Impact of brackish-water aquaculture activity on groundwater vulnerability in coastal alluvial plain: an evaluation to reach sustainability

概要

Doctoral Thesis

Impact of brackish-water aquaculture activity on
groundwater vulnerability in coastal alluvial
plain: an evaluation to reach sustainability

Anna Fadliah Rusydi
Graduate School of Integrated Arts and Sciences
Hiroshima University
March 2021

Outline of Dissertation

ABSTRACT
CHAPTER 1 INTRODUCTION
1.1 Groundwater Issues
1.2 Brackish-water Aquaculture and Possible Impact to Coastal Alluvial Groundwater
1.3 Objectives of Study
1.4 Structure of Thesis
CHAPTER 2 STUDY SITE AND ANALITYCAL METHODS
2. 1 Hydrogeology of Study Site
2. 2 Land Uses of Study Site
2. 3 Field Survey
2. 4 Sediment Analysis
2. 5 Water Quality Analysis
2. 6 Mapping and Statistical Analysis
2. 7 Contaminations of Saline water, Dissolved Metals, and Dissolved Inorganic
Nitrogen
2. 7. 1 Contamination of saline water
2. 7. 2 Contamination of dissolved metals
2. 7. 3 Contamination of dissolved inorganic nitrogen
CHAPTER 3 BRACKISH-WATER AQUACULTURE IMPACT ON SALINITY
IN GROUNDWATER
3. 1 Background
3. 2 Methods
3. 3 Results and Discussion
3. 3. 1 The hydrochemistry of groundwater
3. 3. 2 The ratio between cations and anions
3. 3. 3 The ratio of bromide and chloride
3. 3. 4 Stable isotopes ratios in water and sulfate
3. 3. 5 Potential sources of saline water
3.4 Summary

CHAPTER 4 BRACKISH-WATER AQUACULTURE IMPACT ON
DISSOLVED METALS IN GROUNDWATER
4. 1 Background
4. 2 Methods
4. 3 Results and Discussion
4.3.1 Concentrations and distributions of metals in the groundwater
4.3.2 Relationship metals concentrations with redox-sensitive parameters and
salinity
4. 4 Summary
CHAPTER 5 BRACKISH-WATER AQUACULTURE IMPACT ON NITROGEN
IN GROUNDWATER
5. 1 Background
5. 2 Methods
5. 3 Results and Discussion
5. 3. 1 Chemicals properties in sediment
5. 3. 2 Nitrate-nitrogen, nitrite-nitrogen, and ammonium-nitrogen contents in the
groundwater
5. 3. 3 Potential sources of ammonium-nitrogen in the groundwater
5. 3. 4 Relationship between Ammonium-Nitrogen and Water Chemical Properties
5.4 Summary: conceptual model of ammonium-nitrogen behavior in the groundwater
CHAPTER 6 DEGRADATION OF GROUNDWATER RESOURCES
6. 1 Vulnerability Status of Groundwater
6. 2 Loss of Groundwater Resource
CHAPTER 7 CONCLUSION
ACKNOWLEDGEMENTS
REFERENCES
APPENDICES

