Dissolved P Research Articles

Sediment budget of a Maumee River headwater tributary: how streambank erosion, streambed-sediment storage, and streambed-sediment source inform our understanding of legacy phosphorus

ObjectiveWe described source and phosphorus (P) retention potential of soft, fine-grained, streambed sediment and associated phosphorus (sed-P) during summer low-flow conditions. Combining in-channel, sed-P storage with relative age provided context on relevance to western Lake Erie Basin management goals.MethodsIn 2019, rapid geomorphic assessment (30 reaches) compared streambed-sediment storage (S) to streambank erosion (E), providing annual sediment budgets (S:E). Streambed sediment (13 reaches) was fingerprinted and analyzed for sed-P. The P saturation ratio (PSR; four reaches) quantified potential sorption/desorption of dissolved P (DP) between the water column and streambed sediment. Analyses were supplemented with data from 2017 and 2021. The ratio of two fallout radionuclides, beryllium-7 (54-day half-life) and excess lead-210 (22.3 years), apportioned “new” sediment based on time since rainfall contact.ResultsStreambed sediment was mostly streambank (54–96%) for contributing areas > 2.7 km2; for upstream reaches, a larger percentage was apportioned as upland (cropland, pasture, forest, and road), with < 30% streambank. Streambank erosion correlated with contributing area; however, soil type (ecoregion), stream characteristics, and land use combined to drive streambed-sediment storage. Individual-reach S:E (accumulation of 0.01–35 years of streambank erosion) differentiated erosional and depositional in-channel environments. Most reaches indicated that 17–57% of sediment had recent contact with rainfall. Streambed-sediment PSR indicated a low potential for further sorption of DP from the water column; one reach was a P source when sampled.ConclusionSed-P was higher in streambed sediment than in source samples, which varied by land use and ecoregion. This indicates homogenization resulting from in-stream sorption of DP during sediment transport that occurs over multiple events.

Variation in Phosphorus Concentration and Flux at Zhutuo Section in the Yangtze River and Source Apportionment

Phosphorus (P) is a pollutant of great concern in the Yangtze River Basin. The Xiangjiaba Reservoir and Xiluodu Reservoir on the lower reach of the Jinsha River began to operate in 2012 and 2013, respectively, which greatly changed the concentrations of suspended sediment and characteristics of P form and transport in the reservoirs and the downstream reach from Yibin to Jiangjin of the Yangtze River. The Zhutuo section is representative in the water quality of the Yibin-Jiangjin reach, which can not only reflect the comprehensive effects of the formation of the two reservoirs and changes in the aquatic environment in the Min-Tuo Rivers but also reflect the quality of water flowing into the Three Gorges Reservoir. The runoff, concentrations and fluxes of suspended sediments (SS), and P concentrations and fluxes at Zhutuo section were studied during 2002-2019, and the source of P was apportioned based on the principle of river base flow. The results showed that in the past 18 years, the concentrations and fluxes of total phosphorus (TP) and particulate phosphorus (PP) at Zhutuo section in the wet season were higher than those in the level and dry seasons; the rule of positive correlation between PP and SS concentrations remained unchanged. From 2002 to 2019, the concentrations and fluxes of TP, PP, and dissolved P (DP) generally increased first and then decreased, and the operation of the Xiangjiaba Reservoir was a time node for the trend turning. Compared with that in the period from 2002-2012, the SS concentration and flux decreased by 94% and 77%, TP and PP concentrations decreased by 46% and 70%, and TP and PP fluxes decreased by 58% and 74%, respectively, during 2014-2019. The decline mainly occurred in the wet season, followed by that in the level season. After the formation of the two reservoirs, the relationship between water and sediment and the form of P greatly changed, and the proportion of DP in TP increased significantly, whereas the proportion of PP was the opposite. The TP pool in overlying water in the dry and level seasons shifted from mainly particulate to mainly dissolved. The change in water and sediment conditions was the main driving force for the significant change in P concentration, flux, and form. Before the operation of the Xiangjiaba Reservoir, the Jinsha River was the maximum contributor to the whole and diffuse source part of the TP load at Zhutuo section among the contributing catchment sub-basins; however, the Minjiang River became the largest contributor after the operation. The average TP load at Zhutuo section from 2017-2019 was 3.575×104 t·a-1 (after deducting the natural background value), of which the contribution of diffuse sources and point sources accounted for 68% and 32%, respectively. The Minjiang River represented 49%, 43%, and 62% of the total TP load, diffuse source TP load, and point source TP load at Zhutuo section, respectively. Considering the load contribution and pollution intensity, the key area for P pollution control in the area upstream of the Three Gorges Reservoir was the Min-Tuo River Basin.

