Study of Surface Water Quality Using Biological Indicators Inside the Ruean Thai Pond Area, Nakhon Si Thammarat Rajabhat University

Abstract

Biological monitoring using macroinvertebrate bioindicators provides an ecologically integrative approach to water quality assessment, capturing cumulative pollution effects that physicochemical measurements alone cannot reflect. This study assessed the surface water quality of the Ruean Thai Pond, a natural spring-fed water body within Nakhon Si Thammarat Rajabhat University, using aquatic macroinvertebrate assemblages. Five sampling stations were established along the pond. Sampling was conducted four times over two months (September–October 2021), totaling 20 station-sampling events. Aquatic insect larvae and associated bioindicator organisms were collected using brick substrates and colander nets, then identified to family level and classified into water quality categories according to the Stream Detective Manual (Green World Foundation, 2018). A total of 13 bioindicator types (morphotypes) representing 5 orders and 9 families were recorded. Ephemeroptera was the most diverse order with 3 families (Leptophlebiidae, Potamanthidae, Baetidae), followed by Gastropoda and Trichoptera (2 families each), and Caridea, Odonata, and Hemiptera (1 family each). "Very clean water" bioindicators — branched-gill and feathered-gill mayfly larvae (Leptophlebiidae, Potamanthidae) and cased and uncased caddisfly larvae (Odontoceridae, Hydropsychidae) — dominated Stations 2–5, accounting for 54–78% of total bioindicator counts. Station 1 (pond entrance station) was the only station classified as "fair–clean," where fair-category organisms (n = 30) outnumbered very-clean-category organisms (n = 0). Four of five stations (80%) were consistently classified as "very clean water" across all sampling rounds, yielding an overall classification of "very clean" for the Ruean Thai Pond. These findings provide a preliminary wet-season biological assessment for university water resource management and for downstream community water-use planning.