Stages Of Eutrophication Research Articles

淀山湖富营养化过程的统计学特征

The statistical characteristics of total nitrogen(TN) and total phosphorus(TP) nutrient input and their responses during the lake eutrophication process are of increasing concern.An increase in the mean(μ) and/or variance of TN and TP input may increase the probability of exceeding the critical threshold at which algal blooms proliferate. Dianshan Lake,a shallow temperate lake in the Taihu Plain,is an important source of drinking water for Shanghai and is subject to a subtropical monsoon climate.Its trophic state transitioned from eutrophic to hypereutrophic in 1999,causing the lake to suffer from bluegreen algal blooms ever since.Beginning in 2004,some restoration measures have been taken to reduce nutrient inputs into the lake.However,the immediate reduction of nutrient inputs did not instantly reduce the frequency of algal bloom events. In order to understand nutrient input and their responses in a lake ecosystem from a statistical point of view,the frequency distributions of TP,TN and chlorophyll a(Chl a),and the TP-Chl a relationships during two different trophic stages(eutrophic stage: 1986—1999;hypereutrophic stage: 1999—2009) of the lake were analyzed based on long-term data from 1985 to 2009.The means and variances of these parameters were compared with those after restoration measures were undertaken on the lake in 2004. The means and variances of TN and TP increased with the eutrophication process.The probabilities of TN and TP values exceeding the Surface Water Standard for Class V Waters(TN = 2.0mg/L;TP = 0.2mg/L) increased from 62.8% and 12.1% during the eutrophic stage to 91.4% and 51.9% during the hypereutrophic stage,respectively.The increase in Chl a concentration was even greater,with the probability of exceeding the limit of 15 μg/L increasing from 0.5% during the eutrophic stage to 67.5% during the hypertrophic stage. The log-log relationship between TP and Chl a was calculated as per Organization for Economic Co-operation and Development(OECD) methods using three data sets: 1985—1986,2000—2004 and 2004—2008.All of the observed patterns fit the TP control paradigm well,which indicated that TP had been the primary limiting factor.Over the 24-year eutrophication period examined,the slope of the TP-Chl a log-log relationship increased from 0.54 during the 1980s to 0.83 in the early 2000s and then further to 2.46 by 2008,which might indicate an increasing of proportion of bluegreen algae and the frequency of their blooms. After restoration measures were undertaken in 2004,mean TP stayed constant and the discrete degree(variance decreased to 50%,whereas the probability of Chl a exceeding 15 μg/L continued to increase by an additional 20%.Under the hypereutrophic condition,a reduction in peak nutrient values or variance only had a limited contribution to primary algal production.Further study on the effects of TN and TP reductions in eutrophication control is necessary. Here,we showed that statistical parameters such as mean,variance,slope and frequency distribution of nutrients and their responses were able to describe the eutrophication process of Dianshan Lake.These characteristics also offer statistical support for lake restoration assessments,risk assessments for Harmful Algal Bloom and nutrient criteria and standard development.

Paleolimnological reconstruction of the trophic state in Lake Balaton (Hungary) using Cladocera remains

The sediment of Lake Balaton (Hungary) provides important information about the lake’s history, particularly with regard to eutrophication. In this study, we used fossil pigment analysis and subfossil Cladocera remains preserved in a dated sediment core to identify trophic stages from ~250 bc to present. Dates of the most recent eutrophic events are in good agreement with previously published data. In general, the abundance and diversity of the Cladocera community increased with eutrophication and decreased with oligotrophication. The sediments of Lake Balaton were characterised by Chydoridae remains, of which Alona species were the most abundant. Of these, Alona quadrangularis and Alona affinis accounted for 40 and 20% of the total Cladocera remains, respectively. The trophic state of Lake Balaton varied between mesotrophic and eutrophic regimes. Seven different trophic periods were identified in Lake Balaton on the basis of Sedimentary Pigment Degradation Unit (SPDU) content of the sediment. Eutrophic states were (1) from ~250 to ~30 bc, (3) between ~300 and ~590 ad, (5) between 1834 and 1944 and (7) from the 1960s until present. Mesotrophic states were (2) ~30 bc to ~300 ad, (4) 590–1834, (6) 1944–1960s. Discriminant analysis of the cladoceran data confirmed these historic events, except for the short mesotrophic episode between 1944 and 1960. The first stage of eutrophication of Lake Balaton (~250 to ~30 bc) was characterised by extensive macrophyte vegetation, as indicated by the increasing abundance of vegetation-associated Cladocera species (Eurycercus lamellatus, Sida crystallina, Pleuroxus sp.). Intensification of eutrophication was identified since the 1980s, reflected by a high abundance of Bosmina species. The most significant planktivorous fish of Lake Balaton was the Sabre carp (Pelecus cultratus), and when its number decreased, the abundance of Bosmina species increased. This study shows that Cladocera are responsive to trophic state changes, underlining their importance as a tool for the assessment of lake eutrophication.

