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1.
Stable isotope analysis was used to investigate the migratory status and to determine the relative contribution of allochthonous and autochthonous sources of carbon for the major riverine fish species ( Barbus altianalis and Labeo victorianus ) in rivers draining the Kenyan side of Lake Victoria. The two fish species derived carbon from both C4 and C3 plant sources, although L. victorianus exhibited less enriched isotopic carbon values. Fish samples from stations under direct influence of effluents from sugar factories exhibited enriched δ13 C signals. Assuming that this reflects carbon sourcing from riparian C4 plants, it suggests that carbon from terrestrial sources can be a major energy source in some rivers. This heavy carbon enrichment associated with sugar factories was spatially restricted and occurred in all seasons, implying that sub-populations of the two fish species are non-migratory. The large migratory populations of these two species, for which Lake Victoria was once famous, may be no more. 相似文献
2.
Understanding future ecosystem changes is central to sustainable natural resource management especially when coupled with in-depth understanding of impacts of drivers, such as governance, demographic, economic and climate variations and land use policy. This offers comprehensive information for sustainable ecosystem services provision. A foresight process of systematic and presumptive assessment of future state and ecosystem integrity of Lake Victoria basin, as participatory scenario building technique, is presented. Four scenarios have been illustrated as possible future states of the basin over the next twenty years. Using a scenario building model developed in Ventana Simulation (VENSIM® ) platform, the paper presents a scenario methodology for tracking changes in lake basin ecosystem status. Plausible trends in land use change, changes in lake levels and contribution of fisheries are presented. This is part of an initial attempt to setup long-term environmental policy planning strategies for Lake Victoria basin. The assumptions, driving forces, impacts and opportunities under each scenario depict major departure and convergence points for an integrated transboundary diagnosis and analysis of regional issues in the basin as well as strategic action planning for long-term interventions. The findings have been presented in terms of temporal, spatial, biophysical and human well-being dimensions. The attempts in this study can be embedded in a policy framework for basin management priority setting and may guide partnerships for environmental management. 相似文献
3.
Organochlorine residues in fish from Lake Victoria, Kenya 总被引:1,自引:0,他引:1
Eighty-two samples of either nile perch fish fat or muscle were collected from the Kenyan region of Lake Victoria for detection of organochlorine residues. Nine organochlorine residues were detected in the following percentages: α-BHCIHCB-40%; P-BHC/HCB-40%; y-BHC/HCB/lindane-4%; aldrin-9%; dieldrin-1%; p, p'-DDE-73%; p, p'-DDD-9%; o, p'-DDT-170; and p, p'-DDT-11%. All levels of organochlorine residues were below the Extraneous Residue Limit (ERL), apart from just one sample of fish fat which had 4.51 ppm of sum DDT above ERL. There was a higher level of organochlorines from Mbita than from Luanda fishing point.
Eighty-two échantillons de graisse ou de muscle de perche du Nil ont été récoltés dans la région kényane du lac Victoria pour rechercher des résidus organochlorés. On a détecté 9 résidus organochlorés, avec les pourcentages suivants: α-BHC/HCB-40%; β-BHC/HCB-40%;γ-BHC/HCB/lindane-4%;aldrine-9%; dieldrine-1%; p, p'-DDE-73%; p, p'-DDD-9%; o, p'-DDT-1%; and p, p'-DDT-11%. Tous les taux de résidus organochlorés ktaient infkrieurs a la 'Extraneous Residue Limit' (ERL) sauf pour un seul échantillon de graisse de poisson qui contenait 4,51 ppm de DDT total au-dessus de 1'ERL. I1 y avait un taux plus élevé d'organochlorés a Mbita qu'au point de pêche de Luanda. 相似文献
Résumé
Eighty-two échantillons de graisse ou de muscle de perche du Nil ont été récoltés dans la région kényane du lac Victoria pour rechercher des résidus organochlorés. On a détecté 9 résidus organochlorés, avec les pourcentages suivants: α-BHC/HCB-40%; β-BHC/HCB-40%;γ-BHC/HCB/lindane-4%;aldrine-9%; dieldrine-1%; p, p'-DDE-73%; p, p'-DDD-9%; o, p'-DDT-1%; and p, p'-DDT-11%. Tous les taux de résidus organochlorés ktaient infkrieurs a la 'Extraneous Residue Limit' (ERL) sauf pour un seul échantillon de graisse de poisson qui contenait 4,51 ppm de DDT total au-dessus de 1'ERL. I1 y avait un taux plus élevé d'organochlorés a Mbita qu'au point de pêche de Luanda. 相似文献
4.
