Particulate Phosphorus Research Articles

Structure liming reduces draught requirement on clay soil

Liming with ‘structure lime’, comprising approximately 80–85% ground limestone and 15–20% slaked lime, has been promoted in subsidised environmental schemes in Sweden since 2010 to increase clay aggregate stability and mitigate particulate phosphorus losses to surface waters. To date, approximately 65,000 ha have been structure-limed. Apart from stabilising aggregates, liming may also improve other physical properties, such as soil strength. This study examined the effect of increasing application rate (0–16 t ha-1) of structure lime on soil strength, approximated by horizontal (draught requirement) and vertical (penetrometer resistance) measurements, in eight field soils (clay content 26–38%) to which structure lime had been applied two, three, four or six years previously. Draught requirement when cultivating with a multipurpose cultivator significantly decreased (by 11%) with the highest application rate of structure lime (16 t ha-1) compared with an unlimed control. This reduced the wheel power requirement by 7.1 kW and diesel consumption by 1.2–1.4 L ha-1, and lowered CO2 emissions by 3–4 kg ha-1. To clarify the general effect of structure liming, the mean value of all limed treatments was compared with that of the unlimed control. This showed that structure liming in general significantly reduced the draught requirement (by 7%). However, penetrometer resistance measurements revealed no significant effects of structure liming and no relation between draught requirement and penetrometer resistance measurements. Overall, the results indicate that structure liming can reduce fuel consumption, due to easier soil tillage, and thus lower CO2 emissions.

High-Resolution Estimation of Suspended Solids and Particulate Phosphorus Using Acoustic Devices in a Hydrologically Managed Canal in South Florida, USA.

Conventional methods of measuring total suspended sediments (TSS) and total particulate phosphorus (TPP) are typically low-resolution and miss critical processes that impact their exports in aquatic environments. To create high-resolution TSS and TPP estimates, echo intensity (EI), a biproduct of velocity measurements from acoustic devices, was utilized. An acoustic Doppler velocimeter (ADV) and an acoustic Doppler current profiler (ADCP) were deployed in three locations in the L-29 Canal in South Florida, USA, to obtain estimates near the canal bed and in the water column, respectively. Corrections for transmission losses from the ADCP proved unnecessary due to the low vertical variability in the measured EI. EI calibrations were performed using artificially created TSS obtained from bed sediments (ADV) and gravimetrically measured TSS from water samples that matched the depths and times of the ADCP deployments. The measured TSS values were then analyzed for total phosphorus and converted to TPP estimates. The results showed that high TSS and TPP were caused by the rapid discharge releases typical of managed canals. This work demonstrates that high-resolution estimates are imperative for assessing the effects of such swift hydrologic changes on the potential export of sediments and nutrients to delicate ecosystems downstream.

Effect of Rational Fertilizer for Eggplants on Nitrogen and Phosphorus Pollutants in Agricultural Water Bodies

Excessive fertilizer application in the cropping industry leads to excessive nitrogen and phosphorus in surrounding water bodies, which causes farmers to increase economic cost and damage the environment. To address the problem, we built a crop-soil runoff soil column test system, setting eight fertilizer application levels for eggplants. Then, crop yield, soil fertility and pollutant concentrations in the receiving water bodies were measured. The process of fertilizer application on the water quality of surrounding receiving water bodies and the rationality of fertilizer application were analyzed. The results showed that crop yield, soil fertility, and pollutant concentrations in the receiving water increased with the increase in fertilizer application. The crop yield stabilized when the fertilizer application amount was higher than 0.12 kg/m2; the concentrations of total nitrogen (TN) and total phosphorus (TP) in the water increased significantly with the increase in fertilizer application, where particulate nitrogen (PN) and organic phosphorus (OP) were the key pollutants. In addition, crop growth had an interception effect on pollutant migration. The concentration of pollutants in the water was significantly lower in the late crop growth period (after flowering) than in the early. The crop had the best interception effect on pollutants when the fertilizer application was 0.12 kg/m2. The concentrations of TN and TP in the water were 29.7% and 22.3% after the flowering period, being lower than those before the flowering period. Therefore, a reasonable value of 0.12 kg/m2 is recommended for fertilizer application in this article. It can provide a reference for the fertilization system of eggplant planting in North China and theoretical support for the realization of clean production in small rural watershed planting.

