The model allows the user to define two settling rates for each nutrient and the time of the year during which each settling rate is used. A variation in settling rates is allowed so that impact of temperature and other seasonal factors may be accounted for in the modeling of nutrient settling. To use only one settling rate for the entire year, both variables for the nutrient may be set to the same value. Setting all variables to zero will cause the model to ignore settling of nutrients in the water body.

The chlorophyll a concentration in the reservoir is calculated from the total phosphorus concentration. The equation assumes the system is phosphorus-limited. The chlorophyll a coefficient was added to the equation to allow the user to adjust results to account for other factors not included in the basic equation, e.g. nitrogen limitations.

A negative settling rate indicates that the reservoir sediments are a source of N. A positive settling rate indicates that the reservoir sediments are a sink for N.

A negative settling rate indicates that the reservoir sediments are a source of P. A positive settling rate indicates that the reservoir sediments are a sink for P.

For natural lakes, measured phosphorus settling velocities most frequently fall in the range of 5 to 20 m/year although values less than 1 m/year to over 200 m/year have been reported (Chapra, 1997). Panuska and Robertson (1999) noted that the range in apparent settling velocity values for man-made reservoirs tends to be significantly greater than for natural lakes. Higgins and Kim (1981) reported phosphorus apparent settling velocity values from –90 to 269 m/year for 18 reservoirs in Tennessee with a median value of 42.2 m/year. For 27 Midwestern reservoirs, Walker and Kiihner (1978) reported phosphorus apparent settling velocities ranging from –1 to 125 m/year with an average value of 12.7 m/year.

The table below lists recommended apparent settling velocity values for phosphorus (Panuska and Robertson, 1999):

A negative settling rate indicates that the reservoir sediments are a source of P. A positive settling rate indicates that the reservoir sediments are a sink for P.

For natural lakes, measured phosphorus settling velocities most frequently fall in the range of 5 to 20 m/year although values less than 1 m/year to over 200 m/year have been reported (Chapra, 1997). Panuska and Robertson (1999) noted that the range in apparent settling velocity values for man-made reservoirs tends to be significantly greater than for natural lakes. Higgins and Kim (1981) reported phosphorus apparent settling velocity values from –90 to 269 m/year for 18 reservoirs in Tennessee with a median value of 42.2 m/year. For 27 Midwestern reservoirs, Walker and Kiihner (1978) reported phosphorus apparent settling velocities ranging from –1 to 125 m/year with an average value of 12.7 m/year.

The table below lists recommended apparent settling velocity values for phosphorus (Panuska and Robertson, 1999):

The model allows the user to define two settling rates for each nutrient and the time of the year during which each settling rate is used. A variation in settling rates is allowed so that impact of temperature and other seasonal factors may be accounted for in the modeling of nutrient settling. To use only one settling rate for the entire year, both variables for the nutrient may be set to the same value. Setting all variables to zero will cause the model to ignore settling of nutrients in the water body.

A negative settling rate indicates that the reservoir sediments are a source of N. A positive settling rate indicates that the reservoir sediments are a sink for N.

The name of the reservoir and wetland nutrient record is a primary key referenced by the foreign keys nut in reservoir.res and nut in wetland.wet. All names in the nutrient.res file must be unique.

The clarity of the reservoir is expressed by the secchi-disk depth, which is calculated as a function of chlorophyll a. Because suspended sediment also can affect water clarity, the water clarity coefficient has been added to the equation to allow users to adjust for the impact of factors other than chlorophyll a on water clarity.