Ms. Koch will leave her post on March 1, at which point Mr. Reichelt, 37, will take over her responsibilities.
“When two people don’t harmonize professionally, it can be temporarily compensated by compromise,” Ms. Koch wrote in an email to her colleagues, which was then leaked to German news organizations. “2017 was shaped by this until my willingness to compromise reached its limits.”
The change comes with Bild grappling with sharply declining readership, a trend seen to a degree across the German newspaper industry. In its heyday in the 1980s, Bild had a daily print circulation of over 5.5 million. But that number fell to 1.46 million in the last three months of 2017, according to figures compiled by an industry group. That is in itself a 10 percent drop compared with the same period a year ago.
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The publication, and the wider industry, had also sought to improve the gender balance of newsrooms in recent years.
Pro-Quote, an industry group led by journalists, had set the goal of getting women to hold 30 percent of the top editorial positions at German media organizations by 2017. In the end, only three major papers were recognized as having achieved that goal — one of which was Bild.
But Ms. Koch’s departure casts a shadow on that effort. She is the second female leader to leave the publication in less than a year: In September, Donata Hopfen, the head of the paper’s publishing arm, left the company.
“For this post at the rough and tumble Bild, the boss has to be loud and tough — whether woman or man, they have to be very tough,” said Ulrike Simon, a media critic at Spiegel Daily.
Bild is the flagship of nearly a dozen titles in the Bild family owned by Axel Springer . The parent company was celebrated when it promoted Ms. Koch and several of her female colleagues to leadership positions in 2015. After her announcement on Friday, Axel Springer made a point to pay her tribute.
“With great passion and competence, Tanit Koch managed an unprecedented journalistic career at Axel Springer,” Mathias Döpfner, the chief executive of Axel Springer SE, said in a statement.