Daily Rate Of Change Research Articles

Abstract 14: Post-Traumatic Stress Disorder Symptoms and Physical Activity Behavior After Hospitalization for Suspected Acute Coronary Syndromes

Background: An acute coronary syndrome (ACS) related event can induce post-traumatic stress disorder (PTSD), and post-ACS PTSD is associated with a greater risk for secondary clinical outcomes among ACS survivors. While moderate-vigorous physical activity (MVPA) has been shown to reduce the risk of adverse outcomes after ACS, its impact on PTSD symptoms remains largely unknown. There is a notable absence of empirical evidence, especially from large-scale observational cohort studies with device-based measures of physical activity, on this topic. Aim: To investigate the relationship between physical activity behaviors over the first month post-discharge with PTSD symptoms at one month among patients with suspected ACS. Methods: Patients (n = 434, 48.6% female, 62.6±12.4yrs) evaluated for ACS in the emergency department were fitted with a GENEActiv wrist accelerometer in-hospital and wore the device on their non-dominant wrist for 30 days post-discharge to measure MVPA. Presence and severity of PTSD symptoms were assessed at 1-month follow-up using the PCL-5. Multilevel structural equation modeling was used to simultaneously 1) fit a linear growth curve (GC) model to patients’ 30-day trajectories of MVPA and 2) predict total PTSD symptoms from a) mean daily MVPA, b) average daily change in MVPA (GC slope), and c) covariates (age, biological sex, education, and Charlson Comorbidity Index). Results: Patients engaged in an average of 20.8 (95% CI: 18.4, 23.3, p < 0.001) minutes of MVPA per day. MVPA levels increased at an average rate of 0.11 mins/day (95% CI: 0.05, 0.16, p < 0.001) over the 30 days post-discharge. There was substantial between-patient variability in both average MVPA minutes (SD = 26.0) and daily rate of change in MVPA minutes (SD = 0.38). The daily rate of change in MVPA was significantly associated with 1-month PTSD symptoms (β per 0.5 mins/day difference in daily rate of change in MVPA minutes = -4.5 points on the PCL-5; 95% CI: -6.5, -2.5, p < 0.001), controlling for the above-mentioned covariates. The association between average MVPA minutes and PCL-5 score was small and not statistically significant (β = 0.02; 95% CI: -0.04, 0.07, p = 0.60). Conclusion: PTSD symptoms appear to be mitigated in patients whose MVPA minutes increased over the 30 days post-discharge, whereas no evident association was observed between PTSD symptoms and average daily MVPA minutes. These findings suggest that progressively increasing MVPA by as little as .5 mins/day (i.e., ~1 SD above the mean rate of increase) within the immediate first month post-discharge, as opposed to maintaining a consistent daily average of MVPA, may impede the development of PTSD symptoms in ACS survivors.

Modeling the positive testing rate of COVID-19 in South Africa using a semi-parametric smoother for binomial data.

Identification and isolation of COVID-19 infected persons plays a significant role in the control of COVID-19 pandemic. A country's COVID-19 positive testing rate is useful in understanding and monitoring the disease transmission and spread for the planning of intervention policy. Using publicly available data collected between March 5th, 2020 and May 31st, 2021, we proposed to estimate both the positive testing rate and its daily rate of change in South Africa with a flexible semi-parametric smoothing model for discrete data. There was a gradual increase in the positive testing rate up to a first peak rate in July, 2020, then a decrease before another peak around mid-December 2020 to mid-January 2021. The proposed semi-parametric smoothing model provides a data driven estimates for both the positive testing rate and its change. We provide an online R dashboard that can be used to estimate the positive rate in any country of interest based on publicly available data. We believe this is a useful tool for both researchers and policymakers for planning intervention and understanding the COVID-19 spread.

Short-term pulmonary and systemic effects of hydrocortisone initiated 7–14 days after birth in ventilated very preterm infants: a secondary analysis of a randomised controlled trial

ObjectiveObservational studies in preterm infants suggest that systemic hydrocortisone improves pulmonary condition but may also lead to systemic adverse effects. We report the short-term pulmonary and systemic effects of hydrocortisone...

