Impacts of Water Quality Changes on Eutrophication and Phytoplankton in the Coastal Areas of Chonburi Province in 2022

Abstract

Background and Objectives : The coastal area of Chonburi Province serves as a critical economic hub of Thailand, primarily driven by its tourism, industry, and fisheries sectors. This region boasts abundant natural resources and iconic attractions, including beaches, coral reefs and mangrove forests, which contribute significantly to the nation's economic development. However, rapid urbanization, industrial expansion, and increasing tourism activities have exerted pressure on the coastal environment, leading to declining water quality. Key contributors to this issue include wastewater discharge from communities and tourism establishments, along with nutrient enrichment from water circulation in the Gulf of Thailand. These factors promote eutrophication, often resulting in frequent and large-scale phytoplankton blooms. The proliferation of phytoplankton can severely deplete dissolved oxygen levels, causing hypoxic conditions that threaten marine organisms and ecosystems, ultimately reducing biodiversity and impairing ecosystem functions. Recognizing the critical need to address these challenges, this study aims to explore the intricate relationships between water quality parameters, eutrophication, and phytoplankton community composition in the coastal waters of Chonburi Province. The research will focus on identifying key factors associated with eutrophication and phytoplankton bloom formation. Additionally, it seeks to develop robust monitoring systems and early-warning mechanisms to minimize adverse impacts, ensuring sustainable management and effective mitigation of future environmental challenges in the region.

Methodology : Water quality and phytoplankton samples were collected from four coastal monitoring stations in Chonburi Province: Laem Tan, Wannapha Beach, Bang Phra, and Koh Loi, between June and December 2022, to investigate the relationship between water quality and phytoplankton dynamics. General water quality parameters, such as temperature, salinity, dissolved oxygen, and pH, were measured using a YSI Model 2030 and a pH meter. Surface water samples were collected at a depth of 30 cm to analyze total suspended solids (TSS), chlorophyll a, ammonia, nitrite, nitrate, phosphate, silicate, total dissolved nitrogen (TDN), and total dissolved phosphorus (TDP) in the laboratory. Phytoplankton samples were obtained by filtering 40 liters of water from a depth of 50 cm through a 20-micron plankton net. These samples were then examined under a microscope to classify and count phytoplankton present, allowing for an assessment of their diversity and density. A comparative analysis of water quality and phytoplankton differences across locations and time periods was conducted using One-way ANOVA. Additionally, Pearson’s correlation coefficient and Multiple Linear Regression analysis were performed using Minitab Statistical Software to identify the factors influencing changes in water quality and the composition of phytoplankton in the study area.

Main Results : The results of the general water quality study revealed average values for key parameters, including temperature (30.0±1.3°C), salinity (24.4±5.4 psu), pH (8.1±0.3), dissolved oxygen (4.6±1.5 mg/l), suspended solids (65.3±88.8 mg/l), and chlorophyll a (15.4±29.4 µg/l). Most values were within the standard criteria for coastal water quality suitable for aquaculture, except for chlorophyll a, which exceeded the standard. The elevated chlorophyll a level indicated significant eutrophication, ranging from Eutrophic to Hypertrophic throughout the study period. This was particularly evident in August at the Wannapha Beach station, where a phytoplankton bloom of Bellerochea spp. was observed. The study of dissolved nutrients showed average concentrations of ammonia (186.8±169.0 µg/l), nitrite (17.5±21.5 µg/l), nitrate (67.1±115.8 µg/l), phosphate (29.8±22.2 µg/l), silicate (413.1±195.3 µg/l), total dissolved nitrogen (44.7±24.9 µg/l), and total dissolved phosphorus (44.7±24.9 µg/l). Ammonia concentrations often exceeded standard levels, especially in October. Phytoplankton diversity analysis identified 55 genera from four major classes: Cyanophyceae, Chlorophyceae, Bacillariophyceae, and Dinophyceae. Dominant genera included Chaetoceros spp., Coscinodiscus spp., and Thalassiosira spp., consistently present at all stations. The analysis of the relationships between various factors revealed that rainfall has a negative correlation with water salinity, as rainfall can reduce salinity in coastal areas. Meanwhile, chlorophyll-a is positively correlated with suspended solids and ammonia. Additionally, it was found that the density of Cyanophyceae phytoplankton increases when ammonia levels in the water are high, indicating the occurrence of eutrophication and phytoplankton blooms in the area.

Conclusions  : The study on the correlation of water quality on eutrophication and phytoplankton in the coastal areas of Chonburi revealed that water quality parameters did not vary significantly across the stations, likely due to the smooth flow and mixing of coastal currents. However, seasonal changes were observed, especially in October, when heavy rainfall contributed to an influx of nutrients, causing ammonia concentrations to exceed the standard levels. This nutrient enrichment led to higher chlorophyll concentrations and increased phytoplankton density. Analysis of chlorophyll a and nutrient levels indicated that the coastal waters of Chonburi were consistently classified as eutrophic to hypertrophic throughout the study period. Phytoplankton from the Bacillariophyceae class, such as Chaetoceros spp., Coscinodiscus spp. and Thalassiosira spp. dominated the phytoplankton community in the area. The study also identified ammonia as a critical factor driving eutrophication and phytoplankton blooms. To mitigate these impacts, regulation and continuous monitoring of ammonia concentrations exceeding the standard are essential. These measures aim to prevent potential ecological disturbances, maintain biodiversity, and safeguard the sustainability of fisheries and aquatic resources in the coastal waters of Chonburi Province.