Particulate P Concentrations Research Articles

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.

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.

Impact of preferential flow pathways on phosphorus leaching from typical plastic shed vegetable production soils of China

Despite its importance, the contribution of preferential flow pathways (PFPs) to subsurface phosphorus (P) leaching from heavily-fertilized plastic shed vegetable production (PSVP) soils in China has remained unexplored. To investigate this, five acid fine-textured Orthic Anthrosols and six alkaline coarse-textured Ustic Cambosols intact soil columns (20 cm depth and 15 cm diameter), from two typical PSVP systems in Jiangsu Province, Southeast China, were subjected to six leaching experiments with collection of effluents over 24 h. Leachate samples were analyzed for their concentrations of particulate P (PP) and dissolved reactive P (DRP). Finally, soil columns were photographed for their 2D distribution of PFPs both vertically (0−20 cm) and horizontally at 5 cm intervals after the application of dye tracer (Brilliant Blue). Overall, alkaline coarse-textured Ustic Cambosols with longer history of PSVP had larger PFPs’ volumes than acid fine-textured Orthic Anthrosols with vertical (0−20 cm) values ranging from 812 to 1260 cm2 and 623 to 1104 cm2, respectively. Of soil properties, pH and sand content had significant positive correlations with PFPs’ density (p < 0.05). Whereas, soil contents of clay and oxalate extractable Al and Fe had significant negative correlations with PFPs’ density (p < 0.05). In terms of subsurface P mobilization, preferential water flow had significant impact on DRP leaching (p < 0.05). In contrast, leachate PP concentrations had no significant relationships with both vertical and horizontal PFPs, indicating that PP leaching might occur mostly through soil matrix. However, field assays are still essential for better understanding of P leaching in relation to PFPs through taking into account the soil physiochemical properties and agricultural management.

Particulate phosphorus and suspended solids losses from small agricultural catchments: Links to stream and catchment characteristics

Excessive phosphorus (P) inputs from agriculture are well established as a contributor to freshwater eutrophication. Decreasing these inputs is an important step in improving the ecological state of impaired waters. Particulate P (PP) is a significant contributor to diffuse P inputs in agricultural catchments. Identifying the main correlates for PP losses is an important step in reducing these inputs. However, there are few studies of long term temporal and spatial dynamics of PP in agricultural streams. Here, we investigate the relative importance of hydrology, catchment characteristics and geochemistry on PP concentrations and fluxes in agricultural headwaters. We evaluate long-term monitoring data from eleven small (<35 km2) Swedish catchments with at least seven years of measured flow and flow proportional water quality sampling. Using parametric and non-parametric regression together with principal components analysis (PCA), we identify in-stream and catchment variables relevant for predicting PP concentrations, e.g., suspended solids concentrations (SS), soil texture and average catchment soil P content, measured as ammonium lactate/acetic acid extractable P (P-AL). We show that PP is primarily correlated to SS concentrations, which in turn are correlated to average clay content and land use. However, the SS:PP relationships differ between catchments. No correlation between PP concentrations in the stream and soil P content was found. An increasing clay content decreases the slope of the relationship between SS and PP, i.e., in catchments with higher clay content, less PP is transported per unit SS. The PP/SS ratio increased significantly (p < 0.05) over time in four catchments, despite limited changes in SS or PP concentrations. Our study highlights the importance of long time series since the enrichment of P on SS in the streams is only detected when using long term monitoring data.

