Dissolved Reactive Phosphorus Concentrations Research Articles

Release of phosphorus and metal(loid)s from manured soils to floodwater during a laboratory simulation of snowmelt flooding.

Phosphorus (P) and metal accumulation in manured agricultural soils and subsequent losses to waterways have been extensively studied; however, the magnitudes and the factors governing their losses during spring snowmelt flooding are less known. We examined the P and metal release from long-term manured soil to floodwater under simulated snowmelt flooding with recent manure additions. Intact soil columns collected from field plots located in Randolph, Southern Manitoba, 2 weeks after liquid swine manure treatments (surface-applied, injected, or control with no recent manure addition) were flooded and incubated for 8 weeks at 4± 1°C to simulate snowmelt conditions. Floodwater (syringe filtered through 0.45µm) and soil porewater (extracted using Rhizon-Mom samplers) samples were periodically extracted and analyzed for dissolved reactive phosphorus (DRP), pH, zinc (Zn), manganese (Mn), iron (Fe), magnesium (Mg), calcium (Ca), and arsenic (As). Mean floodwater DRP concentrations (mg L-1) for manure injected (2.0±0.26), surface-applied (2.6±0.26), and control (2.2±0.26) treatments did not differ significantly. Despite manure application, DRP loss to floodwater did not significantly increase compared to the control, possibly due to the elevated residual soil P at this site from the long-term manure use. At the end of simulated flooding, the DRP concentrations increased by 1.5-fold and 5-fold in porewater and floodwater, respectively. Metal(loid) concentrations were not affected by manure treatments in general, except for Zn and Mg on certain days. Unlike DRP, where porewater and floodwater concentrations increased with time, metalloid concentration in porewater and floodwater did not show consistent trends with flooding time.

Establishing riverine nutrient criteria using individual taxa thresholds

Nutrient enrichment is one of the most pervasive impacts on aquatic ecosystems globally. Approaches to establish nutrient criteria that safeguard aquatic ecosystem health are highly variable and, in many instances, criteria are derived from correlations between in-situ nutrient concentrations and biological indices. Summarising entire assemblages with a single index can result in a substantial loss of information and potentially weaker relationships. In this study, we compared the derivation of nutrient criteria using biological indices and those from individual taxa for rivers and streams in New Zealand. Random forest models, including nutrient concentrations, were built to predict two biological indices and individual taxa across New Zealand's river monitoring network. For all acceptable models, the response of the biological indices and individual taxa to increasing Dissolved Inorganic Nitrogen (DIN) and Dissolved Reactive Phosphorus (DRP) were then predicted for every river reach across the nation, and nutrient concentrations that protected 80% of taxa were then identified. Models for the biological indices were poor but were good for most of the taxa, with nutrient concentrations almost always being the most influential factor. To ensure persistence of at least 80% of the taxa within a river reach, we estimated that DIN (Dissolved Inorganic Nitrogen) concentrations would need to be below 0.57–1.32 mg/L, and DRP (Dissolved Reactive Phosphorus) concentrations below 0.019–0.033 mg/L, depending on the river type. In general, high order, low slope rivers and streams required more stringent nutrient criteria than steep, low order streams. The link between nutrient concentrations and biological indices were weak and likely suffer from the loss of information from summarising an entire assemblage into a single numeric. We consider that the derivation of nutrient criteria for waterways should also examine the individual relationships with the taxa in a river system to establish protection for a desired proportion of taxa.

Twenty years of catchment monitoring highlights the predominant role of long-term phosphorus balances and soil phosphorus status in affecting phosphorus loss in livestock-intensive regions

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March–August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R2 = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha−1, the annual mean DRP concentration (range: 49–140 μg L−1; mean: 80 μg L−1) and annual DRP load (range: 0.35–1.46 kg ha−1; mean: 0.65 kg ha−1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R2 = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.

