Journal of Environmental Quality 30:189-193 (2001)
© 2001 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
TECHNICAL REPORT
SURFACE WATER QUALITY
Nitrogen Fertilization Effects on Stream Water Cadmium Concentration
Lars Högbom,
Hans-Örjan Nohrstedt and
Sten Nordlund
SkogForsk—The Forestry Research Institute of Sweden, Uppsala Science Park, SE-751 83, Uppsala, Sweden
Corresponding author (hans-orjan.nohrstedt{at}skogforsk.se)
Received for publication March 6, 2000.
 |
ABSTRACT
|
|---|
High transition metal concentrations were previously unexpectedly observed in soil water extracted by suction lysimeters following forest N fertilization. This observation called for additional measurements to investigate if the finding is a general phenomenon and, if so, whether stream water concentrations of transition metals could increase as a result of N fertilization. The measured levels of Cd in the preliminary findings were well above health limits for drinking water. Hence, the problem could be of major concern. Here we report on soil water and stream water concentrations at two partly fertilized watersheds. All sites were situated in the central part of Sweden. The N application (150 kg N ha-1 in the form of calcium ammonium nitrate) resulted in increased concentrations of nitrate, and a pulse of acidity through the soil profile, which increased the solubility of transition metals (mainly Cd and Zn) and Al. Stream water concentrations of transition metals, on the other hand, were not affected during the studied period by the increased solubility of transition metals in the soil. The data imply that the solubilized transition metals probably insolubilize further down the soil profile, and that there is no risk from forest N fertilization (at normal soil pH levels) of transition metal levels increasing in nearby surface waters. To our knowledge, this is the first time this side effect of N fertilization has been considered.
Abbreviations: CaAN, lime in the form of dolomite mixed with commercial forest fertilizer (ca. 18% dolomite by weight) • TOC, total organic carbon
|
INTRODUCTION
|
|---|
IN two ongoing studies in central Sweden analysis of water from suction lysimeters installed 50 cm below the soil surface detected elevated concentrations of transition metal ions in soil water following N fertilization (Högbom and Nohrstedt, 2000; E. Ring, personal communication, 2000). Of particular interest was the rapid increase of Cd and Zn observed in the soil water. The measured concentrations of Cd were in some cases above the government health limits for the metal (i.e., 5 µg L-1) (e.g., Anonymous, 1993). These findings called for additional measurements in order to find out if the observed increase is a general phenomenon and, more importantly, if adjacent stream water could be subjected to elevated Cd concentrations following practical forest N fertilization.
High concentrations of Cd are hazardous to both the environment and human health. For example, the Itai–Itai disease that appeared in Japan in the early 1960s (resulting in kidney malfunction and signs of oestomalicia) was caused by high Cd concentrations in rice and drinking water (Kobayoshi, 1971). Further health problems caused by Cd in humans are described in detail by various authors (Järup et al., 1998). Cadmium affects the vitamin D and Ca balance in the human body, thus affecting bone strength. Cadmium is also toxic to plants (Prasad, 1995). Excess Cd has been associated with various symptoms, including inhibition of growth and photosynthesis. Cadmium is most probably also carcinogenic.
Forest N fertilization is a common practice in Swedish forestry, in areas not significantly affected by anthropogenic N deposition. Apart from the beneficial effect of N fertilization—increased forest production due to enhanced inorganic N availability in an N-limited system—N fertilization may also have harmful effects on the environment. Fertilization can cause soil acidification and increased nitrate (NO-3) and Al concentrations in runoff water (Tamm, 1991, p. 1–115).
Nitrogen fertilization can theoretically affect soil-solution pH in a number of ways, including: (i) exchange acidity, that is, NH+4 exchanging with protons on the binding sites of soil particles (Nômmik and Wiklander, 1983); (ii) NO-3 leaching accompanied with loss of cations (Nômmik and Wiklander, 1983); (iii) uptake of cations by plants, accompanied by root excretion of H+ (Marschner, 1995); (iv) plant uptake of anions accompanied by root excretion of OH- (Marschner, 1995); and (v) nitrification, which is an acidifying process (Tamm, 1991, p. 1–115). In order to compensate for some of these effects, lime in the form of dolomite is added to commercial forest fertilizers (ca. 18% dolomite by weight). In the following text this mixture is referred to as CaAN. This type of N fertilizer is at present the only one in use in Swedish forestry.
