The end of the year marks the end of the planting stage of the Ashbridge Tree Planting. Since 2019, generous funding from the Pennsylvania Department of Conservation and Natural Resources enabled us to plant nearly 1,500 trees and shrubs of 53 different species. What was just a few years ago an ecologically-barren swath of invasive grass is now an ecologically-rich habitat, supporting diverse pollinators, birds, and other wildlife, all while improving water quality in Ridley Creek. This project was made possible thanks to the help of dozens of staff, interns, board members, and volunteers, who spent hours digging, planting, watering, and weeding. While the planting stage is complete, the maintenance stage is just beginning. Stay tuned in 2024 for volunteer opportunities to help this planting thrive.
The Darby Creek Community Science Monitoring Program (DCCS) is a collaborative project between Willistown Conservation Trust, Darby Creek Valley Association and Stroud Water Research Center. The study began in March 2021 with just two volunteers and has been growing steadily since – there are currently 33 active volunteers and 27 sites! This year alone, volunteers have collected a total of 66 monthly samples, which comes in at 432 water chemistry samples from the Darby and Cobbs Creek watersheds!
As we head into a winter that is predicted to bring snow and ice, the DCCS program will be collecting information about how road salt application to driveways, sidewalks and roads is impacting sensitive stream environments.
You can learn more about the trends that we are seeing in this critical watershed at the new DCCS website: DarbyCreekCommunityScience.com
By Watershed Conservation Research and Data Specialist Anna Willig
Aquatic macroinvertebrates — animals without a backbone that are visible to the naked eye — are some of the most fascinating creatures found in streams. We tend to lump all macroinvertebrates into one category, but there is tremendous diversity found underwater.
Some macroinvertebrates live for a few weeks, others for a few years. Some stay burrowed in the streambed their entire lives, others emerge as flying adults and migrate across the country. Some scrape algae off of rocks, others are voracious hunters. To illustrate this diversity, we are highlighting three sample orders from the class Insecta (the insects) that have vastly different life histories. While there are generalities that are shared between all species of each order, this is akin to generalizing the life history of all passerine birds (order Passeriformes, which includes most songbirds).
Odonata Spotlight | The Dragonflies
First up is the order Odonata, which includes dragonflies and damselflies. Dragonflies and damselflies are similar, but we focus on dragonflies, which are unique among aquatic macroinvertebrates for their large size, long lifespan, and hunting prowess. Dragonflies start their lives as eggs laid near the surface of the water. Eggs hatch within a few weeks, but some dragonflies can delay hatching for a year if they sense stream conditions are suboptimal. Once they hatch, they typically spend less than a year underwater in the larval (juvenile) stage, though some species spend up to six years developing in streams. Larval dragonflies are fearsome hunters that eat anything they can catch, including other insects, small fish, and tadpoles.
In their final days as larvae, dragonflies stop eating! During their metamorphosis from larvae to adult, their mouthparts change and, for a few days, are not functional. They crawl onto land at the end of their metamorphosis and climb out of their larval skin, emerging as adults. Once their wings dry and harden, adults take to the air, where they are as ferocious as they are underwater. They have remarkable vision and can predict where their prey will go, a feat not seen in other insects. Males establish territories over water, keeping other males out and luring females in.
Adult dragonflies live for several months to a year, and a few species, including the Common Green Darner (Anax junius), migrate across the country. Much remains unknown about the migration of Common Green Darners, but, like Monarch Butterflies, a migratory cycle likely lasts a few generations. The first generation emerges in the late winter in southern states and flies north to mate and lay eggs. The second generation hatches in late spring and migrates in late summer, making their way south to a place they have never been. They mate and lay eggs in the south, and the final generation emerges in the fall. This generation overwinters in the south, mating and laying eggs for the next migratory generation.
Ephemeroptera Spotlight | The Mayflies
Our next order is Ephemeroptera, the mayflies. Like dragonflies, mayflies have an aquatic larval stage and a terrestrial adult stage, but they share few other similarities. Mayflies are the only insect with an extra phase of metamorphosis called the subimago life stage. They are short-lived as adults and, in ideal conditions, can form massive swarms. Mayfly eggs often hatch within a few weeks, though some species hatch immediately and others delay hatching for a year in suboptimal stream conditions. Mayflies spend up to two years as aquatic larvae, shedding their skin dozens of times before adulthood. While most larval mayflies eat algae, leaves, and other plant matter, a few are predators (though not nearly as efficient as dragonflies).
