Phosphorus Transport Research Articles

Does quantifying antecedent flow conditions improve stream phosphorus export estimation?

Summary A reliable and economical method for the estimation of nutrient export (e.g. phosphorus) in stream flow from catchments is necessary to quantify the impact of land use or land use change upon aquatic systems. The transport of phosphorus (P) from soil to water is known to impact negatively on water quality. A key observation from studies is that most P export occurs during high stream flow. However, it is not yet clear how flood-antecedent conditions affect the P export during flood events. In this study, the P loss from soil to water as represented by soluble reactive phosphorus (SRP) in stream waters from three different catchments, varying in land use, scale and location in Ireland was monitored over 1 year. This study examined the role of antecedent stream flow conditions on SRP export and identifies a catchment-specific relationship between SRP flood event load (EL) and a flow ratio (FR). The FR is defined as the ratio of the flood event volume (EV) to the pre-event volume (PEV). The latter is the cumulative flow volume for a number of days preceding the event. This PEV period was found to be longer (average 81 days) in the grassland catchments which were known to be saturated with soil P than in the forested catchments (average 21 days) with minimal soil P. This FR ratio is a measure of the antecedent hydrological state (wet or dry) of the catchment. For SRP for each catchment, a specific relationship between SRP EL and FR was identified. The annual SRP export was estimated, using this ratio and compared with the concentration/discharge ( C / Q ) method. The new flow ratio method was used with data from 12 flood events during the year to estimate an annual export of SRP. For the two grassland catchments in the study, using the FR method, we estimated an SRP export of 1.77 and 0.41 kg ha −1 yr −1 . Using the C / Q method, for the same sites, our estimate of SRP export was 1.70 and 0.50 kg ha −1 yr −1 respectively. The C / Q method used SRP concentrations covering 40% of the year while the FR method used only 12 flood events covering less than 2% of the year. This new method which takes account of the antecedent flow state of the river is an alternative to and may be more promising than the traditional C / Q method, particularly when short duration or flood sampling of water quality is carried out.

Climate Change Effects on Runoff, Catchment Phosphorus Loading and Lake Ecological State, and Potential Adaptations

Climate change may have profound effects on phosphorus (P) transport in streams and on lake eutrophication. Phosphorus loading from land to streams is expected to increase in northern temperate coastal regions due to higher winter rainfall and to a decline in warm temperate and arid climates. Model results suggest a 3.3 to 16.5% increase within the next 100 yr in the P loading of Danish streams depending on soil type and region. In lakes, higher eutrophication can be expected, reinforced by temperature-mediated higher P release from the sediment. Furthermore, a shift in fish community structure toward small and abundant plankti-benthivorous fish enhances predator control of zooplankton, resulting in higher phytoplankton biomass. Data from Danish lakes indicate increased chlorophyll a and phytoplankton biomass, higher dominance of dinophytes and cyanobacteria (most notably of nitrogen fixing forms), but lower abundance of diatoms and chrysophytes, reduced size of copepods and cladocerans, and a tendency to reduced zooplankton biomass and zooplankton:phytoplankton biomass ratio when lakes warm. Higher P concentrations are also seen in warm arid lakes despite reduced external loading due to increased evapotranspiration and reduced inflow. Therefore, the critical loading for good ecological state in lakes has to be lowered in a future warmer climate. This calls for adaptation measures, which in the northern temperate zone should include improved P cycling in agriculture, reduced loading from point sources, and (re)-establishment of wetlands and riparian buffer zones. In the arid Southern Europe, restrictions on human use of water are also needed, not least on irrigation.

Electronic Transport and Mechanical Properties of Phosphorus- and Phosphorus−Nitrogen-Doped Carbon Nanotubes

We present a density functional theory study of the electronic structure, quantum transport and mechanical properties of recently synthesized phosphorus (P) and phosphorus-nitrogen (PN) doped single-walled carbon nanotubes. The results demonstrate that substitutional P and PN doping creates localized electronic states that modify the electron transport properties by acting as scattering centers. Nonetheless, for low doping concentrations (1 doping site per ∼200 atoms), the quantum conductance for metallic nanotubes is found to be only slightly reduced. The substitutional doping also alters the mechanical strength, leading to a 50% reduction in the elongation upon fracture, while Young's modulus remains approximately unchanged. Overall, the PN- and P-doped nanotubes display promising properties for components in composite materials and, in particular, for fast response and ultra sensitive sensors operating at the molecular level.