The aim of this study was to investigate whether elevated soil water concentrations of transition metals induced by fertilization would reach stream runoffs, or if the metal ions would be retained further down the soil profile. As far as we know, this aspect of N fertilization has not been considered previously.
|
MATERIALS AND METHODS
|
|---|
Our study had two major experimental components, soil water and runoff water measurements at two watersheds, Furudal and Stugun. In addition, soil samples were taken at both sites and analyzed for transition metals. Both sites were subjected to normal forest fertilization (i.e., 150 kg N ha-1) given once or twice during a rotation period. On these two sites no previous N fertilization has occurred.
The stand at Furudal (61°20' N, 15°17' E) was a 104-yr-old Norway spruce [Picea abies (L.) H. Karst.]–dominated forest. The understorey was dominated by Ericaceous species, mainly bilberry (Vaccinium myrtillus L.). The stand had a standing stem volume of 150 m3 ha-1, and an average annual increment of 4.4 m3 ha-1 yr-1. The soil was a podzolized till overlying a granite bedrock.
The stand at Stugun (63°16' N, 15°15' E) was a 110-yr-old mixed conifer forest (70% Norway spruce and 30% Scotch pine [Pinus sylvestris L.]). The standing volume was 206 m3 ha-1 and the average annual stem-wood production was 4.0 m3 ha-1. The forest was growing on a podzolized till soil overlying gneissic bedrock. Soil water data, prior to the N fertilization, indicated that the soil pH was higher than would normally be expected given the nature of the bedrock of the site, presumably due to glacial movement and transport of material rich in base cations during the last glaciation.
At the two sites, Furudal and Stugun, about 25% of the watershed area was routinely fertilized with a dose corresponding to 150 kg N ha-1, using CaAN as fertilizer (Fig. 1)
. At Furudal, the fertilization (July) was done by helicopter and at Stugun by tractor (July).
View larger version (36K):
[in this window]
[in a new window]
|
Fig. 1. Schematic drawing of the watersheds at Furudal and Stugun, indicating the experimental setup and the sampling points
|
|
At both sites suction lysimeters (P80, Staatliche Porzellan-Manufaktur, Berlin, Germany) were installed 50 cm below the soil surface at the end of May 1998 (i.e., as soon as possible after snowmelt). Six lysimeters were installed at each site in two groups, along a transect extending perpendicularly from both sides of a brook (Fig. 1) and in flat areas characterized as ground water recharge areas with downward water movement and at least 1 m down to the ground water table. Within each group the lysimeters were installed 5 m apart. During the first water sampling occasions the samples were discarded to allow the suction cups to equilibrate before the actual sampling started. The actual sampling of the lysimeters started in June 1998, some samples being taken before the fertilization. In order to obtain a controlled fertilizer effect in the lysimeters, the intention was to cover an area of 3 x 3 m around each lysimeter with plastic sheets. After the broad spread, two of the lysimeters in each group were to be fertilized by a controlled dosage, and the third lysimeter was to be used as an untreated control lysimeter. This concept worked at the Stugun site but at the Furudal site, due to misunderstandings, the broad spread occurred before the lysimeters were covered, hence the applied doses were higher than the planned 150 kg N ha-1.
Stream water was sampled both up- and downstream of the fertilized areas, from the year before the fertilization, which took place in the summer of 1998, to obtain baseline data for the analysis of fertilizer effects on stream water chemistry. Stream water samples were collected on a bimonthly schedule, while soil water samples were taken more sporadically. The water samples were instantly frozen and kept frozen until they were analyzed. The analyses for total organic carbon (TOC) (SS-EN 14841), NH+4 (SS 028 134), NO-3 (SS 028 133), Al (EPA 200.8 mod/AL-NK), Cd (EPA 200.8 mod/CD-NK), Zn (EPA 200.8 mod ZN-NK), Pb (EPA 200.8 mod/PB-NK) and Cu (EPA 200.8 mod/CU-NK) were perfomed by KM Lab AB, a commercial laboratory in Uppsala, Sweden, according to standard methods (standard identification numbers are given in parentheses).
