Dynamics Variation of Soil Labile Organic Carbon Fractions in Different Wetland Types of Dongting Lake under Seasonal Water Level Fluctuation

Soil labile organic carbon (LOC) fractions are very sensitive to environmental change and closely related to soil quality. They play an important role in the study of terrestrial carbon cycles. This study aimed to explore the sensitivity of soil LOC fractions to environmental changes and analyze their main influencing factors during three seasonal water level periods for scientific management of Dongting Lake wetlands. Soil under three typical wetland types (Carextristachya wetland (CTW), Phragmites australis wetland (PAW) and Salix babylonica (SBW)) in East Dongting Lake in China were collected during the normal season (May), rainy season (August) and dry season (December). Seasonal dynamics of soil LOC fractions (i.e., dissolved organic carbon (DOC), microbial biomass carbon (MBC) and easily oxidized carbon (EOC)) within these wetlands and their relationship to soil nutrients and carbon-cycle enzyme activity were analyzed. The results showed that the soil DOC contents of the three wetlands first increased and then decreased, with the exception of CTW from the normal season to the dry season, while the seasonal changes of soil MBC and EOC for all wetlands followed an opposite pattern. CTW had the largest DOC concentration (228.29 mg·kg−1) during dry season, while the highest contents of soil DOC, MBC and EOC were found in PAW during the three observed seasons, which ranged from 82.05 to 203.60 mg·kg−1, 262.54 to 325.74 mg·kg−1 and 3.30 to 4.61 g·kg−1, respectively. However, the contents of soil DOC and their proportions to soil organic carbon (SOC) of all wetlands during the normal season were 56.58~82.05 mg·kg−1 and 0.41~0.47%, respectively, which were the lowest among the three seasons. Nevertheless, the contents of both MBC and EOC as well as their ratios to SOC in these wetlands showed similar seasonal dynamics, with the lowest values recorded in the rainy season. From the normal season to the dry season, invertase activity in all wetlands increased, while cellulase activity decreased by 12.5–31.3%. The seasonal variation of catalase activity for all wetlands was less distinctive, and the highest enzyme activity was during the rainy season. Correlation analysis revealed that soil LOC fractions for all wetlands were closely related to SOC, TN, TP and invertase for the three seasons, especially during the rainy season, but were negatively correlated with TK, cellulase and catalase activity. Generally, soil LOC fractions of the three wetlands were affected by the seasonal fluctuations of water levels and presented different distribution characteristics.

Long-Term Carbon Accumulation in Temperate Swamp Soils: A Case Study from Greenock Swamp, Ontario, Canada

Wetlands that develop peat are a globally significant pool of soil carbon. While some wetland types such as bogs and fens are well characterized by the consistent development of carbon-rich peat, swamps soils are more variable both in terms of their carbon densities and accretion rates. Subcategorizing swamps by forest type may be a useful way of understanding this variability. Here we provide a case study of carbon accumulation in two distinct forest stands of Greenock Swamp located in the Great Lakes – St Lawrence mixed forest region in Bruce County, Ontario, Canada: an Acer - Fraxinus (maple-ash) dominant stand (i.e., broad-leaved swamp) and a Thuja occidentalis (cedar) dominant stand (i.e., needle-leaved swamp). Organic matter and organic carbon contents were analyzed among seven Acer - Fraxinus soil cores and one Thuja occidentalis core collected from Greenock Swamp. The Acer - Fraxinus cores had peat depths ranging from 18-60 cm with a mean organic matter content of 54% and an organic carbon content of 34% of dry mass. The Thuja occidentalis swamp core had at least 4 m of almost homogeneous peat with a mean organic matter content of 89%. Radiocarbon dating indicates that the Acer - Fraxinus swamp accumulates peat episodically whereas the Thuja occidentalis swamp showed continuous peat accumulation since the Middle Holocene. Overall, both broad-leaved and needle-leaved swamps have important soil carbon stocks, and are prevalent wetland types in middle latitudes. Both need to be considered to fully represent the carbon pools and potential sink of temperate wetlands.

Management and Sustainability of Greek Wetlands

Greece has today about 400 large and small wetlands. Some of them are international importance and some are considered as national importance. Several of them are composite and form wetland mosaics or complexes. The most common wetland types in Greece are: rivers, estuaries, deltas, lagoons, shallow lakes, shallow marine formations, marshes. Their total area is still quite large (210,000 ha) in spite of the heavy losses that occurred during the last two generations Threats of degradation are drainage, dam construction, irrigation networks, alteration in river morphology such as diversion flow, clearing of natural vegetation which alter hydrological regime and affect wetland function. Sustainable agriculture in the hydrological basins of important wetlands should be considered because these systems are threaten most.

Urban Areas Create Refugia for Odonates in a Semi-Arid Region

In western Texas, most wetlands are fed from precipitation runoff, making them sensitive to drought regimes, anthropogenic land-use activities in their surrounding watersheds, and the interactive effect between these two factors. We surveyed adult odonates in 133 wetlands (49 in grassland settings, 56 in cropland, and 28 in urban areas) in western Texas from 2003–2020; 33 species were recorded. Most species were widespread generalists, but urban wetlands had the highest species richness, as well as the most unique species of any of the three wetland types. Non-metric, multidimensional scaling ordination revealed that the odonate community in urban wetlands was distinctly different in composition than the odonates in non-urban wetlands. Urban wetlands were smaller in surface area than the other wetland types, but because they were fed from more consistently available urban runoff rather than seasonal precipitation, they had longer hydroperiods, particularly during a multi-year drought when wetlands in other land-cover contexts were dry. This anthropogenically enhanced water supply was associated with higher odonate richness despite presumably impaired water quality, indicating that consistent and prolonged presence of water in this semi-arid region was more important than the presence of native land cover within which the wetland existed. Compared to wetlands in the regional grassland landscape matrix, wetlands in agricultural and urban areas differed in hydroperiod, and presumably also in water quality; these effects translated to differences in the regional odonate assemblage by surrounding land-use type, with the highest richness at urban playas. Odonates in human environments may thus benefit through the creation of a more reliably available wetland habitat in an otherwise dry region.