Reservoir flood regulation affects nutrient transport through altering water and sediment conditions

The effect of reservoir construction on nutrient dynamics is well recognized, at flood event-scale influence of reservoir flood regulation on nutrient transport however has received less attention. Taking the Three Gorges Reservoir (TGR) in the Changjiang River as an example, during the TGR's regulation on a flood in Sep., 2021, this study collected water samples along the mainstream of the reservoir as well as pre/post-dam, with the aim to identify the impact of flood regulation on nutrient (nitrogen and phosphorus) distribution and transportation. Results show that nitrate nitrogen (NO3N) and particulate phosphorus (PP) were the main fraction of the total nitrogen (TN) and total phosphorus (TP) with the proportion of 46.5%-95.6% and 57.4%-81.6%, respectively. N and P responded different to flood regulation: (i) along the stream P concentration significantly decreased due to PP deposited with sediment while N concentration barely changed during flood regulation; (ii) P concentration was significantly higher at post-dam section than at pre-dam section, while N concentration maintained the same. The diffed response to flood regulation caused TN/TP ratio increased from 4 to 8 in the reservoir tail to over 20 near the dam, which probably arise eutrophication in the reservoir head area. This study reveals the influence of flood regulation on nutrient transport in flood event and provides scientific basis for reservoir management.

Modelling rainfall‐induced phosphorus loss with eroded clay and surface runoff

AbstractPhosphorus (P) loss via runoff will reduce soil fertility and cause water eutrophication. Although P is lost as both particulate phosphorus (PP) and soluble phosphorus (SP), the existing P transport models for landscapes rarely consider PP and its exchange with surface runoff. We developed an integrated P transport model which coupled both SP and PP transport mechanisms based on the Rose–Gao model and assessed it via laboratory experiments. We also introduced a temporal varying P partition coefficient Kd into the model to reveal the impacts of rapid changes in the water environment on P adsorption and desorption. Experiments using kaolinite mixed soil and montmorillonite mixed soil were conducted under artificial rainfall events. The results show that the P transport model simulates the concentrations of eroded sediment, SP, and PP in surface runoff, with good agreement with the measured values (all R2 > 0.88). Kaolinite mixed soil had larger sediment and SP concentrations in the runoff than montmorillonite mixed soil. In addition, compared with the no Kd model (Gao model) and the constant Kd model, our model provided simulation results that most closely matched the experimental data. Considering the influence of eroded sediment and the P dynamic partitioning between sediment and water to the surface, the P transport model can provide an effective tool for P dynamics with water and sediment in surface runoff.

Green Manure Amendment Increases Soil Phosphorus Bioavailability and Peanut Absorption of Phosphorus in Red Soil of South China

Peanut (Arachis hypogaea L.) is one of the most important crops produced worldwide. Peanut is the dominant crop in the typical upland red soil areas of China; however, phosphorus bioavailability in red soil is very low, which severely affects peanut production. To improve the phosphorus bioavailability, which substantially promotes the green development of peanut production, a peanut–green manure rotation field experiment was conducted with six treatments (milkvetch; radish; brassica rape; mustard rape; winter fallow and no-tillage), commencing in September 2017 in the red soil area of Jiangxi province, China. The results show that compared with no-tillage (NT) treatments, different green manure returning treatments had significant effects on soil pH, soil phosphorus components and available potassium content. The particulate phosphorus and soil available phosphorus contents in the green manure treatments were significantly higher than those in the winter fallow (WF) treatment. Compared with the WF treatment, the content of particulate phosphorous in brassica rape (BR), radish (R) and milkvetch (MV) treatments was significantly increased by 6.55%, 3.66% and 2.50%, respectively; the available phosphorus content in mustard rape (MR), BR, R and MV was significantly increased by 20.93%, 25.60%, 23.76% and 18.10%, respectively. In addition, the total phosphorus content of peanut shell in the MV and R treatment was significantly higher than that in the WF treatment, increasing by 33.47% and 60.66%, respectively. Compared with the WF treatment, the peanut biomass of MR, BR and R treatments increased significantly by 19.51%, 29.83% and 19.77%, respectively. The total phosphorus accumulation in all green manure treatments was higher than that in the WF treatment, and the MV treatment reached a significant level at 18.83%. Based on these results, the particulate phosphorus (PP) and available phosphorus were significantly affected by different green manure treatments; green manure amendment improves peanut phosphorus uptake. The use of green manure (especially milkvetch and brassica rape) can be recommended to improve phosphorus bioavailability and yield of peanut in red soil areas.

