Mergelgrube bei Hannover, Protected nature reserve in Misburg, Germany.

Mergelgrube bei Hannover is a protected conservation area in Misburg with ponds and wetlands that formed from former limestone quarries. The site features reed beds and open water areas that create diverse habitats for birds and rare amphibians.

The over 100-year-old marl pit HPC I of the Hannoversche Portland-Cementfabrik was shut down about 50 years ago. Poplars that had grown in the meantime were removed, and paths, stairs and an observation box were built. On 8 July 2016 the pit was designated the nature reserve "Mergelgrube bei Hannover (HPC I)".

The former HPC I marl pit of the Hannoverschen Portland-Cementfabrik is now a nature reserve where visitors reach the pit floor by paths, stairs and an observation box. A pump keeps the pit from filling with water, so the ground shows flora and fauna once typical of the Seckbruch landscape northeast of Hannover, alongside coastal species drawn by the marl's raised salt content.

Access to the site is restricted to protect fragile habitats and ensure the safety of rare species. Visitors should stay on marked paths and respect the conservation areas.

The quarry's marl is salt-rich, so coastal plant species grow far inland here. Counts recorded 45 Red List plant species, including two absent from Lower Saxony since 1897. A pump keeps the floor dry, exposing the old Seckbruch flora.