Elsevier

Journal of Hydrology

Volume 588, September 2020, 125021
Journal of Hydrology

Research papers
Comparative analysis of water budgets across the U.S. long-term agroecosystem research network

https://doi.org/10.1016/j.jhydrol.2020.125021Get rights and content

Highlights

  • We developed water budgets for 18 Long-Term Agroecosystem Research sites.

  • We estimated uncertainty of all the water budget components.

  • The average water budget uncertainty was 25% of precipitation.

  • Uncertainties were greatest for percolation and evapotranspiration.

  • LTAR sites span a 0.4 – 1.1 evaporative fraction and a 0.8 – 4.8 aridity index.

Abstract

Understanding the movement and storage of water within agricultural landscapes as functions of management and climate is essential for more efficient and sustainable water use. However, knowledge of water storage and fluxes on U.S. agricultural lands is largely incomplete. The Long-Term Agroecosystem Research (LTAR) network provides a unique and geographically diverse set of agricultural study sites in the United States. The objectives of this study were to: 1) characterize the hydrologic variability across the LTAR network; 2) identify data gaps in the water budgets across the LTAR network; and 3) identify opportunities to leverage the LTAR network to improve understanding of water budgets across agricultural landscapes. For each of the 18 LTAR sites, we developed water budgets on an average annual basis. Uncertainty propagation methods combined individual component uncertainties to calculate an overall water budget uncertainty. Datasets length ranged from three to 50 years. The network covers a range of precipitation from 240 to 1400 mm yr−1, evapotranspiration from 228 to 1080 mm yr−1, and surface runoff and subsurface flow from negligible to 560 mm yr−1. However, uncertainties of where all the water is going remained high, in part because soil water storage and downward movement of water were often neglected or measured for very short periods, resulting in average water budget uncertainty of 25% of the water inputs. More accurate measurement of the major inputs and outputs, and direct measurement of water content and percolation are key to understanding how agricultural lands affect terrestrial water budgets.

Introduction

Intensification of agriculture can affect water availability by increasing land under crop and forage production (Raymond et al., 2008, Schilling et al., 2008, Tomer and Schilling, 2009) or by increasing land productivity (Zeri et al., 2013). Simultaneously, climatic changes in temperature and precipitation can alter available water resources in several ways by: 1) increasing the rate and timing of evapotranspiration through elevated temperatures (Flerchinger et al., 2019, Kingston et al., 2009) and changes in crop planting times (Gautam et al., 2018), 2) altering the amount, timing, and form of seasonal or annual precipitation (i.e., rain or snow [US Global Change Research Program, 2017]), and 3) altering precipitation intensity, which could lead to greater runoff and reduced percolation (Gautam et al., 2018, Groisman et al., 2001).

Key to the adaptation of agriculture across varying climates is the management of water, the natural availability of which ranges from deficit to excess for crops and rangelands. In water-limited environments, agriculture competes with other water users. Conversely, water-replete environments may be challenging because of poorly drained soils. Extreme precipitation events are challenging everywhere because of erosion and loss of water to runoff. Agricultural activities can affect the availability and quality of surface and ground waters, making careful management a fundamental requirement for sustainability.

Conflicts arising from agricultural water management such as water availability for municipal, industrial, or recreational uses (e.g., water shortages in Brazil in 2017, South Africa in 2018, and in India in 2019), and contamination of water bodies from agricultural pollution are becoming more frequent and threaten the well-being of future generations and the environment (United Nations Convention to Combat Desertification, 2017). In the United States, recent droughts (e.g., 2016 in Georgia or 2011–2017 in California) and floods (2008 in Iowa, 2011 and 2019 along the Mississippi and Missouri Rivers) have significantly impacted agricultural production, as well as water quality of receiving water bodies. Understanding the balance between precipitation, evapotranspiration, runoff, and groundwater recharge is critical to evaluating local, regional and global water resources (Healy et al., 2007).

A balanced water budget accounts for all of the major water inputs and outputs over an annual cycle in a defined area. Water budgets depend on topography, climate, soils, land use, and land management. In small catchments, a water budget provides an overview of the fate of water inputs. Evapotranspiration is commonly the main output, with the remaining balance going to groundwater recharge or streamflow generation. Water budgets describe the water pathways through the farm and rangeland management systems. Accurate water budgets for small catchments can also inform integrated land and water management in larger catchments and contribute to the analysis of potential trade-offs between water allocations for agriculture and other uses. Understanding how each budget component may shift as a function of management informs the optimal use of available water resources under varying climate, land use, and agricultural production. Optimization of water resources at the watershed or regional scale may in turn result in specific recommendations for the management of agricultural land in those regions.

