Difference In Rate Of Decline Research Articles

EFFECTS OF LIGHT ON GRAZING AND CANNIBALISM OF PFIESTERIA PISCICIDA (DINOPHYCEAE)

Feinstein, T., Zhang, H., Costa, K. & Lin, S.Department of Marine Sciences, University of Connecticut, Groton, CT 06340 USAThe toxic dinoflagellate Pfiesteria piscicida is primarily a heterotrophic organism, with photosynthetic potential through the ‘stolen’ chloroplasts of its algal prey (‘kleptoplastidy’). Classical predator‐prey oscillation was found in this dinoflagellate fed with Rhodomonas sp. We show that light has an influence on feeding and growth in P. piscicida that transcends its potential influence on kleptoplastidic photosynthesis. To our surprise, we found that light strongly stimulated grazing and heterotrophic growth in P. piscicida. In addition, under starvation conditions, P. piscicida population declined significantly more rapidly in the light, and further experiments suggest that the difference in rates of decline may be explained in part by light‐stimulated cannibalism. The possible biochemical mechanism and ecological significance of light stimulation of grazing and cannibalism will be discussed.

GREATER DECLINE IN MAXIMAL AEROBIC CAPACITY IN ENDURANCE-TRAINED VS. SEDENTARY WOMEN

Using a cross-sectional design we previously reported that the absolute, but no the relative (%), rate of decline in maximal oxygen consumption (VO2max) with age is greater in endurance-trained compared with healthy sedentary women. We tested this hypothesis using a longitudinal approach. Eight sedentary (S; 63 ± 2 y at follow-up) and 16 endurance-trained (ET; 57 ± 2 y) women were re-evaluated after an average follow-up of 7 years. Body mass, fat-free mass, maximal respiratory exchange ratio, and maximal rating perceived exertion did not change in either group. The absoulte rate of decline in VO2max was greater (P < 0.01) in ET (−0.9 ± 0.2 ml/kg/min/y) compared with S (−0.4 ± 0.1), but the relative rates of decline were similar (−1.9 ± 0.2 vs. −1.5 ± 0.4%/y). The different rates of decline in VO2max were not associated with differences in body mass, maximal heart rate, or blood volume. In ET the absolute rate of decline in VO2max was positively associated with the changes in training volume (r = 0.55). As such, the magnitude of decline was greater (P < 0.01) in those who reduced (−1.2 ± 0.2 ml/kg/min/y; n = 10) compared with those who maintained (−0.4 ± 0.2; n = 6) training volume; the latter values were similar to S. These longitudinal data support our previous cross-sectional observations that the decrease in maximal aerobic capacity with advancing aging is greater in endurance-trained women compared with their sedentary peers due to reductions in training volume. Supported by NIH AG00847, AG13038, HL07851, and Basque Govermment AK

Relationship between HIV-1 Env subtypes A and D and disease progression in a rural Ugandan cohort.

To investigate the role of HIV-1 envelope subtypes on disease progression in a rural cohort of Ugandan adults where two major HIV-1 subtypes (A and D) exist. Participants of a clinical cohort seen between December 1995 and December 1998 had blood collected for HIV-1 subtyping. These included prevalent cases (people already infected with HIV at the start of the study in 1990) and incident cases (those who seroconverted between 1990 and December 1998). HIV-1 subtyping was carried out by heteroduplex mobility assay and DNA sequencing in the V3 env region. Disease progression was measured by the rate of CD4 lymphocyte count decline, clinical progression for the incident cases as time from seroconversion to AIDS or death, to first CD4 lymphocyte count < 200 x 10(6)/l and to the World Health Organization clinical stage 3. All analyses were adjusted for age and sex. One hundred and sixty-four individuals, including 47 prevalent and 117 incident cases, had V3 env subtype data of which 65 (40%) were subtyped as A and 99 as D. In the incident cases, 44 (38%) were subtyped as A and 73 as D. There was a suggestion that for most end-points A had a slower progression than D. The cumulative probability of remaining free from AIDS or death at 6 years post-seroconversion was 0.72 [95% confidence interval (CI), 0.50 to 0.85] for A and 0.58 (95% CI, 0.42 to 0.71) for D, and the adjusted hazard ratio of subtype D compared to A was estimated to be 1.39 (95% CI, 0.66 to 2.94; P = 0.39). The estimated difference in rates of decline in square root CD4 lymphocyte counts was -0.41 per year (95% CI, -0.98 to 0.15; P = 0.15). This study suggests that although subtype A may have a slower progression than D, HIV-1 envelope subtype is not a major factor in determining the progression of HIV-1 disease in a rural population in Uganda.