Phosphorus dynamics during storm events in a subtropical rural catchment in southern Brazil

The intensification of agricultural activities increases the transfer of phosphorus (P) to surface water bodies causing a wide range of environmental, social and economic problems, such as eutrophication. This paper describes the dynamics of P loss during rainfall events (intra-event) and between events (inter-event) in a rural catchment with intensive soil use in southern Brazil, emphasizing the relationships of the solutes with the hydrosedimentological variables. The information on the magnitude and the pattern of P transport was obtained during eighth significant rainfall events, in addition to the sampling performed during the baseflow period (between events). During the events, we evaluated the transfer dynamics of the total P (TP), dissolved P (DP), particulate P (PP) and suspended sediment concentration (SSC). Phosphorus (dissolved and particulate) is predominantly lost during events. The concentrations of DP and PP were low in samples collected in the period between events, when groundwater flow predominates. There is predominance of subsurface flow for the total volume of DP drained into the catchment. The hysteresis of TP forms a loop in the counterclockwise direction at the moment the soil is exposed by plowing, due to P transfer from the cropland to the water course. The transfer of P occurred predominantly in the particulate form (88%) due to the high affinity of P with mineral colloids. There was predominance of clockwise hysteresis for TP and SSC during the fallow period and at the beginning of soil mobilization, indicating the presence of P and sediment sources closer to the catchment outlet. However, during the development period of the crop, when the soil was more exposed due to plowing, counterclockwise hysteresis was observed for TP, which indicates a predominance of sources farther from the outlet, such as the cropland. Thus, we believe that efforts towards adopting practices that reduce erosion can contribute to a reduction of P transfer to water sources. Consequently controlling the process of eutrophication.

Can the watershed non-point phosphorus pollution be interpreted by critical soil properties? A new insight of different soil P states

The physicochemical properties of surface soil play a key role in the fate of watershed non-point source pollution. Special emphasis is needed to identify soil properties that are sensitive to both particulate P (PP) pollution and dissolved P (DP) pollution, which is essential for watershed environmental management. The Chaohu Lake basin, a typical eutrophic lake in China, was selected as the study site. The spatial features of the Non-point Source (NPS) PP loads and DP loads were calculated simultaneously based on the integration of sediment delivery distributed model (SEDD) and pollution loads (PLOAD) model. Then several critical physicochemical soil properties, especially various soil P compositions, were innovatively introduced to determine the response of the critical soil properties to NPS P pollution. The findings can be summarized: i) the mean PP load value of the different sub-basins was 5.87 kg, and PP pollution is regarded to be the primary NPS P pollution state, while the DP loads increased rapidly under the rapid urbanization process. ii) iron-bound phosphorus (Fe-P) and aluminum-bound phosphorus (Al-P) are the main components of available P and showed the most sensitive responses to NPS PP pollution, and the correlation coefficients were approximately 0.9. Otherwise, the residual phosphorus (Res-P) was selected as a sensitive soil P state that was significantly negatively correlated with the DP loads. iii) The DP and PP concentrations were represented differently when they were correlated with various soil properties, and the clay proportion was strongly negatively related to the PP loads. Meanwhile, there is a non-linear relationship between the DP loads and the critical soil properties, such as Fe and Total Nitrogen (TN) concentrations. Specifically, a strong inhibitory effect of TN concentration on the DP load was apparent in the Nanfei river (NF) and Paihe (PH) river basins where the R2 reached 0.67, which contrasts with the relatively poor relationship within the other five basins. In addition, the degree of correlation between the Fe and DP loads severely degraded in the basins that were mostly covered by construction land or those that underwent a rapid urbanization process. The findings indicate that land use/cover change (LUCC), especially the distribution of agricultural land and construction land, as well as the soil background information (TN, Fe and Soil organic matters, etc.) can be considered as factors that influence NPS P pollution.

Drainage water management combined with cover crop enhances reduction of soil phosphorus loss

