Anders Wilander

Dissolved organic carbon trends resulting from changes in atmospheric deposition chemistry.

Several hypotheses have been proposed to explain recent, widespread increases in concentrations of dissolved organic carbon (DOC) in the surface waters of glaciated landscapes across eastern North America and northern and central Europe. Some invoke anthropogenic forcing through mechanisms related to climate change, nitrogen deposition or changes in land use, and by implication suggest that current concentrations and fluxes are without precedent. All of these hypotheses imply that DOC levels will continue to rise, with unpredictable consequences for the global carbon cycle. Alternatively, it has been proposed that DOC concentrations are returning toward pre-industrial levels as a result of a gradual decline in the sulphate content of atmospheric deposition. Here we show, through the assessment of time series data from 522 remote lakes and streams in North America and northern Europe, that rising trends in DOC between 1990 and 2004 can be concisely explained by a simple model based solely on changes in deposition chemistry and catchment acid-sensitivity. We demonstrate that DOC concentrations have increased in proportion to the rates at which atmospherically deposited anthropogenic sulphur and sea salt have declined. We conclude that acid deposition to these ecosystems has been partially buffered by changes in organic acidity and that the rise in DOC is integral to recovery from acidification. Over recent decades, deposition-driven increases in organic matter solubility may have increased the export of DOC to the oceans, a potentially important component of regional carbon balances. The increase in DOC concentrations in these regions appears unrelated to other climatic factors.

Recovery from Eutrophication: Experiences of Reduced Phosphorus Input to the Four Largest Lakes of Sweden

Abstract In-lake concentration changes of phosphorus (P) and nitrogen (N) in lakes Vättern, Vänern, Mälaren, and Hjälmaren in response to diminished input has been examined from the mid-1960s onwards. In the former two deep and oligotrophic lakes with slow water renewal, drastic reductions in P-input from the middle of 1970s caused just minor reductions in P-concentration over a very long time. At the same time accumulation occurred in the water mass of inorganic N and possible reasons are discussed. In the latter two mesotrophic to hypertrophic lakes, two shallow basins in L. Hjälmaren showed slow recovery due to release of P from sediments. The same basins and two basins in L. Mälaren have suffered from N-deficiency, particularly during the pre-phosphorus reduction years, and nitrogen fixation was indicated. In two L. Mälaren basins recovery of in-lake P concentrations was better than expected in comparison to the so-called IMSA-model for lake recovery from nutrient pollution. In the other five lakes/basins chlorophyll concentrations after 20 years were similar compared to those modeled.

Heavy Metal Surveys in Nordic Lakes; Concentrations, Geographic Patterns and Relation to Critical Limits

Abstract In the autumn of 1995, coordinated national lake surveys were conducted in the Nordic countries, including Russian Kola. The 11 metals (Pb, Cd, As, Zn, Cu, Ni, Co, Fe, Mn, Cr, V) investigated in nearly 3000 lakes have generally low concentrations and distinct geographical patterns. Direct and indirect influence of long-range transported air pollution is the major important factor for distribution of Pb, Cd, Zn and to a certain degree Co. Total organic carbon (TOC) concentrations in lakes are important for Fe and Mn but also to a certain degree for As, Cr and V. Bedrock geology is the major controlling factor for Cu and Ni, with the exception of areas around the smelters in the Kola peninsula, where the Cu and Ni concentrations in lakes are very high due to local airborne pollution. Bedrock and surficial geology is also an important factor for controlling the concentrations of As, Co, Cr and V. The results indicate that heavy metal pollution in lakes is a minor ecological problem on a regional scale in the Nordic countries.

TRENDS IN NITROGEN TRANSPORT IN SWEDISH RIVERS

Concern about nitrogen loads in marine environments has drawn attention to the existence and possible causes of long-term trends in nitrogen transport in rivers. The present study was based on data from the Swedish environmental monitoring programme for surface water quality; the continuity of these data is internationally unique. A recently developed semiparametric method was employed to study the development of relationships between runoff and river transport of nitrogen since 1971; the observed relationships were then used to produce time series of flow-normalised transports for 66 sites in 39 river basins. Subsequent statistical analyses of flow-normalised data revealed only few significant downward trends (p ≤0.05) during the time period 1971–1994, and the most pronounced of these downward trends were caused by reduced point emissions of nitrogen. The number of significant upward trends was substantially larger (15 for total-N and 18 for NO3-N). Closer examination of obtained results revealed the following: (i) the most pronounced upward trends were present downstream of lakes, and (ii) observed increases in nitrogen transport coincided in time and space with reduced point emissions of phosphorus or organic matter. This indicated that changes in the retention of nitrogen in lakes were responsible for the upward nitrogen trends. The hypothesis that nitrogen saturation of forest soils has caused a general increase in the riverine export of nitrogen from forested catchments in Sweden was not confirmed. Neither did the results indicate that improved agricultural practices have reduced the export of nitrogen from agricultural catchments.

Estimating organic acid dissociation in natural surface waters using total alkalinity and TOC

Abstract Organic acid dissociation has usually been estimated from the difference between measured cations and anions (the anion deficit approach). An alternative is to use alkalinity titrations and an estimate of strong organic acids from TOC as an independent measure of organic acid dissociation (the CBALK approach). This approach may reduce the potential for errors relative to the anion deficit approach, which relies on summing up all measured constituents. Organic acid dissociation in a set of Swedish surface water samples from 700 different lakes, as well as 200 samples from 11 streams was predicted using a triprotic analogue model with buffering characteristics similar to those of the widely used “Oliver” model (OTM), but with a lower site density of organic acids. The average equilibrium pH of the samples in the weakly buffered pH range of 4.7–6.7 could be predicted more precisely (±0.16 pH units) using the CBALK approach, than when using the usual anion deficit approach (±0.41 pH units). The study supports the general applicability of models similar to the empirical OTM for predicting the dissociation of natural organic acids on a regional scale.

