Studies on Assessment and Effect of Seasonal Variations on Zooplankton and Water Quality Parameters of Freshwater Habitats in Dera Ghazi Khan Region, Pakistan

Abstract

Freshwater ecosystems are fundamental to the development and sustainability of human societies. The present study assessed water quality and planktonic communities at four sites within the Suleman Mountain Range, Dera Ghazi Khan Region, Punjab, Pakistan. This region supports distinctive freshwater habitats in the form of hill torrents and their associated pits and ponds. Physico-chemical parameters examined included humidity, air and water temperature, light penetration, pH, dissolved oxygen (DO), free carbon dioxide, carbonates, bicarbonates, total alkalinity, total hardness, sodium, calcium, magnesium, chlorides, sulphates, electrical conductivity (EC) and sodium adsorption ratio (SAR). Plankton density and diversity were evaluated through relative abundance and standard diversity indices (Margalef, Simpson, Shannon–Wiener, Evenness and Sørensen). Data were subjected to statistical analyses. Monthly variations in physico-chemical parameters were recorded across the four sampling sites. Water temperature ranged from 12.65 °C in January to 33.48 °C in July; light penetration from 15.43 cm in August to 31.75 cm in January; pH from 7.68 in January to 8.10 in May–July; DO from 5.77 mg L⁻¹ in July to 8.65 mg L⁻¹ in January; free CO₂ from 5.90 mg L⁻¹ in December to 8.82 mg L⁻¹ in June; carbonates from 11.03 to 17.90 mg L⁻¹ (June); bicarbonates from 472.50 mg L⁻¹ in December to 613.60 mg L⁻¹ in March; total alkalinity from 276.75 mg L⁻¹ in August to 342.50 mg L⁻¹ in May; total hardness from 213.70 mg L⁻¹ in September to 268.70 mg L⁻¹ in April; sodium from 107.50 mg L⁻¹ in July to 186.90 mg L⁻¹ in April; calcium from 169.80 mg L⁻¹ in September to 222.0 mg L⁻¹ in May; magnesium from 44.28 mg L⁻¹ in September to 64.20 mg L⁻¹ in March; chlorides from 153.54 mg L⁻¹ in February to 243.44 mg L⁻¹ in April; sulphates from 204.84 mg L⁻¹ in September to 319.20 mg L⁻¹ in May; EC from 1.85 dS m⁻¹ in August to 2.28 dS m⁻¹ in April; and SAR from 1.89 in December to 3.26 in April. Several parameters exhibited significant site-related differences (TDS, pH, CO₂, CO₃²⁻, HCO₃⁻, total alkalinity, total hardness, Na⁺, Ca²⁺, Mg²⁺, Cl⁻, SO₄²⁻, EC and SAR). Temperature, light penetration, pH, DO and CO₂ showed significant seasonal variation, while temperature, light penetration, TDS, DO and CO₂ varied significantly among months. A total of 119 planktonic taxa were recorded, of which 83 belonged to phytoplankton and 36 to zooplankton. Among phytoplankton, Chlorophyta was the most species-rich group (33 taxa) and Xanthophyta the least (4 taxa).