Enhanced growth of the macrophyte Juncus bulbosus in S Norwegian limed lakes. A regional survey

The effects of liming on the aquatic macrophyte vegetation have been investigated in S and SW Norway. In the western part of the study area, Juncus bulbosus was considerably more frequent in the limed than in the unlimed lakes, whilst in the eastern part there were no such differences, and the J. bulbosus populations were generally not so vital. In some southwestern areas a luxuriant and massiv nuisance growth of Juncus bulbosus in the depth zone 0–4 m was recorded. The most vital plants produced up to 1 m long annual shoots, and developed extensive, dense and vital surface mats in shallow areas (depth zone 0–3 m) after 4–5 years. The original isoetid vegetation had disappeared in the areas of dense J. bulbosus populations, and this development seems to be more or less irreversible. The massive J. bulbosus expansion is seen mainly in directly limed lakes with a sometimes visible layer of calcium carbonate on the sediment surface, but enhanched growth has been observed also in lakes downstream liming. The massive expansion is believed to be due to an increase of CO₂ and ammonium in the sediment pore water, combined with a mild climate with a very high precipitation. In many areas the liming has led to an increase in species diversity, and a (re-)establishment of some acid-intolerant species such as Myriophyllum alterniflorum and Potamogeton spp.     

Lime Residues and Metal Sequestration in Sediments of Excessively Limed Lakes

Sediment profiles from ten excessively limed lakes were used to study the occurrence of lime residues as a result of incomplete lime dissolution and the influence of treatment with very high lime doses on the sequestration of metals in lake sediments. The sediment profiles were subjected to multi-element analysis and compared to sediment profiles from previous studies of lakes limed with normal lime doses and untreated reference lakes. The high lime doses were found to result in large lime residues in the sediment, with lime concentrations of up to 70% of the dry sediment in the studied lakes. Excessive liming, like liming with normal doses, was found to cause increased sequestration in sediments of, e.g. Cd, Co, Ni and Zn, metals where the mobility is known to be highly pH dependent, compared to non-limed reference lakes. No effect of liming on the sequestration of Cu, Cr, Pb and V could be shown. The size of the lime dose did not seem to influence the metal sequestration in the sediment, since no difference between the excessively limed lakes and lakes limed with normal doses was found. On the contrary, the large lime residues were found to cause a dilution of the metal concentrations in the sediments, since lime products used for lake liming generally have lower metal concentrations compared to the sediments.     

Evidence of Lower Productivity in Long Term Limed Lakes as Compared to Unlimed Lakes of Similar pH

Ecosystem development in lime-treated waters in Sweden has been followed since 1989 in a programme for integrated studies of the effects of liming acidified waters (ISELAW). Observations after prolonged liming (>10 y) indicate a phosphorus depletion in the limed lakes which contrasts to the increased phosphorus supply often following within the initial years after lime treatment. After prolonged liming, the levels of total phosphorus are lower as compared to neutral reference lakes at identical TOC, and the phosphorus/TOC -ratio is consequently lower in limed lakes. Depletion of dissolved inorganic nitrogen during the summer is also lower in limed as compared to neutral reference lakes. Phytoplankton biomass and species number also lower in the limed lakes as compared to unlimed neutral references. Furthermore the bacterial number per unit TOC is lower in the long term limed lakes, possibly as a result of phosphorus limitation. As to the higher trophic levels, the benthic soft-bottom fauna of limed lakes (specifically the sublittoral fauna) is poorer in terms of species diversity and abundance. Also fish community composition indicates lower productivity in the limed lakes. Taken together there is thus evidence that the long term limed lakes have a lower trophic level than reference lakes.     

Differences in pre- and post-treatment water qualities for twenty limed lakes

Data analyses for pre- and post-treatment levels for 22 analytes from 20 lakes suggest that liming will, in general, increase water levels of ANC, Ca, pH, DIC, conductivity, as well as possibly NO₃ and TN, and will decrease concentrations of many metals, including AL, Zn and possibly Pb. ANC was the single analyte that best characterized pre- and post-treatment differences in these samples. The metal data from these lakes are equivocal due to the fact that most of the limed lakes in this study were only mildly acidic prior to liming and concentrations for many metals were near detection limits. Comparison of pre- and post-treatment water quality conditions in these lakes indicates that liming was successful in improving water quality conditions for fisheries.     

