Nutrient Dynamics III Posters
Presiding: J Eichmiller, Kansas State University; F Triska, United States Geological Survey
NB33L-01 1330h
Ancient Soils in a Sunburnt Country: Nutrient and Carbon Distributions in an Australian Dryland River System
Riparian systems are hotspots in dryland landscapes for nutrient supply and transformation. Biogeochemical fluxes in riparian systems are closely coupled to hydrological flowpaths, which, in dryland regions, are characterised by catastrophic flooding and long periods of erratic or no flow. Re-wetting of soils stimulates soil microbial processes that drive mineralization of nutrients necessary for plant growth. We present here the first data of a 3-year research project investigating biogeochemical processes in riparian systems in the semi-arid Pilbara region of Western Australia. Spatial patterns of nitrogen, phosphorus and carbon were closely related to topographic zone (across floodplain and channels) and vegetation type. NO3- and PCi concentrations were four-fold higher in channel, bank and riparian soils than in soils of floodplain and riparian-floodplain transition zones. Nitrogen distribution was highly heterogeneous in riparian soils (NO3- CV=102%, NH4+ CV=84%) while phosphorus was particularly heterogeneous in floodplain soils (PCi CV=153%, PCo CV=266%), in comparison to other zones. Phospholipid fatty acid (PLFA) and enzymatic profiles will be used to assess microbial functional groups, combined with mineralisation experiments and stable isotope studies (15N and 13C). These data will improve understanding of biogeochemical cycling in dryland riparian systems, and contribute to improved regional management of water resources.
NB33L-02 1330h
The Influence of Land use on Headwater Stream Primary Production in two Contrasting Biomes
We examined how land use affects stream primary production in 6 semi-arid, sagebrush steppe, spring-fed streams in northwestern Wyoming, and in 6 temperate deciduous forest streams in southwest Michigan. We studied 2 streams dominated by each of 3 major land-use types: agriculture, urban, and native vegetation. Whole-stream gross primary production (GPP) was estimated from the diel change in water-column oxygen corrected for reaeration and groundwater inputs. We estimated benthic primary producer biomass using chlorophyll a measured in epilithon, episammon, and in biofilm colonizing fine benthic organic matter. We quantified riparian characteristics to examine the effect of land-use on both whole-stream GPP and benthic primary producer biomass. GPP varied both within and between biomes with the highest rates observed in Wyoming agricultural streams. Benthic primary producer biomass also varied among substrata types, within and between biomes, with epilithon having the highest chlorophyll a concentrations. GPP was not significantly correlated with benthic primary producer biomass when all streams were combined, but the relationship between GPP and benthic primary producer biomass was related to surrounding watershed land-use. Our results reflect the impact of riparian land-use change on both whole-stream and substratum-specific metrics of primary production.
NB33L-03 1330h
An Interregional Comparison of Channel Structure, Transient Storage and Riparian Canopy With Metabolism in Streams Draining Watersheds in Different Successional Stages.
We related channel structure, transient storage and riparian canopy with net daily metabolism (NDM) in 32 first- through fourth-order streams in the southeastern and northwestern United States. Management histories of the watersheds resulted in a variety of forest successional stages. Channel structure and riparian canopy estimates were collected at 10 points along each 40-100m study reach. Transient storage was calculated as differences in areas under the curves for predicted and actual Cl- transport through the study reaches. NDM was estimated from single-station oxygen changes using the surface renewal model. Channel slope was significantly related to NDM in both the northwestern and southeastern streams, and we classified streams into high (>3%) and low gradient groups. NDM ranged from -150 mg O2 m-2 d-1 in the early successional, high gradient streams to -1590 mg O2 m-2 d-1 in the mid-successional, low gradient streams. NDM in the high gradient streams was significantly correlated with percent of the stream having fast moving water (r=-0.53), transient storage (r=0.38), riparian canopy (r=-0.36) and percent coarse substrates (r=0.29). NDM in the low gradient streams was significantly correlated with stream velocity (r=-0.39) and percent coarse substrates (r=0.32).
NB33L-04 1330h
SRP Transport in the Salto River, Costa Rica: Long-term Monitoring and Short-term Experimental Approaches
Soluble reactive phosphorus (SRP) transport retention was determined since 1988 at 4 sites in three rain forest streams draining La Selva Biological Station, Costa Rica. SRP levels can be naturally high there due to regional geothermal groundwater discharge at ambient temperature. Mean SRP was 89±53ug/L for the Salto (1988-1996) compared to 21±39ug/L for a tributary Pantano (1988-1998) and 26±35ug/L in the nearby Sabalo. After 1997 Salto SRP was determined separately in upland (Upper Salto) and lowland forest (Lower Salto) reaches. Upper Salto SRP is low until enriched at the slope transition. There high SRP springs contribute approximately 36% of long term discharge and 85% of SRP load leaving the watershed. TP is negatively correlated to discharge in all streams. SRP is not correlated to discharge at low SRP sites, but negatively correlated to discharge in Lower Salto when data from 2 ENSO events (EL Nino Southern Oscillation) are removed. Short-term SPR conservative tracer addition experiments indicate high retention at all sites. Retention is dominated by sediment, as indicated by subsequent adsorption-desorption studies. Enhanced input to high SRP streams can affect biotic metabolism, litter decomposition and secondary production in these tropical environments.
