# How Wastewater Addition Reshapes Peatland Vegetation via Linked Abiotic and Biotic Changes

## TL;DR

Adding wastewater to peatlands changes plant communities and increases biomass, risking a shift from carbon sink to carbon source.

## Contribution

The study reveals how domestic sewage input alters peatland vegetation through abiotic and biotic factors.

## Key findings

- Mixed water and domestic sewage promote rapid expansion of Poaceae plants.
- Domestic sewage increases plant diversity by influencing soil and plant nutrients.
- Reclaimed water has minimal impact on plant community structure and biomass.

## Abstract

This study aimed to investigate changes in peatland plant community structure, aboveground biomass, and key driving factors under simulated input conditions of reclaimed water, 50% tap water mixed with 50% domestic sewage (mixed water), and domestic sewage by conducting an experiment on sedge-dominated peatlands in the Changbai Mountains of Northeast China. The results indicated that the input of mixed water and domestic sewage promoted the rapid expansion of Poaceae plants. The input of domestic sewage at different treatment gradients increased plant diversity by influencing soil nutrients and aboveground plant nutrients. Moreover, soil nutrients, aboveground plant nutrients, and species diversity were the main factors driving the increase in aboveground biomass under the input of domestic sewage at different gradients. Additionally, reclaimed water input had little effect on the plant community structure and aboveground biomass. Therefore, the input of domestic sewage into peatlands alters the plant community structure by affecting abiotic and biological factors, promoting the transition of peatlands from Cyperaceae to Gramineae. This transition leads to an increase in aboveground plant biomass and increases the risk of peatlands shifting from a “carbon sink” to a “carbon source”. Reclaimed water holds great potential for water replenishment in peatlands.

Peatlands, as globally important carbon sinks, are highly sensitive to human disturbances. The direct discharge or use of domestic sewage with different treatment gradients as peatland replenishment water affects plant communities, but how the plant community structure and biomass change and what drives these changes remain unclear. This study simulated domestic sewage input to a sedge-dominated peatland in the Changbai Mountain region of Northeast China, explored changes in plant community structure and aboveground biomass and revealed the key factors influencing these plant characteristics. The results revealed the following: (1) Reclaimed water treatment (Z) had little effect on the plant community structure; treatments with 50% tap water and 50% domestic sewage (H) and domestic sewage (W) caused rapid expansion of Poaceae plants, with Echinochloa crus-galli (L.) P. Beauv. occupying dominance. (2) Domestic sewage input increases plant diversity, which is driven jointly by soil nutrients and aboveground plant nutrients. (3) The H and W treatments significantly altered aboveground biomass, which was positively correlated with soil nutrients, aboveground plant nutrients, and diversity, whereas the Z treatment had little effect. This research provides scientific support for the control of domestic sewage discharge and whether reclaimed water can be used for ecological water replenishment in peatlands. It holds significant practical value for the scientific management of peatlands, the maintenance of carbon sink functions, and the mitigation of climate change.