Piedmont Uplands

Two facilities operating side by side along the Potomac have been discharging pollutants at levels that dwarf their permitted limits — not occasionally, but as a sustained, unbroken pattern now stretching back more than two years. The Potomac River Water Filtration plant, which supplies drinking water to hundreds of thousands of people in this region, recorded suspended solids this week at more than twice its permitted limit and aluminum just above its permitted ceiling — and those are the modest figures. At its worst, in the summer of 2025, the plant exceeded its suspended solids limit by nearly a hundredfold. This is not a facility struggling with an unusual event; it is a facility operating in chronic, unresolved violation of the very standards designed to protect the river it draws from.Aluminum sits at the center of this problem in a chemically ironic way. Water treatment plants add aluminum sulfate as a coagulant precisely because it binds to the fine particles suspended in river water, pulling them into clumps heavy enough to settle out before the water is treated for drinking. But when that aluminum-laden waste escapes back into the river — as it clearly has here, quarter after quarter — it becomes a toxicant in its own right. Aluminum binds to gill tissue in fish, interfering with ion exchange and respiration; at elevated concentrations it can be acutely lethal to sensitive species and chronically damaging even at lower levels. The aquatic invertebrates that form the base of the river's food web are particularly vulnerable, and July, with its warm temperatures and compressed oxygen levels, is the worst possible time for this kind of loading.Downstream and compounding this picture, the USDA East-Side WWTP has maintained its own unbroken record of copper violations, running between three and ten times its permitted limit every quarter for the past three years, with the current reading again sitting above four times the allowed concentration. Copper is acutely toxic to aquatic invertebrates — particularly mayflies, stoneflies, and caddisflies, the three orders whose presence or absence ecologists use as the primary index of stream health. A river receiving persistent copper loading in excess of four times the legal limit is not a river that can sustain a recovering macroinvertebrate community, no matter what restoration work is happening elsewhere in the watershed.The Northern Piedmont rivers running through this landscape have a complicated history. The Potomac was, within living memory, one of the most degraded large rivers in the eastern United States — described in the 1960s as an open sewer running past the capital. The cleanup that followed, driven by the Clean Water Act and billions in public investment over five decades, was real and measurable: shad returned, bald eagles nested along the banks, submerged aquatic vegetation spread back across the tidal reaches. That recovery was never complete, and the river remains on state and federal impairment lists. What these discharge records show is that some of the infrastructure meant to serve the public good is quietly working against the ecological recovery the public has paid dearly to achieve.What to watch for next is straightforward, if disheartening: whether the pattern that has held since at least mid-2023 continues into the late summer, when thermal stress peaks and the river's capacity to buffer chemical insults is at its lowest. Suspended solids in warm, slow water drive dissolved oxygen down further; aluminum toxicity increases as pH fluctuates with algal cycles; copper accumulates in sediments where invertebrates forage and spawn. Each quarter that passes without a corrective response is another quarter of data confirming that these are not aberrations. They are, at this point, the baseline.

Stoneflies (Plecoptera) are emerging along Rock Creek and its tributary Cabin John this July — a suite of fourteen records over the past three months marking one of the clearest ecological signals of improving water health. These mayfly-like insects are relentless indicators; their nymphs cannot tolerate even trace levels of organic pollution, and they vanish entirely from waters under stress.The distribution tells a hopeful story. Maryland's mainstem of Rock Creek has now achieved full attainment for all designated uses, a milestone reached in 2024 after years of stormwater and sewage management work. The DC sections, by contrast, remain on the impaired list — yet even there, stonefly nymphs are establishing themselves in cleaner pockets of the channel. A stonefly on the wing in midsummer is a stream announcing, quietly but unmistakably, that it is coming back.

Herons and cormorants are returning to the Anacostia, a sign of ecological recovery that feels tentative and urgent in equal measure. The river's listed status and restoration efforts have drawn more wading birds back to the shallows in recent seasons — but they are feeding and roosting in water contaminated far beyond legal limits.The Washington Navy Yard has been discharging aromatic hydrocarbons (PAHs) into the river at levels exceeding 35,000 percent of its permit limit — a violation sustained across multiple quarters and multiple discharge points. These compounds bioaccumulate in fish and aquatic birds, concentrating up the food chain. The longer birds feed here, the greater their body burden of toxins.Ecological recovery without enforcement is an illusion. The river's restoration can only hold as long as compliance does — and right now, that margin is neither narrow nor safe.