At five points along the lysimeter transect 10 soil cores at each point (core diameter = 6 cm) were taken prior to the fertilization for analysis of ambient transition metal concentrations (Cd, Cu, Pb, Zn) in the humus layer. The 10 samples were put together to form one general sample per point. After sieving (5.6-mm mesh size), air-dried material was extracted with 7 M HNO3. The samples were analyzed by the Department of Soil Science, Swedish University of Agricultural Sciences, Uppsala.
|
RESULTS
|
|---|
At both watersheds, as expected, the NO-3 concentrations in the soil water increased rapidly (Fig. 2a)
. At Furudal, there was a sharp drop in soil water pH from the levels before the N application, while the decrease was much less pronounced at Stugun (Fig. 2b). The concentrations of transition metals and Al also increased, especially at Furudal. At Stugun, the concentrations of transitions metals and Al were much less strongly affected. The concentrations of Al, Cd, and Zn were related to soil water pH and NO-3 concentration (Fig. 3)
. At pH levels below about 4.2 at Furudal, there were clear increases in soil water concentrations of Cd, Zn, and Al. Two high Zn concentrations were found at higher pH levels (around pH 6), which could probably be regarded as outliers. At Stugun, on the other hand, soil water pH was well above 4.2.
View larger version (16K):
[in this window]
[in a new window]
|
Fig. 3. Concentrations of Al, Cd, Zn, and Pb in soil water in relation to soil water pH, and the relationship between NO-3 concentration and pH. Open symbols refer to Stugun, while closed symbols refer to Furudal
|
|
The analysis of humus-layer material revealed that there were no significant differences in transition metal concentrations between the two sites, except for Pb (Table 1). The Pb concentration was significantly higher at Furudal than at Stugun.
View this table:
[in this window]
[in a new window]
|
Table 1. Concentrations of Cd, Cu, Pb, and Zn (mean ± SE) in the humus layer at the Furudal and Stugun sites, and comparison between the sites (Student's t-test, n = 5)
|
|
Before the fertilization the downstream concentrations of most of the studied elements at the Furudal site, except for Cd, Cu, and Zn, were positively related to the upstream concentrations (Table 2). At Stugun a positive relation was found for Al, NO-3, and TOC, in most of the other cases the concentrations were below the detection limits of the analysis. Only in two cases (pH and Zn) did the N application significantly alter the slope of the regression between up- and downstream water concentration of the studied constituents (Table 2).
View this table:
[in this window]
[in a new window]
|
Table 2. Regression between up- and downstream water chemistry before and after the N fertilization event at the Furudal (F) and Stugun (S) sites. The p value refers to the parameter estimate for the slope. The comparison between slopes has been made according to Zar (1984)
|
|
Nitrate increased rapidly downstream of the application after the CaAN fertilization in both cases, but the peak in NO-3 concentration, which occurred soon after fertilization in both watersheds, decreased much more rapidly at Furudal than at Stugun (Fig. 4) . At both sites no elevation in Cd concentrations could be found, the concentrations of that element were in all cases close to or under the detection limit for the chemical analysis.
