Whole-stream metabolism in two montane streams: Contribution of the hyporheic zone

Limnology and Oceanography (Impact Factor: 3.62). 01/2001; DOI: 10.4319/lo.2001.46.3.0523
Source: OAI

ABSTRACT We used whole-stream and benthic chamber methods to measure rates of metabolism and determine the contribution of the hyporheic zone to ecosystem respiration (R) in two streams with differing surface–subsurface exchange characteristics, Rio Calaveras and Gallina Creek, New Mexico. We used the difference between whole-stream and benthic R to calculate the rate of hyporheic zone R and coupled this estimate to an independent measure of hyporheic sediment R to estimate the cross-sectional area of the hyporheic zone (AH) for two reaches from each stream. Conservative tracer injections and solute transport modeling were used to characterize surface–subsurface hydrologic exchange by determining values of the cross-sectional area of the transient storage zone (As). The hyporheic zone contributed a substantial proportion of whole-stream R in all four study reaches, ranging from 40 to 93%. Wholestream R, hyporheic R, and percent contribution of hyporheic R all increased as transient storage increased, with whole-stream and hyporheic R exhibiting significant relationships with As. All three measures of respiration and values of AH were much greater for both reaches of the stream with greater surface–subsurface exchange. AH is valuable for cross-site comparisons because it accounts for differences in rates of both benthic and hyporheic sediment R and can be used to predict the importance of the hyporheic zone to other stream ecosystem processes. Yes Yes

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    Journal of Scientific Research and Reports. 01/2014; 3(6):844-865.
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    ABSTRACT: Human-induced changes to the nitrogen cycle have led to a growing interest in processes that remove nitrogen from water. Denitrification, which is the microbial reduction of nitrate to gaseous nitrogen (mainly N 2 plus small amounts of N 2 O), can remove a large fraction of the fixed nitrogen that reaches a body of water, but rates of denitrification are highly variable in space and time (Sjodin et al. 1998; Hill et al. 2000; Saunders and Kalff 2001). In aquatic systems, rates of denitrification usually have been estimated in cores or chambers from rates of change in the con-centration of N 2 or N 2 O (Seitzinger et al. 1993; Garcia-Ruiz et al. 1998). Most commonly, cores have been incubated in the labo-ratory, and denitrification has been estimated by the acetylene inhibition (block) technique (Sørensen 1978). The acetylene inhibition technique, however, tends to underestimate denitri-fication because acetylene inhibits nitrification and does not completely block the reduction of N 2 O to N 2 (Seitzinger et al. 1993). Although estimates also have been based on flux of N 2 from sediment cores and chambers (Devol 1991; Seitzinger et al. 1993; Saunders and Kalff 2001), rates obtained by use of cores or chambers cannot easily be extrapolated to entire ecosystems where spatial heterogeneity in rates of denitrification is high. Like denitrification, ecosystem metabolism (photosynthesis and respiration) has been estimated in chambers from rates of change in the concentration of dissolved O 2 (e.g., Fellows et al. 2001). Integrated estimates of oxygen metabolism are possible by use of an open-channel method involving mass balance of O 2 (Odum 1956; Marzolf et al. 1994; Ortiz-Zayas 1998; Fellows et al. 2001). Similarly, estimation of denitrification by an open-channel method is feasible in concept but would require measurement of small changes in the concentration of N 2 . Rates of change in the concentration of N 2 O can be measured with high precision rela-tive to ambient concentrations, but open-channel estimates of denitrification based on N 2 O would depend on assumptions about the ratio of N 2 : N 2 O produced by denitrification. In many aquatic systems, most of the N 2 O produced during denitrifica-tion is subsequently reduced to N 2 , but the ratio of N 2 : N 2 O is variable (Lindau et al. 1991; Mosier and Schimel 1993). Thus, given that N 2 O presents apparently intractable problems of interpretation, open-channel estimation of denitrification from N 2 flux would be ideal. Recently, Laursen and Seitzinger (2002) described an open-channel method based on measurement of N 2 by membrane-inlet mass spectrometry (MIMS) (Kana et al. 1994; Kana et al. 1998; Cornwell 1999; Eyre et al. 2002). Alternatively, open-channel estimates of denitrification could be based on measurements of N 2 by high-precision gas chromatography (Devol 1991; An and Joye 1997). Abstract Estimates of denitrification based on standard methods often cannot easily be extrapolated to entire ecosys-tems because of high spatial heterogeneity in rates of denitrification. Diel changes in the concentration of dini-trogen (N 2) in running waters provide the basis for estimating denitrification by an open-channel technique in much the same way that ecosystem metabolism can be estimated from diel changes in the concentration of dis-solved oxygen. The open-channel N 2 method was field tested at a site on the South Platte River downstream from Denver, CO; concentrations of N 2 were measured by membrane inlet mass spectrometry. For a date in November 1998, the rate of denitrification was estimated to be 0.19 mol N 2 m –2 d –1 and was similar to rates reported in previous studies based on mass-balance analysis. The open-channel N 2 method is the first method to provide direct, whole-system estimates of denitrification in flowing waters and may help to expand our understanding of nitrogen cycling in running waters.
    Limnology and oceanography, methods 01/2011; 1. · 1.68 Impact Factor

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