GENERAL SUMMARY
This dissertation thesis's main goal is to provide a comprehensive evaluation of
brackish-water aquaculture`s impact on the vulnerability of groundwater in the
coastal alluvial plain. Groundwater in coastal Southeast Asia is reported experiencing
a quality decrease because of human activities, e.g., urbanization and groundwater
extraction. However, research results show that the influence of brackish-water
aquaculture, a well-known Southeast Asia activity, is required for a deeper
investigation. An analysis of an integrated physio-chemical and stable isotopes in
Indramayu, which is one of the most extensive brackish-water aquacultures in
Indonesia, shows deteriorating conditions that are no less severe than other economic
activities. The comparison between the dominant land-uses in the study area shows
that brackish-water aquaculture (LC) groundwater significantly has higher saline
water content than agriculture and residential groundwater (UC). It is found that the
Cl− contents in LC groundwater is ranged from 1660 to 16,100 mg/L, averagely more
than 10-fold higher than UC groundwater. The highest Cl− concentration is observed
in confined LC groundwater within the depth of 20–30 m. The hydrochemistry data
and isotopes ratios of δ2H and δ18O in water confirm enrichment of seawater that is
intentionally introduced to the fishpond.
The results also highlight a significant correlation (P-value < 0.1) of high
salinity versus trace metals and ammonium-nitrogen contents. Whilst high salinity is
potentially categorized as an “anthropogenic” contaminant; the trace metals are
conceivably a “natural contaminant” that experience a dissolution process supported
by high salinity and reductive aquifer. In respect to reductive condition, both LC and
UC groundwater have NH4+–N as the predominant dissolved organic nitrogen as one
indication of the low-redox environment arise. Equal with Cl−, NH4+–N
concentrations in LC groundwater (from 2.4 to 13.0 mg/L) is higher (7-fold) than UC
groundwater. The δ15NNH4 values suggest mineralization of organic material in the
LC sediments as the primary source of NH4+–N. Furthermore, only in the LC site,
NH4+–N is significantly correlated with Na+, which implies that mobilization of
ammonium sediment to groundwater is promoted by cation exchange.

Finally, nearly 2 x 106 m3 confined groundwater in the LC region is
contaminated by Cl− and trace metals contaminations and vulnerable to elevated
NH4+–N. This groundwater is not recommended to directly use as clean water
because the concentrations of Cl−, SO42−, Na+, Fe2+, and Mn2+ are significantly higher
than the guidelines regulated by the World Health organization and Indonesian
Government.

SUMMARY CHAPTER 1 – 7

CHAPTER 1 INTRODUCTION
Chapter 1 describes general introduction, background, and objectives. There
are three subjects as the focus those are:
(i) Evaluation of saline water contamination determined from hydrogeochemical
characteristics (major cations and anions, and bromide concentrations) and
environmental stable isotopes (deuterium δ2H and δ18O in water, and δ34S and
δ18O in sulfate).
(ii) Evaluation of dissolved metals contamination and environmental factors that
contribute to their presence elucidated from arsenic, iron, manganese, salinity,
redox condition, dissolved organic, and geology features.
(iii) Evaluation of nitrogen contamination by analyzing dissolved in organic nitrogen,
stable isotope of nitrogen-15, and geology features.

CHAPTER 2 STUDY SITE AND ANALITYCAL METHODS
Chapter 2 provides knowledge related to selected study site, samples collection,
methods, and study literature. The area under study is Indramayu, which is located
on the north coast of Java Island, Indonesia (107°52′–108°36′ E and 6°15′–6°40′ W).
Indramayu is vital as a rice- and fish-production area with increasing gross domestic
regional product (GRDP) particularly in the farming and fishery sector. It is a
lowland area with groundwater level is generally 3.5 m.a.s.l and flows toward the sea.

The hydrogeology profile shows a thick clay in the north, which comprises a slight to
dense carbonate clay with shell fragments.
A total area of Indramayu is greater than 240,000 ha. The main land-use
categories are agriculture, brackish-water aquaculture, and residential. In this study
brackish-water aquaculture is consistently written as LC while other land-uses is
written as UC.
Samples are collected for sediments and groundwater. The sediments samples
are collected at different depths from two boreholes in UC and LC areas to
understand the geological conditions of the aquifer system. Groundwater samples
are collected two times, in August 2017 (dry) and November 2019 (very dry). There
are 18 groundwater samples (5 from LC; 13 from UC) and 28 groundwater samples
(10 from brackish-water aquaculture area; 18 from agriculture and settlement areas)
collected in the first and second sampling periods.
Water quality are analyzed both in the field and in the laboratory. Water
temperature (WT), pH, oxidation–reduction potential (ORP), dissolved oxygen (DO),
dissolved Fe (Fe2+), and bicarbonate (HCO3−) are measured as field parameters. The
laboratory analysis is conducted for three categories, those are chemicals parameter,
stable isotopes, and biological parameters. The chemical parameters are: (i) major
anions and cations, (ii) metals (arsenic, dissolved iron and manganese), and (iii)
dissolved inorganic nitrogen (nitrate, nitrite, and ammonium). The stable isotopes
analysis is for (i) Deuterium and

18

Oxygen in water, (ii)

34

Sulfur and

18

Oxygen in

sulfate, and (iii) 5Nitrogen in ammonium.

