Diatom community responses to long‐term multiple stressors at Lake Gusinoye, Siberia

Jennifer K Adams,Anson W Mackay,Neil L Rose,Alexander A Shchetnikov,Yumei Peng

doi:10.1002/geo2.72

Abstract

Global freshwater systems are threatened by multiple anthropogenic stressors via impacts on ecological structure and function necessary to maintain their health. In order to properly manage freshwater ecosystems, we must have a better understanding of the ecological response to human‐induced stressors, especially in multiple stressor environments. When long‐term observational records are scarce or non‐existent, paleolimnology provides a means to understanding ecological response to long‐term stress. Lake Gusinoye is a large, deep lake in continental southeast Siberia, and has been subject to multiple human‐induced stressors since the 19th century. Diatom assemblages since the late 17th century were reconstructed from a Lake Gusinoye sediment core to increase our understanding of the response of primary producer communities to centuries of environmental change. Records of anthropogenic contamination of Lake Gusinoye (as indicated by spheroidal carbonaceous particle, trace metal, and element records) indicate increases in regional and local development c. 1920. Diatom assemblages were initially dominated by Aulacoseira granulata, which declined beginning in the 18th century, likely as a response to hydrological change in the Gusinoye basin due to regional climate warming following the termination of the Little Ice Age (LIA). Significant diatom compositional turnover was observed since the 19th century at Lake Gusinoye. Since the early 20th century, Lake Gusinoye diatom assemblages have changed more profoundly as a result of multiple anthropogenic stressors, including nutrient influx, aquaculture, and wastewater discharge from the Gusinoozersk State Regional Power Plant. Recent diatom assemblages are dominated by Lindavia ocellata and nutrient‐rich species, including Fragilaria crotonensis and Asterionella formosa. Evidence of continued nutrient enrichment at Lake Gusinoye is likely due to aquaculture in the lake, and suggests potential interactive effects of warming regional temperatures and increasing nutrients (eutrophication).

Highlights

Whereas in polar regions increased beta-diversity is attributed to the limnological impacts of climate change, we argue that in Lake Gusinoye, species turnover is driven by multiple factors, notably impacts of development around the lake and its catchment over the past 100 years, alongside global warming in the past few decades
Lake Gusinoye is a multi-stressor environment, and numerous human-related changes in the Gusinoozersk region have been documented through the 20th century, all with the potential to impact ecological community structure and function
Trace metal and element records combined with spheroidal carbonaceous particle (SCP) concentrations indicate early impacts of regional and local development c. 1920 AD, concurrent with the onset of increasing livestock numbers and deforestation resulting in increased regional soil erosion

Summary

Introduction

Freshwater lakes are under threat globally from interacting stressors (Mills et al, 2017), including contamination from human activity (Malaj et al, 2014), enrichment from catchment agriculture (Mekonnen & Hoekstra, 2018) and aquaculture (Legaspi et al, 2015), increased warming of surface waters from climate change (O’Reilly et al, 2015), increased deposition of reactive nitrogen (Nr) (Bergstöm & Jansson, 2006), increased hypoxia due to human activities (Jenny et al, 2016), alterations to local biodiversity from biological introductions and invasions (Gallardo et al, 2016), hydrological modifications (Kominoski et al, 2018), and falling water levels from abstraction and shifting precipitation patterns (Wurtsbaugh et al, 2017). Lakes provide freshwater and protein for human populations, and the history of a lake is often intertwined with the regional history of human activity (Dodds et al, 2013; Jackson et al, 2016a). Even though the provision of freshwater ecosystem services is fundamental to human well-being, ecosystem functions are often compromised by human activity, threatening the health of the lake itself. Understanding which threats are most important for individual lakes is crucial to managing freshwater ecosystems, but because different threats have different causes, pinpointing when they first started to have a major impact on an ecosystem needs a long-term perspective (e.g. see Dubois et al, 2018 for a review). While long-term monitoring can provide some of these answers, such records are rather rare and not available for most lacustrine ecosystems. There are several long-term monitoring networks (e.g. The International Long-term Ecological Research (ILTR)

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