Total P Research Articles

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 > 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.

Evaluation of phosphorus runoff from sandy soils under conservation tillage with surface broadcasted recovered phosphates

Potential new sources of phosphorus (P) fertilizer are the recovered P from livestock wastewater through chemical precipitation and the ash from combusting animal manures. Although most of the research on P losses from conservation tillage include high water-soluble P compounds from commercial fertilizer sources, information on the use of non-conventional, low water-soluble, recycled P sources is scarce. Particularly for sandy soils of the United States (US) Southeastern Coastal Plain region, research driven information on P loss into the environment is needed to determine recommendations for a direct use of new recycled P sources as crop P fertilizers. The objective of this study is to investigate the potential P runoff from sandy soils under conservation tillage, fertilized with recovered P from liquid swine manure and turkey litter ash in comparison with commercial P fertilizer triple superphosphate (TSP). The field study included two typical sandy soils of the US Southeastern Coastal Plain region, the Noboco and Norfolk. Simulated rain corresponding to the annual 30-min rainfall in the study site (Florence County, South Carolina) was applied to plots treated with recovered P from liquid swine manure, turkey litter ash, and TSP, including a control with no P added. The runoff was monitored and sampled every 5 min during the test and composite soil samples were collected from the top (0–15 cm) and subsurface (15–30 cm) soil layers in each plot. Laboratory analyses were conducted to quantify both total P (TP) and soluble reactive P (SRP) in runoff samples, and the soil test P in the soil layers. Two-way analyses of variances show significant treatment effects on both TP and SRP runoff. The quantities of SRP runoff from plots treated with the recovered P from swine manure and turkey litter ash represent respectively 1% and 7–8% of SRP runoff from plots treated with TSP. Hence, the use of the recovered P materials as crop P fertilizers through surface broadcast application present less environmental risks compared to commercial TSP.

Modeling phosphorus losses to subsurface drainage under tillage and compost management

While agriculture consumes 80–90 % of the world's annual phosphorus (P) production, only 20 % is utilized effectively by plants. Efforts to reduce agricultural P losses through various best management practices (BMPs) including no-till and organic fertilizer have helped substantially mitigate P pollution. The objective of this study is to investigate the long-term P losses through tile drainage as affected by tillage and compost amendment using the newly-developed RZWQM2-P model. We found that the model accurately simulated field-measured annual drainage water flow, as well as annual particulate P (PP) and total P (TP) losses in tile drainage, although it underestimated dissolved reactive P (DRP) when compost was applied. Long-term simulation results showed that tile drainage flow was negatively correlated with tillage intensity (TI, between 0 and 1), and tile-drainage-borne P losses were negatively correlated with TI and manure/compost P mix efficiency (ME, between 0 and 1) with soil after tillage. Specifically, when TI increased from 0 (no-till) to 0.93 (moldboard plow), drainage flow, DRP, and PP losses decreased by 11.49 %, 48.12 %, and 30.29 %, respectively. Similarly, when ME increased from 0 (no-till) to 0.5 (Tandem Disk), DRP and PP losses through drainage flow reduced by 53.98 % and 30.95 %, respectively. ME was not directly associated with drainage flow volume in the model. Overall, the RZWQM2-P model can accurately simulate PP and TP losses on an annual basis, although DRP loss prediction still needs to be improved, and it can be used as a tool to evaluate tillage effects on P loss from tile-drained agricultural land under manure or compost application.

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.