Prepregnancy Body Mass Index Is Associated with Time-Dependent Changes in Secretory Activation Measures During the First 7 Days Postpartum in Breast Pump-dependent Mothers of Premature Infants.

Background: Little is known about the biology of secretory activation (SA) in overweight and obese (OW/OB) mothers who are breast pump dependent with a premature infant in the neonatal intensive care unit. Objective: To compare time-dependent changes in daily pumped milk volume, maternal milk sodium (Na) concentration, and Na-to-potassium (K) ratios (Na:K) in the first 14 days postpartum in breast pump-dependent mothers with prepregnancy body mass index (BMI) <27 and BMI ≥27 kg/m2. Design/Methods: This secondary analysis for 39 subjects, 44% (n = 17) with prepregnancy BMI <27 and 56% (n = 22) with BMI ≥27, included transformed data of outcome measures, chi-square, t-tests, and growth curve models. Results: For days 1-7, daily pumped milk volume increased significantly more rapidly for mothers with BMI <27 (65.82 mL/d) versus BMI ≥27 (33.08 mL/d), but the daily rate of change in pumped milk volume during days 8-14 was not statistically different. Daily milk Na concentration decreased significantly faster in BMI <27 (-3.93 mM/d) versus BMI ≥27 (-2.00 mM/day) during days 1-7, but was not significantly different for days 8-14. No statistical differences were noted for Na:K ratio for either time period. Conclusion: These data add biologic evidence to previous research, suggesting delayed or impaired SA in OW/OB mothers, and suggest that the window of opportunity for research and clinical interventions is days 1-7 postpartum in this population.

The effect of temperature on the spatial learning rate of zebrafish (Danio rerio)

AbstractTemperature has a wide range of effects on the biology and ecology of ectotherms, including fish. However, the literature provides only a few studies assessing its effect on their cognitive abilities. We tested the effect of temperature on the spatial learning rate of zebrafish by comparing the daily rate of change in the number of fish choosing the correct arm first and behavioural performance (i.e., distance travelled, time needed to locate the daily food reward and swimming speed) in two temperatures (21 and 31°C) in 7 successive sessions. The daily rate of change in behavioural performance was expressed as the percentage difference between the value in a given session and the value in the previous session. Two experiments were performed in a T‐maze with single feeders in the arms, one empty and the other with a food reward. In each of the experiments, we used 10 naive fish, which were placed in the T‐maze individually once a day. The fish were fed between sessions to avoid increasing differences in hunger levels and, in turn, increasing the differences in motivation to find the food between the temperature treatments. The results revealed that the learning rate was greater at the higher temperature, which was apparent in a greater percentage reduction in the time and distance travelled needed to locate the daily food reward between successive sessions at the higher temperature than at the lower temperature. The results show there was a significant effect of temperature on the daily rate of change in the number of fish choosing the correct arm, distance travelled and time needed to locate the daily food reward, which may be attributed to the positive effect of temperature on learning rate, and may indicate the importance of temperature for the cognitive testing of zebrafish.

The dynamic relationship between daily caffeine intake and sleep duration in middle-aged and older adults.

The effect of caffeine on sleep has been well documented. However, most studies examined this relationship in laboratories or used a cross-sectional design analysing between-person differences. This study investigated the within-person relationship between caffeine intake and sleep duration at home. In a national database, 377 participants (aged 35-85years) completed a 7-day diary study. Sleep duration was measured by Actigraphy and caffeine intake was self-reported in sleep logs. Three analytic strategies were used. The average sleep duration and the average caffeine intake were not significantly correlated. Multilevel regressions using daytime caffeine intake to predict night-time sleep, and using night-time sleep to predict next day caffeine intake, also did not detect any significant effect. Then dynamical systems analysis was performed, where the daily change rate and change tendency of caffeine and sleep were estimated, and the relationship among these momentums was examined. Results revealed a significant effect of sleep duration on the change tendency of caffeine use: a shorter sleep duration predicted a stronger tendency to consume caffeine, and this phenomenon was only found in middle-aged adults (aged 35-55years) not in older adults (aged 55+). This study did not detect any effect of daily caffeine intake on sleep duration, implying that habitual use of caffeine in real life may not coincide with laboratory findings, and that using caffeine to compensate for sleep loss is the habit of middle-aged adults, not the elderly. The advantage of using a dynamic approach to analyse interrelated processes with uncertain time lags is also highlighted.

