Loading patterns

Because nitrate load is the product of nitrate concentration and discharge and discharge varies over several orders of magnitude, temporal nitrate loading is strongly correlated with discharge.  Nitrate mass loads are typically low during winter because discharge is usually low during winter. Samples collected during late winter or early spring high discharge events show low nitrate concentrations thought to be due to dilution from snow melt. Nitrate concentrations generally increase to their highest levels during high flow periods in spring and early summer, may decline with declining flow in mid to late summer, and are usually elevated if there is increased flow during late summer or fall. Total nitrogen (TN) concentrations assayed from 2006 through 2018 show that nitrate-N comprises about 84% to 99% of the total nitrogen load at the monitored Iowa wetlands and as could be expected, patterns in TN loads closely follow those of nitrate.