Exploring long-term trends in microcystin toxin values associated with persistent harmful algal blooms in Grand Lake St Marys

High external nutrient loads from agricultural runoff have led to persistent and highly toxic algal blooms in Grand Lake St Marys (GLSM) for decades. These pervasive blooms are concurrent with long-term (2009 – 2021) toxin and environmental monitoring, providing a robust weekly dataset for modeling microcystins. Median weekly microcystin concentrations (23.2 µg/L) routinely exceeded World Health Organization recreational limits (20 µg/L) for the study period (ranged 0.03 - 185.0 µg/L). Here, we used a Bayesian hierarchical dynamic linear model to hindcast weekly microcystin toxins using external nutrient loads from tributary data as well as internal lake nutrient and physicochemical concentrations. Overall, lake TN was the biggest driver of microcystin concentration in GLSM. Likewise, TN:TP was a strong negative driver of microcystin (i.e. low N:P ratios align with lower total microcystins), suggesting that N availability directly impacts toxins. External nutrient loading was positively related to microcystin during winter and spring; however, there was no relationship detected between toxin and external loading during summer or fall (particulate phosphorus exhibited the strongest signal but all external nutrients were unsurprisingly correlated). This lack of direct correlation on a weekly timescale between external loads and cyanobacterial toxins during the summer months likely results from nutrient saturation and reflects the importance of internal loading for bloom maintenance as supported by the correlation between in-lake TN and microcystin. Thus, management goals to reduce the highest biomass and toxins in the summer should focus on reduction of winter and spring external nutrient loads. Supporting this, both 2010 and 2021 had lower rain in the first half of the year (winter/spring), resulting in less loading, and experienced smaller/later low toxicity blooms. This suggests that, although internal nutrient loads are important for bloom maintenance, reduced external loads are an effective management strategy even in nutrient saturated systems such as GLSM.

Long-term dynamics and drivers of particulate phosphorus concentration in eutrophic lake Chaohu, China

Particulate phosphorus (PP) plays an important biological role in the eutrophication process, and is thus an important water quality parameter for assessing climatic change and anthropogenic activity factors that affect aquatic ecosystems. Here, we used 20-year Moderate Resolution Imaging Spectroradiometer (MODIS) data to explore the patterns and trends of PP concentration (CPP) in eutrophic Lake Chaohu based on a new empirical model. The validation results indicated that the developed model performed satisfactorily in estimating CPP, with a mean absolute percentage error of 31.89% and root mean square error of 0.022 mg/L. Long-term MODIS observations (2000–2019) revealed that the CPP of Lake Chaohu has experienced an overall increasing trend and distinct spatiotemporal heterogeneity. The driving factor analysis revealed that the chemical fertilizer consumption, municipal wastewater, industrial sewage, precipitation, and air temperature were the five potential driving factors and collectively explained more than 81% of the long-term variation in CPP. This study provides the long-term datasets of CPP in inland waters and new insights for future water eutrophication control and restoration efforts.