Integrating multiple practices for mitigation of phosphorus (P) loss from soils may enhance the reduction efficiency, but this has not been studied as much as individual ones. A four-year study was conducted to determine the effects of cover crop (CC) (CC vs. no CC, NCC) and drainage water management (DWM) (controlled drainage with sub-irrigation, CDS, vs. regular free tile drainage, RFD) and their interaction on P loss through both surface runoff (SR) and tile drainage (TD) water in a clay loam soil of the Lake Erie region. Cover crop reduced SR flow volume by 32% relative to NCC, regardless of DWM treatment. In contrast, CC increased TD flow volume by 57 and 9.4% with CDS and RFD, respectively, compared to the corresponding DWM treatment with NCC. The total (SR+TD) field water discharge volumes were comparable amongst all the treatments. Cover crop reduced flow-weighted mean (FWM) concentrations of particulate P (PP) by 26% and total P (TP) by 12% in SR, while it didn't affect the FWM dissolved reactive P (DRP) concentration, regardless of DWM treatments. Compared with RFD, CDS reduced FWM DRP concentration in TD water by 19%, while CC reduced FWM PP and TP concentrations in TD by 21 and 17%, respectively. Total (SR+TD) soil TP loss was the least with CDS-CC followed by RFD-CC, CDS-NCC, and RFD-NCC. Compared with RFD-NCC, currently popular practice in the region, total TP loss was reduced by 23% with CDS-CC. The CDS-CC system can be an effective practice to ultimately mitigate soil P loading to water resource.

Spatial Scale and Field Management Affect Patterns of Phosphorus Loss in Cranberry Floodwaters.

Although cranberries ( Ait.) are indigenous to the northeastern United States, phosphorus (P) fertilizer additions and periodic flooding make commercial cranberry a potential source of P to the region's lakes and streams. In this study, we report values of P export in cranberry floodwaters that range from <0.8 to 4.7 kg P ha, generally reflecting differences in the hydrological, edaphic, and management factors underlying soil P transfer to floodwater. The relatively high P loading rate (4.7 P kg P ha) was associated with harvest flooding of organic-rich soils. Periods of winter flooding and the discharge of harvest floodwater from mineral soils resulted in relatively low P loss (<0.8 kg P ha). Increases in concentrations of total dissolved P (DP) and total particulate P (PP) in floodwater as stage decreased below the surface of the cranberry bed were consistent with the transport of dissolved P in soil porewater and mobilization of particulate P in ditches. Variations in floodwater DP, as well as conservative and reactive tracer concentrations, suggested that the processes by which soil P is released to porewater included desorption of near-surface soil P and anaerobic dissolution of iron-P compounds deeper in the soil profile. At the farm scale, concentrations of DP and PP steadily increased over time, presumably because drainage waters from beds farther upgradient had longer contact times with P-rich sources, such as soil porewater and ditch sediments. Overall, the study illustrates the role that scale-dependent processes impart on patterns of P loss in agricultural production systems.

Evaluating the critical source area concept of phosphorus loss from soils to water-bodies in agricultural catchments

Using data collected from six basins located across two hydrologically contrasting agricultural catchments, this study investigated whether transport metrics alone provide better estimates of storm phosphorus (P) loss from basins than critical source area (CSA) metrics which combine source factors as well. Concentrations and loads of P in quickflow (QF) were measured at basin outlets during four storm events and were compared with dynamic (QF magnitude) and static (extent of highly-connected, poorly-drained soils) transport metrics and a CSA metric (extent of highly-connected, poorly-drained soils with excess plant-available P).Pairwise comparisons between basins with similar CSA risks but contrasting QF magnitudes showed that QF flow-weighted mean TRP (total molybdate-reactive P) concentrations and loads were frequently (at least 11 of 14 comparisons) more than 40% higher in basins with the highest QF magnitudes. Furthermore, static transport metrics reliably discerned relative QF magnitudes between these basins. However, particulate P (PP) concentrations were often (6 of 14 comparisons) higher in basins with the lowest QF magnitudes, most likely due to soil-management activities (e.g. ploughing), in these predominantly arable basins at these times. Pairwise comparisons between basins with contrasting CSA risks and similar QF magnitudes showed that TRP and PP concentrations and loads did not reflect trends in CSA risk or QF magnitude. Static transport metrics did not discern relative QF magnitudes between these basins.In basins with contrasting transport risks, storm TRP concentrations and loads were well differentiated by dynamic or static transport metrics alone, regardless of differences in soil P. In basins with similar transport risks, dynamic transport metrics and P source information additional to soil P may be required to predict relative storm TRP concentrations and loads. Regardless of differences in transport risk, information on land use and management, may be required to predict relative differences in storm PP concentrations between these agricultural basins.

