Total Reactive P Research Articles

Far-future hydrology will differentially change the phosphorus transfer continuum

Climate change is likely to exacerbate land to water phosphorus (P) transfers, causing a degradation of water quality in freshwater bodies in Northwestern Europe. Planning for mitigation measures requires an understanding of P loss processes under such conditions. This study assesses how climate induced changes to hydrology will likely influence the P transfer continuum in six contrasting river catchments using Irish national observatories as exemplars. Changes or stability of total P (TP) and total reactive P (TRP) transfer processes were estimated using far-future scenarios (RCP4.5 and RCP8.5) of modelled river discharge under climate change and observed links between hydrological regimes (baseflow and flashiness indices) and transfer processes (mobilisation and delivery indices). While there were no differences in P mobilisation between RCP4.5 and RCP8.5, both mobilisation and delivery were higher for TP. Comparing data from 2080 (2070–2099) with 2020 (2010–2039), suggests that P mobilisation is expected to be relatively stable for the different catchments. While P delivery is highest in hydrologically flashy catchments, the largest increases were in groundwater-fed catchments in RCP8.5 (+ 22% for TRP and + 24% for TP). The inter-annual variability of P delivery in the groundwater-fed catchments is also expected to increase. Since the magnitude of a P source may not fully define its mobility, and hydrological connections of mobilisation areas are expected to increase, we recommend identifying critical mobilisation areas to target future mitigation strategies. These are hydrologically connected areas where controls such as soil/bedrock chemistry, biological activity and hydrological processes are favourable for P mobilisation.

Transferability of a Bayesian Belief Network across diverse agricultural catchments using high-frequency hydrochemistry and land management data

Biogeochemical catchment models are often developed for a single catchment and, as a result, often generalize poorly beyond this. Evaluating their transferability is an important step in improving their predictive power and application range. We assess the transferability of a recently developed Bayesian Belief Network (BBN) that simulated monthly stream phosphorus (P) concentrations in a poorly-drained grassland catchment through application to three further catchments with different hydrological regimes and agricultural land uses. In all catchments, flow and turbidity were measured sub-hourly from 2009 to 2016 and supplemented with 400–500 soil P test measurements. In addition to a previously parameterized BBN, five further model structures were implemented to incorporate in a stepwise way: in-stream P removal using expert elicitation, additional groundwater P stores and delivery, and the presence or absence of septic tank treatment, and, in one case, Sewage Treatment Works. Model performance was tested through comparison of predicted and observed total reactive P (TRP) concentrations and percentage bias (PBIAS). The original BBN accurately simulated the absolute values of observed flow and TRP concentrations in the poorly and moderately drained catchments (albeit with poor apparent percentage bias scores; 76 % ≤ PBIAS≤94 %) irrespective of the dominant land use, but performed less well in the groundwater-dominated catchments. However, including groundwater total dissolved P (TDP) and Sewage Treatment Works (STWs) inputs, and in-stream P uptake improved model performance (−5 % ≤ PBIAS≤18 %). A sensitivity analysis identified redundant variables further helping to streamline the model applications. An enhanced BBN model capable for wider application and generalisation resulted.

Investigation of phosphorus transport dynamics using high-frequency monitoring at a subsurface-drained field in the Western Lake Erie Basin

To minimize the environmental impact of phosphorus (P) loss from subsurface-drained fields to freshwater water bodies like the Great Lakes, a detailed understanding of P transport dynamics is vital. The main objective of this study was to investigate P transport dynamics using high-frequency monitoring. We used the HydroCycle-PO4 instrument to measure total reactive P (TRP) concentration at a high resolution from a subsurface-drained farm with continuous no-till and Blount loam soil. We used a dataset containing hourly TRP concentration and hourly drainage discharge measurements in the analysis. Results showed that there was a good relationship between TRP concentration and drainage discharge (R-squared = 0.60) such that TRP had a transport-limited chemodynamic pattern, that is TRP concentration tended to increase with increase in flow during events. A 1% increase in drainage discharge resulted in a 1.36% increase in TRP load, indicating a significant increase in P concentration during high flows. We found that flow events substantially contributed to P loss (89%) because of capturing the rapid increase in P concentration during high flows. The rate of increase in P concentration during the rising limb ranged from 0.02 to 0.66 mg/L per hour. The highest 7.7% of drainage flow transported 75% of the TRP load during the monitoring period. The hysteresis pattern tended to be positive (clockwise) during the study period, indicating that preferential flow was a pathway for TRP loss. Most flow events (30 out of 36) displayed a flushing effect in which P concentration increased with rise in drainage discharge. In conclusion, high-frequency P sampling showed that management and conservation practices should target flow events to reduce P loss.

