ISSN:
1573-515X
Keywords:
carbon dioxide
;
eastern Tennessee
;
ecosystem metabolism
;
methane
;
streams
;
Smoky Mountains
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
,
Geosciences
Notes:
Abstract The partial pressures of CO2 (pCO2) andCH4 (pCH4) in streams are not only governed byinstream processes, but also by transformations occurring in soil andgroundwater ecosystems. As such, stream water pCO2 andpCH4 can provide a tool to assess ecosystem respiration andanaerobic metabolism throughout drainage basins. We conducted three surveyssampling the gas content of streams in eastern Tennessee and western NorthCarolina to assess factors regulating ecosystem metabolism in catchmentswith contrasting geomorphologies, elevations and soil organic matterstorage. In our first survey, the influence of drainage basin geomorphologyon ecosystem respiration was examined by sampling streams drainingcatchments underlain by either shale or dolomite. Geomorphology isinfluenced by geology with shale catchments having shallower soils, broader,unconstrained valley floors compared with dolomite catchments.pCO2 varied little between catchment types but increased froman average of 3340 ppmv in spring to 9927 ppmv in summer or 9.3 and 28 timesatmospheric equilibrium (pCO2(equilib)), respectively. Incontrast, pCH4 was over twice as high in streams drainingshale catchments (306 ppmv; pCH4(equilib) = 116) compared withmore steeply incised dolomite basins (130 ppmv; pCH4(equilib)= 51). Using the ratio of pCH4:pCO2 as an indexof anaerobic metabolism, shale catchments had nearly twice as muchanaerobiosis (pCH4:pCO2 = 0.046) than dolomitedrainages (pCH4:pCO2 = 0.024). In our secondsurvey, streams were sampled along an elevational gradient (525 to 1700 m)in the Great Smoky Mountains National Park, USA where soil organic matterstorage increases with elevation. pCO2 did not vary betweenstreams but increased from 5340 ppmv (pCO2(equilib) = 15) to8565 ppmv (pCO2(equilib) = 24) from spring to summer,respectively. During spring pCH4 was low and constant acrossstreams, but during summer increased with elevation ranging from 17 to 2068ppmv (pCH4(equilib) = 10 to 1216). The contribution ofanaerobiosis to total respiration was constant during spring(pCH4:pCO2 = 0.017) but during summer increasedwith elevation from 0.002 at 524 m to 0.289 at 1286 m. In our last survey,we examined how pCO2 and pCH4 changed withcatchment size along two rivers (ca. 60 km stretches in both riverscorresponding to increases in basin size from 1.7–477km2 and 2.5–275 km2). pCO2and pCH4 showed opposite trends, with pCO2decreasing ca. 50% along the rivers, whereas pCH4roughly doubled in concentration downstream. These opposing shifts resultedin a nearly five-fold increase of pCH4:pCO2along the rivers from a low of 0.012 in headwaters to a high of 0.266 65-kmdownstream. pCO2 likely declines moving downstream asgroundwater influences on stream chemistry decreases, whereaspCH4 may increase as the prevalence of anoxia in riversexpands due to finer-grained sediments and reduced hydrologic exchange withoxygenated surface water.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1005914121280
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