Molecular composition and bioavailability of dissolved organic nitrogen in a lake flow-influenced river in south Florida, USA
- 419 Downloads
Dissolved organic nitrogen (DON) represents a large percentage of the total nitrogen in rivers and estuaries, and can contribute to coastal eutrophication and hypoxia. This study reports on the composition and bioavailability of DON along the Caloosahatchee River (Florida), a heavily managed system receiving inputs from Lake Okeechobee as well as agricultural and urban runoff from the surrounding watershed. Water samples were collected bimonthly for 1 year beginning December 2014 at three stations along the river. Treatments included 28-day dark incubations with and without prior photo-irradiation. Concentrations of DON, ammonium, nitrate–nitrite, total hydrolyzable amino acids (THAA), and urea, as well as bacterial numbers, leucine aminopeptidase activity, and fluorescent optical properties were measured. Ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to characterize the molecular composition of DON before and after incubation for selective samples. The total dissolved N pool was dominated by DON (61–99%), with low inorganic N (1–39%), and small amounts of THAA-N (0.1–23%) and urea-N (0.6–3.2%). The mean percentage of biologically available DON (BDON) for the study was 15% (−12–61% range) with highest values occurring when water inputs from Lake Okeechobee were the most dominant freshwater source. FT-ICR MS analysis revealed the presence of a wide range of N-containing formulas and the generation of aliphatic and ‘peptide-like’ structures likely due to microbial alteration of the carbon skeleton of DON compounds. Effects of light exposure prior to incubation did not have a measurable effect on %BDON but did affect bacterial biomass and DON composition. These findings may help predict nutrient loading effects to the Caloosahatchee River estuary and may aid in understanding wetland potential as a treatment technology for removing N in this and other freshwater systems sensitive to N loading.
KeywordsEstuary Eutrophication Amino acids Urea Optical properties FT-ICR MS
This work was funded through the South Florida Water Management District (SFWMD Contract #4600003105) and supported, in part, by a Section 319 Nonpoint Source Management Program Implementation grant from the U.S. Environmental Protection Agency through an agreement/contract with the Nonpoint Source Management Section of the Florida Department of Environmental Protection. The authors thank the field crew from the SFWMD for logistical support, and the National High Magnetic Field Laboratory at Florida State University for the mass spectrometric analyses (NSF DMR-1157490). Additional support from the George Barley Endowment and the FCE-LTER program (Grant No. DEB-1237517) is acknowledged. This is contribution number 832 from the Southeast Environmental Research Center in the Institute of Water & Environment at Florida International University.
- Antonini GA, Fann DA, Roat P (2002) A historical geography of southwest Florida waterways, volume 2, Placida Harbor to Marco Island. National Seagrant College Program, Silver SpringGoogle Scholar
- Bailey N, Magley W, Mandrup-Poulsen J, O’Donnell K, Peets R (2009) Nutrient TMDL for the Caloosahatchee Estuary (WBIDs 3240 A, 3240B, and 3240C). Florida Department of Environmental Protection. TMDL Report, p 119Google Scholar
- Doering PH, Haunert KE, Qiu C, Coley T (2011) Caloosahatchee River estuary and southern Charlotte Harbor. 2010 South Florida Environmental Report, volume 1, Chap 12, p 189Google Scholar
- Findlay SEG, Sinsabaugh RL (2003) Aquatic ecosystems: interactivity of dissolved organic matter. Academic Press, San DiegoGoogle Scholar
- Ikenberry C, Bhimani S, McDonald S, Jenkins D, Dennis G, Gray R (2002) Bioavailability of dissolved organic nitrogen in WWTP effluent: a Truckee River case study. In: Proceedings of the Water Environment Federation, WEFTEC 2002: Session 61–70, pp 575–585Google Scholar
- Osborne DM, Podgorski DC, Bronk DA, Roberts Q, Sipler RE, Austin D, Bays JS, Cooper WT (2013) Molecular-level characterization of reactive and refractory dissolved natural organic nitrogen compounds by atmospheric pressure photoionization coupled to Fourier transform ion cyclotron resonance mass spectrometry. Rapid Commun Mass Spectrom 27:851–858CrossRefPubMedGoogle Scholar
- Redfield AC (1958) The biological control of chemical factors in the environment. Am Sci 46:205–221Google Scholar
- Sterner RW, Elser JJ (2002) Ecological Stoichiometry: the biology of elements from molecules to the biosphere. Princeton University Press, PrincetonGoogle Scholar
- Varela MM, Barquero S, Bode A, Fernández E, González N, Teira E, Varela M (2003) Microplanktonic regeneration of ammonium and dissolved organic nitrogen in the upwelling area of the NW of Spain: relationships with dissolved organic carbon production andphytoplankton size-structure. J Plankton Res 25:719–736CrossRefGoogle Scholar
- Wetland Solutions (2012) Evaluation of total nitrogen reduction options for the C-43 Water Quality Treatment Area Test Facility, Final Task 2 Report. Prepared for the South Florida Water Management DistrictGoogle Scholar