Effectiveness Overview of Agricultural Conservation Practices for Water Quality Improvement Part II

Highlights This article summarizes ten agricultural conservation practices reviewed in both editions of the collection. Mean sediment load was reduced 73%-80% by residue and tillage management, filter strips, and cover crops. Mean nitrate-N load reduction ranged from 34%-46% for filter strips and water management practices. Phosphorus loads and concentrations were reduced by most practices, but dissolved P increased with two practices. Cost effectiveness varied widely, and these results may help in efforts to prioritize conservation implementation. Abstract. Although significant governmental investment has been provided to implement agricultural conservation practices (ACPs) for water quality improvement, eutrophication and hypoxia persist in coastal and fresh waters. A better understanding of the comparative effectiveness of ACPs is needed to improve environmental outcomes with the funding available. The objectives of this overview article are to (1) compare the performance and cost effectiveness among all the ACPs reviewed in both the first and second editions of the Special Collection and (2) present critical perspectives for researchers, policymakers, and funding entities seeking to improve water quality. The ten ACPs reviewed encompassed a range of goals, strategies, and landscape placement and varied widely in performance for their reduction of sediment, nitrogen (N), and phosphorus (P) and their cost-effectiveness. Three ACPs included performance measures for all three constituents: sediment, N, and P, whereas others focused only on N (nine ACPs) and/or P (six ACPs). The four ACPs that are considered “water management” practices: drainage water management, denitrifying bioreactor, saturated buffer, and constructed wetland were all effective in mitigating the effects of nutrients in subsurface drainage water and showed average nitrate-N load reductions of 40%-46%. In contrast, few practices were found effective in reducing dissolved P (DP) loss from agricultural fields. Four ACPs (residue and tillage management, conservation crop rotation, drainage water management, and nutrient management) demonstrated possible net economic benefits, while perspectives were provided for prioritizing financial assistance for other ACPs. Monitoring recommendations developed during the literature reviews highlighted the need for more long-term field-scale monitoring to better reflect multi-year climatic variability. Keywords: Constructed wetland, Cost effectiveness, Cover crop, Crop rotation, Denitrifying bioreactor, Drainage water management, Filter strip, Monitoring, Nitrogen, Nutrient management, Performance effectiveness, Phosphorus, Residue and tillage management, Saturat

Phosphorus and its solubility in aerosols from continental and marine sources in the sea areas near China: Results from a 40-day cruise mission in late spring

Accurate assessments of soluble phosphorus (P) in aerosol particles are essential to understand the atmospheric nutrients supply to the marine ecosystem. We quantified total P (TP) and dissolved P (DP) in the aerosol particles collected in the sea areas near China in a cruise mission from May 1 to June 11, 2016. The overall concentrations of TP and DP were 3.5–99.9 ng m−3 and 2.5–27.0 ng m−3, respectively. When the air originating from the desert areas, TP and DP were 28.7–99.9 ng m−3 and 10.8–27.0 ng m−3, respectively, and P solubility was 24.1–54.6 %. When the air influenced mainly by anthropogenic emissions from eastern China, TP and DP were 11.7–12.3 ng m−3 and 5.7–6.3 ng m−3, respectively, and P solubility was 46.0–53.7 %. More than half of the TP and more than 70 % of the DP were from pyrogenic particles, with a considerable DP converted via aerosol acidification after the particles met humid marine air. On average, aerosol acidification promoted the fractional solubility of dissolved inorganic P (DIP) to TP from 22 % to 43 %. When the air originating from the marine areas, TP and DP were 3.5–22.0 ng m−3 and 2.5–8.4 ng m−3, respectively, and P solubility was 34.6–93.6 %. About one-third of the DP was from biological emissions in organic forms (DOP), leading to higher solubility than in the particles from continental sources. These results reveal the dominance of inorganic P in TP and DP from the desert and anthropogenic mineral dust and the significant contribution of organic P from marine sources. The results also indicate the necessity to treat aerosol P carefully according to different sources of the aerosol particles and atmospheric processes the particles experience in assessing aerosol P input to seawater.