Flux and form of phosphorus in overlying water at the effluent section of the Three Gorges Reservoir from 1998 to 2019

总磷是长江流域备受关注的污染物。来自长江上游的物质输送对长江中下游、对入海口水域水生态都具有重要影响。研究了1998-2019时期长江上游和中下游之间的衔接断面暨三峡水库出水断面的磷通量及形态变化。整个研究时段分为3个阶段:1998-2002(阶段Ⅰ,三峡水库运行之前),2003-2013(阶段Ⅱ,作为过渡时期)及2014-2019(阶段Ⅲ,三峡水库实现175 m正常蓄水位且金沙江下游段向家坝和溪洛渡水库运行后),以阶段Ⅰ、Ⅲ为重点时段进行对比分析。研究表明,2014-2019年总磷年通量平均为5.67万t/a,比1998-2002年减少了38.0%;溶解态磷年通量为4.02万t/a,增加了60.0%;颗粒态磷年通量为1.67万t/a,减少了74.9%。磷的主导形态由颗粒态变为溶解态,溶解态磷通量占比由27.5%上升为70.9%;相应地,颗粒态磷通量占比由72.5%下降为29.1%。总磷、溶解态磷和颗粒态磷通量均表现为丰水期>平水期>枯水期。近20年来,水沙关系发生了巨大变化,含沙量(SS)与水量(Q)正相关性大幅下降,其拟合方程的斜率由1.44下降为0.10,R²由0.83下降为0.57。溶解态磷月通量在总磷月通量中的占比(λ_DF)随输沙量或泥沙含量(SS)的增加而减小的规律基本未变,2014-2019年λ_DF与SS的经验模型为λ_DF=1.2883-0.3688×lgSS(mg/L)。三大水库的拦沙作用和流域水土保持作用导致的水沙条件变化是磷通量及形态变化的主要原因。三峡水库出水生物可利用磷浓度升高及光能吸收增强对初级生产力的促进作用及藻类密度的影响等生态效应值得关注。;Phosphorus (P) is a pollutant of great concern in the Yangtze River basin, which has an important impact on the water ecology of the Yangtze River basin. The P flux and form at the Three Gorges Reservoir (TGR) outlet section during 1998-2019 were studied, and the whole period was divided into three stages: 1998-2002 (stage Ⅰ, pre-TGR period), 2003-2013 (stage Ⅱ, as interim period), and 2014-2019 (stage Ⅲ, after TGR achieved 175 m normal water level and completion of Xiangjiaba Reservoir and Xiluodu Reservoir), and Ⅰ and Ⅲ as key periods in comparison. The results show that the average annual total phosphorus (TP) flux in stage Ⅲ was 5.67×10⁴ t/a, 38.0% less than that in stage Ⅰ. Wherein, dissolved phosphorus (DP) flux and particulate phosphorus (PP) flux were 4.02×10⁴ t/a and 1.67×10⁴ t/a in stage Ⅲ, with an increase of 60.0% and a decrease of 74.9% comparing to stage Ⅰ, respectively. The main form of P has changed from particulate to dissolved. In 1998-2002, the DP flux accounted for 27.5% in TP flux, but rose to 70.9% in 2014-2019. Accordingly, the percentage of PP flux decreased from 72.5% to 29.1%. Seasonality of TP, DP and PP flux are shown as wet season>even season>dry season. In the past two decades, the relationship between runoff (Q) and suspended sediment (SS) has changed greatly, and the positive correlation between them has decreased significantly, the slope of correlation equation decreased from 1.44 to 0.10, and R² from 0.83 to 0.57. The rule that the percentage of monthly DP flux decreases with increasing SS remains unchanged, and the empirical model was established as λ_DF=1.2883-0.3688×lgSS (mg/L) based on data during 2014-2019. The changes of P flux and form characteristics were mainly attributed to sediment trapping of three reservoirs and soil and water conservation in the basin. Attention should be paid to the ecological effects resulted from the increase of bioavailable P concentration and the enhancement of light energy absorption.

