TY - JOUR T1 - Comparisons of nitrification and denitrification in prairie and agriculturally influenced streams JF - Ecological Applications Y1 - 2002 A1 - Kemp, M.J. A1 - W. K. Dodds KW - nitrification KW - prairie KW - stream AB - Whole-stream nitrification and denitrification rates were calculated from field incubation studies of representative substrata in Kings Creek and Shane Creek watersheds at the Konza Prairie Biological Station, Kansas, USA. Substrata from a relatively pristine upstream and an agriculturally influenced downstream reach were measured in both watersheds. Rates were scaled to the whole stream by the mass of each substratum in the stream reach. Substrata sampled included epilithon, leaf packs and wood (coarse benthic organic matter, CBOM), filamentous green algae, bryophytes, fine benthic organic matter (FBOM), and suspended particulate organic matter. Upstream sites had significantly lower nitrification and denitrification rates than downstream sites. Nitrification rates were dominated by nitrification associated with epilithon and filamentous green algae. Downstream sites had a higher proportion of nitrification occurring in the water column relative to upstream sites. Whole-stream denitrification was dominated by denitrification associated with FBOM and CBOM and was higher downstream. Water column ammonium (NH4+) and nitrate (NO3−) concentrations were correlated with whole-stream nitrification rates but not whole-stream denitrification rates. Whole-stream nitrification rates were positively correlated with whole-stream denitrification rates, being coupled at the whole-stream level, but not at the substratum level. Relative to the amount of NO3− produced through nitrification, the proportion of NO3− denitrified was 1.4–4.6 times greater in the downstream sites compared to the upstream sites, but the proportion of the in-stream NO3− load denitrified was ∼10 times greater in the upstream sites. These data indicate that changes in stream nitrogen cycling related to increased dissolved inorganic nitrogen concentrations do not result in a large enough increase in denitrification (the stream's capacity to retain nitrogen) to compensate for the increased nitrogen loading. Data also suggest that whole-stream nitrification and denitrification may be decoupled at the reach level by factors that decrease habitat heterogeneity (the variety of substrata types) in stream channels. This indicates that anthropogenic disturbances of small streams, such as channelization and removal of riparian vegetation, would be expected to decrease the capacity of streams to retain nitrogen. VL - 12 ER - TY - JOUR T1 - The influence of ammonium, nitrate, and dissolved oxygen concentration on uptake, nitrification, and denitrification rates associated with prairie stream substrata JF - Limnology and Oceanography Y1 - 2002 A1 - Kemp, M.J. A1 - W. K. Dodds AB -

Substrata samples were collected from Kings Creek on Konza Prairie Biological Station (Manhattan, Kansas) and incubated with varying levels of ammonium (NH4+), nitrate (NO3−), and dissolved oxygen (O2) to examine the response of nitrogen (N) uptake and transformation rates. Substrata collected were fine benthic organic matter (FBOM), coarse benthic organic matter, filamentous green algae, bryophytes, suspended particulate organic matter, and epilithic diatoms. Nitrification and denitrification were estimated by use of the nitrapyrin and acetylene inhibition methods, respectively. Ammonium uptake demonstrated Michaelis-Menten kinetics, with the highest maximum rates (Vmax) associated with filamentous green algae (5.90 mg N gdm−1 d−1) and epilithic diatoms (4.96 mg N gdm−1 d−1). Nitrate uptake did not saturate at the highest NO3− addition (25 µg N L−1) above ambient when associated with FBOM. Overall, maximum uptake rates of NH4+ were 10-fold higher than for NO3−. Nitrification response to increasing NH4+ concentrations was highly variable, depending on the substrata type. Nitrification was lowest under low O2 conditions, being undetectable when NO3− was added but not when NH4+ was added. Denitrification increased linearly with NO3− concentration when associated with epilithic diatoms and FBOM but became saturated at ~20 µg N L−1 above ambient concentrations when associated with filamentous green algae. Samples purged with N2 gas had the highest rates of denitrification. We predicted stream ecosystem rates using equations derived from the experimental data and substrata mass estimates measured in the field. Substantial temporal variability was predicted in uptake (0–1,300 mg NH4+−N m−2 d−1; 0–5.2 mg NO3−−N m−2 d−1), nitrification (0–35 mg NH4+−N m−2 d−1), and denitrification (0–130 µg N2O-N m−2 d−1) as due to natural variation in water column NH4+, NO3−, and O2 concentrations.

