Legacy effects of cemeteries on groundwater quality and nitrate loads to a headwater stream

Abstract

Residential development and urbanization have increased nutrient loads to streams and groundwater through increased use of fertilizers and discharge of wastewater effluent. Stream degradation in urbanizing areas has simultaneously reduced natural attenuation of nutrients. In this context, cemeteries are an often-overlooked land use that may contribute to nutrient loading in urbanizing watersheds. Although cemeteries provide ecosystem services, such as infiltration of stormwater, micrometeorology control, and greenspace, they also pose a unique threat to groundwater quality due to degradation and leaching of organic material. To assess the potential legacy impact of cemeteries on water quality, we explored the impact of a large cemetery that comprises 9% of the total area of a suburban watershed on groundwater nitrate concentrations and stream nitrate loads. We found nitrate concentrations were significantly higher in cemetery groundwater (median = 6.2 mg l-1) than in residential groundwater (median = 0.05 mg l-1). During summer months (June through September), the stream is consistently a gaining stream receiving groundwater discharge. During this time, stream nitrate concentrations increase by 1.4-1.9 mg l-1 between the upstream edge of the cemetery and the downstream edge (from 0.03-0.46 mg l-1 to 1.6 mg l-1-2.1 mg l-1, respectively). Stream nitrate loads observed at gauging stations located about 500 m upstream and downstream of the cemetery property show that the stream nitrate load is consistently 20-40 kg NO3-/day higher downstream of the cemetery between June to September. Given that the cemetery handles about 350-500 burials per year, it is estimated that 25%-50% of the nitrate load between the gauging stations could be attributable to groundwater discharge of burial decay products. Our observations of nitrate concentrations in cemetery groundwater, coupled with the increases in nitrate loads in a stream traversing the cemetery property, suggest cemeteries may be an overlooked source of nutrient loading in developed watersheds.