At the end of their larval stage, mayflies crawl out the stream and shed their larval skin. However, they are not yet adults. This post-emergent, pre-adult form is a life stage unique to mayflies called a subimago. Subimagos have a hairy covering over their wings and must molt one more time to remove this covering, after which point they are adults. Adults only live for a few hours to days. During this ephemeral time, they have one task: reproduce. They lose the ability to eat during their metamorphosis into adults, forcing them to focus all their energy on finding a mate instead of finding food. Males form massive swarms, sometimes large enough to be detectable by weather radar, twirling and dancing to attract females. Females fly into the swarm, find a mate, and speed off to the nearest body of water, where their final act is laying eggs.
Coleoptera Spotlight | The Water Beetles
Another unique order is Coleoptera, the beetles, which is the largest order in the animal kingdom, containing an estimated 25% of all animal species. Unlike Odonata and Ephemeroptera, which include exclusively insects with an aquatic life stage, only a small fraction of Coleopterans have an aquatic life stage. Common water beetles include water pennies, diving beetles, and riffle beetles. Water beetles are aquatic for their larval and adult stages, only emerging for a few weeks to pupate. They hatch from eggs laid in the water, typically within two weeks, as most cannot delay hatching. Larval water beetles have diverse diets; some scrape algae off of rocks, some shred leaves, and some are predatory. They spend anywhere from a few months to a year in their larval stage and crawl onto the banks to metamorphose.
On the banks, larvae burrow into soft sand and mud to metamorphose, emerging as adults several weeks later. They fly briefly until they find a suitable place to enter the water. Once they re-enter the water, many water beetles never return to the surface. Some even lose their wings. Adults do not have gills and carry an air bubble to breathe, maintaining an equilibrium with the oxygen in the water that constantly replenishes their air. Some adults are short-lived and may not have mouthparts, while others can live for up to three years and have a variety of feeding strategies. Adults mate and lay their eggs underwater, setting the stage for the next generation.
Each of these orders contains multiple families, each family contains multiple genera, and each genus contains multiple species, each with a unique life history. Each stream contains its own community of macroinvertebrates, an unknown diversity hiding just beneath the waters. And these insects are not exclusive to local streams — there are thousands of species of dragonflies, mayflies, and water beetles found on all continents except Antarctica. Since 2018, the Watershed Team has collected annual macroinvertebrate samples from the headwaters of Ridley, Crum, and Darby Creeks. We are busy sorting and identifying our samples and are looking forward to sharing what these unique creatures can tell us about local stream health.
References and Resources
Interested in learning more about macroinvertebrates? Check out macroinvertebrates.org for information about and pictures of many of our local macroinvertebrates.
By Watershed Conservation Research and Data Specialist Anna Willig
One of the most basic, yet most critical, aspects of stream health is temperature. Temperature sits behind the scenes, governing nearly everything that happens in a stream. Make a stream too warm or too cold, and the wildlife will disappear.
While measuring the temperature of a stream seems straightforward — just stick a thermometer in the water — the reality is much more complicated. In small streams, such as the headwaters of Ridley, Crum, and Darby Creeks, temperature is incredibly variable. At the same spot in a stream, temperature can change by several degrees depending on the time of day, current weather, and time of year. Each day, water temperature rises and falls with the sun. Weather matters — a hot, sunny day will warm a stream more than a cool, cloudy day. Temperature also changes with the seasons, rising throughout the spring and summer and dropping in the fall and winter.
Location in a stream is important as well. In shady areas, streams will be cooler than in sunny areas. Slow-moving stretches tend to be warmer than fast-moving areas. Muddy water gets warmer than clear water. Shallow areas can warm more than deep sections. The variation of water temperature over time and across space in streams makes it crucial to measure temperature many times at many places in a stream in order to understand temperature trends.
Changes in land use further alter water temperature. When forests are leveled and replaced with strip malls and subdivisions, streams heat up. In undeveloped areas, rainfall soaks into the ground and cools as it flows underground towards streams. In developed areas, rainfall instead runs off of (often hot) parking lots, roads, houses, and sidewalks right into streams. This water cannot cool off and can make streams hotter. Removing streamside trees, building dams, and creating ponds all expose water to more sunlight, ultimately heating the stream.
Add in climate change, which will warm our region drastically in the next few decades, and it is clear that our streams are heating up. But why is this a problem? What does temperature have to do with the animals that live in our streams?
The danger of warm water temperature starts at the molecular level. Temperature governs the rate of chemical reactions and, in water, the amount of oxygen available. As a stream warms, chemical reactions occur faster and the water holds less oxygen. Most animals that live in streams — insects, mussels, fish, frogs, turtles — are cold-blooded, meaning their body temperatures change with the stream temperature. If a stream warms up, so will body temperature, speeding up respiration, metabolic reactions, and all other internal chemical processes that keep the animal alive. However, since warm water holds less oxygen, there will be less oxygen to support these processes, causing stress.
