Stable Isotope Analysis Reveals the Importance of Riparian Resources as Carbon Subsidies for Fish Species in the Daning River, a Tributary of the Three Gorges Reservoir, China

Abstract

The patterns of carbon flow in large rivers influenced by dams are still not well known. We hypothesized that spatial variation in fish assimilation of basal production sources would be affected by heterogeneity of landscape-scale hydrology within a watershed due to the impoundment. We used stable isotope analysis and Bayesian mixing models to estimate relative contributions of basal production sources to fish consumers in a tributary of the Three Gorges Reservoir (TGR) with remarkably heterogeneous habitats between the upper and lower reaches. Model estimates indicated that riparian C 3 plants were the main basal food source irrespective of reaches or feeding groups. Autochthonous algae carbon also appeared to be important as secondary carbon sources. However, the major contributive aquatic algae in the upstream were benthic algae while planktonic algae were important in the downstream, and this difference was related to their distinct hydrological characteristics. The contribution from C 4 plants was comparatively less important to all fish consumers. Our results highlighted the significance of the riparian C 3 carbon source to fish consumers in the TGR tributary and that the difference in landscape-scale characteristics was not enough to influence the pattern, which may be attributed to abundant standing stock of the riparian plants as well as hydrologic regimes in this river.

Responses of Trophic Structure Variation in Fish Assemblage to Hydrologic Regulation in a Tributary of the Three Gorges Reservoir, China

“…These fish species could integrate the food carbon source from the mainstream. On the other hand, although the former study has verified that riparian C3 plants are the main basal food source irrespective of reaches or feeding groups (Deng et al, 2018), the CRs, which are indicative of food source diversity in the backwater area are significantly larger than those in the upper lotic reaches (Fig. 4).…”

“…Smaller NND and SDNND indicate greater trophic redundancy, which means, groups have more similar trophic niches (Abrantes et al, 2014; Masese et al, 2018). Because riparian plants are the major carbon source to fishes and widespread along the river channel (Deng et al, 2018), the range in potential source δ 13 C was similar for all sites, meaning that the community-wide metrics are comparable among sites and periods (Layman et al, 2007a). In order to provide more robust metrics that are unbiased with respect to variations in the number of groups and allow for statistical comparisons among sites and periods, Bayesian methodology was implemented to generate a posterior distribution of estimates of these metrics, thus providing a measure of uncertainty of these metrics for the fish communities at each site and period (Jackson et al, 2011).…”

“…For selected individuals, fish were weighed (g), measured (mm), and dissected to extract approximately 5-10 g of dorsal muscle tissue for isotopic analysis. Samples of basal carbon sources were also collected and detailed information are described in Deng et al (2018).…”

“…The Daning River is one of these important tributaries with less damaged natural landscape in particular in the pristine upper reaches. Previous study has analyzed whether the impoundment affected assimilation of carbon sources by fish consumers in this tributary (Deng et al, 2018 plants are the consistently major energy source for fish consumers irrespective of reaches or feeding strategies because of abundant standing stock of riparian vegetation and hydrologic regimes in this river (Deng et al, 2018). This tributary suffers the same hydrological regulation in the backwater accompanied by seasonal flood flows from the uppers as other tributaries in TGR.…”

Riparian forest subsidises the biomass of fish in a recently formed subtropical reservoir

“…Moreover, the where the geological location, geometry, hydrological pattern, system productivity, floodplain size and land use characteristics differ greatly (Wang et al, 2014). These conditions may explain the contrasting findings in the literature (Clapcott, 2003;Deng et al, 2018;Doi, 2009) and could also explain why these results differ from those found in other relatively close reservoirs within the La Plata Basin (Hoeinghaus et al, 2007). Moreover, the age of the impoundment may also play a role determining a higher allochthonous subsidy in the first years of creation (situation of our studied system) than in older impoundments.…”