Molybdate-reactive Phosphorus Concentrations Research Articles

Impact of anthropogenic induced nitrogen input and liming on phosphorus leaching in forest soils

AbstractPhosphorus (P) is essential for sustainable forest growth, yet the impact of anthropogenic impacts on P leaching losses from forest soils is hardly known. We conducted an irrigation experiment with 128 mesocosms from three forest sites representing a gradient of resin extractable P of the A‐horizon. On each site we selected a Fagus sylvatica and a Picea abies managed subsite. We simulated ambient rain (AR), anthropogenic nitrogen input (NI) of 100 kg (ha · a)−1 and forest liming (FL) with a dolomite input of 0.3 Mg (ha · a)−1. Soil solution was extracted from the organic layer, 10 cm depth and 20 cm depth of the mesocosms, and analyzed for molybdate reactive phosphorus (MRP) and molybdate unreactive phosphorus (MUP). Additionally, we separated colloids from the soil solution using Asymmetric Field Flow Fractionation for assessing the colloidal fraction of total element concentrations. NI increased MRP and MUP concentrations for all plots with one exception, while FL decreased MRP and MUP with the exception of another plot. While the irrigation treatments had little impact on the P‐richest site, MRP and MUP concentrations changed strongly at the poorer sites. The colloidal fraction of P in the soil solution equaled 38–47% of the total P load. Nitrogen input and liming also affected the Fe, Al, Ca, and Corg contents of the colloidal fraction.

A predictive geospatial approach for modelling phosphorus concentrations in rivers at the landscape scale

• Spatiality of phosphorus in rivers explored, accounting for environmental conditions. • Hydrological transportation and connectivity more influential than pollutant source. • Geospatial models better explain phosphorus variance than simple regression models. • Geospatial models can optimise management and monitoring for river water quality. Enrichment by phosphorus (P) constitutes a significant pressure on river systems, and is one of the main causes of freshwater pollution globally. Catchment environmental conditions influence the timing and magnitude of P release and transfer to water bodies, and therefore can potentially provide a basis for identifying water bodies vulnerable to impairment by P and/or resistant to restoration efforts. The current research involved construction of a geospatial database, comprising monthly values for flow-weighted concentrations of molybdate reactive phosphorus (fwMRP) sampled in rivers from 2006 to 2008 together with spatially-expressed environmental data relating to 18 different variables for 54 catchments in the Republic of Ireland. A regression–kriging modelling methodology within a landscape-scale, geospatial approach was tested. Environmental conditions relating to hydrological transportation and connectivity (slope, degree of surface saturation, soil water content) were found to exert greater influence over concentrations of P in rivers than direct proxies of sources of P (e.g. human population level or land use). Geospatial models provided greater explanation of P variance than regression models (an improvement in predictive capability of up to 8.5%). Data for fwMRP were segregated sub-annually into two periods, one focused on summer and the other on winter months. A geospatial model for the period including winter months was found to have a better predictive capability than the one that centred upon the summer, with the latter routinely overestimating fwMRP when compared with observed (test) data. Geospatial models potentially provide a means of optimising monitoring regimes for river water quality, and can also be used as a screening tool to focus management and remediation measures where they are likely to prove most effective.

IDENTIFICATION OF HYDROLOGICAL FACTORS CONTROLLING PHOSPHORUS CONCENTRATION IN DRAINAGE WATER IN SANDY SOILS

ABSTRACT The relationship between total phosphorus (TP) and molybdate-reactive phosphorus (MRP) concentrations in subsurface drainage waters in the hydrological conditions prevailing during autumn and spring flow events was statistically analysed using multiple linear regression analysis. Data on hydrological conditions in three drainage experimental plots in a loamy sand in south-east Sweden complemented with DRAINMOD-predicted data were used as independent variables. Regression models explained at least 80% of the variation in TP and MRP concentrations in drain outflow, based on adjusted coefficient of determination ( R 2adj ) calculations. DRAINMOD-predicted cumulative infiltration ( INFIL cum ) was identified as the most important hydrological condition controlling TP and MRP concentrations in drain outflow in three autumn events and in two out of three spring events. This suggests that the first infiltrating water found more soluble P forms available for transport, after which TP and MRP concentration in drainage outflows gradually decreased during the flow events.

