Michigan Lake Plain

Hartford wastewater treatment plant has exceeded its permitted mercury discharge limit in every reporting quarter for at least the past year, with a fresh exceedance recorded just days ago. That alone would be a serious regulatory failure — but the timing sharpens the concern considerably. Stream flow has fallen to just 35 cubic feet per second, the lowest it has been in weeks, stripping the water column of the dilution capacity that, under better conditions, at least partially buffers what comes through that discharge pipe.The chemistry of low-flow, warm-water conditions turns mercury from a chronic problem into an acute one. When water moves slowly through sediment-laden reaches, anaerobic bacteria convert inorganic mercury into methylmercury — the organic, bioavailable form that accumulates in tissue rather than flushing through. Methylmercury biomagnifies with extraordinary efficiency, concentrating by a factor of roughly one million from water to top predators. Herons, kingfishers, and the people who eat fish from these waters sit at the end of that chain. The conditions for methylation — warm temperatures, low dissolved oxygen, sluggish flow, fine sediments — are precisely what a midsummer low-flow event delivers.Odonates along the stream corridor right now include American Rubyspot (Hetaerina americana) and Ebony Jewelwing (Calopteryx maculata), both of which are meaningful here. These are stream-dependent damselflies whose larvae require clean, well-oxygenated water with intact riffle structure — they are routinely used as biological indicators in water-quality assessments, and their presence in reasonable numbers signals that the stream hasn't yet crossed into gross degradation. But biological indicators reflect the past, not the present. A larval cohort that hatched before the current discharge pattern intensified may be producing adults we're watching now — their flight doesn't clear the water of what's accumulating in the sediment beneath them.The broader odonate assemblage here — diverse, apparently healthy — sits in an ecological region with a complicated industrial and agricultural history. The Michigan Lake Plain has had its stream systems drained, tiled, and channelized for more than a century, and the stretches that still support sensitive odonates represent a fraction of what existed before European settlement. That context matters: when we read a community of jewelwings and rubyspots as a sign of health, we are reading it against an already-diminished baseline. The margin for additional stress is not what it would appear to be if the system were intact.Mercury's long residence time in sediment means that exceedances don't reset at the end of a quarter — each pulse deposits a legacy that persists through seasons and into years. As late-summer flows remain low and temperatures stay elevated, the window for active methylation stays open. The odonates are still here, still flying, still completing a life cycle that threads through the water and the air above it. The question the regulatory record raises is not whether the system is healthy today, but whether it can absorb one more year of quarterly exceedances without the biotic signal catching up to the chemical one.

Stream flow has dropped to 60 cubic feet per second — a ninety-fold decline from the 460 cubic feet per second recorded just weeks ago. At such austere levels, the chemistry of the water shifts. Mercury, which lingers in sediment and driftwood, begins to methylate: bacteria convert it into an organic form that fish absorb readily, concentrating as it moves up the food chain to herons and other predators.During this vulnerable season, the treatment plant has exceeded its mercury permit limit for four consecutive quarters, with nineteen percent over the threshold in the most recent month alone. The prior three quarters show a troubling pattern: exceedances of 16, 27, and 38 percent. Nearby stream reaches are federally listed as impaired — a designation that reflects precisely this kind of cumulative stress, where low flow amplifies the toxicity of discharges that might be manageable at higher water levels.

Flow in the stream surged from a near-trickle to nearly 400 cubic feet per second over the course of a single week — a tenfold pulse that reflects the flashy hydrology of this glaciated landscape. In systems this responsive to rainfall, rapid discharge sweeps sediment and anything bound to it downstream in a matter of hours.That mobilization carries particular weight in a watershed still under active Superfund remediation for PCB contamination. High flows that resuspend legacy pollutants buried in streambed sediments can undo years of settling, pushing contamination further into groundwater and downstream environments where it poses ongoing risk to aquatic life and the food webs that depend on it.

Stream flow has dropped to a bare 74 cubic feet per second — roughly one-fifth of the high-water baseline — as upstream operations push the water column into a narrower, more concentrated state. When flows contract like this in summer heat, dissolved contaminants don't dilute; they concentrate. Mercury, the heavy metal that accumulates through food webs and doesn't break down, climbs steadily into forage fish, then into the herons and eagles that hunt them.The wastewater treatment plant upstream exceeded its mercury permit limit for two consecutive quarters — 38 percent over in Q3, and 27 percent over in Q4 — during a season when the stream's own ability to dilute that load was already failing. Four waterways in this region are already listed as impaired, with total maximum daily loads set by the state. In a system this tight, even small exceedances have room to compound.

