Some Methods of Binding Prawn Diets and Their Effects on Growth and Assimilation     

Forster  J. R. M. 《ICES Journal of Marine Science》1972,34(2):200-216

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Relationship of intertidal surface sediment chlorophyll concentration to hyperspectral reflectance and chlorophyll fluorescence     

Jacco C. Kromkamp  Edward P. Morris  Rodney M. Forster  Claire Honeywill  Scott Hagerthey  David M. Paterson 《Estuaries and Coasts》2006,29(2):183-196

Estimating biomass of microphytobenthos (MPB) on intertidal mud flats is extremely difficult due to their patchy occurrence, especially at the scale of an entire mud flat. We tested two optical approaches that can be applied in situ: spectral reflectance and chlorophyll fluorescence. These two approaches were applied in 4 European estuaries with different sediment characteristics. At each site, paired replicate measurements of hyperspectral reflectance, chlorophyll fluorescence (after 15 min dark adaptation, F_o ¹⁵), sediment water content, and chlorophylla concentrations were taken (including breakdown products: [chla+phaeo]). Sediments were further characterized by grain size and organic content analysis. The spectral signatures of tidal flats dominated by benthic microalgae, mainly diatoms, could be easily distinguished from sites dominated by macrophytes; we present a 3 waveband algorithm that can be used to detect the presence of macrophytes. The normalized difference vegetation index (NDVI) was found to be most strongly correlated to sediment [chla+phaeo], except for the predominantly sandy Sylt stations. F_o ¹⁵ was also significantly correlated to sediment [chla+phaeo] in all but one grid (Sylt grid A). Our results suggest that the functional relationships (i.e., the slopes) between NDVI or fluorescence and [chla+ phaeo] were not significantly different in the muddier grids, although the intercepts could differ significantly, especially for F_o ¹⁵. This suggests a mismatch of the optical depth seen by the reflectometer or fluorometer and the depth sampled for pigment analysis. NDVI appears to be a robust proxy for sediment [chla+phaeo] and can be used to quantify MPB biomass in muddy sediments of mid latitude estuaries.  相似文献   

Lake-Level Fluctuations and Small-Scale Vegetation Patterns During the Late Glacial in The Netherlands     

Johanna A. A. Bos  Sjoerd J. P. Bohncke  C. Roel Janssen 《Journal of Paleolimnology》2006,35(2):211-238

Late glacial changes in the vegetation were studied in and around a former lake on the southeastern side of a coversand ridge near Milheeze (southern Netherlands). Analyses of microfossils and macroremains and AMS ¹⁴C dating were performed on four sediment cores along a transect from sand ridge to the lake centre. Small-scale vegetation patterns and lake-level fluctuations were reconstructed in detail based on the information provided by the transect. For the first time in The Netherlands, cores along a transect within one lake were used to reconstruct the amplitude of late glacial lake-level fluctuations. Near Milheeze, a small and shallow lake was formed during the Bølling. The large increase in the water level during the Bølling and early Allerød, and the transition to more eutrophic conditions at the start of the Allerød, were probably related to the disappearance of permafrost. During the Allerød, open birch and pine woodlands developed in the area. In the lake, organic deposits accumulated, and the lake size and depth fluctuated. At the start of the Younger Dryas, higher lake water levels were recorded and woodlands became more open as a result of both a drop in the temperature and an increase in the effective precipitation. During the late Younger Dryas the lake water level dropped as the climate became drier and temperatures slightly increased. Accumulation of organic deposits in the lake ceased at the end of the Younger Dryas, which was caused by a drop in the water level in combination with the hydroseral succession process within the lake itself. The climatic signal reflected in the late glacial flora and lake-level fluctuations agree well with other published data from The Netherlands.  相似文献   

Regional and temporal changes in epizoobiontic bryozoan-communities of Flustra foliacea (Linnaeus, 1758) and implications for North Sea ecology     