My memories of Jack Vallentyne

My memories of Jack Vallentyne

Effects of water quality and trophic status on helminth infections in the cyprinid fish,Schizothorax nigerHeckel, 1838 from three lakes in the Kashmir Himalayas

Water quality greatly influences the population density of aquatic biota, including parasites. In order to evaluate the relationship between fish parasites and water quality in Kashmir Himalayas, we assessed helminth parasite densities in Schizothorax niger Heckel, 1838 (an endemic cyprinid fish of Kashmir) from three lakes, namely Anchar, Manasbal and Dal, which reflected the varied stages of eutrophication. The overall prevalence of helminth infections was higher in the hypertrophic Anchar Lake (prevalence = 18.6%) compared to Manasbal Lake, which was the least eutrophied (prevalence = 6.4%). Furthermore, mean prevalence of monoxenous and heteroxenous parasites was higher in lakes containing higher levels of water degradation (Anchar and Dal). The mean number of helminth species per fish host was the highest in the hypertrophic lake (1.3 ± 0.3) in comparison to the least eutrophic lake (0.2 ± 1.5). Variability of calculated infection indices (prevalence, mean intensity and mean abundance) revealed that helminth parasite composition in the fish was affected by the lakes' environmental stress (degraded water quality). Therefore, data on the density of helminth parasites in fish can provide supplementary information on the pollution status of a water body.

δ15N and δ13C reveal differences in carbon flow through estuarine benthic food webs in response to the relative availability of macroalgae and eelgrass

Eutrophication forces shifts in estuarine producer assemblages from seagrass meadows to communities dominated by macroalgae. This restructuring of the benthic producer assemblage presents challenges and alters food resources available to consumers. We examined food web relationships in 3 sub-estuaries of the Waquoit Bay system, Massachusetts, USA, that span a gradient of relatively low nitrogen loads of 5, 10, and 34 kg N ha–1 yr–1. We detected effects on benthic macrophytes across this range of N loads with reduced seagrass cover and higher macroalgal biomass as N loading increased. The difference in N loading to these estuaries could also be detected in δ15N signatures of the benthic community. Producers and consumers were enriched in δ15N in response to increasing N load and incorporation of isotopically heavy nitrogen from wastewater sources. The differences in the relative availability of seagrass and macroalgae associated with the N load gradient were reflected in consumer diets. δ13C of producers were similar among the estuaries, but for consumers the isotopic signatures differed, suggesting they did not feed on the same primary producer sources. Using IsoSource, we modeled the diets of 2 herbivores, the amphipod Cymadusa compta and the isopod Erichsonella filiformis. At the lower N loads, more seagrass and detritus were consumed, whereas at the high N load where macroalgae was the dominant vegetation type, algae dominated the diet. The resulting C isotopic signatures appear to have permeated to higher trophic levels, suggesting C flow through the system differs across the range of N loads sampled. In the most pristine estuary, the overall food web was supported mainly by seagrass, its epiphytes and detritus, but macroalgal C was more important where this was the dominant type of macrophyte. These results demonstrate that C pathways through coastal food webs may be altered at earlier stages of eutrophication than previous studies have suggested.

The role of emergent macrophytes in nutrient cycling in Lake Niepruszewskie (western Poland)

The role of emergent macrophytes in nutrient cycling in Lake Niepruszewskie (western Poland) The role of emergent macrophytes in nutrient cycling was investigated in the littoral zone of Lake Niepruszewskie, which is dominated by this type of vegetation. The lake is characterized by an advanced stage of eutrophication as is evident in the frequent blooms that cause low transparency and high concentrations of chlorophyll a and seston. The shoot biomass of Phragmites australis and Typha angustifolia is the major component of the plant cover with respect to nutrient accumulation. Other plants play a marginal role in the nutrient turnover of the studied lake.