NB33L-05 1330h
Characterizing the Effect of Microhabitat on Bacterial Diversity in Sediments Along Topographic Gradients
Ongoing riparian restoration including the conversion of agricultural fields back to forested areas is being conducted within the Monocacy Wildlife Management area providing the opportunity to analyze bacterial microhabitat characteristics of sediments under varying degrees of disturbance. The objective of this study is to develop greater understanding of the role of physical and chemical microhabitat differences on bacterial presence within sediments in different habitat types (i.e., upland, riparian, and in-stream) and under different degrees of disturbance. Physical and chemical microhabitat components determined were temperature, percent sediment organic matter, percent sediment moisture, concentrations of ammonia, pH, and total sediment carbon and nitrogen. Total bacterial populations of sediment were measured using 4',6-diamidino-2-phenylindole (DAPI). Polymerase chain reactions have been performed selecting for universal bacterial genes and specific nitrogen fixing, nitrifying, and denitrification genes. Bacterial diversity measurements using denaturing gradient gel electrophoresis are ongoing. Remaining chemical and physical components of microhabitat have been completed and are being analyzed. Results indicate moisture inhibits bacterial abundance while nutrient presence in sediment is associated with larger bacterial biomass. These parameters of microhabitat do not have differing effects along elevations.
NB33L-06 1330h
Influence of Elevated Levels of Arsenic on Microbial Activity in a Headwater Stream
Microbial communities play central roles in nutrient uptake, metabolism and leaf decomposition in streams. Research has shown that metazoans are extremely sensitive to arsenic pollution but microbial communities and processes appear more resistant to the influences of heavy metals and metalloids. In the case of arsenic and phosphorus, the dominant forms in aquatic ecosystems, (i.e., arsenate and phosphate) are chemically analogous. This makes it difficult for an organism to differentiate between these two molecules, potentially increasing arsenic toxicity under P-limiting situations. The primary goal of this study was determine how low phosphate concentrations and elevated levels of arsenic affected microbial activity in a headwater stream adjacent to an abandoned arsenic mine. Microbial respiration and phosphorus uptake measured on leaves and rocks were compared between an upstream (reference) and a `disturbed' reach adjacent to the arsenic mine during fall of 2004. Arsenic in stream water was <10 ppb in the reference reach and increased to 1000 ppb at the bottom of the mine-influenced reach. Soluble reactive phosphorus concentrations were <10 ppb and nitrate concentrations ranged from 400 to 800 ppb across both reaches. Microcosm respiration (0.7-1.1 g O2/m2/d) and P uptake rates (80-1600 Îœg P/m2/d) were influenced by arsenic toxicity.
NB33L-07 1330h
Nitrogen dynamics and foodweb interactions in two contrasting Arctic streams
We used a 15N tracer addition to quantify nitrogen dynamics and foodweb interactions in two contrasting tributaries of the Ivishak River in the Arctic National Wildlife Refuge, Alaska. We added 15NH4Cl simultaneously to spring and mountain streams for 4 weeks in summer of 2002 and measured 15N: 14N ratios in inorganic and biomass compartments over distance and time. 15N labeling was rapid in both streams despite low temperatures and higher than expected discharge. Compartment-specific ammonium uptake lengths (Sw) in the flashy mountain stream were initially high (7 km) due to elevated discharge, but decreased significantly thereafter (200-400 m). Uptake lengths in the hydrologically stable spring stream were similar throughout the release, but varied slightly between compartments (80-150 m). Most of the added 15N-NH4 in the spring stream was taken up by bryophytes, whereas active uptake of N in the mountain stream was by filamentous algae. Chironomids (Diamesinae and Orthocladiinae) appeared to be feeding primarily on epilithon and filamentous algae, whereas simuliids were feeding on seston in both streams. Our data show that nitrogen retention in the two streams differed and depended on turnover of organism biomass, which was controlled by physical conditions such as temperature and discharge variability.
