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1.
鲫(Carassius auratus)是我国各类淡水水体的优势鱼类之一.作为底栖杂食性鱼类,一方面,鲫可以通过排泄和扰动沉积物影响湖泊营养和光照水平,通过"上行效应"促进浮游植物生长;另一方面,鲫也可以捕食浮游动物,通过"下行控制"影响藻类生长以及营养盐循环.对于浅水湖泊,两种途径对于生态系统影响的相对重要性仍有待研究.本研究设计了一个两因素户外中宇宙实验,通过在沉积物表面添加隔网的方式,比较两种情况下(能、否接触沉积物),鲫对水体浊度、营养盐和浮游生物生物量的影响.实验在16个大型钢化玻璃桶(400 L)中进行,持续36 d(2019年8月6日—9月11日).研究结果表明:1)在能接触沉积物的条件下,鲫显著促进了沉积物再悬浮,表现为水体的总悬浮物(TSS)和无机悬浮物(ISS)浓度大幅升高;水体的光衰减系数(Kd)增加,总氮(TN)和总磷(TP)浓度明显升高; 2)在不能接触沉积物的条件下,鲫对水体悬浮物(TSS和ISS)浓度和Kd的影响不明显,但是显著降低了水体TN和TP浓度; 3)在两种情况下,鲫对浮游植物叶绿素a浓度以及浮游动物生物量的影响均不显著.本研究表明鲫只有在能够接触沉积物的条件下,才会显著提高水体浊度和营养水平.因此,在缺乏沉水植被的浅水湖泊中,鲫扰动沉积物产生的"上行效应"可能是其对生态系统产生负面影响的主要途径.  相似文献   

2.
Acidification of freshwater ecosystems changes phytoplankton biomass and reduces species composition. However, there are contradictory statements with respect to the occurrence of cyanobacteria below pH 4.5. Textbooks have not reported cyanobacteria in acid and very acid environments, whereas only a few papers on acidification of lakes through acid precipitation noted the occurrence of cyanobacteria in those environments. In a phytoplankton survey of 10 lakes in the Bavarian Forest as well as the lignite mining districts of Bavaria (Upper Palatine) and Lusatia, covering a pH gradient from 8.0 to 2.8, we demonstrate that acid-tolerant cyanobacteria do exist. Most strikingly, one of the most acid lakes (pH 2.9), Lichtenauer See (Lusatia), was inhabited by two populations of filamentous cyanobacteria, resembling Oscillatorial/Limnothrix and Spirulina spp. Eukaryotic phytoplankton was almost absent in this lake at the time. In contrast to filamentous cyanobacteria, picoplanktic ones were totally lacking where pH < 4.5. This indicates that members of coccal picoplanktic cyanobacteria and filamentous cyanobacteria have different acid tolerances. At present, it is not known how the acid-tolerant cyanobacteria described here maintain a strong transmembrane pH gradient.  相似文献   

3.
The stoichiometric composition of lake water chemistry affects nutrient limitation among phytoplankton. I show how TN:TP and DIN:TP ratios vary in oligotrophic lakes of Europe and the USA affected by different amounts of N deposition, and evaluate whether the DIN:TP ratio is a better indicator than the TN:TP ratio for discriminating between N and P limitation of phytoplankton. Data were compiled from boreal and low to high alpine lakes, and comprise epilimnetic lake water chemistry data (106 lakes) and results from short-term nutrient bioassay experiments (28 lakes). A large share (54%) of the oligotrophic lakes in the study had low TN:TP mass ratios (<25). DIN:TP ratios showed higher variability than TN:TP ratios. Variability in DIN:TP ratios was related to N deposition, but also to catchment characteristics. Data from short-term bioassay experiments with separate addition of N and P showed that the DIN:TP ratio was a better indicator than the TN:TP ratio for N and P limitation of phytoplankton. Phytoplankton shift from N to P limitation when DIN:TP mass ratios increase from 1.5 to 3.4. High DIN:TP ratios, indicating P limitation of phytoplankton, were generally found in alpine lakes with low to moderate N deposition and in boreal lakes with high to very high amounts of N deposition.  相似文献   