Nutrient retention in tile‐fed and non‐tile reconstructed oxbows in north central Iowa

AbstractNutrient export from the agricultural Midwest threatens the Gulf of Mexico and new conservation practices are needed to reduce the loss of nutrient from subsurface tile drainage systems. Oxbows are natural waterbodies formed when a river cuts off a meander loop and water quality benefits of reconstructed oxbows are being increasingly recognized. In this study, we monitored four reconstructed oxbow sites (two tile‐fed, two non‐tile) over a 2‐year period in north‐central Iowa and assessed their capacity for NO3‐N and dissolved reactive phosphorus (DRP) reductions. Water flow and quality monitoring of tiles, shallow groundwater, oxbow and receiving streams documented that the oxbows were dominated by tile drainage inputs. NO3‐N concentrations were highest in the drainage tiles flowing into the tile‐fed oxbows (mean 8–10 mg/L) and much lower in floodplain groundwater (&lt;1–2 mg/L). Annual NO3‐N loads into the tile‐fed oxbows were substantially larger than input loads into the non‐tiled oxbows. For the two tile‐fed oxbows, the 2‐year NO3‐N retention efficiencies were very similar (0.76–0.77) and on a monthly basis, greater retention efficiencies were measured in summer and fall. DRP concentrations and loads into the tile‐fed oxbows were too low to allow for meaningful estimates of retention. Reconstructing oxbows to receive tile drainage water should be considered a sustainable conservation practice for tile drainage treatment in agricultural areas.

Is glyphosate an underlying cause of increased dissolved reactive phosphorus loading in the Western Lake Erie basin?

The western Lake Erie basin has been experiencing increasing dissolved reactive phosphorus (DRP) loads since approximately 1994, the causes of which are not well understood. Changing agricultural practices such as no-till agriculture and tile drainage are certain to have an effect on DRP loads. This study examines glyphosate as a potential driver of the observed increase in the western Lake Erie basin DRP loads since 1994 by examining adoption of herbicide-tolerant crops, glyphosate use, and both DRP loads and concentrations from the mid-1990’s to the present. Glyphosate’s widespread usage contributes to DRP loadings and eutrophication in the western Lake Erie basin.

Resolving new and old phosphorus source contributions to subsurface tile drainage with weighted regressions on discharge and season.

Agricultural losses of dissolved reactive phosphorus (DRP) emanate from both historic P applications (i.e., "old P") and recently applied fertilizer (i.e., "new P"). Understanding the relative contributions of these sources is important for mitigating DRP losses from agriculture. This study provides a proof-of-concept for resolving new P vs. old P source contributions to DRP losses in subsurface tile drainage using edge-of-field water quality data and management records from eight fields in Ohio. Weighted regressions on discharge and season (WRDS) were fitted using data from periods without P fertilizer applications and then used to predict DRP losses in tile drainage during new P loss risk periods (default length, 90 d) after fertilizer applications. Differences between observed and predicted DRP concentrations during the new P loss risk period were attributed to the new P source. Remaining losses were attributed to the old soil P source. The WRDS model performance was modest (modified Kling-Gupta efficiency ranged from -0.074 to 0.484). New P sources contributed between 0 and 17% of overall DRP losses (average, 7%), with old soil P contributing 83-100%. Individual P fertilizer applications were associated with new DRP losses up to 192g P ha-1 . Increasing the length of the risk period for new P losses up to 180 d after fertilizer application marginally increased the estimated contribution of the new P source. The WRDS-based analysis provides a novel approach for resolving the contributions of new and old sources to edge-of-field DRP losses.

Effectiveness of Nutrient Management for Reducing Phosphorus Losses from Agricultural Areas

Highlights Dissolved reactive P concentration increased with an increased fertilization rate. Subsurface placement of P fertilizer can reduce acute DRP export regardless of fertilization rates. More research connecting P fertilizer use and P export at the field-scale is needed. Abstract. Dissolved reactive phosphorus (DRP) export from agricultural areas is a leading cause of nutrient pollution in freshwater systems (e.g., the North American Great Lakes). A potential solution to mitigate the excessive release of DRP is the use of nutrient management. To evaluate the effectiveness of nutrient management for phosphorus (P) in the United States, we conducted a review to synthesize P management and DRP export data from peer-reviewed articles published between 2000 to 2022. We identified 15 publications and extracted 113 and 90 observations from plot- and field-scale studies, respectively. At the plot scale, mean DRP concentrations were approximately 60% lower when P application rates were below the maximum recommended rate. In addition to the lower mean value, more extreme DRP export events occurred when the P fertilization rate was greater than the maximum recommended rate. In terms of application method, subsurface placement reduced mean DRP concentrations during rainfall simulations by 88% relative to surface placement (i.e., broadcasting). For fertilizer sources, mean DRP concentrations were similar between inorganic and organic fertilizers. However, at high application rates, organic fertilizers had a greater potential to produce extreme DRP export events. At the field-scale, organic fertilizers applied at high rates had the potential to produce extreme DRP export events. However, field-scale results for the other nutrient management techniques were generally inconclusive due to a limited number of studies and confounding factors. Overall, these results displayed the potential adverse impacts of overfertilization and the surface application of P fertilizers and highlighted the need for further research into the influence of nutrient management on P losses. Keywords: 4R management, Agricultural runoff, Conservation practice, Phosphorus export.

