The Patuxent: Good from Afar, Far from Good

Sometimes called the ‘most studied river in Maryland’, state agencies, academic institutions, and community scientists have performed routine monitoring for over thirty years along the Patuxent. Our data analysis team used this robust data set to discover interesting trends on the Patuxent, but more importantly, the need for water chemistry data to be contextualized by historical research and lived experience.
Water Reporter
January 10, 2022
The Patuxent: Good from Afar, Far from Good

It is well understood that human induced climate change is increasing air temperature. From the Arctic to Death Valley, the past century and particularly the past decade have seen significant warming. The implications for lake and river ecosystems around the world are considerable. Factors like reduced snowpack for snowmelt fed rivers and ice over on cold climate lakes threatens already impaired waterbodies. Research has shown that lakes and rivers are warming, and in some cases like the Great Lakes, at an alarming rate. In addition, climate change is increasing the frequency of intense storms, which can lead to overwhelmed wastewater infrastructure causing sanitary sewage overflows, further debilitating urban waterways. Another factor at play is the intrinsic relationship between water temperature and dissolved oxygen. When temperatures are higher water holds less oxygen, potentially harming aquatic life. My plan was to investigate the effects of air temperature on river health and I began looking for historical water chemistry datasets for candidates.

View from Patuxent River Park in Upper Marlboro. Source:

A River of Data

Despite rigorous ongoing efforts from groups like Blue Water Baltimore and James River Association, no rivers had robust data stored in WaterReporter going back before 2000, except for one, the Patuxent. Sometimes called the ‘most studied river in Maryland’, state agencies, academic institutions, and community scientists have performed routine monitoring for over thirty years. This choice would lead me to discover interesting trends on the Patuxent, but more importantly, the need for water chemistry data to be contextualized by historical research and lived experience.

I’ve spent countless hours on the Chesapeake Bay and its tributaries, from fly fishing the Gunpowder, to overnight voyages down the Bay. My role as a data analyst at the Commons affords me the ability to investigate the places I love the most, often waterways suffering from pollution. I am no stranger to impaired rivers and streams. However, I have neglected the Patuxent from both a recreation and research perspective. It’s the only major river entirely held within Maryland, beginning as a narrow stream just southeast of Frederick, flowing 110 miles southeast before terminating as a large tidal river in southern Maryland. Its watershed encompasses eight densely suburban, urban, and agricultural counties of Howard, Montgomery, Anne Arundel, Prince George’s, Calvert, Charles and St Mary’s.

Map of tidal and non tidal Patuxent

My research journey on the Patuxent began by using this dataset from the Chesapeake Bay Program, Maryland Department of the Environment, and to explore parallels between rising air temperatures and the possible effect on the river’s dissolved oxygen levels. With ten stations spread across the tidal Patuxent, subsurface and surface measurements of dissolved oxygen and other parameters, this was the perfect dataset with almost 6,000 unique sampling events from 1986–2018.

Graph of Oxygen solubility in water.

Low dissolved oxygen makes life difficult for anything living in the river, and rising temperatures from climate change could spell disaster. Assuming water quality on the Patuxent has remained constant, increasing air temperatures should have an effect on water temperature and consequently dissolved oxygen. As shown in this basic water solubility curve, changes in water temperature directly affect water’s ability to retain oxygen and therefore support life. When water temperature goes up, oxygen goes down, particularly lower in the water column as increasing water pressure forces oxygen, and organisms, to the surface. Below roughly 4 mg/L of dissolved oxygen, most large and sensitive marine life cannot thrive.

Building Relationships

To test my hypothesis, I first looked at publicly available air temperature data from NOAA collected at BWI airport and Naval Air Station Patuxent River (NAS Pax) to get a sense of regional warming trends. These stations roughly bookend the Patuxent watershed, BWI to the north, and NAS Pax to the south. As expected, there has been a steady increase in air temperature from 1986 to 2018 at both stations, roughly 1 degree centigrade. I presumed such an increase must have affected water temperature and, consequently, reduced dissolved oxygen. What I found surprised me. Not only was there a clear relationship between dissolved oxygen and temperature on the Patuxent, but since 2010 water temperature had cooled and dissolved oxygen had improved slightly, roughly 4%. This can be seen in the chart below, with the blue line, dissolved oxygen, climbing after 2010. Note that yearly rise and falls are likely due to fluctuations in yearly precipitation.

Intrigued, I dug deeper and decided to break things down by month. Are certain times of year getting warmer? Interestingly, although water temperature on average has been decreasing over the past 10 years, certain months, particularly November, saw significant temperature increases. My local Marylanders will agree that fall has gotten significantly warmer in the past few years, especially this year.

