Article

Comparison of metabolic rates among macrophyte and nonmacrophyte habitats in streams

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Abstract

Little is known about the relative contribution of different stream habitats to reach-scale metabolism. We measured in situ metabolism in sand, gravel, stone, and macrophyte habitats to compare metabolic rates among these habitat types and to compare habitat-weighted measurements with reach-scale measurements. We used open-bottom chambers in sand, gravel, and macrophyte habitats and closed-bottom chambers in stones, and we estimated reach-scale metabolism from 2-station O2 budgets. Macrophyte habitats had a significantly higher gross primary production (GPP) and community respiration (CR) than stone, gravel, and sand habitats. A large part of this difference was associated with epiphytic biofilm: 28% of net ecosystem production (NEP), 20% of CR, and 24% of GPP. Macrophyte habitats contributed proportionally more to reach-scale metabolism than did the other habitat types. Forty-one percent of reach-scale NEP, 60% of ecosystem respiration (ER), and 50% of GPP were associated with this habitat type even though only 14% of the reach was covered by macro-phytes. We found significant linear relationships between GPP and CR and the amount of autotrophic biomass in the streams. The rates reported in 11 literature studies fit into our observed relationships, showing the generality of our findings. The rates we obtained expand the range of reported metabolic values in relation to auto-trophic biomass for both low and high biomass. The importance of macrophyte habitat can be ascribed to the macrophytes themselves, the associated epiphytic biofilm, and the fine organic material trapped in the dense stands. We conclude that besides having an effect on the structural elements in streams, macrophytes contribute significantly to stream ecosystem functions.

