This article analyses the success and failure factors underlying smallholder farmers’ resilience to drought in Sub-Saharan Africa based on a literature review of the period 2007–19. The analysis is guided by transformation theory, which states that transformation requires adequate preconditions in three spheres: practical, political and personal. While significant progress has occurred in the practical sphere, only moderate change characterizes the political sphere, and the most limited progress is within the personal sphere. We argue that increasing drought resilience requires innovative solutions, including components from all transformation spheres. Interactions with local stakeholders and the empowerment of smallholder farmers are essential.

Peatlands play a key role in the carbon cycle by being a considerable source of atmospheric methane. Thus, an understanding of the microbial production of methane is important in relation to environmental changes of peatlands. We applied real-time PCR on the mcrA gene and transcript to investigate the peat methanogen community response to the combined effect of 18 years of simulated warming and deposition of nitrogen (N) and sulphur (S) at a boreal oligotrophic mire in Sweden. The long-term effects of the experimental treatments on the methanogens was highly dependent on interactions between the treatment factors Enhanced N deposition amplified the effect of warming, resulting in a further increase of the abundance of active methanogens. The effect of the perturbations was modulated by the depth horizon, with the strongest effect at the water level, where the interaction between enhanced N and S deposition, and warming, resulted in an increase of active methanogens. These results indicate that increasing average temperatures and simultaneously higher N deposition rates will substantially increase the methanogenic activity in northern ombrotrophic peatlands. These findings strongly highlight the importance of accounting for any possible interactive perturbation effects when investigating the response of peat methanogens to environmental change.

Sediments underlying hypoxic or anoxic water bodies constitute a net source of phosphorus to the bottom water. This source has the potential to enhance eutrophication. Benthic fluxes of dissolved phosphorus, iron and manganese were measured from hypoxic, normoxic, and normoxic bioturbated by the invasive polychaete Marenzelleria arctia sediment in a mesocosm experiment. The highest benthic phosphorus efflux was detected in mesocosms with the hypoxic treatment. Normoxic, bioturbated sediments led to weaker retention of phosphorus compared to oxic, defaunated sediments. Both iron and manganese fluxes increased under bioturbated conditions compared to defaunated sediments. This study shows that re-oxygenation of previously anoxic coastal sediments enhance phosphorus retention in the sediments. Colonisation by M. arctia induce strong mobilisation of iron and manganese due to its intense bioirrigation, which facilitates organic matter degradation and decreases the phosphorus retention by metal oxides in sediment.

In the present study, we investigated how sediment fluxes of dissolved silica (DSi) and dissolved inorganic phosphorus (DIP) were affected by dissolved oxygen (DO) availability in bottom waters. Sediments from two sites in the Baltic proper were incubated under changing oxygen conditions. Our results show that when DO availability decreased from oxic to hypoxic level, the average DSi fluxes decreased significantly at the two sites from 2.12 +/- 0.04 to 0.87 +/- 0.18 and from 2.37 +/- 0.09 to 1.91 +/- 0.55 mmol Si m(-2) d(-1), respectively. Average DIP fluxes increased significantly at one site from 0.06 +/- 0.01 to 0.14 +/- 0.02 mmol P m(-2) d(-1), but not at the other (from 0.06 +/- 0.01 to 0.07 +/- 0.01 mmol P m(-2) d(-1)). These results indicate that a change from highly oxic to hypoxic conditions in bottom waters may decrease DSi fluxes and increase DIP fluxes. However, sediment characteristics can lead to spatial differences in the response of DSi and DI Pfluxes to oxygen availabilit.

Understanding fluid rheology is important for optimal design and operation of continuous stirred-tank biogas reactors (CSTBRs) and is the basis for power requirement estimates. Conflicting results have been reported regarding the applicability of total solid (TS) and/or total volatile solid (TVS) contents of CSTBR fluids as proxies for rheological properties. Thus, the present study investigates relationships between rheological properties of 12 full-scale CSTBR fluids, their substrate profiles, and major operational conditions, including pH, TS and TVS contents, organic loading rate, hydraulic retention time, and temperature. Rheology-driven power requirements based on various fluid characteristics were evaluated for a general biogas reactor setup. The results revealed a significant correlation only between the rheological fluid properties and TS or TVS contents for sewage sludge digesters and thermophilic co-digesters (CD), but not for mesophilic CD. Furthermore, the calculated power requirements for pumping and mixing, based on the various fluid characteristics of the studied CSTBRs, varied broadly irrespective of TS and TVS contents. Thus, this study shows that the TS and/or TVS contents of digester fluid are not reliable estimators of the rheological properties in CSTBRs digesting substrates other than sewage sludge.

This article deals with the interrelationship between overall chemical speciation of S, Fe, Co, and Ni in relation to metals bio-uptake processes in continuous stirred tank biogas reactors (CSTBR). To address this topic, laboratory CSTBRs digesting sulfur(S)-rich stillage, as well as full-scale CSTBRs treating sewage sludge and various combinations of organic wastes, termed co-digestion, were targeted. Sulfur speciation was evaluated using acid volatile sulfide extraction and X-ray absorption spectroscopy. Metal speciation was evaluated by chemical fractionation, kinetic and thermodynamic analyses. Relative Fe to S content is identified as a critical factor for chemical speciation and bio-uptake of metals. In reactors treating sewage sludge, quantity of Fe exceeds that of S, inducing Fe-dominated conditions, while sulfide dominates in laboratory and co-digestion reactors due to an excess of S over Fe. Under sulfide-dominated conditions, metals availability for microorganisms is restricted due to formation of metal-sulfide precipitates. However, aqueous concentrations of different Co and Ni species were shown to be sufficient to support metal acquisition by microorganisms under sulfidic conditions. Concentrations of free metal ions and labile metal complexes in aqueous phase, which directly participate in bio-uptake processes, are higher under Fe-dominated conditions. This in turn enhances metal adsorption on cell surfaces and bio-uptake rates.

