02874nas a2200325 4500008004100000245007600041210006900117300001300186490000800199520193800207653001602145653005802161653000802219653002002227653001102247653002302258100002002281700002102301700001702322700001302339700001502352700001702367700001702384700001802401700001402419700001902433700001502452700001502467856006602482 2011 eng d00aCross-stream comparison of substrate-specific denitrification potential0 aCrossstream comparison of substratespecific denitrification pote a381 -3920 v1043 a
Headwater streams have a demonstrated ability to denitrify a portion of their nitrate (NO3 −) load but there has not been an extensive consideration of where in a stream this process is occurring and how various habitats contribute to total denitrification capability. As part of the Lotic Intersite Nitrogen Experiment II (LINX II) we measured denitrification potential in 65 streams spanning eight regions of the US and draining three land-use types. In each stream, potential denitrification rates were measured in common substrate types found across many streams as well as locations unique to particular streams. Overall, habitats from streams draining urban and agricultural land-uses showed higher potential rates of denitrification than reference streams draining native vegetation. This difference among streams was probably driven by higher ambient nitrate concentrations found in urban or agricultural streams. Within streams, sandy habitats and accumulations of fine benthic organic matter contributed more than half of the total denitrification capacity (mg N removed m−2 h−1). A particular rate of potential denitrification per unit area could be achieved either by high activity per unit organic matter or lower activities associated with larger standing stocks of organic matter. We found that both small patches with high rates (hot spots) or more widespread but less active areas (cool matrix) contributed significantly to whole stream denitrification capacity. Denitrification estimated from scaled-up denitrification enzyme assay (DEA) potentials were not always dramatically higher than in situ rates of denitrification measured as 15N gas generation following 24-h 15N–NO3 tracer additions. In general, headwater streams draining varying land-use types have significant potential to remove nitrate via denitrification and some appear to be functioning near their maximal capacity.
10aComparative10aComparison of potential with realized denitrification10aDEA10adenitrification10astream10aSubstrate-specific1 aFindlay, S.E.G.1 aMulholland, P.J.1 aHamilton, S.1 aTank, J.1 aBernot, M.1 aBurgin, A.J.1 aCrenshaw, C.1 aDodds, W., K.1 aGrimm, N.1 aMcDowell, W.H.1 aPotter, J.1 aSobota, D. uhttps://link.springer.com/article/10.1007%2Fs10533-010-9512-802515nas a2200313 4500008004100000245007600041210006900117300001300186490000800199520160300207653001101810653002601821653001301847653001801860653001201878100001801890700001401908700001301922700001801935700001901953700001601972700001701988700001902005700001902024700001702043700001802060700001602078856010702094 2004 eng d00aCarbon and nitrogen stoichiometry and nitrogen cycling rates in streams0 aCarbon and nitrogen stoichiometry and nitrogen cycling rates in a458 -4670 v1403 aStoichiometric analyses can be used to investigate the linkages between N and C cycles and how these linkages influence biogeochemistry at many scales, from components of individual ecosystems up to the biosphere. N-specific NH4 + uptake rates were measured in eight streams using short-term 15N tracer additions, and C to N ratios (C:N) were determined from living and non-living organic matter collected from ten streams. These data were also compared to previously published data compiled from studies of lakes, ponds, wetlands, forests, and tundra. There was a significant negative relationship between C:N and N-specific uptake rate; C:N could account for 41% of the variance in N-specific uptake rate across all streams, and the relationship held in five of eight streams. Most of the variation in N-specific uptake rate was contributed by detrital and primary producer compartments with large values of C:N and small values for N-specific uptake rate. In streams, particulate materials are not as likely to move downstream as dissolved N, so if N is cycling in a particulate compartment, N retention is likely to be greater. Together, these data suggest that N retention may depend in part on C:N of living and non-living organic matter in streams. Factors that alter C:N of stream ecosystem compartments, such as removal of riparian vegetation or N fertilization, may influence the amount of retention attributed to these ecosystem compartments by causing shifts in stoichiometry. Our analysis suggests that C:N of ecosystem compartments can be used to link N-cycling models across streams.10acarbon10aCarbon:Nitrogen ratio10anitrogen10astoichiometry10astreams1 aDodds, W., K.1 aMarti, E.1 aTank, J.1 aPontius, J.L.1 aHamilton, S.K.1 aGrimm, N.B.1 aBowden, W.B.1 aMcDowell, W.H.1 aPeterson, B.J.1 aValett, H.M.1 aWebster, J.R.1 aGregory, S. uhttp://lter.konza.ksu.edu/content/carbon-and-nitrogen-stoichiometry-and-nitrogen-cycling-rates-streams00772nas a2200229 4500008004100000245010100041210006900142300001100211490000700222100002000229700001300249700001200262700001800274700002100292700001900313700001600332700001900348700001600367700001800383700001700401856012400418 2002 eng d00aA cross-system comparison of bacterial and fungal biomass in detritus pools of headwater streams0 acrosssystem comparison of bacterial and fungal biomass in detrit a55 -660 v431 aFindlay, S.E.G.1 aTank, J.1 aDye, S.1 aVallett, H.M.1 aMulholland, P.J.1 aMcDowell, W.H.1 aJohnson, S.1 aHamilton, S.K.1 aEdmonds, J.1 aDodds, W., K.1 aBowden, W.B. uhttp://lter.konza.ksu.edu/content/cross-system-comparison-bacterial-and-fungal-biomass-detritus-pools-headwater-streams