Lysimeter Experiments to Determine the Ability of Soil to Reduce Concentrations of BOD, Available P and Inorganic N in Dirty Water

Lysimeter experiments were conducted to determine the ability of different soils to reduce levels of biochemical oxygen demand (BOD) and concentrations of molybdate reactive phosphorus (MRP) and ammonium-N (NH4 +-N) in dirty water and the impact of applications on nitrate leaching. An additional experiment investigated the effect of dirty water components on leaching quality. This information is required to assess the potential risk of dirty water applications on polluting groundwater and to assess the use of such soils in the development of treatment systems for dirty water. Intact and disturbed soil lysimeters, 0.5 and 1m deep were constructed from four soils; a coarse free-draining sandy loam, a sandy loam over soft sandstone, a calcareous silty clay over chalk and a sandy loam over granite. For the coarse free-draining sandy loam, lysimeters were also constructed from disturbed soil with and without the addition of lime, to assess if this could increase phosphorus immobilisation. Levels of BOD and concentrations of MRP, NH4 +-N and nitrate (NO3 − -N) of leachates were measured following dirty water applications at 2 and 8 mm day−1 under laboratory conditions. Under the daily 2mm application, all soils were effective at treating dirty water, reducing concentrations of BOD, MRP and NH4 +- N by ≥ 98% but NO3 −-N concentrations increased up to 80 mg l−1 from the 0.5 m deep lysimeters of the sandy loam over granite. Soils were less effective at reducing levels of BOD, MRP and NH4 +-N at the 8 mm daily rate of application, with maximum NO3 − -N concentrations of leachates of 200 mg l−1 from disturbed soils.

Effects of Storage by Freezing on Concentrations of Molybdate Reactive Phosphorus in Poultry Litter Extracts

In the laboratory, excessive variability in molybdate reactive phosphorus (MRP) concentrations in water extracts of poultry litter that appeared to be associated with storage by freezing was frequently observed. In one experiment, repeated twice, the effects of a factorial combination of storage temperatures [freezing (−16 to −15°C) or room temperature (21–24°C)] was studied for 60–62 h with poultry litter type (three broiler and one pullet) on MRP concentrations in water extracts. An additional experiment was conducted to compare the effects on phosphorus (P) concentration of a 1 mg P L−1 standard of spiking with 1 mg L−1 of Fe+3 or Al+3 and storage under room temperature or freezing for two and five days. No statistical differences were observed in MRP levels of extracts kept at room temperature measured immediately after the extraction, after 62 h or eight days. Freezing, however, consistently decreased MRP concentrations measured immediately after thawing compared to measurements in extracts kept at room temperature. Reductions ranged from less than 1% to 46%, depending on poultry litter composition, especially total iron (Fe) and aluminum (Al) concentrations. Freezing effects were reversible and after five days MRP concentrations were comparable to those of extracts kept always at room temperature. Spiking with Al+3 did not affect P solubility but spiking with Fe+3 and freezing for five days reduced the MRP concentrations in the P standard when measured immediately or two days after thawing. The results from the P, Fe+3, and Al+3 experiment plus the observation of precipitates containing P and Fe in some of the poultry litter extracts suggested complexing between these elements as a partial explanation of these responses. Organic compounds and Al+3 might also be involved. The solubilization of the floccules upon thawing might be retarded by changes induced by freezing. In consequence, freezing of water extracts of poultry litter can bring about significant, albeit transient, decreases in soluble orthophosphate concentrations.

Colloidal phosphorus in surface runoff and water extracts from semiarid soils of the western United States.