The influence of bird colonies on the zooplankton in the Rybinsk Reservoir overgrown shallows

This article describes the peculiarities of the structural organization of zooplankton influenced by the waste products of the black-headed gull (Larus ridibundus Linnaeus) nesting colony in the protected overgrown shallow in Rybinsk Reservoir. The bird colony facilitates a modification of the zooplankton structure that is similar to the modifications of communities at early stages of eutrophication: the number of invertebrate species increases thanks to rotifers and cladocerans and the number and biomass of community increases due to cladocerans and copepods.

Development of a phytoplankton indicator system for the ecological assessment of brackish coastal waters (German Baltic Sea coast)

The implementation of the European Water Framework Directive (WFD) requires the development of ecologically-based classification systems for anthropogenically-induced eutrophication in all types of water bodies. Due to the inherent high temporal and spatial variability of hydrological and geochemical parameters of the coastal waters of the southern Baltic Sea, discrimination between anthropogenic impact and natural variability is necessary. The development of statistical methods for this discrimination was the main aim of this study. These methods were used to derive indicative phytoplankton parameters for different stages of eutrophication for the investigation area. For this purpose, a long-term phytoplankton data series was analysed, which covered a broad salinity and eutrophication gradient. In order to detect eutrophication effects, the analysis was restricted to phytoplankton spring bloom events and to the salinity range between 5 and 10 psu, i.e. superimposing seasonal and hydrodynamic effects were eliminated. An artificial abiotic degradation vector was developed based on four typical water quality parameters. A total of 11 potentially indicative phytoplankton parameters on different taxonomical levels arose from a correlation analysis with this degradation vector. These indicators were then tested for their ability to discriminate between three eutrophication levels. Finally, seven phytoplankton indices could be proposed: total phytoplankton biovolume, the percentage of diatoms and the biovolume of different size ranges of diatoms and one indicative species (Woronichinia compacta).

Eutrophication in shallow coastal bays and lagoons: the role of plants in the coastal filter

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 348:1-18 (2007) - DOI: https://doi.org/10.3354/meps07132 Eutrophication in shallow coastal bays and lagoons: the role of plants in the coastal filter Karen J. McGlathery1,*, Kristina Sundbäck2, Iris C. Anderson3 1Department of Environmental Sciences, University of Virginia, 291 McCormick Road, PO Box 400123, Charlottesville, Virginia 22903, USA 2Department of Marine Ecology, Marine Botany, Göteborg University, PO Box 461, 40530 Göteborg, Sweden 3School of Marine Science, Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, Virginia 23602, USA *Email: kjm4k@virginia.edu ABSTRACT: Nutrient loading to coastal bay ecosystems is of a similar magnitude as that to deeper, river-fed estuaries, yet our understanding of the eutrophication process in these shallow systems lags far behind. In this synthesis, we focus on one type of biotic feedback that influences eutrophication patterns in coastal bays—the important role of primary producers in the ‘coastal filter’. We discuss the 2 aspects of plant-mediated nutrient cycling as eutrophication induces a shift in primary producer dominance: (1) the fate of nutrients bound in plant biomass, and (2) the effects of primary producers on biogeochemical processes that influence nutrient retention. We suggest the following generalizations as eutrophication proceeds in coastal bays: (1) Long-term retention of recalcitrant dissolved and particulate organic matter will decline as seagrasses are replaced by algae with less refractory material. (2) Benthic grazers buffer the early effects of nutrient enrichment, but consumption rates will decline as physico-chemical conditions stress consumer populations. (3) Mass transport of plant-bound nutrients will increase because attached perennial macrophytes will be replaced by unattached ephemeral algae that move with the water. (4) Denitrification will be an unimportant sink for N because primary producers typically outcompete bacteria for available N, and partitioning of nitrate reduction will shift to dissimilatory nitrate reduction to ammonium in later stages of eutrophication. In tropical/subtropical systems dominated by carbonate sediments, eutrophication will likely result in a positive feedback where increased sulfate reduction and sulfide accumulation in sediments will decrease P adsorption to Fe and enhance the release of P to the overlying water. KEY WORDS: Eutrophication · Coastal bay · Lagoon · Nitrogen · Phosphorus · Seagrass · Macroalgae · Phytoplankton Full text in pdf format NextCite this article as: McGlathery KJ, Sundbäck K, Anderson IC (2007) Eutrophication in shallow coastal bays and lagoons: the role of plants in the coastal filter. Mar Ecol Prog Ser 348:1-18. https://doi.org/10.3354/meps07132 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 348. Online publication date: October 25, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Crustacean zooplankton size structure in aquaculture lakes: is larger size structure always associated with higher grazing pressure?

