The Trophic Diatom Index: a new index for monitoring eutrophication in rivers

A index for monitoring the trophic status of rivers based on diatom composition (‚trophic diatom index’, TDI) has been developed, in response to the National Rivers Authority (England & Wales)'s needs under the terms of the Urban Wastewater Treatment Directive of the European Community. The index is based on a suite of 86 taxa selected both for their indicator value and ease of identification. When tested on a dataset from 70 sites free of significant organic pollution, this index was more highly correlated with aqueous P concentrations than previous diatom indices. However, where there was heavy organic pollution, it was difficult to separate the effects of eutrophication from other effects. For this reason, the value of TDI is supplemented by an indication of the proportion of the sample that is composed of taxa tolerant to organic pollution. The index was tested on the R. Browney, N-E. England, above and below a major sewage discharge. TDI values indicated that the effect of inorganic nutrients on the river downstream of the discharge was slight as the river was already nutrient-rich, but there was a large increase in the proportion of organic pollution-tolerant taxa. This indicates that the river was already so eutrophic upstream of the discharge that tertiary treatment to remove P would not be effective unless other aspects of the discharge were also improved.     

Biological monitoring of eutrophication in rivers

There is an increasing awareness of the need to assess the impact of nutrient enrichment on river ecosystems separately from the impacts of organic effluents. A range of methods have been proposed and some have moved from the development stage to practical use by water management organizations. The methods can be applied to broad surveys or provide baseline information to assess possible future change. In the latter case it is recommended that several different methods are used, especially where it is important to get reliable information on the long-term impact of improvements in effluent quality. Estimates of biomass measured as chlorophyll a have often been used for phytoplankton and sometimes also for benthic communities. However, a lot of care is needed in applying this method, because of the range of factors besides nutrient concentration which can influence values. Approaches based on the whole community have been developed by a number of research groups, usually involving semiquantitative estimates of abundance. There has also been a rapid increase in the use of indices based on the relative proportions of epilithic diatom species. The methodologies used by a number of research groups in Europe are broadly similar, making it possible to compare results between different regions. The development of indices based on macrophyte floristic composition in relation to river nutrient status is also under development, especially in France and UK. However, interpretation of the results is complicated where long-term changes are taking place in nutrient concentrations in the water, because of the varying contributions of sediment and water to different species of rooted plant. Bioassays can be especially helpful where it is desired to establish whether either N or P is limiting for a population of community.     

Coastal eutrophication assessment in the United States

Recent national assessments document that nitrogen-driven coastal eutrophication is widespread and increasing in the United States. This significant coastal pollution problem includes impacts including increased areas and severity of hypoxic and anoxic waters; alteration of food webs; degradation and loss of sea grass beds, kelp beds and coral reefs; loss of biodiversity; and increased incidences and duration of harmful algal blooms. In this paper, we review two complementary approaches to assessing the causes and consequences of these trends, as well as potential remedies for them. The first is a national-scale assessment, drawn primarily from expert knowledge of those most familiar with the individual estuaries and integrated into a common analysis framework. The second approach, focused on the Mississippi/Atchafalaya basin – the largest US drainage basin – draws upon both quantitative and qualitative analyses within a comprehensive framework, Integrated Assessment.     

Diatom evidence for the timing and causes of eutrophication in Lake Victoria,East Africa

The determination of the history and causes of recent eutrophication and intensified thermal stratification in Lake Victoria is still hampered by the sparsity of paleolimnologic coverage of the enormous lake. Five new diatom records from Ugandan waters now show that a transition from Aulacoseira-dominated planktonic assemblages to those dominated by long Nitzschia spp., occurred in northern coastal sites from the mid-1970s to mid-1980s. Similar transitions developed from the late 1960s to early 1970s offshore and from the 1940s to early 1950s along the Kenyan coast, suggesting a time-transgressive process. These changes are not readily attributable to the trophic effects of Nile perch population growth during the early 1980s, but more likely reflect responses to long-term nutrient enrichment and climatic instability in the region. The diversity of planktonic diatom communities has declined dramatically, and a namesake variety of Aulacoseira nyassensis may now be nearly extirpated. Although local phytoplankton communities varied considerably in the past, the current domination of diatom assemblages by Nitzschia is apparently unprecedented in the 15,000-year history of Lake Victoria.     

Strength and uncertainty of phytoplankton metrics for assessing eutrophication impacts in lakes

Phytoplankton constitutes a diverse array of short-lived organisms which derive their nutrients from the water column of lakes. These features make this community the most direct and earliest indicator of the impacts of changing nutrient conditions on lake ecosystems. It also makes them particularly suitable for measuring the success of restoration measures following reductions in nutrient loads. This paper integrates a large volume of work on a number of measures, or metrics, developed for using phytoplankton to assess the ecological status of European lakes, as required for the Water Framework Directive. It assesses the indicator strength of these metrics, specifically in relation to representing the impacts of eutrophication. It also examines how these measures vary naturally at different locations within a lake, as well as between lakes, and how much variability is associated with different replicate samples, different months within a year and between years. On the basis of this analysis, three of the strongest metrics (chlorophyll-a, phytoplankton trophic index (PTI), and cyanobacterial biovolume) are recommended for use as robust measures for assessing the ecological quality of lakes in relation to nutrient-enrichment pressures and a minimum recommended sampling frequency is provided for these three metrics.     