Monarchs are flowing through the region this month — twenty-one sightings logged from Silver Spring to the C&O Canal, all part of the summer breeding generation refueling on their migration north. The timing feels tight: all three local milkweed species opened within a narrow window at the end of June, offering just days of peak nectar availability.Common milkweed (Asclepias syriaca) led the way in mid-June, followed by swamp milkweed (Asclepias incarnata) and butterfly milkweed (Asclepias tuberosa) in the final days of the month. That synchrony is not guaranteed. Heat can push milkweed past bloom before the butterflies arrive — a phenological mismatch that can starve a migration cohort — so when all three species open together, it's worth marking as a working landscape.

Buttonbush is in peak bloom from Alexandria to Great Falls — a brief nectar window for bumblebees and sphinx moths. Nineteen of 26 nearby water bodies are officially impaired, yet this native shrub persists in floodplain soils. Not a clean bill of health, but the riparian fringe still holds.

The light is still fading at nine o'clock. In the understory along Bethesda's wooded edges, where flowering dogwood and pawpaw hold the middle layer and the canopy closes overhead, the first flashes appear low to the ground, maybe a foot or two above the grass. They are yellow-green, brief, and arcing slightly upward. By the time full dark settles in, there are dozens of them.These are common eastern fireflies, and what you are watching is a conversation. The males fly and flash; the females wait, perched on vegetation, watching. The male's signal follows a precise pattern: a single flash lasting about half a second, then a pause of roughly six seconds, then another flash. The arc of the flight is part of it too. Females who are ready to mate flash back after a fixed delay, typically about two seconds. That timing is the key. Males scanning the dark learn to read it. A female who answers at the right interval draws the male toward her, and he flashes again, and she answers again, and he homes in. The whole exchange can take several minutes before the male lands.This is peak season for them. The nights are the shortest they will be all year, which means the window for signaling is compressed. But the warmth matters as much as the darkness. Common eastern fireflies are most active when air temperatures stay above roughly 21 degrees Celsius after sunset, and summer nights here hold that heat. The flashing typically begins in the first hour after dark and tapers off by midnight. On a warm, still night with low wind, the signals carry well and the activity is dense. On cooler nights, or nights with rain, it falls away quickly.The light itself is produced in the abdomen, in a specialized organ that runs a chemical reaction involving a compound called luciferin, an enzyme called luciferase, and oxygen. The reaction produces light with almost no heat, which is unusual for a light-producing process. The firefly controls the flash by controlling the oxygen supply to the organ. The precision of the timing, the duration, the interval, is all physiological, controlled by the nervous system. Different firefly species in the same habitat use different flash patterns and different colors, which is how a female tells her own species from others flying nearby. In the same meadow edge, you might have several species active at once, each running a different signal.The larvae spend most of their lives underground or in leaf litter, where they are predators of soft-bodied invertebrates including earthworms and snails. The adult firefly, the one flashing now, does not eat at all, or eats very little. The adult stage is entirely about reproduction. The females of some firefly species mimic the flash responses of other species to lure males and eat them, but common eastern fireflies do not do this. The adults live only a few weeks.Spotted lanternfly, an invasive species now established in this area, feeds heavily on a wide range of woody plants in summer, and its presence has altered some of the understory structure that fireflies depend on. Invasive Amur honeysuckle thickens the shrub layer in ways that can reduce the open, grassy edges where males fly and females perch to watch. These are slow pressures, not sudden ones, but they shape what the habitat looks like over time.If you are outside now, or near a window facing a wooded edge, look low. The males rarely fly more than a few meters off the ground during the early display. The flash lasts less than a second, then the beetle coasts dark for six seconds before flashing again. If you count the interval, you can tell whether what you are seeing is a male searching or a female answering. The females tend to flash from a fixed point; the males move. Watch one long enough and you can see the arc of the flight between flashes, a faint shape moving through the dark.

