近日，陈光杰教授团队博士后Anna-Marie Klamt（现就职于南丹麦大学）作为第一作者以“The rise and fall of primary producers and consumers in a multiply-stressed shallow lake (Lake Qilu, China) over the last 200 years”为题，发表了关于近两百年来杞麓湖初级生产者和消费者响应流域开发与水环境变化的研究论文，该文章发表在国际SCI期刊《Ecological Indicators》（2020年环境科学与生态学大类学科二区期刊，影响因子：4.2）。
Lake Qilu is a large (surface area: >35km2) and shallow (average/maximum depth: 4/6.8 m) lake, located on the Yunnan-Guizhou Plateau. It has probably been nutrient-rich for several centuries since relatively high population densities in the catchment area are recorded for the Ming and Qing Dynasties (from the 14th century). However, anthropogenic changes were particularly big during the last century and comprised for instance eutrophication and water-level fluctuations. In this multi-proxy palaeo study, we investigated the response of primary producers and consumers to these disturbances.
Fig. 1. Time series of sedimentation rates of pigments (total carotenoids, chlorophyll derivatives, oscillaxanthin, and myxoxanthophyll).
We found that eutrophication and water-level changes (partly inferred by bisaccate pollen grains) are well-reflected in changes in sedimentation rates of pigments, diatom and cladoceran species composition and other proxies (e.g. Rhabdocoela oocytes). Specifically, the stepwise decrease in relative abundance of Pediastrum simplex compared to P. boryanum/P. duplex proved to be a good indicator for eutrophication intensity. Furthermore, reductions in the body size (i.e. coenobia diameter) of Pediastrum simplex were clearly related to phases of low visibility (“anti-sedimentation response”) that were caused by lake damming in the 1950s and by accelerating eutrophication in the 1990s. During the latter period, strong algal growth led to turbid conditions, which are indicated by the co-occurrence of the diatoms Fragilaria crotonensis, Aulacoseira ambigua and A. granulata, the green algae Staurastrum sp. as well as the cladoceran Anthalona cf. milleri. Our results also show that lake restoration measures have to be chosen carefully. For Lake Qilu, sediment dredging in the early 2000s resulted, despite short-term improvement, in a collapse of certain groups of primary producers and of the cladoceran community. Ultimately, this has favoured the present dominance of cyanobacteria in the heavily-stressed system.
Fig. 2. Time series of most abundant cladoceran species and genera. Lines show sedimentation rates in # cm− 2 yr− 1 and shaded areas show relative abundances in %.
This study highlights that subfossil remains, which are often found in, for instance, standard cladoceran analysis (green algae such as Pediastrum spp. and Staurastrum spp. or bisaccate pollen grains), can add valuable information to the reconstruction of past environmental conditions and biotic response. Such better and more holistic understanding of freshwater ecosystems is crucial to meet future challenges in a rapidly changing world. In particular, our results suggest that the relative abundance and body size of non-motile chlorophytes are sensitive and valuable proxies of eutrophication and light conditions, respectively, for (palaeo)limnological research. This finding is, to our knowledge, new to the literature. However, changes in abiotic conditions and biotic responses are complex and hence further research is needed to validate the applicability of this new proxy.
Fig. 3. Time series of selected subfossil remains (sedimentation rate of bisaccate pollen grains, sedimentation rate of Pediastrum spp. coenobia, relative abundance of Pediastrum spp. coenobia, body size (coenobia diameter) of Pediastrum simplex, and sedimentation rate of Staurastrum sp.).