Potential Indicator Value of Subfossil Gastropods in Assessing the Ecological Health of the Middle and Lower Reaches of the Yangtze River Floodplain System (China)

Application of subfossil Bosmina and its δ13C values in tracing the long-term food web dynamics of shallow eutrophic lakes: A case in Taihu Lake, southeast China

Cladoceran subfossil assemblages have been used successfully to trace the signals of long-term changes in lake eutrophication. However, their potential for reconstructing food webs has not yet been explored extensively. Here, we assess whether the stable carbon isotope analysis (SCIA) of subfossil Bosmina can be used to reconstruct the eutrophication and food web history of a shallow lake in southeast China. Two ²¹⁰Pb-dated sediment cores were collected from the western and central parts of Taihu Lake, one of the largest eutrophic lakes in the region. Multiproxy analyses of the cores were performed, including of the subfossil Bosmina assemblages, stable carbon isotopes of subfossil Bosmina (δ¹³C_s-bos) and bulk sediment (δ¹³C_org), total organic carbon (TOC), loss on ignition (LOI), C/N, total nitrogen (TN), and total phosphorous (TP). Stable carbon isotopes of living algae (δ¹³C_alg) and Bosmina (δ¹³C_l-bos) were also measured at the same sampling locations. The δ¹³C_s-bos gradually declined over time with reciprocal increases in the assemblages of subfossil Bosmina and total cladocerans and in the TOC, LOI, TN and TP in both cores. The δ¹³C_alg and δ¹³C_l-bos values further revealed depleted ¹³C. The changes in the δ¹³C_s-bos in relation to the other proxies indicated rapid nutrient enrichment and a possible shift in the food web in Taihu Lake, providing new insight into the reconstruction of food webs and eutrophication in shallow lakes in southeast China.

Application of Bipartite Networks to the Study of Water Quality

Water is a basic natural resource for life and the sustainable development of society. Methods to assess water quality in freshwater ecosystems based on environmental quality bioindicators have proven to be low cost, reliable, and can be adapted to ecosystems with well-defined structures. The objective of this paper is to propose an interdisciplinary approach for the assessment of water quality in freshwater ecosystems through bioindicators. From the presence/absence of bioindicator organisms and their sensitivity/tolerance to environmental stress, we constructed a bipartite network, G. In this direction, we propose a new method that combines two research approaches, Graph Theory and Random Matrix Theory (RMT). Through the topological properties of the graph G, we introduce a topological index, called J P ( G ) , to evaluate the water quality, and we study its properties and relationships with known indices, such as Biological Monitoring Working Party ( B M W P ) and Shannon diversity ( H ′ ). Furthermore, we perform a scaling analysis of random bipartite networks with already specialized parameters for our case study. We validate our proposal for its application in the reservoir of Guájaro, Colombia. The results obtained allow us to infer that the proposed techniques are useful for the study of water quality, since they detect significant changes in the ecosystem.