NB33L-08 1330h
Effects of Small-Scale Substratum Heterogeneity on Respiration Rates in Streams
Substratum heterogeneity is an important driver of nutrient transformations and organic carbon production in streams. Little information is available on small-scale (< 1 m) heterogeneity and its effects on larger scale stream functions such as whole-stream respiration. We used in situ incubations of small-scale (14.5 cm x 21.5 cm) containers broken into 12 compartments with each compartment containing small gravel or sand arranged in three levels of heterogeneity. We expected that more heterogeneous systems would have greater respiration rates due to closer proximity of oxic and anoxic zones. Oxygen microelectrodes were used to determine depth to anoxia within each section of the grids and whole-container respiration was determined by enclosure in a recirculating chamber in light and dark. There was no significant difference in respiration among heterogeneity levels. There was a significant difference in depth to anoxia between substrata types at each heterogeneity level, and average depth to anoxia in small gravel of high heterogeneity grids was 22 and 25 mm deeper than in medium and low heterogeneity grids, respectively. The differences in oxic/anoxic conditions between heterogeneity levels indicates that more heterogeneous systems are likely to house "hot spots" of microbial activity could be important to larger scale stream functions.
NB33L-09 1330h
Use of Isotope Abundance of 15NO3-N in a Nitrate Rich Stream Below a Wastewater Treatment Plant to Evaluate Denitrification
Using natural isotope abundances of nitrate-nitrogen, in conjunction with nitrate concentrations along a stream transect, can provide information about nitrate input versus downstream export and losses due to denitrification. Given that denitrifying microbes prefer the lighter isotope, isotopic fractionation should occur in nitrate rich streams resulting in enrichment of 15NO3-N if denitrification is an important process resulting in an inverse relationship between nitrate and Δ 15NO3-N. Conversely, if the relationship between 15NO3-N and Δ 15N is not inversely proportional, denitrification is likely of minor importance in the reach. Variable nonlinear patterns could be indicative of 15NO3-N rich input from groundwater, tributaries or concentrations in excess of microbial demand leading to massive downstream export. We measured stream 15NO3-N concentrations in an urban stream receiving high nitrogen inputs from a wastewater treatment plant. Although observed NO3-N concentrations varied from 3-6 mg L-1 in the stream reach, the relationship between ln NO3 and Δ 15NO3-N was very weak, suggesting limited importance of denitrification.
NB33L-10 1330h
Separating Autotrophic and Heterotrophic Respiration in Streams and the Importance for Carbon Cycling: a Preliminary Study
Autotrophic and heterotrophic organisms confer different effects on nutrient cycling, especially on carbon (C). In stream ecosystems, net ecosystem production determines the amount and form of C exported; however any transformation due to different respiratory (R) mechanisms are not separated. These mechanisms highly influence the form and lability of the C transported. To understand the current state of knowledge and estimate the importance of autotrophic versus heterotrophic R, we obtained a range of respiratory rates from the literature and modeled effects of different balances of rates on bulk dissolved inorganic and organic C chemistry. Preliminary results show that a wide range of estimates of autotrophic R exist and that these can effect bulk properties of exported C. While specific effects are highly dependent upon physical structure of the study watershed, we offer that separating R mechanisms provides further insight into ecosystem C cycling. We also propose a method to measure autotrophic and heterotrophic R at the ecosystem scale and obtain watershed-level estimates of the importance of these processes on C cycling.
NB33L-11 1330h
Effects of Discontinuous Permafrost on Dissolved Organic Matter Dynamics and Whole Stream Metabolism in Boreal Forest Catchments of Interior Alaska
In the boreal forest of Interior Alaska, discontinuous permafrost is an important control on groundwater flowpaths and, consequently, regulates dissolved organic matter (DOM) and nutrient inputs into streams. Permafrost restricts ground water to the organic soil horizon, presumably resulting in streams with high DOM and low nutrient concentrations. Conversely, in catchments with less permafrost, groundwater percolates to the deeper mineral horizons, causing streams to receive higher nutrient and lower DOM loads. The effect of discontinuous permafrost on carbon and nitrogen dynamics and whole stream metabolism was examined in the Caribou-Poker Creeks Research Watershed during the summer of 2004. Metabolism was determined using whole stream measurements of change in dissolved oxygen. Oxygen evasion was quantified with injections of conservative solute and volatile gas tracers. Results support the proposed model of watershed hydrology and biogeochemistry with the high permafrost catchment having an average DOC concentration of 7.5 mgC/L compared to 3.0 mgC/L in the low permafrost site. In contrast, nitrate concentration was 115 ÎœgN/L in the high permafrost catchment and 175 ÎœgN/L in the low permafrost catchment. Due to higher concentration of DOM and lower nitrate concentration, we hypothesize that stream respiration will be higher and GPP lower in higher permafrost streams.
