Vegetation dynamics and their implications for the management of wetlands in the lowlands of Nepal

The maintenance of species richness is often a priority in the management of nature reserves, where consumptive use of resources is generally prohibited. The purpose of this research was to improve management by understanding the vegetation dynamics in the lowlands of Nepal. The objectives were to determine vegetation associations in relation to environments and human-induced disturbances that affect vegetation dynamics on floodplains, where upstream barrages had altered flooding patterns, and consumptive use of plant resources was influencing natural processes. Floodplain vegetation in relation to physical environments and disturbances were studied along transects, perpendicular to the course of the Mahakali River in the western Terai, Nepal. Forest structural changes were studied for three years in ten plots. A randomized split-block experiment with nine burning and grazing treatments was performed in seasonally flooded grasslands. A semi-structured questionnaire was used to assess people's socio-economic status, natural resource use patterns and conservation attitudes. ^ Elevation, soil organic matter, nitrogen, percentage of sand and grazing intensity were significant in delineating herbaceous vegetation assemblages, whereas elevation and livestock grazing were significant in defining forest type boundaries. On the floodplain islands, highly grazed Dalbergia sissoo-Acacia catechu forests were devoid of understory woody vegetation, but the lightly grazed D. sissoo-mixed forests had a well-developed second canopy layer, comprising woody species other than D. sissoo and A. catechu. In grasslands, species richness and biomass production were highest at intermediate disturbance level represented by the lightly grazed and ungrazed early-burned treatments. Ethnicity, education and resource use patterns were important in influencing conservation attitudes. A succession towards the mixed forests would occur in D. sissoo-dominated floodplain forests, where dams and barrages reduce flooding and associated fluvial processes, and if livestock grazing is stopped, as occasionally suggested by nature conservationists. In seasonally flooded grasslands, early burning with moderate grazing would enhance the species diversity and productivity. There is a need to implement a participatory integrated wetland management plan, to include community development, education and off farm income generation, to assure participatory conservation and management of wetlands in Nepal. ^

Biotic and abiotic determinants of intermediate-consumer trophic diversity in the Florida everglades

Food-web structure can shape population dynamics and ecosystem functioning and stability. We investigated the structure of a food-web fragment consisting of dominant intermediate consumers (fishes and crayfishes) in the Florida Everglades, using stable isotope analysis to quantify trophic diversity along gradients of primary production (periphyton), disturbance (marsh drying) and intermediate-consumer density (a possible indicator of competition). We predicted that trophic diversity would increase with resource availability and decrease after disturbance, and that competition could result in greater trophic diversity by favouring resource partitioning. Total trophic diversity, measured by niche area, decreased with periphyton biomass and an ordination axis representing several bluegreen algae species. Consumers’ basal resource diversity, estimated by δ13C values, was similarly related to algal community structure. The range of trophic levels (δ15N range) increased with time since the most recent drying and reflooding event, but decreased with intermediate-consumer density, and was positively related to the ordination axis reflecting increases in green algae and decreases in filamentous bluegreen algae. Our findings suggest that algal quality, independent of quantity, influences food-web structure and demonstrate an indirect role of nutrient enrichment mediated by its effects on periphyton palatability and biomass. These results reveal potential mechanisms for anthropogenic effects on Everglades communities.

Environmental Dynamics of Dissolved Black Carbon in Aquatic Ecosystems

Black carbon (BC), the incomplete combustion product from biomass and fossil fuel burning, is ubiquitously found in soils, sediments, ice, water and atmosphere. Because of its polyaromatic molecular characteristic, BC is believed to contribute significantly to the global carbon budget as a slow-cycling, refractory carbon pool. However, the mass balance between global BC generation and accumulation does not match, suggesting a removal mechanism of BC to the active carbon pool, most probable in a dissolved form. The presence of BC in waters as part of the dissolved organic matter (DOM) pool was recently confirmed via ultrahigh resolution mass spectrometry, and dissolved black carbon (DBC), a degradation product of charcoal, was found in marine and coastal environments. However, information on the loadings of DBC in freshwater environments and its global riverine flux from terrestrial systems to the oceans remained unclear. The main objectives of this study were to quantify DBC in diverse aquatic ecosystems and to determine its environmental dynamics. Surface water samples were collected from aquatic environments with a spatially significant global distribution, and DBC concentrations were determined by a chemical oxidation method coupled with HPLC detection. While it was clear that biomass burning was the main sources of BC, the translocation mechanism of BC to the dissolved phase was not well understood. Data from the regional studies and the developed global model revealed a strong positive correlation between DBC and dissolved organic carbon (DOC) dynamics, indicating a co-generation and co-translocation between soil OC and BC. In addition, a DOC-assistant DBC translocation mechanism was identified. Taking advantage of the DOC-DBC correlation model, a global riverine DBC flux to oceans on the order of 26.5 Mt C yr-1 (1 Mt = 1012 g) was determined, accounting for 10.6% of the global DOC flux. The results not only indicated that DOC was an important environmental intermediate for BC transfer and storage, but also provided an estimate of a major missing link in the global BC budget. The ever increasing DBC export caused by global warming will change the marine DOM quality and may have important consequences for carbon cycling in marine ecosystem.