on trophic state. To test this hypothesis, composition, abundance, and size-spectrum of phytoplankton were studied in a Chinese shallow lake (Lake Donghu), together with concentrations and sorption behaviors of phosphorus in water column and sediment. Relationships among these variables were also examined by structural equation model. In the basins with the lowest phosphorus concentration, sediment was a phosphorus source as judged by equilibrium phosphorus concentration, directly affecting the abundance of phytoplankton with smaller size. Contrastingly, in the basins with the highest phosphorus concentration, sediment tended to uptake phosphorus, companied by the lowest ratio of nitrogen to phosphorus, diversity, and evenness of phytoplankton with the smaller size one dominating. Oscillatoria sp. was directly affected by ammonia and phosphorus. Moreover, with a balanced exchange of phosphorus between sediment and water column, phytoplankton increased markedly with the highest diversity and evenness in the basins having intermediate phosphorus concentration. Overall, trophic state modulated sediment functions to supply nutrient and was in turn greatly affected by the sediment in shallow lakes.

A Phosphorus Dynamic model for lowland Polder systems (PDP)

Estimating phosphorus export from the lowland polder areas is a critical step for controlling phosphorus loading of a watershed. However, most existing models assumed lowland polder area to be a freely draining catchment, and did not adequately represent its phosphorus dynamics. To better estimate the phosphorus sink and source of the polder systems, a process-based Phosphorus Dynamic model for lowland Polder systems (PDP) consisting of six modules was developed to simulate the daily phosphorus exchanges between lowland polder systems and their surrounding rivers. The unique pattern of water and phosphorus dynamics in polder systems (i.e., manual operation of water exchange between the polder and its surrounding rivers and the phosphorus dynamics in the water area) was accounted for in PDP. Based on a dataset collected from Polder Jian located in Lake Taihu Basin, China during 2014, seven sensitive parameters in PDP were identified based on sensitivity analysis, and were optimized using Genetic Algorithm. A k-fold cross-validation method was used to assess model goodness-of-fit, and resulted in an acceptable model with an r2 (coefficient of determination) value of 0.594. The case study in Polder Jian showed the reliability of PDP to estimate the phosphorus source and sink from polder systems. Such estimation is helpful for water managers to identify the phosphorus source, and thus take corresponding measures to control the aquatic eutrophication.

Sediment phosphorus forms and levels in two tropical floodplain wetlands

Inorganic phosphorus is one of the critical nutrients determining trophic state and freshwater productivity. Sediment may act as a sink or source of phosphorus to the overlying water depending on its pH, redox state, various forms of phosphorus present, etc. To examine potential sorption or mobilization of sediment phosphorus in floodplain wetlands, the amount and distribution of phosphorus fractions were evaluated using a sequential chemical extraction procedure. Exceedingly high levels of total phosphorus (mean: 6040 ± 344, 5470 ± 363 mg kg−1), consisting largely of organic and refractory fraction (70 – 98%), followed by calcium-phosphorus (mean: 584 ± 31.3, 143 ± 8.42 mg kg−1) and iron-phosphorus (mean: 108 ± 10.1, 91.0 ± 7.68 mg kg−1) were recorded respectively in Bhomra and Akaipur wetlands of West Bengal, India. The inorganic phosphorus, comprising the loosely sorbed phosphorus and all the mineral bound forms contributed only about 6–14% to the total phosphorus indicating their less significance in phosphorus sorption or desorption in these tropical wetlands. Although the loosely sorbed phosphorus was in moderate level (2.69 ± 0.69, 1.54 ± 0.53 mg kg−1), water dissolved phosphorus was recorded at higher concentrations (mean: 0.16 ± 0.02 mg l−1 in Akaipur and 1.08 ± 0.12 mg l−1 in Bhomra). However, the higher level of water available phosphorus was not reflected in plankton production since the dominance of weeds suppresses their growth. This study recorded large accumulation of organic matter and nutrients in the form of detritus in these wetlands which may be channelized for fish production through stocking of suitable detritivorous fishes and/or reducing macrophyte coverage that would give space and nutrients for phytoplankton growth.

