Water source utilization under differing surface flow regimes in the riparian species Liquidambar styraciflua, in the southern Appalachian foothills, USA

Abstract

Studies across the United States and globally have revealed that mature riparian trees often utilize little streamwater, relying on soil moisture and groundwater instead. Contrastingly, riparian plants growing in wetland systems in the southeastern US use greater proportions of swamp water. The purpose of the present study was to determine if plant water uptake was linked to surface flow regime of the riparian system, characterized by stream flow and standing pond water nearby. Water sources of Liquidambar styraciflua growing along Whetstone Creek, a perennial stream in Stoneville, NC, were determined and compared to those of individuals growing along adjacent spring-fed ponds by analyzing stable isotopic compositions of plant water. Plant water status and environmental variables were also monitored due to possible influences on the specific water sources accessed. It was expected that pondside individuals, due to the lower flow rate and increased pond water availability, would utilize a greater amount of surface water than groundwater, which is shallow at the site, compared to streamside trees. However, trees at both sites appeared to rely about equally on shallow soil and surface water, while groundwater contributed only a minor proportion to trees at both sites. There were no meaningful relationships between the water sources measured and environmental factors, and plant water status was consistently high for trees at both sites. The current study is one of the first to demonstrate quantitatively a strong reliance on surface water by mature riparian trees in the southeastern US.