Effect of water sampling strategies on the uncertainty of phosphorus load estimation in subsurface drainage discharge.

Accurate phosphorus (P) load estimation in subsurface drainage water is critical to assess the field-scale efficacy of conservation practices. The HydroCycle-PO4 instrument measures real-time total reactive P (TRP) concentration without the need for sample filtration, thereby enabling comparative evaluation of different sampling strategies. The main objective of this study was to evaluate the effects of water sampling strategies on the uncertainty of P load estimation. Hourly TRP concentration and hourly drainage discharge measurements formed the reference P load dataset. Four hypothetical water sampling strategies were evaluated: (a) time-proportional discrete sampling, (b) time-proportional composite sampling, (c) flow-proportional discrete sampling, and (d) flow-proportional composite sampling. All sampling strategies underestimated TRP load compared with the reference dataset. Total reactive P load underestimation changed from 0.2 to 51% as time-proportional discrete sampling intervals increased from 3 h to 14 d. Total reactive P load underestimation changed from 12 to 43% as the time-proportional compositing scenario increased from 1 to 7 d, each with one aliquot per day. In the case of flow-proportional discrete sampling scenario, the lowest (0.6%) and the highest (-5.1%) uncertainties were observed when 1- and 5-mm flow intervals were used. The relative error based on the results provided by the flow-proportional composite sampling ranged from 0.2% when using 1-mm flow interval to -6.7% when using 5-mm flow interval. In conclusion, the flow-proportional sampling strategies provided a more accurate estimate of cumulative P load with fewer number of samples because a greater portion of samples were taken at higher flow rates compared with time-proportional sampling strategies.

Identifying Flow Pathways for Phosphorus Transport Using Observed Event Forensics and the CRAFT (Catchment Runoff Attenuation Flux Tool)

Identifying key flow pathways is critical in order to understand the transport of Phosphorus (P) from agricultural headwater catchments. High frequency/resolution datasets from two such catchments in Northwest England enabled individual events to be examined to identify the flow (Q) and Total P (TP) and Total Reactive P (TRP) dynamics (forensics). Detailed analysis of multiple flow and water quality parameters is referred to here as the event forensics. Are there more flow pathways than just surface runoff (dominated by overland flow) and baseflow (mainly groundwater) contributing at the outlet of these catchments? If so, hydrograph separation alone will not be sufficient. This forensic analysis gives a classification of four storm event response types. Three classes are based on the balance of old and new water giving enrichment and dilution of TRP pattern in the subsurface flow. A fourth type was observed where a plume of nutrient is lost to the channel when there is no observed flow. Modelling is also essential when used in combination with the event forensics as this additional tool can identify distinct flow pathways in a robust form. A case study will apply the Catchment Runoff Attenuation Flux Tool (CRAFT) to two contrasting small headwater catchments in Northwest England, which formed part of the Demonstration Test Catchments (DTC) Programme. The model will use data collected during a series of events observed in the two catchments between the period 2012 and 2014. It has the ability to simulate fast near surface (that can represent flow in the upper soil horizons and field drains) and event subsurface soil flow, plus slower groundwater discharge. The model can capture P enrichment, dilution and the role that displacement of “old” P rich water has during events by mixing these flows. CRAFT captures the dominant flow and P fluxes as seen in the forensic analysis and can create outputs including smart export coefficients (based on flow pathways) that can be conveyed to policy makers to better underpin decision making.

A sub-field scale critical source area index for legacy phosphorus management using high resolution data