4.
张民  史小丽  阳振  陈开宁 《湖泊科学》2021,33(4):1051-1061
随着我国湖泊治理力度的加大,太湖和巢湖的营养盐水平,特别是氮水平近年来明显下降,如2007年以后太湖总氮和近年来巢湖的氨氮水平都呈现下降趋势,但是2个湖泊水华蓝藻的优势种却向相反的方向演化,太湖的长孢藻(Dolichospermum)比例在增加,而巢湖的长孢藻比例却在降低,为阐明这种变化过程和驱动因素,本研究利用太湖(19932015年)和巢湖(2012 2018年)的历史数据分析了2个湖泊中的水华蓝藻——微囊藻(Microcystis)和长孢藻生物量的历史变化过程,并结合营养盐数据分析了影响2种水华蓝藻变动的驱动因素.结果显示:太湖和巢湖的微囊藻生物量多年来始终保持高位波动,近年来均有升高的趋势,这与2个湖泊磷的高位波动具有明显的相关性,磷是决定微囊藻生物量长尺度变化的主要驱动因素;太湖的长孢藻生物量呈现较大波动变化,2007年以后明显升高,巢湖的长孢藻生物量则明显下降,氮与长孢藻生物量呈现负相关关系,而且这种负相关仅在低磷浓度时具有显著性.微囊藻生物量对磷浓度变化敏感的正反馈响应是其水华形成的重要机制之一,在高温高磷条件下,微囊藻可以快速繁殖,并竞争性排除长孢藻,从而形成优势;而长孢藻可以通过温度生态位和固氮两种方式占据优势,在氮浓度相对较低,且温度低于微囊藻形成水华的温度范围时,长孢藻可以依靠温度生态位的优势形成水华,而在氮限制的条件下,即使在夏季高温时,长孢藻依然可以利用固氮作用形成水华,但是关键的温度阈值和开始固氮的氮浓度阈值仍不清楚.基于2种水华蓝藻对营养盐变化响应的差异,建议在进行蓝藻水华治理、污染削减过程中,应针对不同水华蓝藻的特性进行分时段分类别的营养盐控制策略.  相似文献   

5.
Bacteria and phytoplankton are integral in the mobilization and transfer of organic matter to higher trophic levels. Hence, we examined their role in zooplankton diets and assessed trends in their nitrogen isotopic variability. We performed feeding experiments with natural particulate organic matter (POM) and four zooplankton groups (Daphnia, Holopedium, large calanoids and small calanoids) to (1) examine whether there are differences in consumption (presented as clearance and ingestion rates) of phytoplankton and bacteria, and (2) determine whether differences in zooplankton clearance and ingestion rates are correlated with their δ15N isotopic signatures. In general, phytoplankton and bacteria clearance rates and biomass ingested per animal varied significantly among different zooplankton groups within lakes and between lakes for a given zooplankton group. Within a given lake, Daphnia and Holopedium had the highest phytoplankton and bacteria clearance and ingestion rates, followed by large calanoids, and then small calanoids. For a given zooplankton group, bacteria and phytoplankton clearance rates varied among lakes. In contrast, phytoplankton ingestion rates were consistently highest in Dickie Lake for all taxa, whereas bacteria ingestion rates were more variable among lakes for the different zooplankton taxa. The percentage contribution of different phytoplankton taxa to the biomass of phytoplankton ingested also varied significantly among lakes for a given taxa, but there were few differences within a given lake among zooplankton. Zooplankton δ15NDOMC values were correlated with their size adjusted phytoplankton and bacteria clearance and ingestion rates. The correlations were stronger with (1) phytoplankton compared to bacteria, and (2) clearance rates compared to ingestion rates of biomass. Together our results suggest that zooplankton taxa with low phytoplankton and bacteria clearance and ingestion rates and higher δ15NDOMC are likely exploiting food sources from higher trophic levels.  相似文献   