Vivianite is a major sink for phosphorus in methanogenic coastal surface sediments

Studies of authigenic phosphorus (P) minerals in marine sediments typically focus on authigenic carbonate fluorapatite, which is considered to be the major sink for P in marine sediments and can easily be semi-quantitatively extracted with the SEDEX sequential extraction method. The role of other potentially important authigenic P phases, such as the reduced iron (Fe) phosphate mineral vivianite (Fe(II)3(PO4)*8H2O) has so far largely been ignored in marine systems. This is, in part, likely due to the fact that the SEDEX method does not distinguish between vivianite and P associated with Fe-oxides. Here, we show that vivianite can be quantified in marine sediments by combining the SEDEX method with microscopic and spectroscopic techniques such as micro X-ray fluorescence (μXRF) elemental mapping of resin-embedded sediments, as well as scanning electron microscope–energy dispersive spectroscopy (SEM–EDS) and powder X-ray diffraction (XRD). We further demonstrate that resin embedding of vertically intact sediment sub-cores enables the use of synchrotron-based microanalysis (X-ray absorption near-edge structure (XANES) spectroscopy) to differentiate between different P burial phases in aquatic sediments. Our results reveal that vivianite represents a major burial sink for P below a shallow sulfate/methane transition zone in Bothnian Sea sediments, accounting for 40–50% of total P burial. We further show that anaerobic oxidation of methane (AOM) drives a sink-switching from Fe-oxide bound P to vivianite by driving the release of both phosphate (AOM with sulfate and Fe-oxides) and ferrous Fe (AOM with Fe-oxides) to the pore water allowing supersaturation with respect to vivianite to be reached. The vivianite in the sediment contains significant amounts of manganese (∼4–8wt.%), similar to vivianite obtained from freshwater sediments. Our results indicate that methane dynamics play a key role in providing conditions that allow for vivianite authigenesis in coastal surface sediments. We suggest that vivianite may act as an important burial sink for P in brackish coastal environments worldwide.

Phosphorus Sorption Capacity of Six Iowa Soils before and after Five Years of Use as Vegetative Treatment Areas

Abstract. Accumulation of phosphorus in soil is a major factor limiting the operational life (period of time where the soil can serve as an effective phosphorus sink) of land application waste disposal systems. Better evaluation of phosphorus operational life requires improved understanding of how manure application to soil can affect its phosphorus sorption characteristics. In this study, laboratory experiments were conducted to investigate the impact of feedlot runoff effluent application on phosphorus sorption capacities, equilibrium phosphorus concentrations, and phosphorus buffering capacities of six Iowa soils. Soil samples were collected from vegetative treatment areas that had received feedlot runoff application for the previous five years and from a paired grassed area that did not. Subsamples of each soil were incubated with a series of 12 phosphorus solutions ranging in concentration from 0 to 200 mg P/L to determine the sorption characteristics and results fitted to the Langmuir model to determine the phosphorus equilibrium concentration, phosphorus buffering capacity, and maximum phosphorus sorption capacity. Results indicated that vegetative treatment areas generally had elevated phosphorus equilibrium concentrations, indicating an elevated risk of loss of dissolved phosphorus. In most cases, the ability of the soil to sorb phosphorus was significantly increased, as was the remaining phosphorus sorption capacity of the soil. These results indicate that vegetative treatment area life could be greatly extended due to soil property modifications that occur as a result of system operation.

Phosphorus storage and mobilization in coastal Phragmites wetlands: Influence of local-scale hydrodynamics