Reliming and reacidification effects on lakewater

Long term liming and reacidification effects were studied in SW Sweden. This report is a concentrated summary. Lake liming reduces toxic levels of Al, Cd and Zn so that pH-sensitive species can survive. But it mobilizes nutrients and causes internal eutrophication, which in shallow lakes may give problems as macrophyte expansion. Reacidification kills much of the flora and fauna, that adapted during limed conditions. The reasons are lowered pH and toxic levels: Al 500 ug/1, Cd 0.4 ug/1 and Zn 50 ug/1. Sediments are fragile and temporary refuges for metals and nutrients. Conclusively, surface waters should be limed before they reach lakes.     

The Swedish liming programme

To mitigate the acidification problem in surface waters the Swedish government is funding a liming programme. Limestone or dolomite powder has been applied to acidified waters since 1976 and on a large scale since 1982. In most projects, limestone is applied directly to the lake, but in several cases supplementary liming is carried out on wetlands and in streams using dosers or other techniques. At present 7,500 Swedish lakes and more than 11,000 kilometers of streams are limed repeatedly with a total of some 200,000 tonne of limestone every year. In 1994 about US$ 25 million was invested by the Swedish government in the liming programme. The biological objective of the liming operations is to detoxify the water so that the natural fauna and flora can survive or recolonize. The chemical aim is to raise the pH above 6.0 and the alkalinity above 0.1 meq/l, which gives an acceptable buffering capacity. In addition, dissolved metals will be deposited after liming, thus reducing their toxicity. Overdosing must be avoided, with natural softwater characteristics being the objective. The chemical and biological effects in water of the liming operations are encouraging. The Swedish liming programme has so far resulted in restoration in 80–90% of the limed surface waters. The fauna often shows an initial dominance by a few species but diversity increases with time, In general, flora and fauna in limed waters show a great resemblance to those in waters not acidified. An undesired effect of liming is significant changes in mosses and lichens after wetland liming.     

In situ net N transformations in pine,fir, and oak stands of different ages on acid sandy soil, 3 years after liming

Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha^-1 of dolomitic lime. Limed plots had a higher net NO _inf3 ^sup- production and a higher potential for NO _inf3 ^sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.     

Integrated studies of the effects of liming acidified waters (ISELAW-programme)

To assess the long-term (>15 years) effects of liming, an integrated programme for studies of the effects of liming in acidified waters (ISELAW) was initiated in 1989. At present, 14 lakes and 14 streams are included in the programme. Although on average of 14 years have passed since the first lime treatment, and the chemical goal of liming have been achieved in all lakes, i.e. to raise pH over 6.0 and alkalinity over 0.1 meq 1–1, changes in biota could still be observed in several of the lakes. Species richness and species diversity was in general not different in the limed lakes as compared to circumneutral reference lakes, although the composition of the fauna did not resembled that of neutral lakes. Among zooplankton, rotifers were still more abundant than expected in limed lakes. The fish communities appeared unstable and the species proportions as well as population structures are changing, partly as a result of re-colonisation of acid-sensitive species after liming. The results indicate that the long-term changes may persist for more than 15 years after liming and emphasise the importance of comparable time series in non-limed lakes.     

Liming restores the benthic invertebrate community to “pristine” state

After liming of twelve acidified rivulets in central Sweden, the fauna increased its mean similarity to the fauna in unlimed non-acidified references. All species which were found after liming were also found in other waters north and south of the limed area. The species composition after liming should thus be considered as typical of the limed geographical area. Before liming, the fauna was characterized by the acid tolerant mayfly Leptophlebia spp. After liming the fauna was characterized by the acid sensitive mayfly genus Baetis, an important food organism for young brown trout. The restoration of the water quality by liming resulted in an apparently “pristine” benthic invertebrate community, enhancing the conditions for salmonid fish.     

Long-Term Ecological Effects of Liming — The Iselaw Programme

The Swedish liming programme was initiated in 1977 to counteract the effects of anthropogenic acidification on aquatic ecosystems until the acid deposition has been reduced. Ecosystem development in limed waters has been followed since 1989 in a programme for integrated studies of the effects of liming acidified waters (ISELAW). The main objectives are to assess a) the long-term ecological effects of liming, b) to what extent ecosystems recover to a pre-acidification state, and c) to elucidate possible detrimental effects of lime treatment. The programme comprises monitoring of water chemistry, phyto- and zooplankton, vegetation, benthic invertebrates and fish in 13 limed and 5 non-limed lakes, and 12 limed and 10 non-limed streams. Paleolimnological studies are performed to reveal pre-acidification lake history. The results show that lime treatment detoxifies the water, although chemical and biological development varies among and within sites. In general the long-term changes are small compared to the initial changes associated with first treatment. Water chemical changes over time are reflected as reduced sulfur concentrations and increased nitrogen concentrations. Treated ecosystems seem not to recover fully to the situation before acidification, and due to re-colonization failure, several species are lacking in the limed waters.     