6.
This study aimed to understand changes in the biogeochemical processing of organic matter (OM) in response to multiple stressors (e.g., littoral area expansion, wastewater input, and hydrological regulation) in East Dongting Lake (Central China) over the past 60 years, using analyses of total organic carbon (TOC), total nitrogen (TN), C/N ratios, δ13C, δ15N, and diatoms from 2 sediment cores collected from the littoral and central parts of the lake. OM mainly originated from phytoplankton and C3 plant‐derived soil OM based on the ranges of C/N ratios (from 7 to 11) and δ13C (between ?27‰ and ?23‰). Littoral area expansion due to siltation caused an increasing influx of terrestrial soil OM in the 1980s and the 1990s, subsequently lowering δ13C values and rising C/N ratios in both sediment cores. Meanwhile, higher δ15N was linked to a high influx of isotopically heavy nitrate from urban and agricultural wastewaters. After 2000, slight decreases in TOC and TN in the littoral area were attributable to reducing inputs of external OM, likely linked to declining sediment influx from the upper reaches resulting from the Three Gorges Dam impoundment. Contrasting increases in TOC, TN, and C/N ratios in the central part indicated a high influx of terrestrial soil OM due to the declining distance from the shoreline with littoral area expansion. Declining δ15N values after 2000 indicated an increase in N2‐fixing cyanobacteria with eutrophication. Changes in diatom assemblages in both the littoral and central zones reflected nutrient enrichment and hydrological alterations. These results indicate that littoral expansion, declining riverine influx, and anthropogenic nutrient inputs are potential driving forces for the biogeochemical processing of OM in floodplain lakes. This study provides sedimentary biogeochemical clues for tracking past limnological conditions of floodplain lakes that are subjected to increasing disturbances from hydrological regulation and eutrophication.  相似文献   

7.
Vertical distributions of chlorophyll in deep, warm monomictic lakes   总被引：1，自引：0，他引：1  
The factors affecting vertical distributions of chlorophyll fluorescence were examined in four temperate, warm monomictic lakes. Each of the lakes (maximum depth >80 m) was sampled over 2 years at intervals from monthly to seasonal. Profiles were taken of chlorophyll fluorescence (as a proxy for algal biomass), temperature and irradiance, as well as integrated samples from the surface mixed layer for chlorophyll a (chl a) and nutrient concentrations in each lake. Depth profiles of chlorophyll fluorescence were also made along transects of the longest axis of each lake. Chlorophyll fluorescence maxima occurred at depths closely correlated with euphotic depth (r 2 = 0.67, P < 0.01), which varied with nutrient status of the lakes. While seasonal thermal density stratification is a prerequisite for the existence of a deep chlorophyll maximum (DCM), our study provides evidence that the depth of light penetration largely dictates the DCM depth during stratification. Reduction in water clarity through eutrophication can cause a shift in phytoplankton distributions from a DCM in spring or summer to a surface chlorophyll maximum within the surface mixed layer when the depth of the euphotic zone (z eu) is consistently shallower than the depth of the surface mixed layer (z SML). Trophic status has a key role in determining vertical distributions of chlorophyll in the four lakes, but does not appear to disrupt the annual cycle of maximum chlorophyll in winter.  相似文献   

8.
The study of seasonal dynamics of net phytoplankton was carried out above and below the hydroelectric plant (HP) on the Pas ka River. Correlations were found between the abundance of diatoms and conductivity, O2, PO4; the abundance of cyanobacteria and water temperature and conductivity, and the abundance of chlorophytes and O2 and Ntot. Multiple correlations revealed the most significant factor for diatom development is PO4, for cyanobacteria is water temperature, and for chlorophytes is Ntot. A lower abundance and biomass of phytoplankton, and less species diversity and nutrient concentrations were registered below the HP than above it. The seasonal dynamics of phytoplankton abundance provided similar results. The maximum biomass of the assemblage was found earlier below the HP, in April, than above it, in May. However, no differences were recorded in the dominant species within phytoplankton abundance. The phytoplankton biomass was dominated by the Melosira varians and Spirogyra sp., which are typical taxa of plant periphyton and possibly emanate from the concrete elements of the dam. This HP changed the local hydrological and environmental conditions, affecting available nutrients, and thereby phytoplankton development in the vegetative season.  相似文献   