Long-term variations and causal factors in nitrogen and phosphorus transport in the Yellow River, China

This paper is to examine the water quality of the Yellow River basin on the basis of collated data of nitrogen (40 years) and phosphorus (20 years), and also of the relevant chemical fertilizer application, population, and industrial wastewater, etc. Relationship among these elements was discussed in order to explore their causal links, in relation to the temporal variation of nitrogen and phosphorus transportation. Results indicate that the transported nitrogen load in the lower Yellow River has had an increasing trend during the past 40 years but declined considerably in the later 1990s due to the reduction in flow discharge that led to desiccation of the lower reaches of the Yellow River. Whereas, nitrogen contribution to the estuary from Huayuankou to Lijin reach was minus due to the large amount of water diversion from the Yellow River for irrigation purpose. Phosphorus content fluctuated within a certain range without any tendency, but also decreased in the later 1990s due to the desiccation in the lower reaches. Our analysis indicates that nitrogen load in the Yellow River has been mainly impacted by population growth and nitrogen fertilizer application, but showed no statistically significant relationship with wastewater loads. In contrast, total phosphorus content in the Yellow River showed no relationship with population, fertilizer use and wastewater discharge in the basin, but presented significant correlation with suspended solids concentration of the Yellow River. Calculations indicate that the phosphorus content in suspended solids of the Yellow River was 0.54 g/kg, which is quite close to the background value of phosphorus in the soil of the Loess Plateau – the intensive soil erosion area in China, through which the Yellow River flows. Therefore, we conclude that phosphorus transportation in the Yellow River is dominantly controlled by soil erosion from the Loess Plateau. The results are significant for estuarine management in that nitrogen, a key factor in marine eutrophication, is chiefly from anthropogenic sources whereas the large phosphorus loads are controlled by erosion of loess soils.

Phosphorus sorption and fraction characteristics in the upper, middle and low reach sediments of the Daliao river systems, China

Stream sediments play an important role in the transport and storage of phosphorus in the stream ecosystems. This research investigated the sorption and fraction of P in the sediments of a long-term seriously contaminated river, the Daliao river system, using isotherm sorption and selective sequentially extraction tests. Results indicated that the total content of P in the sediments was 479–1202 mg kg −1, depending on iron content in the sediments. The content of potential bioavailable P, including soluble and loosely bound P, Al bound P, Fe bound P, and reductant soluble P was only 10–20% of total P in the sediments of the Hun river and Taizi river, while it was 40–55% in the sediments of the Daliao river, the downstream of the river system. Equilibrium phosphorus concentration without net P sorption (EPC 0) was from 0.05 to 0.54 mg L −1, with an increasing trend from upstream to downstream, indicating increasingly release potential. On the other hand, the upstream sediment generally sorbed more P than the downstream sediment for each river at the same equilibrium P concentration. The binding energy constant of P on the strong sites of the sediments generally decreased from 2.24 to 2.65 L mg −1 at upstream to 0.41 L mg −1 at downstream or estuary, suggesting that the strong binding sites have been occupied and partly saturated by the phosphate added by point and diffuse sources along the river. On the other hand, molar ratio of Fe to TP contents in the sediments showed sorption capacity of the sediments to P might be under-saturated. The added or sorbed P by the isotherm test was primarily bound to Fe oxides and secondly to Al oxides. Long-term pollution of the river lead to the decrease of P sorption capacity of the river sediment and the increase of P release potential.