This thermal stress affects how fast organisms grow, how big they get, and how well they reproduce. Researchers from Stroud Water Research Center tested the impacts of water temperature on aquatic insects, which form the base of the food chain in streams. While there was a threshold above which all insects died, there were concerning effects even before temperature reached lethal levels. As temperatures warmed, insects developed and matured faster, but they did not become as large and consequently struggled to reproduce. If streams become too hot for aquatic insects to survive and reproduce, they will disappear, with catastrophic consequences for the entire ecosystem.
Fish are also sensitive to changes in stream temperature. Brook trout, Pennsylvania’s only native trout, currently cannot reproduce in local streams because temperatures are too warm. Even though trout are stocked by anglers every spring in local streams, the thermal stress forces these fish to devote so much energy to survival that they have no energy left for reproduction. Even less sensitive types of fish, like bass and sunfish, will show signs of stress when temperatures get too high.
If we want to keep our streams healthy, if we want to protect all the animals that depend upon them, we need to keep them cool. Limiting deforestation, especially along stream banks, will protect shady areas that cool streams. Establishing and expanding forested streamside buffers will create new shade and cool streams. Limiting new development will prevent the expansion of hot pavement. Shifting from stormwater management strategies that hold water, such as retention basins, to strategies that encourage infiltration, such as rain gardens, will force more water into the soil, where it can cool before reaching a stream.
You can make a difference at home by replacing lawns with gardens or meadows full of native plants, which will allow more water to enter the soil. Adding rain barrels will reduce the amount of hot runoff flowing off rooftops into streams. Planting trees, even if you are far from a stream, will also cool water down. Climate change means that rising temperatures will remain a constant threat, but making stream-conscious decisions can help ensure our streams remain healthy and full of life.
References and Resources
Check out this lecture on temperature from Dr. John Jackson of Stroud Water Research Center (lecture starts at 18:20): https://youtu.be/8Y1ey45053Q?t=1100.
Check out this research article about the impacts of temperature on mayflies from Stroud Water Research Center.
To see a streamside buffer restoration in progress, visit the Watershed Team’s Tree Planting at Ashbridge Preserve! Since 2019, we have put in nearly 1,500 trees with the goal of lowering water temperature in Ridley Creek.
By Anna Willig, Watershed Conservation Research and Data Specialist
This March, the Darby Creek Community Science Monitoring Program (DCCS) — a collaboration between Willistown Conservation Trust, Darby Creek Valley Association, and Stroud Water Research Center — celebrated its second birthday! We officially launched the DCCS in March 2021 with two stalwart volunteers sampling at two sites in Berwyn. Today, 28 volunteers actively monitor 21 sample sites throughout the watershed, extending past Folcroft (Figure 1). The goals of the DCCS are to learn about the health of Darby Creek and its tributaries and identify key restoration sites through monthly water quality monitoring visits.
Water temperature is a key indicator of stream health. As water warms, it holds less oxygen and becomes inhospitable to aquatic wildlife. Trout fishes are one of the most sensitive groups to high water temperature and are a benchmark for healthy streams. If streams are too warm for trout, they are likely too warm for a host of other aquatic species, including mussels and macroinvertebrates. Water temperatures in Darby Creek are often too warm to support the reproduction and survival of trout species (Figure 2). The removal of trees along a stream, increases in development, and stormwater runoff can all contribute to warming streams. The best way to cool streams down is by reforesting stream banks, planting native plants, and designing stormwater management that allows rain to soak into the soil.
Another indicator of stream health is chloride concentration. Chloride is an ion that reflects the amount of salt in streams. Road salt is the main source of salt in streams and is increasingly recognized as a major pollutant. Chloride concentration varies widely between sites in Darby Creek (Figure 3). Generally, chloride concentrations are below the chronic exposure threshold set by the EPA, but are above levels that researchers have found harmful to aquatic organisms. While road salt is necessary for safe winter travel, limiting use and sweeping salt up after storms can reduce salt pollution in streams.
While temperature and chloride concentration reflect a host of threats to the health of Darby Creek, our volunteers have found good news in Darby Creek. One volunteer found a small population of freshwater mussels — which are uncommon in Darby Creek — at one sample site. Freshwater mussels are one of the most imperiled groups globally, and finding them in Darby Creek is a clear indicator that, despite development and pollution, the creek is still a critical resource deserving of protection. We are working with research groups to document and protect this precious group of mussels.
We are incredibly grateful to all the fantastic volunteers who participate in this program. Through their dedication and enthusiasm, the DCCS has exceeded all expectations! The heart of this program is partnership, and we are thankful for support from Stroud Water Research Center and Darby Creek Valley Association. As the DCCS enters its third year, we are excited to build on partnerships, gain new insights, and leverage our volunteers’ data to improve the health of Darby Creek.