Association of neutrophil, platelet, and lymphocyte ratios with prognosis in metastatic pancreatic cancer.

767 Background: High mortality associated with pancreatic ductal adenocarcinoma (PDA) warrants research into prognostic factors. We examined the relationship between the daily rate of change of CA19-9 over the first 90 days of treatment (DRC90) and pretreatment levels of neutrophils, lymphocytes, and platelets with overall survival (OS) and progression free survival (PFS) in patients with stage IV PDA that received chemotherapy. Methods: We retrospectively evaluated 102 locally advanced and metastatic PDA patients treated at KU Cancer Center between Jan 2011 and Sep 2019. We compared the ratio of pretreatment absolute neutrophil count to pretreatment absolute lymphocyte count (NLR) and the ratio between pretreatment platelet count to pretreatment absolute lymphocyte count (PLR) with OS and PFS. We also compared DRC90 to OS and PFS. Log-rank trend test using the mean of NLR, PLR, and DRC90 as the threshold for two groups within each variable. Results: Baseline demographics are shown in the table. Pts with ≥ mean NLR (4.6) had significantly lower OS [p = 0.0444] and PFS [p = 0.0483] than Pts below the mean. Pts with PLR ≥ mean (3.9) did not have significantly different OS [p = 0.507] or PFS [p = 0.643] than Pts below the mean. Pts with DRC90 ≥ mean (-1%) did not have significantly different OS [p = 0.342] or PFS [p = 0.313] than Pts below the mean. Conclusions: Pts with NLR ≥ mean (4.6) had significantly lower OS and PFS than Pts with NLR below the mean. This implies the possibility of NLR as a prognostic marker in PDA that could guide treatment approach but needs validation in a larger cohort. [Table: see text]

Interim Tumor Progression and Volumetric Changes of Surgical Cavities during the Surgery-to-Radiotherapy Interval in Anaplastic Gliomas: Implications for Additional Pre-radiotherapy Magnetic Resonance Imaging.

PurposeThis study was designed to investigate the incidence of interim disease progression (IPD) and volumetric changes of the surgical cavity (SC) during the surgery-to-radiotherapy interval (SRI), and eventually assess the value of magnetic resonance imaging (MRI) at the time of radiotherapy (RT) planning in newly diagnosed anaplastic gliomas.Materials and MethodsAmong 195 anaplastic glioma patients who underwent RT, 121 were evaluable with two separate MRIs during SRI. The presence of IPD was determined using the updated Response Assessment in Neuro-Oncology size criteria. In 84 patients who underwent surgical resection, each SC was contoured by a radiation oncologist and the volumetric changes of the SCs were calculated between the two separate MRIs. Daily rate of change in the SC volume was calculated assuming an exponential and linear change.ResultsFive of 121 patients (4.13%) demonstrated IPD during SRI, and the incidence was significantly higher in patients undergoing biopsy (vs. surgical resection, 12.9% vs. 1.1%, p=0.015) and in patients with remnant contrast-enhancing tumor after surgery (15.8 vs. 2.0%, p=0.027). The mean daily rate of absolute change in SC was 1.06% (95% confidence interval [CI], 0.89 to 1.23) and 0.89% (95% CI, 0.77 to 1.02) according to the exponential and linear model, respectively. The expected mean volumetric change at 2 weeks were 16.64% (95% CI, 13.77 to 19.52) and 12.51% (95% CI, 10.77 to 14.26), respectively.ConclusionIPD during the SRI is rare in surgically resected anaplastic gliomas. However, pre-RT MRI is essential for accurate RT-target delineation and disease evaluation for patients initiating RT beyond postoperative 2 weeks and undergoing biopsy, respectively.

