Browsing by Subject "STREAM"

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  • Miettinen, Jenni; Ollikainen, Markku; Aroviita, Jukka; Haikarainen, Soili; Nieminen, Mika; Turunen, Jarno; Valsta, Lauri (2020)
    Ditch network maintenance promotes forest growth in drained peatland forests but increases nutrient and sediment loads, which are detrimental to water quality. Society needs to balance the harvest revenue from improved forest growth against deteriorating water quality. We examine socially optimal even-aged forest management in drained peatlands when harvesting and ditch network maintenance cause nutrient and sediment loading. The means to reduce loading include establishing overland flow fields and abstaining from ditch network maintenance. We characterize this choice analytically in a rotation framework and examine, in a numerical model, the key factors affecting the choice of forest management and water protection measures. We choose a drained peatland forest site located in northeastern Finland in the vicinity of ecologically vulnerable forest headwater streams. On the given drained forest site, we find a set of parameters under which implementing ditch network maintenance is privately but not socially optimal.
  • Ye, Quanzhi; Granvik, Mikael (2019)
    The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter greater than or similar to 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every similar to 2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.'s near-Earth object population model, and find that they evolve 10-70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.
  • Astikainen, Piia; Mällo, Tanel; Ruusuvirta, Timo; Naatanen, Risto (2014)
  • Zhang, Fan; Shi, Xiaohong; Zhao, Shegnan; Arvola, Lauri; Huotari, Jussi; Hao, Ruonan (2022)
    Water quality monitoring buoy installed in the center of the eutrophic shallow lake Ulansuhai was used to explore the dissolved oxygen balance. A revised dissolved oxygen model for shallow eutrophic lakes was applied to identify trends in the lake's dissolved oxygen content during the non-frozen period and determine the equilibrium relationship of dissolved oxygen in the water body. The coefficient of determination and the Nash efficiency of the model proved the feasibility of the model. The main drivers affecting the dissolved oxygen balance of the lake were photosynthesis, aeration and the lateral movements of oxygen rich water, which accounted for 49.28, 14.72 and 36%, respectively, whereas respiration and sediment oxygen consumption, on the other hand, accounted for 1.56 and 98.44%, respectively. These findings suggest that photosynthesis and sediment oxygen consumption dominate the dissolved oxygen balance in eutrophic shallow lakes. A trend analysis of the average oxygen production and consumption rates indicated a maximum of 0.22 mg/L center dot h for photosynthesis and 0.20 mg/L center dot h for sediment oxygen consumption. A correlation analysis showed that water temperature was involved in changing the dissolved oxygen level of the lake mainly by affecting the oxygen consumption process.
  • Atashgahi, Siavash; Aydin, Rozelin; Dimitrov, Mauricio R.; Sipkema, Detmer; Hamonts, Kelly; Lahti, Leo; Maphosa, Farai; Kruse, Thomas; Saccenti, Edoardo; Springael, Dirk; Dejonghe, Winnie; Smidt, Hauke (2015)
    The impact of the installation of a technologically advanced wastewater treatment plant (WWTP) on the benthic microbial community of a vinyl chloride (VC) impacted eutrophic river was examined two years before, and three and four years after installation of the WWTP. Reduced dissolved organic carbon and increased dissolved oxygen concentrations in surface water and reduced total organic carbon and total nitrogen content in the sediment were recorded in the post-WWTP samples. Pyrosequencing of bacterial 16S rRNA gene fragments in sediment cores showed reduced relative abundance of heterotrophs and fermenters such as Chloroflexi and Firmicutes in more oxic and nutrient poor post-WWTP sediments. Similarly, quantitative PCR analysis showed 1-3 orders of magnitude reduction in phylogenetic and functional genes of sulphate reducers, denitrifiers, ammonium oxidizers, methanogens and VC-respiring Dehalococcoides mccartyi. In contrast, members of Proteobacteria adapted to nutrient-poor conditions were enriched in post-WWTP samples. This transition in the trophic state of the hyporheic sediments reduced but did not abolish the VC respiration potential in the post-WWTP sediments as an important hyporheic sediment function. Our results highlight effective nutrient load reduction and parallel microbial ecological state restoration of a human-stressed urban river as a result of installation of a WWTP.
  • Kortelainen, Pirkko; Larmola, Tuula; Rantakari, Miitta; Juutinen, Sari; Alm, Jukka; Martikainen, Pertti J. (2020)
    Abstract Estimates of regional and global freshwater N2O emissions have remained inaccurate due to scarce data and complexity of the multiple processes driving N2O fluxes the focus predominantly being on summer time measurements from emission hot spots, agricultural streams. Here we present four-season data of N2O concentrations in the water columns of randomly selected boreal lakes covering a large variation in latitude, lake type, area, depth, water chemistry and land use cover. Nitrate was the key driver for N2O dynamics, explaining as much as 78% of the variation of the seasonal mean N2O concentrations across all lakes. Nitrate concentrations varied among seasons being highest in winter and lowest in summer. Of the surface water samples 71% were oversaturated with N2O relative to the atmosphere. Largest oversaturation was measured in winter and lowest in summer stressing the importance to include full year N2O measurements in annual emission estimates. Including winter data resulted in four-fold annual N2O emission estimates compared to summer only measurements. Nutrient rich calcareous and large humic lakes had the highest annual N2O emissions. Our emission estimates for Finnish and boreal lakes are 0.6 Gg and 29 Gg N2O-N y-1, respectively. The Global Warming Potential (GWP) of N2O cannot be neglected in the boreal landscape, being 35% of that of diffusive CH4 emission in Finnish lakes.
  • Sgarbi, Luciano F.; Bini, Luis M.; Heino, Jani; Jyrkankallio-Mikkola, Jenny; Landeiro, Victor L.; Santos, Edineusa P.; Schneck, Fabiana; Siqueira, Tadeu; Soininen, Janne; Tolonen, Kimmo T.; Melo, Adriano S. (2020)
    Reliable biological assessments are essential to answer ecological and management questions but require well-designed studies and representative sample sizes. However, large sampling effort is rarely possible, because it demands large financial resources and time, restricting the number of sites sampled, the duration of the study and the sampling effort at each site. In this context, we need methods and protocols allowing cost-effective surveys that would, consequently, increase the knowledge about how biodiversity is distributed in space and time. Here, we assessed the minimal sampling effort required to correctly estimate the assemblage structure of stream insects sampled in near-pristine boreal and subtropical regions. We used five methods grouped into two different approaches. The first approach consisted of the removal of individuals 1) randomly or 2) based on a count threshold. The second approach consisted of simplification in terms of 1) sequential removal from rare to common species; 2) sequential removal from common to rare species; and 3) random species removal. The reliability of the methods was assessed using Procrustes analysis, which indicated the correlation between a reduced matrix (after removal of individuals or species) and the complete matrix. In many cases, we found a strong relationship between ordination patterns derived from presence/absence data (the extreme count threshold of a single individual) and those patterns derived from abundance data. Also, major multivariate patterns derived from the complete data matrices were retained even after the random removal of more than half of the individuals. Procrustes correlation was generally high ( > 0.8), even with the removal of 50% of the species. Removal of common species produced lower correlation than removal of rare species, indicating higher importance of the former to estimate resemblance between assemblages. Thus, we conclude that sampling designs can be optimized by reducing the sampling effort at a site. We recommend that such efforts saved should be redirected to increase the number of sites studied and the duration of the studies, which is essential to encompass larger spatial, temporal and environmental extents, and increase our knowledge of biodiversity.