Controls on dissolved organic matter concentrations in soils and streams from a forested wetland and sloping bog in southeast Alaska

Abstract

AbstractUnderstanding the sources and removal mechanisms for dissolved organic matter (DOM) in soils is critical to determining the importance of peatlands in influencing streamwater DOM concentrations. Soil saturation and soil temperature are the primary factors that influence DOM cycling in soils, but the relationships among these factors vary by soil type and climate. Despite the extent of peatlands that occur within Pacific coastal temperate rainforest (CTR) watersheds, there is little information describing how DOM storage and export patterns are related to soil saturation and temperature in the region. We measured soil water tables, soil temperatures and redox potential and compared these measurements to fluctuations in dissolved organic carbon (DOC) and nitrogen (DON) concentrations in a forested wetland and sloping bog in southeast Alaska to address this key information gap. DOC concentrations ranged from 5 to 140 mg C l−1 in wetland soils, 11 to 46 mg C l−1 in streams, and varied greatly in response to changes in water table, redox potential and soil temperature. Similarly, DON concentrations ranged from 0·03 to 2·4 mg N l−1 in wetland soils, 0·2 to 0·6 mg N l−1 in streams and concentrations also reflected seasonal changes in physical measures. Depth to water table and soil temperature were significant factors related to the concentration of DOC in forested wetland soils and streams, while soil temperature was a significant factor that influenced stream DOC and DON concentrations. Comparing soil solution and stream DOM concentrations indicated that N is retained in bogs, while both dilution and biotic/abiotic retention mechanisms control DOM export in forested wetlands. The relationships among soil saturation, temperature and concentrations of DOC and DON provide preliminary models for estimating DOM fluxes from wetland soils in the CTR. Furthermore, these results can help calibrate regional watershed carbon flux models to predict the potential impacts of climate shifts and management activities on future wetland soil and stream DOM concentrations in CTR watersheds. Copyright © 2009 John Wiley & Sons, Ltd.