Stratification of selected hydrolytic enzyme activities in the sediment in two lakes in Finland

To investigate the stratification of hydrolytic enzyme activities and importance of subsurface layers in depolymerization of detritus biopolymers,nine hydrolytic enzyme activities involved in the cycling of carbon,phosphorus,nitrogen and sulphur were measured in various sediment layers and their extracts at Kylaniemi in Lake Saimaa in southern Finland and in Lake Ahvenjarvi in northern Finland. The results show that for each lake all nine hydrolytic enzyme activities were higher in all sediment layers than in comparable sediment extracts indicating that the major part of enzymes was bound to the sediment particles in all layers in both lakes.Carbohydratase,P-cellobiosidase,activities did not show any gradient with sediment depth at Kylaniemi in Lake Saimaa indicating that there was rapid turnover of carbohydrates in the entire sediment column.The activities of acetate esterase,butyrate esterase,phosphomonoesterase,aminopeptidase,N-acetyl glucosaminidase,sulphatase andβ-glucosidase in the deepest layers were 19-53%of those in the surface sediment indicating that depolymerization of biopolymers involved in the cycling of carbon,nitrogen,phosphorus and sulphur was substantial in subsurface sediment.     

Characterising the origin,nature and fate of sediment exported from catchments perturbed by active tectonics

Changes to the tectonic boundary conditions governing erosional dynamics in upland catchments have a significant effect on the nature and magnitude of sediment supply to neighbouring basins. While these links have been explored in detail by numerical models of landscape evolution, there has been relatively little work to quantify the timing, characteristics and locus of sediment release from upland catchments in response to changing tectonic boundary conditions that are well‐constrained independently. We address this challenge by quantifying the volume and granulometric characteristics of sediment exported from modern rivers draining across active normal faults in the Central Apennines in Italy. We demonstrate that catchments undergoing a transient response to tectonics are associated with significant volumetric export of material derived primarily from the zone upstream of the fault, producing bi‐modal grain‐size distributions with elevated D₈₄ values within the transient reach. This is in direct contrast to the headwaters, where the fluvial capacity to transport sediment is low and the grain‐size distribution of material in transit is fine and uni‐modal. The grain‐size response is driven by landslides feeding coarse material directly into the channel, and we show the amplitude of the signal is modulated by the degree of tectonic perturbation, once the threshold for bedrock landsliding is exceeded. Additionally, we evaluate the length‐scale over which this transient grain‐size signal propagates downstream into the basin. We show that the coarse‐fraction sediment released is retained in the proximal hanging‐wall if rates of tectonic subsidence are high and if the axial river system is small or far from the fault‐bounded mountain front. Our results therefore provide some of the first quantitative data to evaluate how transient landscape responses affect the locus, magnitude and calibre of sediment supply to basins.     

Airborne remote sensing of spatiotemporal change (1955–2004) in indigenous and exotic forest cover in the Taita Hills,Kenya

We studied changes in area and species composition of six indigenous forest fragments in the Taita Hills, Kenya using 1955 and 1995 aerial photography with 2004 airborne digital camera mosaics. The study area is part of Eastern Arc Mountains, a global biodiversity hot spot that boasts an outstanding diversity of flora and fauna and a high level of endemism. While a total of 260 ha (50%) of indigenous tropical cloud forest was lost to agriculture and bushland between 1955 and 2004, large-scale planting of exotic pines, eucalyptus, grevillea, black wattle and cypress on barren land during the same period resulted in a balanced total forest area. In the Taita Hills, like in other Afrotropical forests, indigenous forest loss may adversely affect ecosystem services.     

Computations with finite element methods for the Brinkman problem

Various finite element families for the Brinkman flow (or Stokes–Darcy flow) are tested numerically. Particularly, the effect of small permeability is studied. The tested finite elements are the MINI element, the Taylor–Hood element, and the stabilized equal order methods. The numerical tests include both a priori analysis and adaptive methods.     

Extreme wave events and sampling variability

Ocean Dynamics - Wave field data are affected not only by the accuracy of instruments recording them but also by sampling variability, an uncertainty due to the limited number of observations. For...     

Experimental and modelling investigations of the biogeochemistry of gas production from low and intermediate level radioactive waste

The degradation of organic wastes and the corrosion of metallic wastes and steel containers in low and intermediate level radioactive waste (LLW/ILW) repositories are important processes that affect repository geochemistry and the speciation and transport of radionuclides. Gas is generated in association with these degradation processes and this has the potential to overpressure the repository, which can promote transport of groundwater and gas, and consequently radionuclide transport. Microbial activity plays an important role in organic degradation, corrosion and gas generation through the mediation of reduction–oxidation reactions.     

Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland

We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08'N, 27° 17'E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH₄ exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (R_tot' opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO₂ exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 μmol m_-2 s_-1) varied during the measurement period from −59 mg CO₂-C m⁻²h⁻¹ (release) to 250 (uptake). The mean CH₄ emission during the measuring period was 78 mg CH_4-Cm⁻² d⁻¹ on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana ) were in general net sources of CO₂, even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO₂. Areally integrated chamber results showed lower CO₂ and higher CH₄ fluxes than predicted from the eddy covariance measurements.