Long-term temporal dynamics and trends of particle-bound phosphorus and nitrate in agricultural stream waters

One problem in evaluating efforts to reduce phosphorus (P) and nitrogen (N) losses to waters is that variations in weather conditions cause nutrient concentrations and waterflow to vary. Analyses of biweekly stream water samples collected manually from two small, neighbouring Swedish agricultural catchments with clay soil (E23 and E24) demonstrated unpredictability in P and N concentrations. However, particulate P (PP) concentrations in the two separate catchments, usually sampled within 2–3 hours on the same day, were clearly correlated to each other (Spearman correlation coefficient r=0.70). Corresponding nitrate–nitrogen (NO3–N) concentrations were also correlated to each other (r=0.79). Particulate P concentrations could reasonably be predicted from suspended solid (SS) concentrations above base flow (BF) in both catchments (regression coefficient R 2=0.84 and 0.86, respectively). In the period 1993–2009, before eutrophication control programmes were introduced in catchment E23, there was no general trend in PP or SS in either catchment. Mean PP (0.13 mg L−1) predicted (R 2=0.88) from high-resolution (15 minute) turbidity concentrations was significantly higher than flow-weighted mean PP concentration estimated from discrete samples (0.10 mg L−1) collected manually at the catchment E23 outlet. Mean PP concentration estimated directly from flow-proportional sampling was also higher. High synoptic concentrations of PP (up to 0.65 mg L−1) were recorded along the open reach of the stream in the ascending limb of high-flow pulses. Using high-resolution monitoring at the catchment outlet, episodes with a clear clockwise hysteresis effect for PP concentration (seen as turbidity) were frequently observed. By contrast, the NO3–N peak appeared 4–7 hours after the flow peak and anticlockwise hysteresis was observed. Significant erosion along stream banks may take place, and the degree of erosion was estimated based both on farmers’ observations and on results from a distributed erosion model (USPED). Monitoring and erosion mapping are currently being used in practical remedial work.

Bioavailable Phosphorus in Fine‐Sized Sediments Transported from Agricultural Fields

Sediments transported from agricultural fields in surface and subsurface waters contain particulate P (PP) that could be partitioned into two pools—one available for aquatic organisms including cyanobacteria, namely bioavailable particulate P (BAPP, determined by 0.1 mol L−1 NaOH extraction), and the remainder not bioavailable (non‐BAPP). This study aimed to quantify the PP and BAPP concentrations in surface runoff and tile drainage water from eight agricultural fields with clay and sandy soils in the Missisquoi Bay region of Quebec, Canada. Particulate P in surface and drainage water varied spatially (among fields) and temporally, with concentrations as high as 3181 μg P L−1 in surface runoff and 1346 μg P L−1 in tile drainage. About 30% of PP was BAPP regardless of the drainage pathway. The PP and BAPP concentrations were related linearly (R2 = 0.86) to total suspended solids (TSS) in fine (0.05–1‐μm) and coarse (1–100‐μm) fractions. About 68% of the PP in clay soils and 50% of the PP in sandy soils were associated with the 0.05‐ to 1‐μm size particles, which had more BAPP, on average 0.46 g P kg−1, than the coarser 1‐ to 100‐μm fraction (0.22 g P kg−1). Soil parameters such as Mehlich‐3 extractable (M3) P, M3Fe, and the degree of soil P saturation were related to the PP and BAPP concentrations in TSS and particle size fractions. We concluded that sediments with particle size &lt;1 μm contained more BAPP and their loss from agricultural fields could contribute to the eutrophication downstream.

