A common tool for measuring water clarity is the Secchi disk. One condition for its optimal use is that the disk be used when the sun is directly overhead. To comply with this condition means that there is a small window of opportunity for which monitoring conditions are ideal. Because of these daily considerations, it is often helpful to select consistent sampling times for many water quality parameters. However, ideal sampling times may also depend on tides, which could expose nothing but mud where there had been water only a few hours earlier.
Tidal stages vary from day to day.
Time of Year Environmental conditions change with the seasons, and monitoring results can reflect those variations. For example, nutrient and pesticide concentrations in estuaries vary considerably from season to season. More runoff enters the estuary during wet weather periods, delivering pollutants and fresh water. Consequently, pollution concentrations can be higher and salinity lower at these times. On the other hand, dry weather periods mean less runoff to the estuary.