06735nas a2200373 4500008004100000245012300041210006900164300000800233490000700241520565500248100001505903700001405918700001305932700002105945700002005966700001805986700001706004700001906021700001706040700002006057700001906077700001606096700002006112700001606132700001906148700001806167700001906185700001706204700001506221700001606236700001706252700001806269856007406287 2018 eng d00aPartitioning assimilatory nitrogen uptake in streams: an analysis of stable isotope tracer additions across continents0 aPartitioning assimilatory nitrogen uptake in streams an analysis a1380 v883 a

Headwater streams remove, transform, and store inorganic nitrogen (N) delivered from surrounding watersheds, but excessive N inputs from human activity can saturate removal capacity. Most research has focused on quantifying N removal from the water column over short periods and in individual reaches, and these ecosystem-scale measurements suggest that assimilatory N uptake accounts for most N removal. However, cross-system comparisons addressing the relative role of particular biota responsible for incorporating inorganic N into biomass are lacking. Here we assess the importance of different primary uptake compartments on reach-scale ammonium (NH4+-N) uptake and storage across a wide range of streams varying in abundance of biota and local environmental factors. We analyzed data from 17 15N-NH4+tracer addition experiments globally, and found that assimilatory N uptake by autotrophic compartments (i.e., epilithic biofilm, filamentous algae, bryophytes/macrophytes) was higher but more variable than for heterotrophic microorganisms colonizing detrital organic matter (i.e., leaves, small wood, and fine particles). Autotrophic compartments played a disproportionate role in N uptake relative to their biomass, although uptake rates were similar when we rescaled heterotrophic assimilatory N uptake associated only with live microbial biomass. Assimilatory NH4+-N uptake, either estimated as removal from the water column or from the sum uptake of all individual compartments, was four times higher in open- than in closed-canopy streams. Using Bayesian Model Averaging, we found that canopy cover and gross primary production (GPP) controlled autotrophic assimilatory N uptake while ecosystem respiration (ER) was more important for the heterotrophic contribution. The ratio of autotrophic to heterotrophic N storage was positively correlated with metabolism (GPP: ER), which was also higher in open- than in closed-canopy streams. Our analysis shows riparian canopy cover influences the relative abundance of different biotic uptake compartments and thus GPP:ER. As such, the simple categorical variable of canopy cover explained differences in assimilatory N uptake among streams at the reach scale, as well as the relative roles of autotrophs and heterotrophs in N storage. Finally, this synthesis links cumulative N uptake by stream biota to reach-scale N demand and provides a mechanistic and predictive framework for estimating and modeling N cycling in other streams.

1 aTank, J.L.1 aMarti, E.1 aRiis, T.1 avon Schiller, D.1 aReisinger, A.J.1 aDodds, W., K.1 aWhiles, M.R.1 aAshkenas, L.R.1 aBowden, W.B.1 aCollins, S., M.1 aCrenshaw, C.L.1 aCrowl, T.A.1 aGriffiths, N.A.1 aGrimm, N.B.1 aHamilton, S.K.1 aJohnson, S.L.1 aMcDowell, W.H.1 aNorman, B.M.1 aRosi, E.J.1 aSimon, K.S.1 aThomas, S.A.1 aWebster, J.R. uhttps://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecm.128002680nas a2200229 4500008004100000245009800041210006900139300001300208490000700221520195100228653002002179653002102199653002002220653002402240653002202264653002302286100002002309700002002329700001702349700001802366856006602384 2013 eng d00aWoody vegetation removal stimulates riparian and benthic denitrification in tallgrass prairie0 aWoody vegetation removal stimulates riparian and benthic denitri a547 -5600 v163 a

Expansion of woody vegetation into areas that were historically grass-dominated is a significant contemporary threat to grasslands, including native tallgrass prairie ecosystems of the Midwestern United States. In tallgrass prairie, much of this woody expansion is concentrated in riparian zones with potential impacts on biogeochemical processes there. Although the effects of woody riparian vegetation on denitrification in both riparian soils and streams have been well studied in naturally wooded ecosystems, less is known about the impacts of woody vegetation encroachment in ecosystems that were historically dominated by herbaceous vegetation. Here, we analyze the effect of afforestation and subsequent woody plant removal on riparian and benthic denitrification. Denitrification rates in riparian soil and selected benthic compartments were measured seasonally in naturally grass-dominated riparian zones, woody encroached riparian zones, and riparian zones with woody vegetation removed in two separate watersheds. Riparian soil denitrification was highly seasonal, with the greatest rates in early spring. Benthic denitrification also exhibited high temporal variability, but no seasonality. Soil denitrification rates were greatest in riparian zones where woody vegetation was removed. Additionally, concentrations of nitrate, carbon, and soil moisture (indicative of potential anoxia) were greatest in wood removal soils. Differences in the presence and abundance of benthic compartments reflected riparian vegetation, and may have indirectly affected denitrification in streams. Riparian soil denitrification increased with soil water content and NO3 −. Management of tallgrass prairies that includes removal of woody vegetation encroaching on riparian areas may alter biogeochemical cycling by increasing nitrogen removed via denitrification while the restored riparian zones return to a natural grass-dominated state.