Study on the sediment and phosphorus flux processes under the effects of mega dams upstream of Yangtze River

The upper Yangtze River (UYR) plays an important role in water supply, hydropower generation, environmental and ecological protection. Constructions of Mega cascade reservoirs have significantly affected the transport of sediment and P, but the evolution of sediment and P in the mega cascade reservoirs of the UYR is unclear. This study investigated the variations in sediment load and total P (TP) flux based on the flow and sediment data from 1990 to 2019 and TP concentrations from 2005 to 2019. In addition, the proportion of sediment load and TP flux from tributaries, variations in the concentrations of particulate P (PP) and dissolved P, trapping effect of dams, and statistical uncertainties were analyzed and discussed. The main results are as follows: (1) the sediment load and TP flux evidently decreased after the impoundment of reservoirs in the UYR and Jinsha River, and the contribution rate of TP flux from main tributaries (except Wu River) to mainstream increased by 3.82–24 %; (2) the error of TP flux calculated by daily and monthly data is within 30 %, which shows that the uncertainty range is clear at some degree attributed to the different monitoring frequency, and the concentration of PP in flood season is greater than that in non-flood season; (3) the total retention rates of sediment and TP in the Three Gorges Reservoir and Gezhouba were 86.78 %, and 49.83 % (2009–2012), respectively, but decreased to 82.85 % and 15.26 % (2013–2019), and the values in Xiangjiaba and Xiluodu were 97.83 % and 60.27 % (2013–2019). The retention rates of newly built reservoirs (Wudongde and Baihetan) were predicted using an empirical method, and the results revealed that new dams would facilitate long-term reduction in sediment downstream.

Nitrogen, Phosphorus, and Snowmelt Runoff Losses after Application of Dairy Manure with Variable Solids Content

Snowmelt nutrient loss is an important but poorly understood process in cold climates. We measured nutrient losses at three sites after dairy manure was applied on top of an established snowpack. Treatments included no manure controls and three manure solids levels (12–19.4% solids = High; 7.5–8.0% = Medium; 2.9–5.5% = Low) applied at 26,670 L ha−1 to all treatments. Snowmelt runoff was monitored and analyzed for dissolved reactive P (DRP), total P (TP), total N (TN), ammonium-N, organic-N, and total solids (TS) concentrations. Results showed that manure application dramatically increased N and P loading compared to controls. Across site-years, manure application increased average runoff TP, DRP, and TN concentrations by 1.3- to 13.3-fold, 1.5- to 21-fold, and 1.4- to 14.2-fold, respectively, relative to controls. While cumulative N, P, and TS losses generally increased with manure solids, Medium/Low showed equal or greater nutrient transfer to runoff for some events. TN and TP lost in runoff were linearly related to manure solids concentration; however, N and P loss as a percent of applied showed the opposite trend. The results indicate that applying manure on top of snow resulted in high nutrient losses when runoff occurred regardless of manure solids content.

Characteristics of Organic Phosphorus Pool in Soil of Typical Agriculture Systems in South China

Organic phosphorus (P) is an important potential source of plant P nutrition in agro-ecosystems. It was hypothesized that the soil organic P pools were distinguished one from another by different land-utilization patterns. A total of 38 sites were sampled, to clarify the organic P pool and its distribution in paddy fields, vegetable fields, and orchards. Soil organic P fractions, including labile organic P (LOP), moderately labile organic P (MLOP), moderately resistant organic P (MROP) and highly resistant organic P (HROP) were examined. Results showed that the soil total P (TP) and available P (AP) concentration have enhanced by 138% and 1559%, respectively, over the last four decades. The soil total organic P (TOP) accounted for 21.4% of the TP pool. Soil MLOP dominated the organic P reservoir, irrespective of land-planting pattern. Soil organic P fractions ranked as MLOP > MROP > HROP > LOP. The highest accumulations of TP, AP and TOP were in the vegetable fields, followed by orchards and paddy fields. The vegetable fields had higher LOP and MLOP levels than those of the paddy fields and orchards, whereas the paddy fields exhibited higher concentrations of MROP, and HROP. Soil pH, organic matter and available nitrogen all contributed to the buildup of the organic P pool. It was suggested that soil organic P should be considered preferentially in the management of the plant P nutrient in regional planting systems.