Subsurface Transport of Phosphorus in Riparian Floodplains: Influence of Preferential Flow Paths

For phosphorus (P) transport from upland areas to surface water systems, the primary transport mechanism is typically considered to be surface runoff with subsurface transport assumed negligible. However, certain local conditions can lead to an environment where subsurface transport may be significant. The objective of this research was to determine the potential of subsurface transport of P along streams characterized by cherty or gravel subsoils, especially the impact of preferential flow paths on P transport. At a field site along the Barren Fork Creek in northeastern Oklahoma, a trench was installed with the bottom at the topsoil/alluvial gravel interface. Fifteen piezometers were installed surrounding the trench to monitor flow and transport. In three experiments, water was pumped into the trench from the Barren Fork Creek to maintain a constant head. At the same time, a conservative tracer (Rhodamine WT) and/or potassium phosphate solution were injected into the trench at concentrations at 3 and 100 mg/L for Rhodamine WT and at 100 mg/L for P. Laboratory flow-cell experiments were also conducted on soil material <2 mm in size to determine the effect that flow velocity had on P sorption. Rhodamine WT and P were detected in some piezometers at equivalent concentrations as measured in the trench, suggesting the presence of preferential flow pathways and heterogeneous interaction between streams and subsurface transport pathways, even in nonstructured, coarse gravel soils. Phosphorus transport was retarded in nonpreferential flow paths. Breakthrough times were approximately equivalent for Rhodamine WT and P suggesting no colloidal-facilitated P transport. Results from laboratory flow-cell experiments suggested that higher velocity resulted in less P sorption for the alluvial subsoil. Therefore, differences in flow rates between preferential and nonpreferential flow pathways in the field led to variable sorption. The potential for nutrient subsurface transport shown by this alluvial system has implications regarding management of similar riparian floodplain systems.

Management practices for control of runoff losses from cotton furrows under storm rainfall. III. Cover and wheel traffic effects on nutrients (N and P) in runoff from a black Vertosol

Transport of nitrogen (N) and phosphorus (P) in runoff was measured using a rainfall simulator on a cotton hill–furrow system with a range of on-ground cover (0–60%), each with and without prior wheel traffic in the furrow. Total N and P losses in runoff (kg/ha) from the bare plots on a whole-field basis (wheel and non-wheel tracks) were equivalent to 1.5% and 1%, respectively, of fertiliser applied that season (218 kg N/ha, 27 kg P/ha). This was for a single runoff event of 17 mm, about 1/10 of the total runoff expected in a season. Retaining surface cover and avoiding wheel traffic were both effective in reducing runoff losses of total N and P, especially when used together. Retaining cover gave considerably lower concentrations of total P, and of N and P associated with sediment, with no significant differences (P &gt; 0.05) between wheel and non-wheel tracks. The majority of nutrients were transported with sediment, for P for all treatments, and for N from low cover plots. Concentrations of dissolved N, dominantly as NO3-N, were unaffected by cover on non-wheel tracks but increased with cover on wheel track plots where runoff occurred as shallow interflow. On a whole-field basis, N was mainly in dissolved form at higher covers, because most runoff came from wheel tracks where interflow occurred. Reducing the ratio of wheel tracks to non-wheel tracks will reduce runoff of N and P. Interflow or exfiltration above an infiltration throttle layer is a worst-case scenario for runoff transport of soluble, poorly sorbed chemicals such as NO3-N, which would otherwise leach and not enter runoff. To improve water quality, for both sorbed and dissolved forms, the combination of retaining cover and avoiding wheel traffic and subsoil compaction is needed. Similarly, land uses involving high nutrient inputs should be avoided on soils with shallow subsurface restrictions to infiltration, which are thus prone to interflow. Primary (dispersed) clay and silt were slightly enriched in sediment in runoff, while primary fine and coarse sand were depleted. However, sediments were not enriched in total N and P compared with the soil surface, and organic carbon was only slightly enriched (enrichment ratio 1.06). This is typical of the behaviour of well-aggregated soils of high clay content.

Impact of Dredging on Phosphorus Transport in Agricultural Drainage Ditches of the Atlantic Coastal Plain1

