The little marsh was an ecosystem of reeds, dragonflies and argumentative frogs. (ecosystem: alternate name ecological system) By the northern summer solstice it was silent. (solstice: alternate name June solstice, midsummer) An outsider took the tranquility as proof of recovery. (tranquility: serenity, calm, peacefulness) The keeper had been there at the northern spring equinox and remembered the frogs. (equinox: alternate name March equinox, vernal equinox) To him the still water was ominous. (ominous: threatening, menacing, foreboding)
He resisted the temptation to attribute the silence to a single cause. (attribute: ascribe, impute, credit) An endogenous change inside the pond might account for it, or an alteration beyond the ditch might have choked off the flow. (endogenous: internal, internally generated, endogenic) An indigenous reed had spread, but its being native gave no assurance that it explained the missing frogs. (indigenous: native, autochthonous; assurance: promise, pledge, guarantee) One rare beetle was endemic to the valley. (endemic: native and restricted, locally confined) To extirpate its reed bed on a conjecture would be foolhardy. (extirpate: eradicate, uproot, eliminate; conjecture: guess, surmise, speculation; foolhardy: reckless, rash, imprudent)
The keeper found a shopping bag jammed in the sluice. Its removal let a thin thread of water run. He made an observation every evening for a month. (observation: inspection, check) A frog finally called from the far bank, then another answered. In the report he struck out the words "marsh restored." What he could affirm was that two frogs had broken the silence. (affirm: assert, declare, avow)