Planktonic and Littoral Microcrustaceans as Indices of Recovery in Limed Lakes in SE Norway

A two year study of planktonic and littoral microcrustaceans (Cladocera and Copepoda) from 15 lakes in the southeastern part of Norway, Østfold county, document the recovery of acidified lakes due to liming. Six lakes that where limed about 10 years ago, seven acid and two neutral reference lakes, were sampled twice a year (1998 and 1999). One acid lake was limed in autumn 1998. Qualitative nethaul samples from the deepest part of the lake and from the most frequent habitat in the littoral zone were used. The limed lakes had a species composition which indicates that these lakes are about to recover. Species associated with neutral lakes dominates while acid-tolerant species were rare. The acid-sensitive species, Daphnia longispina and D. cristata, were found in the limed lakes. This study shows the usefulness of a low-cost sampling program where microcrustaceans are used as bioindicators of recovery.     

Fumigation-extraction and substrate-induced respiration derived microbial biomass C,and respiration rate in limed soil of Scots pine sapling stands

The effect of liming on microbial biomass C and respiration activity was studied in four liming experiments on young pine plantations. One of the experimental sites had been limed and planted 12 years before, two 5 years before, and one a year before soil sampling. The youngest experimental site was also treated with ash fertilizer. Liming raised the pH_KCl of the humus layer by 1.5 units or less. Microbial biomass was measured using the fumigation-extraction and substrate-induced respiration methods. Liming did not significantly affect microbial biomass C, except in the experiment which had been limed 11 years ago, where there was a slight biomass increase. Basal respiration, which was measured by the evolution of CO₂, increased in the limed soils, except for the youngest experiment, where there was no effect. Ash fertilization raised the soil pH_KCl by about 0.5 unit, but did not influence microbial biomass C or basal respiration. Fumigation-extraction and substrate-induced respiration derived microbial biomass C values were correlated positively with each other (r=0.65), but substrate-induced respiration gave approximately 1.3 times higher results. In addition, the effect of storing the soil samples at +6 and -18°C was evaluated. The effects were variable but, generally, the substrate-induced respiration derived microbial biomass C decreased, and the fumigation-extraction derived microbial biomass C and basal respiration decreased or were not affected by storage.     

Can forest-soil liming mitigate acidification of surface waters in Sweden?

Acidification of surface waters and forest soils is severe in large parts of southern Sweden. The shallow groundwaters are also affected. Large scale liming of surface waters and streams is in operation, often combined with wetland liming to limit the effects of acid episodes, e.g. at snow melt. Acid episodes are perhaps the most severe problem in limed surface waters and in many as yet well buffered waters, because of temperature-layered acid inflow, often superficial. As a result of some investigations, a large scale forest liming programme covering 6.500–10.000 km² was recently suggested. The main objectives of this forest liming programme are to retard cation depletion and to prevent nutrient imbalance and forest decline in acidified areas. This paper deals with the effects of forest soil liming on streams and surface waters. The response of water chemistry is very dependent on hydrological and soil properties. Although pH itself may be little affected by liming, the acidity (or negative ANC) decreases, inorganic Al-species decrease and the Al/BC-ratio increases in the runoff water. Especially interesting is that this is also true during acid episodes. This means that toxicity for acid sensitive biota decreases. These results indicate that large scale liming may have beneficial effects on surface water chemistry. Furthermore, as surface waters are expected to respond to smaller decreases in acid deposition than do forests soils, forest soil liming may allow less frequent liming of lakes. Consequently, forest soil liming in combination with the anticipated emission reductions may have very beneficial results on surface waters in certain areas of Sweden.     