Planktonic bloom-forming Cyanobacteria and the eutrophication of lakes and rivers

SUMMARY. 1. Eutrophication of water bodies involves the enrichment of plant nutrients, often followed by significant shifts in the phytoplankton towards Cyanobacteria. When comparing different aquatic systems, even with similar nutrient contents and in the same climatic region, inverse deductions are not valid; i.e. (a) the presence of Cyanobacteria does not necessarily indicate eutrophic conditions, or (b) eutrophic or even poly-trophic conditions do not necessarily support cyanobacterial development.
2. Above a threshold of 10 μg 1⁻¹ total phosphorus, the development of Cyanobacteria can be described by physical factors, such as water column stability. By characterizing different forms of turbulence, the presence or absence of Cyanobacteria in lakes and rivers can be predicted.
3.When the turbulence of the water column is rather low, as it is in sheltered or meromictic lakes, Cyanobacteria can build up dense populations. In nutrient poor systems, species of Oscillatoria and (seldom) Aphanizomenon are dominating.
4.If the turbulence of the water column is high (mixing depth much greater than euphotic depth) or the mixing pattern is irregular, as in slowly flowing or regulated rivers, Cyanobacteria are outcompeted.
5. In the presence of frequent or permanent turbulence, but with mixing depths lower or not much greater than the euphotic zone (as it is the case in shallow, unstratified lakes, mostly eutrophic or even hypertrophic), Cyanobacteria can outgrow normally dominant r -strategists under conditions of low N:P ratios, high water temperatures, pH >9.0 or low light availabilities.
6. If turbulence is comparatively great (10 to $15 m) and stable for a longer period of time, some cyanobacteria are able to adapt.
7. Our statements are discussed on the basis of physiological characteristics.     

Harmful algal blooms and eutrophication: Examining linkages from selected coastal regions of the United States

Coastal waters of the United States (U.S.) are subject to many of the major harmful algal bloom (HAB) poisoning syndromes and impacts. These include paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP), ciguatera fish poisoning (CFP) and various other HAB phenomena such as fish kills, loss of submerged vegetation, shellfish mortalities, and widespread marine mammal mortalities. Here, the occurrences of selected HABs in a selected set of regions are described in terms of their relationship to eutrophication, illustrating a range of responses. Evidence suggestive of changes in the frequency, extent or magnitude of HABs in these areas is explored in the context of the nutrient sources underlying those blooms, both natural and anthropogenic. In some regions of the U.S., the linkages between HABs and eutrophication are clear and well documented, whereas in others, information is limited, thereby highlighting important areas for further research.     

筑坝河流磷素的迁移转化及其富营养化特征

人类活动过量营养物质输入是导致河流富营养化的主要原因,而河道过度的人为调控则进一步复杂化了河流的营养状态变化。闸坝是河流人为调控的重要工程措施之一,提高水资源利用效率的同时严重干扰了河流自然的生物地球化学循环,产生诸多负面生态环境效应。磷素的迁移转化对河流的营养限制作用受到越来越多的关注,国内外已有研究在筑坝河流磷的富营养化特征方面,已经取得了较为深刻的认识:水库闸坝建设滞留大量磷素,导致河流水体磷含量升高、营养物质比例变化,沉积物储存过量磷素形成的内源释放威胁,以及进一步浮游植物和有害藻类的生长响应等,使得筑坝河流的富营养化生态风险升高;在此基础上,也提出了根据降雨分配和闸控库区储水,合理设置闸坝泄流方式,以改善筑坝河流富营养化生态风险的重要管理思路。对于闸坝调控作用与水体富营养化的定量关系还有待进一步的探讨,而且随着河流资源开发和人为调控力度的增强,河流闸坝建设所产生的系列生态环境问题日益严峻,对此提出还需要系统研究的方向:闸坝调控作用下河流磷素的富营养化机制及其与氮、碳等元素的耦合作用,筑坝河流沉积物内源污染的综合管理,以及闸控景观河流的生态建设和修复等。     

Structure and seasonal dynamics of hyporheic zone microbial communities in free-stone rivers of the estern United States