VL - 47 ER - TY - JOUR T1 - Centimeter-scale patterns of oxygen concentrations related to nitrification in prairie stream substrate JF - Journal of the North American Benthological Society Y1 - 2001 A1 - Kemp, M.J. A1 - W. K. Dodds KW - Algae KW - microelectrodes KW - N cycling KW - nitrification KW - O2 concentration KW - streams KW - tallgrass prairie AB - Dissolved oxygen (O2) was measured with microelectrodes in shallow subsurface microsites in a prairie stream and related to rates of nitrification determined in the laboratory using the nitrapyrin method. Substrata sampled included diatom mats, leaves and wood (coarse benthic organic matter, CBOM), filamentous green algae, bryophytes, and fine benthic organic matter (FBOM). Significant differences in O2 concentrations were found among the substrata, with anoxic zones occurring primarily in FBOM from deep pool sediments and CBOM from litter accumulations. Filamentous green algae and bryophytes had average O2 concentrations near saturation and intermediate rates of nitrification. Diatom mats had the highest concentrations of O2 (up to several times saturation) and the highest rates of nitrification. In the summer, O2 concentrations were above saturation in epilithon and filamentous green algal mats. Nitrification rates were highest in epilithon and filamentous green algae samples taken in the spring and autumn. A significant positive relationship between nitrification rates and O2 concentration was observed in all seasons except summer. These data suggest that O2 concentration could control nitrification in prairie streams. VL - 20 ER - TY - THES T1 - Factors Controlling Spatial and Temporal Patterns of Nitrogen Cycling in Tallgrass Prairie Streams Y1 - 2001 A1 - Kemp, M.J. KW - tallgrass prairie AB -

The factors regulating nitrogen cycling in streams draining Konza Prairie Biological Station, Kansas, were analyzed to examine the influence of agricultural activity and non-anthropogenic factors. Patterns of total nitrogen concentrations in the water-column were driven largely by changes in nitrate concentration. A gradient of increasing nitrate occurred from pristine upland reaches to the more agriculturally influenced lowland reaches. The relatively pristine upstream sites had significantly lower nitrification and denitrification rates than the downstream, more agriculturally influenced, sites. Water-column ammonium and nitrate concentrations were correlated with whole stream nitrification rates, but not whole stream denitrification rates. Nitrification rates were positively correlated with denitrification rates at the whole stream level, but not at the substratum level. A significant positive relationship was observed between substrata nitrification rates and dissolved oxygen concentration in all seasons except summer, when concentrations were super saturated. Nitrogen uptake followed Michaelis-Menton kinetics when associated with all substrata, and was 10-fold higher for ammonium relative to nitrate. Nitrification and denitrification responses to variable ammonium, nitrate, and oxygen concentrations differed with substrata type. Substantial temporal variability (< 30%) was predicted in uptake, nitrification, and denitrification due to natural variation in water-column ammonium, nitrate, and oxygen concentrations. These data suggest that natural processes lead to less than 10-fold variation in nitrate concentrations in relatively pristine prairie streams, whereas variation due to agricultural inputs is < 100 fold. Data also suggest that whole stream nitrification and denitrification may be decoupled at the reach level by factors that decrease substrata heterogeneity in stream channels.