Age is no kinder to the better educated: absence of an association investigated using latent growth techniques in a community sample.

Higher education has been posited to protect against cognitive decline, either because the rate of decline is slower in the more highly educated or the start of decline is delayed. Latent growth models provide improved methodology to examine this issue. The sample consisted of 887 participants aged 70-93 years in 1991 and followed up in 1994 and 1998. Latent growth models and standard regression techniques were used to examine the rate of cognitive decline in four cognitive measures while controlling for health status and sex. A delayed start model was examined by incorporating interaction effects in a regression model. Neither the latent growth models nor the regression techniques revealed a slower rate of decline for the more highly educated. The proportion of the highly educated showing no change was no larger than the proportion of the less well educated. There were no significant age by education interaction effects, no chronologically later accelerations in the rate of change as a function of education, and no differences in rate of decline between the first measurement interval and the second. Education may not protect against cognitive decline although it is associated with long-term individual differences in level of functioning. The discrepancy between our study and others may be attributable to attrition effects, follow-up length, sample age, scaling artefacts and negative publication bias. Most importantly, practice effects may favour the better educated and hence account for the supposed protective effect in many longitudinal studies of cognitive change.

Modelling nematode population growth and damage

Recent results on the population dynamics and damage relationships of root-knot nematode (RKN, Meloidogyne incognita) and of potato cyst nematode (PCN, Globodera pallida) are modelled, and a computer-based programme is used to explore different strategies for PCN control. Damage by RKN was shown to be density dependent, to increase with increasing duration of plant growth, and to be much greater for good than poor hosts. PCN populations both increase and decline more slowly than those of RKN, and modelling suggested that, when non-hosts are grown, differences in decline rates will have an accumulative effect on the effectiveness of rotation. Similarly, differences in nematicide effectiveness will have a major effect on post-harvest PCN populations, and nematicides were shown to be most effective when PCN populations are small. Host resistance is a key component of integrated management of nematodes and, because gene flow in soil is limited, it can be durable.

Gamma-Ray Burst Environments and Progenitors

Likely progenitors for gamma-ray bursts (GRBs) are the mergers of compact objects or the explosions of massive stars. These two cases have distinctive environments for the GRB afterglow: the compact object explosions occur in the interstellar medium (ISM) and those of massive stars occur in the preburst stellar wind. We calculate the expected afterglow for a burst in a Wolf-Rayet star wind and compare the results with those for constant, interstellar density. The optical afterglow for the wind case is generally expected to decline more steeply than in the constant density case, but this effect may be masked by variations in electron spectral index, and the two cases have the same evolution in the cooling regime. Observations of the concurrent radio and optical/X-ray evolution are especially useful for distinguishing between the two cases. The different rates of decline of the optical and X-ray afterglows of GRB 990123 suggest constant density interaction for this case. We have previously found strong evidence for wind interaction in SN 1998bw/GRB 980425 and here present a wind model for GRB 980519. We thus suggest that there are both wind-type GRB afterglows with massive star progenitors and ISM-type afterglows with compact binary star progenitors. The wind-type bursts are likely to be accompanied by a supernova, but not the ISM type.

Accelerated decline in apolipoprotein E-epsilon4 homozygotes with Alzheimer's disease.

