Water, soil and vegetation under the influence of high atmospheric nitrogen deposition in a cutover and rewetted raised bog in Northwest Germany

Abstract

Bogs located near agricultural areas often receive high atmospheric nitrogen (N) depositions, and this may result in an increased soil and water N pool and enhanced N supply for plants and microorganisms. The consequences are changes in plant species composition and diffuse emissions of N species from these bogs. However, research on the resilience of rewetted bogs to high atmospheric N inputs is still sparse. Our aim was to evaluate the influence of N depositions on a bog that was rewetted after peat extraction down to bare ‘black’ (highly decomposed) bog peat. We monitored dry (NH3) and wet (NH4+ and NO3-) deposition, and plant available N as NH4+ and NO3- in soil and water, over the course of one year. The amount of N stored in vegetation was also quantified. We detected a total N deposition of 32 kg ha-1 y-1 which by far exceeded the critical load (5–10 kg ha-1 y-1) for bogs, but there were no signs of deposition induced N increase in soil and bog water. Our findings suggest, rather, that levels of plant available N were crucially affected by mineralisation in areas with lower water table. Depending on the sampling station, the amount of N stored in the vegetation was 23 or 30 kg ha-1. Although it was likely that uptake by vegetation played a decisive role in buffering the high N depositions, it did not completely explain the whereabouts of excess N. Accordingly, other processes like peat growth, N removal by mowing or denitrification must have contributed to buffering N levels in soil and water.

Keywords

• leegmoor
• mineralisation
• nitrogen content
• nitrogen load
• nutrient relocation
• restoration