Intensification of harmful cyanobacterial blooms in a eutrophic, temperate lake caused by nitrogen, temperature, and CO2

Warmer temperatures can significantly increase the intensity of cyanobacterial harmful algal blooms (CHABs) in eutrophic freshwater ecosystems. However, few studies have examined the effects of CO2 enrichment in tandem with elevated temperature and/or nutrients on cyanobacterial taxa in freshwater ecosystems. Here, we observed changes in the biomass of cyanobacteria, nutrients, pH, and carbonate chemistry over a two-year period in a shallow, eutrophic freshwater lake and performed experiments to examine the effects and co-effects of CO2, temperature, and nutrient enrichment on cyanobacterial and N2-fixing (diazotrophic) communities assessed via high throughput sequencing of the 16S rRNA and nifH genes, respectively. During both years, there were significant CHABs (50-500 μg cyanobacterial chlorophyll-a L-1) and lake CO2 levels were undersaturated (≤300 μatm pCO2). NH4+ significantly increased the net growth rates of cyanobacteria as well as the biomass of the diazotrophic cyanobacterial order Nostocales under elevated and ambient CO2 conditions. In a fall experiment, the N2 fixation rates of Nostocales were significantly higher when populations were enriched with CO2 and P, relative to CO2-enriched populations that were not amended with P. During a summer experiment, N2 fixation rates increased significantly under N and CO2 - enriched conditions relative to N-enriched and ambient CO2 conditions. Nostocales dominated the diazotrophic communities of both experiments, achieving the highest relative abundance under CO2-enriched conditions when N was added in the first experiment and when CO2 and temperature were elevated in the second experiment, when N2 fixation rates also increased significantly. Collectively, this study indicates that N promotes cyanobacterial blooms including those formed by Dolichospermum and that the biomass and N2 fixation rates of diazotrophic cyanobacterial taxa may benefit from enhanced CO2 levels in eutrophic lakes.

Elevated CO2 significantly increases N2 fixation, growth rates, and alters microcystin, anatoxin, and saxitoxin cell quotas in strains of the bloom-forming cyanobacteria, Dolichospermum

The effect of rising CO₂ levels on cyanobacterial harmful algal blooms (CHABs) is an emerging concern, particularly within eutrophic ecosystems. While elevated pCO₂ has been associated with enhanced growth rates of some cyanobacteria, few studies have explored the effect of CO₂ and nitrogen availability on diazotrophic (N₂-fixing) cyanobacteria that produce cyanotoxins. Here, the effects of elevated CO₂ and fixed nitrogen (NO₃^-) availability on the growth rates, toxin production, and N₂ fixation of microcystin, saxitoxin, and anatoxin-a - producing strains of the genus Dolichospermum were quantified. Growth rates of all Dolichospermum spp. were significantly increased by CO₂ or both CO₂ and NO₃^- with rates being highest in treatments with the highest levels of CO₂ and NO₃^-for all strains. While NO₃^- suppressed N₂ fixation, diazotrophy significantly increased when NO₃^--enriched Dolichospermum spp. were supplied with higher CO₂ compared to cultures grown under lower CO₂ levels. This suggests that diazotrophy will play an increasingly important role in N cycling in CO₂-enriched, eutrophic lentic systems. NO₃^- significantly increased quotas of the N-rich cyanotoxins, microcystin and saxitoxin, at ambient and enriched CO₂ levels, respectively. In contrast, elevated CO₂ significantly decreased cell quotas of microcystin and saxitoxin, but significantly increased cell quotas of the N-poor cyanotoxin, anatoxin. N₂ fixation was significantly negatively and positively correlated with quotas of N-rich and N-poor cyanotoxins, respectively. Findings suggest cellular quotas of N-rich toxins (microcystin and saxitoxin) may be significantly reduced, or cellular quotas of N-poor toxins (anatoxin) may be significantly enhanced, under elevated CO₂ conditions during diazotrophic cyanobacterial blooms. Finally, in the future, ecosystems that experience combinations of excessive N loading and CO₂ enrichment may become more prone to toxic blooms of Dolichospermum.