Source and transport controls on nutrient delivery to tile drains

Apportioning sources, assessing flow pathways, and quantifying the interaction between source and transport factors are critical for decreasing nutrient loss from agricultural catchments. In this study, water, nutrient, and tracer (δ18O, electrical conductivity) fluxes were measured over two years from a tile-drained field in Indiana, USA to quantify linkages among water flow pathways, management practices, and nutrient delivery to tile drains. Three-component hydrograph separation showed that tile discharge was, on average, sourced from groundwater (65 ± 31%), shallow soil water (10–20-cm deep; 29 ± 28%), and precipitation (6 ± 8%). Daily nitrate-N (NO3-N) and dissolved reactive phosphorus (DRP) load ranged from 0.0 to 1.8 kg ha−1 and 0–101 g ha−1, respectively, while cumulative loads were 30.7 kg ha−1 and 1,040 g ha−1. Nutrient management practices (fertilizer rate, placement, timing) directly influenced the magnitude of incidental nutrient loss and proportion of load that was derived from a fertilizer source. It was estimated that 52% and 46% of cumulative NO3-N and DRP load, respectively, was incidental loss that occurred within 30 d of fertilizer application. Continuous re-distribution of NO3-N throughout the soil profile following fertilizer application resulted in a broad range of concentration across flow pathways and antecedent conditions. In contrast, dry conditions with tile water sourced from shallow soil water or precipitation resulted in greater, but more variable, DRP concentration compared to wetter conditions when tile water was largely comprised of groundwater. Findings suggest that groundwater table dynamics exerted a strong control over DRP concentration, as similar surface-tile hydrologic connectivity occurred during both dry and wet conditions but produced different water quality outcomes. Groundwater may therefore serve both as a chemical and hydrologic buffer of DRP concentration. Combined measurements of water, nutrient, and tracer fluxes revealed novel insights into processes controlling nutrient delivery to tile drains, with direct applicability for conservation practice implementation and improving process representation in models.

Stimulation of high-concentration dissolved nitrogen and reactive phosphorus in Lake Taihu sediments on the initiation and maintenance of cyanobacterial blooms

The spatio-temporal variation of dissolved inorganic nitrogen (DIN: NH4+-N, NO2−-N, and NO3−-N) and dissolved reactive phosphorus (DRP) in Meiliang Bay of Lake Taihu sediments and their potential effects on the cyanobacterial blooms were studied. Monthly sampling was performed using high-resolution dialysis sampling devices (HR-Peeper) and two important results were observed in April (the initiation period of cyanobacterial bloom) and June–August (the maintenance period of cyanobacterial blooms). In April, high concentrations of dissolved NO2−-N and NO3−-N, probably caused by the groundwater influx, were observed in deep anoxic sediments (below 110 mm). NO2−-N and NO3−-N are good electron acceptors for the mineralization of organic P under anaerobic conditions and should lead to an increase in DRP concentrations in sediments, DRP released from sediments thus further stimulating the cyanobacterial growth and the outbreak of severe cyanobacterial blooms in May due to the extremely low concentrations of DRP in the water body. From June to August, high concentrations of NO2−-N, NO3−-N, and DRP were observed in the surface sediment, which was caused by the release of NH4+-N from the mineralization of cyanobacterial debris. This should play an important role in maintaining cyanobacterial growth, especially in stimulating the occurrence of cyanobacterial blooms during September, when N and P were co-limited. This study revealed high-concentration DIN and DRP in Lake Taihu sediments potentially stimulated the initiation and maintenance of cyanobacterial blooms.