A Comparison of Soil C, N, and P Stoichiometry Characteristics under Different Thinning Intensities in a Subtropical Moso bamboo (Phyllostachys edulis) Forest of China

Land management using suitable thinning intensities can promote the yield of Moso bamboo (Phyllostachys edulis) forests and alter the nutrient content and stoichiometric characteristics within the soil. However, the effects of different thinning intensities on soil carbon (C), nitrogen (N), and phosphorus (P) stoichiometry of P. edulis forests have not been comprehensively studied. Here, we evaluated the effects of three thinning intensities—no thinning control (NT), moderate thinning (annual removal of 15% of mature bamboo, MT), and heavy thinning (annual removal of 33% of mature bamboo, IT)—on the soil organic C (SOC), total N (TN), and total P (TP) stocks and their stoichiometry characteristics of a P. edulis forest located in the subtropical zone. The results showed that SOC, TN, and TP stocks decreased with increasing soil depth after three years of thinning. The SOC, TN, and TP stocks and the ecological stoichiometry ratios were varied with the change of thinning intensity and SOC stocks declining with the increased thinning intensity, but TN and TP stocks for the MT treatment were enhanced. The order of TN and TP stocks was MT > NT > IT. In comparison to CK, TN and TP stocks for MT increased significantly by 18.8 and 37.3%, while SOC, TN, and TP stocks for IT decreased by 31.0%, 7.2%, and 21.4%, respectively. The C:N and C:P ratios of MT decreased by 32.8% and 39.0%, and those of IT decreased by 26.5% and 15.6%, respectively. In summary, we conclude that the MT is an effective management strategy to promote soil nutrient cycling and provides a reference for formulating management strategies in subtropical Moso bamboo forests.

Influence of Potamogeton crispus harvesting on phosphorus composition of Lake Yimeng

Harvesting is an important method used to control the overproduction of Potamogeton crispus in lakes. A three-year comparative field study was performed in a eutrophic lake (harvested area) and its connected lake (non-harvested area) to determine the effects of harvesting on the phosphorus (P) composition and environmental factors in the water and sediment. Results revealed that harvesting significantly reduced the dissolved total P and dissolved organic P (DOP) and increased the alkaline phosphatase activity and particulate P (PP) in the water. No significant differences were detected in the water total P (TP), soluble reactive P, chlorophyll-a, pH, and dissolved oxygen between the harvested and non-harvested areas. Sediment TP and organic P (OP) were significantly reduced in the harvested area. Harvesting changed the P composition in the water. In the non-harvested area, P was mainly formed by DOP (40%) in the water body, while in the harvested area, PP was the main water component (47%). Harvesting increased the proportion of inorganic P (IP) in the sediment and decreased the proportion of OP. In the water, the IP to TP ratio in the non-harvested and harvested areas were 58.26% and 63.51%, respectively. Our results showed that harvesting changed the P composition in the water and sediment. In the harvesting of submerged vegetation, our results can serve as a reference for the management of vegetation-rich lakes.

Phosphorus Fractions in Temperate Grassland Soils and Their Interactions with Agronomic P Tests

Phosphorus (P) is a major nutrient for plant growth and animal health, and its availability in soil is influenced by agronomic management and soil properties. This study examined the distribution of labile and non-labile soil P fractions in grassland and the properties that influence their distribution in temperate grasslands. Eleven fractions were identified as, labile (H2O.P and NaHCO3.P), moderately labile (NaOH.P) and plant non-available (NaOH.P, HCl.P and residual P). The residual P, moderately labile organic (NaOH.Po) and inorganic (NaOH.Pi) fractions comprised 38%, 24% and 15% of the total P (TP), respectively. The residual and organic (Po) fractions were associated with extractable Fe, and the NaOH.Pi fraction was associated with extractable Al. Agronomic reagents (Morgan’s and Mehlich3) targeted specific fractions based on their affinity for different soil elements. Morgan’s P was associated with extractable and residual Ca and in high Ca soils, and overestimated plant-available P by extracting non-labile Ca.P forms (HCl.P). The Mehlich3 P test was associated with NaOH.Pi fraction and showed a preference for Al.P oxides. This study indicates that Mehlich3 reagent, which provides a wider suite of elements such as P, Ca, Al and Fe, will suit as a better indicator for soil P dynamics and improved P advice to farmers. The inclusion of additional soil chemico-physical characteristics would improve agronomic soil testing, benefitting farmers’ advice.

