Acid rain workshop

Environmental and Experimental Botany, Vol. 23, No. 3, pp. 197 to 201, 1983

I)098-8472/83 $3.00 + 0.00 q" 1983. Pergamon Press l a d

Printed in Great Britain

ACID R A I N W O R K S H O P

EPRI PERSPECTIVE

PREFACE

A WORKSHOPwas conducted on 12-13 M a y 1981, at Battelle's Columbus Laboratories in Columbus, Ohio, to examine the response of agricultural soils to acid deposition. T h e purpose of the meeting was to assemble representatives of industry, government and academia to objectively evaluate the potential beneficial and harmtul impacts of atmospheric acid deposition on agricultural soils; and to identify those issues requiring further research. The workshop, which included live presentations concerning important aspects of acid deposition on soils, was supplemented bv a brief review of the relevant literature. The results of the workshop corroborated previously published results and suggested that atmospheric acid deposition, defined as both wet and dry tbrms of acidogenic materials, is insignificant on managed agricultural soils as compared to the acidity of materials added as t~rtilizers. ( I o m m o n tarming practices, such as the addition of limestone to acid-sensitive soils, should more than neutralize the acidifying components of atmospheric acid deposition. In addition, atmospheric acid deposition of sulfur most probably pre\cnts sulthr deticiencies in m a n y agricultural soils. N o n - m a n a g e d acid-sensitive soils, vegetati()n and aquatic ecosystems are prohahly mu('h more suscepti/)lc to acid deposition than are agricultural soils. Future research efforts should involve a synthesis ofintbrmation relating known responses of soils to treatments with acidic and I)asic additives and relating this infi)rmation t~, the det)osili(m of materials from the atmosphere in order to establish a model that could calculale the consequences in soils resulting from the inadvertent addition tiom the atmosphere. Experiments o n very sensitive soils and an expanded monitoring network for measuring deposition ( l o s e s a t ( ' a l s ( ~ nee(ted.

Project description This project under RP1904-1 addressed the response of agricultural soils to acid deposition. A literature review and working papers were prepared by soils specialists and a workshop-tbrmat meeting was then convened. T h e working papers provided the initiation of discussion o n all aspects of soil acidification. Participants at the workshop included representatives of academia, industry and government from the United States and Canada. This document is a compilation ot" the working papers, literature review and subsequent discussions by the participants during the workshop. It summarizes the conclusions reached bv the participants and delineates fiJrther research needs.

Project ot?]ecM~es The ohjectives were to provide an assessment of the intluences of atmospheric acid deposition on agricuhural soils and to delineate [hrther research needs. While agriculturally-managed soils are relatively stable, their resilience has limils. These limits were to bc identified by systematically reviewing the knowledge of the major physical, chemical and biological processes in relation to lhe properties of xarious types of soils and cultivational practices.

Project re,sulLs The participants concluded that normal agronomic practices (t~rtilization, liming, etc. will usually overwhelm the amounts of material deposited from the atmosphere. Possihlc exceptions are some u n m a n a g e d soils, tbresls and regions where precipitation exceeds ewq)otranspiration. No in silu detrimental effects on soils have been documented from atmospheric deposition except in the vicinity of major uncontrolled emission sources. I t was recognized that deposition of sulfur 1!)7

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and nitrogen compounds from the atmosphere is beneficial to agricultural crops. The most important research needs are associated with the development of a diagnostic model, the monitoring of both wet and dry deposition, the testing and long-term studies of potentially-changing soil properties, the response of microttora to surges during snowmelts, the identification and monitoring of sensitive areas and the study of long-term changes in soil properties. It was recommended that the needed research should be implemented in accordance with a 5-year plan. JOHN W. HUCKABEE, Project Manager PETER K. MUELLER, Project Manager Energy Analysis and Environment Division

SUMMARY

The response of agricultural soils to acid deposition was addressed at a workshop held on 12 13 M a y 1981, at Battelle's Columbus Laboratories in Columbus, Ohio. Sponsored by the Electric Power Research Institute, Palo Alto, California, the workshop assembled American and Canadian representatives in soil chemistry, soil physics, soil microbiology, plant and crop physiology and environmental sciences. The workshop had [bur primary objectives: (i) to examine the potential impacts of atmospheric acid deposition on agricultural soils from physical, chemical and biological perspectives; (ii) to compare the significance of atmospheric acid deposition to other soil-acidifying processes (e.g., fertilization); (iii) to evaluate both the potentially harnfful and potentially beneficial effects of acid deposition on the productive potential of agricultural soils; and (iv) to assess further research needs and goals and approximate technical approaches and funding levels required to accomplish the research objectives. For the purposes of this workshop, acid deposition was defined as . all acidifying components--both wetfall and dryfalldeposited from the atmosphere as a result of anthropogenic activities. In addition, agricultural soils were considered to be those managed