Natural chlorination of organic matter is common in soils. The abundance of chlorinated organic compounds frequently exceeds chloride in surface soils, and the ability to chlorinate soil organic matter (SOM) appears widespread among microorganisms. Yet, the environmental control of chlorination is unclear. Laboratory incubations with Cl-36 as a Cl tracer were performed to test how combinations of environmental factors, including levels of soil moisture, nitrate, chloride, and labile organic carbon, influenced chlorination of SOM from a boreal forest. Total chlorination was hampered by addition of nitrate or by nitrate in combination with water but enhanced by addition of chloride or most additions including labile organic matter (glucose and maltose). The greatest chlorination was observed after 15 days when nitrate and water were added together with labile organic matter. The effect that labile organic matter strongly stimulated the chlorination rates was confirmed by a second independent experiment showing higher stimulation at increased availability of labile organic matter. Our results highlight cause-effect links between chlorination and the studied environmental variables in podsol soil-with consistent stimulation by labile organic matter that did overrule the negative effects of nitrate.

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Lakes are major sources of methane (CH4) to the atmosphere that contribute significantly to the global budget. Recent studies have shown that diffusive fluxes, ebullition and surface water CH4 concentrations can differ significantly within lakes—spatially and temporally. CH4 fluxes may be affected at longer scales in response to seasons, temperature, lake mixing events, short term weather events like pressure variations, shifting winds and diel cycles. Frequent measurements of fluxes in the same system and integrated assessments of the impacts of the spatio-temporal variability are rare. Thereby, large scale assessments frequently lack information on this variability which can potentially lead to biased estimates. In this study, we analysed the variability of CH4 fluxes and surface water CH4 concentrations across open water areas of lakes in a small catchment in southwest Sweden over two annual cycles. Significant patterns in CH4 concentrations, diffusive fluxes, ebullition and total fluxes were observed in space (between and within lakes) and in time (over diel cycles to years). Differences observed among the lakes can be associated with lake characteristics. The spatial variability within lakes was linked to depth or distance to stream inlets. Temporal variability was observed at diel to seasonal scales and was influenced by weather events. The fluxes increased exponentially with temperature in all three lakes, with stronger temperature dependence with decreasing depth. By comparing subsets of our data with estimates using all data we show that considering the spatio-temporal variability in CH4 fluxes is critical when making whole lake or annual budgets.

Students’ problems with learning science in school have been documented for a long time. Differences in student interest in and attitudes towards science due to gender and age are well documented. Fewer studies have focused on the details at a content level. This paper presents a statistical analysis of student interest in specific content areas and combines this with student experience of science and science-related activities outside school. The result shows that interest and experience are significantly linked and influence student choices for upper secondary education. The results are presented on both a detailed content and experience level, and are discussed in relation to the purpose of compulsory science education and in relation to experiences outside school. The study is an important addition to the discussion about establishing a science education curriculum that can both prepare students for future science studies and meet the need for a public understanding of science.

A common way of quantifying and communicating climate vulnerability is to calculate composite indices from indicators, visualizing these as maps. Inherent methodological uncertainties in vulnerability assessments, however, require greater attention. This study examines Swedish agricultural vulnerability to climate change, the aim being to review various indicator approaches for assessing agricultural vulnerability to climate change and to evaluate differences in climate vulnerability depending on the weighting and summarizing methods. The reviewed methods are evaluated by being tested at the municipal level. Three weighting and summarizing methods, representative of climate vulnerability indices in general, are analysed. The results indicate that 34 of 36 method combinations differ signifi- cantly from each other. We argue that representing agricultural vulnerability in a single composite index might be insufficient to guide climate adaptation. We emphasize the need for further research into how to measure and visualize agricultural vulnerability and into how to communicate uncertainties in both data and methods.

This paper reports on Swedish results from a worldwide research project concerned with the Interest and Recruitment in Science Education (the IRIS-International study) together with results from a longitudinal national study on girl's views on out of school experience in science and technology in upper secondary education. The studies are framed in the structural situation of the Swedish educational system. The results show that there are reform and policy effects to consider in the discussion of recruiting more students in STEM. Interest in the subject, earlier school experience, achievement and teacher feedback is found to be important for educational choice in STEM. Specifically girls point out societal relevance as important. In addition there are elements outside the school setting with importance for educational choice. Moreover, girls point out visits to a museum and watching films and boys popularized forms of science and computer games. All students consider TV and activities outside school as important for their educational choice in STEM. When trying to implement outside school experience with girls in a longitudinal study in upper secondary education the interplay with school subject teaching is identified as missing. The friction between subject teaching in schools and connections with the surrounding world is proposed as important for future studies.

