Phosphorus is a non-renewable resource that is heavily used in agriculture to ensure food security to the growing world population. However, a large amount of the phosphorus used in agriculture is lost to nonpoint runoff causing excess phosphorus in surface water systems. This can lead to eutrophication, toxic algal blooms, and other harmful environmental impacts as well as representing a large loss of this valuable nutrient resource. Attempting to recover the lost phosphorus in runoff sediment presents a huge opportunity to mitigate environmental impact, regain the lost nutrient resource for reuse as fertilizer, and to reduce the demand for mined phosphorus ores with finite supplies and currently the only viable source of phosphorus for fertilizer. We have recently published preliminary results demonstrating the viability of sequestering particulate-bound phosphorus from intercepted runoff sediments via P-solubilizing fungi (PSF)-mediated bioextraction . However, it is important to understand how P contents and speciation (i.e., the chemical forms of bound P available in the sediment matrix) change across watershed sites. This is critical for ensuring robustness of the P bioextraction technology for processing sediments with different bound P chemical distributions and identify optimum interception sites within a watershed to maximize P recovery. The objectives of this study were to characterize the phosphorus content and inorganic phosphorus speciation of runoff sediments obtained from seven different locations within the eutrophic Macatawa River Watershed located in Southwestern Michigan and observe how changes in the phosphorus characterization correlate to site and sediment characteristics. Qualitative observations of site and sediment characteristics were taken at the time of sediment collection. Sediments were then preserved before standard methods were used to determine the total, inorganic, and organic phosphorus content as well as quantifying the amount of loosely-sorbed, iron-bound, aluminum-bound, calcium-bound, and reductant soluble phosphorus. The results of our study show that for this particular watershed, the highest quantity of total phosphorus correlated to the presence of wetlands at the upstream-most and downstream-most collection sites. However, majority of the bound P in sediments from these sites are of the organic P form, which requires increased selectivity of PSF phosphatase activities during PSF-mediated sediment biotreatment. There appears to be little correlation between sediment sampling sites and the fraction of loosely-sorbed, iron-bound, and calcium-bound phosphorus, although all middle sites showed significantly lower total bound P than the upstream headwaters and downstream sites prior to discharge to Lake Macatawa. Continuing studies are looking at temporal variation of P loading and speciation to examine possible optimal annual seasonal timeframes for runoff sediment collection and processing for P recovery within the same watershed as well as in other eutrophic watershed regions.
1. Mondala, A., Shields, S., Gaviglio, K. and Kaczmarek, S. (2017), Influence of fungal low molecular weight organic acids on extraction and speciation of runoff particulate-associated phosphorus: Implications for nonpoint phosphorus recovery and beneficial reuse. Environ. Prog. Sustainable Energy. doi: 10.1002/ep.12622