Nutrient Uptake In Streams Research Articles

Improving in-stream nutrient retention potential through factitious manipulation: the stepping stone structures of flying-geese pattern and their reinforcement structures.

Small streams are essential parts of water ecosystems, such as rivers, lakes, and reservoirs, performing vital functions in the attenuation of nutrient pollution. As eutrophication becomes an increasingly severe problem in waters, it is necessary to investigate how to improve nutrient retention potential in streams. In this study, the effect of artificial manipulation was examined on transient storage and nutrient uptake in streams by setting up the stepping stone structures of flying-geese pattern (SG) and the combination mode of SG and bilaterally staggered spur dikes (SG+SD) in the channel. The tracer experiments were performed to confirm the effectiveness of SG and SG+SD in two headwater streams, which are tributaries of the Chaohu Lake basin. Additionally, the transient storage and nutrient uptake potential were assessed by the OTIS (one-dimensional transport with inflow and storage) model and the nutrient spiraling theory. Compared with the control, the implementation of SG in the Banqiao River increased the retention of ammonium (NH4+) and phosphate (PO43). Furthermore, the transient storage capacity and nutrient uptake potential in the Ershibu River were strengthened with the addition of bilaterally staggered spur dikes based on SG. These results highlight the importance of manipulating the geomorphology of the streambed to enhance the nutrient retention potential in streams.

Changes in hydrology affects stream nutrient uptake and primary production in a high-Arctic stream

Global change is predicted to have a marked impact on freshwater ecosystems in the High Arctic, including temperature increase, enhanced precipitation, permafrost degradation and increased vegetation cover. These changes in river catchments can alter flow regime, solute transport to streams and substantially affect stream ecosystem functioning. The objective of this study was to evaluate changes in stream functioning in a high-Arctic stream in relation to changes in discharge, and runoff flow path. We measured environmental factors, biofilm structure, nutrient uptake rates and metabolism. We studied three reaches in a headwater stream in NE Greenland with different catchment characteristics in early and late summer (during two different years) to evaluate the potential influence of environmental change on Arctic stream ecosystem functioning. Highest nutrient uptake, primary production and ecosystem respiration was found in late summer showing that streams are more efficient at retaining nutrients and have higher autotrophic production, likely due to less impact of snowmelt, and lower discharge increasing the surface to volume ratio between streambed and water column. Nutrient uptake rates in late summer from high-Arctic tundra streams were comparable to uptake rates in temperate pristine streams, likely due to no shading by bank vegetation and longer days in the high-Arctic summer compared to temperate streams. Overall, the results of this study aids in the endeavor of predicting how climate-derived changes will affect in-stream nutrient uptake and metabolism in high-Arctic streams. The results suggest that their capacity to transport, cycle and retain carbon and nutrient may increase if the importance of soil water flow paths for streams also increase, thus with effect to stream trophic relations and solute export to coastal areas.

A comparison of nutrient uptake efficiency and growth rate between different macrophyte growth forms

Aquatic macrophytes grow abundantly in many lowland streams and play a key role in ecosystem functioning, such as nutrient retention. In this study, we performed a microcosm experiment to quantify and compare the contribution of two freshwater macrophyte growth forms to nutrient cycling. We measured and compared inorganic nitrogen (NH4–N and NO3–N) and phosphorus (PO4–P) uptake kinetic parameters (Vmax and Cmin) in 12 submerged and seven amphibious plant species. We tested whether relative growth rate (RGR) was related to high Vmax and low Cmin, and quantified changes in nutrient uptake kinetic in a subset of six out of 19 plants species during the growth season. Uptake rates of NH4–N were higher in submerged compared to amphibious plants, whereas uptake rates of NO3–N were significantly higher in amphibious species; PO4–P uptake kinetics were not significantly different between the two growth forms. There were also significant seasonal differences in Vmax NH4–N rate among both submerged and amphibious species and in Vmax NO3–N among amphibious species. Highest uptake rates were observed in summer for both submerged and amphibious species. Overall, we found that nutrient uptake kinetics differed between the two growth forms within and between seasons. Consequently, the presence of both growth forms should extend the period of nutrient uptake across the year and enhance nutrient uptake within seasons. We conclude that higher functional diversity enhances annual nutrient uptake in streams and that stream restoration efforts should consider increasing the niche space available for both submerged and amphibious species.