Conversion of Forest Hillslopes into Tea Fields Increases Soil Nutrient Losses through Surface Runoff

The conversion of forest hillslopes into tea fields changes the slope structure, soil properties, and vegetation, which may increase the great variations in the nitrogen (N) and phosphorus (P) losses through the surface runoff and induce agricultural non-point source pollution, particularly during the first years of conversion. Therefore, a natural forest system and a newly reclaimed tea system were compared to determine the land use conversion effects on the surface runoff and resulting N and P losses during 2013–2016. The results showed that the soil bulk density (BD) at all the depths and the saturated soil conductivities (Ks) in the surface soil were higher in the tea system than in the forest system, indicating that great land use conversion impacts soil’s physical and hydraulic properties. The annual surface runoff volumes and ratios were significantly higher in the tea system than in the forest system (p &lt; 0.05), and this increased surface runoff was largely attributed to the slope structure and soil property changes. The total P (TP), dissolved P (DP), and particle P (PP) concentrations in the surface runoff volumes were similar in the two systems, while the total N (TN) concentrations were higher in the tea system than in the forest system due to the high N fertilizer application rates in the tea system. The percentages of dissolved N (DN) in the TN and particle N (PN) in the TN were, respectively, lower and higher in the tea system than in the forest system, which was associated with increased soil erodibility due to the land use conversion. The mean annual N and P losses through the surface runoff were higher in the tea system (11.07 ± 4.03 kg N ha−1 yr−1 and 1.73 ± 0.19 kg P ha−1 yr−1) than in the forest system (4.51 ± 0.66 kg N ha−1 yr−1 and 0.78 ± 0.18 kg P ha−1 yr−1). The N and P losses exponentially correlated with the surface runoff in both systems; however, the coefficients of determination (R2) were higher in the forest system than in the tea system, indicating that the exponential relationship between the surface runoff and the N and P losses should be more stable in the forest system than in the newly reclaimed tea system. Therefore, more effort should be dedicated to reducing the N and P losses though the surface runoff when forest hillslopes are converted into tea fields, particularly during the first three years of conversion.

Long-Term Nitrogen and Phosphorus Outflow from an Instream Constructed Wetland under Precipitation Variability

In many agricultural watersheds, surface runoff often causes unwanted nitrogen (N) and phosphorus (P) losses from croplands into stream networks. When this phenomenon is pronounced, it significantly changes N and P concentrations in streams affecting aquatic ecosystems. To protect stream water quality, the installation of instream-constructed wetlands (ICWs) for treating runoff water is often reported as a low-cost alternative to conventional water treatment systems. Indeed, ICWs have the capacity to collect and temporarily retain nutrients transported from agricultural landscapes and then slowly release them into downstream networks. However, the long-term hydrologic behavior of ICWs relative to N and P outflow control is still insufficiently reported. Especially in the context of climate change, it is relevant to investigate the effect of precipitation variability on ICWs N and P outflow. This study uses the soil and water assessment tool (SWAT) model to approximate the long-term hydrologic behavior of an experimental ICW installed in a small agricultural watershed. The model was set assuming a continuous corn and soybean rotation on croplands, then a multidecadal (period 2001–2020) simulation was used to evaluate the implication of precipitation variability on total nitrogen (TN), nitrate-N (NO3-N), total P (TP), and dissolved P (DP) outflows. Results show meaningful changes in the precipitation pattern with contrasting effects on N and P outflows. While analyses show significant trends in the maximum monthly precipitation, nutrient outflows during two consecutive decades, 2001–2010 and 2011–2020, show increases of 46% for TN, and 82% for TP. At the watershed scale, month-to- month TN and TP outflows range from 24 to 810 kg N and 26 to 1358 kg P during 2011–2020, compared with 42 to 398 kg N and 40 to 566 kg P during 2001–2010. The increase in nutrient outflow is particularly pronounced for TP and DP which show significant trends and high correlations (r &gt; 0.70) with maximum monthly precipitation. An exception is nitrate-N outflow, which counts on average for less than 5% of TN outflow but appears more affected by the timing of N fertilization in the watershed.

Optimizing phosphate fertilizer input to reduce phosphorus loss in rice-oilseed rape rotation.

