Variation In Acid Neutralizing Capacity Research Articles

Diatom-inference models for acid neutralizing capacity and nitrate based on 41 calibration lakes in the Sierra Nevada, California, USA

We investigated relationships among modern diatom species composition and physical and chemical characteristics of high-elevation lakes of the Sierra Nevada (California), to develop transfer functions that can be used to infer historic lake conditions. Data were collected from 50 lakes in National Parks and Forests of the central and southern Sierra Nevada. Multivariate statistical methods revealed that acid neutralizing capacity (ANC) and nitrate accounted for significant variation in diatom taxa. A training set with 242 modern diatom taxa from a subset of 41 lakes was used to develop transfer functions for ANC and nitrate using weighted averaging techniques. ANC and nitrate calibration ranges were 23.0–137 μEq/L and 0.18–9.5 μM, respectively. Coefficients of determination for the models were: ANC: R2 = 0.76, and R jackknife 2 = 0.44; NO3: R2 = 0.67, and R jackknife 2 = 0.27. The ANC model was applied to the top 50 cm of sediments in Moat Lake to reconstruct ANC from ca. AD 350 to 2005. The reconstruction suggests that ANC declined by about 40 % (101–60 μEq/L) between the 1920s and the 1960s and then recovered to pre-1920s levels during 1980–2000. The magnitude of this ANC excursion was the largest observed during the past 1,600 years. We hypothesize that temporal variations in ANC were influenced by: (1) changes in rates of acid deposition, especially nitric acid and (2) variations in the timing and magnitude of snowmelt runoff.

Partitioning the variation within the acid neutralizing capacity of surface waters in Scotland in relation to land cover, soil and atmospheric depositional factors

A method of decomposing the variation in the acid neutralizing capacity (ANC) of surface waters in Scotland is described. Using national datasets, a series of variables relating to 703 catchments across Scotland is divided into three components representing (i) land cover, (ii) soil and (iii) atmospheric deposition/altitude. Redundancy analysis (RDA) and (partial) redundancy analysis are used to quantify the amount of variation in ANC uniquely attributable to each of these components, independent of the effects of the others. The variation accounted for by covarying combinations of these components is also determined. Approximately 55% of the total variation in ANC across the 703 sites is explained by the variables representing catchment characteristics and atmospheric deposition. Of this, 8.5%, 2.4% and 6.9% are uniquely attributable to the land cover, soil and deposition/altitude components, respectively. A further 38% of ANC variation is associated with the covariation between components, with 18% accounted for by the combination of all three. Approximately 45% of the variation in ANC remains unexplained. The results reflect the integrated nature of catchment processes and demonstrate, for these data, that it is a combination of land cover, soil and deposition and altitude factors which most explain variation in freshwater ANC level. The approach offers a tool with which to assess the sensitivity of surface waters to acid deposition at a regional scale and provides a way of identifying regional differences in catchment response to acid loading.

Seasalt Effects on the Acid Neutralizing Capacity of Streamwaters in Southern Norway

Input of neutral salt, primarily NaCl, from sea spray is an important factor for short-term acidification of surface water, primarily in already acidified areas, because Na may substitute for H+ and cationic aluminium by cation-exchange reactions in the soil. By evaluating the variation of non-marine sodium (Na*) separately it is possible to estimate the major effect of seasalt episodes on the neutralizing capacity (ANC) of stream water. At four long-term monitored Norwegian catchments, the Na* in stream water on average explained 28 ± 4% of the monthly variations of ANC in stream water at Birkenes, and 27 ± 3%, 20 ± 2% and 56 ± 5% of the correspondent variations at Storgama, Langtjern and Kaarvatn, during the respective monitoring periods. The remaining variations in acid neutralizing capacity are explained by the difference between non-marine base cations (ΣCa*,Mg*,K*) and non-marine sulphate (SO4*) and NO3. This paper also indicates that seasalt episodes are probably of greater importance for the periodic variations in ANC of stream water than commonly recognized. During the last years, extreme seasalt episodes have occurred in southern Norway, and more frequently at winter-time, which means that seasalt inputs have played a more important role for the short-term variations of ANC in stream water the last years. This tendency is also strengthened by the fact that there has been a significant decline in the input of acidic sulphur compounds and non-marine base cations in stream water during the last 10-15 years. Because the decline in soil-derived base cations in stream water is somewhat lower than the correspondent decline of sulphate, a slowly improving ANC of stream water should be expected on long-term basis. Seasalt episodes of the same magnitude as those present during the last years, will therefore most likely cause less extreme water-chemical conditions in the years to come. Because the seasalt effect seems to be a short-term effect, there is no reason to claim that these effects may cause long-term acidification, a conclusion earlier drawn from several correspondent studies.