Nitrogen and phosphorus significantly alter growth, nitrogen fixation, anatoxin-a content, and the transcriptome of the bloom-forming cyanobacterium, Dolichospermum

While freshwater cyanobacteria are traditionally thought to be limited by the availability of phosphorus (P), fixed nitrogen (N) supply can promote the growth and/or toxin production of some genera. This study characterizes how growth on N2 (control), nitrate (NO3 -), ammonium (NH4 +), and urea as well as P limitation altered the growth, toxin production, N2 fixation, and gene expression of an anatoxin-a (ATX-A) - producing strain of Dolichospermum sp. 54. The transcriptomes of fixed N and P-limited cultures differed significantly from those of fixed N-deplete, P-replete (control) cultures, while the transcriptomes of P-replete cultures amended with either NH4 + or NO3 - were not significantly different relative to those of the control. Growth rates of Dolichospermum (sp. 54) were significantly higher when grown on fixed N relative to without fixed N; growth on NH4 + was also significantly greater than growth on NO3 -. NH4 + and urea significantly lowered N2 fixation and nifD gene transcript abundance relative to the control while cultures amended with NO3 - exhibited N2 fixation and nifD gene transcript abundance that was not different from the control. Cultures grown on NH4 + exhibited the lowest ATX-A content per cell and lower transcript abundance of genes associated ATX-A synthesis (ana), while the abundance of transcripts of several ana genes were highest under fixed N and P - limited conditions. The significant negative correlation between growth rate and cellular anatoxin quota as well as the significantly higher number of transcripts of ana genes in cultures deprived of fixed N and P relative to P-replete cultures amended with NH4 + suggests ATX-A was being actively synthesized under P limitation. Collectively, these findings indicate that management strategies that do not regulate fixed N loading will leave eutrophic water bodies vulnerable to more intense and toxic (due to increased biomass) blooms of Dolichospermum.

Uptake and localization of fluorescently-labeled Karenia brevis metabolites in non-toxic marine microbial taxa

Brevetoxin (PbTx) is a neurotoxic secondary metabolite of the dinoflagellate Karenia brevis. We used a novel, fluorescent BODIPY-labeled conjugate of brevetoxin congener PbTx-2 (B-PbTx) to track absorption of the metabolite into a variety of marine microbes. The labeled toxin was taken up and brightly fluoresced in lipid-rich regions of several marine microbes including diatoms and coccolithophores. The microzooplankton (20-200 μm) tintinnid ciliate Favella sp. and the rotifer Brachionus rotundiformis also took up B-PbTx. Uptake and intracellular fluorescence of B-PbTx was weak or undetectable in phytoplankton species representative of dinoflagellates, cryptophytes, and cyanobacteria over the same (4 h) time course. The cellular fate of two additional BODIPY-conjugated K. brevis associated secondary metabolites, brevenal (B-Bn) and brevisin (B-Bs), were examined in all the species tested. All taxa exhibited minimal or undetectable fluorescence when exposed to the former conjugate, while most brightly fluoresced when treated with the latter. This is the first study to observe the uptake of fluorescently-tagged brevetoxin conjugates in non-toxic phytoplankton and zooplankton taxa, demonstrating their potential in investigating whether marine microbes can serve as a significant biological sink for algal toxins. The highly variable uptake of B-PbTx observed among taxa suggests some may play a more significant role than others in vectoring lipophilic toxins in the marine environment.

The Individual and Combined Effects of the Cyanotoxins, Anatoxin-a and Microcystin-LR, on the Growth, Toxin Production, and Nitrogen Fixation of Prokaryotic and Eukaryotic Algae

Globally, eutrophication and warming of aquatic ecosystems has increased the frequency and intensity of cyanobacterial blooms and their associated toxins, with the simultaneous detection of multiple cyanotoxins often occurring. Despite the co-occurrence of cyanotoxins such as microcystins and anatoxin-a (ATX) in water bodies, their effects on phytoplankton communities are poorly understood. The individual and combined effects of microcystin-LR (MC-LR) and ATX on the cyanobacteria Microcystis spp., and Anabaena variabilis (a.k.a. Trichormus variabilis), and the chlorophyte, Selenastrum capricornutum were investigated in the present study. Cell density, chlorophyll-a content, and the maximum quantum efficiency of photosystem II (Fv/Fm) of Microcystis cells were generally lowered after exposure to ATX or MC-LR, while the combined treatment with MC-LR and ATX synergistically reduced the chlorophyll-a concentration of Microcystis strain LE-3. Intracellular levels of microcystin in Microcystis LE-3 significantly increased following exposure to MC-LR + ATX. The maximum quantum efficiency of photosystem II of Anabaena strain UTEX B377 declined during exposure to the cyanotoxins. Nitrogen fixation by Anabaena UTEX B377 was significantly inhibited by exposure to ATX, but was unaffected by MC-LR. In contrast, the combination of both cyanotoxins (MC-LR + ATX) caused a synergistic increase in the growth of S. capricornutum. While the toxins caused an increase in the activity of enzymes that scavenge reactive oxygen species in cyanobacteria, enzyme activity was unchanged or decreased in S. capricornutum. Collectively this study demonstrates that MC-LR and ATX can selectively promote and inhibit the growth and performance of green algae and cyanobacteria, respectively, and that the combined effect of these cyanotoxins was often more intense than their individual effects on some strains. This suggests that the release of multiple cyanotoxins in aquatic ecosystems, following the collapse of blooms, may influence the succession of plankton communities.

