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Marianne Holmer Ole Pedersen Dorte Krause-Jensen Birgit Olesen Malene Hedegrd Petersen Stephanie Schopmeyer Marguerite Koch Bente Aa. Lomstein Henning S. Jensen 《Estuarine, Coastal and Shelf Science》2009,85(2):319-326
Sulfur and oxygen dynamics in the seagrasses Thalassia testudinum and Syringodium filiforme and their sediments were studied in the US Virgin Islands (USVI) in order to explore sulfide intrusion into tropical seagrasses. Four study sites were selected based on the iron concentration in sediments and on proximity to anthropogenic nutrient sources. Meadow characteristics (shoot density, above- and below-ground biomass, nutrient content) were sampled along with sediment biogeochemistry. Sulfide intrusion was high in T. testudinum, as up to 96% of total sulfur in the plant was derived from sediment-derived sulfides. The sulfide intrusion was negatively correlated to the turnover of sulfides in the sediments regulated by both plant parameters and sediment sulfur pools. Sediment iron content played an indirect role by affecting sulfide turnover rates. Leaf production was negatively correlated with sulfide intrusion suggesting that active growth reduced sulfide intrusion. Sulfide intrusion was lower in S. filiforme (up to 44%) compared to T. testudinum consistent with a higher internal nighttime oxygen concentrations found for S. filiforme. When S. filiforme can take advantage of its ability to maintain high internal oxygen concentrations, as was the case on the USVI, it could increase its success in colonizing unvegetated disturbed sediments with potentially high sulfide concentrations. 相似文献
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Birger Ulf Hansen Ole Humlum Niels Nielsen Dorte P. Lundqvist Ditte L. Jansen Christian Christiansen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):93-109
An automatic meteorological station has been operating at the Arctic Station (69°15'N, 53°31'W) in West Greenland since 1990. This paper summarises meteorological parameters during 2002, including snow cover, ground temperatures and active layer development, and air temperatures at the Station during the last 12 years are compared to large scale trends during the last century. A compilation of 93 sedimentation rate determinations based on 210Pb dating has been carried out for the North Sea-Baltic Sea transition area from a database containing 165 determinations carried out by Danish institutions. In the depositional parts of the area sedimentation rates generally range 25–6403 g m?2 y?1. An extreme rate of 13351 g m?2 y?1 is observed on a station in the Skagerrak. Sedimentation rates significantly increase with depth indicating that the Skagerrak and northern parts of the Kattegat as well as the deep basins in the Baltic Sea act as depocentres for fine-grained sediments. Apparently, sedimentation rates have increased in recent years. 相似文献
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Concentration profiles of O2, NH4 +, NO3 −, and PO4 3− were measured at high spatial resolution in a 12-cm thick benthic mat of the filamentous macroalga Chaetomorpha linum. Oxygen and nutrient concentration profiles varied depending on algal activity and water turbulence. High surface irradiance stimulated O2 production in the surface layers and introduced O2 to deeper parts of the mat while the bottom layers of the mat and the underlying sediment were anoxic. Nutrient concentrations were highest in the bottom layers of the mat directly above the sediment nutrient source and decreased towards the surface layers due to algal assimilation and enhanced mixing with the overlying water column. Increased turbulence during windy periods resulted in more homogeneous oxygen and nutrient concentration profiles and shifted the oxic-anoxic interface downward. Denitrification within the mat, as measured by the isotope pairing technique on addition of 15NO3 −, was found to take place directly below the oxic-anoxic interface. Denitrification activity was always due to coupled nitrification-denitrification, whereby nitrifiers in the mat utilize NH4 + diffusing from below and O2 diffusing from above. The denitrification rate in the mat ranged from 22 μmol m−2 h−1 to 28 μmol m−2 h−1, approximately equivalent to that measured in the surrounding nonvegetated sediment. Although sediment denitrification is suppressed when the sediment surface is covered by a dense macroalgal mat, the denitrification zone may migrate up into the mat. In eutrophic estuaries with a large area of macroalgal cover, the physical structure and growth stage of algal mats may thus play an important role in the regulation of nitrogen removal by denitrification. 相似文献
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Use of alternative conceptual models to assess the impact of a buried valley on groundwater vulnerability 总被引：2，自引：1，他引：1
Dorte Seifert Torben O. Sonnenborg Peter Scharling Klaus Hinsby 《Hydrogeology Journal》2008,16(4):659-674
A buried valley incised into a sequence of pre-Quaternary sediments is shown to seriously affect the vulnerability of groundwater. Often the existence of buried valleys is not known or is not described explicitly in a hydrogeological model. In the present study, two numerical groundwater models, representing two alternative conceptual models, were produced to help quantify the effect of the valley on groundwater vulnerability. One model included the buried valley and the other did not. Both models were subjected to calibration and were found to describe hydraulic head and river discharge equally well. Even though the two models showed similar calibration statistics; fluxes, travel paths and travel times were affected by the inclusion of the buried valley. The recharge area and the groundwater age of potential abstraction wells placed in the pre-Quaternary deep aquifers surrounding the buried valley were different for the two models, with significantly higher vulnerability when the valley was included in the model. Based on the results of the present study, it is concluded that a buried valley may not always be detectable when calibrating a wrong conceptual model. If reliable results should be obtained a good geological model has to be constructed. 相似文献
