The effects of soil erosion on chironomid assemblages in Lugu Lake over the past 120 years

Abstract

Lakes in Yunnan Province, SW China, have been subjected to increased environmental stress over the last century. In order to assess the impacts of these stresses on the biota, a sediment core was collected from Lugu Lake covering the past 120 years, and detailed chemical, biological (subfossil chironomids), and physical analyses of the lake sediments were undertaken. The analyses indicated consistent trends of increased soil erosion since the early 1970s associated with significant changes in chironomid assemblages, which occurred simultaneously with the sedimentological proxies. A redundancy analysis (RDA) using a range of sedimentary proxies indicated that the shifts in the chironomid communities were mainly attributable to soil erosion. Constant soil erosion caused dramatic reductions in the available organic materials and large increases in fine sediments, leading to changes in the chironomid fauna and reduced chironomid abundance. The chironomid succession revealed that Procladius, the likely top predator in the chironomid community food chain, decreased in abundance under the impact of soil erosion, whereas the proportion of small forms of filter feeders, represented by Tanytarsus mendax‐type, increased rapidly. Due to the loss of suitable habitats, the population of some bottom collector‐gatherers (e.g., Polypedilum nubeculosum‐type) decreased sharply. The results of this study suggest that increased catchment soil erosion may seriously impact benthic communities and potentially alter ecosystem functioning.

Long-chain n-alkenes in recent sediment of Lake Lugu (SW China) and their ecological implications

“…In contrast, TP abundances significantly increase in section I of the LG-1 core (Fig. 3c), which could be caused by catchment soil erosion and anthropogenic sewage inputs to the lake (Zhang et al, 2013). TOC/TN ratios (molar ratio) in the LG-1 core sediment are in the range of 8.6-11.1, and generally exhibit a decreasing trend from bottom to the top core (Fig.…”

“…The Lake Lugu region has a subtropical monsoonal climate, with 926 mm annual precipitation (two-thirds of the precipitation during summer monsoons), a mean annual temperature of 12.5 • C and mean summer and winter temperature of 17.6 • C and 6.2 • C, respectively (Guo et al, 2013). The lake is mainly charged by karst groundwater and by precipitation and is located in the catchment of the Yalong River, which is a tributary of the Yangtze River (Zhang et al, 2013). Lake Lugu is currently clear and oligotrophic with a Secchi depth up to 15 m and total phosphorus (TP) concentration of 18.5 g/L.…”

“…Decrease of the algal (species A eustigmatophyte and S. quadricauda) productivities since 1982 is probably a result of climate (especially temperature) changes and human activities around the lake (Guo et al, 2013;Zhang et al, 2013). A causal relation was generally present between cold weather and low algal productivity, because a slight variation in temperature can have a dramatic effect on phytoplankton organisms due to their low temperature compensation ability (Liu et al, 2013).…”

“…Lake Lugu is an oligotrophic alpine lake in Yunnan Province, SW China, and is an ideal site for studies of responses of lake ecosystems to climate changes due to its continuous sedimentation, lack of industrial pollution and low population density in the catchment (Zhang et al, 2013). Nevertheless, some anthropogenic activities around the lake could change the local environmental conditions, including increased agriculture since 1940s, large-scale deforestation in 1970s and 1980s and tourism growth since 1990s (Zhang et al, 2013;Guo et al, 2013).…”

“…Nevertheless, some anthropogenic activities around the lake could change the local environmental conditions, including increased agriculture since 1940s, large-scale deforestation in 1970s and 1980s and tourism growth since 1990s (Zhang et al, 2013;Guo et al, 2013). Deforestation is generally associated with erosion, which increases both sediment and nutrient load in the lake (O'Reilly et al, 2005).…”