Ombrotrophic raised bogs are nutrient poor acidic peatlands accumulating organic matter. They are widely spread on northern latitudes and are substantial sources of methane emissions to the atmosphere being of great concern from a climate change perspective. We investigated the methanogen community composition along microtopographic gradients within three bogs in Scandinavia, receiving different amounts of nitrogen precipitation. Methanogenic community analyses by terminal restriction fragment length polymorphism of the mcrA gene showed different profiles among the three sites, while no in- fluence of the microtopographic gradients was observed. Peat temperature and dissolved organic carbon were the major edaphic variables explaining 38% of the variation of the methanogenic community di- versity among the bogs. The family Methanoregulaceae (hydrogenotrophic methanogens) showed the largest relative proportion and highest activity in all three sites. Quantitative PCR of the mcrA gene and transcripts showed that the most northern site, receiving the lowest atmospheric nitrogen load, had significantly lower abundance and activity of methanogens (4.7 106 and 2.4 104 mcrA copies per gram of soil, respectively), compared to the most southern site (8.2 107 and 4.6 105 mcrA copies per gram of soil, respectively), receiving the highest nitrogen load. No patterns of the mcrA gene and tran- script abundances were observed along the microtopography. The results indicated that the difference in occurrence of methanogens is mainly due to geoclimatological conditions rather than site intrinsic microtopographic variation. The study further suggests that environmental changes on the site intrinsic topography will not affect the methanogenic activity, while increasing average temperatures in Scan- dinavian ombrotrophic raised bogs might contribute to an increase of the methanogenic archaeal activity resulting in an increase of methane production. 

The effects of sulfide removal by addition of Fe on chemical speciation of Co and Ni and how it may affect the microbial metal uptake processes in biogas reactors were assessed. The influent Fe concentration was increased in a semi-continuous stirred tank biogas reactor fed with sulfur-rich stillage. Performance of the reactor, turnover kinetics of volatile carboxylic acids as well as changes in the chemical speciation of Co and Ni were investigated. The results demonstrated that approximately 95% decrease in gaseous hydrogen sulfide content of the biogas, which was caused by addition of Fe, had no apparent effects on methane production and process stability, while it enhanced the short-term turnover time of propionate. Sulfide removal decreased the overall solubility of Co and Ni partially by 1) lowering the formation of the dominant Co- and Ni-sulfide complexes in the aqueous phase and 2) by promoting processes such as adsorption and coprecipitation of Co and Ni with FeS(s). Combination of chemical speciation and bio-uptake models suggested that a higher concentration of free Co and Ni ions is achieved at low sulfide concentrations which favors the active bio-uptake of these metals. However, it was argued that the decrease in soluble metal concentrations, which was induced as a result of the addition of Fe, demotes potential diffusion-driven, passive metal uptake by microorganisms.

The objective of the present study was to assess major chemical reactions and chemical forms contributing to solubility and speciation of Fe(II), Co(II), and Ni(II) during anaerobic digestion of sulfur (S)-rich stillage in semi-continuous stirred tank biogas reactors (SCSTR). These metals are essential supplements for efficient and stable performance of stillage-fed SCSTR. In particular, the influence of reduced inorganic and organic S species on kinetics and thermodynamics of the metals and their partitioning between aqueous and solid phases were investigated. Solid phase S speciation was determined by use of S Kedge X-ray absorption near-edge spectroscopy. Results demonstrated that the solubility and speciation of supplemented Fe were controlled by precipitation of FeS(s) and formation of the aqueous complexes of Fe-sulfide and Fe-thiol. The relatively high solubility of Co (similar to 20% of total Co content) was attributed to the formation of compounds other than Co-sulfide and Co-thiol, presumably of microbial origin. Nickel had lower solubility than Co and its speciation was regulated by interactions with FeS(s) (e.g. co-precipitation, adsorption, and ion substitution) in addition to precipitation/dissolution of discrete NiS(s) phase and formation of aqueous Ni-sulfide complexes.

Silica (Si) is a key nutrient for diatoms. Over the last century, Si concentrations within the Baltic Sea decreased significantly. This is mainly attributed to ongoing eutrophication, increased production and subsequent deposition and accumulation of organic matter including biogenic silica. As a consequence of the eutrophication, hypoxic and anoxic bottom waters have spread affecting nutrient cycling. This paper looks at the potential impact of oxygen on dissolved silica (DSi). It presents a statistical analysis of the relationship between DSi concentrations and oxygen conditions (O-2) in the deep water of the Baltic Proper. The idea is not new, but this is the first time it is studied in more detail in this area. Regression analysis shows that DSi concentrations decrease significantly with O-2 concentrations, and that the major intrusion of saline water in 1993 strengthened this relationship. Increased hypoxia will significantly affect the cycling of Si in the Baltic Sea.

Despite the general assumption that nitrogen fixed by associated cyanobacteria will be readily utilised for growth by the Sphagnum, no empirical evidence is available in the literature. Therefore the effects of nitrogen transfer from cyanobacteria associated with S. riparium were investigated. less thanbrgreater than less thanbrgreater thanCultivation of S. riparium with and without cyanobacteria was performed under laboratory conditions for 57 days. less thanbrgreater than less thanbrgreater thanWe show that nitrogen fixation by cyanobacteria associated with Sphagnum mosses, influences moss growth by transfer of fixed nitrogen to the moss. More than 35 % of the nitrogen fixed by cyanobacteria was transferred to the newly formed moss biomass and resulted in an increase in the growth of Sphagnum biomass compared to the controls. The variation in the increase of nitrogen content explained 76 % of the biomass increment. less thanbrgreater than less thanbrgreater thanHence, nitrogen fixation will have immediate effect on the carbon fixation by Sphagnum. This shows that factors regulating nitrogen fixation will have a direct effect on the role of Sphagnum dominated ecosystems with respect to carbon cycling.

Rheological properties of reactor liquids are important for the construction and intensity mixing systems in biogas reactors. Most frequently the total solids content (TS) is used as a proxy to guide in these matters. In order to establish a more comprehensive basis the rheology of twelve full-scale continuously stirred tank biogas reactors was characterized and related to differences in substrate composition and operational conditions. Reactor material from eight mesophilic (36−38°C) and four thermophilic (52−55°C) reactors were sampled at two occasions. The feedstocks of nine of these reactors were included in the analysis. Two of the mesophilic and one of the thermophilic digesters were fed sewage sludge (SS), while the others digested mixtures of organic matter including slaughterhouse waste (SHW), food industry waste (FIW), fat, manure, fodder residues and the organic fraction of municipal solid waste (OFMSW). The organic loading rates ranged 2.4−3.6 kg VS m^-3 d^-1 and the TS of the reactor materials were at 1.8−5.3% . The rheological characteristics of the reactor liquids were interpreted from flow- and viscosity curves as well as from determination of dynamic viscosity, limit viscosity, yield stress, flow behavior and consistency index.