Saturated buffer design flow and performance in Illinois.

There are few peer-reviewed studies documenting saturated buffer annual nitrate (NO3 ) removal or that have assessed the federal practice standard design criteria. Drainage flow, NO3 , and dissolved reactive phosphorus (DRP) were monitored at three saturated buffers in Illinois, USA, for a combined 10 site-years. Nitrate loss reduction averaged 48 ± 19% with removals of 3.5-25.2kg NO3 -N ha-1 annually. Median DRP concentrations at all sampling locations were at the analytical detection limit of 0.01mg L-1 . The current design paradigm (i.e., USDA practice standard) prescribes there should be no flow bypassing the saturated buffer at flow rates that are ≤5% of the peak drainage system flow rate. The drainage coefficient-based and Manning's equation-based peak flow estimates were higher and lower, respectively, than the observed annual peaks in all years. This illustrated inherent uncertainty introduced early in the design process, which can be further compounded by dynamic in-buffer hydrology. The percentage of the observed peak flow rate at which bypass initiated ranged across an order of magnitude between sites (4.4-8.1% of peak flow rate at one site and 42-49% of peak at another) despite the buffers providing relatively similar NO3 removal. Bypass at one site (SB2) was related to the concept of "antecedent buffer capacity filled," which was defined as the 5-d average water depth in the middle control structure chamber expressed as a relative percentage of the bypass stop log height. This design flow analysis serves as a call to further evaluate predictive relationships and design models for edge-of-field practices.

Assessing Bioavailability of Typical Lakes and Reservoirs in Northeast China Based on Phosphorus Fractions

To explore the eutrophication degree in the typical lakes and reservoirs of the northeast region of China, the bioavailability of dissolved organic phosphorus (DOP) of the lakes has been examined in this study. The laboratory incubation was carried out at 20 °C for 55 days and the concentrations of total dissolved phosphorus (TDP), dissolved reactive phosphorus (DRP), DOP and the microbial biomass have been detected. Results showed that, during the process of incubation, the concentrations of TDP and DRP were increased, whereas the DOP was decreased, which leads to the decreased mineralization rate. In addition, the changes of microbial biomass were fluctuant, but they had significantly positive effects on the concentration changes and mineralization rate of DOP (p &lt; 0.05). The correlation analysis among the phosphate fractions showed that the TDP significantly promoted the DRP concentration, mineralization rate of DOP and the cumulative mineralization of DOP. The kinetics model was conducted to predict the further mineralization of DOP and to analyze the pollution degree of the eight lakes and reservoirs. Accordingly, the lakes with high DRP and TDP had worse water quality and are prone to algae blooms.

Dynamics of dissolved reactive phosphorus loss from phosphorus source and sink soils in tile-drained systems

Understanding the processes controlling dissolved reactive phosphorus (DRP) loss in tile-drained systems is essential to better define critical source areas and inform nutrient and conservation practice recommendations. Concentration-discharge (C-Q) relationships have been used to infer solute sources, reactivity, proximity, and transport mechanisms governing solute fluxes. In this study, we compare DRP loads and flow-weighted mean DRP (FDRP) concentrations from P source and sink soils at an annual and event scale, and use power law analysis coupled with index-based approaches in order to identify the predominant DRP C-Q behavior in these soils at a daily and event scale. Results indicate that, in general, P source soils consistently lost higher DRP loads and exhibited greater FDRP concentrations when compared to P sink soils when examined at both annual and event scales. At the daily scale, C-Q patterns were linked to the soil P status whereby a chemostatic (<i>b</i> = 1) and dilution (<i>b</i> &lt; 1) behavior was observed for P source and P sink soils, respectively. At the event scale, C-Q patterns were linked to soil P status with a potential contributing influence of flow path connectivity and mixing of event water with matrix and shallow groundwater. Events in P source soils had variable hysteretic behavior with 21%, 7%, 6%, 9%, and 15% exhibiting anticlockwise with dilution, anticlockwise with flushing, clockwise with dilution, clockwise with flushing, and no hysteresis behavior, respectively. These variable C-Q responses suggest that, in addition to discharge and soil P status, rapid exchanges between P pools, the magnitude of discharge events (Q), and the relative number of days to discharge peak (RL) also regulated solute delivery. On the other hand, the predominant nonhysteretic C-Q behavior of events in P sink soils (67%) suggests that DRP loss from these soils can be discounted. These findings highlight the need for nutrient and conservation practices addressing P draw down, P sequestration, and P supply according to crop need, which will likely be required to convert P sources to sinks and to avoid the conversion of P sinks to P sources.