Our current knowledge of water fluxes across agricultural landscapes in the United States is largely incomplete. For areas the size of a field, studies in agroecosystems focus on individual components of the water budget, often overland or subsurface runoff, or evapotranspiration (e.g., Bosch et al., 2012, Buckley et al., 2010). For large watersheds, water budget estimates are often based on models, which are calibrated with streamflow data measured at the outlet of the watershed (Afinowicz et al., 2005, Green et al., 2006, Schilling et al., 2008), or not calibrated if the modeling objective is to understand the primary hydrologic processes (Abatzoglou and Ficklin, 2017, Gobin et al., 2017). Regional research networks provide an opportunity to benefit from long-term ecological and hydrologic process site studies across a gradient of climatic conditions, land use, and land management. For example, data from the U.S. Long-Term Ecological Research network as well as other North American networks have helped identify forest-type susceptibility to climate warming (Creed et al., 2014).

The Long-Term Agroecosystem Research (LTAR) network is a partnership of 18 long-term research sites maintained by the U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) and academic institutions (Spiegal et al., 2018, Walbridge and Shafer, 2011). The LTAR network was established in 2014 to provide information in support of research for improved sustainability and intensification of U.S. agriculture over the next 20 to 50 years (Kleinman et al., 2018). The LTAR network includes 18 experimental watersheds (11 USDA-ARS) and ranges where precipitation and other hydro-meteorological variables have been systematically measured and archived for decades.

The LTAR network offers an opportunity to estimate and compare water budget components across a gradient of agroecosystems and climatic conditions as a baseline from which to evaluate the impacts and sensitivity of management in a changing climate. These water budgets provide a mechanism to identify deficiencies in monitoring instrumentation, the availability of data for additional comparative studies, and the identification of aspirational goals for regional watershed management. These data also provide an opportunity to evaluate the uncertainty of water budget components for accurate cross-site and regional analysis.

The objectives of this study were to: 1) characterize the hydrologic variability across the LTAR network; 2) identify data gaps in the water budgets across the LTAR network; and 3) identify opportunities to leverage the LTAR network to improve understanding of water budgets across agricultural landscapes. Analyses were conducted for 13 small catchments (< 50 ha) and 13 large catchments (> 400 ha) distributed among the 18 LTAR site locations.

Section snippets

Study sites

A water budget assessment was conducted at 26 study areas across 18 LTAR sites (Fig. 1). Each LTAR site was responsible for selecting one or more representative study areas, determining a period for which data were available, and calculating the mean and standard deviation of annual values for each water budget component. The assessments cover a range of soil, land use (Supplemental Table S1), and climatological conditions (Supplemental Fig. S1). The 26 locations were divided based on the size

Water budgets across the LTAR network

The magnitudes and uncertainty of each water budget component are described for each catchment in Supplemental Tables S16 and S17 and are summarized in Fig. 3, Fig. 4 and Table 1, Table 2. The LTAR network covers a gradient of precipitation from 240 mm yr−1 at JER to 1400 mm yr−1 at LMRB. Precipitation was the component measured with the smallest relative uncertainty (5%-17%, Table 1, Table 2). However, it was also the largest component and the absolute uncertainties related to precipitation

Opportunities for reducing uncertainties

These results highlight opportunities to reduce measurement uncertainties and to improve closure of the water budgets. Longer datasets and concurrent measurements for all the components, which is one objective of the LTAR network, will produce more accurate annual mean values. However, greater measurement accuracy is achievable as well. We discuss here opportunities for reducing errors and setting achievable goals.

Given that precipitation is the largest component of the water budget, improving

Conclusions

Water budgets were developed using multi-annual data from small and large catchments at the 18 LTAR sites in the United States by estimating precipitation, evapotranspiration, surface outflows (surface and subsurface flow), percolation, and change in water storage. Hydrologic characterization of each catchment was performed using indicators such as evapotranspiration and surface outflow. A Budyko plot of all the sites illustrates the spectrum of network sites across gradients of water and

CRediT authorship contribution statement

Claire Baffaut: Conceptualization, Methodology, Formal analysis, Writing - original draft, Writing - review & editing. John M. Baker: Writing - original draft, Writing - review & editing. Joel A. Biederman: Writing - review & editing. David D. Bosch: Investigation, Data curation, Writing - review & editing. Erin S. Brooks: Writing - original draft, Writing - review & editing. Anthony R. Buda: Investigation, Data curation. Eleonora M. Demaria: Visualization, Data curation, Writing - review &

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This research was a contribution from the Long-Term Agroecosystem Research (LTAR) network. LTAR is supported by the United States Department of Agriculture.

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