31 Jan. 2024, WEPA International Workshop in Hayama, Japan

Introducing the standard for
Bottom Dissolved Oxygen in Closed Water- Case Study of Water Environmental Policy Change in Japan -Sui KANAZAWA, IGES

11/23

Key points of the presentation
Target setting
Understandingof state ofwater quality• Why previous EWQS** alone wereinadequate?
• How the standard was establishedin the absence of sufficient specificscientific references?

Target setting for water
environmental conservation

Identificationof pollution source

Implementation ofmeasurements

Bottom DO*
Evaluation of measures& Policy reviewAmendment/Rechecking of Japanese water quality standards• New rationales and/or improved scientific approaches and information• Incorporation of different water quality parameters relative to new or changed pollution source• Change in water usage and consideration of an amended compliance period relative to thechange use.

To conserve the water environment,
it is essential to continually incorporate changes in how we view
environmental issues, applying sound scientific judgment
and ensuring the necessary revisions are made.
* Dissolved oxygen in bottom layer, **Environmental Water Quality Standard

Reference: https://www.env.go.jp/kijun/mizu.html, 水質汚濁に係る環境基準 (MOEJ)

2/23

1. Background“Why does Japan need to add new criteria, Bottom DO?”

2. Overview of bottom DO
3. Establishment of bottom DO standard
4. Future initiatives
5. Conclusion
3/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

1) The basic concept of EWQS

The basic concepts in Japan• Protection of human health• Conservation of the living environment• Defined its widest sense• Including natural biota* itself,
as well as the surrounding environment* Biota: the animals and plants living in a particular place, time, or habitat

4/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The purpose for EWQS 1/3

Appropriate water quality level according to living environment= Environmental Water quality standards (EWQS)

Example1. EWQS of COD for Coastal waters

 How much algae count in the state of prevention of red tide?

 How much organic matter is acceptable for sufficient DO to remain
after the organic matter decomposes?
TypeABCWater use, target fishery
Sea bream/真鯛, Yellowtail/ブリ, Seaweed/わかめ… , bathing,conservation of the natural environment, and uses listed in Type B

Mullet/ボラ, Seaweed laver/ノリ, …industry water,and uses listed in Type C

Conservation of the environment

COD≤2mg/L≤3mg/L≤8mg/L

5/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The purpose of EWQS 2/3

Example2. EWQS of TN and TP for Coastal waters

Past survey results
Quantitative relationship between N and P conc. - water quality indicators in the sea.
Higher nitrogen and phosphorus concentrations▷ increased chlorophyll α & COD conc. ▷ reduced transparency & summer bottom DO.

Purpose of sea area use and desired N & P conc. levels

a. Conservation of the natural environmentb. Marine recreation/ bathingac. Conservation of the aquatic ecosystem
Low oxygen zone
Progresses of eutrophication
💦💦
▷ increased organic matter due to internal production▷ Occurred low oxygen zone in the bottom layer▷ Effects on aquatic organisms (especially benthic organisms)◎ To maintain a minimum DO in bottom to ensure the survival of benthic organisms

d. Fisheries
Aquatic organisms living in the bottom layer
Eutrophication ▷ Changes in catch compositioneg. Increased abundance of planktonic sardines and clams<-> decreased catches of shrimp and crabs due to oxygen deficit in the bottom layer.
◎ Analyzing aquatic organisms with catch changes during eutrophication progression
to determine necessary water quality levels for fisheries.

6/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The purpose of EWQS 3/3

Example2. EWQS of TN and TP for Coastal waters (1/2)-> What is the level of TN and TP relative to bottom DO and transparency
that should be maintained?
TypeIIIIII

IV

Water use, target fisheryConservation of the natural environment, and uses listed in Type II-III
Diverse aquatic organisms, including benthic fish and shellfish,
are harvested in a balanced and stable manner.
Benthic fish/底魚類(eg. Black porgy/クロダイ, Sea eel/ 鱧, …),
Shellfish/甲殻類 (Prawn/海老, Octopus/タコ, Clam/ハマグリ, …), bathing,
and uses listed in Type III-IV

Except for some benthic species, fisheries primarily target fish,
resulting in a high yield.
Sardines/イワシ, Dotted gizzard shad/コノシロ, Sea bass/スズキ,Flat fish/カレイ, Mantis shrimp/シャコ, Sea cucumber/ナマコ, …,and uses listed in Type IV
Specifically adapted aquatic organisms resilient to pollution are
the main focus of the harvest.
Sardines/イワシ, Short-neck calm/アサリ, …,
Industrial water, and Conservation of habitable environments for marine biotaTN