The apolipoprotein E-epsilon4 (APOE-epsilon4) allele is a powerful genetic risk factor for the development of Alzheimer's disease (AD). AD patients who are APOE-epsilon4 homozygotes have an earlier age at onset, increased amyloid burden, and decreased acetylcholine levels--findings that suggest differences in disease severity or rate of progression. Studies of genotype differences in rate of decline, however, have produced negative results that may be due to methodologic biases. The current study examined rate of decline in the largest sample of APOE-genotyped AD patients for whom longitudinal cognitive data have been reported. Newly diagnosed patients with probable AD (n = 201) comprised four genotype groups: epsilon2/3 (n = 14), epsilon3/3 (n = 75), epsilon3/4 (n = 82), and epsilon4/4 (n = 30). The Dementia Rating Scale (DRS) was administered at baseline and then annually for 1 to 6 years (mean, 2.5 years). For each subject, a DRS slope was calculated reflecting annual rate of decline. Rate of decline as measured by DRS slope differed according to genotype, with the effect modified by DRS score (p < 0.014). At the mean DRS score observed in our sample (DRS = 105), the epsilon4/4 group had an increased rate of decline (11.9 points per year) relative to the epsilon2/3 (5.8 points per year; p < 0.003), epsilon3/3 (9.3 points per year; p < 0.076), and epsilon3/4 (9.6 points per year; p < 0.055) groups. At a lower DRS score (DRS = 80), even larger differences were observed among genotypes; the epsilon4/4 group had a increased rate of decline (22.2 points per year) relative to the epsilon2/3 (9.7 points per year; p < 0.0006), epsilon3/4 (15.8 points per year; p < 0.020), and epsilon3/3 (18.2 points per year; p < 0.173) groups. The epsilon2/3 group had a significantly slower rate of decline than all other groups at DRS scores of 80 or 105. APOE-epsilon4 homozygosity is associated with a faster rate of cognitive decline, whereas the epsilon2 allele slows disease progression. These findings suggest that APOE plays a mechanistic role in the progression of AD, and is not simply related to disease onset.

Rate of decline of percentage CD4+ cells is faster in HIV-1 than in HIV-2 infection.

Increasing evidence suggests that the pathogenesis of HIV-1 is different from that of HIV-2. Thus, we have measured, longitudinally at various times over a median follow-up of 2.1 years, the percentage CD4+ cells of 94 patients infected with HIV-1 and 164 patients infected with HIV-2. The pattern of decline of CD4% over time was linear for patients with either infection. Multilevel statistical modeling techniques showed that after stratifying for HIV status, the rate of decline of CD4% was faster among patients who died than among those who survived (difference in rate of decline = 2.34% CD4+ cells/year; p = 0.0002). After stratifying for survival status, the rate of decline was faster and less variable among patients infected with HIV-1 than among patients infected with HIV-2 (difference in rate of decline = 1.12% CD4+ cells/year; p = 0.05). The proportion of patients who showed no fall in CD4+ cells was higher in HIV-2 than in HIV-1 infection (p = 0.026). These data suggest fundamental differences between the two infections, with HIV-1 being more pathogenic resulting in a faster and more homogeneous rate of decline than HIV-2. In HIV-2 infection, disease in many patients progresses slowly, but in some the advance is just as fast as that in HIV-1 infection. The reasons for this marked heterogeneity need elucidation to understand the disease and to target therapeutic interventions against HIV-2 in those most at risk.

Trends in stroke mortality in Greater London and south east England--evidence for a cohort effect?

OBJECTIVE AND SETTING: To examine time trends in stroke mortality in Greater London compared with the surrounding South East Region of England. DESIGN: Age-cohort analysis based on routine mortality data....

Comorbidity and survival in HIV-Infected men in the San Francisco Men's Health Survey

The course of disease associated with infection with the human immmunodeficiency virus varies widely. Some patients deteriorate rapidly, while others live for years, even after an illness that defines the acquired immunodeficiency syndrome (AIDS). In this study, comorbidity, or the presence of concurrent health problems, was investigated prospectively as a possible co-factor for different rates of decline in 395 homosexual/bisexual men in the San Francisco Men's Health Study (SFMHS) who were infected with the human immunodeficiency virus (HIV). Comorbidity data obtained from baseline interviews included both chronic and infectious diseases as well as depression. Smoking, alcohol, and drug use were also examined. The most prevalent comorbid conditions were sexually transmitted diseases (90%) and hepatitis B infection (76%). Most chronic and acute concurrent health conditions were not significant discrete predictors of survival to AIDS or death after controlling for immune status and markers of disease progression. Significantly, other risk factors (e.g., depression and smoking) were found to be associated with more rapid progression. Men with symptoms of depression had a higher risk of progression to AIDS diagnosis; the relative hazard (RH) was 1.4 (95% confidence interval [CI], 1.00–2.08); smoking was associated with higher risk of death (RH, 1.6; 95% CI, 1.20–2.17). Older age was marginally associated with poorer survival to death. No associations were found between survival and alcohol and drug use.