But overall, water temperature was decreasing. The deeper I dug, the more complicated the patterns became. I wanted to ask the data another question about dissolved oxygen. Has there been a decrease in low dissolved oxygen averages, ones that can lead to fish kills? I picked 5 mg/L, a rough lower bound for rockfish and shade and a minimum threshold from the state of Maryland COMAR. Between 1986 and 2019, average subsurface dissolved oxygen levels fell below 5 mg/L 201 sampled times, or 36%. Recently, between 2010 and 2019 they fell below the threshold 38% of the time. Now I was stumped. How can surface and subsurface dissolved oxygen be increasing overall, despite increasing air temperature, and simultaneously have an increase in the number of sample days with readings below 5 mg/L? I was starting to understand that I didn’t understand this River. Something else must be affecting dissolved oxygen and temperature. I decided to turn towards the nutrient data to better understand the complexity of the Patuxent.

Too much of a Good Thing

Water quality monitoring programs often test for nitrates and phosphates as they are the basic building blocks of aquatic life. Aquatic vegetation consumes nutrients, which then get eaten by larger and larger creatures, eventually sustaining iconic organisms like Blue Heron and Rockfish. However, these nutrients exceed normal ranges when runoff from agriculture, wastewater treatment, and urban sources make their way downstream, especially during intense rain events. The excess nutrients can cause algae blooms, either appearing on the surface as large mats, or suspended in the water column, giving the water a green or red hue, sometimes called Red Tide or Mahogany Tide. These blooms eventually die after nutrients levels return to normal. In an anaerobic process, bacteria consumes the dying bloom which leads to hypoxia or dead zones through a phenomenon called eutrophication. Looking at trends for nitrates and phosphates in Patuxent samples, I saw a continual and significant improvement in nutrient levels, particularly looking at nitrogen levels from upstream stations TF1.3 and TF1.4 located closest to where the Patuxent widens and becomes tidal and also major population centers.

It seemed like the reduction in nutrients could be causing the average water temperature and oxygen improvements through a reduction in algae bloom events. Not only does the bloom cycle reduce oxygen, but algae also absorbs sunlight, further raising temperatures. However, relying only on the data in hand and my lack of training as a water quality scientist, I couldn’t be certain, especially considering the slight increase in below threshold dissolved oxygen days. So yes, things might be trending upward, but are still relatively poor. How poor to be exact? According to EcoReport card, a platform created by University Maryland’s Center for Environmental Science, the Patuxent earns an overall health rating of D-. It’s beat to the bottom only by the Patapsco Baltimore area region, earning a 24 and 23 respectively, out of the 100 point composite score. Good from afar, far from good.

A Birds Eye View

A thirty year dataset provides an incredible window into the pulses of the Patuxent, but I knew I needed to connect with researchers, advocates, and community members to better understand these data. To learn more I had the fortunate opportunity to chat with Fred Tutman, the Patuxent Riverkeeper.

Fred Tutman. Source: Nigel Perry, WaterKeeper Alliance

Fred has been fighting for the River and its communities for decades and is a living encyclopedia of Patuxent knowledge. He grew up in Prince George’s county on his family’s 7th generation farm along the banks of the Patuxent and knows the river as well as anyone. I eagerly showed Fred my findings indicating a rebound of dissolved oxygen and decreases in nutrient loads to get his take on what the data represented. Despite his interest and excitement in my initial analysis, he was quick to point out an issue. I neglected to acknowledge the absolute nutrient concentrations, which despite improvements were incredibly high, and dissolved oxygen levels relatively low. Yes, there’s been a downward trend and that’s nice to see, but Fred pointed out there’s much more to the story.

In general, water quality data can be split into three camps, observational, forensic, and predictive. We discussed how Fred prefers the last two, forensic and predictive. He uses forensic data to target specific sources of pollution like a wastewater treatment plant believed to be out of compliance. He is also collects data to help predict the general direction and future of water quality, similar to how financial institutions predict a company’s future stock price. My data was a blend of observational and predictive, it is interesting, but not very helpful. Forensic and predictive data however, are actionable. We can use predictions for goal setting and advocacy or execute on forensic data to address a specific pollution source. Observational on the other hand, begs the question “Well, so what?”.