tor agricultural, horticultural, or silvicultural purposes. Because information specific to the effects of acid deposition on agricultural soils is limited, a brief literature review was compiled by Battelle for the purpose of placing in proper perspective the workshop proceedings. In order to make use of available literature, the review also addressed the responses of nonagricultural soils to acid deposition. Prior to the general workshop discussion, five agronomic scientists presented working papers on the following aspects of acid deposition: its effects on the carbon, nitrogen, phosphorus and sulfur cycles; its impacts on micronutrient cycling in agroecosystems; its effects on soil biota; and sensitivities of soils to acid deposition. The basic conclusions from the presentations are as follows: properly managed and limed soils most probably will not be detrimentally impacted due to acid deposition; proper management of acidified soils will prevent any detrimental effects of acid deposition on essential nutrient (P, K, N, and S) cycles; soil organisms near the soil surface are potentially the most vulnerable to effects of acid deposition; if they are seriously affected, the rate of nutrient cycling may be decreased; Mn, AI and B toxicity are potential manifestations of acid deposition in sensitive soils; sensitive soils include those of sandy texture, low cation exchange capacity, low base saturation and low organic matter content; and, substantial areas of sensitive soils exist in North America, but most of these soils are not used for agricultural purposes. From such an initial perspective, workshop participants discussed many aspects of the effects of acid deposition on agricultural soils. To facilitate discussion, participants met in two concurrent working groups over the 2-day period. The basic conclusions fiom the workshop sessions were: atmospheric acid deposition on managed agricultural soils is normally neutralized by standard agricultural practices required to offset acidifying effects from other sources, such as fertilization; the effects of increased acidity due to atmospherically deposited materials are potentially

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more severe on unmanaged soils than on managed agricultural soils; accelerated aluminum leaching may be the significant manifestation of further acidification of forest soils; soil sensitivity to atmospheric acid deposition should be based on management practice and the buffering capacity of the soil and not on the basis of broad regions of North America; the buffering capacity should be determined by considering total exchangeable bases, CEC, percent base saturation, pH, mineralogy, organic matter and texture; n o in situ detrimental effects on soils or plants, attributed to increased anthropogenic deposition, have been documented except for historic uncontrolled emissions from industrial sources (e.g., Sudbury, Canada); in regions where precipitation exceeds evapotranspiration, soil acidification is a natural process; increased acidity associated with anthropogenic sources may accelerate the rate of this natural process; in the majority of cases, amounts of atmospherically deposited components other than acids (e.g., metals) are very low compared to amounts already present in soils; experiments with metal additions to soils from sludge applications that are orders of magnitude greater than those likely to come from atmospheric deposition have shown no detrimental effects on productivity; atmospheric deposition of S and N compounds is economically beneficial for crop yields in some cases; S fertilization probably would be required on agricultural soils throughout much of the United States if sulfur depositions from the atmosphere were eliminated; and the soil microflora should be able to adapt to the effects of atmospheric acid deposition; during periods ofsnowmelt, however, excess acidity may temporarily affect microorganisms; these effects should be determined.

include mineralogy, organic matter, texture, pH, base saturation and nutrient cycling parameters; such an approach should establish the magnitude of the acid deposition problem and identify important research needs; existing quantitative techniques and networks used to monitor acid deposition need to be expanded and improved in terms of scientific rigor; existing knowledge on the effects of deliberate soil acidification (e.g., fertilization) needs to be synthesized and related to our knowledge of atmospheric acid deposition; certain sensitive areas of the United States and Canada may be adversely affected by acid deposition; these areas need to be identified according to valid criteria established by a knowledgeable scientific community; testing of the hypothesis that acid deposition will have an adverse effect on the most 'sensitive' soils is an important research priority; the hypothesis that sensitive soils exposed to acid deposition affect the quality of local aquifers should be tested; long-term effects potentially may be studied at agricultural experiment stations possessing field plots which have undergone many years of acidification due to fertilization experiments: it is doubtful that short-term studies using increased quantities of dilute acid or concentrated acid solutions accurately simulate the long-term effects of acid deposition on agricultural soils; effects of the plant canopy on the chemical composition of atmospherically derived materials reaching the soil surface and their effects on the chemical, physical and mineralogical properties of agricultural soils require further study; and a 5-year research plan concerning the effects of atmospheric deposition should be formulated and implemented promptly.

