Browsing by Subject "vaihtelu"

Sort by: Order: Results:

Now showing items 1-20 of 20
  • Kahru, Mati; Bittig, Henry; Elmgren, Ragnar; Fleming, Vivi; Lee, Zhongping; Rehder, Gregor (Inter-Research Science Center, 2022)
    Marine Ecology Progress Series
    Water transparency can be measured with optical instruments and estimated with satellite sensors, but such measurements have been widely available for only a few decades. Estimates of water transparency using a white disk called a Secchi disk have been made for over a century and can be used to estimate long-term trends. However, historic in situ measurements of the Secchi depth (ZSd) were irregular in space and time and are difficult to interpret in regular time series due to biases introduced by changing locations and the timing of measurements. Satellite data time series, on the other hand, have consistent resolution in both space and time but cover too short a time to resolve climate-scale trends. We normalized historic ZSd measurements in the Baltic Sea with a satellite-derived mean climatology at 5 d temporal and 4 km spatial resolutions and created a merged time series of ZSd for the last century. The mean ZSd in the Baltic Sea from 1927-2020 decreased by 4.2 +/- 0.6 m at a rate of 0.045 +/- 0.06 m yr-1. Most of the change happened before 1987, and a further decrease was evident primarily in the satellite data during the 1998-2008 period. After 2008, no significant trend in ZSd and or the coefficient of diffuse light attenuation was detected in the Baltic Sea. However, in some sub-basins of the Baltic Sea, the decrease in ZSd continued even after that. The decrease in spectral water transparency in recent decades was highest in the 412 nm band, indicating an increase in the concentration of chromophoric dissolved organic matter.
  • Lehtinen, Sirpa (University of Helsinki, 2000)
  • Kärkkäinen, Matti (Suomen metsätieteellinen seura, 1972)
  • Smolander, Heikki (Suomen metsätieteellinen seura, 1984)
    Measurements were made of temporal and spatial microvariations in irradiance in a small part of the canopy of a 20-yr-old Scots pine stand. Linear integration of the variations gave biased estimates; second order Taylor series approximations were satisfactory only for a low curvature response; two-point distribution approximations were applicable to high and low curvature response but presupposed that the mean and variance were known. It is suggested that a light measuring method in which first power (mean) and second power (variance) of irradiance are integrated resolves these problems; the method takes into account the geometry of the shoot and can also be used in transpiration studies.
  • Alho, Pentti (Suomen metsätieteellinen seura, 1975)
  • Nygren, Markku (Suomen metsätieteellinen seura, 1990)
  • Kärkkäinen, Matti (Suomen metsätieteellinen seura, 1973)
  • Vilmi, Annika; Tolonen, Kimmo T.; Karjalainen, Satu Maaria; Heino, Jani (Elsevier, 2019)
    Ecological Indicators, 99, 159-166
    We examined how niche position, niche breadth, biological traits and taxonomic relatedness affect interspecific variation in occupancy and abundance of two commonly-used biological indicator groups, i.e. diatoms and macroinvertebrates. We studied 291 diatom and 103 macroinvertebrate species that occupied the littoral zones of a large (305 km2) highly-connected freshwater system. We collated information on the biological traits and taxonomic relatedness of each species. Using principal coordinates analysis, we formed biological trait and taxonomic vectors describing distances between species and used the resulting vectors as predictor variables. As environmental data, we had site-specific physico-chemical variables, which were used in outlying mean index analyses to determine the niche position and niche breadth of each species. We used linear models to study if and how these two niche parameters and biological traits as well as taxonomic relatedness affected occupancy and abundance. We observed positive occupancy-abundance relationships for both diatoms and macroinvertebrates. We further found that, for both groups, occupancy was better explained by the predictor variables compared with abundance. We also observed that niche parameters, especially niche position, were the main determinants of variation in occupancy and abundance for both diatoms and macroinvertebrates. Local abundances of diatom and macroinvertebrate species were also, to a small degree, affected by biological traits or taxonomic relatedness. We further saw that the relationship between niche position and occupancy was negative, indicating that the more marginal the niche position, the rarer a species is. Our findings provide support for the use of diatoms and macroinvertebrates as ecological indicators as their occupancies and abundances were affected by niche parameters, which is not necessarily always clear in challenging study systems with high connectivity (i.e. high movement of material and species) among sites. These findings also suggest that indices using information on species’ occupancy, abundance and niche requirements are useful in environmental assessment.
