Funding was made available by the Vermont Water Resources and Lake Studies Center through an agreement with the U.S. Geological Survey. Conclusions and opinions are those of the authors and not the Vermont Water Resources and Lake Studies Center or the USGS.

1. Sample collection
<ol>
	<li>Collect approximately 4 L of soil (or sediment) from desired sites. Collection areas should be relatively small to limit spatial variation in P and soil properties.</li>
	<li>Sieve samples through a coarse (20 mm) screen followed a 2 mm screen. Thoroughly hand-mix samples after sieving.</li>
	<li>Weigh out 100 g of field-moist soil or sediment. Dry in an oven at 105 &#176;C for 24 h and calculate gravimetric water content (soil water mass/dry soil mass).</li>
	<li>Take a 500 mL subsample ...

<ol>
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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphate+release+from+seasonally+flooded+soils:+a+laboratory+microcosm+study.">Phosphate release from seasonally flooded soils: a laboratory microcosm study.</a> Journal of Environmental Quality. 30 (1), 91-101 (2001).</li><li>Henderson, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Anoxia-induced+release+of+colloid-+and+nanoparticle-bound+phosphorus+in+grassland+soils.">Anoxia-induced release of colloid- and nanoparticle-bound phosphorus in grassland soils.</a> Environmental Science &amp; Technology. 46 (21), 11727-11734 (2012).</li><li>Vidon, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hot+spots+and+hot+moments+in+riparian+zones:+potential+for+improved+water+quality+management.">Hot spots and hot moments in riparian zones: potential for improved water quality management.</a> Journal of the American Water Resources Association. 46 (2), 278-298 (2010).</li><li>Young, E. O., Ross, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+mobilization+in+flooded+riparian+soils+from+the+Lake+Champlain+Basin,+VT,+USA.">Phosphorus mobilization in flooded riparian soils from the Lake Champlain Basin, VT, USA.</a> Frontiers in Environmental Science. 6 (120), 1-12 (2018).</li><li>McIntosh, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bray+and+Morgan+soil+extractants+modified+for+testing+acid+soils+from+different+parent+materials.">Bray and Morgan soil extractants modified for testing acid soils from different parent materials.</a> Agronomy Journal. 61 (2), 259-265 (1969).</li><li>Young, E. O., Ross, D. S., Cade-Menun, B. J., Liu, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+speciation+in+riparian+soils:+a+phosphorus-31+nuclear+magnetic+resonance+and+enzyme+hydrolysis+study.">Phosphorus speciation in riparian soils: a phosphorus-31 nuclear magnetic resonance and enzyme hydrolysis study.</a> Soil Science Society of America Journal. 77 (5), 1636-1647 (2013).</li><li>McGechan, M. B., Lewis, D. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sorption+of+phosphorus+by+soil:+Part+1.+Principles,+equations,+and+models.">Sorption of phosphorus by soil: Part 1. Principles, equations, and models.</a> Biosystems Engineering. 82 (1), 1-24 (2002).</li><li>Cabrera, M. L., Radcliffe, D. E., Cabrera, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Modeling+phosphorus+in+runoff:+Basic+approaches.">Modeling phosphorus in runoff: Basic approaches.</a> Modeling Phosphorus in the Environment. , 65-81 (2007).</li><li>Gbur, E. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Analysis of Generalized Linear Mixed Models in the Agricultural and Natural Resources Sciences. , (2012).</li><li>Moore, P. A., Reddy, K. R., Fisher, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+flux+between+sediment+and+overlying+water+in+Lake+Okeechobee,+Florida:+Spatial+and+temporal+variations.">Phosphorus flux between sediment and overlying water in Lake Okeechobee, Florida: Spatial and temporal variations.</a> Journal of Environmental Quality. 27 (6), 1428-1439 (1998).</li><li>Young, E. O., Briggs, R. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+concentrations+in+soil+and+subsurface+water:+A+field+study+among+cropland+and+riparian+Buffers.">Phosphorus concentrations in soil and subsurface water: A field study among cropland and riparian Buffers.</a> Journal of Environmental Quality. 37 (1), 69-78 (2008).</li><li>Hoffmann, C. C., Kjaergaard, C., Uusi-K&#228;mpp&#228;, J., Hansen, H. C. B., Kronvang, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+retention+in+riparian+buffers:+review+of+their+efficiency.">Phosphorus retention in riparian buffers: review of their efficiency.</a> Journal of Environmental Quality. 38 (5), 1942-1955 (2009).</li><li>Bartlett, R. J., Ross, D. S., Tabatabai, M. A., Sparks, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+of+Redox+Processes+in+Soils.">Chemistry of Redox Processes in Soils.</a> Chemical Processes in Soils, SSSA Book Ser. 8. , 461-487 (2005).</li><li>Radcliffe, D. E., Freer, J., Schoumans, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diffuse+phosphorus+models+in+the+United+States+and+Europe:+Their+usages,+scales,+and+uncertainties.">Diffuse phosphorus models in the United States and Europe: Their usages, scales, and uncertainties.</a> Journal of Environmental Quality. 38 (5), 1956-1967 (2009).</li><li>Bartlett, R. J., James, B. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Studying+dried,+stored+soil+samples&#8212;some+pitfalls.">Studying dried, stored soil samples&#8212;some pitfalls.</a> Soil Science Society of America Journal. 44 (4), 721-724 (1980).</li><li>Turner, B. L., McKelvie, I. D., Haygarth, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+water+extractable+soil+organic+phosphorus+by+phosphatase+hydrolysis.">Characterization of water extractable soil organic phosphorus by phosphatase hydrolysis.</a> Soil Biology &amp; Biochemistry. 34 (1), 27-35 (2002).</li><li>Turner, B. L., Haygarth, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus+solubilization+in+rewetted+soils.">Phosphorus solubilization in rewetted soils.</a> Nature. 411, 258 (2001).</li><li>Sparks, D. L., Sparks, D. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Kinetics+of+reactions+in+pure+and+mixed+systems.">Kinetics of reactions in pure and mixed systems.</a> Soil Physical Chemistry. , (1986).</li></ol>

