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1.
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
2.
Marine fish farming is increasing rapidly in the Mediterranean and in contrast to the Atlantic the coastal zone in the Mediterranean is characterized by clear waters with high transparency. This allows benthic primary producers such as the slow-growing seagrass Posidonia oceanica to grow at large depths at locations suitable for fish farming and generating a conflict between the conservation of these meadows and the growth of aquaculture operations in the Mediterranean. In this paper we review the current knowledge on environmental interactions between fish farming and benthic primary producers with particular focus on P. oceanica, as this seagrass is a key component along Mediterranean coasts. The recovery times of P. oceanica are very long, in the order of centuries, and losses of this species are thus considered to be irreversible at managerial time scales. 相似文献
3.
Eskil Mattsson Madelene Ostwald S.P. Nissanka Björn Holmer Matilda Palm 《Ocean & Coastal Management》2009,52(1):1-9
By using an integrated approach, tsunami affected land, vegetation and inhabitants were assessed to evaluate the potential to restore and protect coastal land in the context of Kyoto Protocol's Clean Development Mechanism in Hambantota district in the south-eastern part of Sri Lanka. Firstly, assessments of the status of the tsunami affected area were carried out by collecting soil and well water samplings for carbon and salinity analysis. Secondly, identification of potential tree species for carbon sequestration and sustainable development was conducted to determine carbon stock and suitability to grow under the prevailing conditions. In addition, interviews to understand the local people's perception of forest plantations and land use were conducted. The results showed that the resilience process of salt intruded lands from the 2004 Asian tsunami has progressed rapidly with low salinity level in the soils 14 months after the event, while the well water showed evidence of salinity contamination. The carbon stock was highest in natural forests followed by coconut plantations. Land users could envision expanding their present plantations or establish new ones. The barriers were defined as lack of financial investment capital and limited land for extended plantations. If a Clean Development Mechanism project is to be established, the coconut tree was found to be the most appropriate tree species since it has high carbon content, had co-benefits and possesses a salt-tolerant characteristic. Finally, the tsunami event has triggered land users to perceive environmental benefits of protection from mangrove or other adequate vegetation such as coconut plantations as welcome and desired to decrease their vulnerability. The assessment of multi-functionality of forest plantations, such as small-scale community based Clean Development Mechanism, its generated income from carbon credits as well as the wish for environmental protection should be considered to increase the attractiveness of plantation projects in the coastal areas. 相似文献
4.
Janina Konarska Fredrik Lindberg Annika Larsson Sofia Thorsson Björn Holmer 《Theoretical and Applied Climatology》2014,117(3-4):363-376
Trees play an important role in mitigating heat stress on hot summer days, mainly due to their ability to provide shade. However, an important issue is also the reduction of solar radiation caused by trees in winter, in particular at high latitudes. In this study, we examine the transmissivity of total and direct solar radiation through crowns of single street trees in Göteborg, Sweden. One coniferous and four deciduous trees of species common in northern European cities were selected for case study. Radiation measurements were conducted on nine clear days in 2011–2012 in foliated and leafless tree conditions using two sunshine pyranometers—one located in shade of a tree and the other one on the roof of an adjacent building. The measurements showed a significant reduction of total and direct shortwave radiation in the shade of the studied trees, both foliated and leafless. Average transmissivity of direct solar radiation through the foliated and defoliated tree crowns ranged from 1.3 to 5.3 % and from 40.2 to 51.9 %, respectively. The results confirm the potential of a single urban tree to reduce heat stress in urban environment. However, the relatively low transmissivity through defoliated trees should be considered while planning street trees in high latitude cities, where the solar access in winter is limited. The results were used for parameterisation of SOLWEIG model for a better estimation of the mean radiant temperature (Tmrt). Measured values of transmissivity of solar radiation through both foliated and leafless trees were found to improve the model performance. 相似文献
5.
Marianne Holmer Núria Marbà Morgane Lamote Carlos M. Duarte 《Estuaries and Coasts》2009,32(3):456-466
Species of the macroalgae Caulerpa sp. are increasingly being observed in meadows of the endemic Mediterranean seagrass Posidonia oceanica, and in particular Caulerpa taxifolia, has been considered as an invasive species leading to seagrass decline. Studies have so far failed to reveal the underlying
mechanisms of the success of the macroalgae, and here, we examine how biogeochemical changes of the environment associated
to indigenous (Caulerpa prolifera) and non-indigenous (Caulerpa racemosa and C. taxifolia) species affect the habitat of P. oceanica. Two of the species (C. prolifera and C. racemosa) affect the sediment biogeochemical conditions by increasing organic matter pools, microbial activity, and sulfide pools
of the sediments, and limited effects were found for C. taxifolia. Biomass of the macroalgae contributed to the extent of impacts, and high sulfide invasion into the seagrasses and regression
of the meadow were pronounced at the location with the highest Caulerpa biomass. This suggests that Caulerpa invasion contributes to seagrass decline probably because Caulerpa thrives better than the seagrasses in the modified environment. 相似文献
6.