Identifying the major sources and critical periods of P loss from agricultural fields provides important guidance for reducing P loss. A rice-oilseed rape rotation with no P fertilization (NP, control), medium P fertilization (MP, 90kg P2O5 ha-1 season-1), and high P fertilization (HP, 180kg P2O5 ha-1 season-1) was conducted from 2019 to 2021 in the middle Yangtze River Basin. Runoff and leaching P losses were measured simultaneously using runoff event monitoring and a percolation device. Applying P fertilizer increased the P concentration in the field ponding water and percolation water of the rice-oilseed rape rotation. During the rice growing season, total P (TP), dissolved P (DP), and particulate P (PP) concentrations in the field ponding water and percolation water peaked 1day after P was applied, and then decreased rapidly. After 10days of fertilization, P concentration in the field ponding water of the MP treatment decreased to a minimum and stabilized, while the HP treatment extended this period to 20days. The highest P concentration in percolation water was observed at the first sampling during the oilseed rape season, and then it continued to decrease. Inputting P fertilizer increased P loss by 55.0-109.9% compared to the NP treatment, with annual P losses of 0.89-1.10kg P ha-1, of which runoff loss accounted for 61.7-62.9%. Fertilization and precipitation resulted in varied P loss within and between seasons. Runoff from heavy precipitation during the rice season was the main source of P loss, while PP accounted for 54.7-77.6% of runoff P loss. The strong utilization of soil P by rice resulted in a lower demand for exogenous P fertilizer than oilseed rape. Excessive P input increased the soil P surplus and vertical migration. Therefore, reducing rice season P fertilizer inputs to achieve annual P balance in rice-oilseed rape rotation can effectively reduce soil P surplus and loss while ensuring crop P demand, and the initial 10 d after fertilization in the rice season was a critical period for reducing P runoff loss.

Quantifying groundwater phosphorus flux to rivers in a typical agricultural watershed in eastern China.

Increasing evidence indicates that groundwater can contain high dissolved phosphorus (P) concentrations, thereby contributing as a potential pollution source for surface waters. However, limited quantitative knowledge is available concerning groundwater P fluxes to rivers. Based on monthly hydrochemical monitoring data for rivers and groundwater in 2017-2020, this study combined baseflow separation methods and a load apportionment model (LAM) to quantify contributions from point sources, surface runoff, and groundwater/subsurface runoff to riverine P pollution in a typical agricultural watershed of eastern China. In the studied Shuanggang River, most total P (TP) and dissolved P (DP) concentrations exceeded targeted water quality standards (i.e., TP ≤ 0.2mg P L-1, DP ≤ 0.05mg P L-1), with DP (76 ± 20%) being the major riverine P form. Observed DP concentrations in groundwater were generally higher than those of river waters. There was a strong correlation between river and groundwater P concentrations, implying that groundwater might be a considerable P pollution source to rivers. The nonlinear reservoir algorithm estimated that baseflow/groundwater contributed 66-68% of monthly riverine water discharge on average, which was consistent with results estimated by an isotope-based sine-wave fitting method. The LAM incorporating point sources, surface runoff, and groundwater effectively predicted daily riverine TP [calibration: coefficient of determination (R2) = 0.76-0.82, Nash-Sutcliffe Efficiency (NSE) = 0.61-0.77; validation: R2 = 0.88-0.98, NSE = 0.54-0.64] and DP loads (calibration: R2 = 0.73-0.84, NSE = 0.67-0.72; validation: R2 = 0.88-0.97, NSE = 0.56-0.83). The LAM estimated point source, surface runoff, and groundwater contributions to riverine loads were 15-18%, 14-35%, and 46-70% for TP loads and 7-9%, 10-32%, and 59-82% for DP loads, respectively. Groundwater was the dominant riverine P source due to long-term accumulation of P from excess fertilizer and farmyard manure applications. The developed methodology provides an alternative method for quantifying P pollution loads from point sources, surface runoff, and groundwater to rivers. This study highlights the importance of controlling groundwater P pollution from agricultural lands to address riverine water quality objectives and further implies that decreasing fertilizer P application rates and utilizing legacy soil P for crop uptake are required to reduce groundwater P loads to rivers.

