WILLISTOWN CONSERVATION TRUST

GIVE

State of Our Streams Report Chapter 3: Specific Conductivity, Chloride, and Nutrients

By

By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

Cover Photo by Jennifer Mathes

Since 2018, the Watershed Protection Program has monitored water quality at ten sample sites in the headwaters of Darby, Crum, and Ridley Creeks (Map 1). Every four weeks, the team visited each of the ten sites to take in-stream measurements and collect samples for analysis in the lab. We are proud to present our findings on water quality based on analysis of our data collected from 2018 through 2021, which includes 41 monitoring visits and over 7500 different measurements. 

August is National Water Quality month, and each week we will publish excerpts from one chapter from the report. Last week, Chapter 2 focused on discharge, turbidity, and total suspended solids. Chapter 1 gave an introduction to water chemistry. This week, we are focusing on specific conductivity, chlorides, and nutrients. The full report, which includes more information than is provided in the blog posts, can be found here. 

To better understand potential sources of pollution to the headwaters of Darby, Crum, and Ridley Creeks, we examined specific conductivity, salts, and nutrients. Specific conductivity is a broad water quality measurement that reflects the presence of ions in the water. These ions include compounds that are formed when salts and nutrients dissolve in water. Higher specific conductivity measurements indicate a higher concentration of ions. However, specific conductivity does not provide insight into the type or concentration of ions in the streams. To explain changes in specific conductivity over time or across sites, we monitored salt and nutrient concentrations. 

Chloride is an ion that forms when salts and, to a lesser extent, fertilizers dissolve in water. Elevated chloride concentrations can be toxic for stream organisms. Nutrients, mainly nitrogen and phosphorus, enter streams from fertilizer runoff and leaky septic and sewer systems, all of which increase specific conductivity. When nitrogen and phosphorus are too high, rapid algal growth can occur. This eventually leads to a depletion of dissolved oxygen. Chloride, nitrogen, and phosphorus are all naturally present in low concentrations in streams. However, changes in local land use — specifically increases in development and impervious surface cover — can increase the concentration of these compounds, threatening water quality. An impervious surface is any surface that water cannot pass through, such as buildings, roads, parking lots, and sidewalks. 

All stream samples have elevated specific conductivity (Figure 1). Elevated specific conductivity is driven by salts and nutrients, as indicated by high chloride, total nitrogen, and total phosphorus concentrations, though sites in Crum Creek are less impacted than Ridley and Darby Creek sites. While chloride and total nitrogen do not exceed levels deemed unsafe for human consumption (there are no such regulations for total phosphorus), they are still present in excess, potentially posing a threat to stream organisms. Warm water temperatures (see Chapter 1) may exacerbate the hazards posed by elevated chloride to stream life. 

Monitoring specific conductivity, chloride concentration, and nutrients reveals the importance of land protection for maintaining and improving water quality in our area. Catchments, or drainage areas, with low impervious surface cover have better water quality, as demonstrated by lower specific conductivity, chloride concentration, and nutrient concentration, than catchments with high impervious surface cover (Figure 2). The most impaired sites are Darby Creek at Waterloo Mills (DCWM1) and West Branch Ridley Creek (WBRC1), both of which have 20% impervious cover in their surrounding catchments and a high percentage of developed land. The least impaired site is West Branch Crum Creek (WBCC1), which has 9% impervious cover in its catchment, the lowest of all sites. Improving water quality, especially in Darby and Ridley Creeks, will require a reduction in excessive road salt and fertilizer use. Limiting development upstream of WBCC1 is crucial to protecting and maintaining the health of Crum Creek.

For a primer on statistical tests and how to read boxplots and scatterplots, click here.

Specific Conductivity

Figure 1. Specific conductivity from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time.

Specific conductivity measures how well electricity travels through water. Pure water is a poor conductor and has a low specific conductivity. Ions – often from salts (such as sodium chloride), nitrogen and phosphorus-based nutrients, and metal cations – all increase specific conductivity. As many of these ions come from anthropogenic sources, specific conductivity provides insight into the general impact of human activities on waterways. Higher specific conductivity indicates a more heavily impacted stream, but it does not indicate which compounds are entering waterways. Though there are no federal or state standards for specific conductivity, natural background levels of specific conductivity in the sampled stretches of stream are estimated to be between 75 and 95 µS/cm, which is far lower than any values measured.1 Elevated specific conductivity is expected due to the long history of human activity and development within the study area. 

There are significant differences in specific conductivity between sites. Specific conductivity is significantly lower at all Crum Creek sites than at DCWM1 and most Ridley Creek sites (Figure 1a). Interestingly, mean specific conductivity is significantly higher at WBRC1 than Main Stem Ridley Creek (RC1), despite their physical proximity (Figure 1a, Map 1). Check out this blog post to learn more about these two sites. 

Figure 2. The relationship between percent impervious surface cover and mean specific conductivity at ten sample sites in the headwaters of Darby, Crum, and Ridley Creeks from January 2018 through December 2021. Error bars represent standard error. The blue line represents a linear trendline and the shaded region shows the 95% confidence interval. 

Some spatial differences in specific conductivity between sites can be explained by the percent impervious cover in the surrounding watershed. There is a significant positive relationship between mean specific conductivity and percent impervious surface cover (Figure 2). As impervious surface cover reflects the density of human development and specific conductivity reflects human influence on streams, this relationship is unsurprising.

