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  • ELSEVIER SCIENCE BV
  • 2020-2020
  • 2005-2009  (5)
  • 1
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    ELSEVIER SCIENCE BV
    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 220(18), pp. 2173-2186, ISSN: 0304-3800
    Publication Date: 2018-02-16
    Description: We present a five-year (1997-2001) numerical simulation of daily mean chlorophyll a concentrations at station Geesthacht Weir on the lower Elbe River (Germany) using an extremely simple Lagrangian model driven by (a) water discharge, global radiation, water temperature, and (b) silica observations at station Schmilka in the upper reach of the Elbe River. Notwithstanding the lack of many mechanistic details, the model is able to reproduce observed chlorophyll a variability surprisingly well, including a number of sharp valleys and ascents/descents in the observed time series. The model's success is based on the assumption of three key effects: prevailing light conditions, sporadic limitation of algal growth due to lack of silica and algae loss rates that increase above an empirically specified temperature threshold of 20 degrees C. Trimmed-down model versions are studied to analyse the model's success in terms of these mechanisms. In each of the five years the model consistently fails, however, to properly simulate characteristic steep increases of chlorophyll a concentrations after pronounced spring minima. Curing this model deficiency by global model re-calibration was found to be impossible. However, suspension of silica consumption by algae for up to 10 days in spring is shown to serve as a successful placeholder for processes that are disregarded in the model but apparently play an important role in the distinctly marked period of model failure. For the remainder of the year the very simple model was found to be adequate
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    ELSEVIER SCIENCE BV
    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 213(2), pp. 229-244, ISSN: 0304-3800
    Publication Date: 2018-02-16
    Description: A simple Lagrangian water quality model was designed to investigate the hypothesis of sporadic silica limitations of diatom growth in the lower Elbe River in Germany. For each fluid parcel a limited reservoir of silica was specified to be consumed by diatoms. The model's simplicity notwithstanding, a set of six selected model parameters could not be fully identified from existing observations at one station. After the introduction of prior knowledge of the ranges of meaningful parameter values, calibration of the over-parameterised model manifested itself primarily in the generation of posterior parameter covariances. Estimations of the covariance matrix based on (a) second order partial derivatives of a quadratic cost function at its optimum and (b) Monte Carlo simulations exploring the whole space of parameter values gave consistent results. Diagonalisation of the covariance matrix yielded two linear parameter combinations that were most effectively controlled by data from periods with and without lack of silica, respectively. The two parameter combinations were identified as the essential inputs that govern the successful simulation of intermittently decreasing chlorophyll a concentrations in summer. A satisfactory simulation of the pronounced chlorophyll a minimum in spring, by contrast, was found to be beyond the means of the simple model.
    Repository Name: EPIC Alfred Wegener Institut
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  • 3
    Publication Date: 2019-08-23
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 254(3-4), pp. 197-215, ISSN: 0025-3227
    Publication Date: 2019-07-17
    Description: We studied the impact of the last glacial (late Weichselian) sea level cycle on sediment architecture in theinner Kara Sea using high-resolution acoustic sub-bottom profiling. The acoustic lines were ground-truthedwith dated sediment cores. Furthermore we refined the location of the eastern LGM ice margin, by new subbottom profiles. New model results of post-Last Glacial Maximum (LGM) isostatic rebound for this area allowa well-constrained interpretation of acoustic units in terms of sequence stratigraphy. The lowstand (orregressive) system tract sediments are absent but are represented by an unconformity atop of Pleistocenesediments on the shelf and by a major incised dendritic paleo-river network. The subsequent transgressiveand highstand system tracts are best preserved in the incised channels and the recent estuaries while onlyminor sediment accumulation on the adjacent shelf areas is documented. The Kara Sea can be subdividedinto three areas: estuaries (A), the shelf (B) and (C) deeper lying areas that accumulated a total of 114 x1010 t of Holocene sediments.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    ELSEVIER SCIENCE BV
    In:  EPIC3Aquaculture, ELSEVIER SCIENCE BV, 254(1-4), pp. 714-729, ISSN: 0044-8486
    Publication Date: 2015-06-25
    Description: For most fish species raised in marine aquaculture, the use of live feeds cannot be replaced by formulated diets. Artemia nauplii and rotifers are still the most commonly used live feeds. A good alternative lies in the use of copepods which could lead to the cultivation of new fish species. Cold stored subitaneous eggs from the continuously cultured calanoid copepod Acartia tonsa were used to investigate the effect of storage upon the viability of the eggs, the development of the copepod community originating from the cold stored eggs. Finally a 3 days snapshot of the egg production of the first generation of females was followed. This was done in order to develop a database usable within copepod dependent hatcheries. The viability of cold stored A. tonsa eggs remained high (〉 70% hatching rate) for 11 months of storage. Generally, the period of storage was observed to decrease the viability (hatching rate) of the eggs and no hatching was observed after twenty months of cold storage. Hatched populations of copepods experienced increased mortality rate with longer storage of the eggs from which they originated. This mortality ranged from 0.035 to 0.13 d− 1 for non-stored (fresh) and 12 months stored eggs, respectively. However, all copepod communities originating from fresh to 12 months stored eggs reached adulthood. Additionally, the egg production from the stored generation was apparently normal and the viability of their eggs was not statistically different when compared to productions from non-stored communities. Contents of total fatty acids decreased during the storage period. Contents of free amino acids were not statistically different for eggs cold stored up to 12 months, but had decreased severely by 20 months. In conclusion, we consider it safe to store the eggs for up to one year at 2–3 °C during which the eggs retain their viability and biochemical composition. Cold storage of calanoid copepod eggs is relevant for aquaculture as inoculum for culturing live food.
    Repository Name: EPIC Alfred Wegener Institut
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