The urban surface wind field in the dry-tropical city of Ouagadougou, Burkina Faso was studied based on data collected at one urban and one suburban station during early dry season. An intra-urban thermal breeze, creating almost opposite wind directions at the two sites, was found during nights with high atmospheric stability. The high atmospheric stability suggests a decoupling of the surface wind layer from the layer above, allowing the wind system to develop due to the strong intra-urban temperature gradients in the city. Frequent temporary breakdowns of the thermal wind system were noticed, generally generating a turn in wind direction towards that of the regional wind, thus indicating a re-coupling with a stronger wind flow in the wind layer above. 相似文献
7.
A nomogram is developed to show that pH, redox potentials (EhNHE) and measures of dissolved sulfides (H2S + HS− + S2−)(total free S2−) can be used to classify organic enrichment impacts in marine sediments. The biogeochemical cycle of sulfur in marine sediments is described to show that changes in macrobenthic infauna community structure associated with high levels of organic matter supply result from stress due to oxygen deficiency (hypoxia and anoxia) and toxic effects of S2−. The changes reflect enhancement of microbial sulfate reduction under conditions of high organic matter sedimentation and the progressive formation of hypoxic–anoxic conditions measured by decreased EhNHE and increased concentrations of S2−. The nomogram provides a basis for classification of the oxic status of marine sediments based on changes in inter-related biological and biogeochemical variables along an organic enrichment gradient. 相似文献
8.
Summary The paper presents a study of the Urban Heat Island Circulation (UHIC) in Göteborg, Sweden. Observations and recordings have been carried out from 1981 to 1986 during winter nights with anticyclonic weather conditions. The UHIC develops in general at a large negative net radiation balance, when the heat island intensity is at least 2.5°C, the wind speed less than 3 m/s and the sky is clear. If the weather conditions are favourable the UHIC starts 4–6 hours after midnight and stops a few hours after sunrise. An increase in cloud cover during the late night will not prevent the development of the UHIC. The UHIC layer extends to 40–70 metres in the vertical direction and to 10–13 km in the horizontal direction. The UHIC layer is capped by an inversion and the flow is almost independent of the direction of the regional flow. The UHIC is of great importance for the concentrations of air pollutions in Göteborg, as it transports both polluted and clean air. The study is a part of a clean air programme in the Göteborg area.With 7 Figures 相似文献
9.
A histopathological assessment of the gonad of male fish was performed as part of biological field studies carried out in coastal waters and small rivers in Mecklenburg-Western Pomerania, northeastern Germany. In the marine environment the eelpout (Zoarces viviparus) was selected as sentinel species. The three spined stickleback (Gasterosteus aculeatus) and perch (Perca fluviatilis) were chosen at freshwater locations. Histopathology of the testis revealed the presence of intersexuality in specimens of all three species. The intersex condition was defined by the simultaneous presence of primary oocytes within the apparently normal testis tissue. In comparison to stickleback and perch the eelpout exhibited the highest intersex prevalence and the most severe histological alterations. Fish with intersex were found at contaminated marine and freshwater stations as well as at sites with apparently little pollution. The findings suggest that feminised male fish were exposed to endocrine disrupting substances in the aquatic environment. 相似文献
10.
P. Jonsson I. Eliasson B. Holmer C. S. B. Grimmond 《Theoretical and Applied Climatology》2006,85(3-4):185-201
Summary This study investigates differences in longwave incoming radiation (L↓) within and between three African cities, Dar es Salaam (Tanzania), Ouagadougou (Burkina Faso), and Gaborone (Botswana),
during the dry season, and evaluates the performance of a model to simulate these fluxes. In each city, direct observations
of L↓, shortwave incoming radiation (K↓), air temperature, air humidity, and total suspended particle (TSP) concentration for three land uses (CBD, green residential,
and traditional residential) were taken. The observed L↓ flux decreases with increasing latitude, and temperature becomes an increasingly important factor in governing L↓ variations further from the Equator. Humidity, as well as particle loading, differs significantly between the three cities.
Differences between observed and modelled ɛsky for rural stations near all cities showed a clear diurnal variation, with maximum differences of 0.08 between day and night.
This diurnal difference was incorporated in the model and, for urban areas the model overestimates L↓ by around 25 Wm−2. However, this model performs equally well regardless of the land use considered in any of the cities. The residual (difference
between observed and modelled urban L↓) did not show any correlation with particulate pollution. However, the difference between observed and calculated ɛsky is around 0.05 higher in Ouagadougou compared to the other cities, likely due to the heavy dust load observed here. It is
concluded that tropical urban longwave radiation is not dramatically different from the mid latitudes. 相似文献