Extinction considerations for diadromous fishes   总被引：1，自引：0，他引：1  

Jonsson  B.; Waples  R. S.; Friedland  K. D. 《ICES Journal of Marine Science》1999,56(4):405-409

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Carbon stock assessment of mangrove ecosystems in Batticaloa Lagoon,Sri Lanka,with different degrees of human disturbances     

Maja Naemi Jonsson  Astrid Margaretha Hedman 《Singapore journal of tropical geography》2019,40(2):199-218

This article presents a carbon stock assessment to illustrate the organic carbon distribution and storage within mangrove ecosystems in Sri Lanka. The living tree biomass and soil carbon pools were investigated in three sites with varying degree of human disturbance in Batticaloa Lagoon. Soil carbon content was derived by the Walkley Black method from soil samples and mangrove trees were measured for calculations in general allometric equations. The mangroves that were extremely converted into a shrimp farm in Kokkaddicholai recorded a carbon (C) stock of 100.9 kg m‐2. Dominated by the poisonous Excoecaria agallocha stands, the regenerating mangroves in Manmunai Bridge Island hosted the largest C stock measuring 786.4 kg C m‐2. The Kannankudah site—dominated by Avicennia marina, Lumnitzera racemosa and Excoecaria agallocha stands, recorded a C stock of 593.1 kg C m‐2. Cuts and stumps indicated wood harvesting for local livelihoods. The soil C content pool contributed most significantly to the total C stock, with the top 30 cm containing the largest C concentration in all soil profiles. The soil carbon content was highest (5.1 per cent) in Kannankudah, second highest (3.6 per cent) in the disturbed but regenerating forest at Manmunai Bridge Island, and the lowest (0.3 per cent) at the converted site of Kokkaddicholai.  相似文献   

Episodic riverine influence on surface DIC in the coastal Gulf of Maine     

Joseph Salisbury  Douglas Vandemark  Christopher Hunt  Janet Campbell  Bror Jonsson  Amala Mahadevan  Wade McGillis  Huijie Xue 《Estuarine, Coastal and Shelf Science》2009

Anomalously high precipitation and river discharge during the spring of 2005 caused considerable freshening and depletion of dissolved inorganic carbon (DIC) in surface waters along the coastal Gulf of Maine. Surface pCO₂ and total alkalinity (TA) were monitored by repeated underway sampling of a cross-shelf transect in the western Gulf of Maine (GOM) during 2004–05 to examine how riverine fluxes, mixing, and subsequent biological activity exert control on surface DIC in this region. Most of the variability in surface DIC concentration was attributable to mixing of low DIC river water with higher DIC, saline GOM waters, but net biological uptake of DIC was significant especially during the spring and summer seasons. The extent and persistence of the coastal freshwater intrusion exerted considerable influence on net carbon dynamics. Integrated over the 10-m surface layer of our study region (∼5 × 10⁴ km²), net biological DIC uptake was 0.48 × 10⁸ mol C during April–July of 2004 compared to 1.33 × 10⁸ mol C during April–July of 2005. We found the temporal signature and magnitude of DIC cycling to be different in adjacent plume-influenced and non-plume regions. Extreme events such as the freshwater anomaly observed in 2005 will affect mean estimates of coastal carbon fluxes, thus budgets based on short time series of observations may be skewed and should be viewed with caution.  相似文献   

Drought is the major limiting factor for tree-ring growth of high-altitude Canary Island pines on Tenerife   总被引：2，自引：0，他引：2  

Stig Jonsson  Björn Gunnarson  & Constantino Criado 《Geografiska Annaler: Series A, Physical Geography》2002,84(1):51-71

This is a detailed study of 50 wood cores sampled from 25 Canary Island pines ( Pinus canariensis ) growing in a subtropical climate close to the tree limit (at Lomo de Retamar, 2000–2100 m a.s.l.) on the southern, leeward side of Tenerife.
The Canary Island pines form tree-rings and, similarly to temperate pines, earlywood is formed during spring. But many pines fail to form tree-rings every year and one purpose for this paper has been to find a way to overcome this problem. Another purpose has been to see what correlations, if any, exist between the ring widths and meteorological data. Meteorological data have been collected since 1916 at the nearby Izaña meteorological observatory. It was also important to find the limiting factor for growth of Canary Island pines close to the tree limit.
Through cross-dating, missing rings were found to be typical for younger parts of older trees; in the same years younger trees instead had low growth. Some trees lacked more than 20 rings in a century. This study shows that it is possible to compensate for missing rings, at least when the number of missing rings is less than 10%.
Correlation studies showed that the growth of the tree rings was mainly due to the precipitation factor, particularly the annual precipitation one year before the ring formation, but also due to temperature. Strangely enough, multiple linear regression gave the highest correlation coefficient (0.50) for a combination of annual precipitation one year earlier and temperature four years earlier.  相似文献   

