Preface: Stream ecology and environmental gradients.

This document is a preface to a special issue of the journal Hydrobiologia on the topic of stream ecology and environmental gradients. The preface explains that human activities have fragmented natural landscapes, leading to changes in environmental gradients and a decline in biodiversity. The document highlights the importance of understanding the effects of environmental gradients on aquatic communities and ecosystem services. The special issue includes 10 papers from authors of various nationalities, focusing on the effects of land use, vegetation cover, water pollution, and other disturbances on diatoms, macroinvertebrates, and fish communities. The studies demonstrate that environmental gradients can alter water quality, habitat availability, and the structure and composition of aquatic communities. The document concludes by expressing gratitude to the reviewers and authors who contributed to the special issue. [Extracted from the article]