Evaluating the effects of hydrogeologic processes on the fate of salinity and halogens in headwater catchments

The transport of solutes from their source to natural water systems is a critical control on the chemistry and potability of drinking water supplies. Therefore, developing a thorough understanding not only of contaminant sources, but also of the controls on the movement of solutes through catchments, is essential to providing accurate assessments of how future environmental stressors (e.g. land cover, population growth, and climate change) may affect water resources. Halogens (specifically, chloride (Cl), bromide (Br), and iodine (I)) occur naturally at low levels in terrestrial aquatic ecosystems, and may also originate from a suite of anthropogenic sources. Due to their largely conservative behavior, and preferential incorporation into mineral crystal lattices during evaporation processes resulting from differences in ionic radii, ratios of Cl/Br are used to identify sources of salinity to freshwater systems. This approach can broadly distinguish endmember sources of salinity (e.g. road salts from basin brines) from one another, although has proven ineffective in distinguishing saline endmembers originating from the same processes (e.g. formation waters of different ages), thus warranting development of alternate approaches. Elevated levels of Cl are harmful to sensitive biota, threaten riparian ecosystems, and may increase the corrosivity of affected waters. Anthropogenic practices may introduce Cl to drinking water supplies. Present-day controls on the salinization of freshwater systems have been rigorously evaluated. Although, prior to this dissertation, no future predictions of the impacts of continued deicing practices on freshwater salinization had incorporated changes in climate coupled with dynamic population and land use. Iodinated disinfection by-products (I-DBPs) form when source waters containing halogens and organic matter are disinfected via chloramination during wastewater treatment processes. Despite the emergence of I-DBPs as highly toxic, teratogenic, and potentially carcinogenic agents, controls on the transport of iodine in terrestrial aquatic environments have yet to be fully constrained. As source water iodine is a major source of iodine in the formation of I-DBPs, developing a thorough understanding of the controls on the natural cycling of iodine in paired surface water-groundwater systems is essential to providing accurate assessments for the potential of adverse environmental and health effects following modern wastewater treatment practices. Individual components of the terrestrial aquatic iodine cycle have been studied extensively, although a single study has yet to evaluate variation of total dissolved iodine concentrations at the catchment scale across both time and space. The purpose of this dissertation research was to evaluate the effects of anthropogenic and hydrogeologic processes on the fate of salinity and halogens at the catchment scale. We focus our efforts in the East and West Branches of the Tioughnioga River Watershed in Upstate New York State (NYS), USA. Spatially and temporally resolved series of major and trace halogens (Cl, Br, and I) were used in combination with graphical, statistical, and numerical approaches to elucidate controls on halogen sources and solute flow paths in headwater catchments with mixed land cover in temperate climates. Salinity in the Tioughnioga River watershed has been increasing since the late 1930’s. This trend increased precipitously after the completion of a major interstate highway (Interstate-81) in the West Branch catchment area during the 1950’s. We used two independent approaches to characterized sources of Cl to both East and West Branches of the Tioughnioga River over a two-year interval: (1) Cl/Br ratios to graphically separate waters impacted by road salts from other sources of contamination and (2) linear discriminant analysis (LDA) to quantitatively determine the most likely source of contamination to individual water samples. Ratios of Cl/Br suggested that road salt affected waters are present in both branches, but are more prominent in the West Branch, which has a greater percentage of urban land cover. LDA supports the results of Cl/Br in the West Branch and further reveals volumetrically minor contributions of Appalachian Basin Brines to surface waters in the East Branch. Downstream profiles of Cl concentrations in surface waters indicate that sources of pollution are concentrated around urban areas and may impact surface water chemistry year-round. We used a simple mixing model to estimate a residence time of Cl in the watershed of approximately 20 to 30 years, suggesting that stream Cl concentrations may continue to rise for several decades given no change in conditions. Assessment of the potential future impacts of continued de-icing practices is regularly evaluated using numerical and statistical models. These methods have undoubtedly advanced our understanding of the prolonged effects of de-icing practices on aquatic environments and drinking water quality. Although, these approaches have not incorporated future changes in climate that are projected to impact hydrogeology. To address this deficit, we use an INtegrated CAtchment (INCA) model to simulate Cl concentrations in the Tioughnioga River watershed. We ran the model over a baseline period (1961-1990) and over three future intervals (2010-2039; 2040-2069; 2070-2099) for future climate scenarios from a range of global climate models (GCMs). Model projections suggest that Cl concentrations in the catchment will continue to rise for several decades, before beginning to decline roughly mid-century, with all scenarios resulting in reduced winter snowfall totals and associated salt applications over the course of the 21st century. We attributed the delay in stream response to climate change and continued contribution of Cl from aquifers. By 2100, surface water Cl concentrations will decrease to below 1960’s values. Decreasing trends in average surface water Cl are moderate in catchments dominated by urban lands compared to those in forested catchments. We evaluate the controls on contributions of iodine to surface water from different sources under variable hydrologic conditions across spatial and temporal scales in the Tioughnioga River watershed. Our findings reveal that iodine varies seasonally with temperature, suggesting a linkage to export of dissolved organic carbon. Iodine may be elevated temporarily during high flow events, resulting from near-stream subsurface storage during dry periods. Based on major ion analysis, LDA, and endmember mixing analysis, under low flow conditions, iodine in surface water likely originates from groundwater. Additionally, our findings illustrate that iodine varies significantly across a catchment, suggesting influence from local hydrologic controls. In addition to atmospheric deposition of iodine in rainwater, additional controls on transport may be linked to weathering of exposed rocks. Thus, we propose that terrestrial iodine fluxes in temperate forested catchments are closely tied to both surface sources and local hydrogeology and thus, suggest that waste water treatment facilities closely monitor source water iodine concentrations and adjust treatment practices accordingly. This dissertation ultimately contributes to the growing and collective body of knowledge regarding halogen transport and sources in freshwater systems and provides valuable insights to future water resources security