Hot moments and hot spots of nutrient losses from a mixed land use watershed

Summary Non-point nitrogen (N) and phosphorus (P) pollution from agriculture has increasingly received more public attention. In this study, NO 3 –N, dissolved P (DP) and particulate P (PP) concentrations and loads were investigated for four sub-basins (labeled 1–4 going up the watershed) within a mixed land use watershed (39.5 ha) in the Appalachian Valley and Ridge Physiographic Province. The hot moments of NO 3 –N concentration and load occurred in base flow and during the non-growing season. Great and temporally variable DP and PP concentrations were observed in storm flow. The hot moments of DP concentration and load were in storm flow from May to December and from September to Nov, respectively, while the hot moments of PP concentration and load were in storm flow from January to June. The NO 3 –N, DP, and PP loads were compared for all four sub-basins on a loss per length of stream reach basis to determine the hot spots and their corresponding losses. The hot spots and hot moments of NO 3 –N loads were in Sub-basins 1 and 4 during the non-growing season base flow period and Sub-basin 2 during the post-growing season base flow period (>110 g m −1 mo −1 ). The hot spots of DP loads were also in Sub-basins 1 and 4, but during the growing and post-growing season storm flow period (>1.4 g m −1 mo −1 ). In contrast, the hot spots and hot moments of PP load were in Sub-basin 3 during the pre-growing and growing season storm flow, as much as 13.4 and 14.1 g m −1 mo −1 , respectively. Controlling factors of nutrient export were discussed in this study, including season, hydrology (base flow, storm flow, surface and subsurface runoff), and land use. Although different hot moments and hot spots within the watershed were identified for NO 3 –N, DP, and PP losses, the implementation of a couple of management practices (cover crops and no-till) might be sufficient to effectively reduce nutrient losses from this and similar Valley and Ridge watersheds.

Seasonal phosphorus depletion and microbial responses to the change in phosphorus availability in a subarctic coastal environment

Temporal variations of phosphorus (P) pools (soluble reactive P (SRP), dissolved organic P (DOP), and particulate P (PP)), alkaline phosphatase activity (APA), and orthophosphate uptake were measured in Funka Bay to describe the annual P cycle in the bay and determine the phytoplankton and bacterial responses to the change in P availability. Observations over 4 years demonstrated that SRP concentrations in the surface waters decreased from the winter maximum of 1.0 μmol L −1 to 0.3 μmol L −1 at the end of the spring phytoplankton bloom, and then to under the detection limit by around August. The DOP concentration was relatively constant at 0.1 μmol L −1 throughout the year with higher concentrations up to 0.3 μmol L −1 just after the peak of the spring bloom. PP concentrations varied around 0.1 μmol L −1 with higher concentrations up to 0.6 μmol L −1 during the high chlorophyll a concentration period. SRP comprised 85% of the total P pool prior to the spring bloom, but the contribution decreased to less than 30% in the post-bloom period and DOP dominated the P pool in the surface. Most of the measured APA was less than 0.1 nmol L −1 min −1 in the whole water column, but exceptionally high values up to 1.4 nmol L −1 min −1 were observed in low SRP surface waters during summer. When SRP decreased from 0.3 μmol L −1 in spring to under the detection limit in summer, turnover time for orthophosphate at 10 m depth decreased from 61 days to 4.2 h. The high APA and short turnover time for orthophosphate suggested that microbes in the surface mixed layer experienced severe P stress in summer. Under severely P stressed conditions, APA was detected mostly in the > 10 μm fraction, suggesting that large phytoplankton would acquire P from DOP to overcome the P stress. This was supported by the result that large phytoplankton were outcompeted by the 0.2–1 μm sized microbes for orthophosphate uptake.

