Quantitative and Qualitative Aspects of Dissolved Organic Carbon Leached from Senescent Plants in an Oligotrophic Wetland

We conducted a series of experiments whereby dissolved organic matter (DOM) was leached from various wetland and estuarine plants, namely sawgrass (Cladium jamaicense), spikerush (Eleocharis cellulosa), red mangrove (Rhizophora mangle), cattail (Typha domingensis), periphyton (dry and wet mat), and a seagrass (turtle grass; Thalassia testudinum). All are abundant in the Florida Coastal Everglades (FCE) except for cattail, but this species has a potential to proliferate in this environment. Senescent plant samples were immersed into ultrapure water with and without addition of 0.1% NaN3 (w/ and w/o NaN3, respectively) for 36 days. We replaced the water every 3 days. The amount of dissolved organic carbon (DOC), sugars, and phenols in the leachates were analyzed. The contribution of plant leachates to the ultrafiltered high molecular weight fraction of DOM (>1 kDa; UDOM) in natural waters in the FCE was also investigated. UDOM in plant leachates was obtained by tangential flow ultrafiltration and its carbon and phenolic compound compositions were analyzed using solid state 13C cross-polarization magic angle spinning nuclear magnetic resonance (13C CPMAS NMR) spectroscopy and thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH thermochemolysis), respectively. The maximum yield of DOC leached from plants over the 36-day incubations ranged from 13.0 to 55.2 g C kg−1 dry weight. This amount was lower in w/o NaN3 treatments (more DOC was consumed by microbes than produced) except for periphyton. During the first 2 weeks of the 5 week incubation period, 60–85% of the total amount of DOC was leached, and exponential decay models fit the leaching rates except for periphyton w/o NaN3. Leached DOC (w/ NaN3) contained different concentrations of sugars and phenols depending on the plant types (1.09–7.22 and 0.38–12.4 g C kg−1 dry weight, respectively), and those biomolecules comprised 8–34% and 4–28% of the total DOC, respectively. This result shows that polyphenols that readily leach from senescent plants can be an important source of chromophoric DOM (CDOM) in wetland environments. The O-alkyl C was found to be the major C form (55±9%) of UDOM in plant leachates as determined by 13C CPMAS NMR. The relative abundance of alkyl C and carbonyl C was consistently lower in plant-leached UDOM than that in natural water UDOM in the FCE, which suggests that these constituents increase in relative abundance during diagenetic processing. TMAH thermochemolysis analysis revealed that the phenolic composition was different among the UDOM leached from different plants, and was expected to serve as a source indicator of UDOM in natural water. Polyphenols are, however, very reactive and photosensitive in aquatic environments, and thus may loose their plant-specific molecular characteristics shortly. Our study suggests that variations in vegetative cover across a wetland landscape will affect the quantity and quality of DOM leached into the water, and such differences in DOM characteristics may affect other biogeochemical processes.

Middle school teachers perspectives on inclusion: A qualitative study

Historically, research has placed considerable emphasis on developing a systematic body of knowledge about education in which little voice has been given to teachers themselves. The critical role that teachers play in this generative process such as reflecting, acting and theorizing upon practices that shape life in the classroom has largely been ignored in favor of technical innovation and organizational procedure. As schools struggle to reform and restructure, an understanding of how teachers interpret their practices in context and how the culture of schools influence, constrain, or encourage these practices become critical aspects of school success or failure. ^ This study examined the perspectives on inclusion of seven middle school teachers as they attempted to include exceptional students in regular classes. The study utilized three forms of data collection: observations were made of participant interactions as they led their everyday school lives; document analysis was used as a means to gain an understanding of programs affecting exceptional students, and interviews were used to give voice to teacher's perceptions regarding inclusion, allowing description in their own words rather than those imposed by an outside inquirer. Data collection and analysis sought to identify emerging themes, categories and patterns, allowing for the creation of substantive theory grounded in empirical data. ^ The key issues that emerged in the study were considered in terms of three general categories. The first, teaching and learning, revealed stark contrasts in opinions regarding the type of human support thought necessary for successful inclusion. Regular educators clung to the traditional notion of solitary teachers directing all class activity, while exceptional educators preferred a more team-oriented approach. The second, school structure, revealed that highly collaborative structures were only partially successful in creating additional conversation between regular and exceptional educators. Collegiality was affected by lack of staff experience with the process as well as its implementation in a top-down fashion. The third, school culture and climate, revealed that regular educators believed the school was prepared for a limited amount of inclusion. Although exceptional educators acknowledged school readiness, they did not believe that inclusion was an important item on the school's reform agenda. ^