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Biomass-Cover Relationship for Eelgrass Meadows 总被引：1，自引：0，他引：1
Eelgrass meadows play key roles in coastal ecosystems, and the extent of the standing biomass is focal to address ecosystem functioning. Eelgrass cover is commonly assessed in marine monitoring programs while biomass sampling is destructive and expensive. Therefore, we have proposed a functional relationship that translates eelgrass cover into aboveground biomass using site-specific information on Secchi depth or light attenuation. The relationship was estimated by non-linear regression on 791 combined observations of eelgrass cover and biomass from eight different coastal sites in Denmark. Eelgrass biomass initially increased with cover and flattened out as cover exceeded 40–50 % due to increased self-shading. Decreasing light energy with depth reduced the eelgrass biomass potential (assessed at 100 % cover), and this reduction was stronger for coastal sites with lower water transparency. Moreover, the biomass potential varied seasonally from around 110–140 g DW m?2 in spring months to a peak of 241 g DW m?2 in August, consistent with other seasonal studies. The model explained 56 % of the variation in log-transformed biomasses, but significant variation between coastal sites still remained, deviating between ?23 and 39 % from the mean relationship. These site-specific deviations could be due to differences in losses related to grazing, drifting algae and epiphytes, better light capture by dense canopies, as well as differences in how well light conditions within eelgrass meadows are represented by actual measurements of Secchi depth and light attenuation. The relationship can be employed to estimate eelgrass biomass of entire coastal ecosystems from observations of eelgrass cover and depth. 相似文献
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Based on a large data set from the national Danish monitoring program, spatial and temporal variability in total algal cover and in the fraction of opportunistic macroalgae was analysed in relation to environmental variables. Variations in water clarity and salinity combined with information on geographical location of sampling areas were found to explain almost 80% of the large-scale variation in algal cover between areas. As water clarity was largely regulated by concentrations of total-nitrogen (TN), and TN-concentrations by TN-input from land, total algal cover at given water depths was partly related to TN-input from land. The fraction of opportunistic algae responded predominantly to differences in salinity, the highest fractions being found in the most brackish areas. Temporal variability in algal cover and fraction of opportunists over the 14-year investigation period was much smaller than the variability between areas and could not be predicted from variations in environmental variables. In order for macroalgal cover to become a more sensitive indicator of water quality it would be necessary to either increase the sensitivity of the method or identify and include supplementary regulating factors in the model. 相似文献
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Carlos M. Duarte Núria Marbà Dorte Krause-Jensen María Sánchez-Camacho 《Estuaries and Coasts》2007,30(4):652-656
The power of equations predicting seagrass depth limit (Zc) from light extinction (K
z) was tested on data on seagrass depth limits collected from the literature. The test data set comprised 424 reports of seagrass
colonization depth and water transparency, including data for 10 seagrass species. This data set confirmed the strong negative
relationship betweenZ
c andK
z. The regression equation in Duarte (1991) overestimated the realized seagrass colonization depths at colonization depths
< 5 m, while there was no prediction bias above this threshold. These results indicated that seagrass colonizing turbid waters
(K
z 0.27 m-1) have higher apparent light requirements than those growing in clearer waters. The relationship between seagrass colonization
depth and light attenuation shifts at a threshold of light attenuation of 0.27 m-1, requiring separate equations to predictZ
c for seagrass growing in more turbid waters and clearer waters, and to set targets for seagrass restoration and conservation
efforts. 相似文献
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Benthic flora can contribute significantly to gross primary production (GPP) of shallow coastal waters where light reaches
the sea bottom. We quantified and compared benthic and pelagic GPP along nutrient gradients in time and space in the shallow
estuary, Limfjorden, Denmark, based on monitoring data combined with historical information. Limfjorden experienced a shift
from a pristine, benthic-dominated clear water regime with high total GPP in the early twentieth century to a eutrophic, plankton-dominated
regime still with high total GPP in the 1980s when nutrient loadings peaked. Recent reductions in nutrient loadings reduced
pelagic GPP, particularly in spring, but water clarity and benthic GPP did not increase correspondingly, so total GPP declined.
The most nutrient-rich basins have remained plankton-dominated, with benthic vegetation constrained to shallow waters. The
results support existing evidence that total GPP of shallow coastal areas does not increase systematically with eutrophication.
Furthermore, the results suggest that total GPP may decline temporarily during oligotrophication as pelagic GPP declines,
while feedback mechanisms delay or prevent restoration to a state with benthic dominance of GPP. 相似文献