|
DISCUSSION
|
|---|
The solubility of metal ions in soil is strongly influenced by the soil solution pH. There are a number of studies from acidified sites showing close relationships between soil pH and the solubility of transition metals (e.g., Hornburg and Brümmer, 1993; Filius et al., 1998). But also organic matter content is important for the solubility of Cd (Krishnamurti et al., 1997). In mining areas in Germany, Luwe (1995) found high heavy metal concentrations in the soil solution after extraction with NH4Cl, and that the concentrations of soluble Cd, Ni, and Zn increased with decreasing pH. Nitrogen fertilization of forests could be regarded as being equivalent to soil extraction with NH4NO3, at least in some respects. One very rapid result of such fertilization is ion exchange at the surface of soil particles, which increases the soil water concentration of other cations (e.g., H+ and Al3+) since NH+4 displaces them. Nitrate acts like a mobile counter ion in such cases, promoting downward transport of cations. Our findings of increased Cd concentrations are in agreement with preliminary data from the experimental site at Riddarhyttan (E. Ring, personal communication, 2000) and Hagfors (Högbom and Nohrstedt, 2000) and with other studies of soil pH and heavy metal solubility (e.g., Berdén et al., 1987), all of which describe strong correlations between soil water pH and Cd concentrations. Based on our findings we propose the following model. Forest N fertilization induces a wave of acidity moving downward through the soil profile due to ion exchange at soil particle surfaces. This temporary decrease in soil pH increases the solubility of various metal ions, including Al, Cd, and Zn. Further down in the soil profile, pH increases and the metal ions become less mobile. However, to verify this hypothesis further investigations involving soil and soil water sampling at various depth are needed.
The soil transition metals content data from our studied sites were are all close to or below the average values for Swedish humus layers reported by Andersson et al. (1991) after a large scale screening (except for Zn at both sites, and Pb at Furudal, where the concentrations were higher than average).
Nevertheless, our basic objective with this study, to investigate if the concentrations of transition metals in stream water are affected or not by the N fertilization, was met—no elevated concentrations were found.
The long-term elevation of the NO-3 concentrations at the Stugun site was unexpected. Usually, fertilization by tractor results in much lower spillage into streams and discharge areas in the vicinity of brooks than fertilization by helicopter (e.g., Nohrstedt and Ring, 1991). However, the largest residual fertilizer effect in this study was found at the tractor-fertilized area. There could be a number of reasons for this deviation from the norm, for example nitrification could have been stronger at Stugun because of the apparently higher soil pH, or fertilization of the discharge areas surrounding the brook channels may have differed between the sites. Other possible contributory factors may have been related to weather (e.g., differences in precipitation) or physiography, such as steepness of the slopes.
It was slightly unexpected that the soil water pH decreased despite the presence of dolomite in the CaAN fertilizer. As far as we know, a drop in soil water pH following fertilization with CaAN has not been shown previously. The mishap, that the lysimeters at the Furudal site may have received a double dose 300 kg N ha-1 as compared with the 150 kg N ha-1 that was planned, could at least somewhat have affected the results. Addition of pure ammonium nitrate has previously been shown to reduce pH values in soil water (Nohrstedt, 1992) and both pH values and alkalinity in surface water (Nohrstedt, 1986, 1989). Indeed, the main reason the Swedish forestry sector changed N fertilizer from AN to CaAN was to reduce the probability of fertilization reducing the pH and alkalinity of surface waters. In other studies, amendment with lime has caused a decrease in soil water pH at 50 cm (Nohrstedt, 1992). It is therefore quite possible that the same effect could occur following a normal dose of CaAN fertilization. A similar result was found in an N fertilizer experiment (Högbom and Nohrstedt, 2000).
In conclusion, N fertilization caused a rapid increase in soil water Cd concentration if soil water pH was lowered, but no elevated Cd concentrations were found in adjacent stream water.
|
ACKNOWLEDGMENTS
|
|---|
We would like to thank the two forest companies SCA AB and Korsnäs AB for giving us access to their land to do our measurements, and Mr. Roine Strandin (Furudal), and Mr. Jan Olov Blixt (Stugun) for taking the samples. This study was financially supported by the Gunnar and Birgitta Nordins foundation and the Foundation of Plant Nutrition Research.
|
REFERENCES
|
|---|
- Andersson, A., Å. Nilsson, and L. Håkanson. 1991. Metal concentrations of the mor layer in Sweden as influenced by deposition and soil parent material. Rep. 3990. National Swedish Environment Protection Board, Stockholm.
- Anonymous. 1993. Livsmedelsverkets kungörelse om dricksvatten. (In Swedish.) Livsmedelsverket SLV FS 1993:35. National Food Administration, Uppsala, Sweden.