Correlation of neutrophil lymphocyte ratio, platelet lymphocyte ratio and rate of change of CA 19.9 in predicting outcome for metastatic pancreatic cancer.

326 Background: CA19.9, NLR and PLR have all been proposed as prognostic in pancreatic cancer. We analysed correlation between NLR, PLR and rate of change of CA19.9. Methods: A total of 63 metastatic pancreatic cancer patients were identified from our database and evaluated retrospectively for blood count, NLR, PLR and serial CA19.9 levels during treatment. Daily Rate of Change of CA19.9 levels were calculated for the first 90 days (DRC90) of the patient’s treatment. Kaplan-Meir curves, univariate and multivariate Cox-regression analyses were calculated to assess the effects of these 3 markers on overall survival. Results: In a univariate analysis, PLR &gt; 240, NLR &gt; 5 and DRC90 &gt; 0.4% were all significantly associated with deceased overall survival. The Cox proportional hazards model showed that NLR &lt; 5 (HR 0.475, 95% CI 0.259 to 0.873, P = 0.017), PLR &lt; 240 (HR 0.444, 95% CI 0.229 to 0.861, P = 0.016), and a DRC90 &lt; 0.4% (HR 0.294, 95% CI 0.102 to 0.851, P = 0.024) were independent predictors of good prognosis (22.6 months vs. 9.6 months, 22.3 months vs 12.4 months and 23.9 months vs. 9.3 months respectively). In multivariate analysis, only a DRC90 &lt; 0.4% was independently associated with a longer survival (HR 0.239, 95% CI 0.076 to 0.752, P = 0.014). The formula (F) {PLR + (NLRxNLR) + (DRC90 x 100)} was predictive for survival, as patients with F &gt; 190 (HR 3.295, 95% CI 1.232 to 8.807, P = 0.017), having a significantly lower survival rate than patients with F &lt; 190 (25.1 months vs. 10.6 months, log-rank P = 0.009). Conclusions: These findings indicate the prognostic utility of the rate of CA 19.9 decline - measured as a standardised daily percentage change in value over 90 days. Our data validates daily rate of change of CA 19.9 over 90 days as an independent variable that correlates with prognosis, independent of PLR and NLR. We also identified a novel formula - PLR + (NLRxNLR) + (DRC90 x 100) - as being predictive for survival. We would like to increase the sample size to further validate our initial findings and investigate possible relationships in combining these variables for better prognostication in metastatic pancreatic cancer.

Factors controlling the daily change in groundwater level during the growing season on the Great Hungarian Plain: a statistical approach

The phenomenon of diurnal fluctuation in the groundwater level (GWL) often reflects the water uptake by plants. The rate of evapotranspiration from the groundwater (ETgw) can be calculated from the daily rate of change in GWL, but several factors may influence the vertical groundwater dynamics. The occurrence of diurnal fluctuation and the daily rate of change in GWL were determined in 20 monitoring wells on the Great Hungarian Plain with different vegetation cover (Quercus robur L., Robinia pseudoacacia L., Populus × euramericana and unforested control sites) and with differences in the water table depth (WTD) and in soil and salinity characteristics. ETgw was calculated for eight selected sites. Forest vegetation significantly increased the occurrence of diurnal fluctuation (8 out of 11 cases), and the mean daily change in GWL multiplied by the specific yield (S y) was 2.2 times higher for forest sites than for the unforested control sites. The median daily change in GWL showed a significant negative correlation with S y, where the vegetation effect was manifested as ETgw-induced diurnal fluctuation. A significant correlation was obtained at each monitoring well between the meteorological parameters controlling the evaporative demand and the daily rate of change in GWL. A reduction in groundwater uptake after rainfall events and increasing groundwater consumption during dry periods were also revealed. A significant positive correlation was found at some study sites between the daily change in GWL and WTD, and between ETgw and the leaf area index (LAI). Mean ETgw was 8.2 mm day−1 for oak stand and 0.4 mm day−1 for black locust stand, while it ranged from 1.7 to 6.0 mm day−1 for the four poplar stands, which may reflect the variability in water demand, LAI, groundwater and soil characteristics.