Drivers of ecosystem change and their impacts on human well-being in Lake Victoria basin 总被引:1,自引:0,他引:1
To offer an increased understanding of the spatial patterns, temporal, social and physical predictors of the conversion and transformations of land use in Lake Victoria basin, an assessment of proximate and underlying forces is presented. This study discusses key theoretical underpinnings for the manifold linkages existing between selected drivers of land-use changes around the basin and their consequences on human well-being. Using a meta-analytical research design, the paper analyses ecosystems level cases of the causes of land use and cover changes in the basin, to determine any spatio-temporal or institutional patterns and dynamics. A suite of recurrent core variables has been identified to influence land use and cover changes in the basin. The most prominent of these at the underlying category are climatic factors, economic factors, institutions, national and regional policies, population growth and other remote influences. At the proximate level, these factors drive cropland expansion, overgrazing, infrastructure extension and rates of land degradation. These are supported by empirical evidence from the basin. This assessment is crucial for appropriate local and transboundary policy interventions, which have to be fine-tuned to the locale-specific dynamic patterns associated with the inherent ecosystems changes. 相似文献
5.
Luca Bracchini Steven Arthur Loiselle Antonio Tognazzi Arduino M. Dattilo Silvia Focardi Andrés Cózar Claudio Rossi 《Wetlands Ecology and Management》2007,15(6):509-519
In tropical lakes, the characteristics and dimension of the coastal wetlands can have a strong influence on the quality of
the inshore waters. The interaction between littoral wetlands and the open water environment is complex and requires an understanding
of the material and energy exchanges between these compartments. In the present analysis, we examine the impact of wetlands
on the optical properties (underwater light environment) of two adjacent bays on the Ugandan side of Lake Victoria. We use
both irradiance profiles within the water column as well as measurements of the dissolved and particulate fractions of the
water column. By introducing a new term to identify that part of the solar spectrum most affected by wetland released dissolved
organic matter, it is possible to determine the area of each bay that is influenced by the wetland. Depending on the period
of analysis, wetland released chromophoric dissolved organic matter can play a dominating role in the attenuation of UV and
visible radiation in the underwater environment. 相似文献
6.
The aquatic macrophytic vegetation constituting the wetlands situated along the coast of Lake Victoria provides valuable services
to both local and regional communities as well as an important ecological function through the transition between terrestrial
and aquatic ecosystems. The wetland vegetation is typically rooted in the substrate on the landward side of the lake, but
forms a floating mat towards the middle of the wetland and at the wetland/lake interface. Cyperus papyrus and Miscanthidium violaceum vegetation typically dominate the permanently inundated wetland areas along most of the shores of Lake Victoria. Due to the
prevailing climatic and hydrological catchment conditions, these macrophytic plants (papyrus in particular) tend to exhibit
high net productivity and nutrient uptake which strongly influences both wetland status and lake water quality. In addition,
these wetlands provide important economic livelihoods for the local populations. The integrity and physical structure of these
wetlands strongly influences their associated mass transport mechanisms (water, nutrients and carbon) and ecosystem processes.
Wetland degradation in Africa is an increasing problem, as these ecosystems are relied upon to attenuate industrial, urban
and agricultural pollution and supply numerous services and resources. In an integrated project focused on the wetlands of
Lake Victoria, the ecological and economic aspects of littoral wetlands were examined and new instruments developed for their
sustainable management. 相似文献
7.