Beaver pond biogeochemistry: Acid neutralizing capacity generation in a headwater wetland

A beaver pond and its associated inlet and outlet waters in the Adirondack Mountains of New York were monitored for major chemical solutes for 26 months in an effort to quantify underlying chemical controls on the production and consumption of acid neutralizing capacity (ANC). The pond was a net annual sink for inlet Al, SO4 2−, NO3 −; and H4SiO4. The pond was a net annual source of dissolved organic carbon (DOC), NH4 +, and Fe2−. Losses of ANC resulting from Al and basic cation retention, as well as organic anion release (RCOO−) associated with DOC, were more than offset by SO4 2−, and NO3 − retention and Fe2− and NH4 + release, resulting in a net production of ANC. Rates of ANC generation were 120 meq m−2 yr−1 and 310 meq m−2 yr−1, respectively (based on pond surface area), for the non-summer (October-June) and summer (July–September) periods. Seasonal variations in ANC in the outlet stream were largely associated with Fe2+ and DOC release, while ANC in the upland inlet stream was associated with Al, NO3 −, and basic cations, with much less seasonal variation. Controls on stream chemistry were temporally and longitudinally different, for the inlet and outlet streams. The shift to seasonal control of outlet stream ANC by processes associated with organic matter decomposition reactions and anaerobic zone nutrient transformations may be characteristic of headwater wetlands, in temperate zones with seasonal temperature extremes. Beaver impoundments and wetlands may also be important in the upstream mobilization or retention of geologically bound solutes like Al, Fe, and H4SiO4. Headwater wetlands, as sinks for solutes associated with acidic deposition and watershed acidification (i.e., SO4 2−, NO3 −, and Al), may play a role in the amelioration of the effects of these solutes on downstream receiving waters and associated biota. Depending on their location in relation to drainage patterns, these ponded systems may influence the nutrient dynamics of receiving waters through nitrogen transformations and organic carbon cycling.

Seasonal and long-term temporal patterns in the chemistry of Adirondack lakes

There is considerable interest in the recovery of surface waters from acidification by acidic deposition. The Adirondack Long-Term Monitoring (ALTM) program was established in 1982 to evaluate changes in the chemistry of 17 Adirondack lakes. The ALTM lakes exhibited relatively uniform concentrations of SO42−. Lake-to-lake variability in acid neutralizing capacity (ANC) was largely due to differences in the supply of basic cations (Ca2+, Mg2+, K+, Na+; CB) to drainage waters. Lakes in the western and southern Adirondacks showed elevated concentrations of NO3−, while lakes in the central and eastern Adirondacks had lower NO3− concentrations during both peak and base flow periods. The ALTM lakes exhibited seasonal variations in ANC. Lake ANC was maximum during the late summer or autumn, and lowest during spring snowmelt. In general Adirondack lakes with ANC near 100 Μeq L−1 during base flow periods may experience decreases in ANC to near or below 0 Μeq L−1 during high flow periods. The ALTM lakes have exhibited long-term temporal trends in water chemistry. Most lakes have demonstrated declining SO42−, consistent with decreases in SO2 emissions and SO42− in precipitation in the eastern U.S. Reductions in SO42− have not coincided with a recovery in ANC. Rather, ANC values have declined in some ALTM lakes. This pattern is most likely due to increasing concentrations of NO3− that occurred in most of the ALTM drainage lakes.

Analysis of the mineral acid‐base components of acid‐neutralizing capacity in Adirondack Lakes

Mineral acids and bases influence pH largely through their effects on acid‐neutralizing capacity (ANC). This influence becomes particularly significant as ANC approaches zero. Analysis of data collected by the Adirondack Lakes Survey Corporation (ALSC) from 1469 lakes throughout the Adirondack region indicates that variations in ANC in these lakes correlate well with base cation concentrations (CB), but not with the sum of mineral acid anion concentrations (CA). This is because (CA) is relatively constant across the Adirondacks, whereas CB varies widely. Processes that supply base cations to solution are ion‐specific. Sodium and silica concentrations are well correlated, indicating a common source, mineral weathering. Calcium and magnesium also covary but do not correlate well with silica. This indicates that ion exchange is a significant source of these cations in the absence of carbonate minerals. Iron and manganese concentrations are elevated in the lower waters of some lakes due to reducing conditions. This leads to an ephemeral increase in CB and ANC. When the lakes mix and oxic conditions are restored, these ions largely precipitate from solution. Sulfate is the dominant mineral acid anion in ALSC lakes. Sulfate concentrations are lowest in seepage lakes, commonly about 40 μeq/L less than in drainage lakes. This is due in part to the longer hydraulic detention time in seepage lakes, which allows slow sulfate reduction reactions more time to decrease lake sulfate concentration. Nitrate typically influences ANC during events such as snowmelt. Chloride concentrations are generally low, except in lakes impacted by road salt.

REGIONAL CHEMISTRY OF LAKES IN MASSACHUSETTS

: We surveyed over 2000 lakes in the State of Massachusetts (1983–1984) to examine the spatial variations in their acid-base chemistry. Our survey differed from previous surveys by including small lakes and nonpristine urban lakes. For samples collected in October 1983 and 1984, the median acid neutralizing capacity (ANC) was 184 μeq L−1 and 5.9 percent were acidic (ANC≤O). Small lakes (<4 ha) were more likely to be acidic than large lakes. Generally, sulfate was the dominant acidifying agent, although organic anions were dominant in some of the lakes in the Cape Cod Region. The ionic composition of the lakes showed strong regional patterns which appear to be related to geology and human population density. An analysis of variance of ANC shows the six regional categories in the state explain 51 percent of the variance, while a combined general linear model of lake drainage type, color, elevation, size, silica, and hydrogen ion deposition could explain only 4.9 percent of the variation in ANC. Calcium rich, high ionic strength lakes were present in the marble bedrock in the west, and relatively dilute lakes dominated by sodium and chloride were found near the coast. Chloride concentrations were also related to population density, suggesting road salt as a likely contributing source.