CHAPTER 3 BRACKISH-WATER AQUACULTURE IMPACT ON SALINITY IN
GROUNDWATER
Chapter 3 aims to respond to the first specific objective. This chapter describes
the possibility of elevated salinity in the groundwater system due to brackish-water
aquaculture activity. It provides a detail examination of the salinity level in
unconfined and confined groundwater by using hydrochemical approach. Also,

groundwater origin and saline water source is elucidated from stable isotopes of δ2H
and δ18O in water, and δ34S and δ18O in sulfate.
The hydrochemistry data coupled with stable H and O isotope ratios in water,
and stable S and O isotope ratios in sulfate reveals that brackish-water aquaculture
activity in selected study area potentially contributes to the elevated salinity. The
groundwater in the brackish-water aquaculture region has significantly different
chemical characteristic compared to agriculture and settlement areas. The chemical
properties of groundwater in the brackish-water aquaculture area are as follows:
1. The hydrochemical characteristics of groundwater indicates high saline-water
contents with characteristics as follows: (i) high and dominant contents of Cl─
and Na+; (ii) strong correlation between Na+ and Cl─; (iii) enrichment of Ca2+
concentration and depreciation of Na+ content; and (iv) a relatively high
Mg2+/Ca2+ ratio but significantly low HCO3─/Cl─ ratio.
2. The δ2H and δ18O compositions in water are significantly higher than other types
of land-use and situated in the vicinity of seawater mixing line. It implies high
saline-water content and evaporation process. Moreover, the impact of salinewater is likely more severe when the precipitation is reduced.
3. The comparison of δ34S and δ18O composition in groundwater and local seawater
describes the possibility of saline-water present in some samples. At the same
time, groundwater from agriculture and settlements potentially contaminates by
detergent and fertilizer.

CHAPTER 4 BRACKISH-WATER AQUACULTURE IMPACT ON DISSOLVED
METALS IN GROUNDWATER
This chapter presents explanation of the second specific objective. Also, it
determines the vulnerable area to dissolved metals contaminations and describes
environmental factors that potentially influence the increase in these metals'
concentration. This chapter has been published in Springer Nature Applied Sciences
(https://doi.org/10.1007/s42452-021-04385-y).

The results show that the groundwater of Indramayu is potentially vulnerable
to natural contamination of Fe2+ and Mn2+. On the other hand, the concentrations of
As are very low or under the threshold of drinking-water regulation. The most
vulnerable area is located primarily at the north tip of Indramayu, a brackish -water
aquaculture area composed of deltaic deposits. With respect to clean water
regulations, the groundwater in Indramayu requires treatment before utilization,
specifically focusing on Mn2+, then Fe2+. The significant different of metals
concentrations between two times of sampling periods are detected in several point
which the metals concentrations are increased significantly.
High salinity is suspected of supporting the leaching of Fe2+ and Mn2+ from
minerals and soils through ion-exchange processes. The reduced environment
indicated by DO and NO3−–N reduction is another crucial factor in the dissolution of
Fe2+ and Mn2+ from soils and minerals to groundwater. This reduction process is
possibly promoted by microorganisms and thus occurs as a function of organic
matter. Finally, it is necessary to consider Fe and Mn as damaging natural
contaminations to alluvial coastal aquifers. Consequently, appropriate groundwater
management strategy is required to maintain sustainability in the region.

