Acid Atmospheric Deposition and its Effects on Terrestial Ecosystems in the Netherlands: The Third and Final Phase (1991-1995)

694 Pages·1997·10.982 MB·3-705\694

by  G.J. Heij and J.W. Erisman (Eds.)

FOREWORD
This report describes the results and conclusions of the third phase of the Dutch Priori yt.
Programme on Acidification (DPPA-III) carried out from 1991 to 1994 and funded by four
ministries (Housing, Spatial Planning and the Environment; Economic Affairs; Transport,
Public Works and Water Management; and Agriculture, Nature Management and Fisheries)
and by the Dutch Electrici~ Generating Board. The results of the scientific research are
described in detail in the final reports of the individual projects. Umbrella theme reports have
been prepared on deposition, stand modelling and effects on forests.
The report marks the end of the coordinated acidification research ni The Netherlands. This
coordination at the national level has taken place since 1984. This is not to say that all the
questions to do with acidification (including the eutrophying effect of nitrogen) have been
answered. In the future, the interactions between the effects of the various acidifying
components, and between these components and CO:, and with "traditional" stress factors
such as frost, drought, diseases and pests, will continue to receive particular attention. It can
nonetheless be contended that important issues have been clarified and that the basis for
Dutch policy on acidification is sufficiently sound. The DPPA-III project group was
responsible for the reporting as a whole, but in addition many others contributed directly or
indirectly to the realization of this report (e.g. by model research, experiments, contributions
to the text, or via comments). Some of them have been mentioned at the head of the
appropriate chapter(s). We would like to thank the following ni particular: Arthur Eijs
(VROM), Bert-Jan Groenenberg (SC-DLO), Cees van Heerden (RIVM), Wilma Jans (IBN-
DLO), Ingrid Jorritsma (IBN-DLO), Jep Karres (LNV), Volkert Keizer (VROM), Hans Kros
(SC-DLO), Harriet Marseille (VROM), Ad Olsthoorn (IBN-DLO), Carolien van der Salm (SC-
DLO), Stan Smeulders (VROM), Aaldrik Tiktak (RIVM), Jan-Renger van de Veen (IBN-
DLO).
Special thanks to Leny Lekkerkerk (National Reference Centre for Agriculture), Hans Brand
(Ministry. of Agriculture, Nature Management and Fisheries/Nature Directorate) and Gijs van
Tol (National Reference Centre for Nature), for their constructive comments on the final draft.
We thank Ottelien van Steenis for her excellent work in the secretariat and for the financial
management of this third phase of the DPPA. Finally, we thank Tineke Buijtendijk-Olij for
her editing work.
.T Schneider Programme Director
G.J. Heij Secretary_
ABRIDGED SUMMARY
Chapter 5 of this report presents a summary of the results of the DPPA-III programme and
the conclusions. This abridged summary presents the most important findings on deposition,
critical loads and the effects on forest and non forest ecosystems.
1 Loads
On average the calculated total potential acid deposition ni The Netherlands has fallen, from
7215 mol in 1980 to 4280 mol ni 1993. This is caused by a sharp decline in the ~OS
deposition and a slight reduction ni the dry deposition of NH~, which has been determined
with a calculated 20% reduction in 3HN emission since 1991. This reduction is not wholly
reconcilable with data from monitoring.
The values of potential acid deposition have changed compared to the DPPA-II report. For
1993 the sex deposition is 38% higher, the yON deposition is 23% lower, the .~HN deposition
is 5% higher and the total acid deposition is 7% higher. These differences are caused by
changes in the estimation of the dry deposition, brought about by improved understanding of
the exchange processes between atmosphere and the earth's surface. One of the most important
changes is the higher estimate of deposition of particles to forests and other high roughness
receptors.
The deposition of acid particles (aerosols) contributes appreciably (20-40%) to the total acid
deposition to forest. This contribution is double the estimate presented in the DPPA-II final
report.
The deposition to the "average Dutch forest" is higher than that to the "average Dutch
landscape": +33% for sex, +34% for NOy, +18% for xHN and +25% for potential acid. These
values are higher than those reported ni DPPA-II. This is because of improved estimates of
the deposition of particles to forest and the combination of great roughness and the gas
exchange processes applied to the forest. The estimates of the acidifying atmospheric
deposition via measurements of concentration/deposition and of the load to the forest soil
obtained by measuring throughfall (and correcting for canopy exchange) are generally in
agreement. This is especially true for sulphur and -though to a lesser extent- for nitrogen
components. Quantified empirical relationships between both methods of estimation enable
a link to be made between soil load and emissions.
The calculated deposition of potential acid is 2340 mol y~-ah ~- for 2000 and 2035 mol ha~y ~-
for 2010, on the basis of the MV3 emission prognoses and assuming that the proposed
national and international reductions in emissions will be achieved. Although the target load
of 2400 mol haly ~ could be achieved on average in The Netherlands by 2000, it will still be
greatly exceeded in some locations. The target for 2010 (1400 mol ha~y ~) will not be
achieved nationally; deposition will be at or below this target in only a small part of the
country.
