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 javabased 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.

Reinventory of the vascular plants of Mormon Island Crane Meadows after forty years of restoration, invasion, and climate change

“…However, wetland plant communities and associated fauna can expand and contract spatially over subsequent wet and dry cycles, and several species may be present under only certain hydrological conditions ( Currier 1984 , 1989 ; Currier and Henszey 1996 ; Henszey et al., 2004 , Davis et al., 2006 ). Precipitation and river discharge patterns have a substantial impact on subirrigated lowland tallgrass prairie and wet meadow ecosystems ( Wesche et al., 1994 ; Davis et al., 2006 ; Brinley Buckley et al., 2021a ). Our finding that Mormon Island was wetter per the vegetation WIS score from 2015-2020 than from 1980-1981 was likely reflective of the relatively wet hydrological conditions present during a significant portion of our study.…”

“…Species richness and floristic quality increased while the mean wetland indicator score decreased (i.e., currently more mesic) since the initial inventory of Mormon Island, which are positive indicators of ecosystem and vegetation community health ( Henszey et al., 2004 ; Davis et al., 2006 ; Brinley Buckley et al., 2021a ). These results likely reflect recent efforts to maintain spring base flows in the Platte River for Whooping Cranes and other species of concern, in addition to wetter than average conditions throughout the study period ( NRC 2005 ).…”

“…The river valley includes a sizeable hyporheic zone and relatively shallow soils, generally ranging from fine sand to loam with varying degrees of organic matter, present atop a deep layer of coarse alluvium ( Chen et al., 2007 ; Dillion et al., 2016 ; USDA 2004 , 2009 ; 2021b ). The river valley as a whole represents a highly connected hydrological system where groundwater elevation and wetland inundation are largely tied to fluctuations in river discharge ( Wesche et al., 1994 ; Chen et al., 2007 ; Brinley Buckley et al., 2021a ). There is also extensive riparian woodland bordering the Platte River, particularly in former and now dry channel beds ( Williams 1978 ; Currier, 1982 ; Johnson 1997 ; Caven et al., 2019b ).…”

“…Riparian prairie and embedded wetlands in the Central Platte River Valley (CPRV) of Nebraska have largely been protected and restored because they represent important habitat components for migratory Whooping Cranes ( Grus americana ) regionally ( USFWS 1978 ; USFWS 1981 ; Currier et al., 1985 , Baasch et al., 2019 ). However, this biologically important and unique ecosystem, with its distinctive hydrology, hosts significant plant diversity on which a variety of wildlife depends ( Nagel and Kolstad 1987 ; Currier 1989 ; Currier and Henszey 1996 ; Henszey et al., 2004 ; Rolfsmeier and Steinauer 2010 ; Kaul et al., 2012 ; Brown and Johnsgard 2013 ; Caven et al., 2017 ; Brinley Buckley et al., 2021a ; 2021b ). Nagel and Kolstad (1987) documented the vascular plant communities of two remnant conservation proprieties in the CPRV in the early 1980s (1980–1981), the Crane Trust (i.e., Mormon Island Crane Meadows) and Audubon's Rowe Sanctuary, but little long-term vegetation research has been published from this region in recent decades ( Johnson 1997 ; Henszey et al., 2004 ).…”