Specific conductivity generally remains constant throughout the year, though it can spike in winter (Figure 1b). Road salts, which are applied in the winter, form chloride when dissolved in water, increasing specific conductivity. The maximum specific conductivity at each site was recorded on days when there was notable snowmelt, indicating that runoff containing road salts is responsible for these spikes.

Chloride 

Figure 3. Monthly analysis of chloride concentration via Quantab strips from January 2019 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. 

Chloride is naturally present in streams at low concentrations due to the weathering of rocks and soils. Road salt is the main anthropogenic source of chloride in streams, though fertilizers can also contribute chloride. Long-term increases in chloride have been reported nation-wide.2 Chloride impacts ecosystems by altering the microbial communities that form the base of the food chain and by disrupting ion transport in aquatic plants and animals.  Though much is still unknown about the effects of chronic exposure to elevated chloride, warmer temperatures increase the toxicity of chlorides to stream insects, with consequences for the rest of the stream ecosystem.3 Click here to learn more about the impact of elevated chloride levels on streams.

Chloride concentration in the sample area has not exceeded the Pennsylvania Department of Environmental Protection potable water supply standard of 250.3 ppm, though WBRC1 and DCWM1 have reached 247 ppm (Figure 3a).4 There are significant differences in monthly chloride concentration between sites. There are no significant differences in monthly chloride concentration between Crum Creek sites (Figure 3a). However, in Ridley Creek, chloride concentration is significantly lower at Ridley Creek State Park (RCSP1) than at WBRC1, indicating either a reduction in chloride entering the stream or dilution as discharge increases (Figure 3a). Chloride concentration in Darby Creek is comparable to most Ridley Creek sites, with RCSP1 and Crum Creek sites having lower concentrations (Figure 3a). Similar to specific conductivity, chloride is significantly higher at WBRC1 than at RC1, despite their proximity (Figure 3a, Map 1). Chloride concentration is generally higher in winter months than in other seasons due to road salt applications (Figure 3b). 

Nutrients

Nutrients are a group of chemical compounds that are essential to the growth and survival of living organisms. The two most common nutrients are nitrogen and phosphorus, which enter the water through animal waste, fertilizer runoff, and leaky septic and sewer systems, and cycle through the environment in a complex system. An excess of nutrients in streams can trigger a process called eutrophication, which is the rapid growth of vegetation and algae that ultimately reduces dissolved oxygen as vegetation dies and decomposes.5

i. Total Nitrogen

Figure 4. Total nitrogen from January 2018 through March 2020 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. The dashed line represents the recommended maximum total nitrogen threshold for streams in this ecoregion. 

Total nitrogen measures the concentration of nitrates, nitrites, and ammonia in the water. Total nitrogen dynamics are mostly driven by nitrates, which are present in higher concentrations than nitrites and ammonia. The Pennsylvania Department of Environmental Protection standard for the maximum concentration of nitrates and nitrites in potable water supply is 10 mg/L.4 Total nitrogen does not approach 10 mg/L at any sample sites. 

Though total nitrogen concentration is not high enough to be dangerous for human consumption, concentrations are high enough to impair streams. Two studies of nutrient concentrations in streams in this area have found that the total nitrogen threshold for streams that are not impaired by nutrients is 2.225 – 2.3 mg/L.6-7 In the sample area, the 2.3 mg/L threshold is exceeded in 141 out of 289 samples: at least 20 times by each Ridley Creek site and at most 8 times by each Darby and Crum Creek site (Figure 4b). Furthermore, natural background concentrations of total nitrogen are estimated to be 0.10 – 0.30 mg/L for this region, which is far lower than measured concentrations at all sites (Figure 4b).8 Total nitrogen concentrations are much higher than natural background levels and regularly exceed recommended thresholds, indicating that excess nitrogen is an impairment. 

There are significant differences in total nitrogen between sites (Figure 4a). In Ridley Creek, most downstream sites have significantly lower total nitrogen than most upstream sites, which could be due to dilution with greater volumes of water (Figure 4a). Despite close physical proximity, total nitrogen is significantly higher at WBRC1 than RC1 (Figure 4a, Map 1). There are no significant differences in total nitrogen between sample sites in Crum Creek, and Crum Creek sites and DCWM1 tend to have significantly lower total nitrogen than Ridley Creek sites (Figure 4a). Total nitrogen does not vary seasonally (Figure 4b).

ii. Total Phosphorus

Figure 5. Total phosphorus concentration from January 2018 through March 2020 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. The shaded region represents estimated natural background concentrations of total phosphorus and the gray hashed line represents the recommended maximum total phosphorus threshold for streams in this ecoregion. 

Total Phosphorus is the total concentration of all phosphorus-containing compounds in streams. Natural background concentrations of total phosphorus are estimated to be 0.025 – 0.060 mg/L for this region.8 In the study area, 55 out of 289 measurements exceed the upper end of this range and 189 exceed the lower end, suggesting that phosphorus may be present in excess (Figure 5b). However, an analysis of nutrient concentrations from 2000 to 2019 in streams in Southeastern Pennsylvania found that the maximum total phosphorus concentration for a stream that is not impaired by nutrients is 0.035 mg/L.7 In the sample area, this threshold is exceeded in almost half of the samples collected (140 out of 289 samples: 24 times each by WBRC1, RCAB1, RCOK1, and RCSP1 and only up to 11 times each by all other sites), indicating that phosphorus is regularly present at high enough concentrations to impair Ridley Creek and is occasionally an impairment in Crum and Darby Creeks. 