Surface runoff and losses of phosphorus from hydrophobic pastoral soils

The impact of soil water repellency (SWR) on soil phosphorus (P) mobility in surface water runoff remains contentious. Although SWR may cause a significant increase in surface runoff, especially in post-summer rainfall events, whether it contributes to background phosphorus losses remains unclear. Surface runoff and P concentrations in runoff were measured on hilly Allophanic pastoral soils with different water repellency levels using seven runoff collectors. Phosphorus fertilizer was broadcasted at 18 kg P ha−1 in the summer over dry soils. Runoff volumes and P concentrations were measured after each natural rain event prompting surface runoff. The highest runoff/rainfall ratios were observed at the early rainfall events following the dry summer and then decreased significantly by the end of autumn and winter. The post-summer surface runoff correlation with SWR had an R2 of 0.46, and hydrophobic soils had significantly higher runoff ratios than wettable soils. Measurements of the dissolved reactive phosphorus (DRP) and total phosphorus (TP) in the surface runoff showed decreasing exponential trends, with the highest values recorded in the first runoff event following P fertilizer application, where over 90% of losses occurred (incidental losses). After the incidental loss phase, DRP concentrations were related to surface runoff ratio, soil P extractability by water, and SWR. Our data point to non-incidental TP loads being related to SWR (R2 = 0.53). The present results will improve the understanding of the SWR effect on surface runoff and will reconcile the controversy regarding its contribution to non-incidental P losses.

Flue gas desulfurization gypsum and grass buffer strip influence on runoff and nutrient loss from inorganically and organically fertilized corn on a US Coastal Plain soil

Broiler litter (BL) and flue gas desulfurization gypsum (FGDG), both readily available in the US Southeast, can potentially ameliorate soil constraints adversely affecting agricultural productivity and environmental quality in the region. However, benefits and risks must be evaluated prior to making recommendations to producers. The effectiveness of a combination of FGDG and grass buffer strips (GBS) to reduce edge-of-field nutrient losses from corn (Zea mays L.) production under inorganic (NPK) or organic (BL) fertilization was evaluated on Coastal Plain soils near Tifton, Georgia, from April of 2014 through January of 2017. Nine treatments were randomly established in each of three replications on plots instrumented to collect runoff. This was the first phase of a three-phase study. Treatments consisted of combinations of three fertilizer treatments (NPK, BL, and BL+FGDG) and three GBS treatments (no GBS [–GBS], GBS without FGDG [GBS−FGDG], and GBS with FGDG [GBS+FGDG]). A tenth treatment of NPK+FGDG without GBS was also included. Annual rates for BL and FGDG were 13.45 Mg ha−1 each. The BL rate was based on a high nitrogen (N) demand of corn and would represent a risky scenario for nutrient loss. Runoff and concentrations and loads of nitrate-nitrogen (NO3-N), ammonium-nitrogen (NH4-N), total Kjeldahl nitrogen (TKN), dissolved reactive phosphorus (DRP), and total P (TP) were determined in runoff from 29 storms from May of 2015, through January of 2017. Rainfall partitioned into runoff (percentage runoff) decreased by 50% to 70% under –GBS with BL or BL+FGDG compared with NPK fertilization, and under GBS–FGDG or GBS+FGDG compared with –GBS for NPK and BL fertilization. Under –GBS, concentration of DRP and TP increased by ~160% from BL compared with NPK fertilization, and by 150% for DRP and by 115% for TP from BL+FGDG compared with NPK fertilization. On the other hand, the combined BL+FGDG and GBS+FGDG treatment reduced nutrient concentration by 65% to 80% compared with BL with –GBS (a standard practice), and nutrient load by 40% to 70% compared with NPK with –GBS (another standard practice) or BL with –GBS. Results indicate the potential for FGDG to improve edge-of-field runoff water quality when applied to fields with BL and to edge-of-field GBS. In planned follow-up articles, results will be compared with phase-2 when BL and FGDG rates were reduced by a third and phase-3 when BL application was discontinued.