Biomass-Size Distribution of the Aquatic Community in Limed, Circumneutral and Acidified Reference Lakes

Semi-quantitative biomass-size distributions (BSD's) along a joint axis of individual size provided an integrated illustration of aquatic communities sampled at different taxonomic and trophic levels. The approach was applied within the Swedish ISELAW-programme (integrated studies of the effects of liming acidified waters) to test the general hypothesis that aquatic communities in limed lakes are not systematically different from communities in comparable non-limed circumneutral lakes. Input data included pelagic phytoplankton and zooplankton, sublittoral/profundal macroinvertebrates, and benthic fish, within twelve Swedish lakes (six limed, two acidic and four circumneutral reference lakes). The four compartments were sampled on different spatial scales, but each designed for between-lakes comparisons. There were no clear-cut differences in overall size distribution between the three categories of lakes. The mean BSD of limed lakes was indeed more similar to the mean BSD of circumneutral lakes than to that of two acidic lakes. Due to high variation within categories, however, acifidication status alone can not be used for reliable prediction of BSD in a certain lake.     

Implications of natural acidification for mitigation strategies in northern Sweden

Northern Sweden has been regarded as unaffected by acid deposition, but many surface waters in the region fall within the definition of acid surface water (pH < 6.0, alkalinity < 50 mmol_c m^?3) permanently or during episodes. Approximatly 100 MSEK in spent annually on liming in northern Sweden. This paper summarizes our conclusions from a workshop on natural versus anthopogenic acidification held in February 1995. It was shown that organic substances have a key role in determining the acidity of surface waters in the region, although anthropogenic effects are documented in some coastal systems and in the southern mountain range. Sulfide oxidation occurs by the coast. It appears clear that many surface waters that were naturally acidic have been limed to unnatural pH levels. New criteria to screen liming candidates should be developed, and one such model based on water chemistry data is proposed.     

Freshwater liming

Operational liming of surface waters is part of Sweden and Norway's strategy to counteract freshwater acidification caused by air pollutants. Smaller scale liming efforts are performed as research or experimental programs in other countries. Yearly, approx. 300,000 tons of fine-grained limestone (CaCO₃) is spread in lakes and streams and on wetlands to raise the pH in surface water at a cost of approximately 40–50 million $US. The chemical target is set by the biological goals and objectives. A total of over 11,000 lakes and streams are treated on a continuing basis. Dose calculations consider pH, inorganic monomeric Al, dissolved organic matter and the necessary buffering. Lake liming, limedosers at streams and terrestrial liming are used. A mix of different liming techniques is often preferred to get an optimal result. The vast majority of changes are desirable and expected Undesirable effects may appear and damaged wetlands are probably the most serious ones. Cost-benefit analysis show that liming may be profitable for the society. Recovery of the systems can take up to 10–20 years. Liming will in the long run restore the ecosystems but will not make them identical to what may be the original ones. In some cases, complementary measures, e.g. facilitation of recolonization, are necessary to enhance recovery. Reduced emissions of acidifying pollutants according to signed protocols will decrease the need for liming, but still liming is needed for several decades in large regions to preserve biodiversity.     

Effects of acidification and liming on feeding groups of nematodes in coniferous forest soils

Summary Nematodes were sampled in untreated, acidified, and limed plots in a Norway spruce (Fexboda) and a Scots pine (Norrliden) stand. At Fexboda, the total number of nematodes was significantly reduced after the acidification. This reduction was probably due to a shock effect, because the samples were taken only 5 months after an application of 200 kg H₂SO₄ ha^-1 to the forest floor. However, the root/fungal-feeding Aphelenchoides was not reduced, probably because it is more tolerant of high acid concentrations than most other nematodes. At Norrliden, where the samples were taken 7 years after the last application of H₂SO₄, no significant differences were found between the acidified and untreated plots. If the treatment with H₂SO₄ caused similar effects as at Fexboda, the results indicate a recovery of the nematode populations. Decreased predation from lumbricids rather than a recovery of microfloral populations probably allowed this recovery. No marked effect of lime, spread 2 (Fexboda) and 12 years (Norrliden) before the sampling on the numbers of any of the nematode feeding groups was found. This correlated with almost no change in bacterial biomass after liming, while the active fraction of fungal hyphae was unaffected by liming at Fexboda and reduced by liming at Norrliden. A tendency for decreasing numbers of all nematode feeding groups in the limed plots at Norrliden coincided with increasing numbers of lumbricids.     