There are significant differences in total phosphorus between sites. Total phosphorus does not vary significantly between sites in Darby and Crum Creeks (Figure 5a). In Ridley Creek, WBRC1 has significantly higher total phosphorus than RCSP1 and RC1 (Figure 5a). Though total phosphorus does not show strong seasonal variation, total phosphorus trended higher and had a broader spread from mid-2019 through 2020 than in 2018 (Figure 5b). 

Key Takeaways

  • Specific conductivity is elevated in all streams, indicating that they are impacted by human activities. 
  • Specific conductivity is related to impervious surface cover in the watershed, highlighting the importance of protecting open space and limiting development.
  • Chloride, nitrogen, and phosphorus concentrations are all elevated, contributing to specific conductivity and threatening stream health.
  • Limiting runoff of road salt by sweeping up excess after storms and reporting large piles on roads to municipalities is critical to improving stream health.
  • Reducing chemical fertilizer use or switching to using compost or other soil amendments can limit the amount of nutrients entering streams. Head over to the Farm Program to learn more about soil health.
  • Native plants act as filters for water, pulling out nutrients and other pollutants before they enter streams. Adding native plants to lawns and gardens is a great way to improve water quality while also creating habitat for wildlife.

To read the full “State of our Streams Report,” click here.

Map 1. Willistown Conservation Trust’s sampling sites. Five sample locations are within the Ridley Creek watershed, four are within the Crum Creek Watershed, and one is within the Darby Creek Watershed. Sampling was conducted at each site every four weeks from January 2018 through December 2021.

Funding 

This report was made possible through a grant from the William Penn Foundation. The WIlliam Penn Foundation, founded in 1945 by Otto and Phoebe Haas, is dedicated to improving the quality of life in the Greater Philadelphia region through efforts that increase educational opportunities for children from low-income families, ensure a sustainable environment, foster creativity that enhances civic life, and advance philanthropy in the Philadelphia region. In 2021, the Foundation will grant more than $117 million to support vital efforts in the region. 

The opinions expressed in this report are those of the author(s) and do not necessarily reflect the views of the William Penn Foundation. 

References

1. Olson, J. R. & Cormier, S. M. Modeling spatial and temporal variation in natural background specific conductivity. Environ. Sci. Technol. 53, 4316–4325 (2019).

2. Kaushal, S. S. et al. Freshwater salinization syndrome: from emerging global problem to managing risks. Biogeochemistry 154, 255–292 (2021).

3. Jackson, J. K. & Funk, D. H. Temperature affects acute mayfly responses to elevated salinity: implications for toxicity of road de-icing salts. Philos. Trans. R. Soc. B Biol. Sci. 374, 20180081 (2019).

4. Pennsylvania Department of Environmental Protection. 25 Pa. Code Chapter 93. Water Quality Standards § 93.7. Specific Water Quality Criteria. https://www.pacodeandbulletin.gov/Display/pacode?file=/secure/pacode/data/025/chapter93/chap93toc.html&d=reduce (2020).

5. United States Geological Survey. Phosphorus and Water. Water Science School https://www.usgs.gov/special-topic/water-science-school/science/phosphorus-and-water?qt-science_center_objects=0#qt-science_center_objects (2018).

6. USEPA. Ambient Water Quality Criteria Recommendations: Rivers and Streams in Ecoregion IX. 108 (2000).

7. Clune, J. W., Crawford, J. K. & Boyer, E. W. Nitrogen and Phosphorus Concentration Thresholds toward Establishing Water Quality Criteria for Pennsylvania, USA. Water 12, 3550 (2020).

8. Smith, R. A., Alexander, R. B. & Schwarz, G. E. Natural Background Concentrations of Nutrients in Streams and Rivers of the Conterminous United States. Environ. Sci. Technol. 37, 3039–3047 (2003).

By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

State of Our Streams Report Chapter 2: Physical Stream Parameters

By

By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

Cover Photo by the Watershed Protection Team

Since 2018, the Watershed Protection Program has monitored water quality at ten sample sites in the headwaters of Darby, Crum, and Ridley Creeks (Map 1). Every four weeks, the team visited each of the ten sites to take in-stream measurements and collect samples for analysis in the lab. We are proud to present our findings on water quality based on analysis of our data collected from 2018 through 2021, which includes 41 monitoring visits and over 7500 different measurements. 

August is National Water Quality month, and each week we will publish excerpts from one chapter from our report. Last week, Chapter 1 we focused on the basic water chemistry parameters of water temperature, dissolved oxygen, and pH. This week, we are focusing on the physical characteristics of the stream: discharge, turbidity, and total suspended solids.

The full report, which includes more information than is provided in the blog posts, can be found here.

_____________________________________________

Monitoring the physical characteristics of streams, in addition to water chemistry, provides deeper insight into water quality and stream health. Discharge is the volume of water flowing through the stream, turbidity is the cloudiness of water, and total suspended solids is a measurement of the total mass of sediment and debris in the water. 

These parameters are influenced by the landscape in the surrounding watershed. Impervious surfaces, or surfaces that block the infiltration of water into the soil, can increase the velocity and energy of water during storm events, allowing stormwater to pick up and carry more sediment into the nearest body of water. By preventing infiltration, impervious surfaces also force more water into streams during storm events, resulting in greater flooding and erosion. The removal of trees and shrubs along waterways destabilizes soil, leading to more sediment in streams. Headwater streams, which are the origins of stream systems, can carry tons of sediment and pollution into the stream throughout the entire waterway, harming downstream ecosystems. Studying discharge and sediment dynamics can help identify areas of rapid erosion that should be targeted for restoration.