Nutrient losses over time via surface runoff and subsurface drainage from an agricultural field in northern Sweden.

Nitrogen (N) and phosphorus (P) losses, via both surface runoff and subsurface drainage water, were monitored in an agricultural field in northern Sweden for 32 yr. The objective was to determine losses of N and P in a long-term perspective in relation to meteorological factors and impacts of agricultural land use, with a focus on relative contributions of surface runoff and subsurface drainage water to N and P losses. In order to collect surface runoff water, an embankment was installed on three sides of the field, and the fourth side had an open ditch that drove runoff water to a measuring station. Subsurface water draining from the field was collected in a fishbone-shaped drainage system that terminated at the measuring station. In 50% of years (16/32), mean annual concentration of total N (TN) was significantly higher in subsurface drainage water than in surface runoff water. An opposing trend was seen for total P (TP), with mean annual concentration being significantly higher in surface runoff water than in subsurface drainage water in all but 3 of the 32 yr monitored. Years with a barley crop had higher TN concentration in subsurface drainage water but no difference in surface runoff compared with years with ley. In contrast, years with barley had lower TN concentration in surface runoff than years with ley, with no difference in TP in subsurface drainage water.

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.

The spatial distribution and characterization of phosphorus and nitrogen in a water-carrying lake: a case study of Lake Jiaogang, China.

The sources of P and N in water-carrying lakes include exogenous input and endogenous release. However, the influence of pollution from different sources on the dynamic distribution of N and P at the sediment-water interface in water-carrying lakes remains unclear. The objectives of this study were to investigate the differences in dynamic distribution characteristics of P compounds and N elements in Lake Jiaogang, a major water-carrying lake in eastern China. Four functional regions with different types of pollutant sources and different kinds of aquatic plants were selected to study the distribution of total P (TP), inorganic P, organic P, ammonium (NH4+-N), and nitrate (NO3--N). The results revealed that regions with internal-source pollutants contained the highest concentration of TP, Ca-P, and Fe-P with high concentrations. L-P, Al-P, mostly organic P, and soluble reactive phosphorous (SRP), the region with internal-source pollutants were lower than that with the imported-source pollutant. The concentration of dissolved NH4+-N showed high in regions with imported-source pollutants, however, in regions with internal-source pollutants, the dissolved NO3--N was with the highest concentration. Overall, P from upstream was still dominant in the sediments despite uptake by the aquatic plants. SRP showed high concentration in regions with imported-source pollutants due to the imported pollution and the improved bioavailability by plant root exudates. Feces and feed residues from aquatic livestock breeding resulted in the highest concentration of TN, NH4+-N, and dissolved NO3--N in the sediments of the region with internal-source pollutants. High concentrations of dissolved NH4+-N were due to the input of N from imported source pollutants. This study provides insights into the contributions of P and N to the eutrophication of the water-carrying lake.