Agriculture influences ammonium and soluble reactive phosphorus retention in South American headwater streams

AbstractAgricultural activities can affect the delivery of nutrients to streams, riparian canopy cover, and the capacity of aquatic systems to process nutrients and sediments. There are few measures of nutrient uptake and metabolism from tropical or subtropical streams in general, and even fewer from tropical regions of South America. We examined ammonium (NH4+) and soluble reactive phosphorus (SRP) retention in streams in Brazil and Argentina. We selected 12 streams with relatively little or extensive agricultural activity and conducted whole‐stream nutrient additions and measurements of gross primary production and ecosystem respiration. We used multiple linear regression to determine potential drivers of nutrient uptake metrics across the streams. Nutrient concentrations and retention differed significantly between land use categories. Both NH4+ and SRP concentrations were higher in the agricultural sites (means of 161 and 495 μg l–1, respectively), whereas metabolic rates were slower and transient storage was smaller. Our analysis indicated that agriculture increased ambient uptake lengths and decreased uptake velocities. The regression models revealed that ambient SRP had a positive effect on NH4+ uptake and vice versa, suggesting strong stoichiometric controls. Drivers for nutrient uptake in streams with low‐intensity agriculture also included canopy cover, temperature, and ecosystem respiration rates. Nutrient assimilation in agricultural sites was influenced by a higher number of variables (gross primary production for SRP, discharge, and transient storage for both nutrients). Our results indicate agricultural activity changes both the magnitude of in‐stream nutrient uptake and the mechanisms that control its variation, with important implications for South American streams under agricultural intensification.

Measurement uncertainty in stream nutrient uptake: Detecting land-use impacts on tropical streams

Abstract Stream nutrient uptake is an important ecosystem service, because it supplies human needs such as water purification. Uncertainty in nutrient uptake measurement determines, in combination with effect magnitude, whether effects of land use, stream restoration or climate change can be detected by this method. However, measurement uncertainty for nutrient uptake metrics is rarely reported. Here, we compared whole-stream phosphate and nitrate uptake among three pristine and three agricultural tropical Cerrado streams. We quantified uncertainty in uptake metrics estimated by kinetic nutrient-addition experiments and evaluated their potential to detect land-use effects. Ambient phosphate and nitrate uptake lengths (SW) ranged from 11 to 106 m and from 29 to 357 m, respectively, in pristine streams and from 41 to 586 m and from 76 to 1372 m in agricultural streams. Moderate measurement uncertainty in SW allowed for the detection of land-use impacts with this metric. However, derived nutrient uptake metrics, such as ambient uptake rates and uptake velocities, as well as parameters of whole-stream saturation kinetics, were associated with high measurement uncertainties that prevented the detection of potential land-use effects. Sensitivity analyses suggested that avoiding high enrichment levels in kinetic addition experiments and increasing sampling effort for plateau nutrient and tracer concentration at the first and last sampling stations of investigated stream reaches are the most promising strategies to reduce measurement uncertainty. Analyzing nutrient uptake without considering measurement uncertainty might lead to poor interpretation in case studies and meta-analyses, such as incorrect evaluations of human impacts or comparisons among systems.

