Title

Long-term zooplankton community records (1996-2017) for Lake Suwa (Japan)

Authors

Masaki Sakamoto¹⁾, Takamaru Nagata²⁾, Takayuki Hanazato³⁾, Yuichi Miyabara³⁾, Jin-Yong Ha⁴⁾, Ho-Dong Park⁴⁾, Hideshige Toda⁴⁾, Hye-Ji Oh⁵⁾, Yusuke Oda⁵⁾ and Kwang-Hyeon Chang⁵⁾

• 1) Department of Environmental and Civil Engineering, Toyama Prefectural University, Imizu, Japan
• 2) Lake Biwa Environmental Research Institute, Otsu, Japan
• 3) Institute of Mountain Science, Shinshu University, Suwa, Japan
• 4) Department of Mountain and Environmental Science, Graduate School of Science and Technology, Shinshu University, Matsumoto, Japan
• 5) Department of Environmental Science and Engineering, Kyung Hee University, Yongin-Si, Korea

Corresponding authors:

1) Masaki Sakamoto
Email: masaki@pu-toyama.ac.jp
Telephone: +81-766-56-7500
Fax: +81-766-56-6182
Address: Department of Environmental Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama 939-0398, Japan

2) Yuichi Miyabara
Email: miyabar@shinshu-u.jp
Telephone: +81-266-52-1955
Fax: +81-266-57-1341
Address: Institute of Mountain Science, Shinshu University, Kogandori 5-2-4, Suwa, Nagano 392-0027, Japan

3) Kwang-Hyeon Chang
Email: chang38@khu.ac.kr
Telephone: +82-31-201-2977
Fax: +82-31-202-8854
Address: Department of Environmental Science and Engineering, Kyung Hee University, 1 Seocheon-dong, Yongin-Si 446-701, Korea

ABSTRACT

The impact of eutrophication on aquatic ecosystems remains an important topic in aquatic ecology; however, recent successes in water quality restoration in highly eutrophicated water bodies present new research potential regarding re-oligotrophication. Successfully reducing nutrient loading from sewage treatment through restoration activities, induces large changes in phytoplankton composition and biomass, particularly replacement of cyanobacterial dominance. In Lake Suwa, a shallow eutrophic lake in central Japan, recovery has occurred due to water quality restoration efforts since the 1970s. The improvement of lake trophic state from hypertrophic to mesotrophic is accompanied by various changes, such as rapid decreases in biomass of phytoplankton, benthic invertebrates and planktivorous pond smelt, and increases in biomass of aquatic vegetation, mainly floating leaved plants. During re-oligotrophication, zooplankton are important because they are major secondary producers in lake ecosystems. In Lake Suwa, the Research and Education Center for Inland Water Environment, Shinshu University has collected bi-weekly zooplankton samples and analyzed species composition since 1996, when the lake was in a hypertrophic state with serious Microcystis blooms. Lake Suwa is one representative lake for re-oligotrophication in a shallow eutrophic system, and our zooplankton dataset can be used to understand the changes in ecosystem structure and function.

KEYWORDS

• rotifers
• cladocerans
• copepods
• zooplankton
• water temperature
• long-term monitoring
• oligotrophication
• Lake Suwa

INTRODUCTION

Lake Suwa is a representative non-stratifying (or weak stratification) lake according to the Plankton Ecology Group (PEG) model of seasonal succession of planktonic events (Sommer et al. 1986). The lake is characterized as a shallow eutrophic lake, having non-limiting concentrations of nutrients and consequent high growth of summer phytoplankton populations. Repeated summer algal blooms have been observed since the 1940s, with Microcystis being the dominant bloom-forming cyanobacteria (Park et al. 1993). Serious summer algal blooms became notorious annual events, affecting not only the lake ecosystem, but also impacting human communities in the surrounding areas. Therefore, increased research regarding impacts on plankton communities, benthic invertebrates and food web perspectives has occurred (Yoshioka et al., 1994; Hanazato et al. 2001; Yokoyama and Park 2002; Chang and Hanazato 2004).

Since the 1970s, efforts to improve water quality have been made, including construction of sewage water treatment facilities, and the trophic index has decreased since 2000. Transparency of the lake water increased from about 50 cm in 1996 to a maximum of 201 cm in 2017 (Miyabara, unpublished data ), coinciding with decreases of total nitrogen (TN) and total phosphorus (TP) concentrations (Hanazato et al. 2009; Miyabara 2013). Improved water quality has resulted in apparent changes to the phytoplankton community, with dominant cyanobacterial species changing from Microcystis spp. to Aphanizomenon flos-aquae, and total biomass of cyanobacteria is continuously decreasing. Additionally, species composition of phytoplankton has changed and the number of species generally found in oligotrophic to mesotrophic lakes has increased, such as filamentous Mougeotia (Futatsugi et al. 2015). Changes in phytoplankton communities due to “re-oligotrophication” can directly and indirectly affect food web structure. Phytoplankton changes are one of the most apparent effects of water quality restoration efforts, which can increase plankton richness (Özkan et al. 2016). In response to the trophic state of Lake Suwa, various ecosystem structure and function effects have occurred. For example, increased transparency has allowed for the proliferation of aquatic vegetation (dominated by Trapa japonica); however, biomass of benthic macroinvertebrates (e.g. Chironomid larvae) and fish (e.g. pond smelt, Hypomesus transpacificus nipponensis) have decreased (Hirabayashi et al. 2003; Miyabara and Yoshida 2016).