Effects of acidification on the concentrations of heavy metals in running waters in Sweden

Heavy metals in running water are analysed within the Swedish Surface Water Monitoring Programme at about 80 stations. Data for selected rivers and brooks has been used to assess the effect of soil acidification on the concentrations of metals in waters. In southern Sweden, acidification shows a significant effect on Zn and Cd. In the upper parts of the drainage areas, there is an marked increased leakage of these metals from soils to waters indicated by elevated concentrations of Zn and Cd in brooks and also by high maxima during periods of low pH values. The increased leaching from forest soils also influences the concentrations in rivers in southern Sweden. During periods of high water flow, the pH values of the rivers decreases and the concentrations of Zn and Cd increases. At pH levels of 6.2–6.5 the concentrations of these metals are mostly 2–5 times higher as compared to pH levels of about 7.0. Since high concentrations of Zn and Cd coincides with high water flow, the transport of these metals has most certainly increased several times compared to the pre-industrial period. Hence, the by far most important human impact on the loading of Zn and Cd on the marine areas, surrounding southern Sweden is the increased leakage of these metals due to acidification. In northern Sweden the effects of acidification on Zn and Cd are less evident. In general, the concentrations of these metals are lower and the connection between pH and these metals are much less significant in the rivers. The links between acidification and the concentrations of Pb and Cu in the watercourses are comparatively much weaker. These two metals are more related to the content of organic matter in the waters and a possible effect of acidification is overshadowed by natural transport processes in soils and waters.

Validating a Simple Equation to Predict and Analyze Organic Anion Charge in Swedish Low Ionic Strength Surface Waters

Acid neutralising capacity (ANC) is substituted by CBALK, a term that has been theoretically introduced in the early 1990s, to evaluate a simple pH equilibrium model used for Swedish surface waters. The CBALK approach with its simple three pKa organic acid analogue is re-evaluated with a new data set of 900 stream water samples. End-point alkalinity and TOC suffice to predict air equilibrated pH in the range 4.5 to 7.5 within 0.08 pH units. This is equivalent to an error in the charge balance of about 5 ueq L−1. In the studied pH range it renders more precise predictions than when using ANC. The model equations can be used to estimate the effect of organic carbon or carbon dioxide on ambient pH during episodes as well as for sample quality control.

Chemical conditions in acidic water in the Plain of Reeds, Viet Nam

Abstract In the Plain of Reeds in the Mekong delta (Viet Nam) about 600,000 ha is covered by pyrite soils. At the beginning of the rainy season acidic material is leached from the soil to water in the canal system. Evaluation of water chemistry data indicate that jurbanite is the acidic mineral which is accumulated at the soil surface and subsequently leached to the canals during the early rains. The results obtained correspond well with published results for acidic soils in other areas. It has earlier been assumed that Fe(II) is the major acidic ion in the water and oxidized slowly. The measurements made in acidic canal indicate that Fe(II) is oxidized to Fe(III) according to a pseudo first-order reaction with a half-time of about 4 h and precipitated as hydroxide. Instead aluminium, produced by weathering, has proved to be the most acidic ion in the water.

Time series of long-term annual fluxes in the streamwater of nine forest catchments from the Swedish environmental monitoring program (PMK 5).

International cooperation has contributed to major declines in SO(2) emission and S deposition during the last two decades in Europe. The chemical recovery from already anthropogenically acidified sites however, has been slow. In the present paper, long-term trends of chemical fluxes from nine selected forested reference catchments were studied, to detect recovery from acidification and leaching of S and base cations (BC). A decline in S deposition resulted in a decreased flux of non-marine sulfate (SO(4)*) in seven of nine streams, with statistically significant changes in four. The two cases with slight increases in SO(4)* flux resulted from increasing water flow. The SO(4)* decrease was followed by a recovery from acidification in terms of increased ANC flux in those sites in southern Sweden that were chronically acidified. The recovery was probably slowed down by leaching of SO(4) from the soil and a decrease in the flux of BC. A better understanding of the processes for leaching of SO(4) and BC is needed in order to quantify the need for further restrictions of sulfur emissions to allow a long term recovery of acidified catchments. The flux calculations available from small catchments such as those in this study, are of value for that understanding.

Effects of Reduced S Deposition on Large-Scale Transport of Sulphur in Swedish Rivers

Sulphur deposition has diminished by about half during the last decade. For Sweden consistent estimates of total deposition are available for 1991, and 1994–97. Based on these estimates and using GIS the deposition for large drainage areas during one decade are calculated. These values are compared with the measured S transport in rivers covering about 85% of the Swedish territory, thus enabling the construction of a S budget for Sweden. The majority of the drainage areas have a net loss of S, which can be attributed to desorption of S in the soil. During the period of high deposition in the 1980:s (>60 meq m-2 yr-1 in southern Sweden) S was adsorbed, and retarded acidification. There still seems to be some S-adsorption in the northern parts of the country, where the deposition is less (now <20 meq m-2 yr-1).