Retardation factors in controlling the transport of inorganic, organic, and particulate phosphorus in fluvo-aquic soil

Excessive application of fertilizers has caused a high load of phosphorus (P) in the North China Plain. The fate of P and its effects on aquatic ecosystems depend on its chemical speciation in soils. However, few studies systematically investigated the transport and retardation of different P species in the fluvo-aquic soil. In this study, the transport of inorganic P (orthophosphate, PO4), organic P (phytic acid, PA) and particulate P (hydroxyapatite nanoparticles, nHAP) in the fluvo-aquic soil were investigated by column experiments, and their retardation from major soil components such as kaolin, CaCO3, Al2O3, and goethite (GT) was also investigated by monitoring breakthrough curves and fitting transport models. The transport of P species in fluvo-aquic soil followed the order of PO4 > PA > nHAP. A high fraction of increased clay and mineral particle-associated P (P-E) was observed for PO4 and PA; while significant Ca-associated P (P-Ca) for nHAP. Under the experimental conditions, both CaCO3 and GT were the most influential factors for PO4, PA, and nHAP retention. Goethite strongly inhibited PO4 transport due to its high PO4 adsorption capacity, while CaCO3 strongly inhibited PA transport due to its strong association with PA under alkaline conditions. Both CaCO3 and GT can severely inhibit nHAP transport due to the favorable electrostatic conditions as well as the Ca2+ bridging effect. These results indicated that CaCO3 played a key role in regulating the retention of organic P and particulate P in the calcareous soil, and also suggested the important role of Fe (hydr)oxides in controlling the transport of inorganic P, which could out-compete that of CaCO3.

A reconnaissance survey of channel bank particulate phosphorus concentrations, controls and estimated contributions to riverine loads across England.

Channel banks can contribute a significant proportion of fine-grained (<63 μm) sediment to rivers, thereby also contributing to riverine total particulate phosphorus loads. Improving water quality through better agricultural practices alone can be difficult since the contributions from non-agricultural sources, including channel banks, can generate a 'spatial mismatch' between the efficacy of best management applied on farms and the likelihood of meeting environmental objectives. Our study undertook a reconnaissance survey (n=76 sites each with 3 profiles sampled) to determine the total phosphorus (TP) concentrations of channel banks across England and to determine if TP content can be predicted using readily accessible secondary data. TP concentrations in adjacent field topsoils, local soil soil type/texture and geological parent material were examined as potential predictors of bank TP. Carbon and nitrogen content were also analysed to explore the impacts of organic matter content on measured TP concentrations. The results suggest that channel bank TP concentrations are primarily controlled by parent material rather than P additions to adjacent topsoils through fertilizer and organic matter inputs, but significant local variability in concentrations prevents the prediction of bank TP content using mapped soil type or geology. A median TP concentration of 873 mg kg-1 was calculated for the middle section of the sampled channel bank profiles, with a 25th percentile of 675 mg kg-1, and 75th percentile of 1159 mg kg-1. Using these concentrations and, in comparison with previously published estimates, the estimated number of inland WFD waterbodies in England for which channel bank erosion contributes >20% of the riverine total PP load increased from 15 to 25 (corresponding range of 17-35 using the 25th and 75th percentiles of measured TP concentrations). Collectively, these 25 waterbodies account for 0.2% of the total inland WFD waterbody area comprising England.

Spatial optimization of ecological ditches for non-point source pollutants under urban growth scenarios.

Non-point source (NPS) pollution is regarded as the major threat to water quality worldwide, and ecological ditches (EDs) are considered an important and widely used method to collect and move NPS pollutants from fields to downstream water bodies. However, few studies have been conducted to optimize the spatial locations of EDs, particularly when the watershed experiences urbanization and rapid land-use changes. As land-use patterns change the spatial distribution of NPS loads, this study used a cellular automata-Markov method to simulate future land-use changes in a typical agricultural watershed. Three scenarios are included as follows: historical trend, rapid urbanization, and ecological protection scenarios. The spatial distributions of particulate phosphorus loads were simulated using the revised universal soil loss equation and sediment transport distribution model. The results suggested that the total particulate phosphorus (TP) load in the Zhuxi watershed decreased by 10,555.2kg from 2000 to 2020, primarily because the quality and quantity of forests in Zhuxi County improved over the last 20years. The TP load in Zhuxi watershed would be 2588.49, 2639.15, and 2553.32kg in 2040 in historical trend, rapid urbanization, and ecological protection scenarios, respectively, compared with 2308.1kg in 2020. This indicated that urban expansion increases the TP load, and the faster the expansion rate, the more the TP load. Consequently, the optimal locations of EDs were determined based on the intercepted loads and the period during which they existed during land-use changes. The results suggested that rapid urbanization would consequently reduce the space available for building EDs and also increase the cost of building EDs to control the NPS pollution in the watershed.

Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN)

Concentrations and elemental stoichiometry of suspended particulate organic carbon, nitrogen, phosphorus, and oxygen demand for respiration (C:N:P:−O2) play a vital role in characterizing and quantifying marine elemental cycles. Here, we present Version 2 of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset. Version 1 is a previously published dataset of particulate organic matter from 70 different studies between 1971 and 2010, while Version 2 is comprised of data collected from recent cruises between 2011 and 2020. The combined GO-POPCORN dataset contains 2673 paired surface POC/N/P measurements from 70°S to 73°N across all major ocean basins at high spatial resolution. Version 2 also includes 965 measurements of oxygen demand for organic carbon respiration. This new dataset can help validate and calibrate the next generation of global ocean biogeochemical models with flexible elemental stoichiometry. We expect that incorporating variable C:N:P:-O2 into models will help improve our estimates of key ocean biogeochemical fluxes such as carbon export, nitrogen fixation, and organic matter remineralization.

Isotopic compositions of copper and zinc in plankton from the Mediterranean Sea (MERITE-HIPPOCAMPE campaign): Tracing trophic transfer and geogenic inputs

This study uses Cu and Zn isotopic compositions as proxies of sources and metal transfers in the planktonic food webs from the Mediterranean Sea. Plankton was collected in spring 2019 in the deep chlorophyll maximum (DCM) along a North-South transect including coastal and offshore zones (MERITE-HIPPOCAMPE campaign). δ65Cu and δ66Zn were determined on four planktonic size fractions from 60 to 2000 μm. Combined δ65Cu and δ66Zn with geochemical tracers (Ti, particulate organic phosphorus) showed that geogenic particles were ubiquitous with plankton assemblages. The δ15N ecological tracer showed that planktonic food web was enriched in heavy isotopes of Cu and Zn in the higher trophic levels. δ65Cu were correlated with picoplankton in the offshore zone, and with zooplankton in the southern coastal zone. Firmicutes bacteria were found correlated with δ66Zn in northern and southern coastal zones suggesting decomposition of particulate matter at the DCM. These findings suggest that biogeochemical process may impact Cu and Zn isotopy in the planktonic community.

Quantifying sediment and particulate phosphorus accumulation in restored floodplain wetlands using beryllium‐7 as a tracer

AbstractFloodplain wetlands in agricultural river basins provide critical ecosystem services such as nutrient retention, flood mitigation, carbon sequestration and ecological habitats and are a key component of a nature‐based solution approach to restoration. In the context of the global challenge to reducing impact increasingly intensive food production on downstream ecosystems, restoration of wetlands in river floodplains offers a practical means for downstream retention and mitigation of P flux from upstream agricultural land. Data on short term, flood event related, accretion rates are, however, difficult to acquire via conventional monitoring yet such information is essential for restoration planning and scenario testing. Here, we evaluate a promising approach that applies naturally‐occurring short‐lived fallout radionuclide (FRN) 7Be as a tracer to quantify sediment and, by association, particulate phosphorus retention rates in restored floodplain wetlands. Following a series of major inundation events, a restored floodplain unit was sampled to determine 7Be inventories of the floodplain relative to an undisturbed reference site. This was undertaken in conjunction with direct measurement of sedimentation as an independent check of FRN results. Accretion rates up to 27 kg m−2 were recorded using 7Be for recent deposition events compared to a longer term annual average rate of ca. 6 kg m−2 derived from 137Cs measurements. While accretion rates varied spatially and temporally, there was excellent coherence between FRN‐based measurements and direct measurements once rigorous correction for particle size effects on tracer properties had been undertaken. The study demonstrates the important contribution that FRN technology can make to support wetland management and restoration initiatives and the essential need for a systems thinking approach across the soil‐sediment continuum. Such decision support tools will become increasingly important in the 21st century with growing anthropogenic pressure on aquatic ecosystems related to upstream food production, and implementation of more nature‐based solutions such as restored wetlands to counteract these pressures.

