Bones to Ashes

Something about a duck…

And then I fell asleep.

Eight A.M. found me in my office at Wilfrid-Derome. It was to be a day of interruptions.

My phone was blinking like a railroad crossing signal. I reviewed the messages, but returned only one call. Frances Suskind, the marine biologist at McGill.

I’d completely forgotten about the diatom samples I’d taken from the teenaged girl found in Lac des Deux Montagnes. Ryan’s DOA number three.

Suskind answered on the first ring.

“Dr. Brennan. I was about to phone you again. My students and I are very excited about our findings.”

“You shared information with students?”

“Graduate level, of course. We found your challenge extraordinarily invigorating.”

Challenge? Invigorating?

“Are you acquainted with the field of limnology?”

“Diatoms have their own ology?” Intended as a joke. Suskind didn’t laugh.

“Diatoms are part of the class Bacillariophyceae of the Chrysophyta phylum of microscopic unicellular plants. Did you know that the members of this group are so numerous they represent the single most abundant oxygen source in our atmosphere?”

“I didn’t.”

I began doodling.

“Let me explain our procedure. First, we collected twelve samples from each of seven sites along the river and around Lac des Deux Montagnes, which is actually part of the river, of course, including L’Île-Bizard, near the point where the body was recovered. Those samples acted as our controls in examining diatom assemblages recovered from the victim. The ones we obtained from the specimens you provided. The bone plug and sock.”

“Uh-huh.” I drew a shell.

“At each site we collected from a variety of habitats. Riverbed. Riverbank. Lakeshore.”

I added spirals to the shell.

“Our control samples yielded ninety-eight different diatom species. The various assemblages are similar and share many species.”

I started a bird.

“The dominant ones include Navicula radiosa, Achnan—”

There are over ten thousand diatom species. Suspecting Suskind was launching into a full roll call, I interrupted. “Perhaps we could let that go until I have your written report.”

“Of course. Well, let me see. There are variations in the presence or absence of minor species, and changes in the proportions of the dominant species. That’s to be expected given the complexity of the microhabitats.”

I added tail feathers.

“Basically, the samples divide into three cluster zones. A midchannel habitat with a depth of over two meters, which experiences moderate water flow. A shallow water habitat of less than two meters, which experiences slow water flow. And a riverbank or lakeshore habitat, above water level.”

An eye. More plumage.

“Perhaps I should explain our statistical treatment. We do cluster analysis, to determine the clusters I just described.” Suskind made a honking sound, which I assumed to be laughter. “Of course. That’s why it’s called cluster analysis.”

I sketched a bill.

“To compare the control samples to the victim samples, we use a transfer function called modern analog technique. We calculate the dissimilarity between a victim sample and the most similar control sample, using the squared chord distance as the dissimilarity coefficient—”

“May we also leave quantitative analysis for the report?”

“Of course. The bottom line. We found that the diatom assemblages recovered from the sock show strong similarity to samples taken from the midlake channel and from the lakeshore.”

Webbed feet.

“Our analog matching technique suggests that the closest lakeshore analogy is with a control sample collected at the bottom of a boat ramp situated in the Bois-de-L’Île-Bizard nature preserve, not far from the body recovery site.”

My pen froze.

“You can pinpoint with that much precision?”

“Of course. What we do—”

“Where is this park?”

She told me. I wrote it down.

“What about the bone plug?”

“I’m afraid that’s a bit more complex.”

Suskind now had my full attention. “Go on.”

“The diatom flora from the bone’s outer surface is similar to that recovered from the sock. We recovered no diatoms from the marrow cavity.”

“Meaning?”

“Interpretation of negative evidence is always risky.”

“Suggest some scenarios.”

“Diatoms find their way into the body via inhalation, via ingestion, and via the aspiration of water. Whatever the initial pathway, assuming they are sufficiently tiny, the diatoms then circulate into the body’s organs and marrow. Diatoms are recovered from the bone marrow of approximately thirty percent of all drowning victims. They occur at significantly lower rates, perhaps as low as ten percent, in cases of bathtub or other city water drownings.”

“Because diatoms and other impurities are filtered out of domestic water,” I guessed.

“Of course. If present in domestic water, they’ve most likely come from household cleaners. But those are unique and recognizable species.”

“You found none.”

“We found nothing in the marrow cavity.”

“So it’s possible the victim may have drowned in treated or filtered water, not in the river?”