Diffuse phosphorus (P) mitigation in agricultural catchments should be targeted at critical source areas (CSAs) that consider source and transport factors. However, development of CSA identification needs to consider the mobilisation potential of legacy soil P sources at the field scale, and the control of (micro)topography on runoff generation and hydrological connectivity at the sub-field scale. To address these limitations, a ‘next generation’ sub-field scale CSA index is presented, which predicts the risk of dissolved P losses in runoff from legacy soil P. The GIS-based CSA Index integrates two factors; mobile soil P concentrations (water extractable P; WEP) and a hydrologically sensitive area (HSA) index. The HSA Index identifies runoff-generating-areas using high resolution LiDAR Digital Elevation Models (DEMs), a soil topographic index (STI) and information on flow sinks and effects on hydrological connectivity. The CSA Index was developed using four intensively monitored agricultural catchments (7.5–11km2) in Ireland with contrasting agri-environmental conditions. Field scale soil WEP concentrations were estimated using catchment and land use specific relationships with Morgan P concentrations. In-stream total reactive P (TRP) concentrations and discharge were measured sub-hourly at catchment outlet bankside analysers and gauging stations during winter closed periods for fertiliser spreading in 2009–14, and hydrograph/loadograph separation methods were used to estimate TRP loads and proportions from quickflow (surface runoff). A strong relationship between TRP concentrations in quickflow and soil WEP concentrations (r2=0.73) was used to predict dissolved P concentrations in runoff at the field scale, which were then multiplied by the HSA Index to generate sub-field scale CSA Index maps. Evaluation of the tool showed a very strong relationship between the total CSA Index value within the HSA and the total TRP load in quickflow (r2=0.86). Using a CSA Index threshold value of ≥0.5, the CSA approach identified 1.1–5.6% of catchment areas at highest risk of legacy soil P transfers, compared with 4.0–26.5% of catchment areas based on an existing approach that uses above agronomic optimum soil P status. The tool could be used to aid cost-effective targeting of sub-field scale mitigation measures and best management practices at delivery points of CSA pathways to reduce dissolved P losses from legacy P stores and support sustainable agricultural production.

Simulating high frequency water quality monitoring data using a catchment runoff attenuation flux tool (CRAFT)

High resolution water quality data has recently become widely available from numerous catchment based monitoring schemes. However, the models that can reproduce time series of concentrations or fluxes have not kept pace with the advances in monitoring data. Model performance at predicting phosphorus (P) and sediment concentrations has frequently been poor with models not fit for purpose except for predicting annual losses. Here, the data from the Eden Demonstration Test Catchments (DTC) project have been used to calibrate the Catchment Runoff Attenuation Flux Tool (CRAFT), a new, parsimonious model developed with the aim of modelling both the generation and attenuation of nutrients and sediments in small to medium sized catchments. The CRAFT has the ability to run on an hourly timestep and can calculate the mass of sediments and nutrients transported by three flow pathways representing rapid surface runoff, fast subsurface drainage and slow groundwater flow (baseflow). The attenuation feature of the model is introduced here; this enables surface runoff and contaminants transported via this pathway to be delayed in reaching the catchment outlet. It was used to investigate some hypotheses of nutrient and sediment transport in the Newby Beck Catchment (NBC) Model performance was assessed using a suite of metrics including visual best fit and the Nash-Sutcliffe efficiency. It was found that this approach for water quality models may be the best assessment method as opposed to using a single metric. Furthermore, it was found that, when the aim of the simulations was to reproduce the time series of total P (TP) or total reactive P (TRP) to get the best visual fit, that attenuation was required. The model will be used in the future to explore the impacts on water quality of different mitigation options in the catchment; these will include attenuation of surface runoff.

The relationship between operational and bioavailable phosphorus fractions in effluents from advanced nutrient removal systems

Because different phosphorus (P) forms vary greatly in their bioavailability, total phosphorus concentrations are a problematic predictor of the eutrophication potential of natural surface waters and wastewater treatment facility effluents. It is currently not known which operational P characterizations (i.e., dissolved/particulate and reactive/non-reactive) best predict effluent P bioavailability. We characterized the P speciation and directly measured the bioavailability of P (BAP) using algal bioassays for 14 full-scale advanced nutrient removal wastewater treatment plants representing a wide range of P removal technologies. A strong statistical relationship was observed between the effluent total BAP (tBAP) and total reactive P (TRP) (r 2 ≈ 0.81), with a tBAP/TRP ratio of 0.61 ± 0.24, indicating that TRP can be used as a conservative surrogate predictor of tBAP. A comparison of different operational categories for phosphorus indicated that sBAP is consistently lower than both soluble P (SP) and soluble reactive P (SRP) with average ratios of 0.34 ± 0.19 and 0.62 ± 0.27, respectively. This shows a large fraction of the dissolved non-reactive P (i.e., SP−SRP), and ≥40 % of the P classified as SRP was not bioavailable. Total BAP concentrations were on average 30 % higher than soluble BAP (sBAP) concentrations, indicating that the particulate P fraction was an important component of the BAP for the tested effluents. Comparisons between different P removal technologies suggest the bioavailability, and P species composition varies with the nutrient removal process, and that in many cases, a large portion (>60 %) of the effluent P is recalcitrant to algal growth.