The air holds thick and still above the Potomac's edge, where the long days of summer stretch into evening. Heat radiates from the pavement and settles into the canopy of white ash and American elm that line these urban streets. If you are walking here, let the sounds of the city fade for a moment. The trees themselves are busy with smaller, quieter dramas.On the bark of a white ash, a cluster of spotted lanternflies feeds. These invasive insects arrived from Asia and have spread rapidly across the mid-Atlantic. The nymphs are black with white spots, about the size of a thumbnail, and they pierce the bark with needle-like mouthparts to reach the tree's phloem. The phloem carries sugar-rich sap from the leaves down to the roots. The lanternflies tap directly into this flow, drawing out the nutrients the tree needs to sustain itself through the growing season.The feeding happens in groups. Where you find one spotted lanternfly, you find dozens. They cluster on the same section of bark, their bodies pressed close together as they probe for the sweetest channels of sap. The ash tree responds by producing more sap to seal the wounds, but this only attracts more lanternflies. The excess sap they cannot process drips down the trunk as honeydew, a sticky substance that coats the bark and feeds sooty mold. The tree's trunk darkens with this black fungus, and the ground below becomes slick with the sugary residue. American elms face the same assault. Their smooth bark shows the telltale weeping where lanternflies have concentrated their feeding. The elms, already stressed by Dutch elm disease and urban conditions, struggle under this additional pressure. A heavily infested tree may lose significant amounts of sap, weakening its ability to transport nutrients and defend against other threats. The honeydew that accumulates on leaves blocks sunlight, reducing photosynthesis when the tree most needs energy to repair the damage.Native insects that might normally feed on these trees find their feeding sites occupied. The spotted lanternflies do not belong to the web of predator and prey relationships that have developed here over thousands of years. Few native birds recognize them as food. Few native parasites can control their numbers. They feed without the natural checks that keep native plant-feeders in balance with their host trees. As the afternoon heat builds, you might notice the sweet, cloying smell of fermenting honeydew rising from an infested tree. The bark feels tacky to the touch where the excess sap has dried. Listen closely, and you can hear the faint sound of dripping as more sap weeps from fresh feeding wounds.

The air carries a faint sweetness across the Potomac Hills neighborhood this morning, where clusters of pink and orange flowers have begun to open on the milkweed plants scattered through yards and along fence lines. Common milkweed stands waist-high with its broad oval leaves, while the lower butterfly milkweed shows off bright orange blooms that seem to glow in the early light. The timing is no accident.Monarch caterpillars are hatching now from eggs laid on these same plants just days ago. The tiny larvae, smaller than a grain of rice, emerge with an immediate need. They eat their own eggshells first, then begin the work that will define their entire existence: consuming milkweed leaves. Nothing else will do. The chemical compounds in milkweed, toxic to most creatures, become the monarch's protection. The caterpillars concentrate these toxins in their bodies, making them unpalatable to birds and other predators.This relationship runs deeper than simple feeding. The milkweed plants are now entering their peak flowering period, their blooms attracting not just the adult monarchs that will lay the next generation of eggs, but dozens of other pollinators. Bees work the flowers methodically, their legs heavy with pollen. The monarch adults, when they visit, are less efficient pollinators than the bees, but they serve the plants in a different way. By laying their eggs exclusively on milkweed, they ensure a steady population of leaf-eating caterpillars that never fully defoliate their host plants. The caterpillars consume enough to stimulate new growth but leave the root systems intact.As the caterpillars grow over the coming weeks, they will shed their skin five times, each molt revealing a larger, more boldly striped larva. The final instar caterpillars, thick as a thumb and marked with yellow, black, and white bands, can strip a milkweed plant of most of its leaves before wandering off to pupate. But the plants recover. Their deep taproots, sometimes extending six feet down, store enough energy to send up new shoots. By late summer, many of these same milkweed plants will bloom again, providing nectar for the monarchs beginning their long migration south.The butterfly milkweed, with its more compact form and brilliant orange flowers, follows a slightly different schedule. Its blooms last longer than those of common milkweed, extending the nectar season well into summer. Both species contain the cardiac glycosides that make monarch caterpillars toxic to predators, but butterfly milkweed produces less of the milky latex that gives common milkweed its name. The caterpillars show no preference between the two species, moving from plant to plant as they outgrow their current food source.In yards where homeowners have planted native milkweeds, this ancient cycle plays out just as it does in prairies and meadows. The plants ask for little: decent drainage, full sun, and patience as they establish their deep root systems. In return, they anchor one of North America's most remarkable migrations. The caterpillars feeding on milkweed leaves today will become the butterflies that travel thousands of miles to overwinter in Mexico, guided by magnetic fields and celestial cues that scientists are still working to understand.Step outside if you can, and look for the milkweeds beginning to bloom in your area. The flowers release their fragrance most strongly in the warm afternoon sun, sweet and slightly cloying. If you find a plant, check the undersides of the leaves. The monarch eggs, when present, appear as tiny white dots, usually laid singly on the youngest, most tender foliage. The whole relationship begins there, with that small white sphere and the vast genetic memory it contains.