F. Bitschofsky  S. Forster  J. Scholz 《Estuarine, Coastal and Shelf Science》2011,91(3):423-433

Until recently, bryozoans have not been used as indicators for changes in bottom communities or climate control in the North Sea Basin, despite a 200-year history of bryozoan collecting. The epizoobiontic bryozoan fauna of Flustra foliacea (Linnaeus, 1758) was analysed on 51 sample stations kept in four German museums. The samples cover the entire North Sea and different time periods (1776–2008, mainly the period of 1904/1905 compared to 1980–87). Cluster analysis shows a differentiation into a northern and a southern North Sea assemblage. The northern assemblage is characterized by Amphiblestrum flemingii (Busk, 1854), Callopora dumerilii (Audouin, 1826) and Tricellaria ternata (Ellis & Solander, 1786), while the southern North Sea is characterized by Electra pilosa (Linnaeus, 1767), Crisia eburnea (Linnaeus, 1758) and Plagioecia patina (Lamarck, 1816). Spatial separation approximately follows the 50 m depth contour. The temporal distribution patterns of bryozoans are discussed in terms of NAO (North Atlantic Oscillation) and temperature variations.  相似文献   

Evaluating property buyouts and disaster recovery assistance (Rebuild) options in Canada: A comparative analysis of Constance Bay,Ontario and Pointe Gatineau,Quebec     

Cottar  Shaieree  Doberstein  Brent  Henstra  Daniel  Wandel  Johanna 《Natural Hazards》2021,109(1):201-220

Natural Hazards - How have property buyouts and disaster recovery assistance programs been implemented in Canadian communities? This paper compares contrasting policies and programs in two Canadian...  相似文献   

Social capital,individual responses to heat waves and climate change adaptation: An empirical study of two UK cities     

Johanna Wolf  W. Neil Adger  Irene Lorenzoni  Vanessa Abrahamson  Rosalind Raine 《Global Environmental Change》2010,20(1):44-52

It has been claimed that high social capital contributes to both positive public health outcomes and to climate change adaptation. Strong social networks have been said to support individuals and collective initiatives of adaptation and enhance resilience. As a result, there is an expectation that social capital could reduce vulnerability to risks from the impacts of climate change in the health sector. This paper examines evidence on the role social networks play in individuals’ responses to heat wave risk in a case study in the UK. Based on interviews with independently living elderly people and their primary social contacts in London and Norwich, we suggest that strong bonding networks could potentially exacerbate rather than reduce the vulnerability of elderly people to the effects of heat waves. Most respondents interviewed did not feel that heat waves posed a significant risk to them personally, and most said that they would be able to cope with hot weather. Bonding networks could perpetuate rather than challenge these narratives and therefore contribute to vulnerability rather than ameliorating it. These results suggest a complex rather than uniformly positive relationship between social capital, health and adaptation to climate change.  相似文献   

Probable causes for cyanobacterial expansion in the Baltic Sea: Role of anoxia and phosphorus retention     

Per?WestmanEmail author  Johanna?Borgendahl  Thomas?S.?Bianchi  Nianhong?Chen 《Estuaries and Coasts》2003,26(3):680-689

This study corroborates the hypothesis that nitrogen-fixing cyanobacteria have probably occurred as an important component of the phytoplankton community in the Baltic Sea at least since brackish water conditions were initiated 8,500¹⁴C yr BP. Pigment analyses indicate that extensive occurrences started prior to a sharp increase in nutrient levels dated to 7,100¹⁴C yr BP. The cyanobacteria could have functioned as a natural trigger for eutrophication in the Baltic Sea by importing nitrogen. This is also verified by a contemporaneous drop in the δ¹⁵N values from 4‰ to around 2‰. We further conclude that the spreading of cyanobacteria was probably caused by a decrease in nitrogen∶phosphorus (N∶P) in the water mass that resulted from the intrusion of oceanic water with high P levels. The fractionation of P in sediments indicated that iron-bound P was efficiently sequestered under anoxic conditions that occurred as a consequence of the establishment of a stable stratification caused by the marine intrusion. This pool only showed minor variations around 3 μmol g⁻¹ at the freshwater-brackish water transition. All P pools except the CaCO₃ fraction showed a distinct increase around 9,300¹⁴C yr BP prior to the transition. We interpreted this increase as a change in preservation of organic matter or in the source of the sediment. Slightly after 4,000¹⁴C yr BP there was a dramatic drop in all P pools without any corresponding decreases in total N and carbon. Total P decreased from around 75 to 25–30 μmol g⁻¹. The most dramatic drop occurred in the organic bound and the detrital apatite fractions, which decreased by a factor of 3–4. We explain this as a preferential regeneration of P, especially organic P, compared to other nutrients due to more prevalent anoxic conditions.  相似文献   