Extreme value modeling for the analysis and prediction of time series of extreme tropospheric ozone levels: A case study

The occurrence of high concentrations of tropospheric ozone is considered as one of the most important issues of air management programs. The prediction of dangerous ozone levels for the public health and the environment, along with the assessment of air quality control programs aimed at reducing their severity, is of considerable interest to the scientific community and to policy makers. The chemical mechanisms of tropospheric ozone formation are complex, and highly variable meteorological conditions contribute additionally to difficulties in accurate study and prediction of high levels of ozone. Statistical methods offer an effective approach to understand the problem and eventually improve the ability to predict maximum levels of ozone. In this paper, an extreme value model is developed to study data sets that consist of periodically collected maxima of tropospheric ozone concentrations and meteorological variables. The methods are applied to daily tropospheric ozone maxima in Guadalajara City, Mexico, for the period January 1997 to December 2006. The model adjusts the daily rate of change in ozone for concurrent impacts of seasonality and present and past meteorological conditions, which include surface temperature, wind speed, wind direction, relative humidity, and ozone. The results indicate that trend, annual effects, and key meteorological variables along with some interactions explain the variation in daily ozone maxima. Prediction performance assessments yield reasonably good results. Implications This paper develops a statistical approach to both analyzing and forecasting daily meteorologically adjusted tropospheric ozone maxima in the presence of seasonality and trend. The methods are applied to a 10-year follow-up of daily maxima of ozone levels for the metropolitan area of Guadalajara. One-day-lagged and present meteorological variables, 1- and 2-day-lagged tropospheric ozone maxima, seasonality, and a curvilinear trend are important predictors of the daily tropospheric ozone maximum in Guadalajara. The method provides a reliable tool to predict ozone levels exceeding a relevant threshold.

Hydromechanics of the Koyna–Warna Region, India

Continuous reservoir-induced seismicity has been observed in the Koyna–Warna region in western India following the beginning of impoundment of Koyna and Warna Reservoirs in 1961 and 1985, respectively. This seismicity includes 19 events with M ≥ 5.0 which occurred in 7 episodes (I–VII) between 1967 and 2005 at non-repeating hypocentral locations. In this study, we examined the first six episodes. The seismicity occurs by diffusion of pore pressures from the reservoirs to hypocentral locations along a saturated, critically stressed network of NE trending faults and NW trending fractures. We used the daily lake levels in the two reservoirs, from impoundment to 2000, to calculate the time history of the diffused pore pressures and their daily rate of change at the hypocentral locations. The results of our analysis indicate that Episodes I and IV are primarily associated with the initial filling of the two reservoirs. The diffused pore pressures are generated by the large (20–45 m) annual fluctuations of lake levels. We interpret that critical excess pore pressures >~300 kPa and >~600 kPa were needed to induce Episodes I–III and Episodes IV–VI, respectively, suggesting the presence of stronger faults in the region. The exceedance of the previous water level maxima (stress memory) was found to be the most important, although not determining factor in inducing the episodes. The annual rise of 40 m or more, rapid filling rates and elevated dp/dt values over a filling cycle, contributed to the rapid increase in pore pressure.

Changes in maternal serum chlorinated pesticide concentrations across critical windows of human reproduction and development