Abstract: Drainage ditches can be a key conduit of phosphorus (P) between agricultural soils of the Atlantic Coastal Plain and local surface waters, including the Chesapeake Bay. This study sought to quantify the effect of a common ditch management practice, sediment dredging, on fate of P in drainage ditches. Sediments from two drainage ditches that had been monitored for seven years and had similar characteristics (flow, P loadings, sediment properties) were sampled (0‐5 cm) after one of the ditches had been dredged, which removed fine textured sediments (clay = 41%) with high organic matter content (85 g/kg) and exposed coarse textured sediments (clay = 15%) with low organic matter content (2.2 g/kg). Sediments were subjected to a three‐phase experiment (equilibrium, uptake, and release) in recirculating 10‐m‐long, 0.2‐m‐wide, and 5‐cm‐deep flumes to evaluate their role as sources and sinks of P. Under conditions of low initial P concentrations in flume water, sediments from the dredged ditch released 13 times less P to the water than did sediments from the ditch that had not been dredged, equivalent to 24 mg dissolved P. However, the sediments from the dredged ditch removed 19% less P (76 mg) from the flume water when it was spiked with dissolved P to approximate long‐term runoff concentrations. Irradiation of sediments to destroy microorganisms revealed that biological processes accounted for up to 30% of P uptake in the coarse textured sediments of the dredged ditch and 18% in the fine textured sediments of the undredged ditch. Results indicate that dredging of coastal plain drainage ditches can potentially impact the P buffering capacity of ditches draining agricultural soils with a high potential for P runoff.

The Fate and Transport of Phosphorus in Turfgrass Ecosystems

Phosphorus losses from turfgrass areas are perceived to contribute to water quality problems, yet a comprehensive review of P fate in turfgrass ecosystems is lacking. According to available data in the literature, phosphorus fertilizer inputs (2–10 kg ha−1) slightly exceed the estimated outputs of phosphorus in clippings (0.4–7.5 kg ha−1). Sediment losses from turf areas are negligible, generally limited to establishment, but runoff and leaching losses of P vary from inconsequential to severe depending on rate, source, and timing of fertilizer application. Soil properties were found to have a larger effect on runoff volume than vegetative properties. Highest runoff and leaching losses of P occurred when rainfall occurred or was simulated shortly after P fertilizer application. Leaching losses of P have historically been considered relatively minor; however, the limited research results available indicate that annual P leaching losses from mineral soils (0.2–0.7 kg ha−1) are similar in magnitude to runoff‐P losses from turfgrass systems. One major gap in the knowledge is how P sources other than fertilizer (i.e., soil and plant tissue) and irrigation affect runoff and leaching losses of P.

Conservation Effects Assessment Project research in the Leon River and Riesel watersheds

The Leon River basin was selected as a benchmark watershed for the Conservation Effects Assessment Project to complement the historical USDA Agricultural Research Service experimental watersheds near Riesel, Texas. Excessive nutrient and bacteria concentrations contributed by agricultural, urban, and natural sources are the primary water quality concerns. Modeling and field evaluations of the hydrologic impact and soil and water quality response to tillage and nutrient management practices are the primary research themes of this project. Water quality data from 15 Leon River watersheds (0.3 ha [0.75 ac] to 6,070 km2 [2,340 mi2]) and 13 Riesel watersheds (1.2 ha [3.0 ac] to 70.4 ha [174 ac]) has improved modeling of phosphorus transformation and transport routines. Modeling research also coupled field- and farm-scale model output to improve the basin-scale Soil and Water Assessment Tool (SWAT) for the national assessment of conservation practices. Additional key products of Conservation Effects Assessment Project research include innovative erosion control methods on military lands, enhanced carbon sequestration estimates for various agricultural land uses, and improved understanding of environmental and economic impacts of organic fertilizer application.

Mobilisation and Transport of Sediment-Associated Phosphorus by Surface Runoff

Surface runoff transporting sediment with high phosphorus (P) concentrations has been identified as a major hydrological pathway for sediment-associated P delivery to surface waters and is considered a major threat to water quality, due to the ability of P to cause eutrophication in fresh water. Not all P-rich sediment that is mobilised by erosion will however be delivered directly to the channel. Some may instead be deposited in intermediate storage away from its source area. The aim of this contribution was to determine the influence of land use and soil type on the P content of surface runoff sediment and sediment deposited in intermediate storage and was undertaken in the largely agricultural and rural catchments of the Rivers Frome and Piddle in Dorset, UK. The study formed part of a larger investigation of hydrological and hydrogeochemical processes and fluxes in lowland permeable catchments in the UK (LOCAR). Soil samples were collected from the main land use types; freshly deposited sediment was sampled from ditches, hedge boundaries and depressions in fields, and sediment-laden runoff was collected during heavy rainfall events. The concentrations of total phosphorus (TP) and the P fractions found in the surface runoff sediment were significantly different from those measured in the original source soils, with a greater degree of enrichment associated with surface runoff sediment from cultivated land than from pasture land. For cultivated land, concentrations of TP and the P fractions in deposited sediment were higher than those in the original source material, while for pasture soils, concentrations of TP and the P fractions tended to be lower than in the original source soils. The relative importance of the P fractions associated with surface runoff sediment and sediment deposits also differed from that for the original soil samples. Surface runoff sediment was finer than source pasture and cultivated soils, reflecting the particle size selectivity of sediment mobilisation and transport. Soil physical properties and land use can both influence the P content of surface runoff and deposited sediment.