The neural correlates of gist-based true and false recognition

When information is thematically related to previously studied information, gist-based processes contribute to false recognition. Using functional MRI, we examined the neural correlates of gist-based recognition as a function of increasing numbers of studied exemplars. Sixteen participants incidentally encoded small, medium, and large sets of pictures, and we compared the neural response at recognition using parametric modulation analyses. For hits, regions in middle occipital, middle temporal, and posterior parietal cortex linearly modulated their activity according to the number of related encoded items. For false alarms, visual, parietal, and hippocampal regions were modulated as a function of the encoded set size. The present results are consistent with prior work in that the neural regions supporting veridical memory also contribute to false memory for related information. The results also reveal that these regions respond to the degree of relatedness among similar items, and implicate perceptual and constructive processes in gist-based false memory.Psycholog

Aging, self-referencing, and medial prefrontal cortex

The lateral prefrontal cortex undergoes both structural and functional changes with healthy aging. In contrast, there is little structural change in the medial prefrontal cortex, but relatively little is known about the functional changes to this region with age. Using an event-related fMRI design, we investigated the response of medial prefrontal cortex during self-referencing in order to compare age groups on a task that young and elderly perform similarly and that is known to actively engage the region in young adults. Nineteen young (M age 23) and seventeen elderly (M age 72) judged whether adjectives described themselves, another person, or were presented in upper case. We assessed the overlap in activations between young and elderly for the self-reference effect (self vs. other person), and found that both groups engage medial prefrontal cortex and mid-cingulate during self-referencing. The only cerebral differences between the groups in self versus other personality assessment were found in somatosensory and motorrelated areas. In contrast, age-related modulations were found in the cerebral network recruited for emotional valence processing. Elderly (but not young) showed increased activity in the dorsal prefrontal cortex for positive relative to negative items, which could reflect an increase in controlled processing of positive information for elderly adults. Aging is associated with declines in cognitive performance in a number of domains. Recent neuroimaging data suggest that changes to the prefrontal cortex may contribute to impaired memory and cognition with age. Structurally, the prefrontal cortex shows pronounced shrinkage with age (Raz, 2000). Functionally, the engagement of frontal mnemonic processes appears to differ in young and elderly adults: Older adults show reduced activation of left inferior fronta

Reduction of the self-reference effect in younger and older adults

Relating information to the self improves memory. However, this self-reference effect (SRE) is typically studied through explicit self-judgments on individual trials. The current study assessed whether a self-referential mode of thought, induced through a writing task, also induced an SRE on a later task. The study also tested the effects of aging on the SRE, given that a long-lasting mnemonic strategy may be especially relevant for this group. Ninety-two younger adults and 60 older adults were assigned to different writing conditions and then completed an unrelated SRE task. Across younger and older adults, the classic SRE effect was observed in the narrative writing condition, reduced in the semantic self-reference condition, and further reduced in the episodic self-reference condition. These results support the induction of a self-referential mode of thought, but this mode does not enhance memory. The classic SRE effect can be reduced after thinking about the self by reflecting on autobiographical memories. Results argue for a single shared self-referential mechanism that can be accessed through self-focused writing or the classic SRE task