Uptake of ammonium and soluble reactive phosphorus in forested streams: influence of dissolved organic matter composition

Many microbes responsible for inorganic nutrient uptake and transformation utilize dissolved organic matter (DOM) as a nutrient or energy source, but little is known about whether DOM composition is an important driver of nutrient uptake in streams. Our goal was to determine whether incorporating DOM composition metrics with other more commonly considered biological, physical, and chemical variables improved our ability to explain patterns of ammonium ( $${\text{NH}}_{4}^{ + }$$ –N) and soluble reactive phosphorus (SRP) uptake across 11 Lake Superior tributaries. Nutrient uptake velocities (Vf) ranged from undetectable to 14.6 mm min−1 for $${\text{NH}}_{4}^{ + }$$ –N and undetectable to 7.2 mm min−1 for SRP. Logistic regressions suggested that DOM composition was a useful predictor of where SRP uptake occurred (4/11 sites) and $${\text{NH}}_{4}^{ + }$$ –N concentration was a useful predictor of where $${\text{NH}}_{4}^{ + }$$ –N uptake occurred (9/11 sites). Multiple regression analysis revealed that the best models included temperature, specific discharge, and canopy cover, and DOM composition as significant predictors of $${\text{NH}}_{4}^{ + }$$ –N Vf. Partial least squares revealed fluorescence index (describing the source of aquatic fulvic acids), specific ultraviolet absorbance at 254 nm (an indicator of DOM aromaticity), temperature, and conductivity were highly influential predictors of $${\text{NH}}_{4}^{ + }$$ –N Vf. Therefore, streams with higher temperatures, lower solute concentrations, more terrestrial DOM signal and greater aromaticity had greater $${\text{NH}}_{4}^{ + }$$ –N Vf. Our results suggest that DOM composition may be an important, yet often overlooked, predictor of $${\text{NH}}_{4}^{ + }$$ –N and SRP uptake in deciduous forest streams that should be considered along with commonly measured predictors.

Sensitivity analysis of a pulse nutrient addition technique for estimating nutrient uptake in large streams

The constant nutrient addition technique has been used extensively to measure nutrient uptake in streams. However, this technique is impractical for large streams, and the pulse nutrient addition (PNA) has been suggested as an alternative. We developed a computer model to simulate Monod kinetics nutrient uptake in large rivers and used this model to evaluate the sensitivity of the PNA technique. We parameterize our model using the average hydrogeomorphological estimates from a pulse release study of ammonium in the Snake River, WY, and used this study to demonstrate how data from a field experiment can be effectively analyzed using a simulation model. To evaluate the sensitivity of the PNA technique, we manipulated the hydrogeomorphology and uptake kinetics of our stream model, simulated a pulse ammonium addition, and measured the downstream response in our model as if it were a field experiment, while ammonium areal uptake at ambient concentration was kept unchanged in the model. Ammonium uptake estimates by the PNA technique were different from the uptake in our model and these differences were nonrandom. The difference was greatest when velocity was high and there was little solute spread, either in the water column or from exchange with transient storage. The difference was also high when the half saturation coefficient for uptake was low. Our estimates of ammonium uptake under the assumption of Monod kinetics were higher than those under the assumption of first‐order kinetics based on direct calculation from the experimental data.

Importance ofTerrestrialArthropods asSubsidies inLowlandNeotropicalRainForestStreamEcosystems

AbstractThe importance of terrestrial arthropods has been documented in temperate stream ecosystems, but little is known about the magnitude of these inputs in tropical streams. Terrestrial arthropods falling from the canopy of tropical forests may be an important subsidy to tropical stream food webs and could also represent an important flux of nitrogen (N) and phosphorus (P) in nutrient‐poor headwater streams. We quantified input rates of terrestrial insects in eight streams draining lowland tropical wet forest inCostaRica. In two focal headwater streams, we also measured capture efficiency by the fish assemblage and quantified terrestrially derivedN‐ andP‐excretion relative to stream nutrient uptake rates. Average input rates of terrestrial insects ranged from 5 to 41 mg dry mass/m2/d, exceeding previous measurements of aquatic invertebrate secondary production in these study streams, and were relatively consistent year‐round, in contrast to values reported in temperate streams. Terrestrial insects accounted for half of the diet of the dominant fish species,Priapicthys annectens. Although terrestrially derived fish excretion was found to be a small flux relative to measured nutrient uptake rates in the focal streams, the efficient capture and processing of terrestrial arthropods by fish made these nutrients available to the local stream ecosystem. This aquatic‐terrestrial linkage is likely being decoupled by deforestation in many tropical regions, with largely unknown but potentially important ecological consequences.

