Pittsburgh's Three Rivers and Their Tributaries
Current and Historical Influences on Water Quality
Introduction
Chemistry of streams matters to rivers
The chemistry of rivers strongly influences water quality and how river water affects human populations and ecosystem health. Water quality in southwestern Pennsylvania inherits a legacy of contamination from varied industrial outputs and human activities. The three mainstem rivers that meet in Pittsburgh, Pennsylvania, the Allegheny, Monongahela, and Ohio (referred to as the “Three Rivers”) are individually fed by many tributaries. Tributaries are smaller streams and rivers which flow into larger rivers. As a result of this flow pattern, pollutants that enter tributaries also flow into mainstem rivers.
In 2019, the Pittsburgh Collaboratory for Water Research, Education, and Outreach (Pittsburgh Water Collaboratory) convened meetings to identify gaps in knowledge and data regarding water in Pittsburgh. During those meetings, the community identified a lack of data on legacy contamination from historical industrial pollution and water quality in tributaries draining to the Three Rivers. More findings from the community meetings can be found in the Pittsburgh Water Collaboratory Community Consensus Report .
See a map below from the Community Consensus Report detailing the lack of data available for the tributaries. Disclaimer: the map was created with data from 2018.
Tributaries in Pittsburgh, PA Classified as Impaired (displayed in red) for Pollutants
The majority of tributaries in Pittsburgh are identified as impaired (meaning that a specific water quality standard is not being attained). But there is limited monitoring of water quality and there are limited data available. Further, unlike the mainstem rivers, tributaries do not have continuous monitoring stations.
View the interactive map to the right to see all impaired streams in Pittsburgh and surrounding areas in Pennsylvania.
What is a Total Maximum Daily Load (TMDL)?
According to the United States Environmental Protection Agency, “A TMDL is the calculation of the maximum amount of a pollutant allowed to enter a waterbody so that the waterbody will meet and continue to meet water quality standards for that particular pollutant. A TMDL determines a pollutant reduction target and allocates load reductions necessary to the source(s) of the pollutant.” [1]
Formation of Collaboration
In 2021 the Pittsburgh Water Collaboratory and 3 Rivers Water Keeper received funding from the University of Pittsburgh's Year of Engagement Program to collect 100 samples from the tributaries that feed the Ohio, Monongahela, and Allegheny Rivers. Together they sampled 25 locations over four quarters from August 2021 to May 2022.
Meet The Team!
Pictured from top left to bottom right: Emelia Sargent (Pittsburgh Water Collaboratory), Kate Zidar (Pittsburgh Water Collaboratory), Megan Guy (Pittsburgh Water Collaboratory), Captain Evan Clark (Three Rivers Waterkeeper), Dr. Heather Hulton Van Tassel (Three Rivers Waterkeeper), Dr. Emily Elliott (Pittsburgh Water Collaboratory), Dr. Daniel Bain (Pittsburgh Water Collaboratory), Dr. John Gardner (Pittsburgh Water Collaboratory), Dr. Anusha Balangoda (Pittsburgh Water Collaboratory), Julie Weitzman (Pittsburgh Water Collaboratory)
Our Approach
Sampling Sites
Team members selected 25 tributary mouths accessible by boat along the Three Rivers. Tributaries were sampled above the first riffle to avoid potential mixing of tributary and main stem river waters in the sample. View sampling sites on the map to the right.
Sampling Parameters
Samples were collected during four sampling quarters to represent seasonality in data. Measurements were taken in August 2021, November 2021, February 2022, and May 2022. The samples collected were analyzed for nutrient and metal concentrations using the parameters seen in the table on the right.
- Quarter 1: August 17 & 19, 2021
- Quarter 2: November 1, 2021
- Quarter 3: February 21, 2022
- Quarter 4: May 2 & 4 & 11, 2022
Nutrients in An Urban Setting
Classifications of land use in Pittsburgh, Pa based on the National Land Cover Database (NLCD)
What are nutrients?