  • Koski, Veikko (Suomen metsätieteellinen seura, 1980)
  • Heikurainen, Leo (Suomen metsätieteellinen seura, 1971)
  • Lehtonen, I.; Westman, C. J.; Kellomäki, S. (Suomen metsätieteellinen seura, 1976)
  • Elovaara, Samu; Degerlund, Maria; Franklin, Daniel J.; Kaartokallio, Hermanni; Tamelander, Tobias (Springer Link, 2020)
    Hydrobiologia 847 11 (2020)
    Cell death drives the magnitude and community composition of phytoplankton and can result in the conversion of particulate organic carbon to dissolved organic carbon (DOC), thereby affecting carbon cycling in the aquatic food web. We used a membrane integrity probe (Sytox Green) to study the seasonal variation in the percentage of viable cells in the phytoplankton population in an estuary in the northern Baltic Sea for 21 months. The associated dissolved and particulate organic matter concentrations were also studied. The viable fraction of phytoplankton cells varied from < 20% to almost 100%, with an average of 62%. Viability was highest when a single phytoplankton group (diatoms or dinoflagellates) dominated the community. Viability of sinking phytoplankton cells, including some motile species, was in general as high as in surface water. Changes in viability were not closely related to nutrient concentrations, virus-like particle abundance, seawater temperature or salinity. There was a weak but significant negative correlation between viability and DOC, although at this location, the DOC pool was mainly influenced by the inflow of riverine water. This study demonstrates that cell viability, and its relationship with carbon export, is highly variable in the complex microbial populations common within estuarine and coastal marine ecosystems.
  • Li, Zhengfei; Tonkin, Jonathan D.; Meng, Xingliang; Liu, Zhenyuan; Zhang, Junqian; Chen, Xiao; Xie, Zhicai; Heino, Jani (Elsevier BV, 2022)
    Ecological Indicators
    To improve our understanding on the temporal aspects of metacommunity structure, we focused on benthic macroinvertebrates collected seasonally (i.e., wet, drying, dry and rewetting seasons) in Dongting Lake, a large subtropical floodplain lake in China. We employed the elements of metacommunity structure (EMS) framework and variation partitioning to examine whether metacommunity structure and its underlying mechanisms vary among seasons with distinct biotic and abiotic features. We found gradual shifts in the main assembly mechanisms throughout the year, from apparent spatial structuring (potentially indicative of mass effects) in the wet season to more environmental filtering dynamics in the dry season. When the degree of connectivity was high in the wet season, the benthic metacommunity was characterized by nested structure associated with clumped species loss, and was shaped mainly by spatial processes. However, quasi-Clemensian structure was assigned to metacommunities in the transitional seasons with intermediate connectivity, during which environmental variables were more important than spatial factors in describing community structure. When the degree of connectivity was low in the dry season, the benthic metacommunity displayed Clementsian structure, which was configured solely by environmental variables. The rapid shifts in metacommunity dynamics between seasons mainly result from the considerable changes in the hydrological conditions of Dongting Lake, as the studied system varies from lacustrine to fluvial phases within a single year. Taken together, our results revealed that taking temporal aspects into account gives a better insight into metacommunity organization, especially when the studied systems embrace remarkable variability in hydrological regimes.
  • Pukkala, Timo (Suomen metsätieteellinen seura, 1987)
  • Helmisaari, Heljä-Sisko (Suomen metsätieteellinen seura, 1992)
  • Hyvärinen, Veli; Vehviläinen, Bertel (Vesihallitus. National Board of Waters, 1981)
    Vesientutkimuslaitoksen julkaisuja 43, 15-23
    Ilmaston ja ihmisen toiminnan vaikutus virtaamanvaihteluihin Suomen vesistöissä
  • Anttinen, Jukka-Pekka (University of Helsinki, 2000)