TP≤0.2mg/L≤0.2mg/L≤0.3mg/L≤0.3mg/L≤0.6mg/L≤0.6mg/L≤1mg/L≤17 mg/L

7/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The gap between the target and EWQS 1/3<Results of the monitoring> e.g. Tokyo bay• The results for COD, TN and TP have improved since 1982.
• The passing rate for TN and TP are 100%.
COD*Type Standard Passing rate
COD

TN

TN
TPTP
1982

2000

2020

A

≤2mg/L0%B≤3mg/L37.5 %

C≤8mg/L100 %II≤0.3mg/L

100 %

III

≤0.6mg/L

100 %

IV

≤1mg/L100 %II≤0.03mg/L

100 %

III

≤0.05mg/L

100 %

IV

≤0.09mg/L

100 %* The data presents bay representative values, calculated as the average of upper and lower tier annual averages for each type.

Reference: 東京湾岸自治体環境保全会議 令和2年度 東京湾水質調査報告書

8/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The gap between the target and EWQS 2/3

Appropriate water quality level according to living environment=EWQS
EWQS are achieved.
Q. Has the natural biota and their living environments been maintained?
A. Still observed low oxygen zone, red/blue tides and reduced catch.
e.g. Tokyo bay

Bottom DO and Transparency in Aug. 2020 Red tide occurrences
Bottom DOTransparency

20012020Catch variation of flat fish from 1958~2020

Reference: 東京湾岸自治体環境保全会議 令和2年度 東京湾水質調査報告書, 千葉県沿岸重要水産資源 令和3年度資源評価

9/23

1. Background “Why does Japan need to add new criteria, Bottom DO?”

2) The gap between the target and EWQS 3/3
Passing rates arealmost 100%!

Gap

The catch has notrecovered yet.

Water quality has improved, but healthy sea has not recovered.
Conventional indicators(COD, TN, TP,…) alone are not always adequate
to evaluate whether the environment is conductive to their growth.
Started to consider new indicators…
It is necessary to monitor "the aquatic environment itself"using "direct indicators" to determine direct impacts.
 The growth and reproduction of aquatic life
e.g. fish, shellfish
 The growth of aquatic plants
e.g. seaweed/ワカメ等の藻類,sea grass/アマモ等の維管束植物

As new criteria to be added,
We have begun to consider bottom DO & transparency.
10/23

1. Background
2. Overview of bottom DO
3. Establishment of bottom DO standard
4. Future initiatives
5. Conclusion
11/23

2. Overview of bottom DO
Bottom DO
One of the important factors for the growth and reproductionof aquatic life that use the bottom layer.

<In the case of ocean>
Low bottom DO -> Make it difficult for their growth-> Produces hydrogen sulfide -> Mass die-offs of aquatic life
DO in Tokyo Bay Widespread low oxygen zone occurs in summer.
Nutrients are released into the bottom layer.
-> Eutrophication is promoted.

Rise of bottom hypoxia zone
to the surface causes massdie-off of tidal flat organisms
such as clams.

Low oxygen zone💦💦

Restriction ofenvironment

Death of aquatic lifein the bottom layer

12/23

1. Background
2. Overview of bottom DO
3. Establishment of bottom DO standard“how was the standard for bottom DO establishedin the absence of specific scientific references?”

4. Future initiatives
5. Conclusion

13/23

3. Establishment of Bottom DO

1) Basic concept of establishing bottom DO
Basic concept Survival of Aquatic life (fish and shellfish) that live in the bottom layer Other associated organisms in the ecosystem Their production
are produced properly.

-> Preservation and restoration of environments that cansustain populations of aquatic life that use the bottom layer.
14/23

3. Establishment of Bottom DO standard2) aquatic life of target

Q. Do we need to preserve all aquatic livings?
A. It is important to maintain the population.
Three types of bottom DO targets:• Target to secure habitat for fish and shellfish• Target to secure fish and shellfish reproduction areas• Target to eliminate dead zones
Data for setting the criteria: low oxygen thresholds• 24hr- LC5: 24 hour lethal concentration for 5% of the test organisms• The survival of susceptible individuals is not even considered.
Susceptible individuals
eliminate inanimate area

15/23

3. Establishment of Bottom DO standard

3) Data supporting the establishment of the criteria
Target aquatic organisms: Fish and shellfish species• inhabit the public waters of Japan (sea areas or lakes)• use the bottom layer of the water body at any stage of their life history
Data of low oxygen tolerance thresholds(1) Derivation from experimental literature(2) Derivation from field observation literature Organized by developmental stage
Growth stage/ reproductive stage
Challenges in Incorporating Japanese Clam “Asari” Data in the criteria• Japanese clam: one of the national food of Japan e.g. Miso soup
• Ecological characteristics differ from other aquatic organisms.
Adultssurvive by closing.