Crustacean zooplankton size structure in 27 aquaculture lakes was studied to test the hypothesis that larger size structure is associated with higher grazing pressure. Mean body length of crustaceans was positively correlated with increasing Chl a (r(2) = 0.40, P = 0.000) and TP (r(2) = 0.38, P = 0.000), contrary to the empirical studies. However, the ratio of zooplankton to phytoplankton biomass decreased significantly with increasing TP (r(2) = 0.27, P = 0.005) and mean body length (r(2) = 0.46, P = 0.000). Meanwhile, size structure showed no significant effect in explaining residual variations of phosphorus-chlorophyll relationship (P = 0.231). These results indicate that larger size structure was not always associated with higher zooplankton grazing pressure. It is likely that in aquaculture lakes crustacean zooplankton size structure was of minor importance in control of phytoplankton biomass, and it was mainly regulated by fish predation. The results showed in our study and the empirical studies might be a reflection of two different stages of lake eutrophication and fish predation intensity.

Characterisation of Selected Lentic Habitats of Dharwad, Haveri and Uttar Kannada Districts of Karnataka State, India

Water quality survey was undertaken to study the current status of water quality of some lentic habitats of Dharwad, Haveri and Uttar Kannada districts, to provide a baseline data, comprising study of their main physical and chemical characteristics and also to evaluate the recent limnological changes those have occurred over a time period in some lentic habitats. Trophic status was also analysed. Present study reveals that Unkal lake, and B.K. Shigigatti tank of Dharwad district, Timmapur, Hosalli, and Krishnapur tanks of Haveri district are fast progressing towards hypereutrophication. Of the other tanks, Galgi tank of Dharwad district, Gudgur, Hanamapur, Medleri, and Kadkol tanks of Haveri district have reached the eutrophic stage. The anthropogenic activities, sewage and fertilizers used in agricultural fields appear to be the major causes of the eutrophication in these tanks. If the habitats have to be preserved for their intended use, sustainable and holistic management measures for the remediation of the tanks are an immediate necessity.

Development of a nutrient pollution indicator using the seagrass, Zostera marina, along nutrient gradients in three New England estuaries

Worldwide, seagrasses provide important habitats in coastal ecosystems, but seagrass meadows are often degraded or destroyed by cultural eutrophication. Presently, there are no available tools for early assessment of nutrient over-enrichment; direct measurements of water column nutrients are ineffective since the nutrients typical of early enrichment are rapidly taken up by plants within the ecosystem. We investigated whether, in a gradient of nutrient availability but prior to actual habitat loss, eelgrass ( Zostera marina L.) plant morphology and tissue nutrients might reflect environmental nutrient availability. Eelgrass responses to nitrogen along estuarine gradients were assessed; two of these plant responses were combined to create an early indicator of nutrient over-enrichment. Eelgrass plant morphology and leaf tissue nitrogen (N) were measured along nutrient gradients in three New England estuaries: Great Bay Estuary (NH), Narragansett Bay (RI) and Waquoit Bay (MA). Eelgrass leaf N was significantly higher in up-estuary sampling stations than stations down-estuary, reflecting environmental nitrogen gradients. Leaf N content showed high variance, however, limiting its ability to discriminate the early stages of eutrophication. To find a stronger indicator, plant morphological characteristics such as number of leaves per shoot, blade width, and leaf and sheath length were examined, but they only weakly correlated with leaf tissue N. Area normalized leaf mass (mg dry weight cm −2), however, exhibited a strong and consistently negative relationship with leaf tissue N and a significant response to the estuarine nutrient gradients. We found the ratio of leaf N to leaf mass to be a more sensitive and consistent indicator of early eutrophication than either characteristic alone. We suggest the use of this ratio as a nutrient pollution indicator (NPI).