Over the last few decades, developing countries have attempted to restore water quality, and many have been successful. Biological communities, particularly phytoplankton and fish, rapidly respond to improved water quality such as phosphorus reduction (Jeppesen et al. 2002); however, the results of re-oligotrophication are not always favorable to stakeholders. The decrease of fish biomass is an important issue for freshwater fisheries. Re-oligotrophication is a relatively new phenomenon, and reliable information on the response of lake ecosystems is insufficient. In Lake Suwa, aquatic ecosystem changes are still progressing and can be used as reference for other shallow eutrophic water bodies undergoing water quality restoration.

Zooplankton play a key role in nutrient cycling because they are direct grazers on phytoplankton and an important food source for higher trophic level organisms, such as fish. Monitoring the response of zooplankton communities to re-oligotrophication is as necessary as monitoring eutrophication effects on aquatic ecosystems (Straile and Geller 1998). Lake Suwa zooplankton data were collected from a period of Microcystis spp. bloom, to the current status of phytoplankton composition changes (1996-2017). Thus, the data are useful for understanding effects of water quality restoration and managing resources and ecosystem services of the lake.

METADATA

1. TITLE

Long-term zooplankton community records (1996-2017) for Lake Suwa (Japan)

2. IDENTIFIER

ERDP-2017-06

3. CONTRIBUTER

A. Dataset Owner

B. Dataset creators

• Masaki Sakamoto, Department of Environmental and Civil Engineering, Toyama Prefectural University
• Takamaru Nagata, Lake Biwa Environmental Research Institute
• Yuichi Miyabara, Institute of Mountain Science, Shinshu University
• Jin-Yong Ha, Department of Mountain and Environmental Science, Graduate School of Science and Technology, Shinshu University
• Hye-Ji Oh, Department of Environmental Science and Engineering, Kyung Hee University
• Kwang-Hyeon Chang, Department of Environmental Science and Engineering, Kyung Hee University

C. Principal investigators

Masaki Sakamoto, Kwang-Hyeon Chang, Jin-Yong Ha, Takamaru Nagata, Hirokazu Takahashi, Masataka Sakuma, Sho Kimijima, Shin-ichiro S Matsuzaki, Yoshinori Ikenaka, Makoto Ishimota, Chika Yoshida, Yuichi Miyabara and Takayuki Hanazato performed the field surveys.

4. PROGRAM

A. Title

Long-term water quality monitoring in Lake Suwa

B. Personal

Organization: Shinshu University
Address: Kogandori 5-2-4, Suwa, Nagano 392-0027, Japan
Phone: +81-266-52-1955
Fax: +81-266-57-1341
Web Address: http://www.shinshu-u.ac.jp/

C. Funding

Shinshu University, Japan

D. Objectives

From the 1960s to 1970s, Lake Suwa underwent a period of strong eutrophication due to increased human activity around the lake. Since 1977, bi-weekly monitoring of water quality and plankton/benthos biomass at the center of this lake has been conducted by laboratory members of Suwa Hydrobiological Station, Shinshu University (current name: Research and Education Center for Inland Water Environment, Shinshu University). Monitoring has continued for four decades, in an effort to promote environmental studies and management of the lake ecosystem. Whole monitoring data (physicochemical data) during 1977–2011 is available through our previous reports (Okino and Hanazato 1997; Hanazato et al. 2003; Miyabara 2007, 2013) (for the data obtained from recent monitoring, please contact Y. Miyabara). Changes of the aquatic ecosystem are still progressing, but the observed changes can be used as a reference for other shallow eutrophic water bodies undergoing water quality restoration.

5. GEOGRAPHIC COVERAGE

A. Geographic description and position (based on WGS84)

Center of Lake Suwa, Japan: 36° 2′ N, 138° 5′ E

6. TEMPORAL COVERAGE

Methods of sampling and the procedures of counting and identification for collected zooplankton during the first two decades (1977-1995) had been different from the last two decades (1996-2017), and thus we arranged only the latter data in this paper. The temporal coverage of data described in this paper is as follows.

