Alternate trajectories in historic trophic change from two lakes in the same catchment, Huayang Basin, middle reach of Yangtze River, China

Abstract

In order to assess how best to manage impacted lake systems, one needs to understand the trophic functioning of the lake system and the recent states through which the lake may have transitioned. Lakes in the middle and lower reaches of the Yangtze have been heavily impacted over recent decades. In order to understand recent changes in functional status, we examined sediment cores covering the last 120 years from two lakes in the same catchment with differing status: one algal-dominated (Taibai Lake) and the other macrophyte-dominated (Longgan Lake). Chironomid head capsules were identified from both sites and an expanded chironomid-total phosphorus (TP) transfer function (21 sites were added to the 30-lake model previously developed by Zhang et al. 2006) was used to assess the lakes' response to recent anthropogenic change. Quantitative chironomidinferred TP (CI-TP) reconstructions showed that Taibai Lake experienced clear changes in trophic status since the 1860s. Before the 1950s, the CI-TP concentration was relatively stable around 50-80 lg L -1 , while it reached to 80-130 lg L -1 in the latter period. CI-TP for Longgan Lake, however, showed a relative decline from the range of 50-75 lg L -1 since the 1880s to 30-40 lg L -1 in recent years, accompanied by strong evidence from the chironomids for increased macrophyte biomass as TP levels declined. Both reconstructions agreed with diatom inferences of TP from the same lakes. The stark difference between these two sites is thought to reflect a function of macrophyte development, with Taibai Lake losing its plants through increased nutrient levels and internal recycling, whereas Longgan Lake, which is much bigger in area and hence potentially more resilient to change, was able to develop macrophyte communities over the same time period. The positive feedbacks associated with abundant macrophytes retained the clear water state of Longgan Lake, but a further increase in nutrients might lead to decrease in resilience of the relatively stable macrophyte state and loss of benthic pathways of primary production, which would push the lake towards eutrophication. Unless nutrient inputs to Longgan are controlled, Longgan Lake might lose macrophyte communities and follow a developmental pathway similar to that observed in Taibai Lake.

Refining the palaeoecology of lacustrine testate amoebae: insights from a plant macrofossil record from a eutrophic Scottish lake

“…These include plant macrofossils (Davidson et al 2005;Sayer et al 2010b), diatoms (Anderson et al 1993;Bennion et al 2011), cladocerans (Brodersen et al 1998;Davidson et al 2011), chironomids (Brooks et al 2001;Zhang et al 2012) and non-pollen palynomorphs (NPP) (Drljepan et al 2014;Volik et al 2016). Due to a lack of instrumental monitoring of lake conditions, palaeolimnological approaches are essential for assessing long-term trends, determining pre-disturbance conditions ) and for informing conservation strategies (Kowalewski et al 2013).…”

A century-scale, human-induced ecohydrological evolution of wetlands of two large river basins in Australia (Murray) and China (Yangtze)

“…The river sediment load of the Yangtze River between the 1960s and 1970s alone was more than 450 Mt yr −1 (Yang et al, 2011a, b). Consequently, many lakes experienced reduced flood retention capacity due to disconnection from the main channel of the Yangtze River by construction of embankments and sluice gates in the river channels, which was subsequently followed by widespread eutrophication (Yu et al, 2009;Zhang et al, 2012). Because of alterations in natural flood pulses, ephemeral and temporary lakes tended to have fewer taxa than semipermanent channels or terminal lake habitats (Sheldon et al, 2002).…”

Sediment records of the metal pollution at Chihu Lake near a copper mine at the middle Yangtze River in China

“…The increased nutrient input to Chihu Lake, caused macrophyte communities to flourish, and contribute the low TP concentration in the water. Brenner et al (1999) and Zhang et al (2012) have found this phenomenon in macrophytes-dominated shallow lakes. The gradual loss of the macrophytes near the mining area, including the CH1 site, risked the transformation of macrophytes domination to algae domination.…”