Use of geochemical mass balance modelling to evaluate the role of weathering in determining stream chemistry in five mid-atlantic watersheds on different lithologies

Abstract

The importance of mineral weathering was assessed and compared for ®ve mid-Atlantic watersheds receiving similar atmospheric inputs but underlain by diering bedrock. Annual solute mass balances and volume-weighted mean solute concentrations were calculated for each watershed for each year of record. In addition, primary and secondary mineralogy were determined for each of the watersheds through analysis of soil samples and thin sections using petrographic, scanning electron microscope, electron microprobe and X-ray diraction techniques. Mineralogical data were also compiled from the literature. These data were input to NETPATH, a geochemical program that calculates the masses of minerals that react with precipitation to produce stream water chemistry. The feasibilities of the weathering scenarios calculated by NETPATH were evaluated based on relative abundances and reactivities of minerals in the watershed. In watersheds underlain by reactive bedrocks, weathering reactions explained the stream base cation loading. In the acid-sensitive watersheds on unreactive bedrock, calculated weathering scenarios were not consistent with the abundance of reactive minerals in the underlying bedrock, and alternative sources of base cations are discussed.

Effects of Protective Limestone Treatment on Water Chemistry and Fisheries Management in Laurel Bed Lake, Virginia

“…The watershed geology was found to consist of low solubility siliciclastic rock resistant to weathering. The lack of carbonate-bearing minerals in the watershed produced stream water with little increase in pH and solutes over the precipitation chemistry, a finding consistent with stream discharge from similar geology observed in other 1987) and Laurel Bed Creek (1996-2002), Laurel Bed Lake pre-liming (1996-1997), post-liming (1998-2002 1.6 ± 0.5 21.8 ± 5.7 25.8 ± 7.4 87.4 ± 32.7 93.6 ± 10.9 Na + 2.6 ± 0.8 9.4 ± 3.2 10.5 ± 4.0 9.0 ± 4.6 8.7 ± 2.2 K + 1.4 ± 0.8 9.4 ± 5.3 10.4 ± 2.7 6.7 ± 1.9 6.6 ± 1.2 H …”

“…studies (Glass et al 1982, Bricker 1986, Bricker and Rice 1989, Bricker and Rice 1993, O'Brien et al 1997. Thus the stream water showed an absence of buffering capacity, was perpetually acidic as it entered the lake and, thus, created a lake pool that was also acidic.…”

Mass‐balance modeling of mineral weathering rates and CO2 consumption in the forested, metabasaltic Hauver Branch watershed, Catoctin Mountain, Maryland, USA

“…() and O'Brien et al . (), we do not believe that epidote is involved in weathering at Hauver Branch based on two lines of evidence. First, epidote is ubiquitous in stream sediment collected at the stream outlet.…”

Predicting radioactive accessory mineral dissolution during chemical weathering: The radiation dose at the solubility threshold for epidote-group detrital grains from the Yangtze River delta, China

“…The persistence of epidote, a common constituent of the heavy mineral fraction of clastic sediments (e.g., Poppe et al, 1995;Uddin and Lundberg, 1998;Schneiderman and Chen, 2007), has been compared to that of quartz (Allen and Hajek, 1995) and zircon (Lång, 2000). In contrast, rapid dissolution of epidote has been invoked in modeling studies of mineral weathering and solute production (e.g., Sverdrup and Warfvinge, 1995;O'Brien et al, 1997;Oliva et al, 2004;Boyle, 2007). Braun and Pagel (1994) found epidote to be destroyed within the first stages of syenite weathering in southwest Cameroon.…”