The impact of spatially varying wetland source signatures on the atmospheric variability of dD-CH4

<p>We present the first spatially varying map of the δD-CH<sub>4 </sub>signature of wetland methane emissions and model its impact on atmospheric δD-CH<sub>4</sub>. The δD-CH<sub>4</sub> signature map is derived by relating the δD-H<sub>2</sub>O of precipitation to the measured δD-CH<sub>4</sub> of methane wetland emissions at a variety of wetland types and locations. Since the δD-H<sub>2</sub>O of precipitation is highly latitude-dependent, including this spatial variation has the potential to have a large impact on the distribution of δD-CH<sub>4</sub> observed in the atmosphere. This latitude-dependence means that wetland emissions at different latitudes can have very different impacts on atmospheric δD-CH<sub>4</sub>, which could provide a useful way to constrain the location of wetland methane emissions in future inverse modelling studies. Here, we assess the implications for model studies on the differences that arise by treating δD-CH<sub>4</sub> wetland source signatures as globally uniform rather than accounting for the large spatial variation. We also assess the potential for δD-CH<sub>4</sub> to provide an independent constraint on wetland emissions over the more abundant and widely measured δ<sup>13</sup>C-CH<sub>4</sub>.</p>

Diversity and Distribution of Waterbirds across Wetlands of Eastern Uganda

Explaining patterns of diversity, and abundance across sites is a central aim of community ecology. Avian communities have been the focus of many studies on species diversity. To be able to explain patterns of waterbirds in wetlands of eastern Uganda, we conducted a rapid assessment in 48 wetlands (38 swamps, two rice paddies and eight lakes) using total counts. We examined waterbird assemblages in these wetlands in relation to wetland area, wetland type, water depth, water pH and the time of year/season. Statistical analysis were conducted using Genstat Version 8.1 (VSN Intl.2003, in which General Linear Mixed Models were used to examine the variations. In total, 9,410 birds from 64 species and 17 families were recorded. Species diversity and overall abundance varied significantly among wetland types and between seasons. Rice paddies were both more species-diverse than lakes and swamps. Wetland area had significant independent and positive effects on the waterbird community. In addition to explaining differences among wetland types in waterbird numbers, water depth had a positive effect on some aspects of the waterbird community with no significant effect of pH. These results imply that an interplay of factors is responsible for the pattern and structure of waterbird communities on wetlands in eastern Uganda.

Coastal Wetland Classification with Deep U-Net Convolutional Networks and Sentinel-2 Imagery: A Case Study at the Tien Yen Estuary of Vietnam

The natural wetland areas in Vietnam, which are transition areas from inland and ocean, play a crucial role in minimizing coastal hazards; however, during the last two decades, about 64% of these areas have been converted from the natural wetland to the human-made wetland. It is anticipated that the conversion rate continues to increase due to economic development and urbanization. Therefore, monitoring and assessment of the wetland are essential for the coastal vulnerability assessment and geo-ecosystem management. The aim of this study is to propose and verify a new deep learning approach to interpret 9 of 19 coastal wetland types classified in the RAMSAR and MONRE systems for the Tien Yen estuary of Vietnam. Herein, a Resnet framework was integrated into the U-Net to optimize the performance of the proposed deep learning model. The Sentinel-2, ALOS-DEM, and NOAA-DEM satellite images were used as the input data, whereas the output is the predefined nine wetland types. As a result, two ResU-Net models using Adam and RMSprop optimizer functions show the accuracy higher than 85%, especially in forested intertidal wetlands, aquaculture ponds, and farm ponds. The better performance of these models was proved, compared to Random Forest and Support Vector Machine methods. After optimizing the ResU-Net models, they were also used to map the coastal wetland areas correctly in the northeastern part of Vietnam. The final model can potentially update new wetland types in the southern parts and islands in Vietnam towards wetland change monitoring in real time.

Spatial ecology of little egret (Egretta garzetta) in Hong Kong uncovers preference for commercial fishponds

Many natural wetlands have been converted to human-influenced wetlands. In some instances, human-influenced wetlands could provide complementary habitats for waterbirds, compensating for the loss of natural wetlands. Inner Deep Bay in Hong Kong is composed of both natural and human-influenced wetlands and is under immense development pressure. From an ecology perspective, we need to understand if different wetland types play the same ecological role. To achieve this, we tracked nine little egrets (Egretta garzetta) using GPS loggers for 14 months to study their spatial ecology, home range, movement and habitat use. We found that over 88% of the home range of all individuals comprised of wetlands (commercial fishponds, mangrove, gei wai, channel, and intertidal mudflat). Among these wetland types, nearly all (seven of nine) individuals preferred commercial fishponds over other habitats in all seasons. Little egrets exhibited seasonal movement and habitat use among seasons, with largest home range, greatest movement, and most frequent visits to commercial fishponds in winter compared to spring and autumn. Our results highlight the significant role of commercial fishponds, providing a feeding ground for little egrets. However, other wetland types cannot be ignored, as they were also used considerably. These findings underscore the importance of maintaining a diversity of wetland types as alternative foraging and breeding habitats.