Integration of geochemical mass balance with sediment transport to calculate rates of soil chemical weathering and transport on hillslopes

An understanding of the processes that control the behavior of major elements with respect to weathering profile is essential to calculate the mobility, redistribution, and mass fluxes of elements. Hence, this study aims to determine the geochemical mass balance, strain, elemental correlation, and transport in weathering profiles. We constructed three weathering profiles for the black shale of Shujingtuo formation. As per the principal component analysis of major elements, density, and pH values, the first component represents the “elemental factor” and the second denotes the “external factor.” The “depletion” pattern is a mass transportation pattern, and Na, K, and Mg are depleted along transect relative to the composition of fresh rock. Fe is redeposited at the bottom half of the saprock zone, whereas Al is accumulated at the regolith zone. The Fe and Al patterns are attributed to the “depletion–addition” and “addition” patterns, respectively. The strain in profiles A and B demonstrates the expansion at the regolith zone and part of the saprock zone. In profile C, however, these zones collapsed at all depths. In chemical weathering, Na, K, Ca, Mg, and Si are depleted in the following order: valley (C) > near mountaintop (B) > ridge (A).

Download Full-text

Rock-Sourced Nitrogen in Semi-Arid, Shale-Derived California Soils

Frontiers in Forests and Global Change ◽

10.3389/ffgc.2021.672522 ◽

2021 ◽

Vol 4 ◽

Author(s):

Nina L. Bingham ◽

Eric W. Slessarev ◽

Peter M. Homyak ◽

Oliver A. Chadwick

Keyword(s):

Mass Balance ◽

Chemical Weathering ◽

Field Studies ◽

N Deposition ◽

Mixing Model ◽

N Fixation ◽

Atmospheric N Deposition ◽

Geochemical Mass Balance ◽

Semi Arid ◽

N Flux

Models suggest that rock-derived nitrogen (N) inputs are of global importance to ecosystem N budgets; however, field studies demonstrating the significance of rock N inputs are rare. We examined rock-derived N fluxes in soils derived from sedimentary rocks along a catena formed under a semi-arid climate. Our measurements demonstrate that there are distinct and traceable pools of N in the soil and bedrock and that the fraction of rock-derived N declines downslope along the catena. We used geochemical mass balance weathering flux measurements to estimate a rock-derived N flux of 0.145 to 0.896 kg ha–1 yr–1 at the ridgecrest. We also developed independent N flux estimates using a 15N-based isotope mixing model. While geochemical mass-balance-based estimates fell within the 95% confidence range derived from the isotope mixing model (−1.1 to 44.3 kg ha–1 yr–1), this range was large due to uncertainty in values for atmospheric 15N deposition. Along the catena, N isotopes suggest a diminishing effect of rock-derived N downslope. Overall, we found that despite relatively large N pools within the saprolite and bedrock, slow chemical weathering and landscape denudation limit the influence of rock-derived N, letting atmospheric N deposition (7.1 kg ha–1 yr–1) and N fixation (0.9–3.1 kg ha–1 yr–1) dominate N inputs to this grassland ecosystem.

Download Full-text

The influence of water–rock interactions on household well water in an area of high prevalence chronic kidney disease of unknown aetiology (CKDu)

npj Clean Water ◽

10.1038/s41545-020-00092-0 ◽

2021 ◽

Vol 4 (1) ◽

Author(s):

Liza K. McDonough ◽

Karina T. Meredith ◽

Chandima Nikagolla ◽

Richard B. Banati

Keyword(s):

Water Quality ◽

Chronic Kidney Disease ◽

Kidney Disease ◽

Water Chemistry ◽

Mass Balance ◽

Stable Carbon Isotopes ◽

Environmental Isotopes ◽

Well Water ◽

High Prevalence ◽

Geochemical Mass Balance

AbstractPoor drinking water quality in household wells is hypothesised as being a potential contributor to the high prevalence of chronic kidney disease of uncertain aetiology (CKDu) among the farming communities of the Medawachchiya area, Anuradhapura, Sri Lanka. One of the natural processes that can affect water quality is the dissolution of minerals contained within an aquifer by water–rock interactions (WRIs). Here we present a comprehensive assessment of WRIs and their influence on the water chemistry in household wells and spring waters in the Medawachchiya area by combining measurements of environmental isotopes, such as strontium, lithium and stable carbon isotopes and inorganic chemistry parameters, and modelling geochemical mass balance reactions between rainfall and groundwater samples. Our results reveal the presence of strontium, dissolved from both silicate and carbonate minerals, with high isotopic (87Sr/86Sr) ratios of up to 0.7316. Geochemical mass balance modelling and prior 87Sr/86Sr studies on the Wanni Complex bedrock suggest these strontium values may be the result of biotite dissolution. We also identify lithium and uranium contributed from the dissolution of silicates, albeit at concentrations too low to constitute a known health risk. In contrast, the levels of magnesium and calcium in our samples are high and demonstrate that, despite the felsic bedrock, well water chemistry in the Medawachchiya area is dominated by carbonate dissolution.

