Geochemical and hydrological study of coastal groundwater discharging to an urban estuary in northern New Jersey

Abstract

Coastal zones of urban area have been highly impacted by human activities, and urban estuaries suffer from environmental pollution and degradation of coastal ecosystems. In addition to surface runoff, submarine groundwater discharge (SGD) has been recognized as an important pathway for transport of chemicals to the marine environment. In summer 2017 and 2018, groundwater (n = 39) and sediment (n = 13) samples were collected at depths of 20–175 cm from a sandy coastal aquifer in addition to surface water samples (n = 10) along the Newark Bay, a highly urbanized estuary. Aquifer sediments consisted dominantly of medium to coarse sand and were highly permeable, while they were poor in organic matter. Groundwater was fresh to saline and the pH ranged from 6.62 to 8.68, while dissolved oxygen ranged from 1 to 8 mg/L. The urban coastal groundwater contained elevated levels of nitrate, ammonium, and phosphate with maximum concentrations of 37.2, 11.1 and 4.1 mg/L, respectively, which were significantly higher than those in surface water from the Newark Bay by 5- to 64-fold. The elevated N and P in groundwater may perhaps result from anthropogenic sources, such as the leakage of underground sewers. Estimated discharge of N and P from the highly permeable coastal aquifer to the Newark Bay is comparable to the transport of N and P from the Hackensack River into the bay during dry periods. Submarine groundwater discharge of anthropogenic nutrients could be a significant source of nutrients in the Newark Bay, but further study is needed to better understand the human impacts on biogeochemical cycling of nutrients in the urban estuary.