How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)

Sullivan, Pamela L.; Stops, Marven W.; Macpherson, G.L.; Li, L.; Hirmas, Daniel R.; Dodds, Walter K.

doi:10.1016/j.chemgeo.2018.12.002

Cited by 43 publications

(41 citation statements)

References 72 publications

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“…In contrast, Upper Hafren in Plynlimon has abundant SOC and DOC in upland peats, where organic‐rich water only connects to the stream during high discharge conditions when the water tables rises sufficiently (Herndon et al, ), which aligns well with the analysis here. Similarly, Sullivan et al () found that stronger landscape heterogeneity in headwater catchments shows a greater degree of chemodynamic behavior for most geogenic species than downstream watersheds.…”

Section: Discussionmentioning

confidence: 90%

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Zhi

Wang

et al. 2019

Water Resources Research

130

166

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Understanding concentration‐discharge (C‐Q) relationships are essential for predicting chemical weathering and biogeochemical cycling under changing climate and anthropogenic conditions. Contrasting C‐Q relationships have been observed widely, yet a mechanistic framework that can interpret diverse patterns remains elusive. This work hypothesizes that seemingly disparate C‐Q patterns are driven by switching dominance of end‐member source waters and their chemical contrasts arising from subsurface biogeochemical heterogeneity. We use data from Coal Creek, a high‐elevation mountainous catchment in Colorado, and a recently developed watershed reactive transport model (BioRT‐Flux‐PIHM). Sensitivity analysis and Monte‐Carlo simulations (500 cases) show that reaction kinetics and thermodynamics and distribution of source materials across depths govern the chemistry gradients of shallow soil water and deeper groundwater entering the stream. The alternating dominance of organic‐poor yet geo‐solute‐rich groundwater under dry conditions and organic‐rich yet geo‐solute‐poor soil water during spring melt leads to the flushing pattern of dissolved organic carbon and the dilution pattern of geogenic solutes (e.g., Na, Ca, and Mg). In addition, the extent of concentration contrasts regulates the power law slopes (b) of C‐Q patterns via a general equation b=δb0.25emCratioCratio,1/2+Cratio+bmin. At low ratios of soil water versus groundwater concentrations (Cratio = Csw/Cgw < 0.6), dilution occurs; at high ratios (Cratio > 1.8), flushing arises; chemostasis occurs in between. This equation quantitatively interprets b values of 11 solutes (dissolved organic carbon, dissolved P, NO3−, K, Si, Ca, Mg, Na, Al, Mn, and Fe) from three catchments (Coal Creek, Shale Hills, and Plynlimon) of differing climate, geologic, and land cover conditions. This indicates potentially broad regulation of subsurface biogeochemical heterogeneity in determining C‐Q patterns and wide applications of this equation in quantifying b values, which can have broad implications for predicting chemical weathering and biogeochemical transformation at the watershed scale.

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Section: Discussionmentioning

confidence: 90%

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Zhi

Wang

et al. 2019

Water Resources Research

130

166

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“…Critical zone processes involving belowground CO2, which equilibrates with groundwater and reacts with soil and rock, are fundamental to understanding water-rock reactions and landscape evolution. Although seasonal variations in belowground CO2 are expected in temperate climates because of seasonal changes in temperature, precipitation, and vegetation, we present here a 26.5-year trend of increasing belowground CO2, manifested by increasing titration alkalinity along with calcium and magnesium [1,2], in a temperate-climate, mid-continent, mesic, tallgrass prairie, the Konza Biological Station, a Prairie Long-Term Ecological Research and NEON Site (Konza). Konza occupies 35 km 2 with relief of ~70 m and is divided into 60 watersheds with different controlled-burn frequencies (annual, 2-, 4-, 10-, & 20-yr) and grazer pressure (bison, cattle, none).…”

Section: Introductionmentioning

confidence: 74%

Increasing groundwater CO₂ in a mid-continent tallgrass prairie: Controlling factors

et al. 2019

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Alkalinity and groundwater CO2 have increased linearly from 1991–2017 at the Konza Prairie Biological Station (KPBS), a tallgrass prairie research site in northeastern Kansas. The projected increase in groundwater alkalinity (as HCO3-) and CO2 based on an earlier trend was confirmed in 2016, with predictions nearly equal to recent values (e.g., 408 ppm vs 410 ppm as HCO3-, respectively). Both the water balance and groundwater CO2 trends within the study watershed could be impacted by long-term changes in land use and climate: 1) encroachment of woody vegetation (1983–2012) as a result of the 4-year fire return interval, 2) re-introduction of bison (phased in, 1994–2006), 3) increases in air temperature, and 4) changes in precipitation patterns. If only linear processes are driving the observed water chemistry changes, then the linear increase in air temperature (1983–2017) that stimulates soil respiration may be the most likely factor enhancing groundwater HCO3- and CO2, as air temperature has risen ~1 to 1.4°C over 34 years. If groundwater chemistry is driven by more threshold behaviour, woody encroachment, which was linear but in three distinct phases, may drive groundwater chemistry. The ~2 to 3‰ decrease in the discontinuous δ13C data in the groundwater-dominated stream suggests enhanced inputs of microbially-respired labile carbon, CO2 sourced from C3 (woody vegetation), or a combination of the two.

