Evapotranspiration in a Subtropical wetland savanna using low-cost Lysimeter, Eddy Covariance and Modeling approaches

Evapotranspiration (ET) constitutes the largest loss of water from subtropical grassland and wetland ecosystems, yet estimates have high uncertainty at the landscape scale as there is little information on plant water use. A major reason for this is the complexity and expense of field-based ET quantification methods such as agricultural lysimeters and eddy covariance systems. This study developed two different low-cost lysimeters – weighing-type and water level based, to measure ET under controlled conditions for single species as well as mixed grassland and wetland communities. Lysimeters were placed in an open sided shadehouse with a transparent roof to exclude rainfall. ET values were then compared with (i) Actual ET measurements from an eddy covariance tower onsite, (ii) vapor transport-based ET models - FAO Penman-Monteith, Modified Turc and Abtew Simple Radiation models, and (iii) ET data from the Florida Automated Weather Network. Both weighing-type and water level lysimeters showed seasonal patterns and annual magnitudes similar to the other ET methods. Annual ET measurements from weighing lysimeters (881-1278 mm for four plant species, n=5 per species) and water level lysimeters (1085 mm, n = 30) were similar to model estimates (1000-1200mm). Actual ET from eddy covariance was 722 mm for ten months (missing data for February and March), similar to lysimeter measurements for the dominant grass Paspalum notatum (885mm for 10 months). Low-cost lysimeters can easily inform regional ET models/remote sensing data lacking field validation and thus are potentially useful for water resources and ecosystem management in data-poor regions of the world.

REVISION OF THE TYPE MATERIALS OF STAURONEIS SCHINZII VAR. ARGENTINA FRENGUELLI AND S. SCHINZII VAR. MAXIMA FRENGUELLI (BACILLARIOPHYCEAE)

Stauroneis schinzii var. argentina and S. schinzii var. maxima were first described from Esteros del Iberá, a large subtropical wetland located in northeast Argentina. The type materials of these varieties were examined with light and scanning electron microscopy and compared to S. schinzii var. schinzii and other infraspecific taxa. As a result of this study the taxonomic validity of both varieties was confirmed, their diagnosis were emended based on the new morphological information derived, and lectotypes and isolectotypes were designated.

Effects of Land Use Types on CH4 and CO2 Production Potentials in Subtropical Wetland Soils

Changes in land use types can alter the soil and environmental characteristics of wetlands, which in turn influence the magnitude of greenhouse gas production by soil microbes. However, the effects of land use change on the production potential of methane (CH4) and carbon dioxide (CO2) in subtropical wetland soils and the underlying controls are still largely unknown. In this study, we examined the soil CH4 and CO2 production potentials under five different land use types (natural mangrove, Gei Wai water channel, Gei Wai forest, reedbed, and freshwater pond) and their relationships with soil physico-chemical properties in a subtropical wetland in Hong Kong using aerobic and anaerobic laboratory incubation experiments. Our results showed an overall decreasing trend of CH4 and CO2 production potentials down the soil profile at all sites, which could be attributed to a reduction in the concentrations of soil organic matter (SOM), total Kjeldahl nitrogen (TKN) and ammonium nitrogen (NH4+-N). Moreover, the soil CH4 and CO2 production potentials varied significantly in the surface soils among land use types, but were more similar across the sites in the deeper soils. The conversion of natural mangrove to other land use types significantly reduced both the aerobic and anaerobic CO2 production potentials in the top 10 cm soils, except for Gei Wai forest, which demonstrated significantly higher CO2 production rates (61.15–97.91 μg g−1 day−1). Meanwhile, the mean CH4 production potential in the surface soils of natural mangrove (0.05 μg g−1 d−1) was significantly lower than that in the Gei Wai forest and Gei Wai channel (0.26–0.27 μg g−1 day−1) but slightly higher than that in the freshwater pond and reedbed (0.00–0.02 μg g−1 day−1). The high soil CH4 and CO2 production potentials observed in the Gei Wai forest could be explained by the high soil concentrations of SOM, TKN and NH4+-N. On the other hand, the lower anaerobic CH4 and aerobic CO2 productions observed in the reedbed could be attributed to the lower concentrations of NH4+-N and available phosphorus. Our findings highlighted the significant impacts of land use types on the CH4 and CO2 production potentials of subtropical wetland soils, which had practical implications for wetland management for climate change mitigation.