A Preliminary Sediment Budget for the Corsica River (MD): Improved Estimates of Nitrogen Burial and Implications for Restoration

The Corsica River, located on Maryland’s eastern shore, has been the site of restoration efforts targeting sediment and nutrient load reductions. Previous work has indicated that agricultural activities supply most of these materials; however, their dynamics and fate are largely unknown. To address these needs, bottom sediments have been collected and analyzed for their chemical and textural properties. Long-term (decadal) accumulation rates are determined with ²¹⁰Pb (half-life 22.3 years), verified with ¹³⁷Cs, and range from 0.18 to 0.84 g/cm²/year in the subtidal region and 0.3–1.89 g/cm²/year in the marshes. These estimates are compared with likely sediment sources to determine the direction of exchange with the adjacent estuary (Chester River), which is a subtributary of Chesapeake Bay, with the Chester River likely supplying 0.94 × 10³ t/year of sediment to the Corsica, ∼16% of the total sediment input. The radiochemical data are used to interpret profiles of grain size and nitrogen and to provide improved estimates of nitrogen burial. Comparison of the Corsica River to similar systems highlights the importance of marshes in trapping sediment and nutrient inputs from the watershed.     

Late Quaternary Qaidam lake histories and implications for an MIS 3 “Greatest Lakes” period in northwest China

Da Qaidam and Xiao Qaidam are two of a number of lakes in northwestern China whose lake histories have been used to support the notion of a “Greatest Lakes” period in the region during marine isotope stage (MIS) 3. Reappraisal of the basins’ geomorphology, however, suggests that both lakes are highly problematic proxies for past climate. Xiao Qaidam has a low overflow threshold, only ~10–12 m above the lake surface, well below previously estimated high stands, and until about 17–23 ka BP Da Qaidam was occasionally fed by a river whose flow into the lake basin was geomorphically, rather than climatically controlled. Based on limited optically stimulated luminescence dating of shoreline and alluvial sediments it appears that highstands in the basins occurred ~100 ka BP or earlier. The two lakes are thus part of an increasing number of lake records that suggest, at least in northwestern China, (1) some lake histories may not record climate events, and (2) that the “Greatest Lakes” high stands occurred much earlier than previously recognized.     

Attitudes toward Water Conservation: The Influence of Site-Specific Factors and Beliefs in Climate Change

Areas affected by drought are increasing, and many lakes that provide potable water and recreation opportunities are located in drought-vulnerable areas. Understanding a population's attitudes toward conservation actions can improve communication initiatives, policy development, and education, which are all necessary for effective water resource management. However, little is known about stakeholders’ interactions with drought-influenced resources and the potential factors that form their water conservation attitudes. Using a mixed methods approach, we evaluated lake recreationists’ (n = 229) attitudes toward water conservation at a drought-impacted lake. We identified the relationships between two site-specific factors (place attachment and awareness of drought impacts), beliefs in climate change, concern for drought impacts, and water conservation attitudes. Results indicated concern for local drought impacts fully mediated the relationships between site-specific factors, beliefs in climate change, and attitudes toward water conservation behaviors. Implications for research, outreach, and water resource management are discussed.     

Chlorinated pesticides and PCBs in the sea-surface microlayer and seawater samples of Singapore

Sea-surface microlayer (SML) and seawater samples collected from Singapore's coastal marine environment were analyzed for selected chlorinated pesticides and polychlorinated biphenyls (PCBs). The SML is a potential site of enrichment of persistent organic pollutants (POPs) compared to the underlying water column. The concentration ranges of SigmaHCH, SigmaDDT and SigmaPCB in subsurface (1 m depth) seawater were 0.4-27.2 ng/l (mean 4.0 ng/l), 0.01-0.6 ng/l (mean 0.1 ng/l) and 0.05-1.8 ng/l (mean 0.5 ng/l) respectively. In the SML, the concentration ranges of SigmaHCH, SigmaDDT and SigmaPCB were 0.6-64.6 ng/l (mean 9.9 ng/l), 0.01-0.7 ng/l (mean 0.2 ng/l) and 0.07-12.4 ng/l (mean 1.3 ng/l) respectively. High spatial and temporal distribution was observed for all POPs measured. However, overall levels measured in the SML were lower than levels reported in the literature for SML samples from temperate coastal regions-possibly due to loss of semi-volatile compounds in the tropical climate of Singapore. Atmospheric wet deposition during the monsoon season may be an important source of POPs to the SML. This study provides the first scientific data on POP concentrations and enrichment factors in the SML for Southeast Asia.     

Temperature and solar zenith angle control of D-region positive ion chemistry

A numerical model is utilized to investigate the temperature (T) and solar zenith angle (χ) control of D-region positive ion chemistry between 75 and 90 km. It is assumed that NO^? is the precursor ion in a chain which involves three-body formation of the intermediary cluster ions NO⁺(H₂O)_m?1(X) (m = 1–3), where X can be N₂,O₂, H₂O, or CO₂, switching reactions which convert these weakly bound clusters to hydrates of NO⁺ and reaction of the third hydrate of NO⁺ with H₂O to initiate the chain to form H⁺(H₂O)_n (n = 1–7). Zonal mean and tidal temperatures from rocket observations and theory are synthesized to obtain the best available estimate of mean latitudinal, seasonal and local time variations of temperature in this height region. Relative compositions of NO⁺(H₂O)_m and H⁺(H₂O)_n are found to vary widely over the complete range of realistic conditions; however, the relative ion populations are entirely explicable in terms of the effects of χ and T on the relative life-times of the intermediary ion clusters with respect to recombination, switching and thermal decomposition. For instance, as χ increases (and electron production decreases) beyond 60° for a given temperature, the recombination times of the intermediate ion cluster species lengthen with respect to the formation time of the H⁺ water clusters, causing the relative H⁺ water cluster population to increase and thus raise the level where the cluster ion and NO⁺ concentrations are equal from about 85 km (normal midday) to 90 km. For a given χ the concentrations of NO⁺H₂O and H⁺(H₂O)₄ increase (decrease) for temperatures less than (greater than) 190 and 205 K, respectively. The transition occurs when the temperature becomes sufficiently high that the lifetimes of intermediary ion clusters with respect to thermal decomposition become less than their lifetimes with respect to H₂O switching (which ultimately leads to the third hydrate of NO⁺ and entry into the water chain). At this point, the formation time of H⁺(H₂O)₄ becomes long compared with its lifetime with respect to thermal decomposition and its relative concentration decreases also. Implications of these results with respect to studies of the D-region are discussed.     

Analytical solutions for Euler parameters

Two new analytical solutions for Poinsot motion in terms of Euler parameters are derived. The first solution is a straightforward ‘universal’ (no branches) time series practical for short time motion calculations or as a basis for analytical continuation. The second, more involved solution is also universal but is not restricted to short times; it is in terms of circular, hyperbolic, and elliptic functions and elliptic integrals.