S. Garner T. P. Birt † C. M. Mlewa ‡ J. M. Green § A. Seifert ¶ V. L. Friesen 《Journal of fish biology》2006,69(SB):189-199
Marbled lungfish Protopterus aethiopicus in Lake Victoria and two nearby smaller lakes were found to have high levels of DNA sequence variation in their mitochondrial control regions (35 haplotypes in 61 fish) but no population genetic structure (ΦST = 0·00). In contrast, marbled lungfish in Lake Baringo, Kenya, appeared to be fixed for a single control region haplotype, which occurred at low frequency in the other lakes. Using FLUCTUATE software, the female effective population size in Lake Victoria during the late Pleistocene was estimated to be c. 500 000, similar to the value estimated for the present-day population. These observations suggest that, during the late Pleistocene dry period, a large marbled lungfish population survived either in wet refugial areas within the lake basin or in surrounding areas. Marbled lungfish were reported to have been introduced into Lake Baringo 30 years ago with a founding population of only three individuals. The lack of control region variation in the Lake Baringo population is consistent with that situation. 相似文献
8.
Sources of organic carbon in the littoral of Lake Gooimeer as indicated by stable carbon isotope and carbohydrate compositions 总被引:1,自引:1,他引:0
The relative importance of potential carbon sources in the littoral of Lake Gooimeer, a lake in the centre of the Netherlands, was studied using a combination of 13C/12C-ratio analysis and carbohydrate composition analysis. The littoral is covered on the land side by a 80 m wide Phragmites australis bed. Potential carbon sources were macrophyte litter, seston and benthic algae. Samples of potential carbon sources, sediments and benthic macrofauna from inside and outside the bed were analyzed for their13C/12C-ratio and some for their carbohydrate composition. Results indicate that inside the bed, macrophyte litter was the main source of carbon for both the sediment organic matter and the benthic macrofauna, and that algal material was of minor importance. Outside the bed, production by benthic algae was the main carbon source, with seston as a second source. No macrophyte derived material could be detected outside the reed bed.Abbreviations DOC
(Dissolved Organic Carbon)
- SOM
(Sediment Organic Matter) 相似文献
9.
A stable carbon isotope study of dissolved inorganic carbon cycling in a softwater lake 总被引:3,自引:0,他引:3
Andrew L. Herczeg 《Biogeochemistry》1987,4(3):231-263
The dissolved inorganic carbon (DIC) cycle in a softwater lake was studied using natural variations of the stable isotopes of carbon,12C and13C. During summer stratification there was a progressive decrease in epilimnion DIC concentration with a concomitant increase in 13CDIC), due to preferential uptake of12C by phytoplankton and a change in the dominant CO2 source from inflow andin situ oxidation to invasion from the atmosphere. There was an increase in hypolimnion DIC concentration throughout summer with a concomitant general decrease in 13CDIC from oxidation of the isotopically light particulate organic carbon that sank down through the thermocline from the epilimnion.Mass balance calculations of DI12C and DI13C in the epilimnion for the summer (June 23–September 25) yield a mean rate of net conversion of DIC to organic carbon (Corg) of 430 ± 150 moles d-1 (6.5 ± 1.8 m moles m-2 d-1. Net CO2 invasion from the atmosphere was 420 ± 120 moles d-1 (6.2 ± 1.8 m moles m-2 d-1) with an exchange coefficient of 0.6 ± 0.3m d-1. These results imply that at least for the summer months the phytoplankton obtained about 90% of their carbon from atmosphere CO2. About 50% of CO2 invasion and conversion to Corg for the summer occurred during a two week interval in mid-summer.DIC concentration increased in the hypolimnion at a rate of 350 ± 70 moles DIC d-1 during summer stratification. The amount of DIC added to the hypolimnion was equivalent to 75 ± 20% of net conversion of DIC to Corg in the euphotic zone over spring and summer implying rapid degradation of POC in the hypolimnion. The 13C of DIC added to the deep water (-22.) was too heavy to have been derived from oxidation of particulate organic carbon alone. About 20% of the added DIC must have diffused from hypolimnetic sediments where relatively heavy CO2 (-7) was produced by a combination of POC oxidation and as a by-product of methanogenesis. 相似文献
10.