The headwaters of Darby, Crum, and Ridley Creeks are highly responsive to rainfall events, as indicated by spikes in discharge after storm events. There is constant, though often low, movement of sediment through the sample sites, as indicated by turbidity and total suspended solids. Sediment movement increases after rainfall or snowmelt events. Though there are no regulations governing acceptable amounts of sediment in streams, it is possible that sediment poses a risk to stream life during storm events. Analysis of sediment movement and erosion dynamics is ongoing to identify areas where restoration should target soil stabilization.

For a primer on statistical tests and how to read boxplots and scatterplots, click here.

Discharge

Figure 1. Stream discharge from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time.

Discharge is the volume of water flowing through a stream and is measured in cubic meters per second (m3/s). Discharge reflects the size of the stream; as more tributaries enter the stream and it gets bigger, discharge increases as well. Prior to June 5, 2019, discharge was not consistently measured on sample days.

There are significant differences in discharge between sites. Within each watershed, discharge is significantly higher at the most downstream site than it is at the most upstream sites, as expected, and discharge at Ridley Creek State Park (RCSP1) is significantly greater than discharge at all other sample sites (Figure 1a). 

Spikes in discharge are related to rainfall or snowmelt events, which increase the amount of water flowing through the stream. Changes can also be caused by debris in the stream channel. For example, the abrupt increase in discharge at RCSP1 on September 25, 2019 was likely caused by a downed tree that dammed Ridley Creek just downstream of the sample site (Figure 1b). By January 8, 2020, the tree was cleared and discharge returned to normal (Figure 1b). Decreases in discharge during summer months are generally caused by lack of rainfall. The lowest discharge at all sites but Crum Creek Main Stem Downstream (CC3) was recorded on August 16, 2021, after an extended period with little rain (Figure 1b).

Turbidity

Figure 2. Turbidity from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. 

Turbidity measures the amount of light that can pass through a water sample. Clear water has low turbidity and cloudy water has high turbidity. Turbidity provides an estimate for the amount of sand, silt, and other sediment in the water; as the amount of sediment in the water increases, so does the turbidity. However, turbidity is sensitive to the type of sediment — differences in the size, texture, and shape of sediment particles impact turbidity measurements — and should be considered a gross approximation for sediment concentration.

There are no significant differences in turbidity between sites (Figure 2a). Turbidity does not vary seasonally (Figure 2b). There is a significant but weak correlation between turbidity and discharge, suggesting that spikes in turbidity are related to influxes of sediment after rainfall or snowmelt events. The weakness of the relationship is likely due to differences in the amount of erosion and the type of sediment at each sample site.

Total Suspended Solids

Figure 3. Total suspended solids from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. (c) The relationship between turbidity and total suspended solids.The blue line is the linear trendline and the shaded region represents the 95% confidence interval.

Closely related to turbidity is total suspended solids, or the mass of suspended particles, usually sediment, in a specified volume of water. While turbidity roughly estimates the amount of sediment in the water, total suspended solids is a more exact approximation. Though the transport of sediment is a natural process in streams and rivers, excess or sudden movement of sediment can harm aquatic organisms. When sediment is deposited on stream beds, it can smother macroinvertebrates and cover crucial streambed habitat. In the water column, suspended solids absorb sunlight, heating up the water and limiting the ability of aquatic plants and algae to photosynthesize. Though total suspended solids analysis helps understand erosion and sediment movement in waterways, there are no state or federal standards governing acceptable concentrations of total suspended solids.

There are no significant differences in total suspended solids between sites (Figure 3a). total suspended solids does not show strong seasonal variation; spikes in total suspended solids are likely due to influxes of sediment after precipitation events (Figure 3b). There is a significant, but weak, correlation between discharge and total suspended solids. There is a significant correlation between turbidity and total suspended solids, indicating that turbidity can reflect total suspended solids (Figure 3c). However, due to differences in sediment characteristics, turbidity should only be used to predict total suspended solids at a site-specific scale.

Future analysis includes developing a rating curve to estimate the amount of sediment moving through a stream, which will help identify areas of rapid erosion that should be targeted for restoration.

Key Takeaways

  • Discharge generally remains constant, but is responsive to rainfall events. 
  • There is constant, though often low, movement of sediment through our streams.
  • Storm events can wash large quantities of sediment into streams, potentially posing a risk to aquatic organisms. 
  • To learn more about discharge, erosion, and flooding, check out Flooding 101 and Flooding 102. 

To read the full “State of our Streams Report,” click here.

Map 1. Willistown Conservation Trust’s sampling sites. Five sample locations are within the Ridley Creek watershed, four are within the Crum Creek Watershed, and one is within the Darby Creek Watershed. Sampling was conducted at each site every four weeks from January 2018 through December 2021.

Funding 

This report was made possible through a grant from the William Penn Foundation. The WIlliam Penn Foundation, founded in 1945 by Otto and Phoebe Haas, is dedicated to improving the quality of life in the Greater Philadelphia region through efforts that increase educational opportunities for children from low-income families, ensure a sustainable environment, foster creativity that enhances civic life, and advance philanthropy in the Philadelphia region. In 2021, the Foundation will grant more than $117 million to support vital efforts in the region. 

The opinions expressed in this report are those of the author(s) and do not necessarily reflect the views of the William Penn Foundation. 