Coastal Phragmites wetlands are at the interface between terrestrial and aquatic ecosystems and are important for nutrient retention and regulation. They can act both as nutrient sinks and sources for phosphorus, depending on environmental conditions, sediment properties as well as antecedent nutrient loadings and sorption capacities of the sediments. The Darss-Zingst Bodden Chain is a shallow lagoon system at the German Baltic coast with a long eutrophication history which is lined almost at its entire length by Phragmites wetlands. In order to elucidate under which conditions these wetlands act as sources or sinks for phosphorus, in-situ data of chemo-physical characteristics of water and sediment samples were combined with hydrodynamic measurements and laboratory experiments. A basin zone within the wetland serves as accumulation sink for fine-grained particles rich in phosphorus, iron, manganese and organic matter. The Phragmites stems reduce the water flow and allow the accumulation of organic matter and minerals. Without turbulent mixing and downward flow the bottom water and the sediment surface lack replenishment of oxygen. The relationship between oxygen saturation in the water and soluble reactive phosphorus (SRP) concentrations showed a threshold-type behavior. Under oxygen deficiency soluble reactive phosphorus concentrations in the water were significantly higher than under aerated conditions (oxygen saturation <10%: mean SRP = 0.22 mg/L vs. oxygen saturation >10%: mean SRP = 0.02 mg/L). During stagnant periods with low water level, low-turbulence and thus low-oxygen conditions phosphorus from the sediments is released. But the sediments are capable of becoming sinks again once oxygen is resupplied. When vertical downward flows are dominant in the water and turbulent kinetic energy rises, oxygen saturation increases. A thin oxic sediment surface layer rich in iron and manganese is able to readsorb phosphorus quickly as kinetic sorption experiments show, but due to its redox sensitivity the immobilization is – at least in part – only temporary. This study demonstrated that sediments in coastal Phragmites wetlands can switch their function from sink to source of soluble reactive phosphorus on a very short time-scale, depending on local-scale hydrodynamic conditions and the state of the oxic–anoxic sediment interface.

Glacio-isostatic control on hypoxia in a high-latitude shelf basin

In high-latitude continental shelf environments, late Pleistocene glacial overdeepening and early Holocene eustatic sea-level rise combined to create restricted marine basins with a high vulnerability to oxygen depletion. Here we show that ongoing glacio-isostatic rebound during the Holocene may have played an important role in determining the distribution of past hypoxia in these environments by controlling the physical exchange of water masses and the distribution of large-scale phosphorus (P) sinks. We focus on the Baltic Sea, where sediment records from a large, presently oxic sub-basin show evidence for intense hypoxia and cyanobacteria blooms during the Holocene Thermal Maximum. Using paleobathymetric modeling, we show that this period was characterized by enhanced deep-water exchange, allowing widespread phosphorus regeneration. Intra-basin sills then shoaled over a period of several thousand years, enhancing P burial in one of the sub-basins. Together with climate forcing, this may have caused the termination of hypoxia throughout the Baltic Sea. Similar rearrangements of physical and chemical processes likely occurred in response to glacio-isostatic rebound in other high-latitude shelf basins during the Holocene.

High Spatial and Fast Changes of Iron Redox State and Phosphorus Solubility in a Seasonally Flooded Temperate Wetland Soil

Wetland soils may act as sinks for phosphorus from agricultural soils but P sorption is sensitive to soil redox conditions. When soils become flooded and anoxic, FeIII is reduced and P sorption decreases. To get improved knowledge about the relationship between redox state and P solubility under field conditions, a grid of 4 × 5 sampling points laid out in an Fe-rich meadow soil bordering a Danish river were monitored during 11 weeks in the spring comprising in total five sampling dates. The redox state was quantified as the degree of Fe reduction (DRFe), i.e. percentage of soluble plus sorbed FeII to total pedogenic, non-silicate Fe. Average DRFe was highest (76 %) at beginning of April and decreased to 36 % within 9 weeks. The temporal and spatial variation of DRFe and the soil solution concentrations of Fe and P were high. Thus, average P in solution (Psol) ranged from 24 to 4 μM, closely correlated with average DRFe (R 2 = 0.83). Soils farthest away from the river drained first and hence exhibited the biggest change in DRFe and Psol over time. The study demonstrates the great spatial and temporal variability of redox state and P solubility in such wetlands. Some likely consequences of redox oscillations are indicated.

A new approach to model oxygen dependent benthic phosphate fluxes in the Baltic Sea