Nitrogen speciation and phosphorus fractionation dynamics in a lowland Chalk catchment

A detailed analysis of temporal and spatial trends in nitrogen (N) speciation and phosphorus (P) fractionation in the Wylye, a lowland Chalk sub-catchment of the Hampshire Avon, UK is presented, identifying the sources contributing to nutrient enrichment, and temporal variability in the fractionation of nutrients in transit from headwaters to lower reaches of the river. Samples were collected weekly from ten monitoring stations with daily sampling at three further sites over one year, and monthly inorganic N and total reactive P (TRP) concentrations at three of the ten weekly monitoring stations over a ten year period are also presented. The data indicate significant daily and seasonal variation in nutrient fractionation in the water column, resulting from plant uptake of dissolved organic and inorganic nutrient fractions in the summer months, increased delivery of both N and P from diffuse sources in the autumn to winter period and during high flow events, and lack of dilution of point source discharges to the Wylye from septic tank, small package Sewage Treatment Works (STW) and urban Waste Water Treatment Works (WwTW) during the summer low flow period. Weekly data show that contributing source areas vary along the river with headwater N and P strongly influenced by diffuse inorganic N and particulate P fluxes, and SRP and organic-rich point source contributions from STW and WwTW having a greater influence in the lower reaches. Long-term data show a decrease in TRP concentrations at all three monitoring stations, with the most pronounced decrease occurring downstream from Warminster WwTW, following the introduction of P stripping at the works in 2001. Inorganic N demonstrates no statistically significant change over the ten year period of record in the rural headwaters, but an increase in the lower reaches downstream from the WwTW which may be due to urban expansion in the lower catchment.

Characterization of Leached Phosphorus from Soil, Manure, and Manure-Amended Soil by Physical and Chemical Fractionation and Diffusive Gradients in Thin Films (DGT)

We are challenged to date to fully understand mechanisms controlling phosphorus (P) mobilization in soil. In this study we evaluated physical properties, chemical reactivity, and potential bioavailability of P mobilized in soil during a leaching event and examined how the amounts and properties of leached P were influenced by surface application of cattle manure. Leaching experiments on manure itself, and on intact soil columns (14.1 cm inner dia., 25 cm height) before and after manure application, were carried out at an irrigation rate of 1 mm h(-1) for 48 h. High concentrations of dissolved reactive P (DRP) were found in manure leachates (up to 32 mg L(-1)), whereas concentrations of P in soil leachates were low both before and after manure application (around 0.04 mg L(-1) before application and up to 0.4 mg L(-1) afterward). This result indicates that the soil retained most of the P added with manure. Manure particles themselves were also largely retained by the soil. Combined physical (centrifugation) and chemical (molybdate reactiveness) fractionation of leached P showed that leachates in the manure treated soils were dominated by dissolved unreactive P (DUP), mainly originating from manure. However, centrifugation only removed a small fraction of total particles from the leachates, indicating that the so-called dissolved fraction may be associated with low density particulate matter. Deployment of Diffusive Gradients in Thin films (DGT) devices in the leachates proved to be a good approach for measuring reactive P in soil leachates. The results indicated that total reactive P (TRP) gave a better estimate of potentially bioavailable P than both total P (TP) and DRP in these experiments.

Transport of Residual Nutrients Through Intact Soil Cores Amended With Fresh or Composted Beef Cattle Manure for Nine Years

Although fresh beef cattle (Bos Taurus) manure has traditionally been applied to cropland in Western Canada, application of composted manure has recently increased, and the environmental impact of increasing application of composted manure is unknown. Our main objective was to compare the effect of fresh versus composted feedlot manure on transport of residual nitrate-nitrogen (NO3-N), chloride (Cl), and total reactive P (TRP) to subsurface soil. Fresh and composted feedlot manure was annually applied at 0 and 77 Mg ha−1 dry wt. for nine years to a clay loam soil in a replicated field experiment. Intact soil cores (0-30 cm depth) were taken from the field in the spring of 2007, and the residual soil chemicals were eluted from the soil cores by applying deionized water to obtain breakthrough curves. Although mean values for peak and flow-weighted mean concentrations, and mass loss of NO3-N, Cl, and TRP were, in general, significantly (P ≤ 0.05) higher for the amended cores compared to the unamended control, there were no significant differences between fresh and composted manure. Asymmetrical breakthrough curves and peak concentrations prior to one volume for NO3-N and Cl indicated preferential transport in macropores, whereas a gradual increase in concentration for TRP indicated transport by matrix flow. The cumulative mass of NO3-N and Cl were described using an exponential equation with asymptote and negative rate constants, and reflected a rapid initial release of these chemicals followed by a steady-state condition. In contrast, TRP loss from amended cores was best fit with an exponential growth equation and positive rate constant, and reflected a gradual slow release of this chemical. Mean peak concentrations exceeded the Canadian drinking water guideline of 10 mg NO3-N L−1 by 44 fold for composted manure (438 mg L−1), 34 fold for fresh manure (339 mg L−1), and 15 fold for the unamended control (153 mg L−1). The P sorption index was similar for fresh and composted manure, but mean values were significantly lower for the amended compared to unamended soil cores. Our findings suggested no statistical evidence for more transport of these nutrients for composted compared to fresh manure but there was a greater risk of transport for amended compared to unamended soils, particularly for macropore transport of NO3-N and Cl.