Larvae (planktonic stage)
do not survive.
16/23

3. Establishment of Bottom DO4) Organization of low oxygen tolerance threshold by development stage
Data from experimental literature
Growth stage

シロメバル - JapaneseWhite Seaperch

3.3

マダイ - RedSeabream
シロギス- Japanese Whiting
ホシガレイ- Spotted Halibut
トラフグ- Tiger Pufferfish

2.6
2.6

キジハタ
- Hong Kong Grouper
クルマエビ- Kuruma Prawn

1.5

Reproductive stageガザミ- Asian Blue Crab

3.7

Data from observation literature
Growth stage
コオニスピオ- Pseudopolydora
paucibranchiata
シノブハネエラスピオ- Paraprionospio patiens

Reproductive stage
1.4
0.4

シャコ
- Japanese Mantis
Shrimp

4.0

2.5
2.5

1.2

(mg/L)
These data are excerpts.

Most aquatic organisms can maintain & restore their habitats for growth and reproduction.

-> bottom DO ≥ 4.0 mg/L

Aquatic organisms can maintain & restore their habitats for growth & reproduction.
-> bottom DO ≥ 3.0 mg/L (excluding organisms that require bottom DO ≥4.0 mg/L)
It allows the habitation of aquatic organisms with low oxygen tolerance (eg. small polychaetes)and serves as the minimum threshold for water bodies where dead zones are resolved.

-> bottom DO ≥ 2.0 mg/L

17/23

3. Establishment of Bottom DO5) Setting the target values
ClassIIIIII

Purpose of designation of water body

Bottom DO

In the growth/ reproduction stage, water bodies that maintain areasthat can support low hypoxia tolerance organisms.
Growth: クルマエビ - Kuruma Prawn, …
Reproduction: シロギス - Japanese Whiting,ヒラメ - Olive Flounder,…

In the growth/ reproduction stage, water bodies that maintain areasthat can support survival of the organisms
excluding those that require bottom DO ≥4.0 mg/L.
Growth:マナマコ - Japanese Sea Cucumber,シロギス - Japanese Whiting,ヒラメ - Olive Flounder,…
Reproduction:マハゼ-Acanthogobius flavimanus.,ヒラメ - Olive Flounder,
クルマエビ - Kuruma Prawn…

In the growth/ reproduction stage, water bodies that maintain areasthat can support high hypoxia tolerance organisms.
Growth:マハゼ-Acanthogobius flavimanus、
Reproduction:マナマコ - Japanese Sea Cucumber

Note Regarding the bottom dissolved oxygen levels, there is a certain correlation with existing environmental parameters such as COD,
total nitrogen, total phosphorus, etc. However, considering the differences in the objectives and methods of target setting,it is generally appropriate to consider a classification different from existing environmental standards, while referring to them.

≥4.0
mg/L

≥3.0mg/L≥2.0mg/L

18/23

3. Establishment of Bottom DO standard6) Designation of water body classes
 Organization of the characteristics of water body Where is the "out of scope" area for the criteria?

 Understanding of the growth condition of aquatic life Where is the zone to eliminate inanimate area?

 Selection of the target aquatic life to be conserved and reagitated Establish bottom DO target
based on low oxygen tolerance threshold and field observations

 Where is the conservation target zone for target species (reproduction stage)?
 Where is the conservation target zone for target species (habitation stage)?

 Designation of water body classes

Class I, ≥ 4.0mg/L

Class II, ≥ 3.0mg/L
Class III, ≥ 2.0mg/L
Out of scope

19/23

1. Background
2. Overview of bottom DO3. Establishment of bottom DO standard
4. Future initiatives
5. Conclusion
20/23

4. Future initiatives
Setting the target bottom DO as an environmental standard

Monitoring & evaluation of the actual condition of the environment

Integrate various measures & promote comprehensive water
environment conservation to view over medium- to long-terms• Conventional water pollution control measures• Restoration of aquatic vegetation
e.g. Seaweed and seagrasses◎ Keep an eye on the future ideal state of the water environment
21/23

1. Background
2. Overview of bottom DO
3. Establishment of bottom DO standard
4. Future initiatives
5. Conclusion
22/23

5. Conclusion
Bottom DO

Target setting
Target setting for water
environmental conservation

Understandingof state of water quality
Identificationof pollution source

To directly evaluate“the environment”
of aquatic organisms
for their growth and reproduction

Evaluation of control measuresand Policy review
Implementation ofmeasurements

Water quality has improved<-> the healthy sea has not recovered.

 Waiting indefinitely for sufficient scientific evidence
would mean environmental standards may never be established.
 Without the ability to assess the state of the water environment,
preservation and improvement efforts are impeded.
 To conserve the water environment, it is essential
to continually incorporate changes in how we view environmental issues,
applying sound scientific judgment and ensuring the necessary revisions
are made.
23/23