Workshop participants also discussed specific research needs in the area of atmospheric acid deposition to agricultural soils. These are summarized as follows:

The available data supported the workshop conclusion that properly managed agricultural soils, which receive fertilizers and limestone, will be minimally impacted by atmospheric acid deposition. Acidification of soils due to fertilization is substantially greater than that due to atmospheric acid deposition. The literature suggests that even in potentially sensitive agricultural soils proper management should ameliorate the

development of a model for diagnosing the efli~cts of atmospheric acid deposition on the biological, chemical and physical properties of agricuhural soils should be considered; this should

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impacts due to acid deposition. However, more intensive study of the long-term effects of acid deposition on sensitive soils may be necessary, including effects on weathering processes, soil buffering capacity, metals mobilization and soil biota. In addition, the literature indicates a definite beneficial effect on agricultural soils due to atmospheric deposition of sulfur and nitrogen compounds. Sulfur deficiencies might be expected if atmospheric deposition of sulfur were halted. The literature also points out the importance of quantifying both wet and dry deposition. Dry forms of acidogenic compounds may be of equal or greater magnitude than wetfall. Accurate determinations, however, are restricted by the available methodology for measuring dry deposition, a serious limitation in acid deposition research. The results of these proceedings and the review of the literature indicate that relative to some other potential impacts from acid deposition, such as direct injury to leaf surfaces or effects on aquatic ecosystems, effects on managed agricultural soils should be negligible. Compared to deliberate soil acidification (fertilization), the amounts deposited from the atmosphere represent a small fraction. However, research is needed for developing a model which is capable of integrating the available knowledge and which would then serve to quantify the impacts of deposition on both supplemented and unsupplemented agricultural soils. The integration of quantitative data, heretofore sparse, would provide insights into the relationship of acid deposition on soils and related ecosystem responses.

INTRODUCTION

THE Electric Power Research Institute (EPRI), in a continuing attempt to define the environmental implications of atmospheric acid deposition, sponsored a workshop entitled "Response of Agricultural Soils to Acid Deposition". For the purposes of this workshop, acid deposition was defined as all acidifying components--both wetfall and dryfall-deposited from the atmosphere as a result of anthropogenic activities. In addition, agricultural soils were considered to be those managed

for agricultural, horticultural, or silvicultural purposes. Coordinated by and held 12-13 May 198l, at Battelle's Columbus Laboratories (BCL) in Columbus, Ohio, the workshop assembled a distinguished group of soil, plant and environmental scientists from the United States and Canada to discuss the implications of atmospheric acid deposition for the long-term stability of agricultural soils. While considerable research has examined aquatic and terrestrial ecosystem-level responses to acid deposition, very little of it has dealt directly with agricultural soils. Thus, the workshop provided a mechanism for E P R I to review long-term research needs and priorities for funding in this important area. Agricultural soils of North America are the resource base on which much of the world's food, feed, fiber, forage and oilseed crops are produced. Fortunately, soils tend to be relatively stable ecosystem components capable of withstanding considerable perturbation. Yet, their resilience is not without limits and considering that within 20 years the United States cropland resource base (currently 220 million potential ha) may be insufficient to meet the nation's needs (Larson, 1981), preservation of available cropland is essential. Agricultural land in the United States is being converted to other uses at an annual rate of about 1.3 million ha. In addition, erosion, a major problem on at least half of the cultivated cropland in the United States, causes substantial soil losses. I f atmospheric acid deposition accelerates soil loss through erosion or reduces soil fertility, the implications for maintaining adequate crop productivity would be serious. Within such a context the members of this workshop approached the discussion of acid deposition on agricultural soils. The four major objectives of the workshop were: to examine the potential impacts of atmospheric acid deposition on agricultural soils from physical, chemical and biological perspectives; to compare the significance of atmospheric acid deposition with other soil-acidifying processes (e.g., fertilization); to evaluate both the potentially harmful and the potentially beneficial effects of acid deposition on the productive potential of agricultural soils; and

ACID RAIN WORKSHOP to assess further research needs and goals and approximate technical approaches and funding levels required to accomplish the research objectives. This report consists of three major sections: five working papers (Section 2), summaries of the workshop proceedings (Section 3) and a supplemental literature review (Section 4). The working papers were designed to establish a framework for discussion by considering initially all major processes important to sustained soil fertility and the relationship of these processes to acidification. The five working papers address, specifically, soil sensitivity, cycling of macronutrients (nitrogen, sulfur, phosphorus, and carbon), cycling of micronutrients and soil biota. The order of presentation at the workshop has been preserved in this report. In each case, the experts

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who authored the working papers related results from acid deposition experiments with current knowledge about soil acidification obtained from agronomic research. In addition, the working papers have been included essentially as they were presented, representing the views of the individual authors; the workshop conclusions may or may not agree with the conclusions presented in the working papers. The literature review draws on many published literature reviews and symposia proceedings that have addressed the scope of the acid deposition problem. To elucidate the effects of atmospheric acid deposition on agricultural soils, per .re, this literature survey includes an assessment of" pertinent information considering soil acidification in general, regardless of the source of acidification.