Effects of environmental and agronomic factors on pond water quality within an intensive agricultural landscape in subtropical southern China

Water quality deterioration, such as eutrophication, can contribute to the degradation of farm pond ecosystems, threatening numerous ecological services and socioeconomic benefits. However, the variability of water quality and the complexity of influencing variables pose large uncertainties for pond management practices and watershed planning. This study integrated a self-organizing map (SOM) and partial least squares structural equation modeling (PLS-SEM) to evaluate the nitrogen (N) and phosphorus (P) variations in 39 typical farm ponds in the Dongting Lake basin, and related the variations to pond internal factors, external environment, and agronomic management. The results indicated that 39 monitored farm ponds faced a high risk of eutrophication owing to high N and P levels, and that total N (TN), total P (TP), and particulate P (PP) generally exceeded the threshold of level V surface water quality standards in China (2.0 mg N L−1 and 0.2 mg P L−1). Simultaneously, pond water quality showed high spatiotemporal variability, and pollution hotspots occurred mostly during the overlapping periods of fallow-dry-winter and planting-rainy-spring. Based on the constructed SEM model, external environmental factors (meteorology, catchment landscape composition, configuration, topography, and soil chemical properties), pond internal characteristics, and agronomic management combined explained 60.2 ± 2.9 % and 54.2 ± 3.1 % of the N and P variations, respectively. There were intricate interactions among the above latent variables, including such meteorology positively moderated the paths of soil chemical properties→pond P and landscape composition→pond N and P; landscape composition, soil, and pond internal characteristics mediated the effects of other variables on variations of N and P. The total effects (indirect effects + direct effects) of landscape composition on the variations of pond N and P were higher than those of other variables. Among all the indicators composing latent variables, agricultural and residential land area percentage, rainfall, water depth, and fish farming were relatively important in pond water quality variations. The constructed model and analytical results offer essential information for the accurate management and restoration of pond water quality.

Effects of Organic Materials on Phosphorus Fractions and phoD-harboring Bacterial Community in Karst Soil

Efficient utilization of organic materials based on the rich resources in the karst region can promote soil fertility. Microorganisms have a crucial influence on soil phosphorus availability. phoD is considered to be the encoding phosphatase gene that can reflect the hydrolysis of organophosphorus compounds for the soil bacterial community. Molecular analysis of the phoD-harboring bacterial gene provides insight into promoting soil phosphorus availability under different fertilization managements. However, the effects of organic materials on soil phosphorus fractions associated with phoD-harboring bacterial communities are poorly understood. This study comprehensively investigated the effects of organic materials on soil phosphorus availability and explored environmental drivers of phoD-harboring bacteria in the Karst region. Here, six treatments were designed in the field as follows:non-fertilized control (CK), inorganic fertilization (NPK), inorganic fertilization combined with straw (NPKS), inorganic fertilization combined with manure (NPKM), inorganic fertilization combined with sludge (NPKL), and inorganic fertilization combined with sugarcane ash (NPKA). The phoD-harboring bacterial community in Karst region soil was analyzed using high-throughput sequencing. The results showed that the content of total P (TP), Olsen-P, and Ca2-P increased with the years after organic material application, whereas the content of CaCl2-P first decreased and then increased. Compared to that under the CK treatment, organic material application, especially NPKL treatment, significantly increased soil total nitrogen (TN), TP, Olsen-P, CaCl2-P, and Ca2-P contents, followed by those in the NPKA and NPKM treatments. Correlation analysis showed that the contents of CaCl2-P, Ca2-P, and Olsen-P were significantly positively correlated with soil exchangeable calcium (Ca-ex) content. Redundancy analysis (RDA) showed that TN, Ca-ex, soil organic carbon (SOC), and total potassium (TK) contents were the key factors affecting soil P fractions. Using high-throughput sequencing, we found that only NPKS increased the richness of phoD-harboring bacteria compared to that under the control treatment. No significant difference was observed in the phoD-harboring bacterial community among all treatments. The RDA model selected the Ca-ex, TK, Olsen-P, pH, and SOC as the key environmental predictors for the phoD-harboring bacterial community. In summary, soil phosphorus availability can be improved through the input of organic materials and inorganic fertilizer combined with manure, sludge, and ash. These additions were suitable for nutrient management and sustainable development in farmland soil in the Karst region of Guangxi.