The fluid dynamic- and limit viscosities of the fluids ranged 5−600 mPa*s and 4−40 mPa*s, respectively. All reactor fluids except one from a thermohilic CD-reactor showed pseudoplastic behavior, since they became thinner with increasing shear stress until the viscosity reached a plateau of limit viscosity. In addition the mesophilic CD reactors were strongly thixothropic, i.e. they exhibited partial structure recovery. The results from the analysis of the thermophilic CD-reactors indicated a weak dilatant behavior, i.e. shear thickening behavior.

The results showed differences in viscosity despite similar TS-content for several reactor liquids. From this survey it is clear that the TS content of biogas reactor fluids is not a good estimator of the fluid viscosity and that the fluid characteristics vary as a result of substrate composition and process operation conditions.

The amount of methane (CH(4)) emitted from northern lakes to the atmosphere is uncertain but is expected to increase as a result of arctic warming. A majority of CH4 is thought to be released through ebullition (bubbling), a pathway with extreme spatial variability that limits the accuracy of measurements. We assessed ebullition during early and late winter by quantifying bubbles trapped in the ice cover of two lakes in a landscape with degrading permafrost in arctic Sweden using random transect sampling and a digital image processing technique. Bubbles covered up to similar to 8% of the lake area and were largely dominated by point source emissions with spatial variabilities of up to 1056%. Bubble occurrence differed significantly between early and late season ice, between the two lakes and among different zones within each lake (p < 0.001). Using a common method, we calculated winter fluxes of up to 129 +/- 486 mg CH(4) m(-2) d(-1). These calculations are, on average, two times higher than estimates from North Siberian and Alaskan lakes and four times higher than emissions measured from the same lakes during summer. Therefore, the calculations are likely overestimates and point to the likelihood that estimating CH(4) fluxes from ice bubble distributions may be more difficult than believed. This study also shows that bubbles quantified using few transects will most likely be unsuitable in making large-scale flux estimates. At least 19 transects covering similar to 1% of the lake area were required to examine ebullition with high precision in our studied lakes.

A budget model covering the Baltic Sea was developed for the time period 1980-2000 to estimate water and dissolved silica (DSi) fluxes as well as internal DSi sinks/sources. The Baltic Sea was resolved by eight basins, where the largest basin - the Baltic Proper - was divided laterally into north/west and southern/east parts as well as vertically to take into account the existence of the permanent halocline. The basins demonstrated rather different patterns with regard to silica cycling. The Gulfs of Finland and Riga together with the northernmost basins, Bothnian Bay and Bothnian Sea. are distinguished by substantial specific rates of silica removal accounting for 1.6-4.9 g Si m(-2) yr(-1). Bearing in mind the large total primary production, the basins comprising the Baltic Proper with the specific removal rates 0.2 and 1.2 g Si m(-2) yr(-1), do not appear as regions with a high silica accumulation. The Arkona and the Kattegat mainly behave as regions of rapid through-flows. These results point out the northernmost Gulf of Bothnia, the Gulfs of Riga and Finland as areas with a larger share of biogenic silica accumulation than in the Baltic Proper. It is attributed to hydrographic and hydrochemical features. An estimate of diatom export production was made for the Baltic Proper showing that the diatom contribution accounts for 19-44% of the net export production.

Previous trend studies have shown increasing nitrogen and phosphorus as well as decreasing silica concentrations ill the water mass of the Baltic Sea. This has had an impact on the amount of primary production, but also on the quality and succession of plankton species. Present study examines the spatial and temporal patterns of potential nutrient limitations in the Baltic Sea for the time period 1970-2000. Generally, low concentrations of DSi can limit the diatom blooms and such conditions are found in the Gulf of Riga and Gulf of Finland during spring and summer. Nutrient ratios, DSi:DIN, DSi:DIP and DIN:DIP, are often used to determine which nutrient may limit the primary production. Annual long-term temporal trends of silica to inorganic nitrogen and phosphorus respectively show consistent decreasing patterns. The largest slopes are detected during spring and summer for DSi: DIN and during spring for DSi:DIP ratios. For the DIN:DIP ratio significant slopes are only found in a few locations despite increasing levels for both nutrients, displaying a large variation in trends. In the open Baltic Proper the present trends are positive during winter and negative during spring and autumn. Gulf of Finland and Gulf of Riga are areas where both DSi:DIP and DSi:DIN ratios are found close to the Redfield ratios for diatoms. Together with the evaluated trends these suggest that the Gulfs may become silica limited in a relatively near future. These findings give some implications on the development and impact of changing nutrient concentrations.

In many parts of the world coastal waters with anthropogenic eutrophication have experienced a gradual depletion of dissolved silica (DSi) stocks. This could put pressure on spring bloom diatom populations, e.g. by limiting the intensity of blooms or by,causing shifts in species composition. In addition, eutrophication driven enhanced diatom growth is responsible for the redistribution of DSi from the water phase to the sediments, and changes in the growth conditions may be reflected in the sediment diatom stratigraphy.