The authors declare that this work was conducted in the absence of any commercial or financial relationships that could be interpreted as a potential conflict of interest.

A main technical advantage of the microcosm approach is its ability to simulate in-situ conditions whereby saturated soil or sediment is immediately overlain by FW that may substantially differ in redox and P status. Landscapes with variable source area hydrology such as drainage ditches, flooded cropland, wetlands, and riparian/near-stream zones are all examples of where reduced PW is periodically overlain by more oxidized water with lower Pi concentrations. These redox gradients can strongly affect Pi sorption...

Phosphorus (P) is a critical limiting nutrient for both crop and aquatic biomass productivity. Surface water hydrology is a main driver of P fate and transport, as it controls the physical transport of sediment and P while also affecting remobilization potential during runoff and flooding/ponding events. Various laboratory-based extraction methods are typically used to estimate P release at the field scale under oxidizing conditions. While different mechanisms can contribute to P release, reductive dissolution of iron-phosphates is a well-established reaction mechanism that can lead to large orthophosphate-P fluxes to water1,2,3,4. In a review of mechanisms controlling P biogeochemistry in wetlands, redox status was hypothesized to be the main variable controlling P release to soils and shallow groundwater5. As such, traditional P tests may not be reliable predictors of P release under prolonged saturation.
Given the importance of water residence time and redox status on P fate and transport, laboratory approaches designed to better simulate in situ conditions could lead to improved P transport risk indices for agricultural and wetland ecosystems subject to variable saturation. Since orthophosphate is immediately bioavailable, the rate and extent of desorption during saturation can be used as an index of nonpoint source P pollution risk. Our method was designed to quantify P desorption to porewater (PW) and mobilization to overlying floodwater (FW), a typical condition in areas with variable source area hydrology (e.g., flooded agricultural fields, wetlands, drainage ditches, and riparian/near-stream zones). The method was originally developed to characterize P release potential in seasonally flooded soils from northern New York (USA) and recently applied to quantify P desorption potential of riparian soils from northwestern Vermont&#8217;s Lake Champlain Basin6. Here, we provide a protocol for the laboratory microcosm method and highlight results from a recently published study demonstrating its ability to quantify P desorption potential. We also demonstrate the relationship between P release potential and the reliability of routine soil tests (labile extractable P, pH) to predict release across sites.
Carrying out the method requires access to an analytical laboratory with adequate climate control, ventilation, water, and a proper acid waste disposal system. The method presumes access to routine chemical reagents and laboratory equipment (sinks, hoods, glassware, etc.). Beyond routine laboratory needs, a membrane filtration (&#8804; 0.45 &#181;m) system is required and a UV spectrophotometer to measure P. A pH meter or multiparameter water quality probe are also recommended but not required. Laboratory temperature is an important factor and should be kept constant unless temperature itself is being investigated as an experimental factor (20 &#176;C is recommended). Unhindered access to an adequate analytical laboratory with proper equipment is a prerequisite to perform the method properly and generate meaningful results.