9.
水体氮、磷营养盐水平对蓝藻优势形成的影响   总被引：1，自引：1，他引：0  
许海  陈洁  朱广伟  秦伯强  张运林 《湖泊科学》2019,31(5):1239-1247
以江苏省南京市富营养化程度不同的清溪、护城河、玄武湖、月牙湖、琵琶湖和前湖为研究对象,调查各水体浮游植物的群落特征和优势种,并结合藻类生长潜力试验,探究不同氮、磷营养水平的自然水体对铜绿微囊藻（Microcystis aeruginosa）和斜生栅藻（Scenedesmus obliquus）生长与竞争的影响.野外调查发现不同营养水平水体浮游植物优势种不同,按水体富营养化程度从高到底依次以绿藻、蓝藻、硅藻和隐藻分别占优势.单一藻种培养时,铜绿微囊藻在清溪、护城河和玄武湖水体中生长均较好,而斜生栅藻仅在高氮、磷浓度的清溪和护城河水体中有较大生长量,说明斜生栅藻对氮、磷的需求高于铜绿微囊藻;两种藻共培养时,清溪水体中斜生栅藻占优势,护城河和玄武湖水体中铜绿微囊藻占优势,但其他水体中两种藻均不能生长,说明氮、磷浓度过高或过低都不利于蓝藻形成优势.对低营养水平的玄武湖、琵琶湖、月牙湖和前湖水体进行氮、磷加富后,两种藻均能较好地生长,且各组没有显著差异,说明藻类在这些水体中生长受到氮、磷的限制,氮、磷浓度升高会增加水华发生的风险.本研究将野外调查和藻类生长潜力实验相结合,深入探究了蓝藻优势形成与水体氮、磷营养水平的关系,揭示了蓝藻水华是湖泊富营养化发展到特定阶段的产物,水体氮、磷浓度过高或过低均不易产生蓝藻优势.  相似文献   

10.
The influence of extreme floods from the River Danube in 2006 on the species composition and vertical distributions of phytoplankton was studied in a shallow floodplain lake, Lake Sakadaš (Kopa?ki Rit Nature Park, Croatia) which in the last few decades was in a turbid state characterised by high phytoplankton concentrations. As a consequence of extremely high floods, the whole floodplain area (approximately 16 km2) became one lentic habitat with well developed macrophyte vegetation. Seasonal dynamics of chlorophyll a (Chl a) concentration in the lake had a characteristic pattern for the shallow lakes with dense macrophyte vegetation. Extremely low mean phytoplankton abundance and biomass were found in the conditions of very high nutrient concentrations. Dominant phytoplankton species were diatoms and chlorococcal green algae from the functional groups characteristic for a mixed environment. The canonical correspondence analysis (CCA) demonstrated that nutrients and temperature were significant environmental variables for their development. The sequence of phytoplankton seasonality, vertical distribution of phytoplankton, as well as the domination of rapidly acclimating phytoplankton forms (R-strategists) indicated clear, well-mixed conditions and a highly disturbed environment. Our results suggest that the occurrence of extreme flooding can be a stressor high enough for the transition from a turbid to a clear state of the floodplain lake. Possibly, cyclic shifts between alternative stable states in floodplain ecosystems can be expected as a consequence of the impact of extreme hydrological events induced by a climate change.  相似文献   

11.
The spatial pattern and seasonal variation of denitrification were investigated during 2010–2011 in the Jiulong River Estuary (JRE) in southeast China. Dissolved N2 was directly measured by changes in the N2:Ar ratio. The results showed that excess dissolved N2 ranged from ?9.9 to 76.4 μmol L?1. Tidal mixing leads to a seaward decline of dissolved gaseous concentrations and water–air fluxes along the river-estuary gradient. Denitrification at freshwater sites varied between seasons, associated with changes in N input and water temperature. The denitrification process was controlled by the nitrate level at freshwater sites, and the excess dissolved N2 observed at the tidal zone largely originated from upstream water transport. Compared to other estuaries, JRE has a relative low gaseous removal efficiency (Ed = 12% of [DIN]; annual N removal = 24% of DIN load), a fact ascribed to strong tidal mixing, coarse-textured sediment with shallow depth before bedrock and high riverine DIN input.  相似文献   