To test for changes in diatom communities we have analyzed four sediment cores from the Baltic Sea covering approximately the last 100 years. The sediment cores originate from the western Gulf of Finland, the Kattegat, the Baltic Proper and the Gulf of Riga. Three out of the four cores reveal only minor changes in composition of diatom assemblages, while the Gulf of Riga core contains major changes, occurring after the second World War. This area is set apart from the other Baltic Sea basins by a high frequency of low after spring bloom DSi concentrations (<2 mu mol L-1) during a relatively well defined time period from 1991-1998. In 1991 to 1993 a rapid decline of DSi spring concentrations and winter stocks (down to 5 mu mol L-1) in the Gulf was preceded by exceptionally intense diatom spring blooms dominated by the heavily silicified species Thalassiosira baltica (1991-1992; up to 5.5 mg ww L-1). T baltica has been the principal spring bloom diatom in the Gulf of Riga since records began in 1975. DSi consumption and biomass yield experiments with cultured T baltica suggest that intense blooms can potentially exhaust the DSi stock of the water column and exceed the annual Si dissolution in the Gulf of Riga. The phytoplankton time series reveals another exceptional T baltica bloom period in 1981-1983 (up to 8 mg L-1), which, however, took place before the regular DSi measurements. These periods may be reflected in the conspicuous accumulation of T baltica frustules in the sediment core corresponding to ca. 1975-1995.

A time-dependent water budget of the Gulf of Bothnia, based on inverse modelling with salinity as a conservative tracer, was developed to estimate monthly water flows for the period 1990-2000. When dealing with time-dependent inverse salinity models, such difficulties as non-physical water flows (too high flows or lack of non-negative flows) between adjacent basins are often encountered. Therefore, different model structures and solution methods were initially tested and evaluated on an array of generated data. The elaboration of the Gulf of Bothnia model was then based on the outcome of these tests. The results showed that the optimisation technique is capable of overcoming the above mentioned difficulties.

The Baltic Sea is one of many aquatic ecosystems that show long-term declines in dissolved silicate (DSi) concentrations due to anthropogenic alteration of the biogeochemical Si cycle. Reductions in DSi in aquatic ecosystems have been coupled to hydrological regulation reducing inputs, but also with eutrophication, although the relative significance of both processes remains unknown for the observed reductions in DSi concentrations. Here we combine present and historical data on water column DSi concentrations, together with estimates of present river DSi loads to the Baltic, the load prior to damming together with estimates of the long-term accumulation of BSi in sediments. In addition, a model has been used to evaluate the past, present and future state of the biogeochemical Si cycle in the Baltic Sea. The present day DSi load to the Baltic Sea is 855 ktons y(-1). Hydrological regulation and eutrophication of inland waters can account for a reduction of 420 ktons y(-1) less riverine DSi entering the Baltic Sea today. Using published data on basin-wide accumulation rates we estimate that 1074 ktons y(-1) of biogenic silica (BSi) is accumulating in the sediments, which is 36% higher than earlier estimates from the literature (791 ktons y(-1)). The difference is largely due to the high reported sedimentation rates in the Bothnian Sea and the Bothnian Bay. Using river DSi loads and estimated BSi accumulation, our model was not able to estimate water column DSi concentrations as burial estimates exceeded DSi inputs. The model was then used to estimate the BSi burial from measured DSi concentrations and DSj load. The model estimate for the total burial of BSi in all three basins was 620 ktons y(-1), 74% less than estimated from sedimentation rates and sediment BSi concentrations. The model predicted 20% less BSi accumulation in the Baltic Proper and 10% less in the Bothnian Bay than estimated, but with significantly less BSi accumulation in the Bothnian Sea by a factor of 3. The model suggests there is an overestimation of basin-wide sedimentation rates in the Bothnian Bay and the Bothnian Sea. In the Baltic Proper, modelling shows that historical DSi concentrations were 2.6 times higher at the turn of the last century (ca. 1900) than at present. Although the DSi decrease has leveled out and at present there are only restricted areas of the Baltic Sea with limiting DSi concentrations, further declines in DSi concentrations will lead to widespread DSi limitation of diatoms with severe implications for the food web.

We developed for the first time a catchment model simulating simultaneously the nutrient land-sea fluxes from all 105 major watersheds within the Baltic Sea drainage area. A consistent modeling approach to all these major watersheds, i.e., a consistent handling of water fluxes (hydrological simulations) and loading functions (emission data), will facilitate a comparison of riverine nutrient transport between Baltic Sea subbasins that differ substantially. Hot spots of riverine emissions, such as from the rivers Vistula, Oder, and Daugava or from the Danish coast, can be easily demonstrated and the comparison between these hot spots, and the relatively unperturbed rivers in the northern catchments show decisionmakers where remedial actions are most effective to improve the environmental state of the Baltic Sea, and, secondly, what percentage reduction of riverine nutrient loads is possible. The relative difference between measured and simulated fluxes during the validation period was generally small. The cumulative deviation (i.e., relative bias) [Sigma(Simulated - Measured)/Sigma Measured X 100 (%)] from monitored water and nutrient fluxes amounted to+8.2% for runoff, to-2.4% for dissolved inorganic nitrogen, to +5.1% for total nitrogen, to +13% for dissolved inorganic phosphorus and to +19% for total phosphorus. Moreover, the model suggests that point sources for total phosphorus compiled by existing pollution load compilations are underestimated because of inconsistencies in calculating effluent loads from municipalities.

Waves induce resuspension of surface sediments and contribute to the long-term mobilisation of particulate matter from erosion to accumulation bottoms. This has a major impact on the nutrient cycle in shallow seas by enhancing degradation, microbial production and recycling. The Baltic Sea represents such an area. The aim of this work is to analyse the spatial and temporal resuspension patterns in the Baltic Sea. To estimate the bottom friction velocity, modelled wave data are used in combination with data on grain size. This new data set is compared to a resuspension threshold of friction velocity to estimate the events of resuspension.

