Water Movement and Connectivity in a Forested Glacial Drift Watershed

Abstract

Water movement through the landscape to streams provides a fundamental linkage between terrestrial and aquatic environments in headwater systems. Headwater streams, which are the smallest and most abundant streams, are critical components of drainage systems, connecting important terrestrial and aquatic biogeochemical cycles and influencing the nutrient dynamics of downstream ecosystems. Given the importance of water presence and movement as a driver of biogeochemical transformations and the transport of material from terrestrial to aquatic ecosystems, the primary goal of this research was to quantify the distribution across and movement of water and other elements through a forested watershed to a headwater stream and ultimately to an inland lake in the glacial drift landscape of northern Michigan, U.S.A. To investigate the temporal dynamics and spatial patterns of water across the watershed and in Honeysuckle Creek, stream discharge, shallow groundwater levels, soil moisture, and water chemistry were measured from 2015–2017. Along the stream, surface flow was seasonal in the main stem and perennial flow was spatially discontinuous for all but the lowest reaches. Spring snowmelt was the dominant hydrological event in the year with peak flows an order of magnitude larger than annual mean discharge. Topography and soil characteristics strongly influence water and dissolved matter movement through the landscape. Water presence across the watershed was highly variable with perennial soil saturation and shallow groundwater within 10 cm of the surface at the lowest landscape positions, low soil moisture and nonexistent groundwater in upland outwash ecosystems, and a mixture of these conditions in the heterogeneous till parent material ecosystems of middle landscape positions. Shallow groundwater was the primary source of water to the headwater stream throughout the year; originating from snowmelt in the spring and shifting to recent precipitation in summer and autumn seasons. The riparian areas and the outwash-lake plain wetland likely have a much stronger influence on stream chemistry and discharge than the upland landscape units, due to the perennial connections between shallow groundwater from these wetland areas and surface water.