Nutrients are the elements essential for biological life and plant growth [2]. Our analysis primarily focused on nitrogen (N) and phosphorus (P). N and P are two of the primary limiting nutrients in most aquatic environments - meaning they control the growth rates of aquatic plants, such as algae [2,3]. Some of the main sources of nutrients in ecosystems are human and animal waste, agricultural fertilizers, and stormwater runoff, in addition to atmospheric deposition. In urban areas like Pittsburgh, where commercial agriculture is not as prevalent (see the National Land Cover Database image above) leaking sewers can be a major source of nutrients.
Why do nutrients matter?
Eutrophication
The concentration and proportion of nutrients in our water directly influences plant growth and primary production. These, in turn, impact water quality, aquatic species composition, and habitat structure [2]. Excess nutrient concentrations can trigger algal blooms and a cascade of impacts called “eutrophication” where excessive algae growth leads to lower oxygen levels, and sometimes death of aquatic life. [6]. After the plants and algae decompose, carbon dioxide levels increase and pH drops, acidifying the water system [6]. Acidic environments impact shellfish populations, including freshwater muscle species native to the Allegheny River – some of which are endangered.
Harmful Algal Blooms
HAB in the Mahoning River Watershed from the Pittsburgh District Army Corp of Engineers (Credit: USACE)
Some algae can produce toxins under certain conditions. These Harmful Algal Blooms (HABs) are another consequence of eutrophication. HABs are caused by nutrient buildup, rising water temperatures, and flood events [6]. In the case of excess nutrient concentrations, HABs occur due to an “overfeeding” effect where algae growth exceeds normal limits [7]. These algal blooms then release toxins, such as neurotoxins and hepatotoxins, which are harmful to human and aquatic life [7].
What is "trophic status" and why should I care?
Trophic status or trophic levels are measures of the relative nutrient concentration in aquatic ecosystems [2]. Phosphorus trophic levels are broken down into four statuses based on total concentration (TP). Nitrogen trophic levels are broken down into three statuses based on total concentration (TN). These trophic statuses are indicators of ecosystem health in many aquatic habitats and have significant implications on water quality. “Oligotrophic” means that there is low biological productivity and water quality is clear and "good". On the other hand, “hypertrophic” describes the “poorest” water quality where nuisance algal blooms blocks sunlight from penetrating the water.
Both breakdowns are in micrograms per liter (mg/L) – also referred to as parts per million (ppm).
Phosphorus Trophic Levels
- TP < 25μg is Oligotrophic
- 25μg > TP < 75μg is Mesotrophic
- 75μg > TP < 100μg is Eutrophic
- TP > 100μg is Hypertrophic
Nitrogen Trophic Levels
- TN < 700μg Oligotrophic
- 700μg > TN < 1500μg is Mesotrophic
- TN > 1500μg is Eutrophic
Where are nutrients coming from?
National Pollutant Discharge Elimination System (NPDES) Permitted Facilities (Purple is Nitrogen, Green in Phosphorus)
There are a variety of sources of N and P in urban settings including sewer system leaks, septic tanks, landfills and waste disposal sites, construction, runoff from impervious surfaces, and industrial effluent discharges [2]. In Pittsburgh, PA, the sewer system is over 100 years old and more than 70 percent of the sewage system combines stormwater and wastewater [4]. This means that leaks and overflows of untreated wastewater reach Pittsburgh’s streams and rivers during dry and wet weather, making the sewer systems a primary source of nutrient pollution and the dominant source of bacteria, like e. coli to waterways. Additional sources of nitrogen can come from the many industries along our waterways with regulated discharge allowances through the National Pollutant Discharge Elimination System (NPDES). These facilities have permits issued by the Pennsylvania Department of Environmental Protection (DEP) that allow them to release pollutants from point sources while complying with discharge limits and monitoring requirements [5]. Phosphate is also used by drinking water utilities to help prevent lead corrosion from drinking water pipes. Given that treated drinking water often cycles back to surface water systems (via leaky infrastructure, stormwater, or wastewater treatment facility discharges), phosphate additives add to the total nutrient loads in streams and river systems.
