Assessing the hydroregime of an archetypal riverine wet meadow in the central Great Plains using time-lapse imagery

Abstract

Wet meadows are a declining and increasingly degraded ecosystem type. They contribute numerous ecosystem services, including nutrient cycling, water storage, and filtration, and provision of wildlife habitat, particularly for wetland-dependent species such as the Whooping Crane (Grus americana). Conservation and restoration of wet meadows rely on understanding their hydrology but characterization of wet meadow hydroregimes is difficult given their hydrologic complexity, high variability, and distinct regional differences. To address this challenge, we used ground-based time-lapse imagery to assess inundation dynamics of an archetypal wet meadow over a six-year period in the Central Platte River Valley, Nebraska, USA. We analyzed over 6500 images from March 2011 to May 2017 in the open-source java-based image processing software ImageJ. We also obtained data on groundwater, streamflow, precipitation, and evapotranspiration. We assessed the relationship between wet meadow inundation and hydrologic variables using wavelet coherence to look at fluctuations across a time–frequency spectrum and used random forest to identify seasonally specific variables of importance. We found hydroperiod, the duration surface water ponded within the wet meadow, had a mean of 141 d, on average lasting from 10 December to 1 May, but varied annually. Inundation generally peaked in the early spring, on average 10 March, but demonstrated a bimodal distribution, peaking again in late spring during wetter years. While inundation responded rapidly to precipitation events, it was highly related to streamflow, while an elevated groundwater table was necessary for sustained inundation. Overall, our study provided a comprehensive hydrological characterization of a reference wet meadow and demonstrated the utility of time-lapse cameras for high-resolution monitoring and assessment of highly variable wetland systems. Considering the uncertainties surrounding land- and water-use changes, climate change, and the increasing demand for freshwater resources by growing human communities, understanding functional wet meadow hydroregimes and interrelated drivers is essential to inform wet meadow restoration, conservation, and management efforts.