Effects of Soil Properties on Phosphorus Subsurface Migration in Sandy Soils

The soil factors influencing the potential migration of dissolved and particulate phosphorus (P) from structurally-weak sandy subsoils were evaluated by means of soil column leaching experiments. Soil colloids were extracted from two types of soils to make the colloid-bound forms of P solution. Eight sandy soils with diverse properties were collected for packing soil columns. The effects of influent solutions varying in concentrations of colloids, P, and electrolyte, on the transport of P and quality of leachates were characterized. P migration in the soils was soil property-dependent. High soil electrical conductivity values retarded the mobility of colloids and transportability of colloid-associated P (particulate P). Soil electrical conductivity was negatively correlated with colloids and reactive particulate P (RPP) concentrations in the leachates, whereas, the total reactive P (TRP) and dissolved reactive P (DRP) concentrations in the leachates were mainly controlled by the P adsorption capacity and the P levels in the subsoil. The reactive particulate P in the leachates was positively correlated with the colloidal concentration. Increased colloidal concentration in the influent could significantly increase the colloidal concentration in the leachates. Elevated P concentration in the influent had little effect on P recovery in the leachates, but it resulted in significant increases in the absolute P concentration in the leachates.

Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.

Eat, drink and be wary: How acid reflux can affect your asthma

Two river waters (a lowland chalk stream and an upland river containing humic materials) and two soil waters (freely drained leachate to 135 cm depth and storm surface runoff, both from grassland soils) were fractionated into unfiltered <0.45, <0.22, <0.1 and <0.025 μm using composite cellulose nitrate/acetate (CNA) membranes, under vacuum at 80 kPa. Fractions less than 10,000 and 1000 molecular weight (MW) size were separated by ultrafiltration at 276 kPa. Molybdate reactive phosphorus (MRP) and dissolved organic carbon (DOC) were measured using the filtrates in each size range. In three of the four waters, the concentration of MRP in the portion <1000 MW was significantly smaller (P < 0.05) than that determined in the fraction <0.45 μm. In the soil surface runoff water, which was dominated by eroded mineral particles and colloidal organic material, the <1000 MW fraction represented 14% of the total reactive P (TRP), and most of the reactive P was associated with the unfiltered (>0.45 μm) fraction, being 71% of the TRP. In contrast, 87% of the TRP in soil leachate and 55% of the TRP in the chalk stream water was <1000 MW, with significantly different but smaller portions in the range <0.45 μm to >1000 MW. Particle and colloidal material plays an important role in the transformations of P. These findings are particularly novel for soils, where implications for mobility within the soil solution need to be considered.

Size distribution of colloidal molybdate reactive phosphorus in river waters and soil solution

Two river waters (a lowland chalk stream and an upland river containing humic materials) and two soil waters (freely drained leachate to 135 cm depth and storm surface runoff, both from grassland soils) were fractionated into unfiltered <0.45, <0.22, <0.1 and <0.025 μm using composite cellulose nitrate/acetate (CNA) membranes, under vacuum at 80 kPa. Fractions less than 10,000 and 1000 molecular weight (MW) size were separated by ultrafiltration at 276 kPa. Molybdate reactive phosphorus (MRP) and dissolved organic carbon (DOC) were measured using the filtrates in each size range. In three of the four waters, the concentration of MRP in the portion <1000 MW was significantly smaller ( P < 0.05) than that determined in the fraction <0.45 μm. In the soil surface runoff water, which was dominated by eroded mineral particles and colloidal organic material, the <1000 MW fraction represented 14% of the total reactive P (TRP), and most of the reactive P was associated with the unfiltered (>0.45 μm) fraction, being 71% of the TRP. In contrast, 87% of the TRP in soil leachate and 55% of the TRP in the chalk stream water was <1000 MW, with significantly different but smaller portions in the range <0.45 μm to >1000 MW. Particle and colloidal material plays an important role in the transformations of P. These findings are particularly novel for soils, where implications for mobility within the soil solution need to be considered.