Effects of storage and filtration methods of riverine dissolved inorganic nutrients on their determination: a case study of the Yellow River water sample

Timely pretreatment and proper storage of nutrient samples are the pre-conditions to ensure the reliability of data. In this study, we examine the differences between frozen storage and preservation with mercury chloride at room temperature for dissolved silicate in the Yellow River water sample that is characterized of high turbidity. We found out that there was no significant difference between the two storage methods. We compared in-situ filtration (freezing stored in 9 mL vacuum polyethylene terephthalate tube) and delayed filtration (freezing stored in 125 mL high density polyethylene bottle) for the nutrients, and discussed the effects of delayed filtration time on nutrients data quality. Nitrite, nitrate and phosphate were not affected by prolonged filtration time, while ammonium was significantly impacted by a decrease of 11%～46%, possibly due to suspended particulate matter adsorption and/or phytoplankton assimilation. As for silicate, storage container and its volume may play a major role in silicate storage while the prolongation of filtration time is much less important.