The Irrigation Effect: How River Regulation Can Promote Some Riparian Vegetation.

River regulation impacts riparian ecosystems by altering the hydrogeomorphic conditions that support streamside vegetation. Obligate riparian plants are often negatively impacted since they are ecological specialists with particular instream flow requirements. Conversely, facultative riparian plants are generalists and may be less vulnerable to river regulation, and could benefit from augmented flows that reduce drought stress during hot and dry periods. To consider this 'irrigation effect' we studied the facultative shrub, netleaf hackberry (Celtis reticulata), the predominant riparian plant along the Hells Canyon corridor of the Snake River, Idaho, USA, where dams produce hydropeaking, diurnal flow variation. Inventories of 235 cross-sectional transects revealed that hackberry was uncommon upstream from the reservoirs, sparse along the reservoir with seasonal draw-down and common along two reservoirs with stabilized water levels. Along the Snake River downstream, hackberry occurred in fairly continuous, dense bands along the high water line. In contrast, hackberry was sparsely scattered along the free-flowing Salmon River, where sandbar willow (Salix exigua), an obligate riparian shrub, was abundant. Below the confluence of the Snake and Salmon rivers, the abundance and distribution of hackberry were intermediate between the two upstream reaches. Thus, river regulation apparently benefited hackberry along the Snake River through Hells Canyon, probably due to diurnal pulsing that wets the riparian margin. We predict similar benefits for some other facultative riparian plants along other regulated rivers with hydropeaking during warm and dry intervals. To analyze the ecological impacts of hydropeaking we recommend assessing daily maxima, as well as daily mean river flows.

Floodplain forest succession reveals fluvial processes: A hydrogeomorphic model for temperate riparian woodlands.

River valley floodplains are physically-dynamic environments where fluvial processes determine habitat gradients for riparian vegetation. These zones support trees and shrubs whose life stages are adapted to specific habitat types and consequently forest composition and successional stage reflect the underlying hydrogeomorphic processes and history. In this study we investigated woodland vegetation composition, successional stage and habitat properties, and compared these with physically-based indicators of hydraulic processes. We thus sought to develop a hydrogeomorphic model to evaluate riparian woodland condition based on the spatial mosaic of successional phases of the floodplain forest. The study investigated free-flowing and dam-impacted reaches of the Kootenai and Flathead Rivers, in Idaho and Montana, USA and British Columbia, Canada. The analyses revealed strong correspondence between vegetation assessments and metrics of fluvial processes indicating morphodynamics (erosion and shear stress), inundation and depth to groundwater. The results indicated that common successional stages generally occupied similar hydraulic environments along the different river segments. Comparison of the spatial patterns between the free-flowing and regulated reaches revealed greater deviation from the natural condition for the braided channel segment than for the meandering segment. This demonstrates the utility of the hydrogeomorphic approach and suggests that riparian woodlands along braided channels could have lower resilience than those along meandering channels and might be more vulnerable to influences such as from river damming or climate change.

Hydrologic linkages between a climate oscillation, river flows, growth, and wood Δ13C of male and female cottonwood trees.

To investigate climatic influence on floodplain trees, we analysed interannual correspondences between the Pacific Decadal Oscillation (PDO), river and groundwater hydrology, and growth and wood (13)C discrimination (Δ(13)C) of narrowleaf cottonwoods (Populus angustifolia) in a semi-arid prairie region. From the Rocky Mountain headwaters, river discharge (Q) was coordinated with the PDO (1910-2008: r(2) = 0.46); this pattern extended to the prairie and was amplified by water withdrawal for irrigation. Floodplain groundwater depth was correlated with river stage (r(2) = 0.96), and the cottonwood trunk basal area growth was coordinated with current- and prior-year Q (1992-2008: r(2) = 0.51), increasing in the mid-1990s, and decreasing in 2000 and 2001. Annual Δ(13)C decreased during low-flow years, especially in trees that were higher or further from the river, suggesting drought stress and stomatal closure, and male trees were more responsive than females (-0.86 versus -0.43‰). With subsequently increased flows, Δ(13)C increased and growth recovered. This demonstrated the linkages between hydroclimatic variation and cottonwood ecophysiology, and we conclude that cottonwoods will be vulnerable to drought from declining river flows due to water withdrawal and climate change. Trees further from the river could be especially affected, leading to narrowing of floodplain forests along some rivers.

