Dag Hongve

Increased colour and organic acid concentrations in Norwegian forest lakes and drinking water – a result of increased precipitation?

Abstract.Recently there have been major increases in water colour and dissolved organic carbon (DOC) in many forest lakes that serve as drinking water reservoirs in the southern part of Norway. We studied changes in the physical and chemical properties in (I) a selected group of lakes and (II) raw water from the municipal waterworks of Oslo since 1983 and 1976, respectively. The largest increase in DOC and water colour occurred between 1997 and 2001. Statistically significant correlations are seen between water colour and accumulated amounts of precipitation, while variation in temperature had no apparent effect. Despite significant reduction in sulphate concentrations in precipitation and lake waters since 1980, the lakes were more acidic in 2000 and 2001 than in previous years. Increases in colour and acidity, together with somewhat minor changes in DOC concentrations, indicate changes in the physical and chemical properties of the natural organic matter (NOM). Alteration in properties of NOM is most probably caused by increased precipitation that has changed the water pathways in the catchments and increased the leaching of organic components from the upper forest floor.

Quantifying the drivers of the increasing colored organic matter in boreal surface waters

Long-term monitoring of surface water quality has shown increasing concentrations of colored dissolved organic matter (CDOM) across large parts of the northern latitudes. This has increased purification costs for domestic water works. Appropriate abatement actions require better knowledge of the governing factors for the increase, and this has motivated a growing scientific interest in understanding the factors and mechanisms promoting the CDOM increase. A proposed water color model for an important raw water source for Oslo, Norway, is based on the precipitations amount and mobile ion concentration. The model explained more than 93% of the temporal variation in CDOM between 1983 and 2008. The model structure was also tested on three adjacent raw water sources and was found to explain 75-82% of the CDOM development throughout the same period. The long-term trend of increasing CDOM was closely related to the decline in sulfate and chloride concentrations in precipitation. Furthermore, interannual fluctuations in CDOM were explained by variation in predominant water flow paths, depending on amounts and intensity of precipitation, both of which are predicted to increase in several parts of the northern latitudes according to climate change scenarios.

Radiocaesium in the sediments of Øvre Heimdalsvatn, a Norwegian subalpine lake

Abstract Lake sediment cores and samples of stream sediments from the catchment of Ovre Heimdalsvatn have been collected. The lake sediments exhibit apparently unsystematic spatial distribution of radiocaesium. This is ascribed to irregular bathygraphy. However, the radiocaesium concentration increased with increasing percentage of organic matter, water content, and with distance from the main inlet. There was no correlation with lake depth. Stream sediments were scarce because of torrential conditions but those present had activities in line with the lake sediments. Therefore they constitute a small potential for further supply of radiocaesium to the lake. Measurements of export from the catchment and retention in the lake show that the total radiocaesium activity in the sediments may remain unchanged or even increase during the years to come.

Chernobyl cesium in the sediments of lake Høysjøen, Central Norway

Abstract The distribution of radiocesium in the sediments of Lake Hoysjoen was analysed 18 months after the Chernobyl fallout event. The concentration in the sediment was similar to concentrations in surrounding terrestrial soils. Local accumulation in a riverine plume is explained by surface runoff from frozen wetland when the snow in the drainage area melted. Most of the radiocesium in the lake was bound in the upper centimetre of sediment.

Decline of acid rain enhances mercury concentrations in fish.