• Earliest sample date: 11 March 1996
• Latest sampling date: 5 July 2017

7. TAXONOMIC COVERAGE

Zooplankton data include 31 rotifer species (taxa), 9 cladoceran species (taxa) and 2 taxa (cyclopoid and calanoid groups) of copepods.

8. METHOD

A. Study site

Lake Suwa (Fig. 1) is located in central Japan (Nagano Prefecture) with an altitude of approximately 757 m. The surface area is 13.3 km² with a catchment area of 531 km². Mean depth is approximately 4 m with a maximum depth of 6 m (center of the lake).

Fig. 1. Sampling point in Lake Suwa.

B. Sampling, sample preservation and counting methods

Zooplankton samples were collected from the center of the lake (Fig. 1; depth of approximately 6 m) using a column sampler (an acrylic tube with 5.5-cm diameter and 2-m length). Three water columns from the surface to near bottom (from surface to 2-m depth, 2–4 m and 4 m to near bottom; total volume = 12.4 L) were collected and filtered with a 40-µm mesh net. The collected animals were fixed with 4% sugar-formalin (Haney and Hall 1973). We collected duplicate samples of zooplankton and one of the two was used for quantitative analysis. The fixed samples were concentrated to 5–20 mL (depending on zooplankton abundance) by settling for 24-h. Aliquots of 1 mL were used for counting rotifers and copepod nauplii. Whole samples were examined for enumeration of cladocerans and copepods (adults and copepodids): the densities of which were often less than one individual per liter. Samples were analyzed using a microscope at 40× or 100× magnification.

C. Taxonomy and systematics

Rotifers and cladocerans were identified to species or genus levels based on Mizuno and Takahashi (1991, 2000). Recently, a cladoceran Leptodora distributed in East-Asia is described as L. richardi (Korovchinsky 2009), therefore, we listed this species as L. cf. kindtii/richardi. Rotifers not clearly identified to the species level, primarily Asplanchna, Cephalodella, Conochilus, Monostyla, Mytilina, Philodina, Polyarthra and Trichocerca were grouped due to varying identification skills of researchers throughout the sampling period. We excluded Ascomorpha species data because we could not confirm the identification by previous samplers (for raw data, please contact Y. Miyabara). Copepods were classified into three groups, calanoids (mainly Eodiaptomus japonicus), cyclopoids (including multiple genera, adults and copepodids) and nauplius due to the difficulties in their identification.

9. DATA STATUS

Latest Update: 24 July 2017

Data were collected from March 1996 to July 2017. During this period, the sampling, sample preservation and counting methods were kept in the same manner. Data were continuously collected through July 2017, and the database was updated when new data were verified.

B. Metadata status

The metadata for the relevant period have been filled and stored with the raw data.

10. ACCESSIBILITY

A. License and usage rights

1) Acceptable use. The dataset should not be used for any illegal purpose or violate the rights of others. Dataset usage should be restricted to academic, research, educational, government, or other not-for-profit professional purposes.

2) Citation. Data users should appropriately cite the present paper in all publications or when citing metadata derived using our data.

3) Notification. Data users should notify the data owner (Y. Miyabara) by email before using the dataset. Publications based on this dataset should be sent (two reprints or a PDF file) to the data owner.

4) Collaboration. Data users are strongly encouraged to consider consultation, collaboration and/or co-authorship with the corresponding authors (M. Sakamoto, K. H. Chang and Y. Miyabara).

5) Disclaimer. In no event shall any author, the data owner, or Shinshu University be liable for loss of profit or for any indirect or incidental damages arising from data use or interpretation.

B. Dataset Contact

Yuichi Miyabara
Institute of Mountain Science, Shinshu University, 5-2-4 Kogandori, Suwa 392-0027, Japan
Phone: +81-266-52-1955
Fax: +81-266-57-1341
Email: miyabar@shinshu-u.jp

C. Storage location

http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2017-06.1/jalter-en

The corresponding authors store the original data.

11. DATA STRUCTURE

A. Data tables

B. Format type

All data files are in ASCII text and comma-delimited (csv) formats.

C. Header Information

In the data files, the first row of each column represents the name of the variable.

D. Definitions of variables

Density data, except for Leptodora cf. kindtii/richardi, are shown as integer numbers. We calculated the density of L. cf. kindtii/richardi to one decimal place because of its very small numbers. A value of "0" in the density data (Suwa_rotifers.csv, Suwa_cladocerans.csv, Suwa_copepods.csv) indicates that we did not encounter this species during specimen counts. "NA" in Suwa_WT.csv means missing data.

12. ACKNOWLEDGENTS

The publication of this data paper was supported in part by Grants-in-Aid for JSPS BRIDGE Fellowship to K. H. Chang (Grant No. BR170902) and JSPS KAKENHI for Scientific Research (C) to M. Sakamoto (Grant No. 17K00584). We thank Edanz Group (www.edanzediting.com/ac) for editing a draft of this manuscript.

13. REFERENCES

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