Increased numbers of primed activated CD8+CD38+CD45RO+ T cells predict the decline of CD4+ T cells in HIV-1-infected patients.

To look for surrogate markers in HIV-1 infection that can predict the decline of CD4+ T cells. Multiparameter flow cytometric analyses of CD8+ lymphocytes were performed. These cells were investigated for their expression of the activation marker CD38+ within the naive (CD45RA+) and primed (CD45RO+) subsets. Serial CD4 counts were plotted for each patient and the straight line that best fitted was obtained using least squares regression. Differences in rate of decline were tested using analysis of variance, after each patient was weighted by the reciprocal of the variance. Baseline levels of percentages of CD8+CD38+ T lymphocytes predict the CD4 decline in HIV-1-infected patients. Within the CD8+ subset, the primed CD8+CD38+CD45RO+ population was responsible for this prediction. Conversely, the naive CD8+CD38+CD45RA+ population was not predictive. Patients who initially showed a percentage of CD8+CD38+ T lymphocytes above the median (> 25%) had a more marked decline in CD4+ T cells when compared to individuals with percentages of CD8+CD38+ T lymphocytes below the median value (79.3 and 21.2 x 10(6)/l mean CD4 cell decline per year, respectively). Similarly, percentages of CD8+CD38+CD45RO+ T cells above the median value (> 7%) were also associated with a more rapid decline (69.4 and 14.2 x 10(6)/l mean CD4+ cell decline per year). These results were statistically significant after adjustment for the baseline CD4 count and beta 2-microglobulin levels. Percentages of activated CD8+ cells expressing CD38+ can predict the rate of decline (slope) of the CD4+ T cells. This resides in the CD45RO+ primed population. An early prediction of the CD4+ slope will allow the clinician to target treatment to those patients that are most likely to benefit.

Rates of progression to end stage renal failure in nephropathy secondary to Type 1 and Type 2 diabetes mellitus

Diabetic nephropathy is now the commonest single cause of end-stage renal failure (ESRF) in New Zealand. To investigate differences in the natural history of established nephropathy in Type 1 and 2 diabetes. Retrospective analysis of the rate of progression to ESRF in 17 subjects with Type 1 diabetes (predominantly European) compared to 29 subjects with Type 2 diabetes (all Polynesian). The rate of decline of renal function was determined from serial creatinine measurements (median 5, range 3-8) during progression of chronic renal failure to end stage. Glomerular filtration rate (GFR) was estimated from creatinine measurements using the Cockcroft Gault equation, and the regression slope of these measurements against time was used to determine rate of change of renal function. GFR fell significantly more rapidly in the group with Type 2 diabetes than in those with Type 1 diabetes: median 1.7 (interquartile range 1.2 to 2.3) mL min-1 month-1 vs 1.1 (interquartile range 0.4 to 1.5) mL min-1 month-1, p = 0.017. During the study period the mean reduction in diastolic blood pressure in subjects with Type 1 diabetes (15 mmHg) was greater than that in the Type 2 subjects (8 mmHg), but the stage at which antihypertensives were commenced was similar in the two groups. Glycaemic control was worse in the subjects with Type 1 diabetes (p < 0.005). The differences in blood pressure control were not significant on analysis of covariance which indicated that ethnicity was the major determinant of the different rates of decline of GFR between the groups. We conclude that in subjects with diabetic nephropathy the rate of progression to ESRF is more rapid in Polynesians with Type 2 diabetes than in Europeans with Type 1 diabetes. This could contribute to the apparent excess of Type 2 diabetic subjects of Polynesian origin on renal replacement programmes in New Zealand.

Depression and HIV How Does One Affect the Other?

The course of human immunodeficiency virus (HIV) disease varies widely. Some patients deteriorate rapidly while others live for years, even after an illness that defines the acquired immunodeficiency syndrome (AIDS). The reasons for these different rates of decline are not known, but psychosocial variables have been put on the list of possible host factors.¹The notion has been that one's adaptive coping or fighting spirit might somehow delay or even prevent HIV's inexorable attack—and conversely, that distress and despair might measurably accelerate progression of the disease. See also pp 2563 and 2568. Such a notion is based on more than the understandable hope that one's mind can prevail over an illness with no known medical cure. Accumulating evidence supports the belief held since Hippocrates that vigor, resilience, and perceived support are associated with more favorable medical outcomes.²Furthermore, stress and depression have been shown to affect the immune