12.
During the high water season, the flooding reduces environmental heterogeneity in aquatic ecosystems of the Pantanal wetland. When the water level recedes, lakes and channels are formed as individual systems. Therefore, we expected the spatial heterogeneity during the low water phase resulting in changes on biological communities leading to high phytoplankton abundance, biomass and diversity within and between habitats. To test this hypothesis, we analyzed eight freshwater systems (five oxbow lakes, two channels, and the river) during the low water period. Phytoplankton biomass, abundance, diversity (alpha, beta, gamma) and diversity metrics as richness (species per sample), Shannon diversity (H′) and evenness were measured in all systems along with nutrient concentrations, zooplankton and bacteria abundances. We found 97 species as gamma diversity. The alpha diversity was unexpectedly low in comparison to most other South American floodplain systems (38 species in river, 24 in channels and 29 in lakes). Also, the systems are relatively similar in composition (beta diversity, 28%). Connectivity differences between systems highlighted differences in phytoplankton abundance and biomass (fresh weight) ranging from 1428 ind mL−1 (river) to 3710 ind mL−1 (lakes) and from 0.71 mg L−1 (river) to 2.9 mg L−1 (lakes), respectively. However, our results did not indicate significant differences in phytoplankton species richness between the systems during the low water. Our main conclusions are that local factors may be responsible for changes on phytoplankton community and the time of isolation during the low water phase was not sufficient to promote changes in phytoplankton diversity between the habitats.  相似文献   

13.
Because of the obvious importance of P as a nutrient that often accelerates growth of phytoplankton (including toxic cyanobacteria) and therefore worsens water quality, much interest has been devoted to P exchange across the sediment-water interface. Generally, the release mode of P from the sediment differed greatly between shallow and deep lakes, and much of the effort has been focused on iron and oxygen, and also on the relevant environmental factors, for example, turbulence and decomposition, but a large part of the P variation in shallow lakes remains unexplained. This paper reviews experimental and field studies on the mechanisms of P release from the sediment in the shallow temperate (in Europe) and subtropical (in the middle and lower reaches of the Yangtze River in China) lakes, and it is suggested that pH rather than DO might be more important in driving the seasonal dynamics of internal P loading in these shallow lakes, i.e., intense photosynthesis of phytoplankton increases pH of the lake water and thus may increase pH of the surface sediment, leading to enhanced release of P (especially iron-bound P) from the sediment. Based on the selective pump of P (but not N) from the sediment by algal blooms, it is concluded that photosynthesis which is closely related to eutrophication level is the driving force for the seasonal variation of internal P loading in shallow lakes. This is a new finding. Additionally, the selective pump of P from the sediment by algal blooms not only explains satisfactorily why both TP and PO4-P in the hypereutrophic Lake Donghu declined significantly since the mid-1980s when heavy cyanobacterial blooms were eliminated by the nontraditional biomanipulation (massive stocking of the filter-feeding silver and bighead carps), but also explains why TP in European lakes decreased remarkably in the spring clear-water phase with less phytoplankton during the seasonal succession of aquatic communities or when phytoplankton biomass was decreased by traditional biomanipulation. Compared with deep lakes, wax and wane of phytoplankton due to alternations in the ecosystem structure is also able to exert significant influences on the P exchange at the sediment-water interface in shallow lakes. In other words, biological activities are also able to drive P release from sediments, and such a static P release process is especially more prominent in eutrophic shallow lakes with dense phytoplankton.  相似文献   

14.
The chemical characteristics and phytoplankton biomass (measured as chlorophyll-a concentrations) of seven lakes and one reservoir in the Ethiopian rift-valley were studied during the wet and dry seasons between 1990 and 2000. Mean concentrations of three major plant nutrients (nitrate-nitrogen, soluble reactive phosphorus, and silicate) increased during the wet seasons in four of the seven lakes, presumably as a result of mixing events and input from runoff. The changes in the major nutrient concentrations in the rest of the lakes were variable, but concentrations were usually higher during the dry seasons, most likely as a response to temporal variation in the phytoplankton biomass. pH measurements of the lakes did not show marked differences between the wet and dry seasons. Salinity (measured as conductivity) and total ions seemed to increase during the wet seasons in some of the lakes, possibly as a result of inflows that might carry high concentrations of solutes due to the heavy rains. Chlorophyll-a concentrations were higher during the dry seasons in most lakes except in three relatively more productive lakes. The results suggest that there could be light limitation in some of the Ethiopian rift-valley lakes, and events associated with the wet and dry seasons could bring about contrasting changes in nutrient levels and phytoplankton biomass in lakes, depending on the physical characteristics of the lakes.  相似文献   