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“…In other words, deeper roots in forests can lead to branching, or partitioning of water more to the depth, which can pump CO 2 -rich water to deeper zones and enhance the contact between CO 2 and primary minerals at depth. As an example, woody encroachment into grassland and associated rooting differences have been attributed to elevated chemical weathering fluxes in carbonate terrains (Sullivan et al 2018). Much remains to be learned about feedbacks among weathering, transport, and biologically-mediated processes with realistic subsurface structures.…”

Section: Drivers Of Chemical Weathering In Natural Systemsmentioning

confidence: 99%

“…A big puzzle in this area is the contrasting CQ relationships that have been observed for different solutes: similar CQ patterns have been observed for different solutes; contrasting CQ relationships have been observed for the same solute in different watersheds (Herndon et al 2015;Musolff et al 2017;Abbott et al 2018;Zarnetske et al 2018). Geogenic species (e.g., Na, Mg, Si) derived from chemical weathering have commonly demonstrated chemostasis (Godsey et al 2009;Sullivan et al 2018). Flushing behaviors are most commonly observed for DOC (Boyer et al 1997;Zarnetske et al 2018).…”

Section: Watershed Response To Hydrological Changes: Concentration DImentioning

confidence: 99%

Watershed Reactive Transport

2019

Reviews in Mineralogy and Geochemistry

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A watershed (also drainage basin, river basin, or catchment) is defined as "… the area that topographically appears to contribute all the water that passes through a specified cross section of a stream (the outlet)" (Dingman 2015). In this chapter, I choose to use the term "watershed" as it is a broadly used one; it should be understood more as small watersheds or catchments. Watersheds are the fundamental units that support river networks, the blood vessels at Earth's surface ultimately draining into the ocean. Watersheds are complex hydro-biogeochemical reactors. They receive water, mass, and energy, transport them to distinct compartments, and transform them into various forms (Fig.1). Hydrological processes partition precipitation to the atmosphere, to the ground surface, and to the subsurface, eventually entering streams. Similarly, plants translate sunlight, water, CO 2 , and nutrients into organic matters (leaves, stems, roots) that fall and deposit in soil. As water routes through soils, it interacts with roots, microbes, and reactive gases (i.e., CO 2 and O 2), releases solutes, and ultimately transporting them out of watersheds. The water flow (discharge) and solute concentrations measured at stream outlets therefore reflect convoluted signature of ecohydrological and biogeochemical coupling. The process interactions and feedbacks are dictated not only by hydroclimatic forcing but also the architecture of watersheds, in particular the above-ground characteristics such as land cover and surface topography, as well as the below-ground structure including soil depth, soil type, geology, and root architecture. The external forcing and internal idiosyncrasies dictate the magnitude, timing, and spatial distribution of water flow and chemistry (Chorover et al. 2011; Brooks et al. 2015), giving rise to non-linear emergent behaviors that are unique of watershed reactive transport processes. Understanding feedbacks and non-linearity requires process-based models that integrate multiple interacting processes. Such integration however does not come easily with traditional boundaries of hydrology versus biogeochemistry relevant disciplines. As will be discussed later in this chapter, relevant model development has been advancing along two separate lines: hydrology models that solve for water storage and fluxes at the watershed scale and beyond (Fatichi et al. 2016), and reactive transport models (RTMs) that center on aqueous and solid concentration changes arising from transport and multi-component biogeochemical reactions typically in "closed" groundwater systems without much interactions with "open" watersheds directly receiving precipitation and sun light (Steefel et al. 2015; Li et al. 2017b). This comes along with a history of hydrologists often trained as physicists studying fluid mechanics, and biogeochemists typically grow up as geologists, chemists, or environmental engineers. There are however considerable needs to reach beyond disciplinary boundaries and integrate the two lines to develop watershed reacti...

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How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)

Cited by 43 publications

References 72 publications

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Increasing groundwater CO₂ in a mid-continent tallgrass prairie: Controlling factors

Watershed Reactive Transport

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How landscape heterogeneity governs stream water concentration-discharge behavior in carbonate terrains (Konza Prairie, USA)

Cited by 43 publications

References 72 publications

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Distinct Source Water Chemistry Shapes Contrasting Concentration‐Discharge Patterns

Increasing groundwater CO2 in a mid-continent tallgrass prairie: Controlling factors

Watershed Reactive Transport

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Increasing groundwater CO₂ in a mid-continent tallgrass prairie: Controlling factors