Recolonization and development of vegetation on mine spoils following brown coal mining in Lusatia

A survey of primary colonization and succession of vegetation on various deposited substrates, littoral and shallow water areas of mining lakes and residual waters of the Lusatian lignite mining district is presented. Dumped substrates are characterized by a high acid potential which is caused by pyrite and marcasite of Tertiary origin. In the process of pyrite oxidation free mineral acids and large quantities of sulphate and bivalent iron are liberated. Residual waters are characterized by extreme acidity with pH values between 1.9 and 3.1 and by extremely high iron contents. Non-linear positive correlations are demonstrated between pH values and free mineral acids and between pH values and free carbonic acids (CO₂) and bivalent iron. In aquatic, semi-aquatic and in terrestrial areas the succession of vegetation can be described by the following five main stages: stage of primary colonization and spontaneous vegetation; stage of monodominant species stands; stage of the formation of vegetation mosaics; stage of the formation of plant associations; final stage of succession. Index species of the terrestrial colonization are Corynephorus canescens and Calamagrostis epigejos, while Juncus bulbosus is the indicator species of aquatic colonization. The succession of vegetation develops in the direction of close-to-nature vegetation conditions which are typical for the heath areas of the Lusatian Lowlands.     

Development of zooplankton in relation to lime treatment in two acidified lakes

Zooplankton has been studied in Lakes Östra Nedsjön and Ömmern (1974–94), two acidified lakes in South-Western Sweden. The former lake was first limed in 1971–73, and secondly in 1982. The first liming increased the pH-level from ca. 5.3 to 6, and the second one from ca. 5.8 to 7–7.5. The pH-value in Lake Ömmern was about 6.1 in 1973, but decreased to 5.3 in 1981, when liming raised the value to 6.5–7. After the first liming in Lake Ö. Nedsjön, the rotatorians represented in average 1% of the total volume of zooplankton. Among the copepods, which made up ca. 22% of the volume, Cyclops was frequent, and both Eudiaptomus gracilis and Heterocope appendiculata were recorded. After the second liming on the other hand the rotatorians increased to in average 28% of the total volume, while the volume of copepods was only ca. 6%. Heterocope disappeared, and Eudiaptomus and Cyclops, usually favoured by liming, were rare. Consequently the supply of larger forms of crustaceans, suitable as fish food was severely reduced. In Lake Ömmern the effects of acidification within the zooplankton were moderate. The species richness was about the same as in unacidified lakes. After liming the development of zooplankton was similar to that in most other limed lakes, i. e. increased frequency of rotatorians, cladocerans and Cyclops spp. In Lake Ö. Nedsjön, however, the small zooplankton volumes and the elimination of copepods was in contrast to the zooplankton development in other limed lakes and in unacidified ones.     

Direct experimental evidence for the contribution of lime to CO2 release from managed peat soil

Liming is a common management practice used to achieve optimum pH for plant growth in agricultural soils. Addition of lime to the soil, however, may cause CO₂ release when the carbonates in lime dissolve in water. Although lime may thereby constitute a significant carbon source, especially under acidic soil conditions, experimental data on the CO₂ release are lacking so far. We conducted a split-plot experiment within a cut-away peatland cultivated with a bioenergy crop (reed canary grass, Phalaris arundinacea L.) with lime and fertilizer treatments to determine effects of lime on the CO₂ emissions from soil and to better understand mechanisms underlying liming effects. Carbon dioxide release was measured over two growing seasons in the field after liming, and complementary laboratory studies were conducted. To differentiate CO₂ derived from lime and biotic respiration the δ¹³C of CO₂ released was determined and the two-pool mixing model was applied. The results showed that lime may contribute significantly to CO₂ release from the soil. In the laboratory, more than 50% of CO₂ release was attributable to lime-carbonates during short-term incubation. Lime-derived CO₂ emissions were much lower in the field, and were only detected during the first (2–4) months after the application. However, a maximum of 12% of monthly CO₂ emissions from the cultivated peatland originated from the lime. Biotic respiration rates were similar in limed and unlimed soils, suggesting that higher pH did not, at least in the short-term, increase carbon losses from cultivated peat soils. Additional fertilization and acidification did not contribute to further CO₂ release from the lime. According to our first estimations about one sixth of the lime applied would be released as CO₂ from the managed peatland, with all lime-derived emissions occurring during the first year of application (equivalent to about 4.6% of the total annual CO₂ losses from the soil in the first year). This suggests that the mass-balance approach as proposed by the IPCC Tier 1 methodology, which assumes that all carbon in lime ends up as CO₂ in the atmosphere, overestimates the emissions from lime. Our study further shows that there is a great risk to overestimate heterotrophic microbial activity in limed soils by measuring the CO₂ release without separating abiotic and biotic CO₂ production.