Nutrient and suspended-sediment concentrations in the Maumee River and tributaries during 2019 rain-induced fallow conditions

Above average precipitation from October 2018 through July 2019 in the Maumee River (R.) Basin resulted in 29% of cropland left fallow, providing a glimpse of potential effects from decreased nutrient application. Ongoing monitoring at 15 water-quality sites on the Maumee R. upstream from Defiance enabled comparison with 2017, which was hydrologically similar to 2019 in precipitation and streamflow. In 2019, nitrate (as nitrogen; NO3-N) for March-July was significantly less than previous years (2015–2018), but the response for phosphorus (P) was more complicated. Relative to 2017, total P (TP) was lower at 7 of 15 sites, but higher at 7, reflecting higher suspended sediment (SS). Dissolved P (DP) was generally lower, but less different than NO3; DP was higher at 3 sites. DP-P:NO3-N was generally higher in 2019, DP-P:TP was lower, and there was less TP relative to SS. Overall, less P was in the system in 2019. However smaller streams showed a large range of difference between 2019 and 2017 for all constituents, indicating variability in land management and physiography. In contrast, all constituents were lower in 2019 in larger (>5000 km2) streams, including the Maumee R. near Defiance, where the difference in NO3 (−37%) exceeded that for TP (−16%), DP (−10%), and SS (−20%). Differences in these relations among N, P, and SS indicate that P was available from legacy sources that are more difficult to distinguish during typical agricultural production years and that some material from 2019 was stored in the system upstream from the largest sites.

Phosphorus sources, forms, and abundance as a function of streamflow and field conditions in a Maumee River tributary, 2016-2019.

Total phosphorus (TP), dissolved P (DP), and suspended sediment (SS) were sampled in Black Creek, Indiana, monthly during base flow and for 100 storm events during water years 2016-2019, enabling analysis of how each of these varied as a function of streamflow and field conditions at nested edge-of-field sites. Particulate P was normalized for SS (PSS =[TP - DP]/SS). Streamflow events were differentiated by maximum TP concentrations co-occurring with maximum SS (SED) or DP (SOL). The combination of new precipitation and high antecedent soil-water storage during months when fields were exposed coincided with higher streamflow that drove SED events. These SED events carried more SS, including sediment eroded from streambanks that added sediment P but also may have provided for sorption of DP. During SOL events, DP was higher and contributed approximately half of TP; SS was lower. These SOL events had higher PSS , more similar to that in base flow as well as composited samples of overland flow and tile-drain discharge from fields. Base-flow samples had significantly higher PSS concentrations than most event samples, with ≤25 times enrichment relative to soil P concentrations in fine-grained source material. Combining base-flow and event samples showed that PSS integrates SS, DP, and streamflow. Addition of new suspended sediment during events may provide for sorption of DP during and after events and storage in the system, delaying delivery of this P to Lake Erie relative to what would be expected for the dissolved form but adding to the legacy P stored in the stream system.

Modelling dissolved phosphorus losses from accumulated soil phosphorus and applied fertilizer and manure for a national risk indicator

Balancing the weighting of various components of phosphorus loss in models is a critical but often overlooked step in accurate estimation of risk of P loss under field conditions. This study compared the P loss coefficients used to predict dissolved P losses from desorption from accumulated P in the soil, and those incidental to applications of P as fertilizer or manure, with extraction coefficients determined from actual P losses reported in literature for sites in Canada, with the addition of some sites with similar soils and climate from some northern states. The extraction coefficients for dissolved P measured in runoff water were 6.5× greater in year-round edge-of-field (EoF) measurements than in runoff boxes, indicating that models using P extraction coefficients derived from runoff box experiments will be underestimating the magnitude of losses from P accumulation in soil. Differences among the measurement methods (runoff box, rainfall simulator, or EoF) were not evident for incidental losses from applied P, but current models appear to overpredict the losses of applied P. Good agreement between measured and predicted dissolved P (DP) concentrations using the equations in the Annual Phosphorous Loss Estimator model were achieved by applying coefficients of 0.275 to the fertilizer equations and 0.219 to the manure equations, implying that 72.5% of fertilizer P and 78% of manure P are not available for runoff. This study underlines the importance of considering the relative weights of the various components of P loss as new models are developed and validated.

Estimating dissolved phosphorus losses from legacy sources in pastures: The limits of soil tests and small-scale rainfall simulators.