<table>
	<tbody>
		<tr>
			<td>1.25 cm plastic hose barbs</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Chemical reagents for phosphorus determination</td>
			<td>numerous</td>
			<td>NA</td>
			<td>P analysis capability is assumed; refer to cited references for details on method</td>
		</tr>
		<tr>
			<td>Chordless or electric drill with 1.25 cm bit</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Graduated plastic beakers (1L)</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Laboratory with fume hoods, temperature control, and acid waste disposal system</td>
			<td>NA</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Nylon mesh filter screen (100um)</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
		<tr>
			<td>UV Spectrophotometer</td>
			<td>numerous</td>
			<td>NA</td>
			<td></td>
		</tr>
	</tbody>
</table>

measuring phosphorus release in laboratory microcosms for water quality assessment

Phosphorus (P) is a critical limiting nutrient in agroecosystems requiring careful management to reduce transport risk to aquatic environments. Routine laboratory measures of P bioavailability are based on chemical extractions performed on dried samples under oxidizing conditions. While useful, these tests are limited with respect to characterizing P release under prolonged water saturation. Labile orthophosphate bound to oxidized iron and other metals can rapidly desorb to solution in reducing environments, increasing P mobilization risk to surface runoff and groundwater. To better quantify P desorption potential and mobility during extended saturation, a laboratory microcosm method was developed based on repeated sampling of porewater and overlying floodwater over time. The method is useful for quantifying P release potential from soils and sediments varying in physicochemical properties and can improve site-specific P mitigation efforts by better characterizing P release risk in hydrologically active areas. Advantages of the method include its ability to simulate in situ dynamics, simplicity, low cost, and flexibility.

Results from a recent study focused on P release potential of riparian areas are highlighted to demonstrate the method&#8217;s ability to characterize site-level P release dynamics6. While some soils showed minimal changes in SRP over time, others had large increases in PW- and FW-SRP concentrations (Figure 1). Two sites with contrasting trends are shown in Figure 1. Soil 7 is a riparian site with low soil pH and characterized by nearly c...

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Measuring Phosphorus Release in Laboratory Microcosms for Water Quality Assessment

Accurate quantification of phosphorus (P) desorption potential in saturated soils and sediments is important for P modeling and transport mitigation efforts. To better account for in situ soil-water redox dynamics and P mobilization under prolonged saturation, a simple approach was developed based on repeated sampling of laboratory microcosms.

Phosphorus (P) is a critical limiting nutrient in agroecosystems requiring careful management to reduce transport risk to aquatic environments. Routine ...