Colloidal particles in runoff may have an important role in P transfer from soils to waterbodies, but remain poorly understood. We investigated colloidal molybdate-reactive phosphorus (MRP) in surface runoff and water extracts of calcareous arable soils from the semiarid western United States. Colloidal MRP was determined by ultrafiltration and operationally defined as MRP associated with particles between 1 microm and 1 nm diameter, although a smaller pore-size filter (0.3 nm) was used to define the lower size limit of colloids in water extracts. In surface runoff from three calcareous soils generated by simulated sprinkler irrigation, colloidal MRP concentrations ranged between 0.16 and 3.07 microM, constituting between 11 and 56% of the MRP in the <1-microm fraction. Concentrations were strongly correlated with agronomic and environmental soil-test P concentrations for individual soils. Water extracts of a range of similar soils contained two size fractions of colloidal MRP: a larger fraction (1.0-0.2 microm) probably associated with fine clays, and a smaller fraction (3-0.3 nm) probably associated with Ca-phosphate minerals. Colloidal MRP was solubilized in the acidic medium of the colorimetric detection procedure, suggesting that a fraction of the filterable MRP in runoff from calcareous soils may not be as readily bioavailable as free phosphate in waterbodies. Our results suggest that colloidal MRP is an important but poorly understood component of P transfer in runoff from calcareous western U.S. soils and should be given greater consideration in mechanistic studies of the P transfer process.

Hydrogeomorphic controls on phosphorus retention in streams

We compared the relative influences of biochemical uptake processes and dynamic hydrology and geomorphology (hydrogeomorphology) on molybdate reactive phosphorus (MRP) retention within a stream. MRP concentrations were measured upstream and downstream of a 4.5‐km reach undergoing dynamic channel adjustment in response to downstream dam removal. Geomorphic adjustments following removal produced measurable changes in velocity and depth, and decreases in MRP retention. Paired upstream and downstream measurements of MRP concentration were used to compute three retention metrics: uptake rate, mass transfer coefficient, and uptake length, which were used as model parameters. Modeling results showed that changes in channel morphology alone following dam removal could result in an approximate 40% increase in downstream MRP concentrations compared with conditions with the dam in place. However, empirical and modeling results indicate that hydrogeomorphology can control nutrient retention on the reach scale only when uptake processes are either sufficiently great or when uptake rates have limited variability. Review of published phosphorus retention values revealed greater variability in biochemical uptake rates than in hydrogeomorphology. Thus uptake rates should exert a stronger control on reach‐scale MRP retention than changing channel morphology or hydrology. These results suggest that maintaining or restoring channel conditions that are conducive to biochemical uptake are of greater priority than restoration of hydrologic or geomorphic conditions alone.

Biogeochemical impacts of clearfelling and reforestation on blanket peatland streams I. phosphorus

Forest drains and streams on blanket peatland in western Ireland were sampled weekly, 1996–2000, using continuous, depth-proportional passive sampling, and analysed for molybdate-reactive phosphorus (MRP) by the acid–antimony-molybdate method. The study area was largely clearfelled and partly reforested with wind-rowing, drainage, planting, and aerially applied rock phosphate equivalent to 70 kg P/ha. Further felled areas were not wind-rowed, drained or fertilised for reforestation. Catchment areas were of the following orders: 1 ha (two forest drains); 10–20 ha (two semi-permanent drains, one permanent stream); 1–3 km 2 (three permanent streams). Streamwater from three undisturbed closed-canopy-forest catchments had pre-felling median concentrations of MRP (all values are μg MRP l −1) of 9 (catchment approximately 1 km 2), 13 (1 ha) and 93 (1 ha). Clearfelling was associated with large increases (maxima 305, 4164 and 3530 μg MRP l −1) in MRP concentrations in each case. Following protracted mechanical operations in four other catchments of ca. 1 km 2, 20, 10 and 10 ha, with apparently existing elevated MRP concentrations (medians 41, 328, 102, 214 μg MRP l −1) fertilising gave major rises (maxima 218, 2723, 806, 2323 μg MRP l −1). The three smaller catchments showed subsequent exponential-type declines, while the 1 km 2 catchment had sustained high values (median 74 μg MRP l −1) over the remaining study period. The higher values in this one larger stream were seasonally cyclical, with a late summer maximum. Annual median MRP values above 70 μg l −1 represent a seriously polluted state for these streams, which qualify as waterways under relevant statutes, but it is not clear what implications these results have for downstream river-water quality in larger channels.

Effect of phosphate fertilizer application on phosphorus (P) losses from paddy soils in Taihu Lake Region. I. Effect of phosphate fertilizer rate on P losses from paddy soil.