Seasonal changes in nitrogen and phosphorus transport in the lower Changjiang River before the construction of the Three Gorges Dam

Water and sediment samples were collected at Datong from June 1998 to March 1999 to examine seasonal changes in the transports of nitrogen (N) and phosphorus (P) from the Changjiang River (Yangtze River) to the East China Sea (ECS). Dissolved inorganic nitrogen (DIN; dominated by nitrate) concentration exhibited small seasonality, and DIN flux was largely controlled by water discharge. Dissolved inorganic phosphorus (DIP) concentration was inversely correlated with water discharge, and DIP was evenly delivered throughout a year. The transports of DIN and DIP from the Changjiang River were consistent with seasonal changes in nutrient distributions and P limitation in the Changjiang Estuary and the adjacent ECS. Dissolved organic and particulate N (DON and PN) and P (DOP and PP) varied parallel to water discharge, and were dominantly transported during a summer flood. The fluxes of DOP and particulate bioavailable P (PBAP) were 2.5 and 4 times that of DIP during this period, respectively. PBAP accounted for 12–16% of total particulate P (PP), and was positively correlated with the summation of adsorbed P, Al–P and Fe–P. Ca–P, the major fraction of PP, increased with increasing percent of CaCO 3. The remobilization of riverine DOP and PBAP likely accounted for the summer elevated primary production in DIP-depleted waters in the Changjiang Estuary and the adjacent ECS. The Changjiang River delivered approximately 6% of DIN (1459 × 10 6 kg), 1% of DIP (12 × 10 6 kg), and 2% of dissolved organic and particulate N and P to the totals of global rivers. The construction of the Three Gorges Dam might have substantially reduced the particulate nutrient loads, thereby augmenting P limitation in the Changjiang Estuary and ECS.

LEACHING BEHAVIOR OF PHOSPHORUS IN SANDY SOILS AMENDED WITH ORGANIC MATERIAL

Transport of phosphorus (P) from agriculture often causes eutrophication of surface water systems, which is particularly a concern in sandy soil regions because of low holding capacity of the soil for nutrients and moisture. Soil amendment is considered to be one of the best management practices in reducing P loss to water. A column leaching study was conducted to evaluate the effectiveness of organic amendment applied together with water-soluble fertilizer in reducing P leaching in two typical agricultural sandy soils (Spodosol and Alfisol) in south Florida. The Spodosol is an Alfic Alaquod, whereas the Alfisol is an Arenic Glossaqualf. Both soils have the same texture with sandy, siliceous, and hyperthermic properties. Organic material (OM) used in this study is marketed as a slow release organic fertilizer (GreenEdge; JEA Inc., Jacksonville, FL), which supplies essential nutrients for plant growth. The treatments consisted of chemical fertilizer (CF) alone, CF + 1.25 g kg -1 OM, CF + 5.0 g kg -1 OM, and CF + 10.0 g kg -1 OM. A control receiving no CF or OM was also included. Leaching of orthophosphate-P (PO 4 -P) and dissolved total P was similar. After seven leaching events, application of CF together with 10.0 g kg -1 OM reduced PO 4 -P and dissolved total P loss by 25.4% and 21.4% in the Spodosol and by 45.3% and 22.6% in the Alfisol and increased soil Olsen-P and Mehlich 3-extractable P by 54% and 31%, respectively, in the Spodosol and by 50% and 94% in the Alfisol, compared with CF alone. Increasing OM application rates increased NaHCO- and NaOH-extractable P but decreased water-extractable P in the two soils. Soil microbial biomass P (MBP) and the percentage of MBP in Olsen-P (MBP/Olsen-P) increased by 585% and 350%, respectively, in the leached Spodosol and by 190% and 127%, respectively, in the leached Alfisol with the treatment of CF together with 10.0 g kg -1 OM, compared with CF alone. It appears that the reduction in P leaching by OM amendment was related to the stimulation of microbial activities, which incorporate water-soluble P from applied CF into organic fractions and retained more P in soil against leaching but available to plants. These results indicate that organic amendment in combination with CF in a 10 g OM kg -1 soil level can increase P utilization efficiency by reducing P leaching and maintaining a larger available P pool in sandy soils.