Divergence between delayed-type hypersensitivity (DTH) to polyoma tumor-associated antigen and antitumor efficacy in polyoma-bearing recipients of therapeutic non-cytolitic, DTH-mediating lymphocytes

Soluble polyoma tumor-associated antigen (TAA) restimulation of splenocytes from polyoma-bearing mice led to production of non-cytolytic lymphocytes of helper-cell phenotype which after i.p. administration mediate inhibition of polyoma and delayed-type hypersensitivity (DTH) to polyoma TAA. The maximum efficacy of the two activities was found in cells isolated on day 9 when also the highest percentage of L3T4 + cells was measured. The different rates of decline along with the extended life of the culture, and also the different degrees of dependence on the recipient's immune system, indicate that these processes are independent. The range of tail swelling in tumor-bearing recipients of immunotherapy reflects only the DTH transfer activity and not the range of cooperation between the recipient's immune system and the transferred T-helper lymphocytes leading to in vivo generation of CTL.

Effects of a history of heavy alcohol consumption on Alzheimer's disease.

Neuropsychological and psychiatric evaluations were made of 39 subjects with possible Alzheimer's disease and a history of excessive alcohol consumption (AD + ETOH), who had been abstinent or had drunk minimally for at least three months before evaluation, and 225 patients with probable Alzheimer's disease (PAD) of comparable age, years of education, and baseline global impairment. At baseline, there were no significant differences between the groups in terms of age of onset of dementia, neuropsychological test scores, or current behavioural or psychiatric symptoms. One year later, no differences in rates of decline between 20 abstinent AD + ETOH patients and 88 PAD subjects could be shown. Thus, past heavy alcohol consumption does not appear to modify the presentation of dementia of the Alzheimer's type, nor does it modify progression over a one-year interval.

The natural history of amyotrophic lateral sclerosis.

Using 42 strength and functional assessments recorded monthly, the natural history of amyotrophic lateral sclerosis (ALS) is described in 167 patients (98 men, 67 women) followed in five medical centers in the western United States. The mean age at onset was 57.4 years, and symptoms were present for 2.64 years before study entry. Although there was a highly variable rate of decline within the group of patients, there were no differences in rate of decline by age or gender. Older patients and women were weaker on entry. Forty-eight patients died during the study. The median survival was 4.0 years for the study cohort but 2.1 years for newly diagnosed cases. Decline in pulmonary function most closely correlated with death. Our results emphasize the importance of considering clinical variability in planning clinical trials. One possible strategy is to identify and stratify patients by rate of decline in pulmonary function since prospectively identifying homogeneous subgroups allows investigators to substantially reduce sample size in therapeutic trials.

Individual trajectories of cognitive decline in patients with dementia of the Alzheimer type.

The course of decline was studied in 16 patients with probable or definite dementia of the Alzheimer type (DAT) over 2.7 to 6.8 years from first to last evaluation. Overall severity of dementia was measured with the Wechsler Adult Intelligence Scale (WAIS), the Dementia Rating Scale (DRS), and the Mini-Mental State Examination (MMSE), at approximately annual intervals. An initial plateau phase, during which language and cognitive functions did not change for periods of 9 to 35 months, was observed in 5 patients who initially had an isolated memory impairment without significant impairment of nonmemory language or visuospatial function. Once nonmemory functions began to decline, the rate of decline was remarkably steady in most individual patients but varied markedly among patients. The initial rate of decline after the plateau phase, as measured with the WAIS and DRS, was a significant predictor of subsequent rate in individual patients (r = .66, p less than .01, and r = .67, p less than .01, for the WAIS and DRS, respectively). The MMSE was a less reliable measure of longitudinal change in dementia severity and did not predict future rates of decline (r = .29). These results demonstrate a biphasic trajectory of decline in patients with DAT. Stable interindividual differences in rate of decline may provide a basis for designing more sensitive studies of treatments intended to slow or halt the progress of DAT.