Organic matter stoichiometry influences nitrogen and phosphorus uptake in a headwater stream

The concept of nutrient spiraling combines the geological, hydrological, and biological processes that influence nutrient cycling in streams. Spiraling studies have demonstrated connections between metabolic and nutrient cycles, organic matter (OM) dynamics, and hydrologic controls. Most spiraling studies have addressed the dynamics of a single element. However, nutrients do not move through ecosystems in isolation. Recent models have used ecological stoichiometric theory to couple N and P cycles, but empirical data to support these conceptual frameworks are generally lacking. We investigated the relationship between N and P uptake and the extent to which OM stoichiometry was related to the relative uptake of N and P in a headwater stream across 2 seasons. In addition, we explored whether our results were consistent with theoretical predictions derived from ecological stoichiometry and consumer–resource imbalances. We found that higher respiration led to higher NH4+ and P uptake rates. NH4+ and P uptake were strongly correlated, but the nature of this relationship shifted with a seasonal change in the dominant OM to fresh leaf litter in autumn. OM stoichiometry was a strong predictor of relative nutrient uptake (NH4∶SRP uptake ratios). Seasonal input of low N∶P leaf litter led to relatively higher NH4+ uptake from the water column, which caused a shift in relative nutrient uptake but did not alter the strength of the coupling. Our results indicate that stoichiometric imbalances between nutrient consumers and resources have a strong influence on nutrient uptake in streams. Moreover, stoichiometric models of consumer–resource imbalances between microbes and dominant OM substrates accurately captured N and P uptake dynamics in our study system. Integrating stoichiometry with metabolic controls provides insights into nutrient dynamics and acts as a framework to link N and P cycles.

Stream nitrate uptake and transient storage over a gradient of geomorphic complexity, north‐central Colorado, USA

AbstractThe understanding of nutrient uptake in streams is impeded by a limited understanding of how geomorphic setting and flow regime interact with biogeochemical processing. This study investigated these interactions as they relate to transient storage and nitrate uptake in small agricultural and urban streams. Sites were selected across a gradient of channel conditions and management modifications and included three 180‐m long geomorphically distinct reaches on each of two streams in north‐central Colorado. The agricultural stream has been subject to historically variable cattle‐grazing practices, and the urban stream exhibits various levels of stabilisation and planform alteration. Reach‐scale geomorphic complexity was characterised using highly detailed surveys of channel morphology, substrate, hydraulics and habitat units. Breakthrough‐curve modelling of conservative bromide (Br−) and nonconservative nitrate (NO3−) tracer injections characterised transient storage and nitrate uptake along each reach. Longitudinal roughness and flow depth were positively associated with transient storage, which was related to nitrate uptake, thus underscoring the importance of geomorphic influences on stream biogeochemical processes. In addition, changes in geomorphic characteristics due to temporal discharge variation led to complex responses in nitrate uptake. Copyright © 2011 John Wiley & Sons, Ltd.

Influence of transient storage on stream nutrient uptake based on substrata manipulation

Quantification of the transient storage zone (As) has become critical in stream biogeochemical studies addressed to examine factors controlling nutrient uptake. It is expected that higher As may enhance the interaction between nutrients and biota and thus, increase nutrient uptake. However, results from the literature are controversial. We hypothesized that besides of the size of As, the intrinsic physical and biological characteristics of stream structures that generate As are also relevant for nutrient uptake. We performed 24 additions of phosphate, ammonium, and chloride in four reaches of a man-made channel where we introduced three types of naturally colonized substrata packs (mud, sand and cobbles) to modify As. We estimated ammonium and phosphate uptake coefficients in both the main channel and As using a solute transport model (OTIS-P) and compared the results among reaches with different substrata types. The introduction of substrata packs decreased water velocity and increased As similarly among treatments. Nutrient uptake coefficients in the main channel were similar among reaches with different type substrata packs; however, nutrient uptake coefficients measured in As differed among them as well as the ratio between ammonium and phosphorus uptake coefficients in As, which were 1.6 in reaches with mud packs and 0.02 in reaches with sand or cobble packs. Results obtained in this study suggest that the contribution of As in nutrient uptake not only depends on the size of As but on the type of materials used to increase As, and thus, have biogeochemical implications on restoration projects aimed to modify channel morphology.