Source contributions (sector) and origin of eht deposition (country)
In 1993 57% of the total potential acid deposition in The Netherlands originated within The
Netherlands. In that year the contributions from The Netherlands were: 32% of the SOx, 40%
of the NO r and 86% of the .~I-IN These percentages are related to the differences in the
behavior of SO~, NO r and ~HN in the atmosphere. Agriculture was the largest contributor
(61%) to the Dutch contribution to the deposition of total acid to The Netherlands in 1993.
Vehicle emissions also made an important contribution (16%), and industry and refineries
each accounted for about .%8 The Dutch contribution to deposition in The Netherlands will
fall to less than 50% in 2000 and 2010 and the contributions from Belgium and Germany will
increase. Agriculture will continue to contribute the largest amount in the future, although its
contribution will decline to 42% by 2010. Vehicle emissions, industry and refineries will then
become relatively more important.
Table 1 shows the differences between the DPPA-II and DPPA-III results for various
parameters.
2 Critical loads
The critical loads for forest, particularly those for the deposition of potential acid, are
somewhat higher than those reported in DPPA-II. This is because new data have become
available and because the underlying criteria have been improved. The method of calculation
has remained unchanged. Table 1 shows the new values for potential acid and for nitrogen,
plus those from DPPA-II.
The mean critical load for potential acid is 1900 mol ha-ly 1 for coniferous forest and 2450
mol ha~y ~ for deciduous forest, if a critical ratio of aluminium to bases (Ca+Mg+K)
concentration is taken as the criterion. It is still possible that the AI buffer will become
depleted in 100-200 years, but without extremely low pH values being reached. The mean
critical load is .ac 1700 tool haly ~- if the most important criterion is taken to be the
prevention of AI depletion.
The mean critical nitrogen load is 700-1400 mol ha~y ~ for coniferous forest and 1100-1400
mol ha~y ~ for deciduous forest, if changes in the vegetation (biodiversity) are given most
weight and only empirical data are used. The mean critical loads are higher if nitrate leaching
is considered to be the most important effect: 2100 mol ha~y ~ for coniferous forest and 3000
mol ha~y ~- for deciduous forest, assuming a concentration of 50 mg 1 1 NO3- in the
groundwater (drinking water standard).
These higher critical loads for total acid and nitrogen in The Netherlands were nevertheless
still substantially exceeded in 1993 (see Table .)1
As regards the non-forest ecosystems, only the critical nitrogen loads for heathland are given,
because these are the only values that can be compared to the DPPA-II report. The new
values for heathland are: 1100-1400 mol y~-ah ~ for dry heathland and 1200-1600 mol ha-ly ~
for wet heathland. These critical loads are currently also being exceeded.
3 Effects on forest ecosystems
The clearest repercussions of the substantial exceedance of the critical loads are observable
in vegetation changes, the foliar chemical composition, the soil moisture and the quality of
the shallow groundwater. In general, eutrophication caused by the increased availability of
nitrogen poses a greater threat in The Netherlands than potential acid - particularly as regards
changes in the vegetation (undergrowth) and disruption of the nutrient balance. The latter
effect is intensified by soil acidification.
Although the contribution from nitrogen to potential acid deposition to Dutch forests is ca.
twice that of sulphur, the current contribution to the ongoing soil acidification is about half
that of sulphur. This is because forests currently sequester 80% of the load of atmospheric
nitrogen on average. The anticipated increase in N saturation in the future will, however, lead
to an increase in the contribution of N to soil acidification (particularly to 1A mobilization),
accompanied by increased leaching of NO3. This will also lead to (appreciably) higher aON
concentrations in the groundwater. If the potential acid deposition remains at current levels,
the ongoing.depletion of the reactive 1A buffer in the forest topsoil is a threat in the longer
term.
The effects of eutrophication on trees are complex. Increased susceptibility to drought, disease
and frost has been observed, in addition to changes to growth (both enhancement and
inhibition occur). As a result, the overall effect in the long term cannot be predicted. Growth
is inhibited at extremely high loads.
Air pollution (03 in particular, and 3HN locally) causes direct damage (reduction in growth,
visible damage) to Dutch forests; however, in practice these effects are considered to be less
important than the effects of eutrophication.
Given that traditional stress factors (e.g. drought, disease, pests) play an important role in
forest health (in addition to exposure to acidifying components and the load of these
components), and that these factors are stochastic, in the future it would be better to evaluate
the effects of acidifying deposition to forest in terms of risk.