Succession and toxicity of Microcystis and Anabaena (Dolichospermum) blooms are controlled by nutrient-dependent allelopathic interactions

Microcystis and Anabaena (Dolichospermum) are among the most toxic cyanobacterial genera and often succeed each other during harmful algal blooms. The role allelopathy plays in the succession of these genera is not fully understood. The allelopathic interactions of six strains of Microcystis and Anabaena under different nutrient conditions in co-culture and in culture-filtrate experiments were investigated. Microcystis strains significantly reduced the growth of Anabaena strains in mixed cultures with direct cell-to-cell contact and high nutrient levels. Cell-free filtrate from Microcystis cultures proved equally potent in suppressing the growth of nutrient replete Anabaena cultures while also significantly reducing anatoxin-a production. Allelopathic interactions between Microcystis and Anabaena were, however, partly dependent on ambient nutrient levels. Anabaena dominated under low N conditions and Microcystis dominated under nutrient replete and low P during which allelochemicals caused the complete suppression of nitrogen fixation by Anabaena and stimulated glutathione S-transferase activity. The microcystin content of Microcystis was lowered with decreasing N and the presence of Anabaena decreased it further under low P and high nutrient conditions. Collectively, these results indicate that strong allelopathic interactions between Microcystis and Anabaena are closely intertwined with the availability of nutrients and that allelopathy may contribute to the succession, nitrogen availability, and toxicity of cyanobacterial blooms.

Urban American Indian aging

Although the majority of American Indians do not live on reservations, little attention has been focused on urban American Indian elderly. Urban American Indian elders have aged in place, and the majority intend to remain in cities. First, the needs of American Indian elders are assessed and the under-utilization of Older Americans Act services documented. Then barriers to access are discussed and means to increase participation recommended.

Husbands caring for wives with dementia: a longitudinal study of continuity and change

The longitudinal study reported in this article examines how the patterns of change over time for husbands who continue to care for their spouses in the community compare with husbands who place their spouses in nursing homes. There were 74 older men enrolled in the study initially; follow-up interviews were conducted with the available husbands who continued to provide care in their own homes or who had placed their spouses in nursing homes after one year. Potential theoretical relevance of the current findings and their implications for health and mental health social workers in terms of assessment, treatment, and program development for older male caregivers is highlighted.

Caregiving as a life course transition among older husbands: a prospective study

Guided primarily by transitions theory, this study examined changes over two points in time (approximately 5 years apart) in multiple life domains (i.e., household tasks, social life, marital relationship, and well-being) between two groups of husbands aged 60 and older, who indicated that their wives were not in need of care or assistance due to an illness or disability at the initial interview. The two groups included husbands who identified themselves as a provider of care at Time 2 (T2; i.e., they had transitioned into the caregiver role; n = 26), and those married to healthy wives at T2 (i.e., noncaregivers; n = 262). Data came from a national probability sample of U.S. adults who were primary respondents to the National Survey of Families and Households in 1987-88, and who were followed up longitudinally in 1992-93. Findings suggested that husbands who entered the caregiving role demonstrated significant changes in household responsibilities, social integration, marital relationship, and well-being. Implications for practice and future research on the older husband caregiver are highlighted.

Differential predictors of strain and gain among husbands caring for wives with dementia

Given that women predominate in the caregiving role, researchers have largely focused on the experience of female caregivers. This cross-sectional study takes a beginning step toward understanding the differential predictors of negative (i.e., strain) and positive (i.e., gain) appraisals among 74 husbands caring for wives with dementia. Using a multivariate model of caregiver adaptation, results indicated that social resources and health were important for understanding the variation in both positive and negative appraisals. Unique predictors of strain included memory and behavior problems, and emotion-focused coping. Alternatively, education and problem-focused coping helped to explain variation found in appraisal of caregiver role gain. Theoretical and practical implications are discussed.

