The concept of novel ecosystems was first proposed in 2006 and has attracted much attention due to the proliferation of new ecosystems resulting from environmental change. Over the past two decades, the novel ecosystem framework has been used to evaluate when ecosystems have reached a tipping point from merely a hybrid system to one that is unique from its previous state. We propose that this framework leaves out an important nuance, what we call de novo ecosystems – completely human-made ecosystems that mimic natural ecosystems in some way. A critical component of de novo ecosystems is that they do not exist prior to human interference – differentiating them from novel ecosystems – yet still allowing them to be subject to some of the same considerations as novel ecosystems. De novo aquatic ecosystems are becoming increasingly common globally, often as a result of resource extractive industries and for management of water in urban and agricultural environments; for example, the construction of mining ponds on land that was previously forested and the construction of stormwater retention ponds on land that was previously grassland. There is therefore a need to consider how these de novo ecosystems behave in comparison to natural and novel ecosystems. In this presentation, we argue for the consideration of de novo ecosystems as unique but important aspects of the landscape that are critically understudied, particularly in regard to biogeochemical processes. We begin by comparing the biogeochemical cycling of nutrients and contaminants in de novo aquatic ecosystems to constructed vs. naturally formed landscapes. We continue by examining how three prominent de novo aquatic ecosystems – abandoned mining ponds, stormwater retention ponds, and agricultural ponds – impact biogeochemical cycling of elements and the implications for ecological function. We conclude with future research directions into de novo ecosystems and how addressing these research gaps could better inform management efforts.