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G.B. Lawrence

Publications and source records attributed to G.B. Lawrence.

At least 19 recordsLinked to original sources
USGS2011

Changes in the chemistry of acidified Adirondack streams from the early 1980s to 2008

Lakes in the Adirondack region of New York have partially recovered in response to declining deposition, but information on stream recovery is limited. Here we report results of Adirondack stream monitoring from the early 1980s to 2008. Despite a 50% reduction in atmospheric deposition of sulfur, overall increases in pH of only 0.28 and ANC of 13 μeq L −1 were observed in 12 streams over 23 years, although greater changes did occur in streams with lower initial ANC, as expected. In the North Tributary of Buck Creek with high dissolved organic carbon (DOC) concentrations, SO 4 2 − "> SO42− concentrations decreased from 1999 to 2008 at a rate of 2.0 μmol L −1 y −1 , whereas in the neighboring South Tributary with low DOC concentrations, the decrease was only 0.73 μmol L −1 y −1 . Ca 2+ leaching decreased in the North Tributary due to the SO 4 2 − "> SO42− decrease, but this was partially offset by an increase in Ca 2+ leaching from increased DOC concentrations.

New York↗
USGS2008

Climatically driven loss of calcium in steppe soil as a sink for atmospheric carbon

During the last several thousand years the semi-arid, cold climate of the Russian steppe formed highly fertile soils rich in organic carbon and calcium (classified as Chernozems in the Russian system). Analysis of archived soil samples collected in Kemannaya Steppe Preserve in 1920, 1947, 1970, and fresh samples collected in 1998 indicated that the native steppe Chernozems, however, lost 17-28 kg m-2 of calcium in the form of carbonates in 1970-1998. Here we demonstrate that the loss of calcium was caused by fundamental shift in the steppe hydrologic balance. Previously unleached soils where precipitation was less than potential evapotranspiration are now being leached due to increased precipitation and, possibly, due to decreased actual evapotranspiration. Because this region receives low levels of acidic deposition, the dissolution of carbonates involves the consumption of atmospheric CO2. Our estimates indicate that this climatically driven terrestrial sink of atmospheric CO2 is ???2.1-7.4 g C m-2 a-1. In addition to the net sink of atmospheric carbon, leaching of pedogenic carbonates significantly amplified seasonal amplitude of CO2 exchange between atmosphere and steppe soil. Copyright 2008 by the American Geophysical Union.

Global Biogeochemical Cycles↗
USGS2008

Chronic and episodic acidification of Adirondack streams from acid rain in 2003-2005

Limited information is available on streams in the Adirondack region of New York, although streams are more prone to acidification than the more studied Adirondack lakes. A stream assessment was therefore undertaken in the Oswegatchie and Black River drainages; an area of 4585 km2 in the western part of the Adirondack region. Acidification was evaluated with the newly developed base-cation surplus (BCS) and the conventional acid-neutralizing capacity by Gran titration (ANCG). During the survey when stream water was most acidic (March 2004), 105 of 188 streams (56%) were acidified based on the criterion of BCS < 0 ??eq L-1, whereas 29% were acidified based on an ANCG value < 0 ??eq L-1. During the survey when stream water was least acidic (August 2003), 15 of 129 streams (12%) were acidified based on the criterion of BCS < 0 ??eq L-1, whereas 5% were acidified based on ANCG value < 0 ??eq L -1. The contribution of acidic deposition to stream acidification was greater than that of strongly acidic organic acids in each of the surveys by factors ranging from approximately 2 to 5, but was greatest during spring snowmelt and least during elevated base flow in August. During snowmelt, the percentage attributable to acidic deposition was 81%, whereas during the October 2003 survey, when dissolved organic carbon (DOC) concentrations were highest, this percentage was 66%. The total length of stream reaches estimated to be prone to acidification was 718 km out of a total of 1237 km of stream reaches that were assessed. Copyright ?? 2008 by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. All rights reserved.

