Limited influence of nutrient additions to the transformation of dissolved and particulate organic matter from a peatland headwater

Peatlands are typically rich in labile dissolved and particulate organic matter (DOM and POM) but poor in nutrients; as these peatland waters flow through a catchment they mix with more nutrient-rich but organic matter (OM) poor waters. These new sources of nutrients may lead to increased OM degradation, driving further release of CO2 to the atmosphere. The aim of this study was to discover if the addition of nutrients changed the rates of peat-derived dissolved and particulate organic carbon (DOC and POC) degradation, or if the additional nutrients were incorporated into the OM structure. The DOM and POM extracted from a peatland stream was characterised at the beginning of the experiment, and after 70-h and 10-days, from water with and without additional nutrients. Results showed adding nutrients to the water had no significant impact on the rate of degradation of DOC or POC over a 10 day period. There were significant differences in the N content and C:N ratios, as well as other composition variables, of the DOM in the treatments with additional nutrients showing that N was incorporated into the DOM structure, but that nutrient addition did not stimulate significant extra DOM or DOC loss. The N content of POM was not impacted, and isotope analysis, supported the conclusion that DOM turnover was occurring even if there was no net change in DOC concentration due to nutrient addition.