Our data show tributaries in the region span a surprisingly wide range of nutrient pollution- from oligotrophic to hypereutrophic conditions. View NPDES map to the right.
Nutrient Data (Including Total Concentration Levels and Trophic Statuses)
FINDINGS
- Tributary nutrient pollution was highly variable, with some tributaries having hypereutrophic conditions (“extremely bad”), while others were oligotrophic (“good”).
- Consistently high concentrations of N & P were found in streams draining to the Monongahela River during all four sampling seasons.
- High N concentrations may be attributable to outdated and poorly maintained sewer systems as well as permitted discharges from NPDES facilities.
- High P concentrations may be attributable to current facilities with P discharge allowances combined with legacy pollution from slag - an industrial byproduct from the iron ore smelting process.
- High concentrations of nutrients are found along streams draining to all Three Rivers. It is notable that most of the sampled tributaries do not have TMDLs for nutrient impairment.
Streams draining to the Allegheny River generally have lower nutrient concentrations relative to the streams draining to the Monongahela River. Part of this difference is likely due to the higher number of CSOs in the Monongahela in comparison to the Allegheny (245 and 149 CSOs, respectively) [8]. Additionally, the Monongahela River has a greater toxic load, meaning more total contamination from permitted discharges [9].
TAKE HOME MESSAGE
- Nutrient contamination of the Three Rivers is moderate to severe and stems from both non-point (leaky sewers) and point (permitted discharges) sources.
- With consistently high concentrations of N and P in the 25 streams sampled, there must be more nutrient management in tributaries to help prevent eutrophication and HABs from occurring.
- The establishment, refinement, and enforcement of TMDLs, as well as investments in the Pittsburgh sewer system, are essential to curbing high nutrient concentrations.
- Legacy and current pollution from industrial discharge points directly impact our water quality. Enforcement of discharge limits are paramount to protect our drinking water.
Legacy Contamination in the Three Rivers
Digitized Underground Mines around Pittsburgh, PA
What is Acid Mine Drainage (AMD)?
Acid Mine Drainage (AMD)
Acid mine drainage (AMD) happens when surface water infiltrates into mines and interacts with pyrite in the coal to produce sulfuric acid. This acid-rich solution dissolves a variety of pollutants from the coal during its travel to neighboring streams and rivers. The discharged water is highly acidic, rich in heavy metals (iron, manganese, and aluminum) and can be toxic to humans and wildlife (10). As seen in the picture to the right, AMD can be an orange or whitish-blue color based on the type of metal present (iron AMD is orange to red and aluminum AMD is white to blue).
What does this have to do with today?
A high demand for coal during the height of steel and coke production in Pittsburgh, PA spurred a surge of above and below ground mining within the city and surrounding areas (11). The DEP estimates that within the city limits of Pittsburgh, there are around 60 abandoned mines, some of which can be seen in the map above (11). This high prevalence of coal mines has made AMD a persistent environmental hazard in Pittsburgh. Legacy concentration of iron (Fe) and manganese (Mn) can still be found in the Three Rivers and surrounding tributaries today.
FINDINGS
- Concerning concentrations of manganese were consistently found in tributaries to the Monongahela and Allegheny rivers during all the sampling quarters.
- Elevated concentrations of iron were found along the streams draining to the Monongahela and Allegheny rivers. iron facilitates the movement of other metals. and the high presence of both iron and manganese in this study may be attributable to that relationship.
- Concentrations of iron and manganese are likely attributable to the high abundance of abandoned mines located within the Monongahela watershed.
- A significant outlier can be seen in the quarter four manganese concentrations at site M1. This outlier may have been caused by cross contamination that occurred during sample filtering.
Why is this important?