The new approach to model the oxygen dependent phosphate release by implementing formulations of the oxygen penetration depths (OPD) and mineral bound inorganic phosphorus pools to the Swedish Coastal and Ocean Biogeochemical model (SCOBI) is described. The phosphorus dynamics and the oxygen concentrations in the Baltic proper sediment are studied during the period 1980–2008 using SCOBI coupled to the 3D-Rossby Centre Ocean model. Model data are compared to observations from monitoring stations and experiments.The impact from oxygen consumption on the determination of the OPD is found to be largest in the coastal zones where also the largest OPD are found. In the deep water the low oxygen concentrations mainly determine the OPD. Highest modelled release rate of phosphate from the sediment is about 59×103t P year−1 and is found on anoxic sediment at depths between 60–150m, corresponding to 17% of the Baltic proper total area. The deposition of organic and inorganic phosphorus on sediments with oxic bottom water is larger than the release of phosphorus, about 43×103t P year−1. For anoxic bottoms the release of total phosphorus during the investigated period is larger than the deposition, about 19×103t P year−1. In total the net Baltic proper sediment sink is about 23.7×103t P year−1. The estimated phosphorus sink efficiency of the entire Baltic Sea is on average about 83% during the period.

Protecting the Florida Everglades wetlands with wetlands: Can stormwater phosphorus be reduced to oligotrophic conditions?

The Florida Everglades is being threatened by high-nutrient stormwater coming from agricultural runoff. The main nutrient problem is phosphorus, which causes the highly oligotrophic sawgrass (Cladium jamaicense) communities in the northern Everglades to become eutrophic Typha latifolia/T. domingensis communities. Current government directives require that the total phosphorus concentration of storm water drainage into the Everglades be limited to approximately 10ppb (μg-P/L). Over 23,000ha treatment wetlands, referred to locally as stormwater treatment areas (STAs), have been created from farmland to treat the stormwater. They are generally effective in removing 60–80% of the total phosphorus; however, the 10ppb goal has rarely been achieved. A three-year experiment, involving mesocosms planted with Everglades-native wetland plants was conducted in the Florida Everglades from March 2010 to March 2013. Eighteen flow-through mesocosms (6m×1m×1m with 40-cm water depth) received about 2.6cm/day inflow. The eighteen mesocosms were randomly assigned with six different plant communities with three replicates of each treatment, consisting of sawgrass (C. jamaicense); waterlily (Nymphaea odorata); cattail (Typha domingensis); submerged aquatic vegetation (SAV) including Najas guadalupensis, and Chara sp. and a Nymphaea–Eleocharis sp. mixed community; and soil without vegetation as a control. Total phosphorus (TP) in the inflow water was 25±1μg-P/L (n=55) over the 3 years. Through 2012 the average outflow of all of the treatments was 34±1μg-P/L, a 51% decrease from the average outflow of 69±6μg-P/L for 2011. Outflows began to be routinely lower than the inflow in the 3rd year of the study. The average total phosphorus concentration decreased overall to 19±1 (n=5) at the end of the study in 2013 suggesting that the suspected phosphorus reflux from the mesocosm soils into the water column slowed after 2–2.5 years of mesocosm operation. Comparing outflows of the individual treatments for 2013, the Nymphaea, control/Chara, and Typha treatments were lower (p<0.05) than the inflow with average outflow concentration of 11±1, 15±3 and 16±1μg-P/L respectively. When the 2013 data are isolated, 4 of the 6 vegetation treatments showed total phosphorus removal, ranging from mixed community (17% removal), to Typha (28% removal), to the control (34% removal) and to Nymphaea (51% removal). We conclude that any treatment wetland constructed with local Florida soils and designed to achieve low (∼10–15ppb P) concentrations would probably take a minimum of 2 years to become sinks of phosphorus. We also conclude that wetlands can be created to achieve these low thresholds if low TP loading and self-design strategies are incorporated into the project design.

