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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #417657
Research Project: Shifting the Balance of Water Resources and Interacting Agroecosystem Services Toward Sustainable Outcomes in Watersheds of the Southern Coastal Plain

Location: Southeast Watershed Research

Title: USDA LTAR Common Experiment measurement: Total phosphorus (TP) and total dissolved phosphorus (TDP) concentration

Author
item HAMILTON, STEPHEN - Michigan State University
item Pisani, Oliva
item Kovar, John
item Malone, Robert - Rob
item Morrow, Amy
item Cole, Kevin

Submitted to: Protocols.io
Publication Type: Research Notes
Publication Acceptance Date: 9/7/2024
Publication Date: 9/7/2024
Citation: Hamilton, S.K., Pisani, O., Kovar, J.L., Malone, R.W., Morrow, A.J., Cole, K.J. 2024. USDA LTAR Common Experiment measurement: Total phosphorus (TP) and total dissolved phosphorus (TDP) concentration. Protocols.io. https://doi.org/10.17504/protocols.io.8epv5r7m6g1b/v1.
DOI: https://doi.org/10.17504/protocols.io.8epv5r7m6g1b/v1

Interpretive Summary: This protocol is part of a set of protocols for the LTAR Cropland Common Experiment. This protocol outlines the measurement of total phosphorus and total dissolved phosphorus in water samples. The phosphorus concentration is determined when assessing the long-term potential for accelerated eutrophication of surface water due to P loading. The goal of this protocol is to provide repeatable guidelines to achieve consistent data collection, instrument maintenance, data processing, and quality control for obtaining these data at established or new sites.

Technical Abstract: Total dissolved P (TDP) includes organic P (e.g., sugars and phospholipids) and orthophosphate. Dissolved orthophosphate (also termed soluble reactive P, dissolved reactive P, dissolved inorganic P, or filterable reactive P) is the form of P most readily available to algae and aquatic plants; however, numerous studies have shown that hydrolysis of other forms of P to the orthophosphate form is possible in natural waters. Therefore, when assessing the long-term potential for accelerated eutrophication of surface water due to P loading, many researchers and watershed managers want to know the total P concentration (regardless of P form) in water samples. Total dissolved P determination involves digesting filtered water samples to convert organic P species to orthophosphate, followed by colorimetric analysis or analysis by inductively coupled plasma with optical emission spectroscopy (ICP-OES). Determining TP involves the same digestion procedure applied to an unfiltered sample, followed by colorimetric or ICP-OES analysis. The recommended P digestion method is the persulfate oxidation technique (USEPA, 1993), performed using an autoclave or microwave. The colorimetric determination of TDP and TP follows the ascorbic acid “blue” method (USEPA, 1978), whereby an intensely colored blue complex forms from the reaction between P compounds and ascorbic acid. The intensity of the blue complex is proportional to the orthophosphate concentration in the sample.