Post-pollination prefertilization drops affect germination rates of heterospecific pollen in larch and Douglas-fir.

Pollen of larch (Larix × marschlinsii) and Douglas-fir (Pseudotsuga menziesii) was used in homospecific and heterospecific crosses. Germination of heterospecific pollen in ovulo was reduced in post-pollination prefertilization drops. This provides evidence of selection against foreign pollen by open-pollinated exposed ovules in these two sister taxa, which share the same type of pollination mechanism. Of the other prezygotic stages in pollen-ovule interactions, uptake of pollen by stigmatic hairs did not show any selection. Pollen tube penetration of the nucellus was similar for hetero- and homospecific pollen tubes, but heterospecific tubes only delivered gametes in one cross. To test for differences in the post-pollination prefertilization drops of each species, drops were gathered and analysed. Glucose and fructose were present in similar amounts in Douglas-fir and larch, while sucrose was found in larch only. Other carbohydrates such as xylose and melezitose were species-specific. In P. menziesii, sucrose is absent due to its conversion to glucose and fructose by apoplastic invertases. In contrast, Larix × marschlinsii drops have sucrose because they lack apoplastic invertases. The presence of invertase activity shows that the composition of gymnosperm post-pollination prefertilization drops is not static but dynamic. Drops of these two species also differed in their calcium concentrations.

Sand and sandbar willow: a feedback loop amplifies environmental sensitivity at the riparian interface.

Riparian or streamside zones support dynamic ecosystems with three interacting components: flowing water, alluvia (river-transported sediments), and vegetation. River damming influences all three, and subsequent responses can provide insight into underlying processes. We investigated these components along the 315-km Hells Canyon corridor of the Snake River that included reaches upstream, along, and downstream from three large dams and reservoirs, and along the Salmon River, a free-flowing tributary. Sandbar willow was generally the woody plant at the lowest bank position and was abundant along upstream reaches (53, 45, 67% of transects), sparse along reservoirs (11, 12, 0%), and sparse along the Snake River downstream (11%). It was prolific along the undammed Salmon River (83%) and intermediate along the Snake River below the Salmon inflow (27%), indicating partial recovery with the contribution of water and sediments. Along these rivers, it commonly occurred on sandy substrates, especially on shallow-sloped surfaces, and emerged from interstitial sands between cobbles on steeper surfaces. However, along the Snake River below the dams, sandbars have eroded and willows were sparse on remnant, degrading sand surfaces. We conclude that a feedback loop exists between sands and sandbar willow. Sand favors willow colonization and clonal expansion, and reciprocally the extensively branched willows create slack-water zones that protect and trap sands. This feedback may sustain surface sands and sandbar willows along free-flowing river systems and it amplifies their mutual vulnerability to river damming. Following damming, sediment-depleted water is released downstream, eroding surface sands and reducing willow colonization and expansion. With willow decline, sands are further exposed and eroded, compounding these impacts. From this feedback, we predict the coordinated depletion of surface sands and riparian willows along dammed rivers throughout the Northern Hemisphere.

Effects of flooding on leaf development, transpiration, and photosynthesis in narrowleaf cottonwood, a willow-like poplar.