Investigators often employ a single cross-sectional measure of in utero exposure when evaluating associations between organochlorine (OCs) pesticides/metabolites and adverse reproductive outcomes. Few data are available on the stability of exposures to OCs over critical windows of human reproduction and development inclusive of the periconception window. Our objective was to measures changes in OC concentrations prior to conception and throughout pregnancy or after 12 unsuccessful months attempting pregnancy. Seventy-nine women planning pregnancy were prospectively enrolled and followed for up to 12 menstrual cycles. Blood specimens were obtained for toxicologic analysis of seven OCs from participating women at baseline (preconception, n=79), at the first prenatal visit following a positive pregnancy test leading to a live birth ( n=54) or after pregnancy loss ( n=10), at approximately 6 weeks post-partum ( n=53), and after 12 unsuccessful cycles ( n=9). Overall and daily rate of change in OCs concentration (ng/g serum) were estimated adjusting for serum lipids and baseline concentration. Significant ( P<0.05) decreases in the overall and daily rate of change in OCs concentrations (ng/mL serum) were observed from baseline to pregnancy for HCB (−0.032, −0.001, respectively) and trans-nonachlor (−0.050, −0.002, respectively) while oxychlordane demonstrated an increase during this critical window (0.029, 0.001, respectively). Significant decreases in aldrin (−0.002, −1.47×10 −4, respectively), HCB (−0.069, −0.003, respectively), and trans-nonachlor (−0.045, −0.002, respectively), and an overall increase for oxychlordane (0.015) were seen for women with pregnancy losses. Significant decreases also were observed among infertile women for aldrin (−0.003, −3.52×10 −6, respectively), DDE (−0.210, −4.29×10 −4, respectively), and HCB (−0.096, −2.03×10 −4, respectively), along with an increase for trans-nonachlor (0.034, 7.59×10 −5, respectively). These data, though limited by sample size and the possibility of laboratory measurement error, suggest that OC concentrations may change over critical windows. This underscores the importance of timing biospecimen collection to critical windows for development in the assessment of reproductive and/or developmental effects.

Maternal Serum Polychlorinated Biphenyl Concentrations across Critical Windows of Human Development

BackgroundFew data are available on polychlorinated biphenyl (PCB) concentrations over critical windows of human reproduction and development inclusive of the periconception window.ObjectivesOur goal was to measure changes in PCB concentrations from preconception to pregnancy, through pregnancy, or after a year without becoming pregnant.MethodsSeventy-nine women planning pregnancies were prospectively enrolled and followed for up to 12 menstrual cycles of attempting pregnancy. Blood specimens were obtained from participating women preconceptionally (n = 79), after a positive pregnancy test leading to a live birth (n = 54) or pregnancy loss (n = 10), at approximately 6 weeks postpartum (n = 53), and after 12 unsuccessful cycles (n = 9) for toxicologic analysis of 76 PCB congeners. We estimated overall and daily rate of change in PCB concentration (nanograms per gram serum) adjusting for relevant covariates, serum lipids, and baseline PCB concentration.ResultsSignificant (p < 0.0001) decreases in the mean overall and daily rate of change in PCB concentrations were observed between the preconception and first pregnancy samples for total (–1.012 and –0.034, respectively), estrogenic (–0.444 and –0.016, respectively), and antiestrogenic (–0.106 and –0.004, respectively) PCBs among women with live births. Similar significant decreases in total (–1.452 and –0.085), estrogenic (–0.647 and –0.040), and antiestrogenic (–0.093 and –0.004) PCB concentrations were seen for women with pregnancy losses. No significant changes were observed for PCB congener 153.ConclusionsThese data suggest that PCB concentrations may change during the periconception interval, questioning the stability of persistent compounds during this critical window.

Development of a remote method for the recording of cattle weights under field conditions

Remote weighing of cattle is advantageous because it is less labour-intensive and less invasive for the animal than conventional methods. An automated system was built using ‘off the shelf’ technology which allowed for cattle to be weighed automatically on pasture when accessing the device. Data collected over a 70-day grazing period was compared with data collected at 2-week intervals by transferring cattle to a centralised weighing facility. Liveweights recorded using the remote system were some 20 kg higher than those measured conventionally. However the daily rate of change was similar for conventional and remote weighing methods, being 1.25 v. 1.20 kg/day, respectively (P = 0.48). This study demonstrated that remote weighting of cattle on pasture is feasible and gives satisfactory results compared with conventional methods. This relatively simple method relies on technologies currently available to the cattle industry and could readily be adapted to a range of commercial situations.

