Abstract
Little research has focused on how rotifer communities respond to eutrophication based on their combined taxonomic and functional indices. In this research, the relationship of the environment and rotifer communities was comparatively investigated in two subtropical lakes over one year. The taxon-based indices, including species number (S), Margalef index (D), Simpson index (d), Shannon-wiener index (H′), and functional traits relying on the guild ratio (GR) and the modified guild ratio (GR′) from the moderately eutrophic Lake Xiyanghu were significantly lower than those from the slightly eutrophic Lake Jinghu. Redundancy analysis (RDA) showed that both lakes were distinct from each other. Taken together, the findings indicate that trophic state was an important factor affecting rotifer community structure. In addition, the average annual GR′ of Lake Xiyanghu was <0, suggesting the dominancy of microphagous rotifers. Over time, S, D, d, and H′ were positively correlated with temperature and phosphorus levels in Lake Jinghu, but were negatively correlated with NH4+-N levels in Lake Xiyanghu. Only GR′ was negatively associated with chlorophyll-a in Lake Xiyanghu, implying that the functional index (GR′) might be an effective tool to explore the relationship between trophic state and the rotifer community in seriously eutrophic lakes.
Highlights
Eutrophication is still considered to be the most pressing water quality problem in both fresh and salt waters[1]
Both lakes showed clear seasonal variations in water temperature (WT) and secchi-disk (SD) clarity readings, with Water temperature (WT) ranging from 4.5 °C to 33.5 °C in both lakes and SD ranging between 0.67–0.87 m in Lake Jinghu and 0.2–0.7 m in Lake Xiyanghu
Lake Xiyanghu showed dramatically seasonal variations in Chl-a, total nitrogen (TN), NO3−-N, NH4+-N, total phosphorus (TP), and PO43− concentrations in contrast with values seen in Lake Jinghu (Fig. 1)
Summary
Eutrophication is still considered to be the most pressing water quality problem in both fresh and salt waters[1]. The functional diversity of crustacean zooplankton communities in 18 lakes in Canada experienced a linear decline over a TP gradient (as an index of trophic status), while species richness exhibited a unimodal relationship along the same gradient[18] This indicates that trophic state might be an important condition affecting functional crustacean zooplankter traits, including cladoceran and copepods. Obertegger & Mancan[29] conducted a case study of the change in GR′ over time, concluding that, compared with the smooth changes observed in taxon-based indices, a dramatic GR′ response to trophic state in rotifer assemblages was found in a deep subalpine lake, Lago Maggiore This implied that function-based parameters are more sensitive to trophic degree than are taxon-based indices, despite the fact that taxon-based indices can still be used as biological indicators for water quality and eutrophication. The effects of trophic state, water temperature, and other environmental variables on the functional traits of rotifer communities in subtropical lakes deserve further investigation
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