M efforts have been made to reduce sulfur emissions in Europe. Acid rain pollution in Norway has diminished substantially, thanks to the 1979 Geneva Convention on Longrange Transboundary Air Pollution, which was implemented starting in 1983. Parallel with the reduction in acid rain, atmospheric concentrations and deposition of mercury (Hg) have also been reduced. Here, we show that reduced acid rain may have increased dissolved organic carbon in runoff, and enhanced transport of mercury from catchments, and increased in-lake Hg methylation. Together, these enhanced processes result in higher concentrations of methymercury in fish. Mercury pollution in Norway mainly originates from distant sources in other European countries. Similar to acid rain, the long-range atmospheric transport of Hg has declined significantly during the past decades. It was therefore unexpected when a recent nationwide survey showed strong increased Hg concentrations in brown trout (Salmo trutta) and European perch (Perca f luviatilis) in a representative set of lakes in southern Norway. We selected two of these lakes for further case studies based on the availability of historic lake chemistry data. The selection includes the lake with the highest Hgincrease in perch as well as one with a slight decline. The greatest health threat to human consumers comes from methyl-mercury (MeHg), a potent neurotoxin which is easily incorporated into living tissues. The methylation process is a key to the understanding of the potential danger posed by environmental Hg. Environmental Hg is methylated predominantly by naturally occurring bacteria known as sulfatereducing bacteria. The process occurs in saturated soils, anoxic lake waters, and in anoxic sediments, although the factors that control the methylation process are not fully understood. In October 2010 we sampled and analyzed modern sediments from two lakes in Norway (Figure 1).

Nationwide data on municipal drinking water and hip fracture: Could calcium and magnesium be protective? A NOREPOS study

Norway has a high incidence of hip fractures, and the incidence varies by degree of urbanization. This variation may reflect a difference in underlying environmental factors, perhaps variations in the concentration of calcium and magnesium in municipal drinking water. A trace metal survey (1986-1991) in 556 waterworks (supplying 64% of the Norwegian population) was linked geographically to hip fractures from hospitals throughout the country (1994-2000). In all, 5472 men and 13,604 women aged 50-85years suffered a hip fracture. Poisson regression models were fitted, adjusting for age, urbanization degree, region of residence, type of water source, and pH. The concentrations of calcium and magnesium in drinking water were generally low. An inverse association was found between concentration of magnesium and risk of hip fracture in both genders (IRR men highest vs. lowest tertile=0.80, 95% CI: 0.74, 0.87; IRR women highest vs. lowest tertile=0.90, 95% CI: 0.85, 0.95), but no consistent association between calcium and hip fracture risk was observed. The highest tertile of urbanization degree (city), compared to the lowest (rural), was related to a 23 and 24% increase in hip fracture risk in men and women, respectively. The association between magnesium and hip fracture did not explain the variation in hip fracture risk between city and rural areas. Magnesium in drinking water may have a protective role against hip fractures; however this association should be further investigated.

On the chemical water quality in Høylandet, a reference area for acidification research

Chemical and physical water quality parameters havebeen analyzed in a synoptic study of 101 lakes and103 rivers and streams in Høylandet, a coastalcatchment in Central Norway. The area is sparselypopulated and most sites were unaffected by localpollution. Cambro-Silurian sedimentary rocks,porphyric granites and migmatitic gneisses arerepresented within the area and gave variableconcentrations of dissolved salts in surface water.Conductivity varied from 0.6 to 20 mS m-1 and pHfrom 5.0 to 7.6. Salt from sea spray dominated indilute water in more elevated parts of the catchmentwhile chemical weathering products were dominant inlower. The concentrations of all major ions and pHdecreased with increasing elevation. Non marinesulfate occurred in moderate concentrations. pHvalues less than 5.5 were rare and the area as a wholedid not seem to be subject to acidification.

Chemical stratigraphy of recent sediments from a depth gradient in a meromictic lake, Nordbytjernet, SE Norway, in relation to variable external loading and sedimentary fluxes