The growing prevalence of metabolic diseases including fatty liver disease and Type 2 diabetes has increased the emphasis on understanding metabolism at the mechanistic level and how it is perturbed in disease. Metabolomics is a continually expanding field that seeks to measure metabolites in biological systems during a physiological stimulus or a genetic alteration. Typically, metabolomics studies provide total pool sizes of metabolites rather than dynamic flux measurements. More recently there has been a resurgence in approaches that use stable isotopes (e.g. 2H and 13C) for the unambiguous tracking of individual atoms through compartmentalised metabolic networks in humans to determine underlying mechanisms. This is known as metabolic flux analysis and enables the capture of a dynamic picture of the metabolome and its interactions with the genome and proteome. In this review, we describe current approaches using stable isotope labelling in the field of metabolomics and provide examples of studies that led to an improved understanding of glucose, fatty acid and amino acid metabolism in humans, particularly in relation to metabolic disease. Examples include the use of stable isotopes of glucose to study tumour bioenergetics as well as brain metabolism during traumatic brain injury. Lipid tracers have also been used to measure non-esterified fatty acid production whilst amino acid tracers have been used to study the rate of protein digestion on whole body postprandial protein metabolism. In addition, we illustrate the use of stable isotopes for measuring flux in human physiology by providing examples of breath tests to measure insulin resistance and gastric emptying rates. 相似文献
11.
Nutrient concentrations in Nyanza Gulf, Lake Victoria, Kenya: light limits algal demand and abundance 总被引:1,自引:0,他引:1
Nyanza Gulf is a large shallow embayment connected to Lake Victoria by the deep narrow Rusinga Channel. Between December 2000 and May 2002 the gradient of nutrients along the axis of Nyanza gulf into the main lake was determined. Nutrient concentrations in the gulf were found to be different from those in the main lake with phosphorus fractions, SRP and TP being significantly higher in the main lake than in the gulf. Well oxygenated conditions in the gulf keep the PO4–P strongly bound to mineral particles whereas in the main lake, where deeper depths allows for development of anoxia, it is released into solution. The low TN:TP molar ratio in the gulf and in the main lake indicates many algae may be N-limited and heterocystous N-fixing cyanobacteria may be favored. However, the high mineral turbidity in the gulf reduces light availability and hence limits algal abundance resulting in easily measure concentrations of mineral nutrients and in particular high levels of dissolved reactive silica. The gulf is a net source of dissolved silica and total nitrogen to the main lake while the main lake is potentially a source of P to the gulf depending on interchange through Rusinga Channel. 相似文献
12.
多稳态现象普遍存在于多种生态系统中,它与生态系统的健康和可持续发展密切相关,已成为生态学研究的热点与难点,但是目前有关滨海湿地生态系统多稳态的形成机制还缺乏深入研究.本文以崇明东滩鸟类自然保护区的潮间带生态系统为研究对象,通过以下内容,开展滨海湿地多稳态研究: 1)通过验证多稳态的判定依据“双峰”和“阈值”特征,证实长江口潮间带生态系统存在多稳态,并确定其稳态类型;2)通过监测潮间带生态系统水动力过程、沉积动力过程以及盐沼植物生长和扩散情况,分析盐沼植被与沉积地貌之间的正反馈作用,进而探讨潮间带生态系统多稳态的形成机制.结果表明: 1)潮间带生态系统的归一化植被指数(NDVI)频度分布存在明显的双峰特征,且盐沼植物成活存在生物量阈值效应,均证实潮间带生态系统存在多稳态,“盐沼”和“光滩”是潮间带生态系统的两种相对稳定状态;2)崇明东滩盐沼前沿的沉积地貌表现出泥沙快速淤积的趋势,显著促进了盐沼植物的生长,盐沼植物与泥沙淤积之间的这种正反馈作用是潮间带生态系统形成多稳态的主要原因;3)盐沼植被扩散格局监测结果在景观尺度上也表明,泥沙淤积作用促进了潮间带生态系统“盐沼”和“光滩”多稳态的形成.本研究既丰富了滨海湿地稳态转换的机理研究,也为我国开展海岸带保护、修复和管理提供了科学依据,具有重要的理论和实践意义. 相似文献
13.