Journal of Environmental Quality↗
USGS2006

Acid rain effects on aluminum mobilization clarified by inclusion of strong organic acids

Assessments of acidic deposition effects on aquatic ecosystems have often been hindered by complications from naturally occurring organic acidity. Measurements of pH and ANCG, the most commonly used indicators of chemical effects, can be substantially influenced by the presence of organic acids. Relationships between pH and inorganic Al, which is toxic to many forms of aquatic biota, are also altered by organic acids. However, when inorganic Al concentrations are plotted against ANC (the sum of Ca2+, Mg 2+, Na+, and K+, minus SO42-, NO3-, and Cl-), a distinct threshold for Al mobilization becomes apparent. If the concentration of strong organic anions is included as a negative component of ANC, the threshold occurs at an ANC value of approximately zero, the value expected from theoretical charge balance constraints. This adjusted ANC is termed the base-cation surplus. The threshold relationship between the base-cation surplus and Al was shown with data from approximately 200 streams in the Adirondack region of New York, during periods with low and high dissolved organic carbon concentrations, and for an additional stream from the Catskill region of New York. These results indicate that (1) strong organic anions can contribute to the mobilization of inorganic Al in combination with SO42- and NO 3-, and (2) the presence of inorganic Al in surface waters is an unambiguous indication of acidic deposition effects. ?? 2007 American Chemical Society.

Environmental Science & Technology↗
USGS2006

Streams in Catskill Mountains still susceptible to acid rain

Precipitation in North America has become less acidic over the past 2 decades because of reduced power plant emissions and compliance with the Clean Air Act Amendments [ Sirois , 19937rsqb;. The 1990 Clean Air Act Amendments were developed to reduce the acidity of sensitive surface waters, which are primarily in upland forested environments, where acidified waters and associated high aluminum concentrations are toxic to many species of aquatic flora and fauna [ Schindler et al. , 1989]. Our studies show that in spite of less acidic precipitation, the buffering capacity of streams in upland forests of the Catskill Mountains in southeastern New York has not increased in recent years. These data suggest that long-term leaching by acid rain has lowered exchangeable calcium ion concentrations in the soil in upland areas, where the underlying, slow-weathering bedrock provides an inadequate supply of cations to neutralize acidity.

New York↗
USGS2006

Diatom diversity in chronically versus episodically acidified adirondack streams

The relationship between algal species richness and diversity, and pH is controversial. Furthermore, it is still unknown how episodic stream acidification following atmospheric deposition affects species richness and diversity. Here we analyzed water chemistry and diatom epiphyton dynamics and showed their contrasting behavior in chronically vs. episodically acidic streams in the Adirondack region. Species richness and diversity were significantly higher in the chronically acidic brown water stream, where organic acidity was significantly higher and the ratio of inorganic to organic monomeric aluminum significantly lower. Conversely, in the episodically acidic clear water stream, the inorganic acidity and pH were significantly higher and the diatom communities were very species-poor. This suggests that episodic acidification in the Adirondacks may be more stressful for stream biota than chronic acidity. Strong negative linear relationships between species diversity, Eunotia exigua, and dissolved organic carbon against pH were revealed after the influence of non-linear temporal trends was partialled out using a novel way of temporal modeling. ?? 2006 WILEY-VCH Verlag GmbH & Co. KGaA.

International Review of Hydrobiology↗
USGS2006

One-day rate measurements for estimating net nitrification potential in humid forest soils

Measurements of net nitrification rates in forest soils have usually been performed by extended sample incubation (2-8 weeks), either in the field or in the lab. Because of disturbance effects, these measurements are only estimates of nitrification potential and shorter incubations may suffice. In three separate studies of northeastern USA forest soil surface horizons, we found that laboratory nitrification rates measured over 1 day related well to those measured over 4 weeks. Soil samples of Oa or A horizons were mixed by hand and the initial extraction of subsamples, using 2 mol L-1 KCl, occurred in the field as soon as feasible after sampling. Soils were kept near field temperature and subsampled again the following day in the laboratory. Rates measured by this method were about three times higher than the 4-week rates. Variability in measured rates was similar over either incubation period. Because NO3- concentrations were usually quite low in the field, average rates from 10 research watersheds could be estimated with only a single, 1-day extraction. Methodological studies showed that the concentration of NH4+ increased slowly during contact time with the KCl extractant and, thus, this contact time should be kept similar during the procedure. This method allows a large number of samples to be rapidly assessed. ?? 2006 Elsevier B.V. All rights reserved.