The variation in bottom friction velocity, resuspension frequency and duration are related to wind climate, fetch, water depth and sediment type. Substantial resuspension can be found down to 40–60 m, with durations from one day to as much as two weeks. The highest winds in the area are highly anisotropic with a dominance of S-SW-W winds and the highest resuspension frequencies are found along the shallow eastern coasts. A seasonal pattern is observed with relatively high friction velocities and high resuspension frequencies during winter. There is also a variation depending on grain size, where sediments with fine and medium sand have a considerably higher percentage of resuspension events than bottoms with other dominant grain sizes. Five sub-areas are identified, characterised by different sediment types, resuspension and wind characteristics. If, in the future, wind speed increases as predicted, resuspension of sediments will also increase with effects on the nutrient cycle.

The Baltic Proper shows many signs of eutrophication. Nutrient changes over time have been discernable, and also within the Sea there are large spatial patterns. Present study analyses the spatial patterns of dissolved inorganic nitrogen and phosphorus as well as dissolved silicate (DSi) in the euphotic zone for the period 1990-2001. The focus is on the spatial heterogeneity with the aim to identify areas significantly different from the overall mean.

Three regions are clearly discernible, the interior, the western and the eastern coastal zones. This is further complicated by the Gulfs of Finland and Riga with distinct different behaviour compared to the other ones. While the coastal zones are re-supplied by their terrestrial sources, the exchange with the interior is limited by geophysical constraints. The western border shows permanently high DSi but low DIN and DIP concentrations. The riverine loads of DIN, DIP and DSi are low but a large transport of DSi probably takes place from the Bothnian Sea to the Kattegat along the western coast with only minor retention. The eastern region, on the other hand, is characterised by both high nutrient loads and high production. These spatial patterns agree well with a conceptual model where the spring bloom leads to an interior generally low in DIN. This favours N-fixating cyanobacteria blooms at the expense of diatoms. This view is supported by decreasing DIP concentrations but unaffected DSi levels. The spatial patterns observed well reflect the riverine nutrient loads. This should be regarded in future remedy plans for the eutrophic Baltic Sea. The terrestrial load can have very different impacts on the ecosystems depending on which coastal section is involved.

Silicon is among the most abundant elements on earth. It plays a key but largely unappreciated role in many biogeochemical processes, including those that regulate climate and undergird marine food webs. The Silicon Cycle is the first book in more than 20 years to present a comprehensive overview of the silicon cycle and issues associated with it. The book summarizes the major outcomes of the project Land-Ocean Interactions: Silica Cycle, initiated by the Scientific Community on Problems of the Environment (SCOPE) of the International Council of Scientific Unions (ICSU). It tracks the pathway of silicon from land to sea and discusses its biotic and abiotic  modifications in transit as well as its cycling in the coastal seas. Natural geological processes in combination with atmospheric and hydrological processes are discussed, as well as human perturbations of the natural controls of the silicon cycle.

Lake Vänern is Sweden's largest freshwater reservoir. It has been significantly affected by mercury contamination during the latter half of the 20th century. The aim of this study was to analyse the spatial and vertical mercury distribution, whereas 46 sediment cores were sampled in 2001 and analysed for total mercury. Several of these cores were dated presenting sediment accumulation rates varying from 6-8 mm yr-1 outside major rivers to ~2 mm yr-1 in the deeper areas. This was made using 137Cs, which was verified by 210Pb dating. Cluster analysis was used to identify five areas with similar accumulation and mercury concentration regimes. In areas far from shore, surface concentrations ranged from 0.1 to 0.5 ppm Hg, while the deeper layers in contaminated areas held concentrations up to 11 ppm Hg. In total, ~50 tonnes of mercury accumulated in the lake's sediment between ~1940-2001, almost 80% (or 37 tonnes) originate from before the mid 70's when the recovery period began, and at least 30 tonnes can be attributed to the former point source - a chlor-alkali industry. © Springer 2006.

Dissolved silica (DSi) is an important nutrient for primary production. During the last decades, negative trends in DSi concentrations have been observed in coastal areas globally, with implications for the marine ecosystem. This tendency is mainly attributed to two processes: decrease in river loadings (as a result of water regulation and building of dams) and eutrophication in the coastal zone, with subsequent silica depletion. One such area affected by both an intensive water regulation and eutrophication is the Baltic Sea. The present study focused on the pelagic DSi trends in different parts of the Baltic Sea for the last three decades. It was found that there are decreasing trends for most of areas and water depths ranging between -0.05 and -1.2 μmol Si l -1 yr-1. The trends are levelling out during the last decade. Since the riverine load of dissolved silica has not changed at a corresponding rate during the time period, the decrement is assumed to be mainly a result of the ongoing eutrophication within the marine water body. This assumption was strengthened by the increasing trends of inorganic nitrogen and phosphorus. © 2005 Elsevier Ltd. All rights reserved.

Surface waves play an important role for the sediment distribution in the shallow Baltic Sea. This paper presents the large-scale spatio-temporal distribution of wave-induced bottom friction velocity, u_*, based on modelled wave data for the years 1999 and 2000. The highest values of u_* are found along the eastern coasts of the Baltic Proper and Bothnian Sea—areas characterised by long fetches for the dominant winds. Temporally, the dynamics follow that of the wind climate with higher velocities during winter and lower during summer.

A smooth bottom is assumed for the calculations. To test this assumption, u_* is compared to other estimates of u_* assuming rough bottoms. The spatio-temporal patterns are similar, although the present approach gives a slight underestimation of u_* at areas with coarse grain sizes.