本研究应用碳、氮稳定同位素技术分析了2017年秋季(10月)和2018年春季(3月)湖北省荆州长湖鱼类营养结构特征,构建了δ13C和δ15N稳定同位素双位图,并计算了7个相关的量化指标。结果显示:所采集的16种鱼类,δ13C均值范围为(-27.7±0.8)‰~(-24.8±0.1)‰,δ15N的均值范围为(11.4±0.3)‰~(16.6±0.5)‰。营养生态位分析显示,长湖鱼类以偏肉食性鱼类黄颡鱼的营养级最高(3.28±0.2),草鱼的营养级最低(1.74±0.1)。稳定同位素的量化指标表明,长湖春季鱼类群落核心生态位空间(standard ellipse area, SEA)、生态位总空间(total area, TA)和基础食物来源(δ13C range, CR)均高于秋季,两个季度的营养多样性(centrifugal distance, CD)和鱼类群落的整体密度(mean nearest neighbor distance, MNND)相似,但春季的营养长度(δ15N range, NR)和鱼类群落营养生态位分布范围(standard deviation of nearest neighbor distance, SDNND)值低于秋季。说明春季长湖的生态位总空间(TA上升)和基础食物来源(CR上升)较为丰富,但因鱼类种类的食性相近,其群落的总食物链降低(NR下降)。该研究可为分析拆围后长湖鱼类群落结构特征积累基础数据,也为长湖的渔业管理策略提供依据。 相似文献
14.
We have measured stable isotopic compositions of Miocene pelagic fine-fraction (<63 μm) carbonates from oligotrophic deep-sea sites in the Pacific and Atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea-surface indicators. Fine-fraction carbonates (primarily polyspecific nannofossils) and surface-dwelling planktic foraminiferal (Globigerinoides) stable isotopes both have been considered to reflect surface-water hydrographic conditions. However, our results indicate that fine-fraction stable isotopes are offset from and do not correlate well with those of Globigerinoides. In contrast, stable isotopic records of the deep-dwelling planktic foraminifer Globoquadrina are in good correspondence with the fine-fraction records in terms of long-term (ca. >1 m.y.) trends and temporal variability. On the basis of a time-series hydrography and flux study site in the oligotrophic subtropical North Atlantic, we interpret the isotopic discrepancies between fine-fraction and Globigerinoides as resulting primarily from season of calcification, as well as possible vital effects. We suggest that fine-fraction stable isotope values from oligotrophic waters reflect late winter–early spring relatively cool, nutrient-rich shallow mixed-layer conditions during the time of deep mixing (i.e., spring bloom), whereas Globigerinoides stable isotope values record conditions that prevailed in the stratified surface waters in the warmer late spring–fall. This implies that paired analyses of fine-fraction and surface-dwelling planktic foraminiferal δ18O could be applied to reconstruct paleoseasonality of the open oceans. However, because the fine-fraction δ13C values are not representative of the annual mean surface-water δ13C, we recommend use of near surface-dwelling planktic foraminiferal δ13C as a proxy for δ13C of stratified surface waters that are more or less in equilibrium with the atmosphere with respect to pCO2. 相似文献
15.
