Samplers for enclosed stratified water columns

Self Cite

In a southern Norwegian fjord (Rosfjord) during POSER a plastic enclosure (1 m 0, 20 m depth) was filled with filtered fjord water enriched with inorganic nutrients and inoculated with a monoculture of Skeletonema costaturn. The enclosure was exposed to fjord conditions from March 18 to April 5, 1979. Pre-filtration had removed ca. 80 % of the bacterial population in the fjord water. Following a short lag phase, bacteria grew exponentially. After consumption of nitrogen-containing organic substances, dissolved carbohydrates were the main energy source; however, bacterial numbers did not increase further, probably due to grazing by nanoflagellates. In spite of sub-optimal light and temperature conditions, S. costaturn reached cell densities as high as 35. 106 dm-3 at 3 m water depth, since competing algae and grazing zooplankton were missing in the enclosure. The diatoms grew exponentially, with a division rate of p = 0.6 d-' and reached the stationary phase after 16 d, when inorganic nutrients were exhausted. During growth of S. costatum relatively high amounts of carbohydrates were released. Maximum concentrations followed the exponential phase, but highest release rates per cell -2.0 pmoles glucose equivalents cell-' d-' -were reached immediately after inoculation. Measurements at 3 h intervals at the end of the experiment showed that concentrations and therefore release activities varied abruptly within a few hours. Main release occurred from noon to midnight. Not all dissolved carbohydrates were immediately taken up by heterotrophic organisms, part of them could not be utilized, others only after adaptation or succession of bacteria. During the experiment, the proportion of the labile fraction to the total dissolved carbohydrates varied greatly.

Section: Methodsmentioning

confidence: 99%

Total dissolved carbohydrates in an enclosure experiment with unialgal Skeletonema costatum culture

Eberlein¹,

Brockmann²,

Hammer³

et al. 1983

Self Cite

“…Raising the bag with a winch on the ring station allowed the bag to fill, thus maintaining the stratification of the water column in the fjord at the time of filling. Samples of phytoplankton and for chemical analysis were collected by a 3 dm3 sampler (Brockmann and Hentzschel, 1983) at standard depths of 0 , 3 , 10.20 and 35 m. All samples for chemical measurements (500 m1 each) were filtered through glass-fibre filters (Whatman GF/C, 1.2 pn retention ability). Nitrate plus nitrite, ammonia, silicate, and phosphate were measured immediately near the station by a Technicon AutoAnalyzer (Eberlein et al, 1983).…”

Section: Methodsmentioning

confidence: 99%

“…Our studies were carried out in water enclosed in bags and in the ambient fjord water. During POSER (Brockmann et al, 1983) the biological and chemical changes in enclosures and fjord were monitored by measuring phytoplankton, zooplankton and nutrient concentrations.…”

Section: Introductionmentioning

confidence: 99%

Nutrient and plankton development in Rosfjorden and enclosed ecosystems captured from changing water bodies during POSER

Kattner¹,

Hammer²,

Eberlein³

et al. 1983

Self Cite

During POSER (Plankton Observations with Sinlultaneous Enclosures in Rosfjorden) in spring 1979, nutrient and plankton development were investigated in an open south Norwegian fjord and in different enclosures. Enclosures were plastic tubes, 1 m in diameter and up to 40 m long, fastened to a central float. The water in the fjord exchanged several times. This could be well documented also by changes in nutrient, phyto-and zooplankton concentrations. Water with different plankton and nutrient concentrations was enclosed in order to exclude advective processes. The experiment was divided into 3 main periods. In the first period the water in the fjord was haline. nutrient-rich, and slightly stratified, due to a bloom of Skeletonema costaturn. During this phase the phytoplankton disappeared in the fjord and in the enclosures within 6 d, likely due to low light intensities. In the second period, following a water exchange, the water was less haline, poorer in nutrients, and richer in phytoplankton (mainly Thalassiosira nordenskioeldii) and in zooplankton. Part of this water was enclosed until silicate and phytoplankton concentrations became depleted and the major zooplankton species. Calanus finmarchicus, had developed to the third copepodite-stage. In the third period, following a new upwelling of haline and nutrient-rich water up to 10 m depth, 1 enclosure was filled with well-stratified water, nutrient-poor in the upper layer, but nutrient-rich below. In spite of sufficient nutrients the phytoplankton biomass decreased in this enclosure as well as in the fjord. This was partly caused by increasing numbers of copepodites, which reached more than 50 '10 of the phytoplankton biomass during the last 8 d of our observations.

“…Sampling methods and analytical methods were described by Brockmann and Hentzschel (1983) and Kuiper et al (1983). A detailed account of physical, chemical and biological variations in the fjord was given by Brockmann et al (1981).…”

Section: Introductionmentioning

confidence: 99%

Influences of bag dimensions on the development of enclosed plankton communities during POSER

Kuiper¹,

Brockmann²,

Groenewoud³

et al. 1983

Self Cite

During POSER (Plankton Observations with Simultaneous Enclosures in Rosfjorden) natural plankton communities were enclosed by large plastic bags anchored in situ. Enclosures of different dimensions, ranging in depth from 3 to 40 m and containing 1.5 to 30 m3 of water, facilitated the study of dimension effects of the enclosure on the development of the plankton inside. When comparing mean values in small bags with those of the total mixed layer of large bags, phytoplankton development was very similar in large and small enclosures. Although large and small enclosures had been filled simultaneously, bacterial numbers increased faster in small than in large enclosures, probably because of closer contact with the substrate. Copepod populations suffered high mortalities, in particular in small bags. Their mortality may have been influenced by the extremely cold weather prevailing during the experiment. It appeared that fluctuations in environmental factors (temperature, light, nutrients, etc.) were much more important for plankton development than the dimensions of the enclosure. The suitability of enclosures for studylng natural plankton ecosystem is discussed. It is concluded that optimum dimensions depend on the aim of the experiment, number of trophic levels enclosed, population density at these levels and on the species present at these levels. For ecotoxicological experiments with marine phyto-and zooplankton communities in eutrophic waters, enclosures of 1 to 2 m3 are sufficiently large, and for practical reasons should be preferred over larger ones. In more oligotrophic waters, enclosures with a volume of ca. 10 m3 are to be preferred, so that larger zooplankton samples can be taken.