Toxic effects of decomposing red algae on littoral organisms   总被引：2，自引：0，他引：2  

Britta Eklund  Andreas P. Svensson  Conny Jonsson  Torleif Malm   《Estuarine, Coastal and Shelf Science》2005,62(4):621-626

Large masses of filamentous red algae of the genera Polysiphonia, Rhodomela, and Ceramium are regularly washed up on beaches of the central Baltic Sea. As the algal masses start to decay, red coloured effluents leak into the water, and this tinge may be traced several hundred meters off shore. In this study, possible toxic effects of these effluents were tested on littoral organisms from different trophic levels. Effects on fertilisation, germination and juvenile survival of the brown seaweed Fucus vesiculosus were investigated, and mortality tests were performed on the crustaceans Artemia salina and Idotea baltica, as well as on larvae and adults of the fish Pomatoschistus microps. Fucus vesiculosus was the most sensitive species of the tested organisms to the red algal extract. The survival of F. vesiculosus recruits was reduced with 50% (LC50) when exposed to a concentration corresponding to 1.7 g l⁻¹ dw red algae. The lethal concentration for I. baltica, A. salina and P. microps were approximately ten times higher. The toxicity to A. salina was reduced if the algal extract was left to decompose during two weeks but the decline in toxicity was not affected by different light or temperature conditions. This study indicates that the filamentous red algae in the central Baltic Sea may produce and release compounds with negative effects on the littoral ecosystem. The effects may be particularly serious for the key species F. vesiculosus, which reproduce in autumn when filamentous red algal blooms are most severe.  相似文献   

Power resource estimate of ocean surface waves     

Ivar G. Jonsson 《Ocean Engineering》1977,4(4-5):211-212

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A review of ecological and behavioural interactions between cultured and wild Atlantic salmon   总被引：3，自引：3，他引：3  

Jonsson  B. 《ICES Journal of Marine Science》1997,54(6):1031-1039

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Energy properties and shoaling of higher-order stokes waves on a current   总被引：1，自引：0，他引：1  

Ivar G. Jonsson  Lars Arneborg 《Ocean Engineering》1995,22(8)

The energy density, the energy flux, the set-down, the radiation stress, and some wave energy velocities have been derived correct to fourth order in wave steepness for waves on a vorticity-free current. The energy flux and the set-down have been used for shoaling predictions for finite amplitude waves with and without a net volume flux. The results with a zero volume flux are compared with more accurate shoaling predictions showing rather good accordance, except for large steepnesses. This also applies to the deep water wave energy transport velocity. The results with a net volume flux show that the steepness of the waves reduces the influence of this flux on the wave evolution. Some problems in connection with the orders in Stokes waves are discussed, among others concerning the dispersion relation and the orders of integral properties. Bed shear and accompanying dissipation is neglected.  相似文献   

Climate variability and the Icelandic marine ecosystem     

Olafur S. Astthorsson  Astthor Gislason  Steingrimur Jonsson   《Deep Sea Research Part II: Topical Studies in Oceanography》2007,54(23-26):2456

This paper describes the main features of the Icelandic marine ecosystem and its response to climate variations during the 20th century. The physical oceanographic character and faunal composition in the southern and western parts of the Icelandic marine ecosystem are different from those in the northern and the eastern areas. The former areas are more or less continuously bathed by warm and saline Atlantic water while the latter are more variable and influenced by Atlantic, Arctic and even Polar water masses to different degrees. Mean annual primary production is higher in the Atlantic water than in the more variable waters north and east of Iceland, and higher closer to land than farther offshore. Similarly, zooplankton production is generally higher in the Atlantic water than in the waters north and east of Iceland. The main spawning grounds of most of the exploited fish stocks are in the Atlantic water south of the country while nursery grounds are off the north coast. In the recent years the total catch of fish and invertebrates has been in the range of 1.6–2.4 million ton. Capelin (Mallotus villosus) is the most important pelagic stock and cod (Gadus morhua) is by far the most important demersal fish stock. Whales are an important component of the Icelandic marine ecosystem, and Icelandic waters are an important habitat for some of the largest seabird populations in the Northeast Atlantic.In the waters to the north and east of Iceland, available information suggests the existence of a simple bottom-up controlled food chain from phytoplankton through Calanus, capelin and to cod. Less is known about the structure of the more complex southern part of the ecosystem. The Icelandic marine ecosystem is highly sensitive to climate variations as demonstrated by abundance and distribution changes of many species during the warm period in the 1930s, the cold period in the late 1960s and warming observed during the recent years. Some of these are highlighted in the paper.  相似文献   

Current-depth refraction of water waves     

Ivar G. Jonsson  John D. Wang   《Ocean Engineering》1980,7(1):153-171

Surface gravity waves propagating on large-scale currents over a gently sloping sea bed are considered. Assuming irrotational flow a general proof is given of the existence of a mean energy level, leading directly to the current wave set-down. The complete set of conservation equations describing combined current-depth refraction is presented and solved in two special ssituations. Also a case with a rotational current is considered. Dissipation is neglected.  相似文献