A field plot study was conducted on two types of paddy soils in the Taihu Lake Region, during the rice season of year 2000 in order to assess phosphorus (P) losses by runoff and vertical leaching, which are considered the two main pathways of P movement from paddy soil into its surrounding water course. Commercial NPK compound fertilizer and single superphosphate fertilizer were applied to furnish 0, 30, 150, and 300 kg applied P ha m(-2). The experiments consisted of three replicates of each treatment in Changshu site and four replicates in Anzhen site, with a plot size of 5 x 6 m2 in a randomized block. Results revealed that the average concentration range for total P (TP) in runoff was 1.857-7.883, 1.038-5.209, 0.783-1.255 and 0.572-0.691 mg P l(-1) respectively for P300, P150, P30 and P0 in Anzhen, while it was 2.431-2.449, 1.578-1.890, 1.050-1.315 and 0.749-0.941 mg P l(-1) respectively in Changshu. In all treatments, particulate P (PP) represented a major portion of the TP lost in runoff, it was 80% in Anzhen, and it was even more (>90%) in Changshu. Phosphate fertilizer treatments significantly affected P concentrations and P loads in the runoff. The mean concentration and average seasonal TP load from the P150 plots were 1.809 mg P l(-1) and 395 g P ha m(-2) season(-1) respectively, and lower than that from the P300 plots (2.957 mg P l(-1) and 652 g P ha m(-2) season(-1)). These were obviously higher than from the P30 (0.761 mg P l(-1) and 221 g P ha m(-2) season(-1)) and P0 (0.484 mg P l(-1) and 146 g P ha m(-2) season(-1)) respectively. There was no significant difference found between the P30 and the P0 in both sites. Under usual P application rate, there were total 31.7 and 20.6 tones P removed by runoff from permeable (Anzhen site) and waterlogged (Changshu site) paddy soils in the southern Jiangsu region (major part of the TLR) in the rice season of the year 2000. But if the P application rate is unusual high, or the Olsen P in soil accumulates to above a certain level, then this could sharply increase in the future. The average concentration of molybdate reactive phosphorus (MRP) in the vertical leachate from the four different P treatments ranged from 0.058 to 0.304 mg P l(-1) in Anzhen and from 0.048 to 0.394 mg P l(-1) in Changshu. P application rate significantly affected the MRP concentration at each depth in both sites, except for the 90 cm in Anzhen. The average MRP loads during the rice season moved by vertical leaching from the four treatments ranged from 163 to 855 g P ha m(-2) season(-1) in Anzhen and 208-1,825 g P ha m(-2) season(-1) in Changshu. Vertical leachate movement does not necessarily mean that it moves towards surface water and contaminate the watercourses in this flat plain paddy soil region, it does, however, imply that P can move down from surface layers of soil to deeper levels.

Soil derived phosphorus in surface runoff from grazed grassland lysimeters

Seven 1 ha grazed lysimeter plots, managed as intensive grassland for the last 12 years, were monitored for total phosphorus (TP) and molybdate reactive phosphorus (MRP) in surface runoff plus interflow to 30 cm depth, for up to ten events during 1994. The mean MRP and TP concentrations determined were 40 and 122 μg 1 −1, respectively, but the data were heavily skewed by low frequency high intensity events. Thus concentrations of MRP and TP of over 1200 and 1700 μg 1 −1 respectively were determined in extreme events, causing a TP export of up to 18 g ha −1 per h and, during one event of 30 h duration, over 0.5 kg TP ha −1 was estimated to have been removed, representing a significant proportion of the triple super phosphate fertiliser added 6 days earlier. One storm was monitored at 3 h intervals and the patterns for TP concentration and TP load were closely related to discharge. MRP concentration did not follow the hydrographic pattern. Excluding the low frequency high intensity events, an empirical model TP (μg 1 −1) = 58 + [42 × discharge] (1 s −1) was postulated, which although significant ( P = 0.0053), only accounted for 14% of the relationship. It was thus concluded that understanding of release mechanisms in the majority of high frequency, low intensity events is inadequate. Conversely, during one period of high phosphorus (P) export, the mechanisms responsible were suggested to be a combination of the presence of cattle (excretal returns and poaching), timing of inorganic P fertiliser additions, and intensity of rainfall. Grassland soils are a significant source of diffuse P inputs to surface and estuarine waters and may cause eutrophication.