— By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

State of Our Streams Report Chapter 1: Introduction and Basic Stream Parameters

By

By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

Cover Photo by Jennifer Mathes

The focus area of Willistown Conservation Trust  (WCT) includes over 190 miles of headwater streams in the Darby Creek, Crum Creek, and Ridley Creek watersheds, which are all tributaries to the Delaware River. Everything that happens in the headwaters of a stream impacts the rest of the system, meaning that any action taken in the WCT focus area has consequences for water quality that extend far beyond our region. 

The Watershed Protection Program was established in 2017 through a generous grant from William Penn Foundation and a strong partnership with the Academy of Natural Sciences of Drexel University. The Watershed Protection Program is part of the Delaware River Watershed Initiative (DRWI), which was established to study existing water conditions within the Delaware River basin and to coordinate efforts, around both data collection and analysis, to develop best management practices for land use that can help improve water quality. With the support of the Academy of Natural Sciences of Drexel University and Stroud Water Research Center, WCT Watershed Protection staff implemented a water quality monitoring program to understand how WCT’s conservation efforts have impacted local stream health. 

Since 2018, the Watershed Protection Program has monitored water quality at ten sample sites in the headwaters of Darby, Crum, and Ridley Creeks (Figure 1). Every four weeks, the team visited each of the ten sites to take in-stream measurements and collect samples for analysis in the lab. We are proud to present our findings on water quality based on analysis of our data collected from 2018 through 2021, which includes 41 monitoring visits and over 7,500 different measurements. 

August is National Water Quality month, and each week we will publish excerpts from one chapter of our report. The full report, which includes more information than is provided in the blog posts, will be released at the end of the month. This week, we are focusing on three parameters that make up the backbone of water quality monitoring: water temperature, dissolved oxygen, and pH.

The full report, which includes more information than is provided in the blog posts, can be found here.

_____________________________________________

Figure 1. Willistown Conservation Trust’s water chemistry sampling sites. Five sample locations are within the Ridley Creek watershed, four are within the Crum Creek Watershed, and one is within the Darby Creek Watershed. Sampling was conducted at each site every four weeks from January 2018 through December 2021.

In the headwater streams studied for this report, water temperature is driven by air temperature, causing strong seasonal variation, with near-freezing temperatures in the winter and high temperatures in the summer. Water temperature is also linked to land use. The removal of trees along streams exposes streams to direct sunlight, warming the water. Additionally, parking lots, roads, and sidewalks all absorb heat in the summer and warm up rainfall before it enters streams, further raising water temperatures. Elevated water temperature is of concern due to its relationship with dissolved oxygen in streams. In waterways, dissolved oxygen represents the amount of oxygen available for use by aquatic organisms. As temperature increases, water can hold less dissolved oxygen, meaning there may not be enough for all organisms living in the stream.  

Another key benchmark for stream health is pH, which measures how acidic or basic the water is. If water is too acidic or basic, it becomes toxic for many aquatic organisms, even if water temperature is not too high and there is enough dissolved oxygen. Thus, measuring water temperature, dissolved oxygen, and pH can quickly reveal how hospitable streams are for aquatic life.

Results from analysis of our data indicate that water temperature is an impairment at our sample sites. Temperature is elevated at all sample sites, especially during summer months, stressing sensitive aquatic organisms such as trout and freshwater mussels. Dissolved oxygen does not drop below levels deemed unsafe for aquatic life, but it is not high enough during summer months to support the reproduction of trout populations. pH remains within the range deemed safe for aquatic life, though it can approach dangerous levels at some sites. 

For a primer on statistical tests and how to read boxplots and scatterplots, click here.

Water Temperature

Figure 2. Water temperature from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time. The lines represent maximum allowable temperatures for a Cold Water Fishery (CWF), Trout Stocked Fishery (TSF), and Warm Water Fishery (WWF). 

Water temperature is the primary parameter by which the Pennsylvania Department of Environmental Protection designates protected uses for streams. Water temperature is closely linked to the amount of dissolved oxygen in the water and, consequently, different species can tolerate different temperatures. The three protected uses that have temperature criteria are Cold Water Fisheries, Warm Water Fisheries and Trout Stocked Fisheries. A Cold Water Fishery supports the survival and reproduction of Salmonidae fish species (including Brook Trout, Salvelinus fontinalis) and other aquatic flora and fauna that require a cold water habitat, while a Warm Water Fishery supports the survival of fish and aquatic flora and fauna that can tolerate a warmer habitat.1 A Trout Stocked Fishery supports the survival of stocked trout from February 15 to July 31 in addition to all the species supported by a Warm Water Fishery.1

There are no significant differences in water temperature between sample sites (Figure 2a). Water temperatures are regularly above Cold Water Fishery maximums at all sample sites throughout the year. In winter and spring months, water temperatures can exceed Warm Water Fishery and Trout Stocked Fishery maximums during unseasonably warm days. During summer months, water temperatures are consistently below Warm Water Fishery maximums but occasionally exceed Trout Stocked Fishery maximums during heat waves. The frequency with which temperature exceeds Cold Water Fishery requirements and the occasional exceedance of Warm Water Fishery and Trout Stocked Fishery maximums signifies that all sites are impaired by elevated temperature (Figure 2b). This stresses sensitive organisms such as Brook Trout, freshwater mussels, and stream insects like mayflies, stoneflies, and caddisflies.

Dissolved Oxygen

Figure 3. Dissolved oxygen content from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time.