Serial CD4 lymphocyte counts and development of AIDS

Low CD4 lymphocyte counts are associated with increased risk of progression to AIDS in human immunodeficiency virus (HIV) infection. We investigated the extent to which the timing of progression to AIDS can be explained solely in terms of decline of the CD4 lymphocyte count in 111 haemophiliacs followed for up to 11 years since infection with H IV. A median of 10 CD4 lymphocyte counts were made per patient. By applying a simple linear model for the decline in CD4 lymphocyte counts over time, we estimated the date of development of AIDS in 96 patients who had at least 5 determinations. 84% (81 of 96) of patients were correctly classified as to development of AIDS before Jan 1, 1990 (p<0·0001), with this model. The results suggest that differences in the time at which patients with HIV will progress to AIDS can largely be explained by differences in rates of decline of CD4 lymphocyte counts.

Durability of “Posthypnotic Suggestions” as a Function of Type of Suggestion and Trance Depth

3 types of "posthypnotic suggestion," based upon factor analytic studies, were administered to high hypnotizable Ss (reals) and to low hypnotizable Ss instructed to simulate hypnosis (simulators) (N = 12 high and 6 low hypnotizable Ss per suggestion). The "posthypnotic suggestions" consisted of instructions given to Ss following a hypnotic induction that, when the posthypnotic cue was later given, they would re-enter the hypnotic state and perform a certain task at that time. Ss were then tested 6 times for durability of "posthypnotic response" during an 8-week period. Responses to the "suggestions" were rated by research assistants (objective scores) and by Ss themselves (subjective scores). There was a significant Trials x Type of "Suggestion" interaction for both types of scores for the reals but not for the simulators, indicating different rates of decline with time for the different "suggestions" for the hypnotic Ss. Depth of reported hypnotic trance during the assessment sessions was found to be strongly related to performance of the "posthypnotic suggestion" for both real and simulating Ss.

Analysis of the Differential Response of Five Annuals to Elevated CO2 during Growth

In order to investigate the effects, without competition, of CO2 on germination, growth, physiological response, and reproduction, we focussed on co—occurring species that are prominent members of an annual community in Illinois. Five species of old field annual plants—Abutilon theophrasti (C3), Amaranthus retroflexus (C4), Ambrosia artemisiifolia (C3), Chenopodium album (C3), and Setaria faberii (C4)–were grown for their entire life cycle as individuals at CO2 concentration of 350 @mL/L, 500 @mL/L, and 700@mL/L. Emergence time, growth rate, shoot water status, photosynthesis, conductance, flowering time, nitrogen content, and biomass and reproductive biomass were measured. There was no detectable effect of enhanced CO2 on timing of emergence in any of the species. Amaranthus relative growth rate (RGR) was always higher at 700 @mL/L CO2 than at 350 @mL/L. In both Abutilon and Ambrosia, RGR was greater at 700 @mL/L than at 350 @mL/L during the first half of the experimental period, but during the second half of the period the reverse was true. Shoot water potential significantly increased (became less negative) with increasing CO2 in Amaranthus and Setaria. Similar but statistically nonsignificant trends were found in Chenopodium and Abutilon. Overall rate of photosynthesis increased with CO2 but there were no significant effects, at the species level, of CO2 on photosynthetic rates. Stomatal conductance decreased with increased CO2 at both high and low light levels in C3 species but only at high light levels in C4 species. In all species, intercellular CO2 increased with external CO2. Amaranthus flowered significantly earlier at 700 @mL/L than at 350 @mL/L, and Setaria flowered significantly later at 700 @mL/L than at either of the other CO2 levels. Both Abutilon and Ambrosia showed a trend towards earlier flowering but this was not statistically significant. Of the morphological characters measured at the final harvest only specific leaf area (SLA) showed a consistent response to CO2, decreasing with increasing CO2. Significant CO2 x species interactions were also found for leaf area, leaf biomass, biomass of reproductive parts, and seed biomass indicating species—specific responses for these characters. The proportion of nitrogen declined with increasing CO2: there was also a significant CO2 x species interaction caused by the different rates of decline in proportion of nitrogen among the species. The response of most characters had a significant species x CO2 interaction. However, this was not simply caused by the C3/C4 dichotomy. Reproductive biomass (seed, fruits, and flowers) increased with increasing CO2 in Amaranthus (C4) and in Chenopodium and Ambrosia (both C3), but there was no change in Setaria (C4), and Abutilon (C3) showed a peak a 500 @mL/L. Species of the same community differed in their response to CO2, and these differences may help explain the outcome of competitive interactions among these species above ambient CO2 levels.