Effect of Storage and Sieving on the Phosphorus Composition of Soil Solution

AbstractIn this study, the effects of storage and sieving of a mineral soil (Typic Fragiorthod) on the P chemistry of the soil solution have been quantified. Intact and sieved soil cores were stored for 0, 1, 3, and 8 d at 4°C prior to obtaining solutions, which were analyzed for total dissolved phosphorus (TDP), molybdate‐reactive phosphorus (MRP), dissolved organic phosphorus (DOP), and dissolved condensed phosphorus (DCP). Storage of both sieved and intact soil cores influenced the amount and chemical composition of P in solution. Concentrations of TDP, MRP, and DOP displayed a rapid decline with increase in storage time, whereas DCP concentrations, which were initially very low, increased. Concentrations of TDP were significantly (P &lt; 0.05) different between solutions extracted from intact and sieved soils on the same day as sampling and this was accounted for by DOP and MRP, which were significantly (P &lt; 0.05) larger in sieved soil. The proportions of MRP, DOP, and DCP were similar in solutions extracted from intact and sieved soils on the same day, even for Day 0 where a large difference in TDP was apparent. The MRP fraction was consistently larger for intact cores (44%) than sieved (38%) on all days and varied little with length of storage. The DOP component, which dominated initially, decreased with increase in storage time, while DCP increased to become the major fraction after 8 d of storage. This study has highlighted the potential effects of soil storage and sieving on the P concentration and composition of soil solution. The results also have important implications for soil solution sampling and subsequent data interpretation.

Molybdate‐Reactive Phosphorus Losses in Surface and Drainage Waters from Permanent Grassland

AbstractAlthough the loss of P in agricultural runoff can provide freshwater eutrophication, little information is available on losses from permanent grasslands. Thus, 14 lysimeter plots (each of 1 ha), established in 1982 on a clay loam soil under grazed grassland management, were monitored between 1989 and 1991 for release of molybdate‐reactive phosphorus (MRP). The plots enabled the daily measurement of discharge through field drains (to 85 cm) or by surface lateral runoff (to 30 cm). Sward type was either perennial ryegrass (Lolium perenne L.) or a perennial ryegrass‐clover (Trifolium sp.) mixture. The plots were grazed continuously by beef cattle and received either 200 or 400 kg N ha−1 yr−1 in various combinations. Having collected &gt;7500 data points during the 3 yr, it was found that there was no significant difference between the effects of either agronomic or drainage variables (P &gt; 0.05) within years. However, there was a significant difference (P &lt; 0.05) between drainage variables when the data from the 3 yr were combined, as there were larger MRP losses from undrained treatments. There was no relationship between concentration of MRP and drainage volume. The MRP concentrations ranged from 0.01 to 0.7 mg L−1 with an average concentration of 0.02 mg L−1. Losses of MRP as great as 0.4 kg ha−1 yr−1 were measured in surface lateral runoff from undrained plots and 0.2 kg ha−1 yr−1 in water percolating through field drains. The data show this type of grassland system may have the potential to be an important diffuse source of P to fresh waters.

Total, organic and extractable-P in humus and soil beneath Sitka spruce planted in pure stands and in mixture with Scots pine

Total, organic and extractable P were measured in the humus and underlying soil to 10 cm depth beneath Sitka spruce (SS) and mixed Sitka spruce and Scots pine (SS+SP) stands planted on upland heath. The humus beneath SS+SP contained significantly (p<0.01) greater amounts of total and organic-P than that in SS and the mixed stands had more effectively retained approximately 87 per cent of previously applied fertilizer-P, totalling 100 kg P ha−1, compared with 70 per cent in SS. Despite the larger amounts of total-P in the mixed plots 0.01 M CaCl2 extractable molybdate reactive phosphorus (MRP) was significantly (p<0.05) greater in SS+SP humus only during March and April. Greater concentrations of MRP were released from the humus and soil during July and August at a mean rate of 58 g P ha−1 day−1. This coincided with drying of the soil during the summer and the rate of release, attributed to death of fine roots and microorganisms, was 4 to 30 times greater than reported values for rates of net mineralization of P from forest soils.