Ecological Influences of Water-Level Fluctuation on Food Web Network

Seasonal water-level fluctuations may lead to changes in river nutrients, which causes corresponding changes in the trophic structure of an aquatic food web, and finally affects the whole ecosystem. In this study, we focused on the Ganjing River, a tributary of the Yangtze River, China. Common organisms were sampled and measured for carbon and nitrogen stable isotopes in the wet and dry seasons, respectively, and the relative contributions of different food sources were combined to construct the food web, so as to realize the influence of water-level fluctuation on aquatic food web. Our results showed that basal food sources for fish consumers were endogenous carbon sources such as POM, zooplankton and zoobenthos in the dry season, while high water level exposed fish to more diverse and abundant food sources, and the contribution proportions of exogenous carbon sources (e.g., terrestrial detritus) to consumers increased in the wet season. In parallel, the abundance and species diversity of fish were higher than those in the dry season. Most fish species had relatively higher trophic levels in the dry season compared to the wet season, because the increase in fish densities led to an increase in piscivores fish. The food web was composed of planktonic and benthic food chains in the dry season. During the wet season, the planktonic food chain was dominant, followed by the herbivorous food chain, and the benthic food chain was relatively less important. Therefore, water-level fluctuation may alter the trophic linkages within fish communities, which contributed to a more complex and interconnected food web. Moreover, as we expect, the stable isotope analysis food web was broadly in line with the gut content analysis food web.

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Seasonal Water Level Fluctuation and Concomitant Change of Nutrients Shift Microeukaryotic Communities in a Shallow Lake

Water ◽

10.3390/w12092317 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2317

Author(s):

Yang Liu ◽

Ze Ren ◽

Xiaodong Qu ◽

Min Zhang ◽

Yang Yu ◽

...

Keyword(s):

Water Level ◽

Soluble Reactive Phosphorus ◽

Dry Season ◽

Water Level Fluctuation ◽

Water Level Fluctuations ◽

Rrna Gene ◽

Level Fluctuation ◽

Wet Season ◽

Concomitant Change ◽

Modular Structures

Seasonal water level fluctuations (WLFs) impose dramatic influences on lake ecosystems. The influences of WLFs have been well studied for many lake biotas but the microeukaryotic community remains one of the least-explored features. This study employed high-throughput 18S rRNA gene sequencing to investigate the spatiotemporal patterns of microeukaryotic communities in the dry and wet seasons with concomitant change of nutrients in Poyang Lake, which experiences huge seasonal WLFs. The results showed that the dry season and wet season had distinct microeukaryotic community compositions and structures. In the dry season, Ciliophora (13.86–40.98%) and Cryptomonas (3.69–18.64%) were the dominant taxa, and the relative abundance of these taxa were significant higher in the dry season than wet season. Ochrophyta (6.88–45.67%) and Chlorophyta (6.31–22.10%) was the dominant taxa of microeukaryotic communities in the wet season. The seasonal variation of microeukaryotic communities was strongly correlated to seasonal nutrient variations. Microeukaryotic communities responded significantly to dissolved organic carbon, total nitrogen, nitrate, and soluble reactive phosphorus in the dry season, and correlated to nitrate and total phosphorus in the wet season. The microeukaryotic community showed different modular structures in two seasons, and nutrient variations were the key factors influencing seasonal variations of the modular structures. Moreover, microeukaryotic community networks based on different seasons indicated that the microeukaryotic community co-occurrence patterns were not constant but varied largely associating with the nitrogen and phosphorus variations under the effects of WLFs. Our results are important for understanding how microeukaryotic communities respond to nutrient variation under seasonal water level fluctuation.

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Carbon sources for aquatic food webs of riverine and lacustrine tropical waterholes with variable groundwater influence

Marine and Freshwater Research ◽

10.1071/mf15365 ◽

2017 ◽

Vol 68 (3) ◽

pp. 442 ◽

Cited By ~ 7

Author(s):

N. E. Pettit ◽

D. M. Warfe ◽

P. G. Close ◽

B. J. Pusey ◽

R. Dobbs ◽

...

Keyword(s):

Food Web ◽

Food Webs ◽

Isotope Analysis ◽

Carbon Sources ◽

Freshwater Wetlands ◽

Food Sources ◽

Web Studies ◽

Aquatic Food Webs ◽

Aquatic Food ◽

Groundwater Reserves

Food web studies integrate ecological information and provide understanding of ecosystem function. Aquatic ecosystems of the Kimberley region (north-western Australia) have high conservation significance as hotspots for maintaining local and regional biodiversity. This study investigated the influence of waterhole type and persistence on the strength of consumer reliance on local energy resources for aquatic food webs. Changes in water isotopic composition indicated groundwater inputs were enough to overcome evaporative losses in some waterholes. Other waterholes had varying levels of isotope enrichment suggesting insufficient groundwater input to ‘compensate’ for evaporative loss. C and N isotope analysis indicated considerable overlap among energy sources in waterholes between macrophytes and periphyton but gradient analysis indicated that periphyton is a major carbon source for aquatic consumers. Groundwater-fed waterholes appeared to have higher quality food sources (indicated by lower C:N ratios), but there was minimal evidence that direct groundwater contributions were related to food web processes. Nonetheless, in a region where groundwater is influential in maintaining aquatic habitats, future development of groundwater reserves will likely affect the ecological and cultural value of freshwater wetlands by either reducing their permanence or size or indirectly through possible alteration to the role of periphyton in supporting the food web.

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