| |
| |
|
|
|
|
| |
 |
Biogeochemical processes in land-ocean interfaces, surface estuaries, subterranean estuaries and sediment-water interface
|
| |
|
|
Sediment nitrogen cycling and removal in tidal freshwater zones of two rivers in south Texas, USA
P-C2-13-S
Xin Xu* , The University of Texas Marine Science Institute, USA
Hengchen Wei, The University of Texas Marine Science Institute, USA
Kevan Moffett, Washington State University at Vancouver, USA
James McClelland, The University of Texas Marine Science Institute, USA
Amber Hardison, The University of Texas Marine Science Institute, USA
Presenter Email: xinxu@utexas.edu |
| Nitrogen is the major limiting nutrient in marine ecosystems, and river-borne sources provide 20-30% of nitrogen input to global oceans. Tidal freshwater zones (TFZs) in the lower reaches of rivers may substantially alter the amount and composition of nitrogen transported from watersheds to estuaries due to longer water residence times (compared to non-tidal river reaches) and associated build-up of organic-rich sediments. We conducted flow-through sediment core incubations from TFZs and upstream riverine sites in the Aransas and Mission rivers in south Texas during multiple seasons and years. We measured net fluxes of different constituents (O2, N2, DIC, NH4+, NO3-) across the sediment-water interface to quantify organic matter decomposition and major nitrogen cycling processes. Our results showed higher respiration and denitrification rates in TFZ sediments than in non-tidal riverine sediments. Average O2 fluxes were -771 +/- 35 umol m-2 hr-1 and -797 +/- 69 umol m-2 hr-1 in summer in the Aransas River TFZ (AR) and the Mission River TFZ (MR), respectively; and -363 +/- 38 umol m-2 hr-1 and -484 +/- 70 umol m-2 hr-1 in winter, with negative values indicating net O2 consumption. Average N2 fluxes were 53 +/- 8 umol m-2 hr-1 (AR) and 22 +/- 5 umol m-2 hr-1 (MR) in summer and 36 +/- 8 umol m-2 hr-1 (AR) and 30 +/- 6 umol m-2 hr-1 (MR) in winter, with positive values indicating net denitrification. Average dissolved inorganic nitrogen (DIN) fluxes were 49 +/- 9 umol m-2 hr-1 (AR) and 106 +/- 9 umol m-2 hr-1 (MR) in summer, and -12 +/- 11 umol m-2 hr-1 (AR) and 22 +/- 6 umol m-2 hr-1 (MR) in winter, with negative values indicating net DIN removal. Within the TFZs, rates of biogeochemical processes varied as a function of sediment physical properties, nutrient loading, and seasonal temperature changes. |
|
|
|
|
|
|
|
|