4 Effects on non-forest ecosystems
Many of the ecological features in The Netherlands that are of national or international
significance are in dry and wet nutrient-poor areas on and along higher-lying Pleistocene
sandy soils and in the dune areas. Research in the 1980's and 1990's revealed that the
atmospheric deposition of ~ and other substances can have severe effects on ecological
features in these areas. Acidification or eutrophication - or a combination of the two - occur,
depending on the abiotic circumstances of the ecosystem. Much weakly buffered surface water
in The Netherlands (including fens) is very susceptible to acidification from atmospheric
deposition. These effects (a decline in the characteristic aquatic plants) are intensified by the
repercussions of N enrichment.
The repercussions of a combination of acidification and N enrichment are also appreciable in
terrestrial, weakly buffered ecosystems (dry or wet nutrient-poor acidic grasslands). This has
led to the disappearance of many endangered rare species in these ecosystems. This
phenomenon and the dry and wet heathlands being taken over by grasses are largely
attributable to the eutrophying effects of N deposition and result in a massive reduction in the
biological diversity in these nature conservation areas. More than one-third of the area of
heathland in The Netherlands has currently been taken over by grass.
Well buffered but nutrient-poor nature conservation areas can also be susceptible to the
deposition of atmospheric nitrogen. In the chalk grasslands of South Limburg it has been
demonstrated that the eutrophying effects of N are resulting in the increase of one grass
species and the sharp decline in many endangered plants.
01
Table 1 Differences in the results of DPPA-II and DPPA-III.
DPPA-II DPPA-III
Ammonia emission (kton) 1980 248 254
3991 208
Total pot. acid deposition in 1980 i 6700 7215
The Netherlands (mol haly 1)
3991 4280
Contribution of acidifying 20 - 40%
10 - 20%
particles to total deposition to
forest
N~
xOS I yON
Contribution in % (various 1980 571 21 13
components)
3991 361 171 47
iUncertainties in deposition of 51 - 30%
15 - 50%
potential acid in The
iNetherlands
H xOS yON NH x H xOS yON xHN
Increase in deposition to 31 21 21 51 52 33 34 81 a
"average Dutch forest"
compared with deposition to
"average Dutch landscape" (in
%)
Total acid deposition in 2000 2240 2340
(mol ha-ly 1)
Retention in Dutch forest soils 50% 80%
IA saturation .ac 15% .ac 0%
(147 stands)
11
Table 1 Differences in the results of DPPA-II and DPPA-III (continued).
DPPA-II DPPA-III
Critical loads for forest (mol coniferous deciduous coniferous deciduous
ha-~y )1-
Total acid
-! 1A depletion 1200 1500 1650 1800
-~ AI bases b 1400 1400 1900 2450
Exceedance factor ca. 3 2-2.5
Nitrogen
- vegetation changes d 400-1400 600-1400 650-1400 700-1400
- increased susceptibility to 1500-3000 1500-3000
stress
nutrient imbalance 800-1250 1500-2000
-
nitrate leaching 1500 2900 2150 3000
-
Exceedance factor >2.5 >2 c
dry wet
heathland heathland
Critical N loads for heathland 700-1100 1100-1400 1200-1600
(mol ha-ly )1-
Exceedance factor ca. 2
a 5x5 km value.
b In DPPA-II related to the A1/Ca ratio in DPPA-III the A1/Ca+Mg+K ratio was used.
If vegetation changes are examined.
a The lowest value is derived from modelling, the highest is from empirical data.
Acid Atmospheric Deposition dna sti Effects no
Terrestrial Ecosystems ni the sdnalrehteN
G.J. Heij dna J.W. Erisman (Editors) 31
7991 Elsevier Science B.V.
1 INTRODUCTION
..J.G Heij (RIVM)
1.1 The first two phases of the Dutch Priority Programme on
Acidification (DPPA)
In 1985, a start was made in The Netherlands on the Dutch Priority Programme on
Acidification (DPPA), to translate into reality the increasing policy interest in the effects
of air pollution (both acidifying and eutrophying), especially on forests. Up to 1995, a
large part of the research on acidification in The Netherlands was coordinated in the
DPPA. The first phase of the programme (1985 - 1988) was intended to answer the
following questions:
- Which substances are responsible for the damage caused by acid rain, especially to
forests, and to what extent?
- How is this damage inflicted, by what means and in what way?
- How effective are abatement measures?
The second phase of the DPPA was carried out in the period 1988 to 1990. In order to be
able to advise on effective policy measures, the second phase of the programme had to
quantify in detail the deposition to forests and heathland, and the effects thereon, as well
as the role played by the various acidifying components. At the same time, critical loads
and levels of the acidifying components for the soil and in the air had to be determined
and the impacts of possible policy measures had to be modelled. The first two phases of
the DPPA produced the following results (Schneider and Bresser, 1988; Heij and
Schneider, 1991):
1. Numeric data on:
* the load of acidifying components (03, SOx, NOy and NH~) on Dutch forests and
heathlands, their origin and the contributions from the different sectors;
* the various types of effects on forests and heathlands (direct effects, including
visible damage near local sources of emission, and indirect effects, including
nitrogen saturation, soil acidification, deterioration of groundwater quality);