Forest Ecology and Management↗
USGS2005

Climate dependency of tree growth suppressed by acid deposition effects on soils in Northwest Russia

Increased tree growth in temperate and boreal forests has been proposed as a direct consequence of a warming climate. Acid deposition effects on nutrient availability may influence the climate dependency of tree growth, however. This study presents an analysis of archived soil samples that has enabled changes in soil chemistry to be tracked with patterns of tree growth through the 20th century. Soil samples collected in 1926, 1964, and 2001, near St. Petersburg, Russia, showed that acid deposition was likely to have decreased root-available concentrations of Ca (an essential element) and increased root-available concentrations of Al (an inhibitor of Ca uptake). These soil changes coincided with decreased diameter growth and a suppression of climate-tree growth relationships in Norway spruce. Expected increases in tree growth from climate warming may be limited by decreased soil fertility in regions of northern and eastern Europe, and eastern North America, where Ca availability has been reduced by acidic deposition. ?? 2005 American Chemical Society.

Environmental Science & Technology↗
USGS2004

Mineralization and nitrification patterns at eight northeastern USA forested research sites

Nitrogen transformation rates in eight northeastern US research sites were measured in soil samples taken in the early season of 2000 and the late season of 2001. Net mineralization and nitrification rates were determined on Oa or A horizon samples by two different sampling methods - intact cores and repeated measurements on composite samples taken from around the cores. Net rates in the composite samples (n=30) showed three different temporal patterns: high net nitrification with minimal NH4+ accumulation, high net nitrification and high NH4+ accumulation, and minimal net nitrification and moderate NH4+ accumulation. The 4-week net rates in intact cores were about half that of the rates from the composite samples but were well related (R2 > 0.70). Composite samples from sites that exhibited high net nitrification were incubated with acetylene and net nitrification was completely stopped, suggesting an autotrophic pathway. Gross mineralization and nitrification (2000 only) rates were estimated using the isotope dilution technique. Gross rates of nitrification and consumption in intact cores were relatively low. Gross rates of mineralization and net rates of nitrification were both related to the soil C/N ratio, with higher rates generally occurring in sites containing Acer saccharum as a dominant or co-dominant species. The comparison of methods suggests that all provide a similar hierarchy of potential rates but that the degree of net nitrification is strongly influenced by the degree of sample disturbance. Differences between sites appear to be related to an interaction of soil (C/N) and vegetation (A. saccharum contribution) characteristics. ?? 2003 Elsevier B.V. All rights reserved.

Forest Ecology and Management↗
USGS2004

Use of stream chemistry for monitoring acidic deposition effects in the Adirondack region of New York

Acid-neutralizing capacity (ANC) and pH were measured weekly from October 1991 through September 2001 in three streams in the western Adirondack Mountain region of New York to identify trends in stream chemistry that might be related to changes in acidic deposition. A decreasing trend in atmospheric deposition of SO42- was observed within the region over the 10-yr period, although most of the decrease occurred between 1991 and 1995. Both ANC and pH were inversely related to flow in all streams; therefore, a trend analysis was conducted on (i) the measured values of ANC and pH and (ii) the residuals of the concentration-discharge relations. In Buck Creek, ANC increased significantly (p < 0.05) over the 10 yr, but the residuals of ANC showed no trend (p > 0.10). In Bald Mountain Brook, ANC and residuals of ANC increased significantly (p < 0.01), although the trend was diatonic-a distinct decrease from 1991 to 1996 was followed by a distinct increase from 1996 to 2001. In Fly Pond outlet, ANC and residuals of ANC increased over the study period (p < 0.01), although the trend of the residuals resulted largely from an abrupt increase in 1997. In general, the trends observed in the three streams are similar to results presented for Adirondack lakes in a previous study, and are consistent with the declining trend in atmospheric deposition for this region, although the observed trends in ANC and pH in streams could not be directly attributed to the trends in acidic deposition.

Conference Paper↗
USGS2000

Atmospheric nitrogen in the Mississippi River Basin: Amissions, deposition and transport

