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The Groundwater Geochemical System
Published in William J. Deutsch, Groundwater Geochemistry, 2020
Alkalinity is a measure of the total acid-neutralizing capacity of the water, and acidity is the base-neutralizing capacity of the water. Whereas buffering reactions tend to maintain a pH value at or near a specific value as an acid or base is added to the water, alkalinity and acidity represent the cumulative reactions that consume hydrogen as acid is added to the solution (alkalinity) or that release hydrogen as a base is added to the solution (acidity). Alkalinity is the acid-neutralizing capacity (ANC), and acidity is the base-neutralizing capacity (BNC) of the solution. The alkalinity of a solution is determined by titrating a water sample with an acid (commonly H2SO4) to an endpoint pH of about 4.5. The acidity of a solution is determined by titrating a water sample with a base (commonly NaOH) to an endpoint pH of about 8.3. The handbook of Standard Methods7 provides the procedures for alkalinity (method 2320) and acidity (method 2310) titrations.
Background and Approach
Published in Timothy J. Sullivan, Aquatic Effects of Acidic Deposition, 2019
Acid neutralizing capacity (ANC) is the principal variable used to quantify the acid-base status of surface waters. Acidic waters are defined here as those with ANC less than or equal to zero. Acidification is often quantified by decreases in ANC, and susceptibility of surface waters to acidic deposition impacts is often evaluated on the basis of ANC (Altshuller and Linthurst, 1984; Schindler, 1988). In regional investigations of acid-base status, ANC has been the principal classification variable (Omernik and Powers, 1982). Acid neutralizing capacity is widely used by simulation models that predict the response of ecosystems to changing atmospheric deposition (Christophersen et al., 1982; Goldstein et al., 1984; Cosby et al., 1985a, b; Lin and Schnoor, 1986). Historical changes in surface water quality have been evaluated using measured (titration) changes in ANC (cf., Smith et al, 1987; Driscoll and van Dreason, 1993; Newell, 1993) or estimated by inferring past and present pH and ANC from lake sediment diatom assemblages (Charles and Smol, 1988; Sullivan et al, 1990a; Davis et al., 1994).
A review on remediation technologies for nickel-contaminated soil
Published in Human and Ecological Risk Assessment: An International Journal, 2020
Xueyan Chen, Deepika Kumari, C J Cao, Grażyna Plaza, Varenyam Achal
Biochar is increasingly being recognized as a promising and effective material to immobilize heavy metals in soil. The major mechanism for the metals immobilization by biochar include physical adsorption, surface (co)precipitation, and surface or inner complexation with functional groups. In addition, the implementation of biochar in soil may increase soil pH, water-holding capacity, and soil fertility, reduce the mobility of plant-available pollutant, and promote the revegetation (Kelly et al. 2014). Biochar has an alkaline surface, which delays the time to reach a hazardous pH by altering the acid-neutralizing capacity (Houben et al. 2013). In addition, the surface functional groups of biochar, which have different biomasses, pyrolysis temperatures, and additives, play an essential role, as they can complex with metals. Therefore, it is necessary to apply a suitable biochar, which is determined on a case-by-case basis. There is a high electric charge on the biochar surface, and biochars can absorb metal cations and detoxify soils. Biochar with negative charges has ability to adsorb the cationic divalent metal ions tightly (Herath et al. 2015).
Assessing the ecological effects of hydromorphological pressures on European lakes
Published in Inland Waters, 2019
Sandra Poikane, Tamar Zohary, Marco Cantonati
When developing methods and pressure–response relationships, the pressure gradient must be described with appropriate pressure metrics (Hering et al. 2006). Eutrophication pressure metrics (nutrient, mainly total phosphorus, concentrations; Lyche-Solheim et al. 2013) and acidification (pH or acid neutralizing capacity) have surprising consensus (McFarland et al. 2010), but metrics describing HyMo pressures are surprisingly variable. The 11 different HyMo metrics used to describe HyMo alterations (Table 7) include 2 simple indices (“winter drawdown,” calculated as the difference between the highest and lowest water levels, and “shore alterations,” calculated as percentage of altered shore length of total shore length) and other more complex indices synthesizing a wide array of different pressure proxies, such as land use, number of in-lake pressures, description of shore structure, shore erosion, and water fluctuation regime.
Browning-related oxygen depletion in an oligotrophic lake
Published in Inland Waters, 2018
Lesley B. Knoll, Craig E. Williamson, Rachel M. Pilla, Taylor H. Leach, Jennifer A. Brentrup, Thomas J. Fisher
Here we examined the potential for an alternative pathway to oxygen depletion via long-term increases in terrestrial DOM in 2 undisturbed lakes in a region experiencing browning. We also explored mechanisms by which browning may influence dissolved oxygen trends. Specifically, we examined lake stability (Schmidt stability) and water transparency (1% photosynthetically active radiation [PAR] depth). We analyzed a long-term dataset (1988–2014) for 2 small lakes—an oligotrophic (“clearer”) lake and a mesotrophic–slightly dystrophic (“browner”) lake—located in protected watersheds. Both lakes have experienced significantly decreasing water transparency (i.e., 1% PAR depth) over the 27-year dataset and have shown trends of increasing DOC concentration, but because of the high interannual variability of DOC concentration in the browner lake, the trend is statistically significant only in the clearer lake (Williamson et al. 2015). The observed reductions in water clarity do not seem to be associated with an increase in phytoplankton biomass because summer chlorophyll concentrations have not changed significantly over the past 27 years in either lake (Williamson et al. 2015). Rather, DOC is the primary factor controlling light attenuation in these lakes (Morris et al. 1995, Williamson et al. 1996). The mechanism driving browning is likely related to both increases in precipitation and recovery from acidification because during the study period, total precipitation significantly increased and sulfate deposition decreased, with concomitant significant increases in pH and acid neutralizing capacity in both lakes (Williamson et al. 2015).