Abstract

BackgroundThe restoration of lake ecosystems requires a good knowledge of the lake’s history and the driving mechanism of environmental changes. In this study, we used Lake Datong, the largest inland lake in Hunan Province China, as an example to study the effects of aquaculture, based on historical data of aquatic creature, diatom inferred-total phosphorous (DI-TP) data, and an Ecopath model. Lake Datong has undergone several stages of aquaculture from 1980, with a rapid increase in fish production and fish feed supplementation at each stage. Its water quality has deteriorated since the introduction of aquaculture and the lake has become moderate eutrophic status.ResultsAccording to the DI-TP data, before 1930, Lake Datong was in a mesotrophic status (50–60 μg/L DI-TP). Between 1930 and 1980, the number of nutrient-tolerant species increased slightly, which indicates a nutrient increase in the lake (66–83 μg/L DI-TP). From the 1980s to 2010 and especially since 2000, eutrophication increased rapidly, with eutrophic species dominating the diatom assemblage, such as Stephanodiscus hantzschii, S. minutulus, and a sudden decrease in Aulacoseira granulata (< 10%). The annual average DI-TP concentration was 202 μg/L. After 2010, DI-TP decreased to 127–152 μg/L. In 2019, consumer biomass in Lake Datong was very low because the large-scale aquaculture was restricted by local government. The biomass of submerged macrophytes was relatively high, indicating that excessive primary producers had not been used by consumers and therefore, had not entered the food web. This led to a reduction in the energy transfer efficiency (TE) of the ecosystem.ConclusionsThe succession of the water ecosystem of Lake Datong is reappeared by DI-TP analysis and historical reference data. Lake Datong has experienced four stages of eutrophication succession following the introduction of aquaculture activities, with dramatic changes in the composition and biomass of its aquatic creatures. After comprehensive management in 2017, the consumer biomass of Lake Datong was at a relatively lower level, and the biomass of submerged macrophytes was higher, meaning a large quantity of primary producers had not been used by consumers, thus had not entered the food web, which consequently reduces the energy TE of the ecosystem. Future management needs to pay attention to making a suitable macrophyte harvest plan, stocking herbivorous and omnivorous fish, and establishing rational fishing, which can not only enhance the energy flows and nutrient cycling of the ecosystem, but also improve the food web structure. Our results provide important reference values and theoretical support for decision-makers and stakeholders in the subsequent management of similar shallow lake-water ecosystems.

Highlights

  • Aquaculture provides nearly 20% of the average daily protein intake of ~ 3.1 billion people across the world [1]

  • Succession of phytoplankton species composition in Lake Datong The abundance and biomass of phytoplankton in Lake Datong remained at a low level, while phytoplankton species have experienced great changes in the past 60 years (Table 1)

  • In 2019, the results of the survey showed that the distribution of phytoplankton in Lake Datong had obvious spatial heterogeneity, with an overall trend of increasing from northeast to southwest (Additional file 3)

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Summary

Introduction

Aquaculture provides nearly 20% of the average daily protein intake of ~ 3.1 billion people across the world [1]. China produces more aquaculture products than any other country, and it accounts for nearly two-thirds (62.1%) of the total supply [2]. According to previous studies in the neighboring provinces of Lake Datong, the total nitrogen (TN) and total phosphorus (TP) concentrations in lake-water column were 219% and 150% higher in culture areas than in non-culture ones [6, 7], respectively. Such high TN and TP concentrations could cause the oxygen depletion, eutrophication, and turbidity of aquaculture lakes [6, 8,9,10]. Its water quality has deteriorated since the introduction of aquaculture and the lake has become moderate eutrophic status

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