Atmospheric deposition of nitrogen has been cited as a major factor in the nitrogen saturation of forests in the north-eastern United States and as a contributor to the eutrophication of coastal waters, including the Gulf of Mexico near the mouth of the Mississippi River. Sources of nitrogen emissions and the resulting spatial patterns of nitrogen deposition within the Mississippi River Basin, however, have not been fully documented. An assessment of atmospheric nitrogen in the Mississippi River Basin was therefore conducted in 1998-1999 to: (1) evaluate the forms in which nitrogen is deposited from the atmosphere; (2) quantify the spatial distribution of atmospheric nitrogen deposition throughout the basin; and (3) relate locations of emission sources to spatial deposition patterns to evaluate atmospheric transport. Deposition data collected through the NADP/NTN (National Atmospheric Deposition Program/National Trends Network) and CASTNet (Clean Air Status and Trends Network) were used for this analysis. NO(x) Tier 1 emission data by county was obtained for 1992 from the US Environmental Protection Agency (Emissions Trends Viewer CD, 1985-1995, version 1.0, September 1996) and NH3 emissions data was derived from the 1992 Census of Agriculture (US Department of Commerce. Census of Agriculture, US Summary and County Level Data, US Department of Commerce, Bureau of the Census. Geographic Area series, 1995:1b) or the National Agricultural Statistics Service (US Department of Agriculture. National Agricultural Statistics Service Historical Data. Accessed 7/98 at URL, 1998. http://www.usda.gov/nass/pubs/hisdata.htm). The highest rates of wet deposition of NO3- were in the north-eastern part of the basin, downwind of electric utility plants and urban areas, whereas the highest rates of wet deposition of NH4+ were in Iowa, near the center of intensive agricultural activities in the Midwest. The lowest rates of atmospheric nitrogen deposition were on the western (windward) side of the basin, which suggests that most of the nitrogen deposited within the basin is derived from internal sources. Atmospheric transport eastward across the basin boundary is greater for NO3- than NH4+, but a significant amount of NH4+ is likely to be transported out of the basin through the formation of (NH4)2SO4 and NH4NO3 particles - a process that greatly increases the atmospheric residence time of NH4+. This process is also a likely factor in the atmospheric transport of nitrogen from the Midwest to upland forest regions in the North-East, such as the western Adirondack region of New York, where NH4+ constitutes 38% of the total wet deposition of N.

Science of Total Environment↗
USGS2000

Atmospheric deposition and watershed nitrogen export along an elevational gradient in the Catskill Mountains, New York

Cumulative effects of atmospheric N deposition may increase N export from watersheds and contribute to the acidification of surface waters, but natural factors (such as forest productivity and soil drainage) that affect forest N cycling can also control watershed N export. To identify factors that are related to stream-water export of N, elevational gradients in atmospheric deposition and natural processes were evaluated in a steep, first-order watershed in the Catskill Mountains of New York, from 1991 to 1994. Atmospheric deposition of SO4/2-, and probably N, increased with increasing elevation within this watershed. Stream-water concentrations of SO4/2- increased with increasing elevation throughout the year, whereas stream-water concentrations of NO3/- decreased with increasing elevation during the winter and spring snowmelt period, and showed no relation with elevation during the growing season or the fall. Annual export of N in stream water for the overall watershed equaled 12% to 17% of the total atmospheric input on the basis of two methods of estimation. This percentage decreased with increasing elevation, from about 25% in the lowest subwatershed to 7% in the highest subwatershed; a probable result of an upslope increase in the thickness of the surface organic horizon, attributable to an elevational gradient in temperature that slows decomposition rates at upper elevations. Balsam fir stands, more prevalent at upper elevations than lower elevations, may also affect the gradient of subwatershed N export by altering nitrification rates in the soil. Variations in climate and vegetation must be considered to determine how future trends in atmospheric deposition will effect watershed export of nitrogen.

Biogeochemistry↗
USGS2000

Composition of fish communities in relation to stream acidification and habitat in the Neversink River, New York

The effects of acidification in lotic systems are not well documented. Spatial and temporal variability of habitat and water quality complicate the evaluation of acidification effects in streams and rivers. The Neversink River in the Catskill Mountains of southeastern New York, the tributaries of which vary from well buffered to severely acidified, provided an opportunity to investigate the extent and magnitude of acidification effects on fish communities of headwater systems. Composition of fish communities, water quality, stream hydrology, stream habitat, and physiographic factors were characterized from 1991 to 1995 at 16 first- to fourth-order sites in the basin. Correlation and regression analyses were used to develop empirical models and to assess the relations among fish species richness, total fish density, and total fish biomass and environmental variables. Chronic and episodic acidification and elevated concentrations of inorganic monomeric aluminum were common, and fish populations were rare or absent from several sites in the upper reaches of the basin; as many as six fish species were collected from sites in the lower reaches of the basin. Species distributions and species richness were most highly related to stream pH, acid-neutralizing capacity (ANC), inorganic monomeric aluminum (Al im ), calcium (Ca) 2+ , and potassium (K) + concentrations, site elevation, watershed drainage area, and water temperature. Fish density was most highly related to stream pH, Al im , ANC, K + , Ca 2+ , and magnesium (Mg) 2+ concentrations. Fish biomass, unlike species richness and fish density, was most highly related to physical habitat characteristics, water temperature, and concentrations of Mg 2+ and silicon. Acidity characteristics were of secondary importance to fish biomass at all but the most severely acidified sites. Our results indicate that (1) the total biomass of fish communities was not seriously affected at moderately to strongly acidified sites; (2) species richness and total density of fish were adversely affected at strongly to severely acidified sites; and (3) possible changes in competitive interactions may mitigate negative effects of acidification on fish communities in parts of the Neversink River Basin.