Out over the 64th Street Grassland, the barn swallows are working. Not perched, not resting — moving, continuously, in long arcing passes that drop low over the grass and wheel back up toward the tree line. Early summer is the most demanding period of the year for them, and the air here is full of what they need.Barn swallows are aerial insectivores, which means they catch everything they eat on the wing. They do not hover or wait. They fly through concentrations of insects and take them one at a time, bill snapping shut mid-air, and then they continue. A pair with nestlings will make several hundred feeding trips per day. The nest — a half-cup of mud and grass, fixed to a beam or rafter in a barn or outbuilding — holds four or five chicks that are growing fast and need protein in volume. Both adults feed them, and both adults spend the longest days of the year doing almost nothing else.What makes early summer the right moment for this is the insects. Aquatic insects are emerging from the standing water and slow streams near Geneva Township in numbers that peak right now. Mayflies crawl out of the water as winged adults after spending a year or more as aquatic larvae. Caddisflies do the same, rising from stream gravel and pond margins. Midges and other small flies emerge in masses from the surface, sometimes thick enough to be visible as a haze over the water at dusk. These are not random events. Each species has its own emergence window, triggered by water temperature and day length, and early summer stacks several of them at once. For the swallows, this is the richest stretch of the year.Barn swallows are built for this kind of foraging. The tail is long and deeply forked, which gives them fine control at speed — they can redirect quickly when an insect changes course, and they can fly efficiently for hours without tiring. The bill is short and wide, which opens into a broad gape, better for intercepting insects in flight than for picking them off a surface. When you watch one hunting low over a field, the flight path looks irregular, but it is tracking real things: a midge column, a rising caddisfly, a cluster of gnats near a wet depression in the grass. The swallow adjusts its line to what the air holds.The grassland itself matters here. Open ground with nearby water is the core of their habitat in this region. The 64th Street Grassland sits within a landscape that still has both. Bobolinks and savannah sparrows nest in the grass below, and killdeer move across the open patches at ground level, but the swallows occupy the airspace above all of it. They are not competing with those birds for food or space. They are using a different part of the same place.The nestlings grow quickly. Within about three weeks of hatching, they are close to adult size and beginning to fledge. The parents' workload through that period is relentless: catch an insect, return to the nest, deliver it, go out again. In the early morning and again in the evening, when insects fly closer to the surface and the air is cooler and denser, the swallows tend to fly lower and faster. If you are out at those hours, the passes can come very close.There is no real rest in this season for them. The chicks that survive to fledge will spend the rest of summer learning to hunt on their own, building the flight skills they will need before the whole population moves south in late summer. But that is weeks away. Right now, the adults are out, the insects are rising, and the air over the grassland is busy with both. Look up and watch one complete a pass — the long glide out, the quick bank, the return — and somewhere in that arc, it has eaten.

The air above the wetlands near Geneva Township carries a different energy in early summer. Close your eyes and listen for the sharp snap of beaks closing on invisible prey. Eastern kingbirds perch on the tallest dead snags, launching themselves into the air with sudden purpose before returning to the same branch. Their white-tipped tails flash against the green backdrop of breaking oak and maple leaves.These aerial hunters have timed their arrival precisely. Beneath the water's surface, mayfly and caddisfly larvae that have spent months or even years developing are now climbing toward the light. The water temperature has reached the threshold that triggers their final transformation. They emerge in waves, their delicate wings still soft as they struggle free from their larval cases. For a brief window, the air fills with insects that have never flown before, their flight patterns erratic and vulnerable.Eastern wood-pewees hunt from lower perches in the mid-canopy, their plaintive calls carrying through the humid air. Unlike the aggressive kingbirds above, pewees make shorter flights, picking off smaller midges and gnats with surgical precision. They return to the same perch repeatedly, their bills clicking shut on each capture. The two species divide the airspace between them, kingbirds claiming the open sky above the treeline while pewees work the shadowed spaces beneath. Both are feeding young now, their breeding cycles synchronized with this abundance. A single wood-pewee may catch three hundred insects in a day during peak emergence, carrying beakfuls of protein back to nestlings that demand food every twenty minutes from dawn to dusk.The emergence itself happens in pulses tied to water temperature and daylight hours. Caddisflies emerge at dusk, their tent-shaped wings catching the last light as they rise from the water in clouds. Mayflies often emerge at dawn, their brief adult lives measured in hours rather than days. Midges emerge throughout the day in smaller numbers, providing a steady food source between the larger hatches. The flycatchers read these patterns, positioning themselves where the insects will be thickest, their hunting territories overlapping with the emergence zones of different species. Listen for that sharp snap again, somewhere in the canopy above you, as another insect completes its ancient journey from water to air to waiting beak.