Phosphorus and nitrogen deposition within a large transboundary watershed: Implications for nutrient stoichiometry and lake vs watershed budgets

Atmospheric deposition is an important source of both phosphorus (P) and nitrogen (N) to lakes and their watersheds, but the two nutrients are rarely reported together. For the first time, we measured total P (TP) and N (total, ammonium, NH4-N and nitrate, NO3-N) bulk deposition to the Lake of the Woods (LoW) watershed, a large international lake that experiences frequent, lake-wide cyanobacterial blooms. Phosphorus deposition was highly variable both spatially and seasonally, with on average >75 % of annual deposition occurring in the spring and summer months, associated with local biogenic input. In contrast, winter TP deposition was relatively low and spatially invariant, and not affected by local sources. Importantly, these results suggest that P deposition may be a much larger source of input to the LoW as a result of its tortuous shoreline and abundance of forested islands (>5000), which are concentrated in the northern, Canadian waters and greatly extend the ‘shoreline influence’ within this lake. We suggest that a single annual TP load estimate is not appropriate for the LoW because winter deposition is likely much lower than past estimates whereas spring/summer deposition is substantially higher and could be an important, but previously unrecognized source, of bioavailable P to the nearshore waters. Further research is needed on the spatial and temporal patterns of P vs N deposition to the lake surface and their influence on primary productivity and algal species composition.

Linking soil phosphorus pools to drainage water quality in intensively cropped organic soils

Higher than average fertilization rates, as applied to mineral soils, are often recommended for cultivated organic soils (>20% organic matter), which over time, have led to phosphorus (P) pollution into receiving water bodies via subsurface tile drainage. Limited studies have documented the P pools within organic soils or their link to tile drainage water quality. This study quantified the different soil P pools found in organic soils under two water management practices: controlled drainage (CD) and pump drainage (PD) systems. Phosphorus availability in these soils was assessed by measuring inorganic P (Pi) and organic P (Po) via sequential fractionation; available P via Bray-1 P testing; and microbial P, along with crop root total P uptake. Drainage water samples were also analyzed for total P (TP) and dissolved reactive P (DRP). The results identified calcium (Ca) bound P as the largest P pool in these organic soils. Its correlation with other P pools suggests that it acts as a P sink in these soils. The correlation analysis further suggests that aluminum (Al) and iron (Fe) bound P is a driving force for P movement in the soil, as it had the most significant relationship with the P parameters in both the soil and drainage water. The regression analysis of TP found that the fertilizer and root P content were significantly related to the changes in drainage water quality at both sites. A P balance indicated that more fertilizer was being applied each year than was being used by the crops or released into the water, causing an accumulation of legacy P in the soil. Overall, the soil P pools affect the fluctuations of P concentration in the tile drainage water quality, featuring the complex relationship of the soil-water P dynamic.

Changes in nitrogen and phosphorus within a decade in waters along a major canal and estuary in South Florida.

The West Palm Beach-C51 (WPB-C51) canal connects Lake Okeechobee with Lake Worth Lagoon (LWL) in South Florida. This canal receives discharges from Lake Okeechobee and from agricultural and urbanized areas. The objectives of this research were to determine spatial and temporal differences and trends of N and P forms along the WPB-C51 canal and LWL for 2009-2019. Data were obtained from the South Florida Water Management District. Average total P (TP) and total N (TN) concentrations at studied stations ranged from 55 to 183μg L-1 and from 0.61 to 2.62mg L-1 , respectively. The TP and TN concentrations at LWL inflow were higher than the State of Florida's regulatory criteria (49μg L-1 and 0.66mg L-1 , respectively). The TP and TN concentrations generally declined from Lake Okeechobee to LWL; however, agricultural drainage was highest for soluble reactive P (SRP) and all N forms. Temporal trends showed predominantly increasing trends for concentrations of P forms. Total P and TN load rates increased by 0.005 and 0.032 t yr-1 , respectively, at LWL inflow. Results suggest nutrient assimilation by plants and P precipitation along the WPB-C51 canal. Possible sources of SRP and N are fertilizers, nitrification, and organic matter mineralization. Increasing trends in P concentration are possibly due to legacy P and urbanization, and increases in TP and TN loads can be due to larger Lake Okeechobee discharges and higher nutrient concentrations. Results emphasize the need to implement strategies to minimize nutrient input into LWL to meet its water quality goals.