Zooplankton of an Oligotrophic Lake at Early Stages of Anthropic Eutrophication

In studies of zooplankton of oligotrophic Lake Turgoyak subjected to intensive anthropic load, it has been found that both oligotrophic and typical eutrophic features are characteristic of this water body. A similar statement is true of other hydrobiological parameters. From this follows the conclusion that a mosaic pattern of indicator values is registered at early stages of rapid eutrophication. Thus, an integrated approach is required to reveal early stages of eutrophication.

Comparison of carbon production and decomposition, benthic nutrient fluxes and denitrification in seagrass, phytoplankton, benthic microalgae- and macroalgae-dominated warm-temperate Australian lagoons

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 229:43-59 (2002) - doi:10.3354/meps229043 Comparison of carbon production and decomposition, benthic nutrient fluxes and denitrification in seagrass, phytoplankton, benthic microalgae- and macroalgae-dominated warm-temperate Australian lagoons Bradley D. Eyre*, Angus J. P. Ferguson Centre for Coastal Management, Southern Cross University, Lismore , New South Wales 2480, Australia *E-mail: beyre@scu.edu.au ABSTRACT: The influence of marine plants representing different stages of eutrophication on carbon decomposition and production, benthic nutrient fluxes and denitrification was examined in 4 shallow warm-temperate Australian lagoons. Differences in carbon production and decomposition across the lagoons were the main regulators of the quantity and quality of benthic nutrient fluxes and the relative proportion of nitrogen lost through denitrification. For example, the efficiency with which the lagoon sediments recycled nitrogen as N2, (i.e. denitrification efficiency: N2-N/(N2-N+DIN), decreased as carbon decomposition rates increased. C:N ratios of the remineralised organic matter in some of the plant-sediment systems were much higher than expected from the stoichiometry of the dominant carbon supply. Dark DON fluxes were also very high in all the plant-sediment systems (30 to 80% of the total nitrogen flux). We offer 2 alternative explanations for the observed sediment and benthic flux characteristics: (1) The low dark C:N ratios of the remineralised organic matter may have been due to dark uptake by benthic microalgae and possibly other plants. The large DON effluxes were either the hydrolysis product of freshly produced in situ organic material or/and associated with the grazing of benthic microalgae. This explanation has important implications regarding the importance of benthic microalage as a sink for nitrogen. (2) Alternatively, the high C:N ratios of the remineralised organic matter may have been directly related to the large dissolved organic nitrogen (DON) effluxes; large DON effluxes with a low C:N ratio increase the C:N ratio of organic matter in the surface sediments, which in turn causes an uptake and accumulation of nitrogen by bacteria due to N-limitation of the microbial decomposition. Production by all the plant groups had a significant influence on benthic nutrient fluxes, with a typical pattern of an efflux during the dark cycle and an uptake during the light cycle. As such, the sediment productivity/respiration ( p/r) ratio was one of the major controls on (best indicators of) net benthic inorganic and organic nutrient fluxes and appears to be one of the key changes which occur in shallow coastal lagoons as these become eutrophic. This has important management implications, demonstrating the need to maintain the balance of benthic autotrophy and heterotrophy. The robustness of the denitrification efficiency and sediment p/r relationships across such a diverse range of plant-sediment systems that represent the different stages of eutrophication suggests that these may be useful in synthesising denitrification and benthic flux data across shallow coastal systems and in defining suitable carbon loading rates. KEY WORDS: Coastal lagoon · Production · Decomposition · Benthic fluxes · Denitrification · Eutrophication Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 229. Online publication date: March 20, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Aspects of the water resources management practice with emphasis on nutrients control in the Chivero Basin, Zimbabwe