The effect of soil phosphorus on particulate phosphorus in land runoff

SummaryAccumulation of surplus phosphorus (P) in the soil and the resulting increased transport of P in land runoff contribute to freshwater eutrophication. The effects of increasing soil P (19–194 mg Olsen‐P (OP) kg−1) on the concentrations of particulate P (PP), and sorption properties (Qmax, k and EPCo) of suspended solids (SS) in overland flow from 15 unreplicated field plots established on a dispersive arable soil were measured over three monitoring periods under natural rainfall. Concentrations of PP in plot runoff increased linearly at a rate of 2.6 μg litre−1 per mg OP kg−1 of soil, but this rate was approximately 50% of the rate of increase in dissolved P (&lt; 0.45 μm). Concentrations of SS in runoff were similar across all plots and contained a greater P sorption capacity (mean + 57%) than the soil because of enrichment with fine silt and clay (0.45–20 μm). As soil P increased, the P enrichment ratio of the SS declined exponentially, and the values of P saturation (Psat; 15–42%) and equilibrium P concentration (EPCo; 0.7–5.5 mg litre−1) in the SS fell within narrower ranges compared with the soils (6–74% and 0.1–10 mg litre−1, respectively). When OP was &lt; 100 mg kg−1, Psat and EPCo values in the SS were smaller than those in the soil and vice‐versa, suggesting that eroding particles from soils with both average and high P fertility would release P on entering the local (Rosemaund) stream. Increasing soil OP from average to high P fertility increased the P content of the SS by approximately 10%, but had no significant (P &gt; 0.05) effect on the Psat, or EPCo, of the SS. Management options to reduce soil P status as a means of reducing P losses in land runoff and minimizing eutrophication risk may therefore have more limited effect than is currently assumed in catchment management.

The effect of farming practices on phosphorus transfer to a headwater stream in England

Characterization of phosphorus (P) sources in catchments is critical to the restoration of stream integrity following eutrophication. To better understand the effects of farming practices on P transfer in a small rural mixed farming catchment (Rosemaund), spatial and temporal patterns in P delivered from a field-drain (Foxbridge, 6 ha), and to two downstream stations (Jubilee, 31 ha and Belmont, 150 ha) were investigated in relation to detailed records on cultivation practices and fertilizer/manure P inputs over a 3-year period (1997–2000) with above-average rainfall. The Belmont catchment also included a farmstead and a small sewage treatment works (STW). The main source of P in drainflow (December–April) was the soil with flow-weighted concentrations of particulate P (PP) up to 2 mg L −1 and concentrations of dissolved-reactive P (DRP) (0.1–0.4 mg DRP L −1) above current riverine targets to limit eutrophication. Agricultural operations carried out in autumn/early winter sporadically increased concentrations of DRP (fertilizer/manure applications) and PP (cultivations) in drain/stream discharge, but only during events that produced small amounts of stormflow. Occasionally large DRP and PP concentrations in drainflow were also recorded during the ecologically sensitive summer months, but this was unrelated to any farming practice. Stream P concentrations were further influenced by processes of baseflow dilution, in-stream retention/release and discharges from the STW and farmstead. The results highlight the disparity between the timing of farming operations at this site (autumn/early winter), the main period of land drainage (winter/spring) and the main period of biological activity (spring and summer). A greater understanding of the ecological significance of variably timed P inputs to headwater streams is needed to develop effective catchment management.

Phosphorus Transport Pathways to Streams in Tile‐Drained Agricultural Watersheds

Agriculture is a major nonpoint source of phosphorus (P) in the Midwest, but how surface runoff and tile drainage interact to affect temporal concentrations and fluxes of both dissolved and particulate P remains unclear. Our objective was to determine the dominant form of P in streams (dissolved or particulate) and identify the mode of transport of this P from fields to streams in tile-drained agricultural watersheds. We measured dissolved reactive P (DRP) and total P (TP) concentrations and loads in stream and tile water in the upper reaches of three watersheds in east-central Illinois (Embarras River, Lake Fork of the Kaskaskia River, and Big Ditch of the Sangamon River). For all 16 water year by watershed combinations examined, annual flow-weighted mean TP concentrations were >0.1 mg L(-1), and seven water year by watershed combinations exceeded 0.2 mg L(-1). Concentrations of DRP and particulate P (PP) increased with stream discharge; however, particulate P was the dominant form during overland runoff events, which greatly affected annual TP loads. Concentrations of DRP and PP in tiles increased with discharge, indicating tiles were a source of P to streams. Across watersheds, the greatest DRP concentrations (as high as 1.25 mg L(-1)) were associated with a precipitation event that followed widespread application of P fertilizer on frozen soils. Although eliminating this practice would reduce the potential for overland runoff of P, soil erosion and tile drainage would continue to be important transport pathways of P to streams in east-central Illinois.