All living animals require oxygen to breathe, and stream-dwelling organisms like fish and aquatic insects are no exception. Dissolved oxygen is temperature dependent. Cold water can hold a higher concentration of dissolved oxygen than warm water; consequently, dissolved oxygen is highest in the winter and lowest in the summer (Figure 3b). Dissolved oxygen is also related to photosynthesis. As aquatic primary producers, or plants and algae, photosynthesize during the day, they increase the amount of dissolved oxygen in the water. Conversely, as these producers cease photosynthesis at night, they consume oxygen through respiration, decreasing the amount of dissolved oxygen in the water. As a result, dissolved oxygen follows a daily cycle, rising during the day and falling during the night.2

The amount of dissolved oxygen in the water impacts the reproduction and survival of many species. If dissolved oxygen drops below a certain level, aquatic organisms will be too stressed to reproduce. If it drops further, these organisms may suffocate and die. The dissolved oxygen standard for a Cold Water Fishery, according to the Pennsylvania Department of Environmental Protection, depends on the presence or absence of naturally reproducing fish in the Salmonidae family, which includes all trout species. To the best of our understanding, none of the sampled streams have naturally reproducing salmonids, so the dissolved oxygen standards for a Cold Water Fishery are at least 6.0 mg/L over a 7-day average with a minimum of 5.0 mg/L at any given time.3 Dissolved oxygen has not dropped below 7.0 mg/L at any sample sites, but all measurements were taken during daylight hours and do not capture nighttime dissolved oxygen minimums. Consequently, it is unclear whether dissolved oxygen is within the range of a Cold Water Fishery at the sample sites. 

There are significant differences in dissolved oxygen between sites, with significantly higher dissolved oxygen  at Ridley Creek at Okehocking Preserve (RCOK1) than at Crum Creek Main Stem Upstream (CC2) and Darby Creek at Waterloo Mills (DCWM1) (Figure 3a). This difference is likely due to sampling time: RCOK1 is sampled in the afternoon, when photosynthesis is highest and dissolved oxygen peaks, while CC2 and DCWM1 are sampled in the morning, when there is less photosynthesis and dissolved oxygen is consequently lower. However, Ridley Creek State Park (RCSP1) and Crum Creek Main Stem Downstream (CC3) are also sampled in the afternoon and are not significantly higher than DCWM1 and CC2, suggesting that other factors, in addition to photosynthesis, may explain the differences in dissolved oxygen at these sites.

pH

Figure 4. Stream pH from January 2018 through December 2021 (a) across ten sample sites in the headwaters of the Darby, Crum, and Ridley Creeks and (b) over time.

Another important water quality parameter is pH, which measures how acidic or basic water is. A pH of 7.0 is neutral, a pH below 7.0 is acidic, and a pH above 7.0 is basic. pH determines how easily an aquatic organism can use nutrients and indicates how toxic pollutants may be. To qualify as a protected fishery by the Pennsylvania Department of Environmental Protection, a stream must have a pH between 6.0 and 9.0.3 When pH is outside this range, nutrients become difficult to absorb and pollutants become more toxic, stressing organisms and leading to a reduction in biodiversity. Stream pH is influenced by in-stream photosynthesis, local soil type, geology, and human-based pollution. 

The pH of each stream in the study area tends to be slightly basic. No sites have pH measurements outside the 6.0 – 9.0 range designated by Pennsylvania Department of Environmental Protection as a protected fishery, though RCOK1 and RCSP1 reach over 8.9.3 pH does not exhibit strong seasonal variation (Figure 4b). 

There are significant differences in pH between sites. pH is significantly higher at RCOK1 than at all other sample sites and is also elevated at CC3 and RCSP1 (Figure 4a). Some variation in pH between sites could be explained by the sampling time. Photosynthesis increases the pH of streams by removing carbon dioxide. Photosynthesis peaks in the afternoon and, consequently, pH tends to be higher in the afternoon. RCOK1, RCSP1, and CC3 are always sampled in the afternoon, therefore, photosynthesis likely explains the elevated pH at these sites. 

Key Takeaways

  • Water temperature is a significant impairment at all sample sites and any effort to restore Darby, Crum, and Ridley Creeks must aim to reduce water temperatures.
  • There is generally enough dissolved oxygen to support the survival of aquatic organisms, though it may be low enough in the summer to stress and limit the reproduction of sensitive groups.
  • pH is within a safe range at all sample sites, though it can approach unsafe levels at RCOK1 and RCSP1. 
  • The best way to address water temperature impairments is to plant native trees and shrubs along waterways. Click here for more information on the role of riparian plants, and check out these resources from WCT’s Stewardship Team to learn more about the best native plants to plant in these areas.

To read the full “State of our Streams Report,” click here.

Funding 

This report was made possible through a grant from the William Penn Foundation. The William Penn Foundation, founded in 1945 by Otto and Phoebe Haas, is dedicated to improving the quality of life in the Greater Philadelphia region through efforts that increase educational opportunities for children from low-income families, ensure a sustainable environment, foster creativity that enhances civic life, and advance philanthropy in the Philadelphia region. In 2021, the Foundation will grant more than $117 million to support vital efforts in the region. 

The opinions expressed in this report are those of the author(s) and do not necessarily reflect the views of the William Penn Foundation. 

References

1. Pennsylvania Department of Environmental Protection. 25 Pa. Code Chapter 93. Water Quality Standards § 93.3. Protected water uses. http://www.pacodeandbulletin.gov/Display/pacode?file=/secure/pacode/data/025/chapter93/chap93toc.html&d=reduce (2009).