《Animal : an international journal of animal bioscience》2013,7(12):1935-1943
Fractional passage rates form a fundamental element within modern feed evaluation systems for ruminants, but knowledge on feed-specific fractional passage is largely lacking. Commonly applied tracer techniques based on externally applied markers, such as chromium-mordanted neutral detergent fibre (Cr-NDF), have been criticised for behaving differently to feed particles. This study describes the use of the carbon stable isotope ratio (13C : 12C) as an internal digesta marker to quantify the fractional passage rate of concentrates through the digestive tract of dairy cows. In a crossover study, five dairy cows were fed low (24.6%) and high (52.6%) levels of concentrates (dry matter (DM) basis) and received a pulse-dosed Cr-NDF and 13C isotopes. The latter was administered orally by exchanging part of the dietary concentrates of low 13C natural abundance with a pulse dose of maize bran-based concentrates of high 13C natural abundance. Fractional passage rates from the rumen (K1) and from the large intestine (K2) were determined from faecal marker concentrations of Cr-NDF and of 13C in the DM (13C-DM), NDF (13C-NDF) and neutral detergent soluble (13C-NDS). No differences in K1 estimates were found for the two concentrate levels fed but significant differences between markers (P<0.001) were observed. Faecal Cr-NDF excretions gave lower K1 estimates (0.037–0.039/h) than 13C-DM (0.054–0.056/h) and 13C-NDF (0.061–0.063/h). The 13C-NDS was calculated by the difference of 13C in the DM and NDF, and K1 values (0.039–0.043/h) were comparable to Cr-NDF. Total mean retention time was considerably higher for Cr-NDF (40.9–42.0 h) as compared to 13C-DM and 13C-NDF (32.0–33.5 h; P<0.001). The accuracy of the curve fits for Cr-NDF and 13C-DM and 13C-NDF was overall good (mean prediction error of 9.9–13.9%). Fractional passage rate of Cr-NDF was comparable to studies where this marker was assumed to represent the fractional passage of roughages. However, K1 estimates based on the 13C : 12C ratio varied considerably from studies based on external markers. Our results suggest that the use of 13C isotopes as digesta passage markers can provide feed component-specific K1 estimates for concentrates and provides new insight into passage kinetics of NDF from technologically treated compound feed. 相似文献
16.
通过测定上海市青浦区东风港百慕大、白花三叶草、高羊茅和白茅等4种典型滨岸草本植物各组织以及不同垂直深度土壤有机质δ13C值,对滨岸草地生态系统的植物-土壤碳稳定同位素特征进行了分析.结果表明: 白花三叶草、高羊茅属于C3植物,百慕大、白茅属于C4植物,其茎叶、凋落物和根系各组织间δ13C值无显著差异.C3和C4植物样带表层土壤有机质δ13C值随着土壤深度递增而呈现截然不同的变化特征,这与样带本底δ13C值以及碳稳定同位素分馏效应有关,同时还受植物根系分布深度的影响.植物输入是土壤有机碳(SOC)的最主要来源,植物有机体δ13C组成对土壤有机质δ13C值有直接影响,植物各组分δ13C值与土壤有机质δ13C值均存在极显著相关.4种草本植物样带SOC含量与δ13C值均呈极显著相关,其中,C3植物样带SOC含量与δ13C值呈线性负相关,C4植物样带SOC含量与δ13C值呈线性正相关. 相似文献
17.
Origin and cycling of riverine inorganic carbon in the Sava River watershed (Slovenia) inferred from major solutes and stable carbon isotopes 总被引:1,自引:0,他引:1
The Sava River and its tributaries in Slovenia represent waters strongly influenced by chemical weathering of limestone and
dolomite. The carbon isotopic compositions of dissolved inorganic carbon (DIC) and suspended organic carbon (POC) fractions
as well as major solute concentrations yielded insights into the origin and fluxes of carbon in the upper Sava River system.
The major solute composition was dominated by carbonic acid dissolution of calcite and dolomite. Waters were generally supersaturated
with respect to calcite, and dissolved CO2 was about fivefold supersaturated relative to the atmosphere. The δ13C of DIC ranged from −13.5 to −3.3‰. Mass balances for riverine inorganic carbon suggest that carbonate dissolution contributes
up to 26%, degradation of organic matter ∼17% and exchange with atmospheric CO2 up to 5%. The concentration and stable isotope diffusion models indicated that atmospheric exchange of CO2 predominates in streams draining impermeable shales and clays while in the carbonate-dominated watersheds dissolution of
the Mesozoic carbonates predominates. 相似文献
18.