Phosphorus and particle retention in constructed wetlands—A catchment comparison

Seven constructed wetlands (0.05–0.69ha), situated in agricultural catchments (22–267ha) in the south of Sweden, were studied for two years with two aims: to (i) quantify their function as sinks for particles and phosphorus (P) lost from the catchments, and (ii) investigate to what degree catchment and wetland characteristics and modeled loads (using hydrochemical catchment models) could be used to explain differences in retention between the wetlands. The wetland areas ranged from 0.04 to 0.8% of the respective catchment area, and they were situated in areas dominated by fine-textured soils with relatively high P losses and the main proportion of P transported in particulate form. Net P and particle retention were estimated during two years from annual accumulation of particles on sedimentation plates (40×40cm) on the bottom of the wetlands.There was an annual net retention of particles and P, but with a large variation (for particles 13–108tha−1yr−1 and for P 11–175kgha−1yr−1), both between wetlands and between years. The difference between the two years was larger than the difference in mean P retention between the seven wetlands. There was a positive relationship between P and particle retention and three catchment factors, i.e. P status (P-AL) of agricultural soils, average slope in the catchments and the livestock density, and a negative relationship with the agricultural soil clay content. In addition, there was a positive relationship with the wetland length:width ratio. Contrary to expectations, neither the modeled hydraulic load nor P load was significantly correlated with the measured particle and P retention. There was also a positive relationship between P concentration in the sediment and soil P status in the catchment. The results imply that considerable errors are introduced when down-scaling modeled regional nutrient losses to estimate the P loads to small wetlands in agriculturally dominated catchments. A more qualitative approach, using catchment characteristics for identification of hot-spot fields, may be equally good to identify suitable locations for constructed wetlands to reduce diffuse P loads.

Stabilization of the coupled oxygen and phosphorus cycles by the evolution of bioturbation

Animal burrowing and sediment-mixing (bioturbation) began during the run up to the Ediacaran/Cambrian boundary1, 2, 3, initiating a transition4, 5 between the stratified Precambrian6 and more well-mixed Phanerozoic7 sedimentary records, against the backdrop of a variable8, 9 global oxygen reservoir probably smaller in size than present10, 11. Phosphorus is the long-term12 limiting nutrient for oxygen production via burial of organic carbon13, and its retention (relative to carbon) within organic matter in marine sediments is enhanced by bioturbation14, 15, 16, 17, 18. Here we explore the biogeochemical implications of a bioturbation-induced organic phosphorus sink in a simple model. We show that increased bioturbation robustly triggers a net decrease in the size of the global oxygen reservoir—the magnitude of which is contingent upon the prescribed difference in carbon to phosphorus ratios between bioturbated and laminated sediments. Bioturbation also reduces steady-state marine phosphate levels, but this effect is offset by the decline in iron-adsorbed phosphate burial that results from a decrease in oxygen concentrations. The introduction of oxygen-sensitive bioturbation to dynamical model runs is sufficient to trigger a negative feedback loop: the intensity of bioturbation is limited by the oxygen decrease it initially causes. The onset of this feedback is consistent with redox variations observed during the early Cambrian rise of bioturbation, leading us to suggest that bioturbation helped to regulate early oxygen and phosphorus cycles.

Retention of phosphorus on calcite and dolomite: speciation and modeling

The intensive application of phosphate fertilizers in agriculture has created an important source of diffuse phosphorus pollution. The interaction of phosphorus with carbonate minerals plays a role in the fate and transport of phosphorus in soil. The object of the present study was to investigate the speciation of phosphorus on two common carbonate minerals, calcite and dolomite, using a combination of batch experiments, ATR-FTIR spectroscopy, XANES analysis, and diffuse layer modeling. Within the pH range 6.0–7.0, the retention of phosphorus by calcite and dolomite is mainly attributed to the formation of amorphous calcium phosphate (Ca3(PO4)2, ACP), dibasic calcium phosphate (CaHPO4·2H2O, DCP), and hydroxyapatite (Ca5(PO4)3OH, HAP). At pH ≥ 8.0 the immobilized phosphorus takes the form of complexes =CaPO4Ca0/=sCaPO4Ca0 on the surface of calcite, followed by the formation of Ca–P phases, including ACP, DCP, and HAP, with increasing phosphorus levels (>2 mg L−1). However, the dolomite surface is initially dominated by the adsorption complex =MgHPO4Ca+ at =Mg sites, and at higher phosphorus levels it then grows due to Ca–P phases and the formation of newberyite (MgHPO4). It is interesting to note that the Mg content in dolomite favors the rapid growth of DCP at phosphorus levels >200 mg L−1. As a result, at pH ≥ 8.0, dolomite shows a stronger capacity for immobilizing phosphorus than does calcite. Dolomite therefore serves as a better phosphorus sink than calcite in calcareous soil environments.

Are iron-phosphate minerals a sink for phosphorus in anoxic Black Sea sediments?

