Effects of land-based trout farms on the benthic macroinvertebrate community in a Turkish brook

Benthic macroinvertebrates and physico-chemical parameters were surveyed at the source of the Karasu Brook in Bozuyuk, Bilecik Province, Turkey, and at the inlets and outlets of five rainbow trout farms that use the brook water and discharge effluents into it. The dissolved oxygen, pH, ammonia-nitrogen, nitrite-nitrogen, nitrate-nitrogen and total phosphorus in the farm effluents were within effluent standards for trout farming in different countries. The macroinvertebrate community in the brook consisted of Mollusca, Gastropoda (Physidae, Limnaedae, Planorbidae, Neritidae), Bivalvia (Spharidae), Annelidae, Oligochaeta (Tubificidae), Hirudinea (Glossiphonidae, Erpobdellidae), Arthropoda, Insecta (Chironomidae, Ephemerellidae) and Crustacea (Gammaridae, Asellidae). Tubificidae and Chironomidae were generally observed in all sampling stations; the highest abundance was in the inlets and outlets of the two farms nearest the source. The most common measures of biodiversity, i.e., richness, Simpson's index, Shannon-Wiener index and evenness, were used during the year-long study.