- Berdén, M., S.I. Nilsson, K. Rosén, and G. Tyler. 1987. Soil acidification extent, causes and consequences–An evaluation of literature information and current research. Rep. 3292. National Swedish Environment Protection Board, Stockholm.
- Filius, A., T. Streck, and J. Richter. 1998. Cadmium sorption and desorption in limed topsoils as influenced by pH: Isotherms and simulated leaching. J. Environ. Qual. 27:12–18.[Abstract/Free Full Text]
- Hornburg, V., and G. Brümmer. 1993. Verhalten von Schwermetallen in Böden: I. Untersuchungen zur Schwermetallmobilität. Z. Pflanzenernaehr. Bodenkd. 156:467–477.
- Högbom, L., and H.-Ö. Nohrstedt. Effects of re-application of nitrogen fertilizer on forest soil-water chemistry, with special reference to cadmium. Rep. no. 2:1-16. SkogForsk, Uppsala, Sweden.
- Järup, L., M. Berglund, C.G. Elinder, G. Nordberg, and M. Vahter. 1998. Health effects of cadmium exposure–A review of the literature and a risk estimate. Scand. J. Work. Health. 24:1–52.
- Kobayoshi, J. 1971. Relation between Itai–Itai disease and the pollution of river water by cadmium from a mine. p. I-25/1-7. In S.H. Jenkins (ed.) Advances in water pollution research. Pergamon Press, Oxford, UK.
- Krishnamurti, G.S.R., G. Cielinski, P.M. Huang, and K.C.J. Van Rees. 1997. Kinetics of cadmium release from soils as influenced by organic acids: Implication in cadmium availability. J. Environ. Qual. 26:271–277.[Abstract/Free Full Text]
- Luwe, M.W.F. 1995. Distribution of nutrients and phytotoxic metal ions in the soil and in two forest floor plant species of a beech (Fagus sylvatica L.) stand. Plant Soil 168/169:195–202.
- Marschner, H. 1995. Mineral nutrition of higher plants. Academic Press, London.
- Nohrstedt, H.-Ö. 1986. Vad händer med bäckvattnet efter gödsling? (In Swedish with English summary.) SST 1:55–65.
- Nohrstedt, H.-Ö. 1989. Some changes of water and soil chemical properties following forest fertilization. Medd. Nor. Inst. Skogforsk. 42:167–176.
- Nohrstedt, H.-Ö. 1992. Soil water chemistry as affected by liming and N fertilization at two Swedish coniferous forest sites. Scand. J. For. Res. 7:143–153.
- Nohrstedt, H.-Ö. and E. Ring. 1991. Brookwater chemistry and leakage after a calcium ammonium nitrate fertilization by tractor. (In Swedish.) Report no. 20. The Institute for Forest Improvement, Uppsala, Sweden.
- Nômmik, H., and G. Wiklander. 1983. Acidifying and basic effects of nitrogen fertilizers on forest soils. (In Swedish with English summary.) Rep. 1657. National Swedish Environmental Protection Board, Solna.
- Prasad, M.N.V. 1995. Cadmium toxicity and tolerance in vascular plants. Environ. Exp. Bot. 35:525–545.
- Tamm, C.-O. 1991. Nitrogen in terrestrial ecosystems. Ecological Studies 81. Spinger–Verlag, Berlin, Germany.
- Zar, J.H. 1984. Biostatistical analysis. Prentice–Hall, Englewood Cliffs, NJ.
This article has been cited by other articles:
|
|
|
|
 
C. G. Crabtree and T. M. Seaman
Suction Lysimeter Modifications to Improve Sampling Efficiency and Prevent Wildlife Damage
Vadose Zone J.,
December 16, 2005;
5(1):
77 - 79.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. A. Aronsson and N. G. A. Ekelund
Biological Effects of Wood Ash Application to Forest and Aquatic Ecosystems
J. Environ. Qual.,
September 1, 2004;
33(5):
1595 - 1605.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
) and Stugun (
) watersheds. Closed symbols refer to lysimeters in the fertilized plots, while open symbols represent the controls. Horizontal bars larger than the symbols indicate ±1 SE