Special Issue on River Flow Hydrodynamics: Physical and Ecological Aspects

As part of the celebration in Minneapolis on May 19–21, 2008, of the 70th year since the St. Anthony Falls Laboratory was first dedicated on November 17, 1938, a minisymposium on the topic of stream restoration fluid mechanics was organized within the inaugural conference of ASCE’s Engineering Mechanics Institute. Ten papers are included in this special issue representing contributions that were made to this minisymposium as well as manuscripts that were solicited from other authors in an effort to expand coverage of the subject. This issue provides the opportunity to review the progress that has been made in some areas of modeling river flow hydrodynamics, with emphasis on physical and ecological aspects. The issue begins with two papers dealing with in-stream structures, including those used for flow training and those that serve as bridge foundations, and their potential effects on river behavior. The first paper, “River Training and Ecological Enhancement Potential Using In-Stream Structures” by Radspinner et al., provides a review of the available literature and engineering design experience. Cross vanes, J-hook vanes, rock vanes, W-weirs, submerged vanes, stream barbs, bendway weirs, spurs, and constructed riffles, which represent the most commonly used instream flow control structures, are considered. Survey results obtained from federal and state agency personnel indicate that in terms of cost, performance, maintenance, and environmental enhancement, in-stream structures are preferable to riprap revetment, dredging, and concrete. Results from case studies and discussions with practitioners highlight the need for better-defined guidelines for the design of these structures. In their paper “Coherent Structure Dynamics in Turbulent Flows Past In-Stream Structures: Some Insights Gained via Numerical Simulation,” Paik et al. review the latest developments in the use of hybrid unsteady Reynolds-averaged Navier-Stokes/large-eddy simulation URANS/LES modeling strategies for simulating turbulent flows around in-stream structures. These computational fluid dynamics CFD techniques are capable of resolving coherent structures, such as the turbulent horseshoe vortex past bed-mounted piers, for a wide range of Reynolds number flows and thus of capturing some intricate aspects of the flow field and associated scour in the vicinity of hydraulic structures. Furthermore, the capability of modeling such structures at ecologically relevant scales is crucial for the development of improved stream restoration designs. The issue continues with a group of three papers that focus on the flow through vegetation hydrodynamics and nutrient uptake in streams. The first of these papers, “Effects of Added Vegetation on Sand Bar Stability and Stream Hydrodynamics” by Rominger

Tracer Additions for Spiraling Curve Characterization (TASCC): Quantifying stream nutrient uptake kinetics from ambient to saturation

Stream nutrient tracer additions and nutrient spiraling metrics are frequently used to quantify lotic ecosystem behavior. Of particular concern is the influence nutrient concentration exerts on nutrient retention and export. However, characterizing spiraling response curves across a range of concentrations has remained challenging, in part due to the large effort required to develop these curves using traditional (e.g., plateau or steadystate) approaches. Here we outline and demonstrate a new approach to quantify nutrient uptake kinetics from ambient to saturation using Tracer Additions for Spiraling Curve Characterization (TASCC). This approach provides a rapid and relatively easy technique for quantifying ambient‐spiraling parameters, nutrient uptake kinetics and kinetic model parameterization, and assessment of stream proximity to saturation. We compare the results from TASCC to traditional breakthrough curve integrated and plateau approaches. We highlight the advantages of the TASCC approach for characterizing continuous spiraling response curves from ambient to saturation with a single tracer addition experiment, and its applicability to larger rivers where achieving plateau conditions (i.e., steady‐state) is impractical.