This paper summarises the results of a study on qualitative, quantitative and environmental aspects of water resources management in the Lake Chivero basin, which is the main source of water supply of the City of Harare, Zimbabwe and is in advanced stage of eutrophication. In terms of water quality, an integrated database has been developed, combining existing monitoring data about natural water quality, effluent discharges and urban storm drainage, and data from research investigations during the period 1995–2000. Background pollution in the basin varied from 0.1 to 0.3 mg/l and from 0.1 to 0.4 mg/l for nitrates and phosphates (as total P), respectively. Spatial variations along the major rivers showed a steady trend of increase in nutrient levels with a peak in 1998. At Marimba River confluence the annual median values recorded were 3.5 and 4.4 mg/l for ammonia and phosphates, respectively, thus exceeding the effluent discharge regulations 7–9 times. The major nutrient sources contributing to this status are associated with operational problems of the treatment facilities and diffuse sources of pollution from pastures irrigated with effluent, as well as from urban storm water. In environmental terms a first step was undertaken towards the development of a biological water quality monitoring system, by evaluating the habitat and a-biotic characteristics of the pristine regions of the basin. As to water quantity, it was found that the existing infrastructure is capable to satisfy present water demand, but the abstraction amounts to 77% of the water generated in the basin, which could be considered as an upper limit. It is not yet clear how some provisions of the new Water Act, such as the recognition of the environment as a legitimate water user, will be implemented. With regard to urban water management, the research focused on the development of a rainfall runoff model for the composite catchment area of the Marimba river basin, a sub-urban micro catchment of the Lake Chivero basin. The paper discusses the above findings, and suggests integrated solutions, considering the provisions of the new Water Act. The extensive amount of data accumulated and analysed during this study could form a sound basis for the development of a Management Information System of the basin, based on a GIS. Such a system could be useful for the catchment councils involved.

Stream phosphorus transport in the Lake Tahoe basin, 1989-1996.

Lake Tahoe is undergoing the initial stages of cultural eutrophication due to human alteration of the airshed and watershed. The lake's switch from nitrogen (N) to phosphorus (P) limitation has been attributed primarily to atmospheric N loading. This places an increased importance on controlling watershed movement of P to the lake. A stream water quality monitoring data set consisting of nine streams in the Lake Tahoe basin has been analyzed to characterize the spatiotemporal variation of P delivery to the lake. This data is from the Lake Tahoe Interagency Monitoring Program (LTIMP), which provides scientific data for planning and regulatory agencies to address environmental problems in the Lake Tahoe basin. Results indicate that P delivery (concentrations, loads) varies greatly at interannual, seasonal, and spatial scales. Annual and seasonal total P (TP) concentrations can vary up to three orders of magnitude in a given stream and are strongly associated with suspended sediment. Particulate P is the major form of P transported by Tahoe streams and was strongly correlated with percent surficial geologic deposits, which are primarily located near streams. Tahoe streams with the highest annual P concentrations often had the lowest annual P loads, and visa versa. P loading is greatest during the spring snowmelt (75% of annual average). Potential watershed parameters influencing P delivery to Lake Tahoe have been identified as precipitation, basin area, basin steepness, and road and human development coverage. Results also suggest that human development impacts on stream P loads are most prevalent during high precipitation years. Identification and quantification of stream sediment and P sources such as streambanks and impervious surface is necessary to aid in watershed restoration efforts.

A long‐term management plan for a watershed in a world metropolis – Istanbul

Ömerli reservoir is the major reservoir of Istanbul in terms of water supply potential. However, rapid population increase, unplanned and illegal housing, irrelevant industries and motorways passing through the protection zones of the catchment area, together with insufficient infrastructure, cause the water quality of the reservoir to tend towards the eutrophic stage from the mesotrophic stage parallel to the land use profile. In order to achieve a long‐term water supply from the reservoir and to arrive at sanitary solutions, new land use plans should be developed. Therefore, the key idea of this paper is to develop a convenient protection strategy to keep the reservoir from further deterioration, in light of the guidelines of a new land use plan, and to allow the watershed to be used in accordance with the tendencies of society in a controlled manner, so as to maintain the sustainability of the reservoir for drinking water supply and to assure continuing control by implementing economic sanctions.