Download Full-text

Mass balance controls on sediment scour and bedrock erosion in waterfall plunge pools

Geology ◽

10.1130/g48881.1 ◽

2021 ◽

Author(s):

Joel S. Scheingross ◽

Michael P. Lamb

Keyword(s):

Sediment Transport ◽

Mass Balance ◽

River Discharge ◽

Sediment Load ◽

Sediment Flux ◽

Habitat Availability ◽

Flux Divergence ◽

Plunge Pool ◽

Bedrock Erosion ◽

Recurrence Intervals

Waterfall plunge pools experience cycles of sediment aggradation and scour that modulate bedrock erosion, habitat availability, and hazard potential. We calculate sediment flux divergence to evaluate the conditions under which pools deposit and scour sediment by comparing the sediment transport capacities of waterfall plunge pools (Qsc_pool) and their adjacent river reaches (Qsc_river). Results show that pools fill with sediment at low river discharge because the waterfall jet is not strong enough to transport the supplied sediment load out of the pool. As discharge increases, the waterfall jet strengthens, allowing pools to transport sediment at greater rates than in adjacent river reaches. This causes sediment scour from pools and bar building at the downstream pool boundary. While pools may be partially emptied of sediment at modest discharge, floods with recurrence intervals >10 yr are typically required for pools to scour to bedrock. These results allow new constraints on paleodischarge estimates made from sediment deposited in plunge pool bars and suggest that bedrock erosion at waterfalls with plunge pools occurs during larger floods than in river reaches lacking waterfalls.

Download Full-text

Quantifying weathering on variable rocks, an extension of geochemical mass balance: Critical zone and landscape evolution

Earth Surface Processes and Landforms ◽

10.1002/esp.4212 ◽

2017 ◽

Vol 42 (14) ◽

pp. 2457-2468 ◽

Cited By ~ 4

Author(s):

Beth A. Fisher ◽

Aaron K. Rendahl ◽

Anthony K. Aufdenkampe ◽

Kyungsoo Yoo

Keyword(s):

Mass Balance ◽

Landscape Evolution ◽

Critical Zone ◽

Geochemical Mass Balance

Download Full-text

Quantification of Chemical Weathering and Mass Balance of Soils Developed on Two Different Catena Derived from Granite and Gneiss in Denizli, Turkey

Asian Journal of Chemistry ◽

10.14233/ajchem.2014.16890 ◽

2014 ◽

Vol 26 (9) ◽

pp. 2789-2796

Author(s):

H. Senol ◽

H.H. Ozaytekin ◽

M. Akgul

Keyword(s):

Mass Balance ◽

Chemical Weathering

Download Full-text

The ratio of mechanical to chemical denudation in alluvial systems, derived from geochemical mass balance

Transactions of the Royal Society of Edinburgh Earth Sciences ◽

10.1017/s0263593300005939 ◽

1993 ◽

Vol 84 (1) ◽

pp. 73-78 ◽

Cited By ~ 6

Author(s):

A. D. Stewart

Keyword(s):

Mass Balance ◽

Chemical Weathering ◽

Amazon Basin ◽

Source Area ◽

Large River ◽

Suspended Load ◽

Bed Load ◽

Load Transport ◽

Bed Load Transport ◽

Dissolved Load

ABSTRACTMass balance equations are derived which link the ratios Ts/ (suspended load/dissolved load from chemical weathering) and Tb/Ts (bed load/suspended load), with any two geochemical components present in the source rock and the alluvial system. If the dissolved load is unknown the ratios can be estimated from the relatively insoluble silica and alumina. The ratio Ts/, which for large river basins depends on climate and relief, can thus potentially be determined from ancient alluvial sequences.The equations help define the source composition of a group of 13 modern rivers for which Ts, and alluvial geochemistry are known. These rivers together drain 27% of the continental surface. For a source area with the average continental sandstone to shale ratio of 0·6 the observed average value of Ts/ is obtained when limestone, sandstone and shale are present in the proportions 6·7:21·6:35·7. The figure of 64% sediment in the source area is very similar to the 66% determined by Blatt and Jones (1975) from geological maps of the continents. The equations also show that average bed load transport rate into these 13 basins is about 27% of total transport, and into the Amazon basin about 37%. Bed load transport rates out of the basins, into the sea, are relatively very small.

Download Full-text