Diurnal variations in dissolved organic matter and ammonium uptake in six open-canopy streams

Daily fluctuations of primary production can result in diurnal variations in labile dissolved organic C (DOC) and N (DON) concentrations, but we know little about how biotic uptake of labile DOC and DON changes from day to night. We compared daytime vs nighttime uptake of ammonium (NH4+), acetate (labile DOC), and glycine (labile DON) using short-term nutrient releases conducted in 6 open-canopy streams in northwestern Wyoming, USA. NH4+ uptake was primarily a function of autotrophic demand because it was often higher during the day, and daytime uptake was driven by gross primary production when placed in context of prior data from the region (r2 = 0.60, p < 0.001). However, acetate uptake showed no significant diurnal change and the quality of fine benthic organic matter explained diurnal variation in uptake across streams, indicating control via heterotrophic demand (r2 = 0.94, p = 0.006). Patterns in glycine uptake were distinct from both NH4+ and acetate uptake. Glycine uptake decreased as the ratio of total dissolved N to soluble reactive P increased (r2 = 0.72, p = 0.002), indicating that DON uptake might be P-limited. Uptake did not differ significantly by solute type, suggesting labile forms of DOC and DON can be cycled as rapidly as NH4+, a solute traditionally considered to be extremely bioreactive in headwater streams. Thus, demand for labile DOC and DON was high despite the fact that bulk DOC and DON concentrations were high relative to inorganic N. This result suggests that ambient availability of labile organic nutrients might not satisfy demand. Last, diurnal variation in NH4+, DOC, and DON demand was as high as annual variation in some forested streams; therefore, future stream nutrient uptake studies should be consider how and when uptake is measured, particularly in streams with open canopies.

Variation in stream C, N and P uptake along an altitudinal gradient: a space-for-time analogue to assess potential impacts of climate change

A space-for-time substitution approach was used to evaluate potential effects of climate change on stream nutrient uptake by examining the relationship between stream environmental parameters and carbon (C), nitrogen (N) and phosphorus (P) uptake along an altitudinal gradient. The study was carried out in 14 streams located in the Central Pyrenees (NE Spain) draining calcareous catchments that cover an altitudinal range of 700–2,100 m a.s.l. In these streams, uptake of inorganic (soluble reactive phosphorus (SRP), ammonium and nitrate) and organic (acetate and glycine) nutrients was estimated. Additionally, several physical, chemical and biological parameters were measured. Results showed higher uptake for both SRP, a potentially limiting nutrient in these streams, and glycine, a labile source of dissolved organic N, than for the rest of the nutrients. Uptake of SRP, nitrate, glycine and acetate varied along stream environmental gradients associated with changes in stream hydromorphology, SRP availability and epilithic biomass. However, these gradients did not vary with altitude. These results indicate that climate change effects on stream nutrient uptake are more likely to be driven by indirect effects on hydromorphology and nutrient availability induced by shifts in the precipitation and run-off regime than by direct modifications in the thermal regime.

NO EVIDENCE OF GENETIC ASSOCIATION BETWEEN DRD3 VARIANTS AND TARDIVE DYSKINESIA IN KOREAN SCHIZOPHRENIC PATIENTS

Stream nutrient uptake is an important ecosystem service, because it supplies human needs such as water purification. Uncertainty in nutrient uptake measurement determines, in combination with effect magnitude, whether effects of land use, stream restoration or climate change can be detected by this method. However, measurement uncertainty for nutrient uptake metrics is rarely reported. Here, we compared whole-stream phosphate and nitrate uptake among three pristine and three agricultural tropical Cerrado streams. We quantified uncertainty in uptake metrics estimated by kinetic nutrient-addition experiments and evaluated their potential to detect land-use effects. Ambient phosphate and nitrate uptake lengths (SW) ranged from 11 to 106 m and from 29 to 357 m, respectively, in pristine streams and from 41 to 586 m and from 76 to 1372 m in agricultural streams. Moderate measurement uncertainty in SW allowed for the detection of land-use impacts with this metric. However, derived nutrient uptake metrics, such as ambient uptake rates and uptake velocities, as well as parameters of whole-stream saturation kinetics, were associated with high measurement uncertainties that prevented the detection of potential land-use effects. Sensitivity analyses suggested that avoiding high enrichment levels in kinetic addition experiments and increasing sampling effort for plateau nutrient and tracer concentration at the first and last sampling stations of investigated stream reaches are the most promising strategies to reduce measurement uncertainty. Analyzing nutrient uptake without considering measurement uncertainty might lead to poor interpretation in case studies and meta-analyses, such as incorrect evaluations of human impacts or comparisons among systems.

