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Sediments in streams that drain agricultural watersheds may be sinks that can adsorb P from the stream or sources that can release P to the stream. Sediment characteristics and environmental factors, including the oxidation-reduction (redox) potential of the water associated with the sediment, determine whether P will be adsorbed or released by the sediment. We investigated P adsorption and release by four sediments [three Holocene-age sediments (Camp Creek, Roberts Creek and Gunder) as well as Pre-Illinoian-age Till] that occur in Walnut Creek, a second-order stream in Jasper County, Iowa, that is representative of many small streams in the glaciated upper Midwest of the US. The effects of two redox potentials on phosphorus buffering capacity (PBC) and equilibrium phosphorus concentration (EPC) were evaluated in batch adsorption experiments. We also simulated aerobic and anerobic conditions over a 24-day period and measured solution-phase P concentrations in stirred systems where the sediments were isolated from the water by dialysis tubing. The batch experiment indicated that the EPCs of the three Holocene-age sediments were similar to one another and increased with decreasing redox potential. In the stirred flow reactors, more dissolved P was released from the Camp Creek and Roberts Creek sediments under anaerobic conditions than from the other sediments. This observation suggests that these two sediments, which are younger and higher in the stratigraphic sequence, are more likely to be P sources in suboxic settings. The P buffering capacity was greatest in the till. Where it is in contact with the stream water, the till is likely to serve as an adsorbing sink for P in the water column., Competing Interests: The authors have declared that no competing interests exist.

The surface waters of Rathbun Lake watershed in southern Iowa are impacted by agricultural sources of sediments and nutrients, including phosphorus (P). Because stream sediments often play an important role in regulating P concentrations in stream water, we investigated sediment-water column P relationships in four creeks within the watershed and then evaluated the relationship between sediment properties and indicators of the risk of P loss. Based on Mehlich-3-extractable P (17 to 68 mg kg(-1)) and degree of P saturation (2 to 12 %), stream bank and bed sediments at the four sites were unlikely to serve as major sources of P. However, equilibrium P concentrations, which ranged from 0.02 to 0.12 mg L(-1), indicated that bed sediments could release P to the water column depending on dissolved P (DP) concentrations in the stream water and the time of year. The likelihood of P desorption from the sediments increased with increasing pH (r = 0.92, p < 0.01) and sand content (r = 0.78, p < 0.05), but decreased with clay content (r = -0.72, p < 0.05) and iron (Fe) (r = -0.93, p < 0.001) associated with organic matter. From these results, we speculate that changes in land use within the riparian areas may, at least initially, have little effect on P concentrations in the streams. Low concentrations of DP relative to total P (TP) in these streams, however, suggest that P loads to Rathbun Lake can be reduced if P inputs from eroded bank sediments are controlled.

Sequential phosphorus (P) fractionation is a procedure often used to assess P dynamics in riparian soils and stream sediments. The most commonly used method to quantify P in fractionation extracts is the molybdate blue-ascorbic acid (MB-AA) colorimetric method. Because sequential P fractionation generates a large number of samples, it would be advantageous to use a single, rapid analytical technique to determine P concentrations. Thus, we investigated the malachite green (MG) colorimetric method for determining P concentrations in the diverse sequential fractionation matrices. For the MG method, a 96-well standard microplate was used, and absorbance was read on a universal microplate reader. We found that the MG and MB-AA methods agreed for determining P concentration in extracts of water, 1 M hydrochloric acid (HCl), and concentrated sulfuric acid (H2SO4). Small differences between the two methods were found for extracts of 0.5 M sodium bicarbonate (NaHCO3) and 0.1 M sodium hydroxide (NaOH), and concentrated HCl, most likely related to differing characteristics of the sediments that were analyzed. Despite this discrepancy for some extracts in the sequential extraction, the microplate system-MG method can be valuable because of its simplicity, sensitivity, and rapidity compared to the MB-AA method. [ABSTRACT FROM AUTHOR]

Investigates the impact of biosolids amendments to soil on the sorption, desorption and buffering capacity of phosphorus. Phosphorus sorption isotherms; Calculated sorption parameters; Exchange of phosphorus and soluble organic carbon.

Although phosphorus (P) is an essential nutrient for biological productivity, it can cause freshwater degradation when present at fairly low concentrations. Monitoring studies using continuous sampling is crucial for documenting P dynamics in freshwater ecosystems and to reduce the risk of eutrophication. Despite literature updates of developments of the analytical methods for measurement of P species in natural waters, there has been no comprehensive review addressing freshwater sample collection, sample preparation, and sample treatment to fractionate and characterize different forms of P. Therefore, this paper aims to elaborate the different techniques for freshwater sampling and to introduce alternative laboratory methods for sample preservation and P fractionation. The advantages and disadvantages of various sampling techniques, including the traditional manual and the recently developed automatic and passive methods, are presented to highlight the importance of collecting representative freshwater samples. Furthermore, we provide suggestions for sample pretreatment, including filtration, transportation, and storage steps to minimize microbial activity and to maximize the accuracy of measurement of various P fractions. Finally, the most common laboratory methods to measure dissolved and particulate as well as the organic and inorganic freshwater P fractions are efficiently provided. Using this guide, a comprehensive monitoring program of P dynamics in freshwater ecosystems can be developed and applied to improve water quality, particularly of P-rich freshwaters. [ABSTRACT FROM AUTHOR]

The amount of P applied to land with biosolids is generally more than plants need when the application rate is based on the potentially available N. The subsequent accumulation of P is of environmental rather than agronomic concern, because it could lead to eutrophication ofwater bodies if P is carried off-site in surface runoff, subsurface drainage water, or eroded soil. In a large-scale field study with three biosolids application rates (approximately 0, 7.4, and 13.0 Mg drymatter ha-1), we investigated the redistribution of P derived from surface-applied biosolids in soil under poplars and switchgrass. Soil samples were collected from two depths (0-5 cm and 5-25 cm), and total P was determined by colorimetry after strong acid digestion. Total P in mobile soil water samples collected by zero-tension lysimeters was determined by inductively coupled plasma spectrometry. After 6 yr of continuous biosolids application to poplar tree (Populus sp.) plots, total P in soil increased significantly (Alpha = 0.05) at both the 0- to 5- and 5- to 25-cm depths under poplars. Also at both depths, a linear relationship between total P in soil and the amount of P applied with biosolids (Alpha = 0.05) was found. Under switchgrass (Panicum virgatum L.), total P increased significantly (Alpha =0.05) at only the 0- to 5-cm depth. A linear relationship between total P in soil and the amount of P applied with biosolids (Alpha = 0.05) was found at the 0- to 5-cm depth under switchgrass but not at the5- to 25-cm depth. The amount of P taken up annually by switchgrass was estimated to be rive times more than that taken up by poplars. The amount of P leached in mobile soil solution of switchgrass plots was estimated to be twice that leached in soil solution of poplar tree plots. Phosphorus that accumulated in the upper 5 cm of the soil accounted for =/>45% or more of the total P applied with biosolids, except for the low biosolids application rate to switchgrass plots where the v [ABSTRACT FROM AUTHOR]