The Allegheny and the Monongahela Rivers are a source of drinking water for Pittsburgh and surrounding communities. The Ohio River is a source of drinking water for nearly 5 million people. Water contaminated with manganese and iron is not hazardous to human health but can cause unpleasant odors, taste, and discoloration (12); however, increased iron in water systems can clog wells, pumps, sprinklers, dishwashers, and other devices. Removing buildup in homes often requires corrosive, toxic cleaning agents that are washed into our wastewater. The EPA has set secondary maximum contamination levels (SMCLs), non-enforceable standards for water quality contaminants not hazardous to human health, at 0.05 mg/L for manganese and 0.3 mg/L for iron (13). As seen in the maps above, concentrations of manganese and iron were above the set SMCLs in the streams draining to the Ohio, Monongahela, and Allegheny Rivers during all four sampling quarters.
Most importantly, these observations of iron and manganese demonstrate the continued impact of acidic mine drainage on the region. The presence of these metals strongly suggests acidity and trace metals associated with that drainage are impacting the tributaries and therefore the river.
TAKE HOME MESSAGES
- Historical mining still has a significant impact on water quality in Pittsburgh.
- AMD introduces substantial amounts of iron and manganese to tributaries and the mainstem rivers.
- Concentrations of manganese and iron metals are both elevated in surface water in tributaries to the Three Rivers.
- Increased AMD restoration efforts can lower iron, manganese, and other metals and improve river system health.
Industrial Legacy Pollution
What are industrial legacies and what do they have to do with today?
Industrial Facilities (Orange Pin Points) and Sampling Sites (Blue Circles)
Pittsburgh’s legacy of steel production and coal industries have left behind contamination that can still be found in the environment today. Industrial processes release harmful contaminants into the air, soil, and water. These contaminants can remain in the soil for centuries. Cadmium (Cd), which is released as a byproduct of coking, is one of the industrial legacy pollutants that can be found in the tributaries and main stem rivers in Pittsburgh. Coking is a process where coal is essentially baked to remove volatile (I.e., explosive) compounds. Therefore, when the coke is placed in the steel blast furnace as fuel, it doesn’t explode and destroy the furnace. Coking productivity has decreased in our region but remains active, particularly in the Monongahela Valley. See the map on the right to view past and current industrial facilities in relation to our sampling sites.
Cadmium Concentrations
Cadmium concentrations are consistently high in the streams draining to the Monongahela River.
FINDINGS
Though in most cases, cadmium levels were below our limit of detection,
- Elevated concentrations of cadmium can be found along streams draining to the Monongahela River, particularly during quarter four.
- Concentrations of cadmium likely result from nearby historical coking facilities distributed along the Monongahela River.
Why is this important?
Our rivers are a source of drinking water in Pittsburgh and surrounding communities. cadmium is considered hazardous to human health and is a cancer-causing pollutant [14]. Consuming even low concentrations of cadmium can cause kidney disease and replace calcium in bones causing them to become fragile [14]. The EPA has set a maximum contaminant level (MCL), which is an enforceable threshold level for a contaminant allowable in a drinking water system, for cadmium at 0.005 mg/L [15]. The data shows this MCL was not exceeded in surface waters. Nevertheless, cadmium in the rivers will impact fish and other wildlife.
TAKE HOME MESESAGES:
- Pittsburgh’s industrial legacy of pollution has created long-lasting impacts on stream and drinking water quality.
- Even with the decline in industrial activity, the Monongahela Valley continues to be impacted by cadmium contamination.
- The inconsistencies in cadmium concentrations found throughout the four sampling quarters indicate further monitoring should be completed to clarify legacy contamination from historical coking and other industrial processes.
Explore the Data
Acknowledgements
We would like to acknowledge the University of Pittsburgh's Year of Engagement for providing funding for the sampling efforts along with the Frederick Honors College and the Heinz Endowments for providing capacity for our Spring 2023 GIS Intern and Graduate Student Researcher. Additionally, thank you to the Three River Waterkeeper for collaborating with us on this project.