Sources and subsurface transport of dissolved reactive phosphorus in a semiarid, no-till catchment with complex topography.

The subsurface transport of dissolved reactive phosphorus (DRP) from artificially drained agricultural fields can impair water quality, especially in no-till fields. The distribution of soil P in the wheat (Triticum aestivum L.)-dominated Palouse region in the inland U.S. Pacific Northwest varies greatly due to its steep and complex topography, and a legacy (∼130 yr) of excessive soil erosion and deposition processes. The primary goal of this research was to better understand the magnitude and temporal dynamics of DRP export from an artificial drain line and the variability of subsurface DRP leaching within a long-term, no-till field. Dissolved reactive P in drain line effluent was monitored across three water years. Large intact soil cores were extracted at contrasting field locations (toe and top slope positions) to measure DRP leachate concentration and relative P sorption. Drain line DRP concentration was predominantly >0.05mg L-1 and often exceeded 0.1mg L-1 during winter and early spring. Mean leachate DRP levels were significantly higher in toe slope cores than in top slope cores (0.11 and 0.02mg L-1 , respectively). Saturated hydraulic conductivity varied widely across cores and was not correlated with leachate DRP concentration. All soil cores exhibited high P sorption potential, even under conditions of preferential flow. These findings suggest that much of the DRP transport in these landscapes is derived from P hotspots located in toe slope positions. Application of soil P fertilizer amounts in variable rates that account for spatial variability in P transport may minimize P enrichment and subsequent leaching in these locations.

Nutrient loss from floodplain soil with controlled subsurface drainage under forage production.

Expansion of subsurface drainage into forage production may have a deleterious effect on surface waters due to increased nitrogen and phosphorus loading. The impact of controlled subsurface drainage (CD) on nitrogen and phosphorus loss compared with free subsurface drainage (FD) in tile drainage water has been explored to a lesser extent from forage production systems. This study quantifies the effects of CD and FD on average seasonal concentrations and cumulative loads of the total suspended solids (TSS), nitrate nitrogen (NO3 -N), and dissolved reactive phosphorus (DRP) in subsurface drainage water from a poorly drained floodplain soil in a cereal rye (Secale cereale L.)-sorghum [Sorghum bicolor (L.) Moench] rotation with rotational cattle grazing. During all crop seasons of sorghum production (2010-2013), CD had 6.03-9.63mg L-1 less NO3 -N than FD. Mean DRP concentration was significantly higher for CD than for FD during all seasons except for sorghum in 2012-2013. Average cumulative discharge was 38 and 314 m3 ha-1 less for CD than for FD during sorghum and cereal rye growing seasons, respectively. Controlled drainage had 0.68-6.14kg ha-1 lower cumulative NO3 -N loads than FD. The DRP loads were dependent on discharge. During sorghum growing seasons, TSS and DRP loads were 79-90% lower in CD compared with FD. The ability to reduce drainage water flow from tiles and subsequent nitrogen and phosphorus loading with CD compared with FD in a floodplain soil indicates that CD can be effective best management practice for forage production systems.

Temperature and freezing effects on phosphorus release from soils to overlying floodwater under flooded-anaerobic conditions.

