Upland Rootzone Soil Water Deficit Regulates Streamflow in a Catchment Dominated by North American Tallgrass Prairie

Andres Patrignani,Nathaniel Parker,Sofia Cominelli

doi:10.3390/w14050759

Abstract

Intermittent tallgrass prairie streams depend on surface runoff and are highly susceptible to hydrological disturbances such as droughts. The objective of this study was to investigate the timing of intermittent streamflow pulses and upstream rootzone soil water deficit in a watershed dominated by tallgrass prairie. The study was conducted from July to December 2021 in the Kings Creek watershed located within the Konza Prairie Biological station, Kansas, USA. Hourly precipitation and soil moisture observations in the 0–10, 10–30, and 30–50 cm depth were obtained from a hydrological network consisting of 16 monitoring stations across the Kings Creek watershed. Rootzone soil water storage (S) was computed at hourly time steps as the sum of the soil water storage of each soil layer. A drained upper limit (DUL) was estimated as the soil moisture remaining 24 h after the soil had been thoroughly wetted during large (~100 mm) rainfall events. A lower limit (LL) was estimated as the lowest rootzone soil water storage during the study period. Hourly soil water deficit (D) was computed as D = (DUL − S)/(DUL − LL). The study period had 19 precipitation events totaling 436 mm, and only 14 out of the 19 precipitation events exceeded a common canopy and litter interception threshold of 4 mm for tallgrass prairies in this region. Only two precipitation events resulted in measurable streamflow, and the inception of these two streamflow events was associated with a negative weighted soil water deficit (i.e., S > DUL). This pilot study revealed that upland rootzone soil water deficit plays a major role controlling the timing of streamflow in the Kings Creek watershed and possibly in other catchment areas with intermittent prairie streams.

Highlights

Native tallgrass prairies used to cover 70 million hectares across North America, but with nearly 95% of the original area lost to agriculture and urbanization, tallgrass prairies are one of the most endangered ecosystems in the continent [1]
The objective of this study was to investigate the timing of intermittent streamflow pulses and upstream rootzone soil water deficit in a watershed dominated by tallgrass prairie
Previous studies show that the selection of the minimum inter-event time (MIT) criteria affects the intra-event rainfall intermittency [15,16]; future studies could further investigate the role of intra-event rainfall intermittency and streamflow intermittency

Summary

Introduction

Native tallgrass prairies used to cover 70 million hectares across North America, but with nearly 95% of the original area lost to agriculture and urbanization, tallgrass prairies are one of the most endangered ecosystems in the continent [1]. The remaining tallgrass prairies in the U.S Great Plains provide essential ecosystem services and are characterized by intermittent streams with distinct periods of flooding and drying that control biogeochemical processes, downstream water quality, and ecological dynamics of biotic communities in the terrestrial–aquatic ecotone [2,3]. Given the complex hydrology and sensitivity of intermittent streams to hydrological disturbances, there is need to better understand the hydrologic drivers of streamflow to better manage and preserve tallgrass prairie ecosystems [4]. This is even more relevant in a climate change scenario, in which the U.S Southern Great Plains is projected to have less summer precipitation and drier soil moisture conditions by the end of the century [5–7]. Since the precipitation-runoff process is highly conditioned by the antecedent soil moisture conditions [9], the low runoff volume and the intermittent discharge observed in prairie streams of this region is likely associated to upstream soil moisture conditions

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