Estuary response to an abrupt, large increase in groundwater nitrate input

Long term measurements of NO 3 - concentrations in two estuaries on Buzzards Bay, Massachusetts, USA, coupled with a large, step-wise increase in the groundwater NO 3 - to one of those estuaries, have allowed the effects on the estuary to be isolated and quantified. The results show that prior to the abrupt increase, the estuary responded in a linear manner to NO 3 - input, as suggested in the literature. After the abrupt increase, the estuary initially absorbed the greatly increased groundwater input, and after a year the response became a fluctuating variable with periods of less than 1 year. It is proposed that this indicates increased recycling from the sediments. This behavior is consistent with models of nutrient-induced regime shift in its early stages, as described in the literature. Future isotopic analysis is suggested as a means to confirm the estuary mechanism.