“Seeing the trees but not the forest”

Observational data is something Fred has seen a lot of while working as Riverkeeper. He describes it as “Data for data’s sake”. In short, this is the plight of the Patuxent, agencies and policy makers collecting heaping binders of data, but somehow water quality hasn’t come close to pre-colonization levels. If observational data works, and the Patuxent is the most studied river in Maryland, should it not also be the healthiest river in Maryland? Fred thinks observational data distracts from the long view of history and inhibits prosecuting individual bad actors or problematic societal habits. A fan of metaphors, Fred says the obsession with data and observational data is akin to “Seeing the trees but not the forest”. That resonated with me and my own journey researching the Patuxent.

A Boardwalk in the Jug Bay Wildlife Sanctuary on the Tidal Patuxent. Source: Jug Bay Wildlife Sanctuary.

As a data analyst, it’s easy to get myopic, to get caught up in charts, outliers, and regressions. Data can amplify a lived experience advocating for environmental or social challenges, but it cannot replace first-hand knowledge. I haven’t spent years on the Patuxent, witnessing fish kills from eutrophication, fighting for regulatory changes and pollution enforcement or planning restoration projects to restore shorelines. I needed to broaden my scope. Fred and his experience living along the Patuxent told me water quality had maybe improved slightly but was still dismally below standards. I spent the majority of the conversation trying to keep up with Fred’s impromptu history lesson, jotting down avenues for future research. Although I couldn’t gain Fred’s experiences on the Patuxent, maybe I could gain some of his knowledge. I set forth to educate myself, reading countless scientific articles, news stories, and historical documents. These qualitative analyses can offer a bird’s eye perspective of the River, allowing me to “see the forest” and address the real questions of the Patuxent’s future in the face of climate change.

Centuries of Damage

The tidal Patuxent River has been a regional hub of civilization for over a millenia. Long before European settlement, the Patuxent or ‘Pawtuxent’ peoples farmed, fished, and hunted along the banks of Patuxent until John Smith explored the area in 1608 remarking “No place more perfect for man’s habitation”. Prior to European contact, the Patuxent was incredibly productive, serving as high quality estuarine habitat for oysters, rockfish, blue crabs, and countless bird species on its expansive tidal marshes. Since that encounter over 400 years ago, the Patuxent has seen major degradation. By 1670, most native Patuxent populations had been forced out by colonizers and joined other native tribes in Virginia and Pennsylvania, known today as the Piscataway Conoy. Soon after, a major colonial tobacco region was born. Driven by slave labor and the Patuxent’s fertile soil, a tobacco region was born. By the 18th century the majority of Maryland’s tobacco production took place along the Patuxent in places like St. George’s county.

Francis Gray, a former Councilman of the Piscataway Conoy, stands on the bank of the Patuxent River in Calvert County, Md. Source: (Will Parson/Chesapeake Bay Program)

Tobacco farming eventually petered out over the next two centuries after soil degradation and slavery abolition made the effort unprofitable. The region saw significant population declines, in favor of growing metropolitan areas like Washington D.C, Baltimore, Annapolis, and the many urban and suburban communities between them. Throughout the 20th century, the whiter, relatively densely populated, and wealthier upstream counties of Howard, Montgomery, and Anne Arundel sent significant pollution in the form of urban runoff and poorly treated wastewater to politically disadvantaged downstream counties of Prince George’s, Charles, Calvert, and St Mary’s. In 1980, Montgomery county, one of the two upstream counties in the Patuxent watershed, had the highest median household income, percent white, and population density of all eight Patuxent watershed counties. At the time, the logic was “The solution to pollution is dilution” an adage that put undue burden on disadvantaged downstream communities and failed to acknowledge the complexities of the natural environment.

Percent White, Patuxent Watershed Counties. Source: 1980 Decennial Census, Social Explorer.

Turning the Tide

A long history of conservation efforts, was first kicked off by advocacy in the late 1970s, spearheaded by Bernie Fowler, a Patuxent River advocate and Calvert County Commissioner at the time. The result was the Patuxent River Watershed Act, passed by the Maryland Legislature in 1980 and the subsequent Patuxent River Commission. The act requires local and state agencies to construct a comprehensive pollution mitigation plan to address point and nonpoint sources of pollution. The plan covers conservation efforts ranging from stormwater and sewage treatment to easements protecting existing forests and wetlands. In addition, many targeted lawsuits have been filed in defence of the Patuxent, challenging specific polluting facilities like Chalk Point power generation station as well as regulatory agencies, the Maryland Department of the Environment (MDE), the US EPA, and the state of Maryland.

