16:45 〜 17:00
[AHW27-24] Impacts of Aquaculture on Water Resources and Coastal Environment in Southeast Asia
キーワード：養殖、栄養塩、水資源、沿岸環境
In Southeast Asia, the expansion of aquaculture in coastal areas including in the land as well as offshores is remarkable due to increased food demands. Brackish aquaculture in the land has generally 50% to 70% salinity of seawater, and the impact of leakage of brackish water into the ground would be significant. On the other hand, nutrient demand in the aquaculture is high, nutrient sequestration is large. However, such impact of expanding aquaculture on the groundwater and coastal environment hasn’t quantified enough. This study aimed to comprehensively clarify the impact on the groundwater and coastal environment in a coastal area in Java, Indonesia.
Our research areas mainly are three, Jakarta Bay, Indramayu city, and Semarang city. We collected water samples in each area.
In Indramayu, Cl- concentrations averaged 8,316 mg/L (minimum 1,660 mg/L to maximum 16,100 mg/L) in the coastal aquaculture (F) area, while 625 mg/L (minimum 11 to maximum 2,450 mg/L) in the surrounding farmland (A) area. Only about 50% of the groundwater in the surrounding agricultural land (A) area was below 200 mg/L, which is the water quality standard for tap water. Among nutrients, dissolved nitrogen, mostly in the form of NH4+-N, averaged 7.01 mg/L (maximum 12.97 mg/L) in the F area and 1.32 mg/L (maximum 3.19 mg/L) in the A area. On the other hand, NO3--N averaged 0.07 mg/L (maximum 0.31 mg/L) in Area F and 0.56 mg/L (maximum 5.23 mg/L) in Area A. Only three sites (10% of the total) had higher concentrations than NH4+-N. This was probably due to the low (almost -value) and reducing ORP values of the groundwater. Compared to the desirable concentration of 0.3 mg/L for NH4+-N as a water supply standard, more than 90% of the sites had concentrations above 0.3 mg/L. The δ15N-NH4 in groundwater in Area F was almost uniform, ranging from +2 to +5‰, and was equivalent to the isotopic ratio of adsorbable NH4 in sediments, suggesting that the sediments (especially clay layers) contributed to the desorption and dissolution of δ15N-NH4, while in Area A it varied greatly, ranging from -3 to +16‰, and the concentrations of -7 to +5‰ of chemical fertilizer and 0 to +10‰ of soil nitrogen, +5 to +8‰ of domestic wastewater, and +5 to +20‰ of livestock manure were assumed to be diverse sources. PO4 was also detected at high concentrations due to leaching from the sediments.
In this region, Cl-, NH4+, and PO4 contamination was observed in agricultural and urban areas throughout the alluvial plain, and especially in brackish water aquaculture areas. Consequently, the loss of water resources and increase of nutrient discharge to the ocean were associated with the expansion of coastal aquaculture.
Our research areas mainly are three, Jakarta Bay, Indramayu city, and Semarang city. We collected water samples in each area.
In Indramayu, Cl- concentrations averaged 8,316 mg/L (minimum 1,660 mg/L to maximum 16,100 mg/L) in the coastal aquaculture (F) area, while 625 mg/L (minimum 11 to maximum 2,450 mg/L) in the surrounding farmland (A) area. Only about 50% of the groundwater in the surrounding agricultural land (A) area was below 200 mg/L, which is the water quality standard for tap water. Among nutrients, dissolved nitrogen, mostly in the form of NH4+-N, averaged 7.01 mg/L (maximum 12.97 mg/L) in the F area and 1.32 mg/L (maximum 3.19 mg/L) in the A area. On the other hand, NO3--N averaged 0.07 mg/L (maximum 0.31 mg/L) in Area F and 0.56 mg/L (maximum 5.23 mg/L) in Area A. Only three sites (10% of the total) had higher concentrations than NH4+-N. This was probably due to the low (almost -value) and reducing ORP values of the groundwater. Compared to the desirable concentration of 0.3 mg/L for NH4+-N as a water supply standard, more than 90% of the sites had concentrations above 0.3 mg/L. The δ15N-NH4 in groundwater in Area F was almost uniform, ranging from +2 to +5‰, and was equivalent to the isotopic ratio of adsorbable NH4 in sediments, suggesting that the sediments (especially clay layers) contributed to the desorption and dissolution of δ15N-NH4, while in Area A it varied greatly, ranging from -3 to +16‰, and the concentrations of -7 to +5‰ of chemical fertilizer and 0 to +10‰ of soil nitrogen, +5 to +8‰ of domestic wastewater, and +5 to +20‰ of livestock manure were assumed to be diverse sources. PO4 was also detected at high concentrations due to leaching from the sediments.
In this region, Cl-, NH4+, and PO4 contamination was observed in agricultural and urban areas throughout the alluvial plain, and especially in brackish water aquaculture areas. Consequently, the loss of water resources and increase of nutrient discharge to the ocean were associated with the expansion of coastal aquaculture.