New York↗
USGS2000

Forest soil chemistry and terrain attributes in a Catskills watershed

Knowledge of soil chemistry is useful in assessing the sensitivity of forested areas to natural and anthropogenic disturbances, but characterizing large areas is expensive because of the large sample numbers required and the cost of soil chemical analyses. We collected and chemically analyzed soil samples from 72 sites within a 214-ha watershed in the Catskill Mountains of New York to evaluate factors that influence soil chemistry and whether terrain features could be used to predict soil chemical properties. Using geographic information system (GIS) techniques, we determined five terrain attributes at each sampling location: (i) slope, (ii) aspect, (iii) elevation, (iv) topographic index, and (v) flow accumulation. These attributes were ineffective in predicting the chemical properties of organic and mineral soil samples; together they explained only 4 to 25% of the variance in pH(w), effective cation-exchange capacity (CEC(e)), exchangeable bases, exchangeable acidity, total C, total N, and C/N ratio. Regressions among soil properties were much better; total C and pH(w) together explained 33 to 66% of the variation in exchangeable bases and CEC(e). Total C was positively correlated with N (r = 0.91 and 0.96 in Oa horizons and mineral soil, respectively), exchangeable bases (r = 0.65, 0.76), and CEC(e) (r = 0.54, 0.44), indicating the importance of organic matter to the chemistry of these acidic soils. The fraction of CEC(e) occupied by H explained 44% of the variation in pH(w). Soil chemical properties at this site vary on spatial scales finer than typical GIS analyses, resulting in relationships with poor predictive power. Thus, interrelationships among soil properties are more reliable for prediction.Knowledge of soil chemistry is useful in assessing the sensitivity of forested areas to natural and anthropogenic disturbances, but characterizing large areas is expensive because of the large sample numbers required and the cost of soil chemical analyses. We collected and chemically analyzed soil samples from 72 sites within a 214-ha watershed in the Catskill Mountains of New York to evaluate factors that influence soil chemistry and whether terrain features could be used to predict soil chemical properties. Using geographic information system (GIS) techniques, we determined five terrain attributes at each sampling location: (i) slope, (ii) aspect, (iii) elevation, (iv) topographic index, and (v) flow accumulation. These attributes were ineffective in predicting the chemical properties of organic and mineral soil samples; together they explained only 4 to 25% of the variance in pHw, effective cation-exchange capacity (CECe), exchangeable bases, exchangeable acidity, total C, total N, and C/N ratio. Regressions among soil properties were much better; total C and pHw together explained 33 to 66% of the variation in exchangeable bases and CECe. Total C was positively correlated with N (r = 0.91 and 0.96 in Oa horizons and mineral soil, respectively), exchangeable bases (r = 0.65, 0.76), and CECe (r = 0.54, 0.44), indicating the importance of organic matter to the chemistry of these acidic soils. The fraction of CECe occupied by H explained 44% of the variation in pHw. Soil chemical properties at this site vary on spatial scales finer than typical GIS analyses, resulting in relationships with poor predictive power. Thus, interrelationships among soil properties are more reliable for prediction.