10adenitrification10anitrogen removal10aprairie streams10ariparian vegetation10atallgrass prairie10awoody encroachment1 aReisinger, A.J.1 aBlair, John, M.1 aRice, C., W.1 aDodds, W., K. uhttps://link.springer.com/article/10.1007%2Fs10021-012-9630-302357nas a2200253 4500008004100000245016000041210006900201300001300270490000700283520155600290653001501846653002001861653002301881653001001904653001101914653001301925653002001938653001301958100002001971700001801991700001702009700001802026856005902044 2011 eng d00aDirect and indirect effects of central stoneroller (Campostoma anomalum) on mesocosm recovery following a flood: can macroconsumers affect denitrification?0 aDirect and indirect effects of central stoneroller Campostoma an a840 -8520 v303 a

Anthropogenic N loadings and perturbations of macroconsumer communities impair ecological and economic services provided by streams. Organisms are adapted to natural disturbances, such as flooding and desiccation, but how anthropogenic and natural disturbances interact is poorly understood. We used large outdoor mesocosms to study the effect of Campostoma anomalum, a common prairie headwater-stream minnow, and NH4+ additions (to simulate fish excretion) on the recovery of ecosystem structure and function following a flood, highlighting the potential for Campostoma (and other macroconsumers) to affect denitrification. Campostoma and NH4+ treatments differentially affected particulate organic matter size and filamentous algal structure. Ecosystem structure responded differently to mesocosm treatment over time, a result suggesting that grazers or NH4+-N availability may be especially important during early recovery periods. The presence of Campostoma did not influence denitrification, but NH4+ additions altered the response of denitrifiers to nutrient and energy amendments, and denitrification rates decreased following the recovery of mesocosms. Temporal changes in denitrification probably were caused by increasing hyporheic dissolved O2 concentrations, which led to potentially fewer anoxic microsites for production of denitrification enzymes. Our study shows that grazers affect the recovery of ecosystem structure, but denitrification in the context of these prairie-stream mesocosms appears to be unaffected by Campostoma.

10aCampostoma10adenitrification10aEcosystem function10aFlood10agrazer10amesocosm10aprairie streams10arecovery1 aReisinger, A.J.1 aPresuma, D.L.1 aGido, K., B.1 aDodds, W., K. uhttps://www.journals.uchicago.edu/doi/10.1899/10-169.103104nas a2200205 4500008004100000245006700041210006700108260004300175490001400218520247600232653001702708653002002725653002302745653001302768653002002781653002302801100002002824700001802844856003602862 2010 eng d00aFactors affecting denitrification in headwater prairie streams0 aFactors affecting denitrification in headwater prairie streams aManhattan, KSbKansas State University0 vMS Thesis3 a

Human-induced stressors such as increased nitrogen (N) loadings, altered watershed land-use, and biodiversity losses are a few of the numerous threats to aquatic systems. Prairie streams experience natural disturbances, such as flooding and desiccation, which may alter responses to anthropogenic stressors. Denitrification, the dissimilatory reduction of NO3- to N gas (N2O or N2), is the only permanent form of N removal from terrestrial or aquatic ecosystems, and is important in mitigating N pollution to streams and downstream waters. Little is known about the relationships between denitrification and riparian prairie vegetation or large consumers. In the first chapter, I used outdoor mesocosms to determine the impact of a grazing minnow, Campostoma anomalum, on structural and functional responses of prairie streams to a simulated flood, focusing on denitrification. In terrestrial ecosystems, grazing can stimulate denitrification, but this has not been studied in streams. Ammonium (NH4+) enrichments, used to simulate fish excretion, alleviated N limitations on denitrification. Both fish and NH4+ affected algal biomass accrual, but only fish affected algal filament lengths and particulate organic matter. In a second experiment, I examined the impact of woody vegetation expansion, a primary threat to tallgrass prairie, on riparian and benthic denitrification. Expansion of woody vegetation in these grasslands is due primarily to altered fire regimes, which historically inhibited woody vegetation growth. To determine the effect of woody vegetation expansion on benthic and riparian denitrification, woody vegetation was removed from the riparian zone of a grazed and an ungrazed watershed. Both soil and benthic denitrification rates from this removal buffer were compared to rates in grassy or woody riparian zones. Riparian soil denitrification was highly seasonal, with greatest rates occurring during early spring, and rates being low throughout the remainder of the year. Benthic denitrification was also temporally variable but did not exhibit seasonal trends, suggesting benthic denitrification is driven by factors other than water temperature. Removal of woody vegetation stimulated soil and benthic denitrification rates over rates found in naturally vegetated riparian zones. Elevated N loadings will continue to affect aquatic ecosystems, and these effects may be exacerbated by biodiversity losses or changing riparian vegetation.

10aBiodiversity10adenitrification10aEcosystem recovery10anitrogen10aprairie streams10awoody encroachment1 aReisinger, A.J.1 aDodds, W., K. uhttp://hdl.handle.net/2097/4273