A legacy of using P fertilizers on grazed pastures has been enhanced soil fertility and an associated increased risk of P loss in runoff. Rainfall simulation has been extensively used to develop relationships between soil test P (STP) and dissolved P (DP) in runoff as part of modeling efforts scrutinizing the impact of legacy P. This review examines the applicability of rainfall simulation to draw inferences related to legacy P. Using available literature, we propose a mixing layer model with chemical transfer to describe DP mobilization from pasture soils where readily available P in the mixing layer is rapidly exhausted and contact time controls DP concentrations responsible for subsequent DP mobilization. That conceptual model was shown to be consistent with field monitoring data and then used to assess the likely effect of rainfall simulation protocols on DP mobilization, highlighting the influence of soil preparation, scale and measurement duration, and, most important, hydrology that can facilitate the physical transport of P into and out of surface flow. We conclude that rainfall simulation experimental protocols can have severe limitations for developing relationships between DP in runoff and STP that are subsequently used to estimate legacy P contributions to downstream water resources.

Larger phosphorus flux triggered by smaller tributary watersheds in a river reservoir system after dam construction

Water level fluctuation and modification in human activities induced by dam construction have significantly affected the production and input of nutrients in the tributary watersheds. In this study, numerical simulation and time series analysis methods are used to explore the input of phosphorus (P) in different types of tributary watersheds around the reservoirs in river reservoir systems and the impact of dam construction on reservoir water quality. Watersheds within a reservoir were divided into larger and smaller tributary watersheds according to whether their area was greater than or less than 1000 km2. The results showed that smaller tributary watersheds, which account for 29% of the area of the Three Gorges Reservoir Region (TGRR), transported approximately 36%~45% of P and 43.7%~47.8% of sediment deposited into the mainstream from 2003 to 2017. P from the smaller tributary watersheds of the reservoir had a stronger influence on the aquatic environment of the river-reservoir system than that from the larger tributary watersheds. In addition, the annual mean contributions of the P inputs from the “three rivers” (the Yangtze River, the Jialingjiang River and the Wujiang River) and tributary watersheds within the reservoir were 68.76% and 31.18% from 2003 to 2017, respectively. The dam altered the composition of the form of P in the river-reservoir system, and the waterbody close to the dam was identified as the main area containing dissolved P (DP) enrichment. Accordingly, the risk of eutrophication remains high in head area of the dam due to the relatively high and stable P concentration. This study provides critical information for the management of nutrients in a river-reservoir system and the prevention of eutrophication of water bodies.

Highly efficient removal of phosphorus from agricultural runoff by a new akadama clay barrier-vegetated drainage ditch system (VDD) and its mechanism

A vegetated drainage ditch (VDD) system is an effective management practice for removing excess phosphorus (P) from agricultural runoff. However, the maximization of P removing efficiency by VDD remains a challenge. In this study, new VDDs with akadama clay barriers (particle size of clay: 1–6 mm; height of barrier: 5–15 cm and length of barrier: 10–90 cm) were designed in lab scale, and the mechanism of phosphate removal by akadama clay was investigated. It was found that a new VDD with akadama clay barriers (particle size:1 mm; height:10 cm and length: 90 cm) exhibited the highest removal efficiency of total P (TP) (97.1%), particulate P(PP) (96.9%), and dissolved P (DP) (97.4%), respectively. The retained P was mainly adsorbed in akadama clay barrier sections, and a low concentration of P was observed in soil sections in the new VDD. The maximum adsorption capacity of phosphate to akadama clay was 5.06 mg/g at 298 K, and XPS analysis indicated that phosphate was adsorbed by the inner-sphere complexation formation with the metal elements (Al, Fe). This study indicates that the new VDD with akadama clay barriers is a promising technique to efficiently remove P from agricultural runoff and significantly minimize the risk of P release into streams through runoff.

An internet-based smart irrigation approach for limiting phosphorus release from organic fertilizer-amended paddy soil

We are still challenged to fully understand to what extent controlling irrigation inputs is important for limiting phosphorus (P) losses from paddy soils and how this affects the contribution of dissolved P (DP), particulate P (PP), and colloidal P (Pcoll) fractions in P losses. For this investigation, an internet-based smart irrigation system was developed to precisely implement different irrigation scenarios––flooding irrigation (FI) and two water-saving irrigation (WSI) scenarios of intermittent (II) and controlled irrigation (CI). A simulation experiment was conducted and the concentrations of total P (TP), DP, PP, and Pcoll released to floodwater (FW) and leachate (LW) were determined during a rice season after the addition of different P forms (chemical fertilizer (CP), biogas slurry (BP), and manure (MP)) at a rate of 40 kg P·ha−1. The results revealed that the CI scenario effectively decreased P losses in FW (∼51%) and LW (∼63%) with a positive WSI ratio (39.1%), while II reduced it in FW by ∼11% and in LW by ∼27% with a WSI ratio of 11.0% compared with FI. The BP and MP additions caused a higher risk of P losses than CP under FI, with lower risk under WSI. DP largely contributed to P losses (FW: 30%–71%; LW: 42%–66%); however, more PP was released to FW under II (37%–54% of TP). The Pcoll (FW: 5%–23% and LW: 6%–24%) was more sensitive to release at initial periods after fertilization on account PP. This work provides a promising approach to timely control irrigation inputs, which could limit P losses from paddy soil; however, there remains a need to assess and generalize our initial evidence at field scales.