New York↗
USGS1999

Soil calcium status and the response of stream chemistry to changing acidic deposition rates

Despite a decreasing trend in acidic deposition rates over the past two to three decades, acidified surface waters in the northeastern United States have shown minimal changes. Depletion of soil Ca pools has been suggested as a cause, although changes in soil Ca pools have not been directly related to long-term records of stream chemistry. To investigate this problem, a comprehensive watershed study was conducted in the Neversink River Basin, in the Catskill Mountains of New York, during 1991–1996. Spatial variations of atmospheric deposition, soil chemistry, and stream chemistry were evaluated over an elevation range of 817–1234 m to determine whether these factors exhibited elevational patterns. An increase in atmospheric deposition of SO 4 with increasing elevation corresponded with upslope decreases of exchangeable soil base concentrations and acid-neutralizing capacity of stream water. Exchangeable base concentrations in homogeneous soil incubated within the soil profile for one year also decreased with increasing elevation. An elevational gradient in precipitation was not observed, and effects of a temperature gradient on soil properties were not detected. Laboratory leaching experiments with soils from this watershed showed that (1) concentrations of Ca in leachate increased as the concentrations of acid anions in added solution increased, and (2) the slope of this relationship was positively correlated with base saturation. Field and laboratory soil analyses are consistent with the interpretation that decreasing trends in acid-neutralizing capacity in stream water in the Neversink Basin, dating back to 1984, are the result of decreases in soil base saturation caused by acidic deposition.

Ecological Applications↗
USGS1998

Effect of chronic nitrogen additions on soil nitrogen fractions in red spruce stands

The responses of temperate and boreal forest ecosystems to increased nitrogen (N) inputs have been varied, and the responses of soil N pools have been difficult to measure. In this study, fractions and pool sizes of N were determined in the forest floor of red spruce stands at four sites in the northeastern U.S. to evaluate the effect of increased N inputs on forest floor N. Two of the stands received 100 kg N ha-1 yr-1 for three years, one stand received 34 kg N ha-1 yr-1 for six years, and the remaining stand received only ambient N inputs. No differences in total N content or N fractions were measured in samples of the Oie and Oa horizons between treated and control plots in the three sites that received N amendments. The predominant N fraction in these samples was amino acid N (31-45 % of total N), followed by hydrolyzable unidentified N (16-31% of total N), acid- soluble N (18-22 % of total N), and NH4/+-N (9-13 % of total N). Rates of atmospheric deposition varied greatly among the four stands. Ammonium N and amino acid N concentrations in the Oie horizon were positively related to wet N deposition, with respective r2 values of 0.92 and 0.94 (n = 4, p < 0.05). These relationships were somewhat stronger than that observed between atmospheric wet N deposition and total N content of the forest floor, suggesting that these pools retain atmospherically deposited N. The NH4/+- N pool may represent atmospherically deposited N that is incorporated into organic matter, whereas the amino acid N pool could result from microbial immobilization of atmospheric N inputs. The response of forest floor N pools to applications of N may be masked, possibly by the large soil N pool, which has been increased by the long-term input of N from atmospheric deposition, thereby overwhelming the short-term treatments.

Water, Air, & Soil Pollution↗
USGS1997

Acidic deposition, cation mobilization, and biochemical indicators of stress in healthy red spruce

Dendrochemical and biochemical markers link stress in apparently healthy red spruce trees ( Picea rubens ) to acidic deposition. Acidic deposition to spruce forests of the northeastern USA increased sharply during the 1960s. Previous reports related visible damage of trees at high elevations to root and soil processes. In this report, dendrochemical and foliar biochemical markers indicate perturbations in biological processes in healthy red spruce trees across the northeastern USA. Previous research on the dendrochemistry of red spruce stemwood indicated that under uniform environmental conditions, stemwood concentrations of Ca and Mg decreased with increasing radial distance from the pith. For nine forest locations, frequency analysis shows that 28 and 52% of samples of red spruce stemwood formed in the 1960s are enriched in Ca and Mg, respectively, relative to wood formed prior to and after the 1960s. This enrichment in trees throughout the northeastern USA may be interpretable as a signal of increased availability of essential cations in forest soils. Such a temporary increase in the availability of Ca and Mg could be caused by cation mobilization, a consequence of increased acidic deposition. During cation mobilization, essential Ca and Mg as well as potentially harmful Al become more available for interaction with binding sites in the soil and absorbing roots. As conditions which favor cation mobilization continue, Ca and Mg can be leached or displaced from the soil. A measure of the interaction between Ca and Al is the Al/Ca binding ratio (molar charge ratio of exchangeable Al to exchangeable Ca). As the Al/Ca binding ratio in the root zone increased from 0.3 to 1.9, the foliar concentration of the biochemical stress marker putrescine also increased from 45 to 145 nm g −1 . The correlation of the putrescine concentration to the Al/Ca binding ratio (adj. r 2 = 0.68, P < 0.027) suggests that foliar stress may be linked to soil chemistry.

Journal of Environmental Quality↗