Association between phosphorus and suspended solids in an Everglades treatment wetland dominated by submersed aquatic vegetation

Restoration of the Everglades requires reduction of total phosphorus (TP) in the influent run-off from the Everglades agricultural area (EAA). The Everglades nutrient removal project tested phosphorus (P) - removal efficiencies of several treatment wetland cells. The best TP reduction has occurred within the submersed aquatic vegetation (SAV) - dominated treatment Cell 4. A significant proportion of the P reduction in Cell 4 over several years has been in the form of particulate P (PP). This study was conducted to (i) determine and compare the components of suspended solids in the Cell 4 influent and effluent waters, and (ii) investigate associations between PP and individual particulate components. Identification and quantification of components were accomplished using X-ray diffraction, thermogravimetry, scanning electron microscopy, and energy dispersive X-ray elemental analysis. The dominant particulate components in the Cell 4 water column are organic matter (OM), biogenic Si (predominantly diatom frustules), and calcite. Concentrations of PP, suspended solids, and particulate OM were greater at the Cell 4 inflow than at the outflow; consistent differences between particulate calcite in the influent vs. the effluent were not found. PP was positively correlated with particulate OM, but was not correlated with calcite. Data suggest that particulate OM, including microbial cells, plays an important role in P transport from the EAA. Possibly, a shift from planktonic to periphytic microbial distribution contributes to PP reduction. The importance of planktonic organisms as vectors of P in Everglades water warrants further study.

Distribution and dynamics of various forms of phosphorus in seawater: insights from field observations in the Pacific Ocean and a laboratory experiment

Particulate and dissolved phosphorus (P) measurements including particulate P (PP), soluble reactive P (SRP), dissolved organic P (DOP), and particulate and dissolved hydrophobic P were made at four stations in the Pacific Ocean. SRP concentrations in surface waters varied widely from 0.01 to 0.43 μM. In contrast, DOP exhibited relatively constant values of 0.21–0.37 μM. At oligotrophic ocean stations, DOP was the most significant P pool accounting for 70–98% of total dissolved P (TDP) or 60–90% of total P (TDP+PP) in the surface euphotic zone. DOP concentrations decreased with increasing water depth and reached levels near the detection limit below 1000 m. PP was a minor component accounting for 3–11% of total P in the euphotic zone at all stations. With depth at the oligotrophic stations PP concentrations decreased rapidly, reaching relatively constant levels of ∼0.5 nM below 500 m. Particulate hydrophobic P concentrations in surface waters ranged from 0.29 to 1.72 nM and sharply decreased to <0.1 nM below the euphotic zone. Dissolved hydrophobic P concentrations were much higher ranging from 6.6 to 17.9 nM at the surface and gradually decreased with depth. Hydrophobic P was a minor fraction of surface P pools. During biodegradation of DOP and PP below the euphotic zone, other P compounds are preferentially utilized relative to hydrophobic P. This results in an increased abundance relative to surface waters of hydrophobic P in DOP (18%) and PP (34%) in deep waters. Enrichment of hydrophobic P during biodegradation is supported by a laboratory experiment during which hydrophobic P increased as the percentage of bulk DOP and PP in a seawater sample. These results suggest that hydrophobic P plays two important roles in marine P cycling. In surface waters labile forms of hydrophobic P are a source of bioavailable P that may help sustain production in oligotrophic ocean regions. Export from surface waters of less reactive hydrophobic P fractions acts as a sink of P from marine ecosystems.

