Assessing variation in below-ground organic matter dynamics in the Ramsar-declared Nylsvley wetland system, South Africa.

Abstract

Wetlands physical and biological processes are fundamental to the distribution and structuring of organic matter in sediments. This study investigated spatial and temporal changes in organic matter sources in sediments within the Nylsvley Wetland, South Africa across two seasons, five sites and three wetland zones and identified pertinent contributors to sediment organic matter. Results showed distributions were uneven throughout the wetlands, with the seasonal zone having slightly high sediment organic matter in the cool-dry season and the permanent zone had high sediment organic matter in the hot-wet season, whereas the temporary zone had low SOM concentrations. Significant differences in nutrient concentrations were observed across wetland zones and seasons for Phosphorous, Potassium, Calcium and Magnesium, with the seasonal zone tending to be the most nutrient-rich in the cool-dry season, and with permanent zone nutrient levels rising substantially in the hot-wet season. Sediment δ13C differed significantly among wetland zones, whereas δ15N was statistically similar. Autochthonous plants were the main sources of organic matter in sediments overall across sites and zones. This study’s findings help to better understand the distribution of organic matter in wetland ecosystems and the role wetland zones play in the seasonal provisioning of allochthonous inputs.