The composition of organic phosphorus in a river during the springtime irrigation period

Study regionThe study region was the Sakura River, a tributary of Lake Kasumigaura, Japan. Study focusWe asked whether particulate organic phosphorus (POP) contributed to the P cycle in rivers. Previous studies have focused on the interaction between PO43– and particulate inorganic P (PIP), but our study focused on whether POP could also be the source of PO43–. New hydrological insights for the regionAfter rain events during irrigation, concentrations of suspended particles and particulate P (PP) increased. POP accounted for 42.4 % of PP concentrations. The PIP and POP concentrations were both positively correlated with suspended particle concentrations. The PO43– concentrations were significantly higher during decomposition experiments when suspended particles were present in the water. Decomposition experiments revealed that the P composition changed and the proportion of organic P decreased as DNA-P disappeared from the PP. The fact that the DOP concentration was significantly lower in the treatment with suspended particles than without suspended particles suggested that DOP mineralization rates were increased by the presence of suspended particles. In addition to mineral-sorbed P, the POP derived from the irrigation of paddy fields may also be bioavailable.

Dairy farm roadway surface materials as a P-source within the nutrient transfer continuum framework

Internal farm roadways are connectors within agricultural landscapes, which act as sub-components of the nutrient transfer continuum (NTC). On dairy farms, roadway surface runoff dissolved and particulate phosphorus (P) sources stem from a combination of cow excreta deposited at locations that impede animal flow, soil deposited from cow hooves or machinery tyres, run-on from up-gradient fields, public roadways or farmyards and incidental spill of organic/inorganic fertilizers. The present study investigates the storage and potential release of P from the underlying roadway material (i.e. composite of soil and stone aggregates) as this source component is not considered in the NTC framework or documented in the literature. Herein, farm roadway materials were sampled (to 1 cm depth) at 17 locations avoiding fresh cow excreta. Multiple location types were selected e.g. straight roadway sections, roadway junctions, before and adjacent standoff areas associated with cattle underpasses, with all locations varying in distance from the farmyard. Roadway samples were analysed for phosphorus (P) and metals (Al, B, Ca, Co, Cu, Fe, K, Mg, and Mn) content. Results showed that the soil component of roadway materials are significant P legacy sources and are in themselves a P-storage component that merits inclusion in the NTC framework. All sampled locations, when compared with fresh roadway stone aggregates or surrounding fields, had highly elevated P with plant available Morgans P &amp;gt; 8 mg L-1 (Index 4, ranging from 10 – 110 mg L-1). Sampling points within 100 m of the farmyard together with roadway junctions and underpasses beyond this distance had highest P concentrations. Critical source areas, where source, mobilisation and transport of P to waters coincided, formed at three locations. Possible mitigation measures are a) divert roadway runoff into fields using low-cost surface water breaks, b) disconnect cattle underpass tanks from receiving waters and c) change roadway infrastructure to improve cow flow and minimise source build-up. Future research should examine P loads in runoff from roadway sections across farm typologies and roadway material types.

