Relationship between Community Structure of Zooplankton and Water Quality of a Mesotrophic Lake Wetland

In order to explore the regular pattern of community succession of zooplankton and the influencing factors in the middle eutrophic reservoir, a systematic investigation was made to the zooplanktons in Baguishan Reservior from February to November in 2016, including the diversity, abundance, biomass of zooplanktons and environmental factors. The water eutrophication level was evaluated by using trophic state index （ TLI ）, and Redundancy Analyses （RDA） was employed to build dynamic changes of structure of protozoa, rotifer and crustacean. Finally, a total of 40 samples were collected. A total of 96 species of zooplankton were identified, including 41 species of protozoa, 34 species of rotifers, 12 species of cladocerans, and 9 species of copepods. TLI varied from 42.8 to 48.9 with an annual average of （45.07±2.02）, indicating that reservoir belonged to mesotrophic water body. Furthermore, Shannon-Wiener biodiversity （ H ′） and Pielou evenness（ J ） showed that the water quality of the Reservoir was β -pollution pattern. The results of RDA showed that the zooplankton community structure changed significantly with months. Chlorophyll a （Chl.a）, water temperature （WT） and ammonia nitrogen （NH 3-N） were the main factors influencing the community of protozoa, and Chl.a, WT, pH, NH 3-N and the ratio of NH 3-N to total phosphorus （TP） were important factors to rotifer community. The changes of crustacean community could be better explained by the factors of TP and WT, pH, and the ratio of NH 3-N to TP.

Relationship between Temporal and Spatial Variation of Planktonic Diatom Community Structure and Water Quality in Mesotrophic Reservoir

In order to clarify the regular pattern of community succession of planktonic diatoms and the relationship between the diatoms and the physic-chemical parameters, the species, abundance, and biomass of planktonic diatoms, and environmental factors in Baiguishan Reservoir （BGR） were investigated in Baiguishan Reservoir from February to November in 2016. Trophic state index （ TLI ） was used to evaluate the trophic state, and factors affecting the dynamics of planktonic diatom community were analyzed by Redundancy analyses （RDA）. The results showed that Baiguishan Reservoir belonged to mesotrophic water body, and all observed phytoplankton belonged to 69 genera of 25 families. The sampling points were divided into the same 2 groups in the clustering analysis based on environmental factors and Non-metric Multi-Dimensional Scaling （NMDS） analysis, indicating that the community structure of planktonic diatoms had the same change trends with the changes of environmental factors. RDA showed that the main factors affecting community structure were total phosphorus （TP）, water temperature （WT） and the ratio of ammonia nitrogen to total phosphorus （NH 3-N/TP）. Therefore, TP was the most important factor influencing the dynamics of planktonic diatom community in mesotrophic reservoir.

Changes in Soil Organic Carbon Dynamics in a Native C4 Plant-Dominated Tidal Marsh Following Spartina alterniflora Invasion

Invasion of an exotic C4 plant Spartina alterniflora has been shown to increase soil organic carbon （SOC） concentrations in native C3 plant-dominated coastal wetlands of China. However, little is known about the effects of S. alterniflora invasion on SOC concentrations and fractions in tidal marshes dominated by native C4 plants. In this study, a field experiment was conducted in a tidal marsh dominated by the native C4 plant Cyperus malaccensis in the Minjiang River estuary, China. Concentrations of SOC and liable SOC fractions, dissolved organic carbon （DOG）, microbial biomass carbon （MBC）, and easily oxidizable carbon （EOC）, were measured in the top 50-cm soils of the C. malaccensis community, as well as those of three S. alterniflova communities with an invasion duration of 0-4 years （SA-4）, 4-8 years （SA-8）, and 8-12 years （SA-12）, respectively. Results showed that both SOC stocks in the 50-cm soils and mean SOC concentrations in the surface soils （0-10 cm） of the C. malaccensis community increased with the duration of S. alterniflora invasion, whereas SOC concentrations in the 10-50-cm soils decreased slightly during the initial period of S. alterniflora invasion, before increasing again. The pattern of changes in labile SOC fractions （DOC, MBC, and EOC） with invasion duration was generally similar to that of SOC, while the ratios of labile SOC fractions to total SOC （DOC：SOC, MBC：SOC, and EOC：SOC） decreased significantly with the duration of S. alterniflora invasion. The findings of this study suggest that invasion of the exotic C4 plant S. alternifora into a marsh dominated by the native C4 plant C. malaecensis would enhance SOC sequestration owing to the greater amount of biomass and lower proportion of labile SOC fractions present in the S. alterniflora communities.