Soil Carbon and Nitrogen Dynamics in the Riparian Zones of Wyaralong Dam in Southeast Queensland, Australia

Abstract

Riparian zones are considered to be dynamic boundaries between terrestrial and aquatic systems, and are of primary importance in maintaining the vitality of landscapes and of surface water bodies. As an important part of the ecosystem, riparian zones are important for ecosystem functions and services, including biodiversity, water quality and recreation. However, riparian areas are often profoundly modified and degraded, with significant losses of ecological significance and functioning. The construction of dam is well known to change the local ecological patterns, especially by reducing the magnitude and frequency and changing duration of flood events. Soil moisture plays a key role in determining the vitality and activity of soil microorganisms by controlling water and oxygen availability in the soils, therefore affecting microbial mediated carbon (C) and nitrogen (N) transformations in the riparian areas. Net accumulation of soil organic matter (SOM) in submerged soils often occur compared with those in the aerobic soils, due to the decrease in SOM decomposition. Nitrogen turnover in riparian soils is especially sensitive to soil moisture regimes. Autotrophic nitrification mainly occurs under aerobic conditions; while ammonification and immobilization of ammonium (NH4 ) could happen under both aerobic and anaerobic conditions. Soil N could be lost as nitrous oxide (N2O) through nitrification under aerobic conditions, and through denitrification under anaerobic conditions. Rewetting dry soil always leads to a pulse of respiration and perhaps N mineralisation.