Response of phytoplankton community composition to physicochemical and meteorological factors under different hydrological conditions in Lake Diefenbaker

Changes in hydro-meteorological conditions due to warming climate and the operation of reservoirs may support algal blooms. Lake Diefenbaker is a large reservoir on the Canadian Prairies. Annual flow volume from its major tributary, the South Saskatchewan River (SSR), varies with precipitation and temperature in the Rocky Mountains. Furthermore, plans are underway to increase water abstraction from Lake Diefenbaker for irrigation. Therefore, we used a nine-year dataset that comprised a drought year (1984), four consecutive high flow years (2011 to 2014), and four subsequent low flow years (2015 to 2018) to investigate how these changes could affect the major phytoplankton groups and cyanobacterial community. Diatoms (38.5%) were the most abundant phytoplankton, followed by cryptomonads (28.9%) under low and high flow years. Diatoms were associated with greater mixing in late spring and fall, whereas the cryptomonads were related to the high nutrients from spring flow. Cyanobacteria (79.3%) contributed the greatest to the total phytoplankton biomass under drought; we hypothesized that the high abundance of cyanobacteria during drought was associated with thermocline deepening and subsequent internal loading of nutrients. Microcystis, a potential bloom-forming and toxin-producing genus, was dominant during the drought and correlated with reduced water level, increased air temperature, and moderate wind speed. Although its biomass was low, another potential bloom-forming and toxin-producing genus, Aphanizomenon, was present in low and high flow years. Aphanizomenon was correlated with decreased SSR flow and increased particulate carbon to particulate phosphorus ratios, which may be related to their ability to cope with P limitation. These results highlight that Lake Diefenbaker and other similar reservoirs are vulnerable to an increase in potential toxic cyanobacteria species with future expectations of climate warming and water abstraction.

Improving quantification of particulate phosphorus

AbstractTotal particulate phosphorus (TPP) is often determined using the high‐temperature dry combustion (HTDC) method followed by hydrolysis of the ash and then molybdenum colorimetry. Here, we show that a higher than traditionally used combustion temperature, 800°C vs. 450–550°C, improves phosphorus recovery from several phosphorus standard compounds, marine phytoplankton cultures, and particulate samples from the field. The ashing auxiliary MgSO4 further improves P recovery by improving decomposition, reducing volatilization during combustion, and increasing the efficiency of hydrolysis. A 0.2 M HCl hydrolysis, under 90°C for 30 min yields a higher P recovery compared with hydrolysis at room temperature or 60°C. In aggregate, these improvements to the method double the P recovery from phospholipids to 97%. TPP recovery from laboratory phytoplankton cultures and field samples increased an average of 11%, primarily due to the improvements in P recovery from phospholipids, polyphosphate, and nucleic acids. We refer to this new method as the eXtra high temperature dry combustion (X‐HTDC) Ash/Hydrol method and recommend its application for measuring particulate phosphorus from organic compounds in aquatic systems.

Hydrological control of the chemical characteristics of suspended particulate phosphorus in the Yasu River watershed, Japan: Implications for its source and bioavailability

AbstractSeveral studies have demonstrated the importance of the bioavailability of particulate phosphorus (PP) exported from various watersheds, especially agricultural land. However, few studies have documented the influence of hydrological conditions on the sources and bioavailability of PP exported from watersheds with multiple land uses. In this study, to assess the sources and bioavailability of PP under different hydrological conditions, we conducted synoptic monitoring of compositional changes in the chemical fractions of PP exported from the Yasu River Watershed, which is covered with a mixture of forest (57.7%) and rice paddy (20.5%) areas. In this river, total phosphorus was composed mainly of PP at all monitoring sites and time points. The sequential extraction of PP revealed that a fraction bound to redox‐sensitive iron and manganese, regarded as bioavailable, was specific to the drainage waters of rice paddies, while a fraction bound to organic matter, regarded as less bioavailable, was specific to a forested stream. In the downstream of the Yasu River covering the whole watershed, PP exported under the base flow and small rainfall conditions was composed mainly of the rice paddy‐derived fraction, while most of the PP exported under heavy rainfall conditions was the forest‐derived fraction. These results suggest that the sources and bioavailability of PP can vary dynamically, depending on the hydrological regimes and land use pattern in the watershed. Even taking into account the fact that the large amount of PP exported during heavy rainfall is considered to be forest‐derived PP with low bioavailability, the monitoring results suggested that the annual amount of bioavailable PP exported is larger than that of dissolved phosphorus, and can have a large impact on phosphorus recycling in the downstream lake ecosystem through sedimentation and regeneration.