Eagle Harbor and the Chalk Point power plant on the Patuxent. Source:

Wastewater treatment improvements began in 1985 and after 35 years, the most notable piece of legislation aimed at reducing nutrient pollution is the Chesapeake Bay Restoration Act signed by Governor Ehrlich in 2004. Colloquially called the ‘flush tax’, it charges Maryland residents $5 a month to pay for wastewater treatment plant (WWTP) upgrades and septic system improvements to mitigate nutrient pollution, netting an estimated $100 million a year. This direct tax on homeowners and the historic efforts beginning in the 1980s have resulted in upgrading all 67 of Maryland’s major WWTPs. This has had significant impacts on nitrogen and phosphorus, evidenced by my analysis and others. A working white paper from the Chesapeake Bay Program estimated a reduction of 22 metric tons per year of total nitrogen and .52 metric tons per year of total phosphorus since 1985. Note that total nitrogen reductions were found to be statistically significant but phosphorus reductions were not. Tackling wastewater treatment pollution from upstream facilities is a significant undertaking and installing system upgrades is a notable achievement in 35 years, however, the landscape of the Patuxent watershed has changed dramatically since.

What’s Next?

Although the Patuxent is home to 6 major wastewater treatment plants and other polluting industries, the single greatest threat to future Patuxent restoration is us — It’s our roadways, lawns, homebuilding, septic systems, and greater urban landscape. The Chesapeake Bay Program estimates that between 1985 and 2019 industrial wastewater facilities have reduced their contribution to nitrogen pollution by 80%, whereas small septic systems, like the kind found on private rural residences and in mobile home communities, increased by 93% and urban areas increased their nitrogen contribution by 58%. The Patuxent watershed has seen solid growth in urban and suburban areas since 1985, and a subsequent decline in natural undeveloped land. Overall, development has increased by 92% from 1985 to 2019, with a third of the Patuxent watershed’s total 552,000 acres now designated as developed. Even the original Patuxent River Policy plan from 1984 identified the rise in urban growth as a contemporary and future risk for Patuxent.

“​​The Patuxent River and its watershed are vital assets for Maryland — for its people, its fish and wildlife, and its economy. Over recent years, development and more intensive use of land for housing, industry, and agriculture have created adverse impacts on the river and life depending on it.”

They were accurate back then, and they were accurate now. We have made significant progress in reducing nutrients into the Patuxent from WTTPs and it has paid off. Programs like the flush tax clearly have had an effect on curbing pollution. Unfortunately, we are actively levying new attacks against the Patuxent, just as it’s showing possible signs of healing. If climate change continues to bring record breaking temperatures and precipitation events to the Mid Atlantic region, increasing developed land and impervious surfaces will only exacerbate the problem. The algae and cyanobacteria that cause eutrophication depend on warm nutrient rich water, the type that comes from our urban runoff. If my hypothesis is correct, that reducing nutrients has improved dissolved oxygen and temperature conditions on the Patuxent by reducing eutrophication, we must double down on these efforts. Fred noted the Patuxent has proven to be incredibly resilient and can recover from significant pollution events in “just a few years”. Although the Patuxent has the potential to heal, the clock is ticking with development and climate change showing no signs of slowing.

The solutions to these challenges are multifaceted. The hardest but most important is to curb development and protect the remaining swaths of existing forests. Slowing or halting urban expansion will guarantee land can play its role in supporting downstream biomes instead of harming them. Short of a moratorium on development within the Patuxent watershed, which is admittedly lofty and impractical, there are many viable avenues for bringing our urban areas more in harmony with nature.

Bioswale for retention. Source: LivingConcepts

Efforts like converting lawns to native plant gardens, installing rain barrels, decreasing impervious surfaces like parking lots and improving stormwater infrastructure with natural solutions like bioswales can help slow the roll of water from our streets to streams. In terms of data, we need deliberate strategies to leverage the wealth of data on the Patuxent. Creating predictive models to better understand the ecosystem, or collecting targeted data for addressing point and nonpoint pollution sources will help move the needle. If the Patuxent ecosystem completely collapses, our mounds of unactionable observational data won’t serve us much good.

Beyond the data, we as individuals can make change. Picking up our pets’ waste, eating less meat, and taking public transit can lower your nutrient and carbon footprint, helping to alleviate eutrophication and help the Patuxent rebound in your own small way. In addition, I encourage you to get involved with or donate to your local watershed organization or Waterkeeper group. Having a direct line to nature and the human processes that impact it will give you more agency in making change and lead you to like minded people. At the very least, get outside and enjoy your local stream or river, you might learn something along the way.

Additional Resources

If you would like to learn more about the Patuxent and the challenges facing the Chesapeake, please visit these resources:

Patuxent Riverkeeper


Chesapeake Bay Program


Special thanks to Fred Tutman for his time and wisdom.