Rolf D. Vogt

Modelling streamwater chemistry as a mixture of soilwater end-members-a step towards second-generation acidification models

Abstract In present acidification models, soilwater characteristics, though modelled, are seldom checked against field observations. Given that such data are now collected as part of many catchment studies, a technique is developed whereby stream water can be predicted as a mixture of the observed soilwater classes or end-members. Provided that a sufficient set of end-members has been identified, a least-squares technique can be used to estimate the contribution to the stream from each end-member, whenever streamwater samples have been taken. For two catchments, Birkenes in southern Norway and Plynlimon in Mid-Wales, the analysis indicates that the soilwater end-members observed to date are insufficient to explain streamwater chemistry. However, properties of the missing soil waters have been identified, thus facilitating future field work. When an adequate set of soilwater end-members has been established, long-term predictions of changes in streamwater chemistry reduce to the problem of predicting the fate of each end-member. Thus, a separate hydrological submodel is not needed, since the mixing patterns are derived from the end-member analysis.

In Inland China, Rice, Rather than Fish, Is the Major Pathway for Methylmercury Exposure

Background Fish consumption is considered the primary pathway of methylmercury (MeHg) exposure for most people in the world. However, in the inland regions of China, most of the residents eat little fish, but they live in areas where a significant amount of mercury (Hg) is present in the environment. Objectives We assessed concentrations of total Hg and MeHg in samples of water, air, agricultural products, and other exposure media to determine the main exposure pathway of Hg in populations in inland China. Methods We selected Guizhou Province for our study because it is highly contaminated with Hg and therefore is representative of other Hg-contaminated areas in China. We selected four study locations in Guizhou Province: three that represent typical environments with severe Hg pollution [due to Hg mining and smelting (Wanshan), traditional zinc smelting (recently closed; Weining), and heavy coal-based industry (Qingzhen)], and a village in a remote nature reserve (Leigong). Results The probable daily intake (PDI) of MeHg for an adult population based on 60 kg body weight (bw) was considerably higher in Wanshan than in the other three locations. With an average PDI of 0.096 μg/kg bw/day (range, 0.015–0.45 μg/kg bw/day), approximately 34% of the inhabitants in Wanshan exceeded the reference dose of 0.1 μg/kg bw/day established by the U.S. Environmental Protection Agency. The PDI of MeHg for residents in the three other locations were all well below 0.1 μg/kg bw/day (averages from 0.017 to 0.023 μg/kg bw/day, with a maximum of 0.095 μg/kg bw/day). In all four areas, rice consumption accounted for 94–96% of the PDI of MeHg. Conclusion We found that rice consumption is by far the most important MeHg exposure route; however, most of the residents (except those in Hg-mining areas) have low PDIs of MeHg.

Acid deposition and its effects in China: an overview

Acid rain is an increasing environmental problem in China. At present SO2 emission is about 20–22 million tons. However with a growing number of large power plants the long-range transport of air pollutants is expected to increase. The highest acid deposition is near the emission sources. Wind-blown, alkaline soil dust is important in neutralizing the acidity of the emissions, especially in large parts of northern China. In the south, where alkaline soil dust contributes less to acid neutralization, the annual pH in precipitation was below 4.5 at monitoring stations in several provinces and as low as 4.1 in some urban areas. Total sulfur deposition has been estimated to be about 10 g S m−2 year−1 in heavily exposed areas. Negative effects on forests, including die-back, have been reported for relatively small areas near large cities. Since large, regional surveys have not been carried out, there are large uncertainties about effects on a regional level. The high concentrations of gaseous pollutants, especially within and near the cities, are likely to have severe effects on human health as well as on materials and vegetation. Several field and laboratory studies, as well as computer simulations, indicate that acidification of soil and soil water has occurred in the past few decades. This has probably caused elevated concentrations of toxic aluminum in soil water. At present, the toxic effect of Al is likely to be counteracted by high concentrations of calcium at many places. The Chinese authorities have recognized air pollution and acid rain as serious environmental problems, however, there are difficulties in implementing effective measures to reduce the problems. With respect to ecological effects we lack a comprehensive regional overview of the extent of the acid deposition problem in China. Such information is necessary before effective countermeasures can be developed.