15.
云贵高原湖泊夏季浮游植物组成及多样性   总被引：2，自引：2，他引：0  
浮游植物是水生生态系统中重要的初级生产者,对维持水生态系统的平衡起着十分重要的作用.根据2008年云贵高原湖泊丰水期浮游植物调查数据,系统地分析了云贵高原13个湖泊中浮游植物的种群密度、生物量、组成及其多样性.云贵高原13个湖泊中共鉴定出浮游植物7门109种(绿藻52种、蓝藻23种、硅藻20种、其他14种).13个湖泊浮游植物Shannon-Wiener指数在0.5-2.2之间,其值大小与单个环境因子无显著相关.相关分析发现浮游植物总量与总氮、总磷、CODMn、硝态氮含量显著正相关,物种丰富度与总氮、总磷(0.1mg/L范围内)、CODMn含量亦显著正相关.另外,研究也发现各湖泊间浮游植物组成的相似性与各湖泊间营养状态差异显著负相关.由此可见,湖泊的营养状态不仅影响浮游植物的总量、组成以及物种丰富度,而且也影响各湖泊物种组成的相似性.  相似文献   

16.
This study aims at investigating the composition and biomass of the phytoplankton community in 15 urban shallow eutrophic lakes as well as the effects of main environmental factors, including nutrient concentrations and the ratio of nitrogen to phosphorus, temperature, COD, BOD, water depth, etc. on the phytoplankton community structure. Lake water samples were taken and analyzed on a bimonthly basis during the period from March 2004 to March 2006. The redundancy analysis (RDA) and regression analysis (RA) were performed to identify the effects of nutrients on the phytoplankton community and biomass in these typical urban lakes. The results indicate that most of these urban lakes were hypertrophic due to high concentrations of total phosphorus (TP) and total nitrogen (TN), with mean levels of 490 and 5380 mg m−3, respectively. The phytoplankton community was dominated by Microcystis aeruginosa and Euglena caudate in summer and Cryptomonas ovata and Cyclotella meneghiniana in winter. The mean biomass of the phytoplankton reached 456.87 mg L−1 in summer months and the annual level was 189.24 mg L−1. Temperature and TP content were found to be the principal limiting factors for phytoplankton growth on an annual basis. On the other hand, the results of RDA and RA demonstrate that the dominant phytoplankton species were not nutrient-limited during summer months. Low TN:TP ratios (<10) were detected accompanied with fewer occurrences of N-fixing cyanobacteria and other filamentous algae in most lakes in summer, which implies that low N:P ratio does not always shifts the dominance of phytoplankton community to the N-fixing cyanobacteria. Moreover, TP always had higher correlation with chlorophyll a (Chl-a) than TN, even when the TN:TP ratios of most samples were lower than 10. Therefore, it is concluded that the TN:TP ratio is not always a suitable index to determine whether nitrogen or phosphorus limits the phytoplankton biomass in urban shallow eutrophic lakes.  相似文献   

17.
Organic matter production and nitrogen fixation in the central Baltic Sea were studied on the basis of high-resolution CO2 partial pressure data that were obtained from an automated measurement system deployed on a cargo ship. The net organic carbon (OC) production was calculated from a surface water CO2 mass balance and used to estimate the nitrogen uptake by organic matter during the period March to August 2005. It was shown that the net OC production continued despite the exhaustion of dissolved inorganic nitrogen (DIN) after the spring bloom in April. The nitrogen demand for this production was calculated on the basis of the C/N ratio of organic matter. It was of the same order of magnitude than the winter DIN concentration that fuelled the spring bloom. Since the atmospheric DIN deposition was negligible and no indications of alternative DIN sources were found, it was assumed that N2 fixation had taken place despite the low temperatures (4–8 °C) in April/May. This “cold fixation” amounted to 74 mmol m?2 whereas a value of 99 mmol m?2 was obtained for the summer N2 fixation during June/July. Due to the contribution of the April/May N2 fixation, a total annual rate (173±35 mmol m?2) was obtained for 2005 which is considerably higher than presently accepted estimates. These findings were confirmed by a nitrogen budget based on long-term data (1993–2006) for total nitrogen and total phosphorus concentrations. Furthermore, these data revealed a 30% increase in N2 fixation during the years 1994–2006.  相似文献   

