Nitrogen Monitoring

Ecology has several monitoring programs in and around Puget Sound that monitor for a variety of water quality parameters, including nitrogen. Ambient monitoring involves repeated sampling at the same stations over a long period of time. The data from these efforts enable us to observe long-term trends in water quality conditions. We also have a few focused nitrogen monitoring efforts designed to answer a more specific question or explore data or water quality conditions in a specific location in more detail. The map below illustrates Ecology’s various monitoring efforts within the Puget Sound ecosystem.

Monitoring Nitrogen in Freshwater

Ecology’s Freshwater Monitoring Unit has monitored major rivers in Washington State for nitrogen and other parameters for over 20 years through the ambient monitoring program. The data are available online and also summarized in annual monitoring reports. Most data are collected at monthly intervals.

Monitoring Nitrogen in Marine Waters

Ecology’s Marine Monitoring Unit has monitored physical, chemical and biological water quality variables in Puget Sound since the 1990s through the marine flight program. The program provides information on the variability and trends of water quality variables relative to site longer-term patterns and reports its findings in the form of the Marine Water Condition Index and yearly marine waters reports. Long-term data are available online.

Eyes Over Puget Sound

Ecology’s Marine Monitoring Unit also produces up-to-date observations of visible water quality conditions in Puget Sound and the Straits. These reports, called “Eyes Over Puget Sound,” combine high-resolution photo observations taken from a floatplane with satellite images, ferry data, and monitoring ambient data into readily available monthly reports. Reports are available within two days of when observations are made. Algal blooms have sometimes been observed and documented via photographs through this effort.

Focused Monitoring: Studies

Nitrogen Isotope Monitoring

Ecology recently started a new monitoring effort in collaboration with the University of Washington’s School of Aquatic and Fisheries Sciences and IsoLab to use novel stable isotopic techniques to determine sources, fate, and transport of nitrate (NO3-) in Puget Sound rivers and estuary.

This monitoring effort involves measuring ratios of stable oxygen isotopes present within the NO3- molecule in both freshwater and marine waters of Puget Sound. The most abundant isotope of oxygen is oxygen-16 (16O), but isotope oxygen-17 (17O) and oxygen-18 (18O) are also present at much lower amounts. However, the proportion of 17O and 18O present in different sources varies naturally.

The ratio of 17O:16O and 18O:16O in nitrate (termed δ17O and δ18O, respectively) can potentially be used to track fate and transport of nitrate. There is a well established relationship between δ17O and δ18O, and if measurements show a deviation from this relationship, it can indicate that nitrate found in water is coming from a particular source. For example, in the atmosphere, there is an abundance of 17O relative to 18O, and this technique is therefore particularly good at tracking atmospheric sources of nitrate.

The monitoring effort so far has analyzed samples from 34 sites from February to June 2014, with preliminary results presented in the figure below. Observed ratios between oxygen isotopes present in NO3- are compared to the expected relationship between δ17O and δ18O (black line in the figure below). Values falling above the line indicating that that particular measurement contained a higher fraction of atmospherically derived nitrate.

Click to enlarge graph on new page.
Graph: Oxygen isotope ratios of dissolved nitrate (NO3-) from the 34 river and marine sites in the Puget Sound in 2014. Click to enlarge image. Colors indicate month of sampling: Blue = February, Gray = April, Light Red = May, and Dark Red = June. The black line is the expected relationship between δ17O and δ18O (δ17O = 0.52 * δ18O) in the absence of atmospheric NO3-. Values falling above the line indicate a higher fraction of atmospheric NO3- present in that sample. Circles are freshwater samples while square are marine.


Preliminary analysis of data collected so far shows that for many rivers, atmospheric NO3- contributes to a small fraction of the total nitrate. However, the Stillaguamish and Skagit Rivers both have an elevated atmospheric nitrate signal relative to other rivers in Puget Sound.

Ultimately, we will have a full annual cycle of monthly samples from all the major rivers to Puget Sound as well as marine samples along a salinity gradient in Whidbey Basin. Using different groups of isotopes, including isotopes of nitrogen in addition to oxygen, we hope to be able to track NO3- derived from the atmosphere, agriculture, and forested areas.

Continuous Nitrogen Monitoring in the Deschutes River

Ecology deployed a continuous nitrate monitoring device, called a Submersible Ultraviolet Nitrate Analyzer (SUNA), in the Deschutes River (at the E. Street Bridge in Tumwater), between October 2009 and November 2010. Continuous data has the potential to give us more information about how nitrogen discharges from rivers varies over small periods of time not captured by monthly ambient monitoring efforts and. For example, continuous data could help us better characterize nitrogen concentrations during or after a storm event, or better understand instream biological processes that take place over the course of a few hours or days.

Sackmann (2011) found some interesting patterns during storm events, where nitrate concentrations generally decreased as streamflow increased due to dilution. However, this did not hold true for one storm event where peak nitrate concentrations were observed during a high-flow storm event, as nitrogen that had accumulated within the watershed during the preceding dry weather spell was mobilized by rainfall.

More information about the study design, sampling techniques, data, and results can be found in the Deschutes River Continuous Nitrate Monitoring report.

Nitrogen Monitoring on Bertrand Creek in the Nooksack Watershed

Ecology has initiated a three-year project to measure the effectiveness of water quality clean up and management activities in the Bertrand Creek watershed, a sub-watershed of the Nooksack River in Whatcom County, WA. The project involves both discrete sampling and continuous monitoring at two upstream and downstream stations for nitrate and other water quality parameters. The data will be used to determine the movement (flux), continuous annual loading (yield) and behavior (seasonal patterns) of nitrate concentrations in the creek. Currently, two of these stations are transmitting live data via satellite to Ecology’s webpage every three hours – you can view live nitrogen data (and other parameters) here: Bertrand Cr.@ 0 St. and Bertrand Cr. nr mouth.