Gain in the caregiving experience: where are we? What next?

This critical review of 29 studies published through 1996 on the gain experienced among informal caregivers of older adults, identifies 13 conceptual (i.e., definitions and theoretical frameworks) and methodological (i.e., sampling, design, measurement, analysis) observations. Key limitations of prior research are highlighted and recommendations necessary for the advancement of research in this area of inquiry are made. Drawing upon relevant theoretical frameworks and the observations noted in this review, a conceptual framework is proposed to bring some consistency to the ways in which future research on positive aspects of caregiving proceeds.

Macrosocial and environmental influences on minority health

Ethnic minority populations show patterns of health, health care use, and mortality that differ from the overall U.S. population. Each of the broad groups of minorities (Asian Hispanic, Native, and African Americans) has a unique background of sociocultural factors that influence these patterns. Thus, the larger social environment for ethnic populations, including political, environmental, historical, and economic factors, is a major variable in possible health outcomes. The individual portions in this panel report of the conference seek to identify such factors for each ethnic group and to suggest those macrosocial influences that are most important for observed health effects.

Alcohol consumption among older urban American Indians

OBJECTIVE

To describe the pattern of alcohol consumption by older urban American Indians in Los Angeles, California, in 1987-89.

METHOD

Data come from a cross-sectional community health survey with a convenience sample of 282 nonhomeless American Indians, both male and female. The sample matched the age and sex distribution reported by the U.S. Census. During the face-to-face structured interview self-reports of alcohol consumption were gathered for American Indians recognized by their community as elders (mean [+/-SD] age 61.1 +/- 11.1 years).

RESULTS

Most elders (73%) did not drink alcohol. More women than men, and more individuals aged 60+ than people under 60 years, abstained. Elders in single generation households tended to consume more alcohol than those in multigeneration households. Among the 76 people we reported drinking, significantly more people under age 60 than over age 60 consumed four or more drinks per sitting (p < .01), and those who lived alone were more likely than drinkers living with others to consume alcohol at least once a week (p < .04).

CONCLUSIONS

Age seemed to be a salient marker with respect to alcohol consumption, with fewer people 60+ years of age drinking as much or as often as people under this age. Abstainers are not necessarily lifetime teetotalers, but may be former drinkers who have quit, and may still on occasion go on short-term binges. Results of this survey replicate findings from surveys of the general elderly population, suggesting that older urban American Indians are not different from other older people with respect to consumption of alcohol.

Macrosocial and environmental influences on minority health

Ethnic minority populations show patterns of health, health care use, and mortality that differ from the overall U.S. population. Each of the broad groups of minorities (Asian Hispanic, Native, and African Americans) has a unique background of sociocultural factors that influence these patterns. Thus, the larger social environment for ethnic populations, including political, environmental, historical, and economic factors, is a major variable in possible health outcomes. The individual portions in this panel report of the conference seek to identify such factors for each ethnic group and to suggest those macrosocial influences that are most important for observed health effects.

American Indian families and home care: macro social and cultural considerations

Administration on Aging and the Indian Health Service are developing or examining the feasibility of programs to support home health care on reservations and American Indian colleges are training home care paraprofessionals to provide high quality home care for frail American Indian elders. Home care links formal and informal systems of health care and is affected by social and cultural issues. These macro-level considerations provide a context for home care of cancer patients and are the focus of this article.

Eldercare and work-role conflict: toward an understanding of gender differences in caregiver burden

This study investigated gender differences in caregiving tasks, role strains, and resources to account for gender variations in burden among a probability sample of employed, nonspousal caregivers (N = 413). Females were more likely to assist with care provision tasks, to report work role strains, and to experience higher levels of burden than males. After controlling for known sociodemographic dissimilarities in predicting burden, the effect of gender decreased at each step when caregiver tasks, work role strains, and resources were entered into the regression equation. Results suggest that these differences may partially explain the greater negative impact experienced by nonspousal, female caregivers.

Health and aging of urban American Indians

Although half of the American Indian population resides off the reservation, mostly in the western states, research on the health of urban American Indians remains sparse. American Indians living in urban areas are not eligible for the federally mandated health care provided by the Indian Health Service and receive health care services in a variety of settings. This population is at high risk for many health problems, especially cardiovascular disease and diabetes mellitus. Social, cultural, and economic barriers that impede access to health care for this group, particularly for elders living in an urban setting, could be reduced if physicians improved their understanding of and communication with American Indian patients.