The mixing zone between limed and acidic river waters : complex aluminium chemistry and extreme toxicity for salmonids

When liming running waters, dosers must compensate for different flow and water qualities and for the downstream inflow from acid tributaries which creates mixing zones. At a certain point in the mixing zone, a constant or fluctuating chemical disequilibrium will appear due to transformation processes. In laboratory assays, over-saturated solutions of aluminium with ongoing active precipitation of aluminium have been found to be especially toxic to fish. Recent experiments in a mixing zone in the limed River Audna, Norway, have confirmed this phenomenon. Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) smolts were exposed to acid and limed waters and mixtures of the two waters downstream from the point of connection. In the acid tributary (mean values: pH=4.8, Ca=1.3 mg litre (-1)), Ali 236 microg litre(-1)=), LT5) was 22 and 40 h for Atlantic salmon and sea trout, respectively. In the mixing zone (pH=4.8-6.5, Ca=1.2-3.2 mg litre(-1), Ali=50-240 microg litre(-1)), LT50 was 7 h for both species, masking the normal species difference in tolerance. Osmoregulatory failure and rapid gill lesions occurred in the mixing zone as an effect of the transformation of Al into high molecular weight precipitating species. This is the first documentation of the existence of such highly toxic mixing zones in nature, and the results clearly show that the mixing zone is even more toxic to fish than acid aluminium-rich waters.

VARIATIONS IN CONCENTRATIONS OF AQUEOUS ALUMINIUM AND OTHER CHEMICAL SPECIES DURING HYDROLOGICAL EPISODES AT BIRKENES, SOUTHERNMOST NORWAY

Abstract Concentrations of H + , aluminium species, total fluoride, silica, TOC, and major cations and anions were measured in stream- and soil water in the Birkenes catchment during base-flow and high discharge hydrological episodes from 1984 to 1986. Snow and meltwater were also sampled before and during the spring snowmelt seasons. During all the rainfall and snowmelt hydrological events for the five field periods analysed, the H + concentration increased with flow, whereas inorganic monomeric aluminium, Al i (including Al 3+ ), increased with flow only during episodes preceded by relatively low flow periods; during subsequent events Al i remained nearly constant or even decreased. Concentrations of Al i and H + in soil water sampled under saturated conditions were generally stable over time compared to the variations for these species in streamwater. The considerable fluctuations observed for chloride Cl − and sulphate SO 2− 4 concentrations illustrated that displacement of soil water occurred. The results confirm the importance of hydrological factors in determining episodic aluminium response. Large variations in the saturation indices show that equilibrium with either Al(OH) 3 (gibbsite) or Al 2 Si 2 O 5 (OH) 4 (kaolinite, halloysite) cannot control aluminium concentrations in streamwater at Birkenes; the same is true for Al(OH)SO 4 (jurbanite) although the saturation index for this mineral is less variable. Most probably, different controlling mechanisms predominate in the different soil layers, producing different chemical signatures which are picked up in the stream to varying degrees depending on hydrological conditions.

Water quality in the Tibetan Plateau: major ions and trace elements in the headwaters of four major Asian rivers.

The Tibetan Plateau covers an area of about one fourth of Europe, has an average elevation over 4000m above sea level, and is the water sources for about 40% of worlds population. In order to foresee future changes in water quality, it is important to understand what pressures are governing the spatial variation in water chemistry. In this paper the chemistry including major ions and trace elements in the headwaters of four major Asian rivers (i.e. the Salween, Mekong, Yangtze River and Yarlung Tsangpo) in the Tibetan Plateau was studied. The results showed that the content of dissolved salts in these Tibetan rivers was relatively high compared to waters from other parts of the world. The chemical composition of the four rivers were rather similar, with Ca(2+) and HCO(3)(-) being the dominating ions. The exception was the Yangtze River on the Plateau, which was enriched in Na(+), Cl(-), SO(4)(2-) and Li due to silicate weathering followed by strong evaporation caused by a negative water balance, dissolution of evaporites in the catchment and some drainage from saline lakes. The concentrations of heavy metals (Cu, Co, Cr, Ni, Cd, Pb, and Hg) and As, NH(4)(+) were generally low in all the rivers. Anthropogenic impacts on the quality of the rivers were identified at a few locations in the Mekong River and Yarlung Tsangpo basins. Generally, the main spatial variation in chemical compositions of these under studied rivers was found to be governed mainly by difference in geological variation and regional climatic-environment. Climate change is, therefore, one of main determining factors on the water chemical characteristics of these headwaters of Asian major rivers in the Tibetan Plateau.