Increased phosphorus (P) availability under flooded, anaerobic conditions may accelerate P loss from soils to water bodies. Existing knowledge on P release to floodwater from flooded soils is limited to summer conditions and/or room temperatures. Spring snowmelt runoff, which occurs under cold temperatures with frequent freeze-thaw events, is the dominant mode of P loss from agricultural lands to water bodies in the Canadian Prairies. This research examined the effects of temperature on P dynamics under flooded conditions in a laboratory study using five agricultural soils from Manitoba, Canada. The treatments were (a) freezing for 1wk at -20°C, thawing and flooding at 4±1°C (frozen, cold); (b) flooding unfrozen soil at 4±1°C (unfrozen, cold); and (c) flooding unfrozen soil at 20±2°C (warm). Pore water and surface water were collected weekly over 8 wk and analyzed for dissolved reactive phosphorus (DRP), pH, calcium, magnesium, iron (Fe), and manganese (Mn). Soils under warm flooding showed enhanced P release with significantly higher DRP concentrations in pore and surface floodwater compared with cold flooding of frozen and unfrozen soils. The development of anaerobic conditions was slow under cold flooding with only a slight decrease in Eh, whereas under warm flooding Eh declined sharply, favoring reductive dissolution reactions releasing P, Fe, and Mn. Pore water and floodwater DRP concentrations were similar between frozen and unfrozen soil under cold flooding, suggesting that one freeze-thaw event prior to flooding had minimal effect on P release under simulated snowmelt conditions.

Ceria oxide nanoparticle-based diffusive gradients in thin films for in situ measurement of dissolved reactive phosphorus in waters and sewage sludge.

A passive sampling method based on diffusive gradients in thin films (DGT) using ceria oxide (CeO2) binding gel was developed for in situ measurement of dissolved reactive phosphorus (DRP). CeO2-based DGT showed excellent uptake performance for DRP, and the uptake mass was consistent with the predication by DGT equation. pH (4.2~9.4) and ionic strength (0.01~500mM) had no effects on the uptake of DRP. Filed deployment of CeO2-DGT in reservoir water and seawater showed that the measureable concentrations of DRP were comparable to those obtained by grab sampling. CeO2-DGT was deployed in sewage sludge, and results showed the ratios (RS) between the concentration (CDGT) by CeO2-DGT and the concentration (CS) obtained by a traditional centrifugation method ranged from 0.23 to 0.58. This result indicated that sludge solid phase was a potential pool of DRP in sludge solution, and the DRP released from sludge solid phase could compensate partly the consumption of DRP at the interface of DGT device during the deployment. The ratios RS had positive correlation with the content of Fe (r= 0.847, p< 0.01) but were reversed with the level of Ca (r= - 0.879, p< 0.01) in sewage sludge. The proposed method provided a powerful tool for in situ measurement of DRP in natural waters and for release behavior of DRP in sludge.

Stream order and connectivity affect phosphorus distribution in plain river network

ABSTRACT The order and connectivity of streams influence phosphorus distribution extensively. In this work, the space-and-time variabilities of total phosphorus (TP), particulate phosphorus (PP), total dissolved phosphorus (TDP), dissolved reactive phosphorus (DRP), and dissolved unreactive phosphorus (DUP) in streams of three orders (Ⅰ, Ⅱ, ⅡⅠ) were analyzed during each spring of 2016-2018 in a plain river network area, China. The results show that: ① PP was the main form of TP and DRP was the main form of TDP. ② The average concentrations of phosphorus in the order Ⅰ streams were significant larger than those in the order ⅡⅠ The concentrations of TP, PP, TDP, and DRP in the poor-connected streams were considerably higher than those in the well-connected streams. Therefore, it is essential to implement effective practices to improve the protection and appropriate connectivity of small streams in plain river network areas.

Impact of Filters to Reduce Phosphorus Losses: Field Observations and Modelling Tests in Tile-Drained Lowland Catchments

In this study, we analyzed Dissolved Reactive Phosphorus (DRP) and Total Phosphorus (TP) concentration dynamics over two years in surface waters of five nested catchments in northeastern Germany. Based on this, we constructed a filter box filled with iron-coated sand for Phosphorus (P) removal at the edge of a tile-drained field. Results of the filter box experiment were used for a model scenario analysis aiming at evaluating the P removal potential at catchment scale. DRP and TP concentrations were generally low but they exceeded occasionally target values. Results of the filter box experiment indicated that 28% of the TP load could be retained but the DRP load reduction was negligible. We assume that DRP could not be reduced due to short residence times and high flow dynamics. Instead, particulate P fractions were probably retained mechanically by the filter material. The scenario analysis revealed that the P removal potential of such filters are highest in areas, in which tile drainage water is the dominant P source. At a larger spatial scale, in which other P (point) sources are likewise important, edge-of-field P filters can only be one part of an integrated catchment strategy involving a variety of measures to reduce P losses.