A Re-evaluation of the Trophic State of Mountain Lake, Virginia, USA

ABSTRACT Limnological studies of Mountain Lake, Giles County, Virginia were conducted from June to October of 1997 and April to October of 1998 to evaluate the lake's trophic state, which was considered to be in an early stage of eutrophication from the late 1980s to early 1990s. Orthophosphate-P levels averaged 1.5μg/L in 1997 and 2.2μg/L in 1998, a return from 27.0μg/L in 1990 to early and mid 1980s levels. Ammonium-N also dropped, but nitrate-N increased in 1997–98 compared to 1990. The N:P ratio of 143:1 in 1997 and 244:1 in 1998 compared to 9.4:1 in 1990 clearly indicated P as the major limiting nutrient. Dissolved silica, hardness, alkalinity, and pH in the lake were similar to earlier studies. Phytoplankton taxa and cell densities were similar to those of the mid-1980s. Mountain Lake is thus oligotrophic and presently shows no signs of eutrophication. Input streams feeding the lake were also low in key nutrients, but precipitation constituted a major source of P, N, and acidity to the lake.

Character and Paleoenvironm ental Significance of the Pigment and Organic δ<sup>13</sup>C in Sediments of Nansihu Lake

湖泊沉积物中的色素含量与种类是研究湖泊初始生产力和湖泊环境的有效手段之一.而有机碳同位素比值反映了沉积有机物来源信息.本文在对南四湖沉积剖面中总有机碳含量分析的基础上,测定了有机碳的同位素比值,同时通过剖面中色素指标的分析,揭示该湖泊环境演化历史.研究表明,南四湖成湖时代为2.45kaB.P,成期水体主要来自黄河泛滥；其次,南四湖东西沉积环境差异较大,西部(微山湖)主要受黄河泛滥影响,东部(独山湖)则为山麓碎屑沉积；近代南四湖中蓝藻大量繁盛,湖泊具有逐步向富营养化发展的趋势.;Content of total organic carbon in lake sedim ents is usually used to obtain the lake paleoprimary productivity．Such organic matter will conduct a series of chemicaI and biological reaction after it deposits in the lake bo ttom． Therefore the total organic carbon in lake sediments only offers rough information about lake paleoprim ary productivity． Based on the content of total organic carbon and the organic 8 C of the sedim ents．the source of sediment has been distinguished． By analyzing the pigment index， the environmental evolution history of the lake has been recovered， These researches made it clear that Nana ihu Lake has formed in 2，45kaBP with the lake water mainly coling from the Yellow River． The deposition environment of the east part of the lake is different from that of the west， In the west part(W eishanhu Lake)the sediments mainly com e from the flood plain materials of the Yellow River．while in the east part (Dushanhu Lake)the sediments mainly come from the footslope materials，Recently，the Cyanophyta is flourishing in the lake and the lake gradually comes into the eutrophication stage.

Effects of sand bar openings on some limnological variables in a hypertrophic tropical coastal lagoon of Brazil

This study describes the spatial and temporal dynamics of several physical, chemical and biological variables in the Grussai lagoon, and their relationship to ephemeral sand bar openings and to a constant in natura waste water input. The spatial variation in pH, dissolved oxygen, electrical conductivity, total alkalinity and nutrients (e.g. soluble reactive silicate, soluble reactive phosphate and ammonium) was associated to the anoxic and nutrient rich groundwater discharge, the development of aquatic macrophytes, the biological activities of phytoplanktonic community and the marine influence. During the period when the sand bar was closed (isolated), the lagoon water was supersaturated with dissolved oxygen and exhibited high values of pH (8–10), total alkalinity (3.000–5.000 µeq l-1), and chlorophyll a contents (60-300 µg l-1), and had low values of dissolved nutrients (nearly undetectable). These suggest a biological processes dominance. When the sand bar was opened, there was an enrichment with dissolved inorganic nutrients (e.g. ammonium and soluble reactive phosphorus up to 120 and 5 µM, respectively) and a decrease in pH (below 8), total alkalinity (below 3.000 µeq l-1) and dissolved oxygen during the initial second to eight days. Subsequently there was a period when the physical and chemical characteristics of seawater prevailed. The lagoon returned chemical to the pre-opening water conditions in a few days (∼ 10–20). This quick return implies highly efficient biological mechanisms. The high levels of chlorophyll a, total nitrogen and phosphorus in the water column indicate a high eutrophication stage in the Grussai lagoon during the sand bar closed periods.