Comprehensive effects of integrated management on reducing nitrogen and phosphorus loss under legume-rice rotations

Paddy fields-based cropping systems are usually located in areas with dense water networks, so nitrogen (N) and phosphorus (P) losses from rice paddy fields caused by runoff might pose a serious pollution risk to their surrounding water bodies. However, current research over establishing a low fertilizer input paddy-based cropping system with comprehensive management for reducing runoff losses of N and P is insufficient. A five-year field trial was carried out with a rice-fava planting system in the Erhai Lake watershed from 2015 to 2019. Three treatments were designed namely chemical fertilizer plus manure (CMF), reduced chemical fertilizer combined with manure at the same application rate under CMF treatment (RF), and returning straw plus chemical and organic fertilizers at the same rate with RF treatment (RFS). The mean annual runoff losses of total N (TN) and total P (TP) range from 0.99 to 1.39 kg ha −1 yr −1 and 0.09–0.12 kg ha −1 yr −1 . Compared with CMF treatment, RF had lower runoff losses of TN and TP by 20.86% and 23.05%, respectively, but the yields and soil fertility were also reduced. After returning straw, soil organic carbon (SOC), TN, and crop yields were maintained or even increased, and runoff losses of TN and TP were further reduced by 9.48% and 7.41%, respectively, compared with RF. Therefore, the runoff losses of N and P decreased by selecting the rice-fava rotation system and reducing chemical fertilizer input through manure application and straw returning, which greatly reduced the surplus N and P in this system. Moreover, the temporal variation in the concentration of TN and TP, along with the N:P ratio approved the existence of potential risk caused by TN and TP losses to the watershed in the early stage of rice growth. Overall, in addition to taking field measures to reduce the N and P runoff losses from paddy fields, the runoff water with high N and P concentrations in early rice growth stage cannot be ignored. • Rice-fava system with low fertilizer maintained yield and had low environment risk. • Straw returning ensured crop yields under substituting chemical fertilizer by manure. • Combined of straw returning and manure substitution reduced nutrient runoff loss. • Runoff N/P concentration and N:P ratio in early stage of rice may need interception.

Phosphorus removal, metals dynamics, and hydraulics in stormwater bioretention systems amended with drinking water treatment residuals.

Drinking water treatment residuals (DWTRs) are a promising media amendment for enhancing phosphorus (P) removal in bioretention systems, but substantial removal of dissolved P by DWTRs has not been demonstrated in field bioretention experiments. We investigated the capacity of a non-amended control media (Control) and a DWTR-amended treatment media (DWTR) to remove soluble reactive P (SRP), dissolved organic P (DOP), particulate P (PP), and total P (TP) from stormwater in a two-year roadside bioretention experiment. Significant reductions m SRP, PP and TP concentrations and loads were observed in both the Control and DWTR media. However, the P removal efficiency of the DWTR cells were greater than those of the Control cells for all P species, particularly during the second monitoring season as P sorption complexes likely began to saturate in the Control cells. The difference in P removal efficiency between the Control and DWTR cells was greatest during large storm events, which transported the majority of dissolved P loads in this study. We also investigated the potential for DWTRs to restrict water flow through bioretention media or leach heavy metals. The DWTRs used in this study did not affect the hydraulic performance of the bioretention cells and no significant evidence of heavy metal leaching was observed during the study period. Contrasting these results with past studies highlights the importance of media design in bioretention system performance and suggests that DWTRs can effectively capture and retain P without affecting system hydraulics if properly incorporated into bioretention media.