To compare the results, the co-variation between the u_* distribution and bottom type distribution from a digitised sediment map is analysed. It shows upon a good agreement. This is also found when comparing critical levels for resuspension found in the literature with the same from modelled u_*. In addition, other processes important for bottom stress, such as mesoscale eddies and coastal jets, are discussed.

Silicon is among the most abundant elements on earth. It plays a key but largely unappreciated role in many biogeochemical processes, including those that regulate climate and undergird marine food webs. The Silicon Cycle is the first book in more than 20 years to present a comprehensive overview of the silicon cycle and issues associated with it. The book summarizes the major outcomes of the project Land-Ocean Interactions: Silica Cycle, initiated by the Scientific Community on Problems of the Environment (SCOPE) of the International Council of Scientific Unions (ICSU). It tracks the pathway of silicon from land to sea and discusses its biotic and abiotic  modifications in transit as well as its cycling in the coastal seas. Natural geological processes in combination with atmospheric and hydrological processes are discussed, as well as human perturbations of the natural controls of the silicon cycle.

Gradients in nutrient distributions and the effects of eutrophication are common features in most coastal marine areas. These structures occur in aquatic systems due to spatial differences in hydrography, nutrient loading and key biogeochemical processes. Two statistical methods, cluster analysis and probability mapping, have been used in the present study to determine characteristics and patterns in water quality variables. Combined, these two methods provide a useful toot to statistically determine spatial homogeneity and representativity of areas and stations. A case study is presented here in which water quality variables (salinity, dissolved inorganic nitrogen, dissolved inorganic phosphorus and chlorophyll) in surface waters of the Kattegat are analysed for the time period 1993-1997. It was found that morphology, the proximity to sources of nutrient loading from land, nutrient uptake and the infrequent water exchange between the Baltic Sea in the south and the Skagerrak in the north all contribute to create distinct regions of water quality. Regions with concentrations significantly different from the overall mean are identified. In addition to identification of regions with similar characteristics, representative stations (as well as not representative stations) for the respective regions were made. This type of information can be used to design new or revise old monitoring programs.

Lake Vänern is Sweden's largest lake and freshwater reservoir. Large quantities of mercury were released into the lake during a large part of the 20th century, resulting in serious contamination. The main load originated from one single point source - a chlor-alkali industry. Its releases were drastically reduced in the early 1970's, but nearby sediments displayed alarmingly high concentrations. During summer 2001, fifty-one sediment cores were taken, and analysed for total mercury. It was found that mercury concentrations in surface sediments have decreased significantly between 1974 and 2001, but the influence of the former single point source was still reflected in the concentration patterns. Thirty years ago, sediments around the dominant point source displayed the highest concentrations. Today, the highest concentrations in surface sediments were still found close to it, but also in deep waters in the central part of the lake. Surprisingly, the gradient from the point source is stronger today compared to 1974. A mercury budget, based on the annual sediment accumulation rate, the bulk density, atmospheric load and outflow of mercury, was formed. The surface sediments (0-1 cm, on average corresponding to ∼5 yr according to 137Cs dating) in accumulation bottoms (water depth >40m) contained approximately 530 kg Hg (corresponding value for year 1974 was 4100 kg Hg). A majority of the present additions of mercury to the lake originates from atmospheric deposition. It was also found that the lake acts as a sink for mercury. In fact, approximately 90-95% of the incoming mercury was retained within the catchment or in the sediments.

We examined the hypothesis that the extent of vegetation cover governs the fluxes of nutrients from boreal and subarctic river catchments to the sea. Fluxes of total organic carbon (TOC) and dissolved inorganic nitrogen, phosphorus, and dissolved silicate (DIN, DIP, and DSi, respectively) are described from 19 river catchments and subcatchments (ranging in size from 34 to 40,000 km2) in northern Sweden with a detailed analysis of the rivers Lulea¨lven and Kalixa¨lven. Fluxes of TOC, DIP, and DSi increase by an order of magnitude with increasing proportion of forest and wetland area, whereas DIN did not follow this pattern but remained constantly low. Principal component analysis on landscape variables showed the importance of almost all land cover and soil type variables associated with vegetation, periglacial environment, soil and bedrock with slow weathering rates, boundary of upper tree line, and percentage of lake area. A cluster analysis of the principal components showed that the river systems could be separated into mountainous headwaters and forest and wetland catchments. This clustering was also valid in relation to river chemistry (TOC, DIP, and DSi) and was confirmed with a redundancy analysis, including river chemistry and principal components as environmental variables. The first axis explains 89% of the variance in river chemistry and almost 100% of the variance in the relation between river chemistry and landscape variables. These results suggest that vegetation change during interglacial periods is likely to have had a major effect on inputs of TOC, DIP, and DSi into the past ocean.

Estuaries are often seen as important filters between land and the sea for inorganic and organic nutrients. This paper aims at estimating the estuarine fluxes of dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) and dissolved silicate for the major oligothrophic and pristine rivers running into the Bothnian Bay (BB) and the Bothnian Sea (BS), the northern subarctic subbasins of the Baltic Sea. Long-term data sets for these rivers and their estuaries as well as for the BB and BS were analyzed to assess whether these estuaries are sinks for inorganic nutrients. Most studied estuaries can be characterized as salt wedge estuaries with little exchange between the fresh seaward-flowing river water and the inward-flowing seawater. Estimates of water transit times ranged between 1 and 14 days. In most estuaries of the BB, N-depleted river water meets P-depleted seawater during the growth period. These findings were corroborated by mixing diagrams showing that the inner areas of the estuaries were N-depleted in summer. In the BS, on the other hand, both rivers and seawater were mostly N-depleted during summer. Thus, for most estuaries of this region of the Baltic Sea, primary productivity is presumably lower than or equal to that of offshore. The low productivity is also reflected in the sediments. The coastal sediments did not differ from the offshore stations in accumulation rates as well as the content of organic matter and nutrients, indicating that estuarine nutrient burial is not always higher as normally observed in other temperate systems. Finally, the estuaries of the pristine rivers in the northernmost part of the BB import DIN during summer, whereas the estuaries of the rivers in the BS import DIP during winter, from the sea. ⌐ 2003 Elsevier Science B.V. All rights reserved.

