The importance and challenges of monitoring water quality

Post by Eric Booth and Chloe Wardropper

Fitbits and other fitness trackers have become popular ways to measure and follow body metrics like the number of steps walked or calories consumed. They allow people to set goals and track their progress on an hourly, daily, and monthly basis.

Similar to tracking changes in our bodies, we can monitor environmental changes, such as fluctuations in fish stocks and the amount of carbon forests can store. One high-profile monitoring effort is the Extreme Ice Survey, made well-known by the documentary Chasing Ice, which uses time-lapse videos of glaciers to show how quickly they’re melting.  

Monitoring water quality is an important part of helping us determine whether or not we are making progress in cleaning up our waterways. It reveals the health and composition of streams, rivers, and lakes at a snapshot in time, as well as over weeks, months, and years.

The importance of tracking changes in water quality can’t be overstated: human health and livelihoods depend on clean, reliable water supplies. Monitoring drinking water is required under the US Safe Drinking Water Act, which sets federal requirements for monitoring water for contaminants, such as microorganisms and chemicals, to protect human health.

We have also been tracking the state of our recreational waters–streams, lakes, and rivers–for a long time. In fact, UW-Madison’s Center for Limnology is the site of some of the earliest research on lake characteristics and processes, which began at the turn of the 20th century. In addition to furthering scientific discovery, monitoring is crucial for ensuring the sustained health of the water bodies we enjoy.

Edward A Birge and Chancey Juday monitor plankton on Madison's Lake Mendota circa 1917. Credit: Wisconsin Historical Society.

Edward A Birge and Chancey Juday monitor plankton on Madison’s Lake Mendota circa 1917. Credit: Wisconsin Historical Society.

The US Clean Water Act (CWA), a landmark piece of environmental legislation that celebrated its 40th birthday in 2012, controls surface water pollution, which can come from numerous sources, including sewage treatment plants, factories, farms and urban roads. Regulation under the CWA is based primarily on monitoring the discharge put into water by known pollution sources, as well as the quality of the water itself. Indicators of water quality include the presence of fecal coliform bacteria, the amount of dissolved oxygen, and nitrate and phosphate levels.

Of particular concern to the WSC project is excessive phosphorus levels in freshwater, a wicked problem due to its numerous sources and difficult-to-find solutions.

Measuring the amount of in-stream phosphorus pollution tells us not only what’s going on at a single point in a stream, but also what is happening on the land upstream of that point. A number of land-use practices, ranging from poorly managed construction sites to farm field erosion, can be sources of that pollution, also known as runoff.

To understand monitoring water for phosphorus runoff, we need to understand two terms: concentration and load.

Phosphorus concentration, is the mass of phosphorus per unit volume of water. In other words, concentration tells us how much phosphorus is in the water. In Wisconsin, the legal limit of phosphorus concentration in most streams is .075 milligrams per liter.

Phosphorus load is the concentration multiplied by the flow of water in the stream. This indicator tells us how much phosphorus is moving downstream at a given point in space and time.

This illustration shows pollutant concentration and load. The concentration of salt in bottles A and B are the same but B has twice as much load. Credit: Dept of Ecology, State of WA

This illustration shows pollutant concentration and load. The concentration of salt in bottles A and B are the same but B has twice as much load. Credit: Dept of Ecology, State of WA

Long-term observations of phosphorus concentration and load are critical to better understanding how changes in land use, management, and precipitation are impacting water quality.

Here in the Yahara Watershed, phosphorus concentration and load data are collected at several long-term stream monitoring locations maintained by the U.S. Geological Survey Wisconsin Water Science Center. This effort began in the 1970s thanks to Dick Lathrop and the Wisconsin Department of Natural Resources.

Even with this data, there are still many places in the Yahara where we have little or no data. That’s because monitoring is expensive and time-intensive, presenting the first of two big challenges to monitoring water quality.

Monitoring a stream’s phosphorus concentration is a cumbersome and expensive process. It involves taking a water sample from a certain point in a stream either manually or remotely with technology and then transporting it to a lab for analysis. Currently, there are no economically viable technologies that can measure phosphorus concentration while in the stream, which would make the process simpler; although, researchers are working to develop better sensors.

In order to accurately quantify phosphorus loading, we need to constantly monitor streams, since how much phosphorus is moving through the system varies widely through time. This also requires time and money that is not yet fully available, and presents a second challenge to monitoring water quality: interpreting variability.

Phosphorus moves through waterways either in a dissolved state or attached to sediment particles from soil erosion. The vast majority of phosphorus is transported from land to water as runoff, which is driven by rainfall and snowmelt. The amount of phosphorus that comes from a piece of land depends on several factors: 1) the land cover (for example, corn fields or streets), 2) how much phosphorus has been added to soil through decaying leaves or fertilizer applications, 3) the steepness of the topography (steeper areas tend to erode more), 4) the soil type (finer grained soils tend to generate more runoff), and 5) precipitation.

Precipitation can be particularly important in driving runoff and increasing the phosphorus load in streams. If we look at a daily record of phosphorus loading (below), we notice that things can change quite dramatically from day to day.

A daily record of phosphorus load and streamflow for Pheasant Branch Creek at Middleton. The “spikiness” and variability are due to episodic rain and snowmelt events. Data from USGS

A daily record of phosphorus load and streamflow for Pheasant Branch Creek at Middleton. The “spikiness” and variability are due to episodic rain and snowmelt events. Data from USGS

This variability is also present from year-to-year (below). Some years are wetter and have more runoff than others.

Annual phosphorus loading as measured at a USGS gage at Pheasant Branch. Data from USGS

Annual phosphorus loading as measured at a USGS gage at Pheasant Branch. Data from USGS

But how do we make sense of this variability when we look at trends through time or the potential impact management practices have on water quality? It’s challenging!

Here is a hypothetical example. An organization installs a management practice meant to reduce phosphorus runoff in a watershed, such as a buffer strip. The following year is particularly rainy, and the organization discovers that the phosphorus load in the stream increases by almost five times. Should they blame that increase on the new practice? No. That increase was probably driven by the spikes in rainfall and subsequent runoff.

In real life, and despite the efforts made to reduce runoff, we have unfortunately not seen a decrease in phosphorus load at the monitored tributaries in the Yahara Watershed, which means local streams continue to receive and transport large amounts of phosphorus. 

On the positive side, phosphorus concentrations have decreased slightly, which suggests that some of the land management practices have been helping.

So how is it possible that loads are not decreasing, but concentrations are? We do not have a definitive answer, but the data suggest that increased precipitation is the culprit. Phosphorus concentration is smaller, but there is more water in the stream as a consequence of increased precipitation and runoff, resulting in no changes in phosphorus load.

To some extent, variability can be accounted for with computer models. For example, to understand how phosphorus runoff varies across a landscape, models help us fill in the gaps where we have not collected observations through monitoring. With models, we can also hold one source of variability, such as rainfall, constant to assess the changes caused by other factors. Stay tuned for a future blog post that will dive further into the world of water quality modeling.

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