The narrowleaf cottonwood, Populus angustifolia, occurs in occasionally flooded, low elevation zones along river valleys near the North American Rocky Mountains. This small poplar has narrow leaves and fine branching and thus resembles willows, which are commonly flood-tolerant. We investigated the flood response of narrowleaf cottonwoods and a related native hybrid, jackii cottonwood (P. x jackii = P. balsamifera x P. deltoides), by studying saplings of 24 clones in a greenhouse, with some pots being inundated to provide the flood treatment. Flooding slightly reduced leaf numbers (-10%), and leaf sizes were reduced by about 21% in female P. angustifolia versus a 50% reduction in the female hybrids. Flooding-reduced stomatal conductance and net photosynthetic rate, and reduced transpiration particularly in P. x jackii. The effects on foliar gas exchange declined over a 5-week interval, suggesting compensation. The moderate impact of flooding supports the hypothesis that narrowleaf cottonwoods are flood-tolerant, and we anticipate that these trees could provide traits to increase the flood tolerance of fast-growing hybrid poplars. The results further indicate that female cottonwoods may be more flood-tolerant than males, and females could be more successful in lower, flood-prone sites.

Complex inheritance and parent-of-origin effect in juvenile myoclonic epilepsy.

BACKGROUND: Juvenile myoclonic epilepsy (JME) is an idiopathic generalized epilepsy (IGE) with complex inheritance. Previous studies have suggested maternal inheritance and female excess in IGEs but have not been specific for JME. We investigated evidence for maternal inheritance, female excess and patterns of familial seizure risk in a well-characterized sample of JME families. METHODS: We ascertained 89 families through a JME proband and 50 families through a non-JME IGE proband. JME families were divided into those with and without evidence of linkage to the EJM1 susceptibility locus on chromosome 6. We analyzed transmission in 43 multigenerational families, calculated the adjusted sex ratio for JME, and looked for evidence of seizure specific risk in 806 family members. RESULTS: We found evidence for preferential maternal transmission in both EJM1-linked and unlinked families (2.7:1), evidence even more marked when potential selection factors were excluded. The adjusted female: male risk ratio was very high in JME (RR=12.5; 95% CI: 1.9-83.7). Absence seizures in JME probands increased the overall risk of seizures in first degree relatives (15.8% vs. 7.0%, P=0.011), as well as first-degree relatives' specific risk of absence seizures (6% vs. 1.6%, P=0.01), but not myoclonic seizures. CONCLUSIONS: We have confirmed the finding of maternal inheritance in JME, which is not restricted to JME families linked to the EJM1 locus. The striking female excess in JME may relate to anatomical and/or endocrine sexual dimorphism in the brain. Evidence for independent inheritance of absence and myoclonic seizures in JME families reinforces a model in which combinations of loci confer susceptibility to the component seizure types of IGE.

Triggers of uncertainty about recurrence and long-term treatment side effects in older African American and Caucasian breast cancer survivors.

PURPOSE/OBJECTIVES: To examine the sources of uncertainty in older African American and Caucasian long-term breast cancer survivors by focusing on frequency of triggers of uncertainty about cancer recurrence and physical symptoms linked to long-term treatment side effects. DESIGN: In the context of a larger randomized, controlled treatment-outcome study, data were gathered from 10 monthly follow-up telephone calls by nurses. SETTING: Rural and urban regions of North Carolina. SAMPLE: 244 older women (mean age = 64 years); 73 African American women and 171 Caucasian women who were five to nine years after breast cancer diagnosis. FINDINGS: The most frequent triggers were hearing about someone else's cancer and new aches and pains. The most frequent symptoms were fatigue, joint stiffness, and pain. Although no ethnic differences occurred in the experience of symptoms, Caucasian women were more likely than African American women to report that their fears of recurrence were triggered by hearing about someone else's cancer, environmental triggers, and information or controversy about breast cancer discussed in the media. CONCLUSIONS: Illness uncertainty persisted long after cancer diagnosis and treatment, with most women experiencing multiple triggers of uncertainty about recurrence and a range of symptoms and treatment side effects. IMPLICATIONS FOR NURSING: Nurses can help cancer survivors to identify, monitor, and manage illness uncertainty and emotional distress.