Lake Vanern, the largest lake in Sweden, has been seriously contaminated with mercury during the 20th century. In the 1970's and 80's the direct load, mainly from a chlor-alkali industry in the area, of mercury was drastically reduced as a response to new legislation, from three to five tons down to between five and ten kg yr(-1). Large amounts of the disposed pollutant have accumulated in the sediments. The question posed in this work is now, is the effect of the drastic load reduction after more than two decades visible in the sediments? The question is relevant as large areas still are blacklisted for fishing, but also as a follow-up of a major remedy action. The lake also serves as a freshwater reservoir for even Sweden's second largest city. This work synthesises and compares data of mercury in the sediments from three major field programs, in 1974, 1984 and 1998. The interest is focused on both spatial heterogeneity and temporal trends. In 1974, the surface concentrations are significantly higher than in subsequent surveys. Significant differences are also found between 1984 and 1998. Significant spatial differences within the lake are found for respective year. The most contaminated area is located in the north, close to the major point source (a former chlor-alkali industry). This is also the area with the largest improvement, as a direct response to the reduction in load. Further from the outlet, the recovery is more affected by burial and transport processes out into the deeper basins.

During recent decades, large-scale effects of pollution on marine estuaries and even entire enclosed coastal seas have become apparent. One of the first regions where this was observed is the Baltic Sea, whereby the appearance of anoxic deep basins, extensive algal blooms and elimination of top predators like eagles and seals indicated effects of both increased nutrient inputs and toxic substances.This book describes the physical, biochemical and ecological processes that govern inputs, distribution and ecological effects of nutrients and toxic substances in the Baltic Sea. Extensive reviews are supplemented by budgets and dynamic simulation models.This book is highly interdisciplinary and uses a systems approach for analyzing and describing a marine ecosystem. It gives an overview of the Baltic Sea, but is useful for any marine scientist studying large marine ecosystems.

Methane emissions from a Swedish landfill were measured with a static chamber technique on three occasions during 1997. Methane flux rates ranged from -15.2 x 10-3 to 40 g of CH4 m-2 h-1, and the spatial variability was high (CV = 343-386%). The spatial distribution of the emissions was estimated with the help of ordinary kriging, which is a spatial interpolation method. Three different approaches to estimate the total amounts were used: kriging on logarithm-transformed data, kriging with extremes excluded, and linear interpolation of measurements. These were compared between themselves and with the flux rates measured with a tracer gas technique. While the latter gave an estimate of 41 kg of CH4 h-1 from the landfill (with small variations), the highest possible estimate obtained with static chambers and geostatistical methods was 9.7 kg of CH4 h-1. The conclusion is that static chambers can hardly be trusted for making more than small-scale estimates of landfill gas emissions.Methane emissions from a Swedish landfill were measured with a static chamber technique on three occasions during 1997. Methane flux rates ranged from -15.2 ╫ 10-3 to 40 g of CH4 m-2 h-1, and the spatial variability was high (CV = 343-386%). The spatial distribution of the emissions was estimated with the help of ordinary kriging, which is a spatial interpolation method. Three different approaches to estimate the total amounts were used: kriging on logarithm-transformed data, kriging with extremes excluded, and linear interpolation of measurements. These were compared between themselves and with the flux rates measured with a tracer gas technique. While the latter gave an estimate of 41 kg of CH4 h-1 from the landfill (with small variations), the highest possible estimate obtained with static chambers and geostatistical methods was 9.7 kg of CH4 h-1. The conclusion is that static chambers can hardly be trusted for making more than small-scale estimates of landfill gas emissions.

In a marine environment the sediments play an important role. They act as sinks, where the concentrations often are higher than in the water mass above, but also as sources for numerous pollutants. Two of the major groups of pollutants are metals and nutrients While the metals may be harmful even in rather small concentrations the latter are mainly studied due to their importance in eutrophication.

Three study areas are used - the Baltic Sea, Kattegat and Skagerrak - that are all effected by heavy metal pollution and high nutrient loads. The sediments, in these areas, can not be seen as homogeneous. Spatial distribution, scales, patterns, covariation between different substances and other characteristics of nutrients and metals in the sediments give important information on e.g. deposition processes and sources.

It is revealed that point sources do not have any major influence on the distribution of pollutants in the sediments. Instead it seems like biogeochemical processes mainly control the patterns found. In all three areas, carbon and nitrogen give similar patterns, indicating similar deposition processes. It is harder to determine correlation scales in Kattegat than in Skagerrak, where the latter has longer scales. This is also seen for the metals where e.g. cadmium, copper and mercury have less clear scales than both carbon, nitrogen and lead, which may be interpreted as a result of different sources and behaviour of substances.

The results suggest that spatial information is important in sediment analysis and in designing future monitoring programs.

A statistical model of the variation of phosphate concentration in the upper layers of the Baltic proper was formed, with the aim of studying the magnitude of this variation and to be able to adjust corrupted time series. The large variation observed is only partially explained by seasonal variations and geographical structures. Despite inclusion of longterm trends and annual variations, the residuals showed a substantial correlation within and between the time series.