Physical Variables in Freshwater Ecosystems

We consider three categories of physical variables that can be measured for different freshwater ecosystems: (1) variables measured or described at the catchment or sub-catchment scale (e.g., bathymetry, depth, topography, geology); (2) those in or near to the water (e.g., temperature, turbidity, solar radiation); and (3) variables used to describe the substrate (e.g., particle size, mineral vs. peat). In this chapter we consider the practical aspects of undertaking a freshwater survey that includes measurement of physical variables; the approaches needed to undertake the survey; choosing a sampling strategy or protocol; practical tips on choice of measurement method or sensor, battery type, equipment calibration, resolution, accuracy, and links to literature providing further detail. The final section provides examples from a diversity of freshwaters where physical variables have been measured as part of an ecological survey, forming the evidence-base for management or conservation decisions.