Ammonium release from a blanket peatland into headwater stream systems

► Headwaters draining eroded South Pennine (UK) peatlands are nitrogen saturated. ► Ammonium & nitrate leaching arises from aeration due to lower water tables. ► Nitrate deposition equals export during storms; ammonium export exceeds input. ► Ammonia input from high atmospheric loading & mineralisation of organic nitrogen. ► Downstream nitrogen trends indicate rapid transformation of ammonium into nitrate.