Discontinuities in stream nutrient uptake below lakes in mountain drainage networks

In many watersheds, lakes and streams are hydrologically linked in spatial patterns that influence material transport and retention. We hypothesized that lakes affect stream nutrient cycling via modifications to stream hydrogeomorphology, source‐waters, and biological communities. We tested this hypothesis in a lake district of the Sawtooth Mountains, Idaho. Uptake of NO3− and PO4−3 was compared among 25 reaches representing the following landscape positions: lake inlets and outlets, reaches &gt;1‐km downstream from lakes, and reference reaches with no nearby lakes. We quantified landscape‐scale hydrographic and reach‐scale hydrogeomorphic, source‐water, and biological variables to characterize these landscape positions and analyze relationships to nutrient uptake. Nitrate uptake was undetectable at most lake outlets, whereas PO4−3 uptake was higher at outlets as compared to reference and lake inlet reaches. Patterns in nutrient demand farther downstream were similar to lake outlets with a gradual shift toward reference‐reach functionality. Nitrate uptake was most correlated to sediment mobility and channel morphology, whereas PO4−3 uptake was most correlated to source‐water characteristics. The best integrated predictor of these patterns in nutrient demand was % contributing area (the proportion of watershed area not routing through a lake). We estimate that NO3− and PO4−3 demand returned to 50% of pre‐lake conditions within 1‐4‐km downstream of a small headwater lake and resetting of nutrient demand was slower downstream of a larger lake set lower in a watershed. Full resetting of these nutrient cycling processes was not reached within 20‐km downstream, indicating that lakes can alter stream ecosystem functioning at large spatial scales throughout mountain watersheds.

Nitrogen spiraling in streams: Comparisons between stable isotope tracer and nutrient addition experiments

A common method to quantify stream nutrient uptake length is to enrich the stream at an upstream point and monitor the downstream decline in the concentration of the added nutrient. However, increasing the nutrient concentration of the stream alters nutrient uptake, and uptake length quantified using this amendment approach does not necessarily reflect uptake length under ambient conditions. We conducted a series of 15NO3− tracer and 14NO3− nutrient amendment experiments to (1) assess the overestimation of amendment‐derived uptake length in streams spanning a gradient of ambient nitrogen concentration, and (2) evaluate a technique to estimate ambient uptake length using data from multiple amendments conducted at different concentrations. Single amendment‐derived uptake lengths were consistently longer than ambient uptake lengths quantified using the stableisotope tracer. The ratio of single amendment‐derived to ambient uptake length ranged more than sixfold across streams but was not related to ambient stream water nitrogen concentration or amendment concentration. Estimated ambient uptake length calculated from the multiple amendment technique was a better predictor of ambient uptake length than single amendment‐derived uptake length in three of five experiments. However, with this technique, calculated uptake length was negative in two streams. Our results suggest that nitrogen limitation was weak in these two streams and that the multiple amendment technique may be ineffective in streams where the nutrient of study is not limiting.