Seals, cod and forage fish: A comparative exploration of variations in the theme of stock collapse and ecosystem change in four Northwest Atlantic ecosystems     

Alida Bundy  Johanna J. Heymans  Lyne Morissette  Claude Savenkoff   《Progress in Oceanography》2009,81(1-4):188

The facts: four Northwest Atlantic ecosystems, three cod stock collapses 15 years ago (plus one severely depleted), seals now top predator in all ecosystems, all had cod as a top predator before collapse, groundfish declines in all areas, forage base increased in most systems. No recovery in any system. Have these ecosystems fundamentally changed? Why? The challenge: compare and contrast these four ecosystems. The answer: using mass balance models, empirical data and a suite of ecosystem indicators, we explore how and why these systems have changed over time. At the ecosystem and community level, we see broad similarities between ecosystems. However, structurally and functionally these systems have shifted to an alternate state, with changes in predator structure, trophic structure and flow.  相似文献   

Extreme weather impacts on freight railways in Europe     

Johanna Ludvigsen  Ronny Klæboe 《Natural Hazards》2014,70(1):767-787

Four cases are studied in this assessment of how the harsh 2010 winter weather affected rail freight operations in Norway, Sweden, Switzerland and Poland and also of the reactive behaviour rail managers mobilised to reduce the adverse outcomes. The results are utilised in a fifth case assessing the proportion of freight train delays in Finland during 2008–2010 by modelling the odds for freight train delays as a function of changes in met-states on the Finnish network and weather-induced infrastructure damage. The results show that rail operators were totally unprepared to deal with the powerful and cascading effects of three harsh weather elements—long spells of low temperatures, heavy snowfalls and strong winds—which affected them concurrently and shut down large swathes of European rail infrastructure and train operations. Rail traffic disruptions spread to downstream and upstream segments of logistics channels, causing shippers and logistics operators to move freight away from rail to road transfer. As a result, railways lost market share for high-value container cargo, revenues and long-term business prospects for international freight movement. Analyses of measures employed to mitigate the immediate damage show that managers improvised their ways of handling crises rather than drew on a priori contingency, i.e. fight-back programmes and crisis management skills. Modelling the co-variation between extreme weather and freight train delays in Finland during 2008–2010 revealed that 60 % of late arrivals were related to winter weather. Furthermore, the combined effect of temperatures below ?7 °C and 10–20 cm changes in snow depth coverage from 1 month to the next explained 62 % of the variation in log odds for freight train delays. Also, it has been shown that changes in the number of days with 10–20 cm snow depth coverage explained 66 % of the variation in late train arrivals, contributing to 626 min or 10.5 additional hours’ delay. Changes in the number of days with snowfalls over 5 mm accounted for 77 % variation in late train arrivals, implying that each additional day with this snowfall could contribute to 19.5 h’ delay. Finally, the combination of increased mean number of days with 5 mm snowfall and temperature below ?20 °C explained 79 % of the variation in late arrivals, contributing to 193 min or 3.25 h’ delay. All results were significant (p = 0.00).  相似文献   

Man as geological agent     

Tony Waltham  & Alan Forster 《Geology Today》1999,15(6):217-220

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