The Effects of N:P Ratios on Nutrient Uptake in Salt Marshes in Oregon Estuaries

The natural capacity for salt marshes to remove nutrients from surface water is becoming increasingly important as an ecosystem service of water quality management in estuaries. Many factors influence nutrient uptake rates and the effects these factors have are important in quantifying the economic value of this ecosystem service. One such factor is the nitrogen to phosphorus ratio (N:P). The purpose of this study is to determine what effects N:P ratios have, if any, on nutrient uptake in a salt marsh on Yaquina Bay in Newport, Oregon. Historical data from the area shows that the mean values for N:P are about 18:1. In addition to the 18:1 treatment, alternative treatments in this study include ratios of 72:1 and 4.5:1. Nutrient uptake experiments are conducted by isolating a portion of marsh with a stainless steel chamber, filling it with nutrient spiked seawater of the various ratios and sampling in 20-minute intervals over one hour. Samples are sent to UC Santa Barbara’s Marine Science Institute for complete analysis and preliminary nitrate analysis is conducted in the lab with the MBARI-ISUS V3 nitrate analyzer. Preliminary results thus far are inconclusive and further analysis will be required to determine if altered uptake is due to concentration or ratio differences. Potential expected outcomes include either phosphate limitation in the 72:1 ratio treatments or merely limitation by all nutrients based on concentrations, where variability in N:P does not impact uptake rates.