Root depth of native and sown perennial grass-based pastures, North-West Slopes, New South Wales. 2. Estimates from changes in soil water content

Root depth of pasture is an important hydrological parameter that has substantial implications for the use of rainfall by plants and in estimating deep drainage using biophysical modelling. Studies were undertaken for native and sown perennial grass-based pastures on the North-West Slopes of New South Wales to investigate 4 approaches that may identify the depth of plant roots based on objective assessments of change in soil water content (SWC). The 4 approaches were to examine traces of SWC measured with a neutron moisture meter (NMM) at about 4-week intervals (0–210 cm profile at 20-cm increments) for defined periods with root depth interpreted as, (i) the maximum depth at which there was a distinct decrease in SWC, (ii) the maximum depth at which there was a &gt;0.01 m3/m3 decrease in SWC, (iii) the uppermost depth at which the change in SWC was significant using t0.05, and (iv) the uppermost depth at which the daily rate of change in SWC was significant using t0.05. For each of these approaches, 4 preliminary criteria were applied as filters to the SWC data before they were used in these analyses, (i) the depth of NMM tubes and maximum depth of measurement of SWC was greater than the anticipated pasture root depth, (ii) the depth of initial profile wetting was greater than the anticipated pasture root depth, (iii) there was a drying period of &gt;3 months duration in the major pasture growth phase to allow pastures to extract soil water to the maximum extent, and (iv) the SWC was measured at a sufficient frequency to determine extraction of soil water by roots. SWC data were available from spring 1997 to spring 2001 for Barraba (45 access tubes, native pasture), Manilla (45 tubes, native pasture) and Nundle (36 tubes, sown pasture). Analyses of monthly rainfall compared with mean values identified 3 times where substantial rainfall was followed by an extended drying period. These periods occurred in 1998, 1999 and 2000. SWC data for the 1998 drying period best met all the preliminary filters, particularly criteria (ii) and (iii). Root depth values estimated from these data using the 4 approaches were not significantly different for Barraba (188 ± 4 to 190 ± 3 cm, n = 45), Nundle (142 ± 5 to 143 ± 7 cm, n = 13) and Manilla Red Chromosol (164 ± 7 to 176 ± 7 cm, n = 14), but were significantly different for Manilla Brown Vertosol (98 ± 7 to 121 ± 7 cm, n = 23). It was concluded that reliable estimates of root depth may be readily obtained for a range of soils and environments by firstly applying the 4 simple criteria used in these studies to the SWC data and by determining the depth of significant drying using t0.05. The depth of significant drying approach was the most objective, providing consistent results among sites and accounting for variance among NMM counts and tubes in these studies.

Nonlinear dependence in British pound exchange rates

The Brock, Dechert and Scheinkman (1987) method is used to test for nonlinear dependence in daily rates of change of the exchange rate of the British pound relative to seven most heavily traded currencies against the pound during the period 2 January 1993 to 7 October 1996. The currencies are the US dollar, the Deutsche mark, the French franc, the Swiss franc, the Canadian dollar, the Japanese yen and the Italian lira. The results suggest that nonlinear dependence exists in all seven British pound exchange rates. Except for the US dollar, nonlinear dependence is due to nonlinearity in the variance and is captured by a GARCH(l,l)-t model. For the US dollar, nonlinear dependence is due to nonlinearity both in the mean and the variance and is captured by a GARCH-in-mean (GARCH-M) model.

Variations in the contribution of transport to changes in planktonic animal abundance: a study of the flux of fish larvae in Conception Bay, Newfoundland

We investigated the magnitude of short-term variations in the flux of several species of fish larvae in Conception Bay, Newfoundland, determined the contribution of these fluxes to changes in the abundance of these species, and assessed the factors that may be causing the variations in these fluxes. The net effect of transport ranged from a daily influx of 5.8% to a daily efflux of 6.2% from the population. Short-term variations in transport were associated with variations in wind stress. The contribution of transport to variations in population abundance ranged from 12 to more than 75% of the average daily rate of change in numbers for the different species. The contribution of physical processes to estimated mortality rates is variable and can have a significant impact on the investigation and interpretation of potential biological processes (e.g., predation and starvation) influencing the survival of larval fish. We predicted that the average correction to the instantaneous mortality rate due to advection and diffusion should be proportional to A−1/2, where A is the area of system under study. This highlights the susceptibility of small systems to estimation error of mortality rates caused by short-term variations in physical forcing.

