Evaluation of constructed wetlands by wastewater purification ability and greenhouse gas emissions.

Domestic wastewater is a significant source of nitrogen and phosphorus, which cause lake eutrophication. Among the wastewater treatment technologies, constructed wetlands are a promising low-cost means of treating point and diffuse sources of domestic wastewater in rural areas. However, the sustainable operation of constructed wetland treatment systems depends upon a high rate conversion of organic and nitrogenous loading into their metabolic gaseous end products, such as N2O and CH4. In this study, we examined and compared the performance of three typical types of constructed wetlands: Free Water Surface (FWS), Subsurface Flow (SF) and Vertical Flow (VF) wetlands. Pollutant removal efficiency and N2O and CH4 emissions were assessed as measures of performance. We found that the pollutant removal rates and gas emissions measured in the wetlands exhibited clear seasonal changes, and these changes were closely associated with plant growth. VF wetlands exhibited stable removal of organic pollutants and NH3-N throughout the experiment regardless of season and showed great potential for CH4 adsorption. SF wetlands showed preferable T-N removal performance and a lower risk of greenhouse gas emissions than FWS wetlands. Soil oxidation reduction potential (ORP) analysis revealed that water flow structure and plant growth influenced constructed wetland oxygen transfer, and these variations resulted in seasonal changes of ORP distribution inside wetlands that were accompanied by fluctuations in pollutant removal and greenhouse gas emissions.

Visual identification rate in search of a missing stimulus.

Subjects searched for a digit which was not presented in an array of nine different digits. The identification rate was estimated from the percent correct. Well-trained subjects identified 6.5 digits with a 50-msec. exposure. This fast identification rate was expected from our procedure using a single answer, an inconsistent target, and equal probability that every digit would be a target. Naive subjects markedly improved their performance in the first two weeks of the trials which were given for a total of 24 days.

Evidence of a rapid matching process for simultaneous reading of several items from visual information storage.

When subjects searched for a digit which did not appear in an array of nine different, briefly displayed digits, they identified them more rapidly than Sperling reported earlier could be done. Subjects stated they could "see" the missing digit. We hypothesized that the "seen" digit would be the only remaining digit after subjects matched an internal set of 10 digits with the displayed set of nine stimuli. This process works early as sensory information storage and facilitates character identification. Here we presented another stimulus array immediately after the first one to examine the matching process by extinguishing the visualized digit. When the two arrays had different missing digits (Condition-D), identification of the missing digit from the first array was worse than when they were the same (Condition-S). For the former condition, the remaining digit was extinguished after it was actually presented in the second array. The results support subjects' self-reports and clarify the matching process in the early information-processing stage.

[The N2 component of event-related potentials to CV syllables in a task-free situation].

Event-related potentials (ERPs) were recorded while subjects simply listened to sequences of consonant-vowel (CV) syllables. Each sequence was presented in random order and consisted of two kinds of CV syllables--90% ('frequent') and 10% ('rare deviant'), respectively. The features separating these two syllables were varied in phoneme (consonant and/or vowel) or intensity in different runs. In all eight conditions, a fronto-centrally dominant, negative wave peaking around 200 ms (N2) was observed for the deviants. The shorter latency N2 was found for the separating features of vowels or intensities but not for consonants. The results were interpreted as showing that N2 reflects a covert orienting response to rare deviants and that its latency can serve as an index for identifying the separating feature. Observation of N2 in the task-free situation suggested that it might be a useful tool for assessing linguistic discriminability in a clinical setting.