The hyporheic zone of a river is characterized by being nonphotic, exhibiting chemical/redox gradients, and having a heterotrophic food web based on the consumption of organic carbon entrained from surface waters. Hyporheic microbial communities constitute the base of food webs in these environments and are important for maintaining a functioning lotic ecosystem. While microbial communities of rivers dominated by fine-grained sediments are relatively well studied, little is known about the structure and seasonal dynamics of microbial communities inhabiting the predominantly gravel and cobble hyporheic zones of rivers of the western United States. Here, we present the first molecular analysis of hyporheic microbial communities of three different stream types (based on mean base discharge, substratum type, and drainage area), in Montana. Utilizing 16S rDNA phylogeny, DGGE pattern analysis, and qPCR, we have analyzed the prokaryotic communities living on the 1.7 to 2.36 mm grain-size fraction of hyporheic sediments from three separate riffles in each stream. DGGE analysis showed clear seasonal community patterns, indicated similar community composition between different riffles within a stream (95.6–96.6% similarity), and allowed differentiation between communities in different streams. Each river supported a unique complement of species; however, several phylogenetic groups were conserved between all three streams including Pseudomonads and members of the genera Aquabacterium, Rhodoferax, Hyphomicrobium, and Pirellula. Each group showed pronounced seasonal trends in abundance, with peaks during the Fall. The Hyphomicrobium group was numerically dominant throughout the year in all three streams. This work provides a framework for investigating the effects of various environmental factors and anthropogenic effects on microbial communities inhabiting the hyporheic zone.     

The Pampean Diatom Index (IDP) for assessment of rivers and streams in Argentina

The rivers and streams of the Pampean plain are subjected to the impact of agriculture, cattle-raising and industrial activities. The largest urban center of Argentina is located here. The most important stresses on rivers and streams in the Pampean plain are organic enrichments (discharge of insufficiently treated sewage), nutrients, heavy metals, pathogenic agents, pesticides, herbicides and physical changes produced by dredging and canalisation. The epipelic community is suitable for biomonitoring purposes because it allows for comparing similar substrates along the rivers and streams. A total of 164 samples of epipelic diatoms were collected during 1995-1999 from Pampean rivers and streams. The analysis of these samples resulted in the development of a specific biotic index: the Pampean Diatom Index (IDP). The results were correlated with the main chemical water characteristics and with other biotic indices. This study suggests that the IDP is integrating organic pollution and eutrophication and can be applied for monitoring the biological quality of rivers and streams in the Pampean plain.     

Compensating for wetland losses in the United States

Impacts of climate change on US wetlands will add to those of historical impacts due to other causes. In the US, wetland losses and degradation result from drainage for agriculture, filling for urbanization and road construction. States that rely heavily on agriculture (California, Iowa, Illinois, Missouri, Ohio, Indiana) have lost over 80% of their historical area of wetlands, and large cities, such as Los Angeles and New York City, have retained only tiny remnants of wetlands, all of which are highly disturbed. The cumulative effects of historical and future degradation will be difficult to abate. A recent review of mitigation efforts in the US shows a net loss of wetland area and function, even though 'no net loss' is the national policy and compensatory measures are mandatory. US policy does not include mitigation of losses due to climate change. Extrapolating from the regulatory experience, one can expect additional losses in wetland areas and in highly valued functions. Coastal wetlands will be hardest hit due to sea-level rise. As wetlands are increasingly inundated, both quantity and quality will decline. Recognition of historical, current and future losses of wetland invokes the precautionary principal: avoid all deliberate loss of coastal wetland area in order to reduce overall net loss. Failing that, our ability to restore and sustain wetlands must be improved substantially.     

Breastfeeding in the United States

The breastfeeding of US infants born in 1974-76 is analyzed using data form the 1976 National Survey of Family Growth. Life table estimates of the proportion of children breastfed by duration since birth and mean breastfeeding durations are presented. The life tables reported are constructed by standard cohort table methods. To compare life tables for children of mothers in various attribute categories, generalised Wilcoxon tests are used, together with multiple classification analysis for continuation at select durations. Variables considered include mother's age at the birth, ethnicity, educational level, education by ethnicity, region of residence and the child's birth order. Findings are restricted to infants remaining with their mothers for at least 2 months following delivery and surviving as of the survey date in January-September 1976. It is found that the proportion of infants breastfed was increasing rapidly, with the highest rates found among white (39%), college-educated (56%), western (56%) mothers and lowest rates among black mothers (17%) mothers with less than a high school education (19%) and mothers living in the south (24%). By age, the highest proportions are mothers at ages 25-29 (44%), followed closely by the mothers under 25 (29%). The proportions breastfeeding were also found to be higher in urban than in rural areas (38% vs. 28%) and higher at parities 1-2 (29%). A multiple classification analysis of the factors most strongly influencing breastfeeding in 1975 shows educational level to be the strongest single predictor of breastfeeding, followed by western residence and white ethnicity. Age effects were found to correlate strongly with education. Reviewing 1971-1981 changes, the proportion of mothers with less than a college education who breastfed their children increased from 19% to 51% over the decade, while the proportion among college-educated mothers rose from 42% to 74%. For children who were breastfed, the median duration was about 4.5 months. The mean was 5.5 months, with a range from about 3.0 months among black mothers with less than a high school education, to 6.0 months among college-educated white women. The nationwide changes in breastfeeding patterns and duration may confer modest health benefits on current generations of youngsters, although not benefits that are easily measured, since human milk substitutes are routinely subjected to rigourous testing for nutritional adequacy.