Phosphorus (P) is a key nutrient for marine organisms. The only long-term removal pathway for P in the marine realm is burial in sediments. Iron (Fe) bound P accounts for a significant proportion of this burial at the global scale. In sediments underlying anoxic bottom waters, burial of Fe-bound P is generally assumed to be negligible because of reductive dissolution of Fe(III) (oxyhydr)oxides and release of the associated P. However, recent work suggests that Fe-bound P is an important burial phase in euxinic (i.e. anoxic and sulfidic) basin sediments in the Baltic Sea. In this study, we investigate the role of Fe-bound P as a potential sink for P in Black Sea sediments overlain by oxic and euxinic bottom waters. Sequential P extractions performed on sediments from six multicores along two shelf-to-basin transects provide evidence for the burial of Fe-bound P at all sites, including those in the euxinic deep basin. In the latter sediments, Fe-bound P accounts for more than 20% of the total sedimentary P pool. We suggest that this P is present in the form of reduced Fe-P minerals. We hypothesize that these minerals may be formed as inclusions in sulfur-disproportionating Deltaproteobacteria. Further research is required to elucidate the exact mineral form and formation mechanism of this P burial phase, as well as its role as a sink for P in sulfide-rich marine sediments.

Hydrologic Controls on Nitrogen and Phosphorous Dynamics in Relict Oxbow Wetlands Adjacent to an Urban Restored Stream

AbstractAlthough wetlands are known to be sinks for nitrogen (N) and phosphorus (P), their function in urban watersheds remains unclear. We analyzed water and nitrate (NO3−) and phosphate (PO43−) dynamics during precipitation events in two oxbow wetlands that were created during geomorphic stream restoration in Baltimore County, Maryland that varied in the nature and extent of connectivity to the adjacent stream. Oxbow 1 (Ox1) received 1.6‐4.2% and Oxbow 2 (Ox2) received 4.2‐7.4% of cumulative streamflow during storm events from subsurface seepage (Ox1) and surface flow (Ox2). The retention time of incoming stormwater ranged from 0.2 to 6.7 days in Ox1 and 1.8 to 4.3 days in Ox2. Retention rates in the wetlands ranged from 0.25 to 2.74 g N/m2/day in Ox1 and 0.29 to 1.94 g N/m2/day in Ox2. Percent retention of the NO3−‐N load that entered the wetlands during the storm events ranged from 64 to 87% and 23 to 26%, in Ox1 and Ox2, respectively. During all four storm events, Ox1 and Ox2 were a small net source of dissolved PO43− to the adjacent stream (i.e., more P exited than entered the wetland), releasing P at a rate of 0.23‐20.83 mg P/m2/day and 3.43‐24.84 mg P/m2/day, respectively. N and P removal efficiency of the oxbows were regulated by hydrologic connectivity, hydraulic loading, and retention time. Incidental oxbow wetlands have potential to receive urban stream and storm flow and to be significant N sinks, but they may be sources of P in urban watersheds.

Optimization of Phosphorus Fertilizer in Supplemental Feed-Fed Based Nile Tilapia (Oreochromis niloticus) Ponds

An experiment was conducted in earthen ponds at the Asian Institute of Technology, Thailand to determine different phosphorus fertilizer dose effects on Nile tilapia production, water quality variables, nutrient utilization and cost-benefit under supplemental feeding. Five phosphorus fertilization rates were used as treatments e.g. 100%, 75%, 50%, 25% and 0% of 7 kg P ha week−1. Nitrogen fertilization rate was fixed at 28 kg N ha week−1 for all the treatments. Sex-reversed Nile tilapia were stocked at 3 fish m−2, and 30% CP floating feed fed at 50% satiation feeding rate. Nutrient budget showed higher phosphorus fertilizer input resulted in higher phosphorus sink in the sediment. Mean weight, mean weight gain, daily weight gain and net yield were not significantly different among treatments (P > 0.05). Total Kjeldahl nitrogen, total phosphorus and soluble reactive phosphorus were significantly different among treatments. Economic analysis showed phosphorus fertilization resulted in positive net returns. Though the gross income was not affected by different fertilization rates, significantly lowest cost was found in the treatment using 25% phosphorus fertilizer. It can be concluded from the research that 25% phosphorus fertilization might be used as an alternative strategy of Nile tilapia pond culture in terms of economic return and nutrient loss in sediment.