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71.
Seasonal nitrogen and phosphorus dynamics during benthic clam and suspended mussel cultivation 总被引:1,自引:0,他引:1
Effects of suspended mussel and infaunal clam cultivation on sediment characteristics, and benthic organic and inorganic nitrogen and phosphorus fluxes were compared in a shallow coastal lagoon. The two species had different impacts on sediment features, but both created “hotspots” of nutrient fluxes with annual N and P regeneration rates being 4.9 and 13.5 (mussel) and 4.5 and 14.9 (clams) fold greater than those of unfarmed control sediments. Mussel farming also caused considerable nutrient regeneration within the water column with the mussel ropes contributing ∼25% of total inorganic N and P production and at times dominating the sediments (e.g. 95% of SRP production in summer and 45% of DIN production in winter). Such nutrient regeneration rates seriously question the proposal that suspension-feeding bivalves act as a eutrophication buffer, especially during summer when nutrient regeneration rates are maximal, but other nutrient sources (freshwater run-off and unfarmed sediments) are at their lowest. 相似文献
72.
Mussel farming as a nutrient reduction measure in the Baltic Sea: consideration of nutrient biogeochemical cycles 总被引:1,自引:0,他引:1
Nutrient loads from the land to the sea must be reduced to combat coastal eutrophication. It has been suggested that further mitigation efforts are needed in the brackish Baltic Sea to decrease nutrients, especially in eutrophic coastal areas. Mussel farming is a potential measure to remove nutrients directly from the sea. Mussels consume phytoplankton containing nitrogen (N) and phosphorus (P); when the mussels are harvested these nutrients are removed from the aquatic system. However, sedimentation of organic material in faeces and pseudo-faeces below a mussel farm consumes oxygen and can lead to hypoxic or even anoxic sediments causing an increased sediment release of ammonium and phosphate. Moreover, N losses from denitrification can be reduced due to low oxygen and reduced numbers of bioturbating organisms. To reveal if mussel farming is a cost-effective mitigation measure in the Baltic Sea the potential for enhanced sediment nutrient release must be assessed. 相似文献
73.
74.
富营养化对海洋生态系统的影响及其围隔实验研究 总被引:17,自引:1,他引:16
陆源的营养盐输入引起海洋中的富营养化,提高了水体中营养盐含量,改变了水体中营养盐比例,引起浮游植物水华甚至赤潮。水华发生时由于沿传统食物链的能流在浮游植物环节阻塞,能量过多地分配到微生物环,细菌大量繁殖分解有机物,导致水体缺氧,造成鱼虾贝类窒息死亡。围隔系统是物质相对守恒的系统,围隔与自然海水没有水交换,利用现场围隔实验可以定量地、系统地研究海洋生态系统对富营养化的响应。围隔实验现已成为全球海洋生态系统动力学研究的重要手段。 相似文献
75.
76.
Laurence Laperrière Marie-Andrée Fallu Sonja Hausmann Reinhard Pienitz Derek Muir 《Journal of Paleolimnology》2008,40(1):309-324
Qualitative and quantitative analysis of fossil diatoms and geochemical signals preserved in the sediments of Lac Dauriat
(subarctic Quebec) were performed to evaluate the impacts of nearby mining activity and the expansion of the town of Schefferville
on the water quality of the lake, and to reconstruct the changes of its trophic status. The presence of taxa typical of nutrient-enriched
environments (e.g., Cyclostephanos invisitatus, Nitzschia gracilis, Nitzschia perminuta) and the low percentages of chrysophytes were indicative of the advanced state of eutrophication of the lake during the peak
of mining activity, and were evidence of the negative impacts of municipal waste on the water quality of Lac Dauriat. Sedimentary
analysis of metals, notably lead, mercury, cadmium, bismuth, cobalt, copper and zinc, showed maximum concentrations between
1940 and 1960 with mining era to pre-development enrichment factors ranging from 4.5 to 7.9. The changes seen in recent sediments
reflected 3 distinct stages in the recent history of this ecosystem: (a) the non-perturbed, pre-mining (1882–1939), (b) the
perturbed, mining period (1939–1977) with accelerated eutrophication, and (c) the post-mining period (1977–1999) with indications
of natural recovery of the system after the installation of a water treatment plant in 1975, the closing of the mine in 1983,
and the subsequent exodus of the town’s population. Despite the trajectory towards a return to the lake’s natural conditions,
water resource managers and (paleo-)limnologists should be alarmed that the impacts of past human disturbance are still in
evidence more than 20 years after the closure of the mines, and that Lac Dauriat has yet to reach its natural state of the
period preceding extreme anthropogenic impact. 相似文献
77.