Performance of a Ditch-Style Phosphorus Removal Structure for Treating Agricultural Drainage Water with Aluminum-Treated Steel Slag

Several structural, treatment, and management approaches exist to minimize phosphorus (P) transport from agricultural landscapes (e.g., cover cropping and conservation tillage). However, many of these practices are designed to minimize particulate P transport and are not as effective in controlling dissolved P (DP) losses. Phosphorus removal structures employ a P sorption material (PSM) to trap DP from flowing water. These structures have been successful in treating surface runoff by utilizing aluminum (Al)-treated steel slag, but subsurface tile drainage has never been tested with this material. The goal of this study was to evaluate the performance and economics of a ditch-style P removal structure using Al-treated steel slag for treating agricultural subsurface drainage discharge. The structure treated subsurface drainage water from a 4.5 ha agricultural field with elevated soil test P levels. Overall, the structure removed approximately 27% and 50% of all DP and total P (TP) entering the structure, respectively (i.e., 2.4 and 9.4 kg DP and TP removal). After an initial period of strong DP removal, the discrete DP removal became highly variable. Flow-through analysis of slag samples showed that the slag used to construct the structure was coarser and less sorptive compared to the slag samples collected prior to construction that were used to design and size the structure. Results of this study highlight the importance of correctly designing the P removal structures using representative PSMs.

Sources, Transport, and Management of Phosphorus Loss during the Cranberry Harvest

Wet (flood) harvesting is essential to commercial cranberry (Vaccinium macrocarpon Ait.) production in Massachusetts, where one‐fifth of the US cranberry crop is produced. However, periodic flooding may lead to impaired water quality in lakes that receive harvest flood discharges. In this study, harvest flood inputs and outputs of P were measured to determine the net flux of P (Mnet) from a 19.2‐ha cranberry bog and its five bog units. Results showed that the cranberry bog was a source of dissolved P (DP) (Mnet = 0.32 kg P ha−1) and a minor sink of particulate P (PP) (Mnet = −0.03 kg P ha−1). For the five bog units, values of Mnet were highly variable, ranging from −0.49 to 1.48 kg P ha−1 with a coefficient of variation of 223% for DP. Variation in Mnet was not strongly related to P fertilizer rate, soil test P, or flood holding time, but was inversely related to the water flux from the cranberry bog to the underlying aquifer. Groundwater concentrations of DP were not statistically different before, during, or after the harvest flood, suggesting minimal subsurface leaching of P to shallow groundwater. Collectively, these findings point to soil P retention in some cranberry bogs, as might be expected in natural wetlands. Although there is potential for subsurface P leaching, the use of select cranberry bogs as filter beds of high‐P floodwater may help to curtail surface water export of P from cranberry agriculture.Core Ideas Wet (flood) harvested cranberry bogs may contribute to water quality problems. Harvest flood P losses varied from 0.49 to 1.48 kg P ha−1 for five cranberry beds. Harvest flood P losses were not related to P fertilizer, soil P, or flood length. Rather, the best indicator of harvest flood P loss was groundwater recharge. Groundwater recharge may facilitate P sorption and reduce harvest flood P losses.

Natural and anthropogenic determinants of riverine phosphorus concentration and loading variability in subtropical agricultural catchments