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.

Increased mortality of fish due to changing Al-chemistry of mixing zones between limed streams and acidic tributaries

The present study is mainly focusing on mortality variations of fish due to changing Alchemistry of mixing zones. An artificial mixing zone was made by pumping water from a limed stream and an acidic tributary into a mixing channel. Atlantic salmon (Salmo salar L.) parr were exposed to the mixed water, limed stream water, and acidic tributary water. Mortality, blood haematocrit and plasma Cl−-concentration were recorded. Neither mortality, nor changes in haematocrit and plasma Cl− were observed when fish were exposed to limed water, while in both acidic and mixed water, mortalities and loss of plasma Cl− were observed. The highest mortality rates were found within the initial part (0 to 20 s) of the mixing zone. Blood haematocrit increased only in fish exposed to acidic tributary water. Our results shows that changes in Al-chemistry and subsequent Al-polymerization occur when acidic tributary water is mixed with limed stream water. We have also demonstrated that the toxicity which can arise in mixing zones are greater than in the original acidic water before mixing. The variations in mortality observed are associated with the quality and quantity of Al-polymerization as well as ageing of the polymers.

Environmental mercury in China: A review

Mercury is a global pollutant that can be transported over long distances and can bioaccumulate. Currently, China is the country that contributes most to atmospheric Hg emissions and has the greatest intentional (industrial) use of Hg. Mercury in the Chinese environment is generally elevated, particularly in air and water bodies. Remote areas in China also show elevated Hg levels in air and water bodies compared to other rural regions in the world. Large river estuaries are often heavily affected by upstream industrial sources. Mercury is also elevated in sediments, a direct result of contamination in river systems. Regardless of the few heavily polluted sites, the urban environment in Chinese cities is comparable to that of other megacities in terms of Hg pollution, considering the size and rapid development of Chinese cities. Studies on Hg in fish showed generally low levels of contamination resulting from low bioaccumulation of Hg in the mostly short food chains. Mercury in rice has recently received increased research interest; elevated concentrations have been reported from rice grown in contaminated areas and may pose a threat to people dependent on such locally grown food. For the general population, Hg exposure from rice is, however, small. In addition, Hg hair concentration in the Chinese population showed generally low levels of exposure to Hg, except for people with special occupational exposure.

Source apportionment of polycyclic aromatic hydrocarbons in soils of Huanghuai Plain, China: comparison of three receptor models.

Receptor models are useful tools to identify sources of a specific pollutant and to estimate the quantitative contributions of each source based on environmental data. This paper reports on similarities and differences in results achieved when testing three receptor models for estimating the sources of polycyclic aromatic hydrocarbons (PAHs) in soils from Huanghuai Plain, China. The three tested models are Principal Component Analysis with Multiple Linear Regression (PCA-MLR), Positive Matrix Factorization (PMF) and Unmix. Overall source contributions as well as modeled ∑PAHs concentrations compared well among models. All three models apportioned three common PAH sources: wood/biomass burning, fossil fuel combustion and traffic emission, which contributed on average 27.7%, 53.0% and 19.3% by PCA-MLR, 36.9%, 27.2% and 16.3% by PMF, and 47.8%, 21.1% and 18.3% by Unmix to the total sum of PAHs (∑PAHs), respectively. Moreover, the spatial evolution of the common sources were well correlated among models (r=0.83-0.99, p<0.001). In addition, the PMF and Unmix models allowed segregating an additional source from the fossil fuel combustion source, with 19.6% and 11.8% contributions to ∑PAHs, respectively. The current findings further validate that different receptor models provide divergent source profiles, which are mainly attributed to both the model itself and/or the underlying dataset. It is therefore generally recommended to apply multiple techniques to determine the source apportionment in order to minimize individual-method weaknesses and thereby to strengthen the conclusion.