Günter Gunkel 《洁净——土壤、空气、水》2009,37(9):726-734
Reservoirs are man‐made lakes that severely impact on river ecosystems, and in addition, the new lake ecosystem can be damaged by several processes. Thus, the benefits of a reservoir, including energy production and flood control, must be measured against their impact on nature. New investigations point out that shallow and tropical reservoirs have high emission rates of the greenhouse gases CO2 and CH4. The methane emissions contribute strongly to climate change because CH4 has a 25 times higher global warming potential than CO2. The pathways for its production include ebullition, diffuse emission via the water‐air interface, and degassing in turbines and downstream of the reservoir in the spillway and the initial river stretch. Greenhouse gas emissions are promoted by a eutrophic state of the reservoir, and, with higher trophic levels, anaerobic conditions occur with the emission of CH4. This means that a qualitative and quantitative jump in greenhouse gas emissions takes place. Available data from Petit Saut, French Guinea, provides a first quantification of these pathways. A simple evaluation of the global warming potential of a reservoir can be undertaken using the energy density, the ratio of the reservoir surface and the hydropower capacity; this parameter is mainly determined by the reservoir's morphometry but not by the hydropower capacity. Energy densities of some reservoirs are given and it is clearly seen that some reservoirs have a global warming potential higher than that of coal use for energy production. 相似文献
78.
Changes in the benthic macroinvertebrate fauna of a large microtidal estuary following extreme modifications aimed at reducing eutrophication 总被引:1,自引:0,他引:1
M.D. Wildsmith T.H. Rose I.C. Potter R.M. Warwick K.R. Clarke F.J. Valesini 《Marine pollution bulletin》2009,58(9):1250-1262
An artificial channel was opened in 1994 between the microtidal Peel–Harvey Estuary and the Indian Ocean to increase tidal exchange and thus ameliorate the problems of eutrophication. Although this greatly reduced macroalgal and cyanobacterial growths and the amount of particulate organic matter, our data indicate that, contrary to managerial expectations, the benthic environment has deteriorated. Thus, although macroinvertebrate density has declined as predicted, taxonomic distinctness (Δ*) has also declined and species composition has become more variable. Macroinvertebrate composition has also changed markedly at the species, family and even phylum levels. The Crustacea, the most sensitive of the major macrobenthic taxa to environmental stress, has become proportionally less abundant and speciose, whereas the Polychaeta, the least sensitive, was unique in showing the reverse trend. The benthos of the Peel–Harvey Estuary is thus apparently more stressed than previously, probably due to the multiple effects of a great increase in system use. 相似文献
79.
Understanding the effects of anthropogenic eutrophication on coastal fisheries may help in the enhancement of fishery production by effective utilization of sewage effluents, as well as in the consequent reduction of eutrophication. In this study, it was revealed that the nitrogen stable isotope ratio (δ15N) in the soft tissues of the manila clam, Ruditapes philippinarum, can be used as an indicator of anthropogenic eutrophication levels in tidal flat environments by investigation of δ15N in dissolved inorganic nitrogen (DIN), particulate organic matter (POM), sedimentary organic matter (SOM) and soft tissues of the clam in five tidal flats in Japan with different levels of DIN concentration. In addition, it was found that the acid insoluble fraction of the shell organic matrix, conchiolin, can be used as a proxy for the soft tissues in δ15N analyses. This will contribute in easier storage handling and the expansion of chances for sample acquisition. 相似文献
80.