NB33L-12 1330h
Trends in Dissolved Organic Carbon Concentrations in Intermittent Prairie Streams
Discharge and dissolved organic carbon (DOC) data from headwater streams of Konza Prairie Research Natural Area, Kansas. Samples taken 3 times per week during periods of flow from 1995-2001 revealed three major trends in DOC dynamics. Streams exhibited low surface water DOC concentrations (1.02 mg/L, SD 0.64, n=589) at baseflow, high storm flows following a drought or low flow period caused 3-5 fold increases in DOC (up to 6.9 mg/L), and gradual resumption of stream flow following drought yielded increased DOC concentrations over several days of continuous flow. We propose a model in which hydrologic flow paths explain observed trends in DOC dynamics. We assume three compartments, soil, groundwater and streamwater. When water flows slowly from the soil to the stream through groundwater, microbial activity lowers DOC concentration. When floods occur, DOC moves rapidly from soil to stream channels. When flow resumes slowly after a dry period, soil DOC is increasingly flushed through the system leading to gradual increases in DOC. The proposed model for DOC dynamics provides a framework for future research and suggests the potential importance of hydrologic flow paths to DOC concentration in prairie streams.
NB33L-13 1330h
Spatial and Temporal Nitrogen Dynamics in Streams of the H.J. Andrews Experimental Forest
Nitrogen concentrations and fluxes have been studied for over 30 years in selected gaged streams at the Andrews Experimental Forest, Oregon. As we expand our scope of study to try to understand N dynamics throughout forested stream networks, we are examining how spatially representative these basins and measurements are within the 6400 ha Lookout Creek Basin. We are also intensively sampling nutrient concentrations during storm flows in several gaged basins across seasons. We have found that the existing monitored basins are not good representatives of headwater stream nitrate concentrations at baseflow within Lookout Creek Basin. NO3-N concentrations are generally low in the Cascades. During baseflow synoptic sampling of headwater streams, concentrations range up to 0.100 mg/L, while in the monitored basins, concentrations are an order of magnitude less (0.005 mg/L). Streams with higher NO3 cannot be explained by forest type. Storm sampling during both spring and fall storms shows similar flushing of DON and DOC on the rising limb of the hydrograph, but NO3 fluxes increase with the first fall storm only in specific basins.
NB33L-14 1330h
Comparison of Alkalizing Solutions Used in Extracellular Enzyme Assays
Extracellular enzymatic activity plays an important role in microbial nutrient cycling, and is commonly studied through the use of fluorogenic substrates. Samples are generally alkalized to maximize fluorescence yield and to prevent among sample variability in pH from affecting sample fluorescence. It is also frequently assumed that the alkaline solutions stop enzymatic reactions. Different alkalizing agents (pH 10 sodium carbonate-bicarbonate buffer, 0.05M glycine-ammonium hydroxide buffer, 40mM sodium hydroxide solution, and 2M sodium hydroxide solution) were explored for their ability to halt periphytic enzymatic activity without degrading the fluorescent product. L-Leucine-7-amido-4-methylcoumarin hydrochloride (LAMC) and 4-Methylumbeliferyl phosphate disodium salt (MUF-P) were used as fluorogenic substrates. Although 2M NaOH solution appeared to stop enzymatic reactions, it completely degraded both the AMC and MUF flurochromes, rendering it unsuitable for use as an alkalizing agent. The remaining three buffers did not greatly erode either fluorochrome, however, they were unable to halt enzymatic activity reliably. This brings into question the method of using alkalizing agents as a means of halting enzymatic reactions for later analysis.
NB33L-15 1330h
Comparison of Transient Storage Analyses Using Slug and Constant Rate Tracer Methods in two Arctic Tundra Streams
Stream ecosystem processes depend on the variability in flow paths that determine hydraulic storage. Conservative tracers are used to quantify storage by inferring hydraulics from tracer concentration dynamics. This study was designed to evaluate differences between two tracer application methods: slug releases (SR) and constant rate injections (CR). Each was performed in two morphologically different streams. Stream I8 had gravel/cobble substrate with frequent runs, and stream IS had fine substrate with frequent pools. After termination of each tracer application, six channel storage sites were sampled as tracer concentrations declined. Downstream tracer concentrations were monitored throughout all applications. In I8, the relative storage capacity (As/A) was modeled as 0.16 from SR data and 0.12 from CR data. In IS, As/A was modeled as 0.30 from SR data and 0.32 from CR data. During SR applications, storage samples demonstrated higher peak tracer concentrations in upstream sites than downstream, but during CR applications storage concentrations were relatively uniform. For these streams, the two methods did not estimate different storage extent relative to the comparison between stream morphologies. However, the tracer concentrations in channel storage suggest care should be taken with slugs in heterogeneous reaches due to preferential loading of upstream storage zones.
http://www.mines.edu/~mgooseff/arctic_proj.html