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Title: Inference of nitrogen cycling in three watersheds of northern Florida, USA, by multivariate statistical analysis

Abstract

Nitrogen in fresh waters of three rivers in northern Florida-the Apalachicola-Chattahoochee-Flint (ACF) River system, Ochlockonee (Och), and Sopchoppy (Sop)- is inferred to be derived mostly from atmospheric deposition. Because the N:P mole ratios in the rivers are nearly three times higher than the Redfield ratio for aquatic photosynthesis, N is saturate in the ecosystems, not a limiting nutrient, although it may be chemically transformed. Absolute principal component analysis (APCA), a receptor model, was applied to many years of monitoring data for Apalachicola River water and rainfall over its basin in order to better understand aquatic chemistry of nitrogen in the watershed. The APCA model aged rain and groundwater. In the fresh rain component, the ratio of atmospheric nitrate to sulfate is close to that in rainwater, as if some samples had been collected following very recent rainfall. The aged rain component of the river water is distinguished by a low NO[sup [minus][sub 3]]/SO[sup 2[minus][sub 4]] ratio, signifying an atmospheric source but with most of its nitrate having been lost or transformed. The groundwater component, inferred from its concentration to contribute on average about one fourth of the river water, contains abundant Ca[sup 2+] but no detectable nitrogen. Results similar tomore » ACF were obtained for Sop and Och, though Och exhibits some association of NO[sup [minus][sub 3]] with the Ca[sup 2+]-rich component. Similar APCA of wet precipitation resolves mainly components that represent acid rain, with NO[sup [minus]][sub 3], SO[sup 2[minus]][sub 4], and NH[sup +][sub 4], and sea salt, with Na[sup +], Cl[sup [minus]], and Mg[sup 2+]. Inland, the acid rain component is relatively more prominent and Cl[sup [minus]] is depleted, while at atmospheric monitoring sites nearer the coastal region sea salt tends to be more prominent.« less

Authors:
;  [1]
  1. (Florida State Univ., Tallahassee, FL (United States))
Publication Date:
OSTI Identifier:
7182966
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geochimica et Cosmochimica Acta; (United States); Journal Volume: 58:6
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; FLORIDA; ACID RAIN; WATERSHEDS; NITROGEN CYCLE; MULTIVARIATE ANALYSIS; ATMOSPHERIC PRECIPITATIONS; DEVELOPED COUNTRIES; MATHEMATICS; NORTH AMERICA; RAIN; STATISTICS; USA; 540320* - Environment, Aquatic- Chemicals Monitoring & Transport- (1990-)