18.
Mean dissolved inorganic nitrogen concentrations ([DIN]) in deep, seasonally stratified lakes with comparable DIN inputs can differ by up to a factor of 3 depending on hydraulic and morphometric properties and/or different trophic states of the lakes. In such lakes, net N sedimentation rates were estimated with two independent methods (sediment core analysis and input-output mass balances). They were higher in eutrophic lakes (Mean: 5.1; SD: ± 1.6 g m–2 yr–1; n = 13) than in oligotrophic lakes (1.6 ± 1.0 g m–2 yr–1; n = 3), but independent of [DIN]. Gaseous N loss rates to the atmosphere, as calculated from combined N- and P-mass balances from selected lakes, ranged from 0.9 to 37.4 g m–2 yr–1 (n = 10) and were positively correlated with [DIN]. Reduction of NO 3 - to N2 is assumed to be the main cause for gaseous N losses. A simple one-box mass balance model for [DIN], based on DIN input and rates and kinetics of N removal processes (net sedimentation and gaseous N loss) is proposed, and validated with a data base on [DIN] and DIN input in 19 deep, seasonally stratified lakes of central Europe. The model illustrated that the amount of water loading per unit surface area of a lake (called water discharge height q) is the critical parameter determining mean lake [DIN] relative to mean input [DIN]. Lakes with a q > 50 m yr–1 have average [DIN] similar to the [DIN] of the inflows regardless of their trophic states, because input and outflow exceed lake-internal N removal processes. A high primary production favors DIN removal in lakes with q < 50 m yr–1. It is concluded that measures to decrease primary production, e.g. by means of P removal programs, lead to an increase of [DIN] in lakes.  相似文献   

19.
This 10-year field data study explores the relevance of water level fluctuations in driving the shift from a free-floating plant (FFP) to a phytoplankton dominated state in a shallow floodplain lake from the Lower Paraná River. The multi-year natural flood pulse pattern in the Lower Paraná River drove the ecosystem regime from a FFP-dominant state during very high waters (1998–1999) to absolute phytoplankton prevalence with blooms of nitrogen fixing Cyanobacteria during extreme low waters (2008–2009). Satellite images support the observed changes over the decade and show the decrease of the surface lake area covered by FFP as well as the modification of the spectral firm in open waters, which documents the significant increases in phytoplankton chlorophyll a concentrations. We discuss the possibility that, despite a slow eutrophication in these highly vegetated systems, water level changes and not nutrients account for the shift from a floating macrophyte community to phytoplankton dominance. Cyclic shifts may occur in response to the seasonal floodpulse, but more strongly, as indicated by our results, in association to the extreme drought and flood events related to the El Niño Southern Oscillation, which is linked to discharge anomalies in the Paraná River.  相似文献   

20.
In inland waters, transparent exopolymer particles (TEP) can affect carbon export and sequestration in sediments with consequences for lake C budgets. We measured TEP concentration in 32 lakes from two contrasting lake districts covering wide ranges in biological and chemical characteristics. North temperate lakes, located in a wet region, have low to moderate ionic strength and low to high dissolved organic carbon with corresponding variation in color (light absorbance). Mediterranean lakes located in a semiarid region were characterized by high ionic strength and high concentrations of dissolved organic carbon but low color. TEP concentrations were large relative to the living portion of the particulate organic carbon pool in both Mediterranean (36%) and north temperate (33%) lakes. TEP concentrations ranged from 36 to 1,462 μg [as Gum Xanthan equivalents (GX eq)] L−1 in north temperate lakes. In the Mediterranean lakes, concentrations were higher that previously reported for other systems and ranged from 66 to 9,038 μg GX eq L−1. TEP concentration was positive and significantly related to chlorophyll a (chl a) in north temperate lakes and in the entire data set. Although a significant and positive relationship between TEP and chl a was also detected in the Mediterranean lakes, bacterial abundance was most strongly related to TEP. In contrast with the positive influence of phytoplankton and bacteria on TEP, there were weaker relationships between TEP and the chemical variables tested. We observed a significant and positive relationship between pH and TEP (for all lakes) but this relationship was indirectly driven by a co-variation of pH with phytoplankton biomass based on multiple regression analysis. For the Mediterranean lakes, the negative (but not significant) trends between TEP and both conductivity and divalent cations suggest thresholds above which TEP will likely be destabilized. Under these conditions, TEP may flocculate or disperse in the water column.  相似文献   

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