Seepage exchange in an Amazon floodplain lake

Exchange of water between the lake and the surrounding groundwater system was computed for a permanent lake on the central Amazon floodplain (Lake Calado) from an empirical seepage model incorporating 240 direct measurements of seepage from the lakebed and seasonal changes in lake stage and morphometry. Seepage rates varied with the daily rate of change in stage height and inversely with depth of the lakebed from the water surface. Since the hypsometric characteristics of the lake are well known, overall seepage for the 1983–1984 water year was estimated by integrating the product of seepage rate per unit area for a given rate of stage change and depth of lakebed with the representative area of lakebed at a given depth as each varied over the annual cycle, then integrating the daily rates of seepage over time. The volume of seepage outflow over the rising‐water period (4 × 106 m3) is plausible if the rate of groundwater flow is constrained by the hydraulic conductivities expected for the soils. The 10‐m annual change in water level and the potential movement of floodwaters into deeply weathered tropical soils, beyond the silt and clay deposits immediately adjacent to the main‐stem river channel, represent conditions that are particularly conducive to seepage exchange and are representative of a significant number of lakes on the Amazon floodplain.

A Dynamic Nutrient Budget of Subsystem Interactions in a Salt Marsh Estuary

In tidal salt marsh estuaries, the different habitats of the ecosystem interact primarily through the tidal creek water column. These interactions include nutrient and materials exchanges with the salt marsh, oyster reefs, creek bottoms, and adjacent uplands. Nutrient budgets are often used to synthesize these kinds of subsystem exchange data, and are usually based on annual totals without accounting for nutrient variability at finer temporal resolutions. In this paper, we present a dynamic budget of carbon (C), nitrogen (N), and phosphorus (P) for the North Inlet estuary, South Carolina that synthesizes subsystem flux data in a new way. We have developed a dynamic budget that uses a tidal hydrology model to generate daily areas of inundated intertidal habitat (i.e. vegetated marsh and oyster reef) from tidal heights calculated hourly and combines them with flux data to determine a net daily input to, or removal from, the water column. Daily surpluses or deficits of each nutrient were compared with daily rates of change in observed tidally-averaged nutrient concentrations. Particular emphasis was placed on evaluating budget output from the intertidal subsystems. We compared our total annual budgets to values from syntheses of two North Inlet flux studies. Although areas of marsh inundated were 150-200 times greater than areas of oyster reef inundated, interactions per unit volume of estuarine water column were comparable in magnitude for soluble reactive P (SRP), particulate organic C (POC), and dissolved organic C (DOC). The marsh dominated the ammonium (NH + 4) and nitrate + nitrite (NN) exchanges in the summer but the NH + 4 and POC output were particularly sensitive to changes in oyster reef area. Winter and spring DOC release by the marsh coincided closely (in timing and magnitude) with the peak in DOC concentrations observed in the North Inlet estuary, suggesting that forest stream inputs of DOC are not nearly as important as has been hypothesized. Comparison of our budget predictions to a previous synthesis of the same subsytem flux data confirmed the power of using tidal hydrology to estimate subsystem interactions between sampling times. These comparisons also emphasized the importance of (1) water column processes to NH + 4 dynamics (2) subtidal benthic fluxes to DOC dynamics, and (3) external inputs to NN dynamics. By incorporating our best current knowledge of estuary-wide subsystem areas, the dynamic budget also allowed us to link subsystem flux data to the results of a study quantifying exchanges between the estuary and the coastal ocean. That comparison indicated the shortcomings of any site-specific extrapolation to whole-system conclusions where a homogeneous ecosystem must be assumed. We used the differences between our total annual C, N, and P budgets and reported exports of those constituents from the system to generate hypotheses and suggest future research efforts both at North Inlet and southeastern salt marsh estuaries in general.