LONG–TERM MANURE AND FERTILIZER APPLICATION EFFECTS ON PHOSPHORUS AND NITROGEN IN RUNOFF

Longterm manure and fertilizer applications to a soil can increase phosphorus (P) and nitrogen (N) transportin runoff. This study was conducted to determine P and N transport in runoff following longterm (since 1953) manure andfertilizer applications. Duplicate soil samples (32) were collected in 1998 from the top 0.1 m of selected plots of a longtermmanure and fertilizer applications field experiment and later placed in 1 m 2 soil pans in the laboratory. Manure and fertilizerwere mixed with 16 of the soil samples, while no treatment was applied to the other half (longterm residual effect). Simulatedrainfall was then applied to the soil during initial and wet (24 hours later) events.<br><br>Manure added just before simulated rainfall resulted in significantly greater concentrations of dissolved P (DP),bioavailable P (BAP), particulate P (PP), total P (TP), NO3N, and NH4N than when the last manure application was theprevious year in 1997. Soil test P level was not a significant factor in DP loss when manure was applied just before rainfall.When the last manure application was the previous year, similar concentrations of DP, BAP, PP, and TP were measured onthe manure and nomanure treatments. Concentrations of NO3N and NH4N in runoff were not influenced by longtermfertilizer application, but significantly increased with increasing N application rate when N was applied just before rainfall.Phosphorus concentration in runoff decreased with time of runoff up to 45 minutes, after which the P concentration remainedconstant. NO3N and total N concentrations continued to decrease for the entire runoff period. Manure and fertilizer shouldnot be applied when the probability of rainfall immediately following application is great.

The phosphorus content of fluvial sediment in rural and industrialized river basins

The phosphorus content of fluvial sediment (suspended sediment and the <63 μm fraction of floodplain and channel bed sediment) has been examined in contrasting rural (moorland and agricultural) and industrialized catchments in Yorkshire, UK. The River Swale drains a rural catchment with no major urban and industrial areas, and the total phosphorus (TP) content of fluvial sediment is generally within the range 500–1500 μg g −1. There is little evidence of any major downstream increase in TP content. In contrast, fluvial sediment from the industrialized catchments of the Rivers Aire and Calder exhibits both higher levels of TP content and marked downstream increases, with values of TP content ranging from <2000 μg g −1 in headwater areas upstream of the main urban and industrial areas, to values >7000 μg g −1 at downstream sites. These elevated levels reflect P inputs from point sources, such as sewage treatment works (STWs) and combined sewer overflows. The influence of STWs is further demonstrated by the downstream increase in the inorganic P/organic P ratio from <2 in the headwaters to >4 in the lower reaches. Comparison of the P content of suspended sediment with that of the <63 μm fraction of potential source materials suggests that topsoil from upland moorland/pasture and from cultivated areas, and channel bank material are likely to be the main sources of particulate P (PP) in the River Swale and in the headwaters of the Rivers Aire and Calder. In the middle and lower reaches of the Rivers Aire and Calder, inputs associated with urban and industrial land uses, such as STWs, industrial effluents and street dust, are likely to represent the dominant sources of PP. During high flow events, such urban inputs may be diluted by inputs from moorland and agricultural land in the headwaters. Consequently, for all three rivers, there are inverse relationships between the TP content of suspended sediment and both discharge and suspended sediment concentration, reflecting changes in sediment and P sources during high flow events. Spatial variations in the P contents of the <63 μm fraction of overbank floodplain deposits and channel bed sediment evidence a similar pattern as those for suspended sediment, with relatively low levels of TP in the River Swale and elevated levels in the middle and downstream reaches of the Rivers Aire and Calder. The PP concentrations associated with floodplain and channel bed sediment are, however, lower than equivalent values for suspended sediment, and this primarily reflects the differences in the particle size composition between the three types of sediments. Rates of floodplain deposition and the amounts of fine-grained sediment stored in the river channels are relatively high, and suggest that such environments may represent important sinks for PP. Based on the sediment samples collected from the study basins, a simple four-fold classification which relates the TP content of suspended sediment to upstream land use has been established. Both the range and the absolute values of TP content tend to increase with an increase in the level of urbanization and industrialization.