Corrigendum

Freshwater BiologyVolume 51, Issue 5 p. 986-987 Free Access Corrigendum First published: 13 April 2006 https://doi.org/10.1111/j.1365-2427.2006.01548.xCitations: 4AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat There is an error in eqn 3, Fig. 3 and associated text in Cross et al. (2005). The corrected equation, figure and text are printed below. The corrected text begins with the last paragraph of page 1905 in Cross et al. (2005). Figure 3Open in figure viewerPowerPoint Hypothetical relationship between stream water column N and P concentrations, uptake rates and uptake lengths (as determined by solute addition experiments) for various scenarios. In scenario I, the water column is the sole source of nutrients for benthic biomass production, assimilation by benthic organisms represents the only nutrient demand, and nutrients are not differentially recycled in the benthic compartment. In scenarios II–IV, these assumptions are altered to assess how each affects nutrient spiralling ratios as determined by solute addition techniques. Solid vertical arrows represent flows of dissolved inorganic N and P. Dotted vertical arrows represent flows of dissolved and/or particulate organic N and P. Correction (corrected text in italics): The utility of beginning with this simplified case is that it helps identify several characteristics of stream ecosystems that can cause UN : UP (and SW–N : SW–P) to vary from the value predicted by BN : BP. For example, the supply of N and P is rarely, if ever, fully provided by dissolved inorganic elements extracted from the water column, although uptake length calculations are almost exclusively determined from these forms. Alternate avenues of nutrient delivery to benthic organisms include local mineralisation of organic matter, perfusion of ground water through stream sediments, and direct use of nutrients in organic matter (Sheibley et al., 2003; Brookshire et al., 2005). Regardless of the mechanism, differential subsidies of N and P will cause UN : UPto vary from BN : BP(Fig. 3). Variable fractions of N and P demand met by flowing water supplies (FNandFP, respectively) will change relative uptake rates such that:(3) For example, if 10% of N demand and 40% of P demand is supplied by non-water column sources (F N and F P equal 0.9 and 0.6, respectively), U N : UPandSW−N : SW−Pwould increase to about 22.5 and 0.5, respectively (Fig. 3, scenario II). In this scenario, gross UN : UP(assimilation of N and P by organisms) has not changed and remains equivalent to BN : BP(=15). However, differential use of N and P from non-water column sources has exaggerated the degree of N limitation. Discrepancies between observed UN : UP and BN : BP could also arise from differential internal recycling of N and P (Fig. 3, scenario III) and non-assimilatory removal of nutrients from the water column (Fig. 3, scenario IV). Denitrification, nitrification, and sorption are a few processes that result in the loss of particular forms of nutrients from solution and are included in tracer-derived estimates of nutrient uptake in streams. Reference Cross W.F., Benstead J.P., Frost P.C. & Thomas S.A. (2005) Ecological stoichiometry in freshwater benthic systems: recent progress and perspectives. Freshwater Biology, 50, 1895– 1912. Wiley Online LibraryCASWeb of Science®Google Scholar Citing Literature Volume51, Issue5May 2006Pages 986-987 FiguresReferencesRelatedInformation

Nutrient uptake in streams draining agricultural catchments of the midwestern United States

Summary1. Agriculture is a major contributor of non‐point source pollution to surface waters in the midwestern United States, resulting in eutrophication of freshwater aquatic ecosystems and development of hypoxia in the Gulf of Mexico. Agriculturally influenced streams are diverse in morphology and have variable nutrient concentrations. Understanding how nutrients are transformed and retained within agricultural streams may aid in mitigating increased nutrient export to downstream ecosystems.2. We studied six agriculturally influenced streams in Indiana and Michigan to develop a more comprehensive understanding of the factors controlling nutrient retention and export in agricultural streams using nutrient addition and isotopic tracer studies.3. Metrics of nutrient uptake indicated that nitrate uptake was saturated in these streams whereas ammonium and phosphorus uptake increased with higher concentrations. Phosphorus uptake was likely approaching saturation as evidenced by decreasing uptake velocities with concentration; ammonium uptake velocity also declined with concentration, though not significantly.4. Higher whole‐stream uptake rates of phosphorus and ammonium were associated with the observed presence of stream autotrophs (e.g. algae and macrophytes). However, there was no significant relationship between measures of nutrient uptake and stream metabolism. Water‐column nutrient concentrations were positively correlated with gross primary production but not community respiration.5. Overall, nutrient uptake and metabolism were affected by nutrient concentrations in these agriculturally influenced streams. Biological uptake of ammonium and phosphorus was not saturated, although nitrate uptake did appear to be saturated in these ecosystems. Biological activity in agriculturally influenced streams is higher relative to more pristine streams and this increased biological activity likely influences nutrient retention and transport to downstream ecosystems.