Impact of fertilizer usage on phosphorus loads to Lake Uluabat

This work investigated the role of fertilizer application rate on phosphorus (P) transport and loading to Lake Uluabat in Turkey. For this purpose ArcView Interface of Soil and Water Assessment Tool 2000 (AVSWAT) was used. Results showed that when the fertilizer amount applied to agricultural lands was doubled, the P load to Lake Uluabat increased by 32%. P transported to Lake Uluabat declined by about 6, 10 and 16%, when the fertilizer usage at the agricultural fields were decreased by 20, 30 and 50%, respectively. In general, a linear relationship was observed between the P load and the fertilizer application rates. The highest and lowest P losses were from the corn and wheat productions, respectively. 70% more P was carried to Lake Uluabat from corn, wheat, and tomato fields when the fertilizer amounts applied were doubled. When the fertilizer usage declined by 20, 30, and 50%, a total of 14, 21 and 35% less P were transported to the lake from the fields, respectively. For the threshold P loading, 56 of 78 subbasins were critical when the fertilizer usage was doubled. For 50% reduction in the fertilizer application rate, the number of critical subbasins decreased to 46. Nevertheless, this decrease was not sufficient to meet the goal P loading to Lake Uluabat.

Transfer and transport of phosphorus and silica in the turbidity maximum zone of the Changjiang estuary

The concentration of suspended particulate matter (SPM), sedimentation flux, and various forms of phosphorus and silica in turbidity maximum zone (TMZ) in the Changjiang (Yangtze) estuary was studied. Based on the budget of P and Si, their mass balances in the TMZ were calculated. Results show that the variation in concentration of dissolved inorganic silicon (DISi) was mainly controlled by seawater dilution, while that of dissolved inorganic phosphorus (DIP) was considerably affected by the buffering of suspended matter and sediment. Our experiments showed that the sedimentation fluxes of SPM and particulate inorganic phosphorus (PIP), total particulate phosphorus (TPP), particulate inorganic silicon (PISi), and biological silicon (BSi) in the TMZ were 238.4 g m −2 d −1 and 28.3, 43.1, 79.0, 63.0 mg m −2 d −1, respectively. In addition, a simple method to estimate the ratio of resuspension of sediment in the TMZ was established, with which the rate in surface and bottom waters of the TMZ accounted for 55.7 and 66.1% of the total SPM, respectively, indicating that the sediment resuspension in the TMZ influenced significantly the mass balances of P and Si. Particulate adsorbed P (60.8%) and 35.5% of total particulate P discharged from the river were filtered and then deposited in the TMZ. The input flux of PIP from the river mouth was 55.9% of that of DIP, being important as biologically available P, while that of PISi was only 3.5% of DISi, showing that particulate adsorbed Si was much less important than particulate adsorbed P.

Development of an estuarine ecosystem model and evaluation of impact of oyster culture on the ecosystem of Etajima Bay

To understand transportation of phosphorus in Etajima Bay, northern part of Hiroshima Bay, and evaluate impacts of oyster culture on the ecosystem, we have developed a pelagic and benthic coupled coastal ecosystem model expressing phosphorus cycle in Etajima Bay. This model consists of three sub-models, i. e. coastal circulation model, pelagic ecosystem model and benthic ecosystem model, considering all the concerned physical and biological processes. We have investigated characteristics of coastal circulation and exchange rate of sea water in Etajima Bay and also have studied the effects of oyster culture on the formation of oxygen-depleted water and resulted breakdown on the benthic ecosystem.