Cores of recent sediments were sampled along a depth gradient in a 23 m deep kettle lake with stagnant deep waters containing exceptionally high concentrations of dissolved iron and manganese. Sediment cores were taken on two occasions, in 1978 and 1997, before and after an incidence of full circulation. The aims of this study are to see how oxic and anoxic conditions in the water column influence stratigraphy and sediment focusing and, to compare cores from 1979 and 1998 to see how measured element fluxes and external events are reflected in the chemical stratigraphy. Element analyses show characteristic stratigraphic patterns that depend on the ability to undergo redox transformations, sorptive properties and chemical equilibria in the anoxic deep waters and porewaters. In sediments from the oxic part of the lake Al, Cr, Co, Ni, Zn Cu, Cd, and Pb were well correlated. Positive correlations are seen between elements associated with primary production and sulphur. In the anoxic part of the lake most metals were positively correlated with carbonate. Phosphorus correlated positively with iron in sediments from oxic waters and negatively with manganese and iron deep-water sediments. Porewater analyses indicate that recycling from the deep-water sediments was negligible. The stratigraphy of lead agrees with the historic variation in atmospheric input and is used as a chronological marker. Assessed deposition rates agree with measurements in sediment traps. Most elements more than double their rates of deposition towards the deepest point of the lake, while sulphur, manganese and carbonate had maxima around the depth of the redoxcline in the water. Variations in the external loading and variable redox conditions in the deep waters explain variations in the chemical composition of recent sediments.

TOC concentrations in Norwegian lakes: The effect of sea-salts and anthropogenic acid components

Concentrations of organic matter have increased in several lakes on the northern hemisphere since the mid 1970s. This is an important feature, since organic matter is an essential constituent for a range of biological, chemical and physical processes in water bodies. There have been several explanations for this increase, including climate change issues. There has however been no uniform increase o f TOC concentrations in lakes (similar situation in several countries on the northern hemisphere; i.e. EvANS et al. 2006, RouLET et al. 2006, SKJELKVÂLE et al. 2001). Changes in ionic strength in precipitation is mainly been controlled by natural sea-salt episodes and anthropogenic acid rain components, and the ionic strength has declined significantly in precipitation over the past decades, mainly due to the decline in sulphate emission from anthropogenic sources. Since the solubility of organic matter is reduced with increased ionic strength (e.g. TIPPING & HURLEY 1988), we have looked at the effect of changes in ionic strength in precipitation, and hence also in catchment surface waters, in Norwegian lakes. We have also looked at the importance of catchment buffer capacity, since pH might control the solubility o f soi l organic matter (i. e. DE WIT et al. 200 l). Our hypothesis has been that lakes with low buffer capacity, and in where sulphate has been a major inorganic constituent, have been the ones with the most pronounced percentage increase in TOC concentrations. Other types of lakes, either with different chemical composition or with some buffer capacity, were thought to have been less affected by the decline in anthropogenic acid components in precipitation.

Recovery of acidified lakes in Østmarka, Norway

Anthropogenic acidification of aquatic ecosystems has been of great concern for several decades in Norway (e.g. MUNIZ & LEIVESTAD 1980, HENRIKSEN er al. 1988, }OHANNESSEN 1995). Aithough rhe southern parr ofNorway has been most seriously affected, other parts of Norway have also received high loads of acid deposirion from distant sources. A regional survey of 56 prisrine soft warer lakes in a foresr area outside the city ofOslo (0srmarka) in 1983 showed rhar pH varied from 4.5 ro 7.2, sulphare was rhe dominant anion and the buffer capacity was generally low (RIISE & HoNGVE 1987). Anthropogenic deposition was regarded as an imporrant source for sulphate in the 0srmarka lakes in 1983. Inrernational protocols in 1984 and 1994 have led to significant reducrions in atmospheric sulphur emissions. Many countries have also recendy succeeded in reducing emissions of orher air pollurants, such as heavy merals. Imporrant quesrions in this respecr are how, and how quickly, surface waters will respond to changed precipirarion chemisrry? These questions may ro some degree be answered from conceptual warer quality models such as MAGIC (WRIGHT er al. 1991). Model simulations are, however, always based on certain assumptions, and rhe need for empirical dara are srill valid. In nacional monitoring programmes on acidification just a few reference stations are extensively studied. To improve the geographical coverage, regional studies carried at a local and more detailed scale are therefore also needed. In this paper, we compare water chemistry da ta from a selection o f 21 non-limed lakes that were sampled in 1983 with data obtained under as identical condirions as possible in 1996 and 1997.