CHAPTER 5 BRACKISH-WATER AQUACULTURE IMPACT ON NITROGEN
IN GROUNDWATER
Chapter 5 is the explanation of the third specific objective. This chapter
evaluates the predominant dissolved inorganic nitrogen (DIN) in the groundwater
system. Furthermore, potential sources of predominant DIN are elucidated from a
combination of stable isotope of

15

Nitrogen, coliform bacterial, major cations,

geology features, and land uses. This chapter has been published in Water
(https://dx.doi.org/10.3390/w13010025).
NH4+–N in the LC region, potentially originated mainly from the
mineralization of soil organic nitrogen to ammonium. In agreement with this origin,
the ratios of δ15N in the sediments indicate the mineralization of nitrogen in sediment.
However, contamination by anthropogenic activity is possible considering the high

values of total coliform bacteria. The strongly positive and significant relationship of
NH4+–N and Na+ suggests that under high salinity, the exchangeable NH4+ is
mobilized from sediments to the groundwater through cation exchange. Additionally,
the high salinity of groundwater possibly arises from the brackish-water pond.
Further, attenuation of ammonium-nitrogen from manure, sewage, and pit
latrines occurs in the groundwater in the UC region. Both total coliform and E. coli
values confirm this condition. The ratios of δ15N in several layers of sediments
suggest the possibility of nitrogen mineralization to ammonium; nevertheless, the
nitrogen contents suggest that this process is more likely in the sediments of lower
coastal region. The significantly lower salinity followed by weak and not significant
relationships of NH4+–N and all major cations indicate less possibility of NH4+–N
mobilize to groundwater through cation exchange.

CHAPTER 6 DEGRADATION OF GROUNDWATER RESOURCES
Analysis of hydrochemical parameters and environmental stable isotopes,
along with an evaluation of land-uses and geology features reveals that brackishwater aquaculture activity potentially contributes to groundwater quality degradation.
The groundwater is vulnerable to the following: (1) salinization (Cl−, SO42−, and Na+),
(2) dissolution of trace metals (Fe2+ and Mn2+), and (3) elevated concentration of
ammonium-nitrogen (NH4+–N). Furthermore, the groundwater vulnerability levels
and specific source for selected contaminants are diverse.
In general, salinity (reflected with Cl−), dissolved metals (reflected with Mn2+),
and NH4+–N concentrations are relatively low in the northern aquifer and gradually
increase to the southern aquifer. The confined groundwater losses due to brackishwater aquaculture activity are potentially ±2.8 x 106 m3 and 1.7 x 106 m3,
respectively due to salinity and trace metals contamination. Equally, there are
possibly ±1.8 x 106 m3 confined groundwater of brackish-water aquaculture site
vulnerable to elevated NH4+–N contents.

CHAPTER 7 CONCLUSION
The groundwater quality analysis results show that the brackish-water
aquculture activity contributes to high contents of saline water, dissolved iron and
manganese. In the meantime, although no indication of dissolved inorganic nitrogen,
the groundwater in LC site is potentially vulnerable to elevated concentration of
ammonium-nitrogen. Consequently, the groundwater is not suitable for drinkingwater purpose. In addition, this resource is possibly problematic in the future without
appropriate management. To protect the sustainability, the government should
consider groundwater resources carefully in management of brackish-water
aquaculture activity.

Published Paper
Rusydi AF, Saito M, Ioka S, Maria R, Onodera SI (2019) Estimation of ammonium sources
in Indonesian coastal alluvial groundwater using Cl− and GIS. Int J of Geomate
17(62):53–58. https://doi.org/10.21660/2019.62.4749
Rusydi AF, Onodera SI, Saito M, Hyodo F, Maeda M, Sugianti K, Wibawa S (2021)
Potential sources of ammonium-nitrogen in the coastal groundwater determined
from a combined analysis of nitrogen Isotope, biological and geological parameters,
and land use. Water 13(1), p.25. https://doi.org/10.3390/w13010025
Rusydi AF, Onodera SI, Saito M, Ioka S, Maria R, Ridwansyah I, Delinom R (2021)
Vulnerability of groundwater to iron and manganese contamination in the coastal
alluvial plain of a developing Indonesian city. SN Appl Sci 3: 399.
https://doi.org/10.1007/s42452-021-04385-y