A Study on Phosphorus Transport Process in Inohana Lake under the Density Stratification during Summer

An intensive field measurement was carried out in Inohana and Hamana Lakes including a narrow channel to investigate the phosphorus transport process in Inohana Lake during summer. Inohana Lake has a two-layer structure of the phosphorus distribution: the particulate phosphors (PP) in the surface layer, while the phosphate phosphorus (PO4-P) in the bottom layer. The phosphorus inflow from Hamana Lake through the bottom layer is dominant over the riverine loading and Inohana Lake becomes a sink of phosphorus from Hamana Lake. The settling and release fluxes of phosphorus are larger than the input and output of the phosphorus in Inohana Lake. The phosphorus budget suggests that the phosphorus accumulates in the sediment during summer.

Microalgal sediment biostabilisation along a salinity gradient in the Eden Estuary, Scotland: unravelling a paradox

Microalgal biostabilisation of cohesive sediments via the production of extracellular polymeric substances (EPS) has been well documented in intertidal ecosystems and represents a key ecosystem service with respect to the regulation of sediment transport. However, recent ecosystem comparison studies have uncovered a paradox in which sediment stability is commonly observed to be lower in freshwater ecosystems (compared with estuarine ecosystems) even though sediment EPS concentrations and microalgal biomass are high. Using a combination of freshwater and estuarine field and mesocosm techniques, the relative and interactive roles of salinity and the production of EPS (carbohydrate concentration) by benthic microalgae in the mediation of sediment stability in the Eden River catchment (river, mudflat and saltmarsh) were assessed. Sediment stability apparently increased with salinity from river (42.43 N m–2 surface stagnation pressure; salinity 0) to mudflat (98.65 N m–2; salinity 25) to saltmarsh (135.48 N m–2; salinity 46). The opposite trend was observed in sediment chlorophyll a and carbohydrate concentrations, indicating that salinity is the main variable driving sediment stability across the ecosystems under moderate EPS concentrations. Observations from mesocosm experiments highlighted the individual and combined importance of salinity and EPS in biostabilisation, with the largest increase in sediment stability observed following combined additions (25-fold increase compared with the control). The biogeochemical processes responsible, and their role in buffering phosphorus transport across the freshwater–saltwater transitional zone, are discussed.

Influx Pathways and Key Stages of Phosphorus and Potassium Transport into Grape Fruits

ABSTRACT Using radioisotope tracer determination of 32P and 86Rb and fruit stalk micro-girdling, the influx pathways and key stages of phosphorus (P) and potassium (K) transport to grape fruits were studied. After fruit stalk micro-girdling, only 5.4% of P and 7.3% of K was transported from leaves to fruits via the xylem, compared with 46.75 and 38.67% from roots via phloem. The influx of 32P and 86Rb into fruits from treated leaves varied significantly according to stage of fruit development. For 32P, the variation was in the order: first stage > third stage > fruit veraision > second stage, while for 86Rb the order was: third stage > first stage > second stage > fruit veraision stage. The above results indicated that both first and third stages of grape fruit development had the greatest requirement for P or K from leaves, and the phloem was the dominant influx pathway for their transport into fruits from leaves.

Transport of Species during Plasma Electrolytic Oxidation of WE43-T6 Magnesium Alloy

Coating growth on WE43-T6 magnesium alloy during direct current plasma electrolytic oxidation is investigated in alkaline phosphate and silicate electrolytes. The study employs sequential treatments in the two electrolytes, followed by analyses of the coatings and the electrolytes. The coatings comprise mainly an outer, relatively compact layer and an inner, more porous layer. A thin barrier layer is located next to the alloy. The coatings contain magnesium, oxygen, phosphorus, silicon, and alloying element species and include crystalline phases of MgO, , , and . Local microstructures suggest melting and solidification in the inner layer. Sequential treatments disclose transport of phosphorus and silicon species through the outer coating along short-circuit paths. Further, analyses of the electrolytes reveal the presence of coating species in relative amounts suggestive of preferential loss of inner coating material. The efficiency of coating formation is to 20%, with the main reduction due to evolution of oxygen.