2. Wilson, P. C. Dissolved Oxygen. 9 https://edis.ifas.ufl.edu/publication/SS525 (2019).

3. Pennsylvania Department of Environmental Protection. 25 Pa. Code Chapter 93. Water Quality Standards § 93.7. Specific Water Quality Criteria. http://www.pacodeandbulletin.gov/Display/pacode?file=/secure/pacode/data/025/chapter93/chap93toc.html&d=reduce (2020).

4. Kellner, E. & Hubbart, J. A. Advancing Understanding of the Surface Water Quality Regime of Contemporary Mixed-Land-Use Watersheds: An Application of the Experimental Watershed Method. Hydrology 4, 31 (2017).

5. Mealy, R. & Bowman, G. Importance of General Chemistry Relationships in Water Treatment. (2004).6. Mesner, N. & Geiger, J. pH. (2005).

— By Anna Willig and Lauren McGrath | Willistown Conservation Trust Watershed Protection Program

Project Plastic and the Hunt for Microplastics

By

By Amy Amatya of Project Plastic

Some of the greatest challenges humanity faces today — pandemics, climate change, water contamination — are invisible. They escalate because we don’t see them coming, or we ignore the data that help us see them. 

Microplastics are no exception. Defined as any plastic smaller than five millimeters in diameter, microplastics pose a big problem to the environment and ourselves. They are easily ingested, potentially toxic, and everywhere. In fact, microplastics are found in nearly every corner of the world, right down to the tissues of living organisms. 

Microplastics exist via two pathways: they are mass-produced to be this size (‘primary’), or they come from the degradation of larger plastics (‘secondary’). Primary microplastics are difficult to target because production is controlled by industries including textiles, cosmetics, and household items. Considerable persuasion of regulators and corporations is necessary to reduce microplastic production. Some progress has been made on this front, as the Microbead-Free Waters Act of 2015 prohibits microplastic use in wash-off cosmetics. However, secondary microplastics are difficult to target because a lot of plastic already exists in the world. The sheer difference in scale between microplastics and the landscapes they inhabit prohibit remediation. Even if we ceased all plastic production today, there are still 200 million tons of plastic circulating in our oceans.

Despite their huge threat, there are no consistent protocols available for the accurate and 

systematic recording of microplastic pollutant concentrations in water. There is also no existing technology available to sequester all microplastics from tributaries, effluent streams, reservoirs and lakes. There are three approaches to reducing microplastic pollution. We can: 

1) Produce less plastic, 

2) Prevent existing plastic from entering the environment, and 

3) Remove microplastics directly from the environment. 

The Project Plastic meets with the ACUA Wastewater Treatment Facility about the future of Plastic Hunters in wastewater management systems. Photo by Project Plastic

Project Plastic was moved by the third approach to develop the world’s first portable, affordable, and environmentally friendly microplastic measuring and sequestration device. Project Plastic is a team of chemists and architectural designers, but we aren’t just a filtration technology company. Driven foremost by the microplastic problem, we follow microplastics to the end of their aquatic lifetime. We strive to collaborate with riverkeepers, water treatment companies, and private bottled water companies to monitor, collect, and upcycle microplastic pollution from waterways. 

Our device utilizes a patented ‘artificial root’ technology that acts as a filter to remove small debris (including microplastics) from the upper water column, where most plastic pollutants accumulate. Our root technology is modeled after organic aquatic plant roots. Long fibrous filaments are suspended in water and sediments physically adhere to the dense fibers on each root. Naturally-occurring biofilms accumulate on the ‘artificial root’ network over time, which further traps small particles. By applying an array of ‘artificial roots’ to the underside of a flotational frame, our device can entrap large quantities of microplastics while allowing aquatic wildlife to swim below or between our filter. Each biofilter is attached to a removable pad, making it easy to swap biofilters once they become saturated. Each pad is housed within a hydrodynamic flotation frame for application in rivers, streams, and reservoirs.

The Plastic Hunter: a portable, affordable microplastic filter inspired by plant roots. Image created by Project Plastic

The Plastic Hunter has a key advantage over conventional filtration technologies: it has no mechanical components, meaning it can operate passively with no electricity and minimal maintenance. This makes the device far cheaper to produce, deploy and maintain compared to any existing microplastic filtration system.

Lastly, our team is currently working on establishing protocols for the separation and purification of contaminated sediments from our filter media. In doing so, our team hopes to extract relatively pure microplastic sediments from our devices to be forwarded to our research collaborators at the University of Washington in St Louis. The aim is to develop a method of converting microplastics into chemical compounds like carotene. If successful, our team may be able to upcycle microplastics into useful chemicals for other industries like pharmaceuticals, turning harmful waste into sustainable resources. This, we hope, will avoid environmentally harmful storage or processing of contaminated sediment through incineration, and instead propagate a circular economy for microplastic waste.

— By Amy Amatya of Project Plastic

Microplastics: The ever present contaminant

By

By Watershed Protection Program Co-Op Vincent Liu

Large-scale plastic production has been around since the 1950s, and while plastics existed prior, it was not until this time where plastics began making their way into many aspects of life. With the rise of plastic as a popular material, microplastics emerged as a new contaminant. Microplastics are small pieces of plastic, less than 5mm in size, and they are everywhere. In even the most remote waters of Earth, microplastics can be found. Microplastics are not a recent environmental concern as they have been extensively studied in the marine environment. The presence and impact of microplastics on freshwater ecosystems, however, has been a topic of interest in recent years. With its ability to persist in the environment and being incredibly difficult to remove efficiently, microplastics have established themselves as a worrying pollutant.

