Phosphorus in acidified lakes: The example of Lake Gårdsjön,Sweden

Supply and turnover of phosphorus was studied in an acidified lake ecosystem, Lake Gårdsjön, located in southwestern Sweden. This study included transport and budget calculations combined with field and laboratory experimental work on abiotic phosphorus chemistry and biological utilization of phosphorus. The main conclusions presented in this paper are:

- The acidification process in inland waters resulting from acid atmospheric deposition is accompanied by ‘oligotrophication’ because of reduced input of phosphorus from the drainage area, possibly due to efficient fixation of phosphorus to aluminium complexes in the B-horizon of podzol soils

- Primary productivity in acidified lakes is limited mainly by low phosphorus supply

- Algal utilization of phosphorus in acidified lakes is impaired, yielding lower biomass than could be expected from ambient phosphorus concentrations. One possible reason for this could be that enzymatic recycling of organic phosphates is prevented by high levels of aluminium in lake water.

     

Origin and production of phosphatases in the acid Lake Gårdsjön

The activity of acid phosphatases was followed for one year in Lake Gårdsjön as well as in the inlet and the outlet of the lake. A budget of the phosphatases was calculated, including an estimation of the production of phosphatases. The phosphatase activity was also measured in two basins upstream of L. Gårdsjön: the north basin and the south basin of L. Stora Hästevatten.The acid phosphatase activity was very high compared with reported alkaline phosphatase activities in other lakes. About 95% of the phosphatases in L. Gårdsjön was produced in the lake, and the production was highest in early summer.Small Chrysophyceae (< 10 µm) probably produced the majority of the acid phosphatases in the investigated lakes, and accordingly could be favoured in environments with low phosphorus supply due to their ability to produce large amounts of phosphatases.     

Experimental simulation of the effects of extreme climatic events on major ions, acidity and dissolved organic carbon leaching from a forested catchment, Gårdsjön, Sweden

Climate change is predicted to lead to an increase in extreme rainfall and, in coastal areas, sea-salt deposition events. The impacts of these two climatic extremes on stream hydrochemistry were separately evaluated via a novel watering manipulation at the Gårdsjön experimental catchment, SW Sweden. In summer 2004, a 2000 m² hillslope draining to a defined stream reach was brought to a high-flow hydrological steady state for a 9 day period by sustained addition of ‘clean’ water using a distributed sprinkler system. Marine ions were then added, to generate a realistic ‘sea salt’ episode. A remarkably well constrained hydrological response was observed, such that a simple two-compartment mixing model could reasonably well reproduce observed conservative tracer (chloride, Cl) measurements, and 78% of added water was recovered in runoff. Stream base cation concentrations and acidity responded predictably to clean water and sea-salt addition, with the former leading to an increase in pH and acid neutralising capacity, and the latter to episodic acidification through hydrogen ion and aluminium displacement from soil exchange sites by marine base cations. Anion responses were less predictable: water addition caused a flush of nitrate, but this was apparently independent of rainfall composition. Sulphate remained near-constant during clean water addition but declined sharply during sea-salt addition, indicative of a strong, pH-dependent solubility control on leaching, presumably adsorption/desorption in the mineral soil. Most strikingly, dissolved organic carbon (DOC) concentrations were stable during clean water addition but varied dramatically in response to sea-salt addition, exhibiting a strong negative correlation with Cl concentrations in water draining the organic soil. These observations provide a robust experimental verification of the hypothesis that deposition chemistry, through its influence on acidity and/or ionic strength, has a major influence on DOC leaching to surface waters.     

Long-term history of land-use and vegetation at Femtingagölen — a small lake in the Småland Uplands, southern Sweden

Pollen analysis was carried out on gyttja from the small lake Femtingagölen in the Småland Uplands, southern Sweden. The interpretation of the pollen diagram focused on land-use history and comparisons were made to archaeological and historical information from the area. An absolute chronology, based on AMS dates from terrestrial plant macrofossils, was complemented by inferred dates. The pollen analytical data suggest interference with the woodland cover from ca. 1700 B.C. onwards. Intensified grazing and forest clearances resulted in semi-open pastures between ca. A.D. 400–600 which was followed by forest regeneration (chronology based on AMS ¹⁴C dates and cross-correlation with other well dated profiles). The landscape became more open again between A.D. 800 and 1400. Animal husbandry was complemented by small-scale shifting cultivation during the Iron Age. Permanent arable fields were probably not introduced until the Late Iron Age or the Middle Ages. Hordeum and Triticum were grown during the Iron Age, Hordeum, Triticum, Secale and Cannabis sativa during the Middle Ages and early Modern time, and Hordeum and Avena in the recent past. Sandy and silty soils, where stone clearance was not necessary, have probably been used for cereal growing in prehistoric and historic time.