During pristine conditions, the landscape was covered with natural vegetation typical of southern New England, dominated by mixed hardwood forests. Much reduced during intensive agriculture in the last century, the forests have regrown during the present century as agriculture has declined. The natural vegetation takes up atmospheric nitrogen in the soils, effectively immobilizing it and delaying its entry into the groundwater. If forest cover increases, more nitrogen may be taken up by trees; conversely, if forests are cut down, more nitrogen may leach to the subsoil or run off paved surfaces, increasing the rate and amount of nitrogen entering the estuary from atmospheric sources. In addition, the season of the year can affect the nitrogen uptake rate by forests.