PB - Kansas State University CY - Manhattan, KS VL - PhD Dissertation UR - http://disccrs.org/dissertation_abstract?abs_id=340 ER - TY - JOUR T1 - Spatial and temporal patterns of nitrogen concentrations in pristine and agriculturally- influenced prairie streams JF - Biogeochemistry Y1 - 2001 A1 - Kemp, M.J. A1 - W. K. Dodds KW - ammonium KW - groundwater KW - Nitrate KW - nutrient cycling KW - riparian buffer zones KW - streams AB - Long-term data on nitrogen chemistry of streams draining Konza Prairie Biological Station (Konza), Kansas were analyzed to assess spatial and temporal patterns and examine the influence of agricultural activity on these patterns. Upland watersheds of Konza are predominantly tallgrass prairies, but agricultural fields and riparian forests border the lower reaches of the streams. We have up to 11 years of data in the relatively pristine upland reaches and 4 years of data on wells and downstream reaches influenced by fertilized croplands. Seasonal and spatial patterns in total nitrogen (TN) concentrations were driven largely by changes in the nitrate (NO3 −) concentrations. A gradient of increasing NO3 − concentrations occurred from pristine upland stream reaches to the more agriculturally-influenced lowland reaches. Nitrate concentrations varied seasonally and were negatively correlated with discharge in areas influenced by row-crop agriculture (p = 0.007). The NO3 − concentrations of stream water in lowland reaches were lowest during times of high precipitation, when the relative influence of groundwater drainage is minimal and water in the channel is primarily derived from upland prairie reaches. The groundwater from cropland increased stream NO3 − concentrations about four-fold during low-discharge periods, even though significant riparian forest corridors existed along most of the lower stream channel. The minimum NO3 − concentrations in the agriculturally influenced reaches were greater than at any time in prairie reaches. Analysis of data before and after introduction of bison to four prairie watersheds revealed a 35% increase of TN concentrations (p < 0.05) in the stream water channels after the introduction of bison. These data suggest that natural processes such as bison grazing, variable discharge, and localized input of groundwater lead to variation in NO3 − concentrations less than 100-fold in prairie streams. Row-crop agriculture can increase NO3 − concentrations well over 100-fold relative to pristine systems, and the influence of this land use process over space and time overrides natural processes. VL - 53 ER - TY - JOUR T1 - Quantification of the nitrogen cycle in a prairie stream JF - Ecosystems Y1 - 2000 A1 - W. K. Dodds A1 - Evans-White, M.A. A1 - N.M. Gerlanc A1 - Gray, L. A1 - Gudder, D.A. A1 - Kemp, M.J. A1 - Lo'pez, A.L. A1 - Stagliano, D. A1 - Strauss, E. A1 - Tank, J.L. A1 - M.R. Whiles A1 - Wollheim, W. KW - aquatic insects KW - C:N ratio KW - nitrogen cycle KW - nitrogen export KW - stream KW - Trophic structure AB - Nitrogen (N) was added for 35 days in the form of 15NH4Cl to Kings Creek on Konza Prairie, Kansas. Standing stocks of N in key compartments (that is, nutrients, detritus, organisms) were quantified, and the amount of labeled N entering the compartments was analyzed. These data were used to calculate turnover and flux rates of N cycling through the food web, as well as nutrient transformation rates. Inorganic N pools turned over much more rapidly in the water column of this stream than in pelagic systems where comparable measurements have been made. As with other systems, the mass of ammonium was low but it was the key compartment mediating nutrient flux through the ecosystem, whereas dissolved organic N, the primary component of N flux through the system, is not actively cycled. Nitrification was also a significant flux of N in the stream, with rates in the water column and surface of benthos accounting for approximately 10% of the total ammonium uptake. Primary consumers assimilated 67% of the inorganic N that entered benthic algae and microbes. Predators acquired 23% of the N that consumers obtained. Invertebrate collectors, omnivorous crayfish (Orconectes spp.), and invertebrate shredders dominated the N flux associated with primary consumers. Mass balance calculations indicated that at least 23% of the 309 mg of 15N added during the 35 days of release was retained within the 210-m stream reach during the release. Overall, the rates of turnover of N in organisms and organic substrata were significantly greater when C:N was low. This ratio may be a surrogate for biological activity with regard to N flux in streams. VL - 3 ER -