Effects of aging and encoding instructions on emotion-induced memory tradeoffs

The effects of emotion on memory are often described in terms of trade-offs: People often remember central, emotional information at the expense of background details. The present experiment examined the effects of aging and encoding instructions on participants' ability to remember the details of central emotional objects and the backgrounds on which those objects were placed. When young and older adults passively viewed scenes, both age groups showed strong emotion-induced trade-offs. They were able to remember the visual details as well as the general theme of the emotional object, but they had difficulties remembering the visual specifics of the scene background. Age differences emerged, however, when participants were given encoding instructions that emphasized elaborative encoding of the entire scene. With these instructions, young adults overcame the trade-offs (i.e., they no longer showed impairing effects of emotion), whereas older adults continued to show good memory for the emotional object but poor memory for its background. These results suggest that aging impairs the ability to flexibly disengage attention from the negative arousing elements of scenes, preventing the successful encoding of nonemotional aspects of the environment

Oxygen depletion recorded in upper waters of the glacial Southern Ocean

Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ~2.5 μmol mol−1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg−1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth’s climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline

Investigation and validation of intersite fMRI studies using the same imaging hardware

Purpose To provide a between-site comparison of functional MRI (fMRI) signal reproducibility in two laboratories equipped with identical imaging hardware and software. Many studies have looked at within-subject reliability and more recent efforts have begun to calibrate responses across sites, magnetic field strengths, and software. By comparing identical imaging hardware and software, we provide a benchmark for future multisite comparisons. Materials and Methods We evaluated system compatibility based on noise and stability properties of phantom scans and contrast estimates from repeated runs of a blocked motor and visual task on the same four subjects at both sites. Results Analysis of variance (ANOVA) and region of interest (ROI) analysis confirmed that site did not play a significant role in explaining variance in our large fMRI dataset. Effect size analysis shows that between-subject differences account for nearly 10 times more variance than site effects. Conclusion We show that quantitative comparisons of contrast estimates derived from cognitive experiments can reliably be compared across two sites. This allows us to establish an effective platform for comparing group differences between two sites using fMRI when group effects are potentially confounded with site, as in the study of neurocultural differences between countries or multicenter clinical trials. J. Magn. Reson. Imaging 2008;28:21–28. © 2008 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60451/1/21419_ftp.pd

The increase of the functional entropy of the human brain with age

We use entropy to characterize intrinsic ageing properties of the human brain. Analysis of fMRI data from a large dataset of individuals, using resting state BOLD signals, demonstrated that a functional entropy associated with brain activity increases with age. During an average lifespan, the entropy, which was calculated from a population of individuals, increased by approximately 0.1 bits, due to correlations in BOLD activity becoming more widely distributed. We attribute this to the number of excitatory neurons and the excitatory conductance decreasing with age. Incorporating these properties into a computational model leads to quantitatively similar results to the fMRI data. Our dataset involved males and females and we found significant differences between them. The entropy of males at birth was lower than that of females. However, the entropies of the two sexes increase at different rates, and intersect at approximately 50 years; after this age, males have a larger entropy

The self-reference effect in dementia: Differential involvement of cortical midline structures in Alzheimer’s disease and behavioural-variant frontotemporal dementia

Encoding information in reference to the self enhances subsequent memory for the source of this information. In healthy adults, self-referential processing has been proposed to be mediated by the cortical midline structures (CMS), with functional differentiation between anterior-ventral, anterior-dorsal and posterior regions. While both Alzheimer’s disease (AD) and behavioural-variant frontotemporal dementia (bvFTD) patients show source memory impairment, it remains unclear whether they show a typical memory advantage for self-referenced materials. We also sought to identify the neural correlates of this so-called ‘self-reference effect’ (SRE) in these patient groups. The SRE paradigm was tested in AD (n=16) and bvFTD (n=22) patients and age-matched healthy controls (n=17). In this task, participants studied pictures of common objects paired with one of two background scenes (sources) under self-reference or other-reference encoding instructions, followed by an item and source recognition memory test. Voxel-based morphometry was used to investigate correlations between SRE measures and regions of grey matter atrophy in the CMS. The behavioural results indicated that self-referential encoding did not ameliorate the significant source memory impairments in AD and bvFTD patients. Furthermore, the reduced benefit of self-referential relative to other-referential encoding was not related to general episodic memory deficits. Our imaging findings revealed that reductions in the SRE were associated with atrophy in the anterior-dorsal CMS across both patient groups, with additional involvement of the posterior CMS in AD and anterior-ventral CMS in bvFTD. These findings suggest that although the SRE is comparably reduced in AD and bvFTD, this arises due to impairments in different subcomponents of self-referential processing