Citation Formats

Fu, Ji-Meng, and Winchester, J.W.. Inference of nitrogen cycling in three watersheds of northern Florida, USA, by multivariate statistical analysis. United States: N. p., 1994. Web. doi:10.1016/0016-7037(94)90561-4.
Fu, Ji-Meng, & Winchester, J.W.. Inference of nitrogen cycling in three watersheds of northern Florida, USA, by multivariate statistical analysis. United States. doi:10.1016/0016-7037(94)90561-4.
Fu, Ji-Meng, and Winchester, J.W.. Tue . "Inference of nitrogen cycling in three watersheds of northern Florida, USA, by multivariate statistical analysis". United States. doi:10.1016/0016-7037(94)90561-4.
@article{osti_7182966,
title = {Inference of nitrogen cycling in three watersheds of northern Florida, USA, by multivariate statistical analysis},
author = {Fu, Ji-Meng and Winchester, J.W.},
abstractNote = {Nitrogen in fresh waters of three rivers in northern Florida-the Apalachicola-Chattahoochee-Flint (ACF) River system, Ochlockonee (Och), and Sopchoppy (Sop)- is inferred to be derived mostly from atmospheric deposition. Because the N:P mole ratios in the rivers are nearly three times higher than the Redfield ratio for aquatic photosynthesis, N is saturate in the ecosystems, not a limiting nutrient, although it may be chemically transformed. Absolute principal component analysis (APCA), a receptor model, was applied to many years of monitoring data for Apalachicola River water and rainfall over its basin in order to better understand aquatic chemistry of nitrogen in the watershed. The APCA model aged rain and groundwater. In the fresh rain component, the ratio of atmospheric nitrate to sulfate is close to that in rainwater, as if some samples had been collected following very recent rainfall. The aged rain component of the river water is distinguished by a low NO[sup [minus][sub 3]]/SO[sup 2[minus][sub 4]] ratio, signifying an atmospheric source but with most of its nitrate having been lost or transformed. The groundwater component, inferred from its concentration to contribute on average about one fourth of the river water, contains abundant Ca[sup 2+] but no detectable nitrogen. Results similar to ACF were obtained for Sop and Och, though Och exhibits some association of NO[sup [minus][sub 3]] with the Ca[sup 2+]-rich component. Similar APCA of wet precipitation resolves mainly components that represent acid rain, with NO[sup [minus]][sub 3], SO[sup 2[minus]][sub 4], and NH[sup +][sub 4], and sea salt, with Na[sup +], Cl[sup [minus]], and Mg[sup 2+]. Inland, the acid rain component is relatively more prominent and Cl[sup [minus]] is depleted, while at atmospheric monitoring sites nearer the coastal region sea salt tends to be more prominent.},
doi = {10.1016/0016-7037(94)90561-4},
journal = {Geochimica et Cosmochimica Acta; (United States)},
number = ,
volume = 58:6,
place = {United States},
year = {Tue Mar 01 00:00:00 EST 1994},
month = {Tue Mar 01 00:00:00 EST 1994}
}
  • Atmospheric deposition is estimated to be the principal source of N in water that flows to the Apalachicola river from the Chattahoochee and Flint Rivers (ACF) as well as in two nearby small rivers, Ochlockonee (Och) and Sopchoppy (Sop), that drain watersheds with different land use characteristics. By mass balance and descriptive statistics of hundreds of rainfall and river water samples from monitoring programs since the 1960s, the average nitrate and ammonium deposition flux from the atmosphere is sufficient to account for N that flows toward Apalachicola Bay, an estuary in which N may be a limiting nutrient. Urban andmore » agricultural sources of N in the three watersheds ACF, Och, and Sop appear to be relatively smaller. The work was based on long-term data bases from the National Atmospheric Deposition Program (NADP) rain chemistry monitoring network and the U.S. Geological Survey (USGS) water monitoring program. Average atmospheric N depositions to the three river watersheds are nearly the same as river fluxes of N in all forms monitored. Nitrogen is not likely to be a limiting nutrient in the three watersheds, since river water N:P exceeds the Redfield ratio. An estimate of largest possible input of urban sewage is several times lower than the atmospheric flux of N to the ACF watershed. And N from N-fertilizer, comparable to the atmospheric deposition flux of N, is likely to be smaller if mostly retained in crops or farmland before it reaches the estuary. Annual nitrogen export from the Apalachicola River to the estuary, 1.22 x 10[sup 9] moles N yr[sup [minus]1], consists of organic nitrogen 60%, nitrate 34%, and NH[sup +][sub 4]6%. Atmospheric nitrate and sulfate depositions are highly correlated, both being principally from fossil fuel combustion. Hydrologic conditions, which exhibit variations on seasonal and longer time scales, play an important role in the transport of nutrients and other species in the rivers.« less
  • Cited by 1
  • Abstract not provided.
  • Nitrogen (N) is an important nutrient as it often limits productivity but in excess can impair water quality. Most studies on watershed N cycling have occurred in upland forested catchments where snowmelt dominates N export; fewer studies have focused on low-relief watersheds that lack snow. We examined watershed N cycling in three adjacent, low-relief watersheds in the Upper Coastal Plain of the southeastern United States to better understand the role of hydrological flow paths and biological transformations of N at the watershed scale. Groundwater was the dominant source of nitrified N to stream water in two of the three watersheds,more » while atmospheric deposition comprised 28% of stream water nitrate in one watershed. The greater atmospheric contribution may have been due to the larger stream channel area relative to total watershed area or the dominance of shallow subsurface flow paths contributing to stream flow in this watershed. There was a positive relationship between temperature and stream water ammonium concentrations and a negative relationship between temperature and stream water nitrate concentrations in each watershed suggesting that N cycling processes (i.e., nitrification and denitrification) varied seasonally. However, there were no clear patterns in the importance of denitrification in different water pools possibly because a variety of factors (i.e., assimilatory uptake, dissimilatory uptake, and mixing) affected nitrate concentrations. In conclusion, together, these results highlight the hydrological and biological controls on N cycling in low-gradient watersheds and variability in N delivery flow paths among adjacent watersheds with similar physical characteristics.« less