Our method helps answer the question of how likely a given soil or sediment is to release soluble phosphorous under prolonged saturation. Quantifying phosphorous release potential in variably saturated environments is important for determining transport risk to streams and designing mitigation practices. The main advantage of the method is its ability to simulate important biogeochemical processes affecting soluble phosphorous release in mobility under field conditions.A scientist trying this method for the first time should not struggle, as its simplicity is one of its main advantages. To begin, collect approximately four liters of soil from desired sites. Limit collection areas to approximately 10 square meters to reduce the amount of spacial variability represented by the sample.Sieve samples through a coarse 20 millimeter screen, followed by a two millimeter screen. Thoroughly hand-mix the samples after sieving. Weigh out 100 grams of the field-moist soil, dry in an oven at 105 degrees Celsius for 24 hours.Weigh the dry soil and calculate percent gravimetric water content. Then, measure out a 500 milliliter subsample using an empty beaker and reserve for chemical analysis. Use the remaining sieved soil for microcosm studies or store in polypropylene bags at five degrees Celsius for later use.Use one liter graduated polypropylene or other nonreactive plastic beakers as individual experimental microcosm units. Wash beakers in 10%hydrochloric acid and triple rinse with distilled water. Measure two centimeters up from the bottom and place a mark next to beaker graduations.Drill a 1.25 centimeter diameter hole at the mark for drainage ports. Place a small bead of silicone around the inside edge of hose barb. Carefully insert the drainage port into the hole.Allow air-drying for 24 hours before proceeding. Trace the outside circumference of hose barbs onto nylon mesh filter screen. Cut out with scissors, apply a thin bead of silicone around the outside edge of the filter screen, and gently press onto the hose inlet.Allow at least 24 hours of drying time before using. Next, fit a short piece of latex hose on hose barbs and clamp with 3.3-centimeter-wide paper binder clips. Fill beakers with approximately 500 milliliters of distilled water, to test for possible leaks.Load 500 milliliters of sample into duplicate microcosms and gently apply distilled water along beaker walls until floodwater reaches the one liter mark. Remove the paraffin film to induce porewater flow through drainage port at desired initial sampling time point. Collect samples by placing clean 20 milliliter beakers directly beneath porewater drainage ports.Allow several milliliters of porewater to drain, discard, and use the next 10 milliliters as a representative sample volume. Filter porewater samples through 0.45 micron membrane filters and immediately analyze for soluble reactive phosphorus on a spectrophotometer. Record absorbance values and time of measurements.Take initial floodwater sample by inserting a 10 milliliter bulb syringe pipette halfway down the water column, and withdraw a sample using a circular motion. Dispense into beakers, filter through 0.45 micron membrane filters, and analyze immediately for soluble reactive phosphorus. Refill beakers to the one liter level with distilled water to consistently maintain a total volume of flooded soil and water column at one liter in all microcosms.Repeat the analysis of soluble reactive phosphorus at desired time points. In this protocol, a riparian site with low soil pH had nearly continuous soluble reactive phosphorus sorption from porewater. Soil that was sampled from an adjoining maize production field with elevated labile inorganic phosphorus demonstrated nearly a sevenfold increase in porewater-soluble reactive phosphorus over the first month of inundation.Porewater ferrous iron concentration, as a proxy for redox status, increased substantially after approximately three weeks, indicating reducing conditions. In contrast, floodwater-soluble reactive phosphorus tended to decrease over time. Flooding dry soil substantially increased inorganic phosphorus desorption to porewater and subsequent mobilization to overlying water compared to flooding the same soil in a field-moist state.The reliability of soil phosphorus tests to predict average soluble reactive phosphorus concentrations, was evaluated. Distilled water and modified Morgan extractable phosphorus were among the best predictors of average porewater and floodwater-soluble reactive phosphorus concentrations. Modified Morgan extractable phosphorus measured by inductively coupled plasma optical emission spectroscopy was not as good of a predictor compared to modified Morgan extractable phosphorus or distilled water measured by molybdate colorimetry.The ratio of porewater-soluble reactive phosphorus over floodwater-soluble reactive phosphorus increased linearly as a function of soil pH. Other experiments characterizing phosphorus dynamics are also possible, for example, phosphorus removal capacity of wetland soils is an important process and can be simulated by spiking floodwater with phosphorus and measuring its rate of disappearance over time. The analytical procedure used for measuring phosphorus involves the use of hydrochloric acid.Proper safety equipment and laboratory facilities are therefore required.

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6.4K visualizações.  United States Department of Agriculture, Agricultural Research Service (USDA-ARS), Institute for Environmentally Integrated Dairy Management. Nosso método ajuda a responder à questão de quão provável é que um determinado solo ou sedimento seja para liberar fósforo solúvel sob saturação prolongada. Quantificar o potencial de liberação de fósforo em ambientes variavelmente saturados é importante para determinar o risco de transporte para os córregos e projetar práticas de mitigação. A principal vantagem do método é sua capacidade de simular importantes processos biogeoquímicos que afetam a liberação de fósforo...