Origin and fate of organic carbon in the freshwater part of the Scheldt Estuary as traced by stable carbon isotope composition 总被引:12,自引:1,他引:11
We investigated the seasonal and geographical variation in the stable carbon isotope ratios of total dissolved inorganic carbon (13CPOC) and suspended matter (13CPOC) in the freshwater part of the River Scheldt. Two major sources of particulate organic matter (POM) occur in this riverine system: riverine phytoplankton and terrestrial detritus. In winter the lowest 13CDIC values are observed due to enhanced input of CO2 from decomposition of 13C-depleted terrestrial plant detritus (average 13CDIC = –/14.3). During summer, when litter input from terrestrial flora is the lowest, water column respiration on POM of terrestrial origin is also the lowest as evidenced by less negative 13CDIC values (average 13CDIC = –9.9). In winter the phytoplankton biomass is low, as indicated by low chlorophyll a concentrations (Chl a < 4.5 gl–1), compared to summer when chlorophyll a concentrations can rise to a maximum of 54 gl–1. Furthermore, in winter the very narrow range of 13CPOC (from –26.5 to –27.6) is associated with relatively high C/N ratios (C/N > 9) suggesting that in winter a major fraction of POC is derived from allochthonous matter. In summer 13CPOC exhibits a very wide range of values, with the most negative values coinciding with high Chl a concentrations and low C/N ratios (C/N < 8). This suggests predominance of phytoplankton carbon in the total particulate carbon pool, utilising a dissolved inorganic carbon reservoir, which is already significantly depleted in 13C. Using a simple two source mixing approach a reconstruction of the relative importance of phytoplankton to the total POC pool and of 13C/12C fractionation by phytoplankton is attempted. 相似文献
19.
A simulation model for nitrogen retention in a papyrus wetland near Lake Victoria,Uganda (East Africa) 总被引:1,自引:0,他引:1
A. A. van Dam A. Dardona P. Kelderman F. Kansiime 《Wetlands Ecology and Management》2007,15(6):469-480
Papyrus wetlands around Lake Victoria, East Africa play an important role in the nutrient flows from the catchment to the
lake. A dynamic model for nitrogen cycling was constructed to understand the processes contributing to nitrogen retention
in the wetland and to evaluate the effects of papyrus harvesting on the nitrogen absorption capacity of the wetlands. The
model had four layers: papyrus mat, water, sludge and sediment. Papyrus growth was modelled as the difference between nitrogen
uptake and loss. Nitrogen uptake was modelled with a logistic equation combined with a Monod-type nitrogen limitation. Nitrogen
compartments were papyrus plants, organic material in the floating mat; and total ammonia, nitrate and organic nitrogen in
the water, sludge and sediment. Apart from the uptake and decay rates of the papyrus, the model included sloughing and settling
of mat material into the water, mineralization of organic matter, and nitrification and diffusion of dissolved inorganic nitrogen.
Literature data and field measurements were used for parameterization. The model was calibrated with data from Kirinya wetland
in Jinja, Uganda which receives effluent from a municipal wastewater treatment plant. The model simulated realistic concentrations
of dissolved nitrogen with a stable biomass density of papyrus and predicted accumulation of organic sludge in the wetland.
Assuming that this sludge is not washed out of the wetland, the overall nitrogen retention of the wetland over a three-year
period was 21.5 g N m−2 year−1 or about 25% of input. Harvesting 10, 20 and 30% of the papyrus biomass per year increased nitrogen retention capacity of
the wetland to 32.3, 36.8 and 38.1 g m−2 year−1, respectively. Although the nutrient flows estimated by the model are within the ranges found in other papyrus wetlands,
the model could be improved with regard to the dynamics of detrital nitrogen. Actual net retention of nitrogen in the sludge
is likely to be lower than 21.5 g N m−2 year−1 because of flushing out of the sludge to the lake during the rainy season. 相似文献
20.
Peter B. O. Ochumba 《Hydrobiologia》1990,208(1-2):93-99
The morphometry and hydrology of the Nyanza Gulf of Lake Victoria can be greatly affected by violent storms. This can result in a condition in which nutrient-rich bottom mud is mixed with the sediment-laden runoff water from neighbouring marshes and rivers. This situation can lead to massive fish kills. It is such an event in 1984 which will be described that caused the sudden death of over 400 000 fish weighing over 2400 tonnes.The unusually low precipitation in the catchment area during that year resulted in a drop in the lake level from 12.4 to 11.8 m. This low water level, combined with a severe storm created the conditions which caused this large fish kill. The species affected were Lates niloticus and Oreochromis niloticus. Mortality was attributed to several factors which included high levels of suspended material in the water column (detritus and algae) which clogged the gills of the fish, low dissolved oxygen, low pH, and high concentrations of algae. 相似文献