Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects
Seagrass meadows and coral reefs along the coast of Saipan, a US commonwealth in the Northern Pacific, have been declining since the 1940s, possibly due to nutrient loading. This study investigated whether submarine groundwater discharge (SGD) contributes to nutrient loading and supports primary pro...
| Main Authors: | , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2020-10-01
|
| Series: | Water |
| Subjects: | |
| Online Access: | https://www.mdpi.com/2073-4441/12/11/3029 |
| _version_ | 1797549520039444480 |
|---|---|
| author | Melissa A. Knapp Naomi Geeraert Kiho Kim Karen L. Knee |
| author_facet | Melissa A. Knapp Naomi Geeraert Kiho Kim Karen L. Knee |
| author_sort | Melissa A. Knapp |
| collection | DOAJ |
| description | Seagrass meadows and coral reefs along the coast of Saipan, a US commonwealth in the Northern Pacific, have been declining since the 1940s, possibly due to nutrient loading. This study investigated whether submarine groundwater discharge (SGD) contributes to nutrient loading and supports primary production on Saipan’s coast. SGD can be an important source of freshwater, nutrients, and other pollutants to coastal waters, especially in oceanic islands without well-developed stream systems. Ra and Rn isotopes were used as natural tracers of SGD. Nitrate, phosphate, and ammonium concentrations, ancillary water quality parameters, δ<sup>15</sup>N and δ<sup>18</sup>O of dissolved nitrate, and δ<sup>15</sup>N of primary producer tissue were measured. Our results pointed to discharge of low-salinity groundwater containing elevated concentrations of sewage-derived N at specific locations along Saipan’s coast. High SGD areas had lower salinity and pH, higher dissolved inorganic nitrogen concentrations, and elevated primary producer δ<sup>15</sup>N, indicative of sewage nitrogen inputs. We estimated that SGD could support 730–6400 and 3000–15,000 mol C d<sup>−1</sup> of primary production in Tanapag and Garapan Lagoons, respectively, or up to approximately 60% of primary production in Garapan Lagoon. Efforts to improve water quality, reduce nutrient loading, and preserve coastal ecosystems must account for groundwater, since our results demonstrate that it is an important pathway of nitrogen delivery. |
| first_indexed | 2024-03-10T15:16:50Z |
| format | Article |
| id | doaj.art-5f9534f23a72460ba1b68e05582af869 |
| institution | Directory Open Access Journal |
| issn | 2073-4441 |
| language | English |
| last_indexed | 2024-03-10T15:16:50Z |
| publishDate | 2020-10-01 |
| publisher | MDPI AG |
| record_format | Article |
| series | Water |
| spelling | doaj.art-5f9534f23a72460ba1b68e05582af8692023-11-20T18:52:38ZengMDPI AGWater2073-44412020-10-011211302910.3390/w12113029Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological EffectsMelissa A. Knapp0Naomi Geeraert1Kiho Kim2Karen L. Knee3Department of Environmental Science, American University, 4400 Massachusetts Ave., NW, Washington, DC 20016, USASwire Institute of Marine Science, T.T. Tsui Building, HK Room 304, 3/F, Pok Fu Lam Rd, Lung Fu Shan, Hong Kong, ChinaDepartment of Environmental Science, American University, 4400 Massachusetts Ave., NW, Washington, DC 20016, USADepartment of Environmental Science, American University, 4400 Massachusetts Ave., NW, Washington, DC 20016, USASeagrass meadows and coral reefs along the coast of Saipan, a US commonwealth in the Northern Pacific, have been declining since the 1940s, possibly due to nutrient loading. This study investigated whether submarine groundwater discharge (SGD) contributes to nutrient loading and supports primary production on Saipan’s coast. SGD can be an important source of freshwater, nutrients, and other pollutants to coastal waters, especially in oceanic islands without well-developed stream systems. Ra and Rn isotopes were used as natural tracers of SGD. Nitrate, phosphate, and ammonium concentrations, ancillary water quality parameters, δ<sup>15</sup>N and δ<sup>18</sup>O of dissolved nitrate, and δ<sup>15</sup>N of primary producer tissue were measured. Our results pointed to discharge of low-salinity groundwater containing elevated concentrations of sewage-derived N at specific locations along Saipan’s coast. High SGD areas had lower salinity and pH, higher dissolved inorganic nitrogen concentrations, and elevated primary producer δ<sup>15</sup>N, indicative of sewage nitrogen inputs. We estimated that SGD could support 730–6400 and 3000–15,000 mol C d<sup>−1</sup> of primary production in Tanapag and Garapan Lagoons, respectively, or up to approximately 60% of primary production in Garapan Lagoon. Efforts to improve water quality, reduce nutrient loading, and preserve coastal ecosystems must account for groundwater, since our results demonstrate that it is an important pathway of nitrogen delivery.https://www.mdpi.com/2073-4441/12/11/3029submarine groundwater discharge (SGD)Saipannitrogennutrientsseagrassescoastal ecosystems |
| spellingShingle | Melissa A. Knapp Naomi Geeraert Kiho Kim Karen L. Knee Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects Water submarine groundwater discharge (SGD) Saipan nitrogen nutrients seagrasses coastal ecosystems |
| title | Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects |
| title_full | Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects |
| title_fullStr | Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects |
| title_full_unstemmed | Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects |
| title_short | Submarine Groundwater Discharge (SGD) to Coastal Waters of Saipan (Commonwealth of the Northern Mariana Islands, USA): Implications for Nitrogen Sources, Transport and Ecological Effects |
| title_sort | submarine groundwater discharge sgd to coastal waters of saipan commonwealth of the northern mariana islands usa implications for nitrogen sources transport and ecological effects |
| topic | submarine groundwater discharge (SGD) Saipan nitrogen nutrients seagrasses coastal ecosystems |
| url | https://www.mdpi.com/2073-4441/12/11/3029 |
| work_keys_str_mv | AT melissaaknapp submarinegroundwaterdischargesgdtocoastalwatersofsaipancommonwealthofthenorthernmarianaislandsusaimplicationsfornitrogensourcestransportandecologicaleffects AT naomigeeraert submarinegroundwaterdischargesgdtocoastalwatersofsaipancommonwealthofthenorthernmarianaislandsusaimplicationsfornitrogensourcestransportandecologicaleffects AT kihokim submarinegroundwaterdischargesgdtocoastalwatersofsaipancommonwealthofthenorthernmarianaislandsusaimplicationsfornitrogensourcestransportandecologicaleffects AT karenlknee submarinegroundwaterdischargesgdtocoastalwatersofsaipancommonwealthofthenorthernmarianaislandsusaimplicationsfornitrogensourcestransportandecologicaleffects |