T256 Urban Geochemistry

Friday, 30 October 2020
10:00 AM - 2:00 PM
Meeting Rooms

MONITORING WATER QUALITY IN BALLONA LAGOON: NITRATE LEVEL FLUCTUATION IN LOW AND HIGH TIDE CONDITIONS

Paper number: T256-13
Program: Technical Sessions
Time: 12:50 PM – 1:00 PM

Authors

Abstract

Ballona Lagoon is located in southern California, which has been reduced in size and degraded its natural habitat in the last century due to urbanization. The objective of this study was to evaluate the nitrate discharge process in the Ballona Lagoon in response to extensive urbanization in dry and wet seasons during high tide (HT) and low tide (LT) conditions. Nitrate concentrations can enter the environment naturally, through atmospheric deposition and groundwater, or anthropogenically, by nitrification/denitrification processes and wastewater runoff. We collected a total of 12 water samples in high and low tide conditions. They were analyzed the same day for nitrate concentration at the American Environmental Testing Laboratory using ion chromatography (Methods SM-4110). Overall, the results showed a higher concentration of nitrate closer to the urbanized area (landward toward the lagoon’s head) than the samples taken closer to the ocean (the mouth of the lagoon). For the wet season, the concentration level for most samples were undetectable (ND) in both high and low tide conditions. The nitrate concentration (ppm) for dry season was 0.54-2.33 (for the LT/dry) and ND-3.85 (for the HT/dry). The wet season nitrate values (ppm) were from ND-2.55 (for the LT/wet) and ND-3.63 (for HT/wet). All values were below the maximum contamination level (MCL) set by the United States Environmental Protection Agency (EPA). Furthermore, the pH level was slightly alkaline and showed no significant change between the lagoon’s mouth and head: 7.04-7.84 (for LT/dry), 6.96-7.37 (for HT/dry), 7.43-7.93 (for LT/wet), and 7.31-7.53 (for HT/wet). The salinity values taken from the four lagoon locations showed slight fluctuation. Moreover, the average salinity values for the dry season in LT was 32.85 0/00 and in HT was 33.4 0/00. The difference indicates that the urban runoff may enter the lagoon in various spots causing lower salinity in the dry season (LT condition). In addition to anthropogenic pressures on the lagoon water such as wastewater runoff, nitrification/denitrification processes may also contribute to higher nitrate levels. To pinpoint the exact sources of the nitrate, further investigation is needed by using stable nitrogen isotope signatures.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357924

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