Microplastics are formed when larger pieces of plastic break apart into smaller ones. They can come from a wide variety of sources, such as textiles, industry, and packaging. Single-use plastics that reach the environment gradually break into microplastics that can then wash into a stream from a storm event. Plastic fibers are easily shed in the washing machine and then end up in wastewater that enters streams and rivers. These are just some of the many ways that microplastics are released into water. The biological effects of microplastics are yet to be clearly defined, but harmful impacts have been found in studies involving freshwater fish and bottom-dwelling macroinvertebrates. Macroinvertebrates are small animals that lack a backbone, and some species are often used by scientists as indicators of stream health. A study by Redondo-Hasselerharm et. al in 2018 showed that the impact of microplastics on macroinvertebrates is species dependent, with some species being highly sensitive to microplastics and others not being affected at all. Specific health effects were also found in fish including liver damage and reduced growth.

I did my senior project on observing microplastics in Pennsylvanian streams while working with the environmental policy organization, PennEnvironment, on their citizen science microplastic project. PennEnvironment staff collected samples while I assisted in processing samples and analyzing the data. The samples were collected in glass jars, to help reduce the plastic contamination, and were run through a filtration system that draws the water sample through a filter, leaving just the suspended solid material from the water. The filter is placed under a microscope to detect the presence of microplastics within the sample. The 4 categories of microplastics that this project looked for were fibers, fragments, films, and beads. Fibers are long, thin strands of plastic that usually come from textiles. Films are flat, wide, and typically transparent. Beads are round spheres, often found in personal care products prior to 2015. Fragments are plastics that do not fit any of the other categories. A microplastic was distinguished from a natural material by using the squish test, which is a simple test done by poking the suspected microplastic with tweezers. Plastic will not break. It will either maintain its shape or mold into a different shape. 

Example of a microfiber viewed under a microscope. Photo by Caitlin Wessel

The results of the project confirmed the presence of microplastics in every stream that was sampled. What was particularly interesting was the low amount of microbeads compared to every other category of plastic. Beads were by far the least common category of microplastic. This can most likely be attributed to the Microbead-Free Waters Act in 2015, which banned plastic microbeads in rinse-off cosmetics. It was also notable that samples had wildly varying amounts of microplastic, though concentration was not calculated for this project. The site photos from where the samples were collected often told a story as well. In one of the sites, there was a blue tarp that was hanging from a tree into the stream just upstream of the collection site. During microplastic analysis for that sample, there was a noticeably high count of blue microfibers. 

Filtration system used to filter microplastic from water and the jars that samples are stored in

Finding ways to remediate microplastic already existing in the environment is an ongoing pursuit, but policy changes can reduce microplastic output from the source. The microbead ban leading to almost a complete disappearance of microbeads in waterways is an example of how legislation can lead to reductions of microplastic contamination. Policy changes in reducing unnecessary plastic usage and encouraging the use of alternative materials will reduce the amount of microplastics entering the streams. After over 70 years of mass plastic production, it may be time to switch gears and look for alternatives. 

— By Watershed Protection Program Co-Op Vincent Liu

References

Parker, B., Andreou, D., Green, I. D., & Britton, J. R. (2021). Microplastics in freshwater fishes: Occurrence, impacts and future perspectives. Fish and Fisheries, 22(3), 467–488. https://doi.org/10.1111/faf.12528

Redondo-Hasselerharm, Paula E., et al. “Microplastic Effect Thresholds for Freshwater Benthic Macroinvertebrates.” Environmental Science & Technology, vol. 52, no. 4, 30 Jan. 2018, pp. 2278–2286, https://pubs.acs.org/doi/10.1021/acs.est.7b05367 

Eerkes-Medrano, D., Thompson, R. C., & Aldridge, D. C. (2015). Microplastics in freshwater systems: A review of the emerging threats, identification of knowledge gaps and prioritisation of research needs. Water Research, 75, 63–82. https://doi.org/10.1016/j.watres.2015.02.012

Birch, Q. T., Potter, P. M., Pinto, P. X., Dionysiou, D. D., & Al-Abed, S. R. (2020). Sources, transport, measurement and impact of nano and microplastics in urban watersheds. Reviews in Environmental Science and Bio/Technology, 19(2), 275–336. https://doi.org/10.1007/s11157-020-09529-x

Geyer, R., Jambeck, J. R., & Law, K. L. (2017). Production, use, and fate of all plastics ever made. Science Advances, 3(7). https://doi.org/10.1126/sciadv.1700782

Center for Food Safety and Applied Nutrition. “The Microbead-Free Waters Act.” U.S. Food and Drug Administration, 2018, www.fda.gov/cosmetics/cosmetics-laws-regulations/microbead-free-waters-act-faqs.b 

OUR NATURE PRESERVES

Our nature preserves are open to the public 365 days per year from sunrise to sunset, providing natural places that offer peace and respite for all. Willistown Conservation Trust owns and manages three nature preserves in the Willistown area - Ashbridge, Kirkwood and Rushton Woods Preserve. We maintain these lands for the … Learn more about our nature preserves.

Upcoming Events

No event found!
Load More

DONATE TODAY!

Invest in Nature! ENGAGE CONNECT SPONSOR LEAVE A LEGACY   If you would like to make a gift of securities, such as stocks, bonds, or mutual fund shares, please contact us at 610-353-2562 for instructions. For more … Donate Today

WHERE WE WORK

The work of the Willistown Conservation Trust is concentrated on 28,000 acres of Willistown Township … read more