Natural and anthropogenic determinants of riverine phosphorus (P) pollution strongly vary with different ecological and socio-economic conditions and represent a substantial challenge to aquatic environment protection and ecological restoration in agricultural catchments. Riverine water flux and total P (TP) and dissolved P (DP) concentrations were observed, and major catchment geometric, landscape and anthropogenic characteristics were investigated in one forest and ten agricultural catchments in subtropical China during 2011–2017 to identify the key determinants of the catchment riverine P levels and loadings and to develop prediction functions for these P levels and loadings. The results suggested that 39% of the collected stream water samples were determined to have TP pollution, indicating moderate riverine P pollution in the catchments. The catchment riverine P levels illustrated an increasing P trend during 2011–2016 but a decreasing P trend in 2017 through the Hodrick-Prescott (HP) filter analysis, and the decreasing trend was mainly caused by reduced catchment livestock density. Landscape configuration (cohesion index (COHESION), aggregation index (AI), mean shape index (SHMN), and patch density (PD)) and anthropogenic activities (livestock density) were identified as the major determinants of riverine P concentrations and loadings through partial least squares regression (PLSR) analysis, of which cohesion index and livestock density were the only two variables that had a variable importance for the projection (VIP) value greater than 1.0; this result confirmed the substantial effects of these variables on riverine P. The multiple linear regression prediction functions showed generally acceptable performances (R2 ≥ 0.40) for riverine P but relatively poor performance in predicting P loadings (R2 = 0.40–0.46) in comparison to predicting P concentrations (R2 = 0.51–0.54), probably due to the variations in the hydrological process in subtropical China. Therefore, the results provide useful information for identifying the natural and anthropogenic determinants of riverine P to control this type of P in subtropical agricultural catchments.

Direct seeding for rice production increased soil erosion and phosphorus runoff losses in subtropical China

Estimating soil erosion and nutrient losses from surface runoff in paddy fields is essential for the assessment of sustainable rice (Oryza sativa L.) production and water quality protection. Different rice establishment methods have been used in the last three decades in Asia; however, it is still unclear how these methods influence sustainable agriculture and environmental protection in humid areas. The aim of this study was to evaluate the impacts of rice establishment method on soil erosion and phosphorus (P) losses from surface runoff in Hydragric Anthrosols under a subtropical monsoon climate. Total suspended solids (TSS), total P (TP), dissolved P (DP), and particulate P (PP) runoff losses were measured under four rice establishment treatments in 2013 and 2014, including traditional manual transplanting (TT), mechanical transplanting (MT), dry direct seeding (DD), and wet direct seeding (WD). The results showed that the seasonal TSS in the runoff varied from 59.9 to 829.8 kg ha−1 in the two years. Compared with TT, the DD significantly increased the TSS by 481% in 2013 and by 349% in 2014, while the WD significantly increased TSS by 783% in 2013 and by 571% in 2014. In the 2013 and 2014 rice seasons, the field-observed TP runoff losses were from 0.18 to 1.51 kg ha−1. Compared with TT, the DD significantly increased the TP lost by 222% in 2013 and by 197% in 2014, whereas the WD significantly increased the TP lost by 483% in 2013 and by 387% in 2014. However, the TSS and P losses from the MT and TT were similar in both years. The PP runoff losses accounted for 58–77% of the seasonal TP lost. These findings demonstrate that the conversion of traditional manual transplanting to direct seeding increased soil erosion and P runoff losses in subtropical China.

Effects of Manure and Tillage on Edge-of-Field Phosphorus Loss in Seasonally Frozen Landscapes.

Environmental conditions and management practices affect nutrient losses in surface runoff, but their relative impacts on phosphorus (P) loss during frozen and nonfrozen ground periods have not been well quantified. More specifically, the relative importance of manure application, tillage, and soil-test P (STP) has not been assessed at the field scale. In this study, we compiled a dataset composed of 125 site-years of data from 26 fields that were continually monitored for edge-of-field P loss during snowmelt and storm events. Regression tree analyses were performed to rank the level of influence each environmental and management factor had on nutrient loads. Dissolved P (DP) was the majority of the total P (TP) during frozen conditions, but a small portion of TP during nonfrozen conditions. Manure application had a greater influence on the flow-weighted mean concentrations (FWMCs) of TP and DP during frozen conditions than during nonfrozen conditions. No-till resulted in greater TP and DP FWMCs during frozen conditions than conventional tillage, whereas the opposite effect for TP FWMC was seen during nonfrozen conditions. However, regression tree analysis revealed that STP (0- to 5-cm depth) was the most important factor in predicting DP and TP FWMCs during frozen conditions and DP FWMC during nonfrozen conditions. Extremely high STP values were associated with late-frozen manure applications and grazed pastures. Reducing surface P loss in seasonally frozen landscapes will require prioritizing management strategies that avoid manure application through early- and late-frozen conditions and lead to a drawdown of STP, particularly in the top 5 cm.