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... Specifically, we predicted that the cutting would significantly reduce the metabolic activity (GPP and ER) as a consequence of both removal of the macrophyte biomass itself and the associated epiphytes that will directly affect primary production and ecosystem respiration (e.g. Alnoee et al., 2016Alnoee et al., , 2020 but also because macrophytes promote sedimentation of fine particulate organic matter (Kleeberg et al., 2010), which may enhance energy transfer to stream detrital pathways by increasing the respiratory activity (Woodward, 2009).We expected that seston will determine whole stream metabolism changes after weed cutting in large rivers, since water column processes has shown to be adding significantly to whole stream metabolism in large rivers compared to smaller streams (Reisinger et al., 2015). ...
... Overall, our results underpin the significance of macrophytes for GPP and ER in stream ecosystems (e.g. Alnoee et al., 2016Alnoee et al., , 2020Levi et al., 2015), and quantifies for the first time the reduction in metabolic rates as a consequence of macrophyte removal at their peak biomass in a large river. We found an immediate 38% and 61% reduction in GPP and 28% and 35% reduction in ER after weed cutting in 2014 and 2020 respectively. ...
... Decrease in GPP was directly related to the reduction of macrophyte biomass, but also to the loss of the autotrophic biofilm growing on the macrophyte surfaces that can otherwise contribute significantly to the total GPP in macrophyte dominated streams (24% was reported by Alnoee et al., 2016). We found that the reduction in GPP was comparable to the 70% reduction reported by Kaenel et al. (2000) in a small stream in Switzerland following removal of the macrophyte biomass being dominated by Ranunculus fluitans and Myriophyllum spicatum and to the 60% reduction observed in a mid-sized stream following removal of the macrophyte biomass being dominated by Stuckenia pectinate in Wisconsin, USA (Madsen et al., 1988). ...
Article
Problems related to extensive macrophyte growth are widespread both in modified and man-made canals and streams, and in streams with natural morphology and rich vegetation. The weed cutting is a common management practice in order to reduce flood risk and enhance water conveyance. Although the short- and long-term impacts on the stream physical habitats and biota have been extensively studied, only little information exists on the effects of weed cutting on ecosystem metabolism, especially for larger rivers. This study aims to quantify effects of weed cutting on metabolic rates in a large lowland river in Denmark. We measured Gross Primary Production (GPP), Ecosystem Respiration (ER) and physical parameters (water depth, discharge, water velocity and reaeration rate) one week prior and 2–6 weeks after weed cutting in 2014 and 2020. Physical river conditions changed significantly after the removal of approximately 60% of macrophytic volume, and a significant reduction in water depth and increased water velocity was recorded. We found an immediate 38% and 61% reduction in GPP and 28% and 35% reduction in ER after weed cutting in 2014 and 2020 respectively. We also found that the metabolic rates did not recover to pre-weed cutting levels within 2–6 weeks after weed cutting. The higher decline in GPP compared to that in ER indicates that the heterotrophic contribution to ER was higher compared to the autotrophic contribution. Our results display that even in a large macrophyte-rich river, where only one-third of the channel is managed by weed cutting, GPP and ER can be reduced significantly. The cascade effects of metabolic rates alterations on ecosystem structure and functioning need to be considered in the future management plans, where higher plant biomass and increased flow is anticipated due to the ongoing climate change and thus, the demand for weed cutting might be intensified.
... Similarly, by measuring 14 C uptake in stream reaches with different macrophyte cover, Hill and Webster (1984) showed that carbon uptake increased with increasing macrophyte biomass. In addition, Alnoee et al. (2016) found that gross primary production (GPP) and ecosystem respiration (ER) were 6-to 17-times higher in macrophyte habitats compared to non-macrophyte habitats in streams. Likewise, Levi et al. (2015) found that macrophyte habitats accounted for 71-98% of nitrogen (N) uptake, while covering only 28-67% of the total stream area. ...
... For example, macrophytes provide substrate for epiphytic biofilms (Tessier et al. 2008;Jaschinski et al. 2010) that may also influence the annual productivity regime. Furthermore, macrophyte beds alter hydrologic flows and sediment dynamics of streams Mebus 1996, Sand-Jensen andPedersen 1999), and can promote organic matter accumulation that may foster heterotrophic respiration (Alnoee et al. 2016). Thus, any seasonal changes in macrophyte biomass is likely to have cascading effects on ecosystem metabolism. ...
... Given the strong seasonality of GPP (Young and Huryn 1999;Alnoee et al. 2016), we expected that GPP in macrophyte rich streams would exceed those streams without macrophytes during summer when macrophyte abundance is highest. Furthermore, we predicted that GPP would be lower but comparable in streams with and without macrophytes the rest of the year (Fig. 1). ...
Article
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In many lowland streams, macrophytes are highly abundant and play a key role in ecosystem structure and function. However, no studies on annual stream metabolism have been conducted in streams with significant macrophyte abundance, despite the well-known effect on both gross primary production (GPP) and ecosystem respiration (ER). Macrophyte abundance in temperate streams is strongly seasonal, with highest biomass during summer and lowest during winter. We expected that this phenological pattern would drive annual fluctuations in GPP and ER. We measured daily metabolism for one year in two stream reaches, one with and one without macrophytes. Our results demonstrated that annual, aggregated GPP and ER were 2.2 and 1.3 times higher in the macrophyte reach. Furthermore, while daily GPP was the same between the two reaches during winter where biomass was negligible, GPP was higher during spring, summer and fall for the macrophyte reach. The range in daily ER was more constrained during summer, but more variable during fall and winter in the macrophyte reach relative to the non-macrophyte reach. Macrophyte abundance and chlorophyll-a controlled 80% of the variation in annual GPP for the macrophyte reach. Similarly, 63% of the variation in annual ER was controlled by macrophyte abundance together with discharge in the macrophyte reach. Although macrophytes enhanced GPP on an annual and seasonal time scale in agricultural lowland streams, both reaches were heterotrophic (i.e., GPP < ER) reflecting high organic matter supply from the landscape and in-stream retention and decomposition of organic matter within the macrophyte beds.
... Epiphytic biofilm plays multiple roles in aquatic ecosystems ( Fig. 1) and is important for maintaining ecosystem structure, specifically community composition and diversity (Jones and Thornber, 2010) and functions, such as primary production and respiration (Allen, 1971;Alnoee et al., 2016;Cattaneo and Kalff, 1979;Sand-Jensen et al., 1989;Shamsudin and Sleigh, 1995;Squires et al., 2009;Vadeboncoeur and Steinman, 2002), trophic interactions (Brönmark, 1985;Jones and Sayer, 2003;Vadeboncoeur and Steinman, 2002), nutrient uptake and cycling (Levi et al., 2015(Levi et al., , 2017Sudo et al., 1978;Vadeboncoeur and Steinman, 2002), decomposition (Rybakova, 2010;Sudo et al., 1978), pollutant removal (Lindell et al., 2016;Phillips et al., 2010), and microbial gene pool preservation (Levi et al., 2017;Rusznyák et al., 2008). Macrophytes are 'ecosystem engineers' as they shape the physical properties of aquatic ecosystems; they alter hydraulics by resisting water flow, aid in sediment particle settlement, and influence light availability by shading and maintaining clear water status (Polvi and Sarneel, 2018). ...
... However, the significance of these differences of epiphytic biofilms compared to biofilms on inert substrates in eutrophic freshwater ecosystems is still being debated (Eminson and Moss, 1980;Kahlert and Pettersson, 2002). With regard to reach-scale metabolism in streams, macrophyte habitats (i.e., consisting of both macrophyte and epiphytic biofilm) have shown considerably higher metabolic rates than inert habitats, such as epipsammon and epilithon (Alnoee et al., 2016). Furthermore, a comparative assessment of biomass-specific summertime nutrient uptake rates in streams has shown that epiphytic biofilm is more efficient in NH 4 -N and PO 4 -P uptake than benthic biofilms (Levi et al., 2015;Wijewardene et al., unpublished data). ...
Article
Epiphytic biofilm is an important component in freshwater ecosystems and is one of the main primary producers in shallow freshwater ecosystems. The epiphytic biofilm is comprised of an autotrophic community made up of diatoms, green algae, and cyanobacteria, and a heterotrophic community consisting of bacteria, protozoa, fungi, and other microorganisms. Macrophytes are the host domain for epiphytic biofilm, providing substrate and influencing epiphytic biofilm via structural characteristics. Strong competitive, mutualistic, and commensalistic relationships between epiphytic biofilm and macrophytes have resulted from interactions for resources (e.g., light and nutrients) and trophic and allelopathic dynamics. Even though these interactions have wider implications on ecosystem structure, function, and integrity, the current understanding of epiphytic biofilm-macrophyte interactions is limited. In this review, we highlight the current understanding of epiphytic biofilms in freshwater ecosystems and synthesize their different interactions with macrophytes by providing illustrative examples. Furthermore, we identify key areas where research is currently lacking and provide directions for future research in this field, which will allow for better integrated aquatic ecosystem management and conservation strategies.
... Moreover, high macrophyte biomass also increases organic-rich sediment retention within beds, generally increasing heterotrophic oxygen demand via decomposition (Sand-Jensen, 1998 Abbreviations: S w , nutrient uptake length; v f , uptake velocity; U, areal uptake; k, removal rate; SRP, soluble reactive phosphorous TA B L E 2 Nutrient spiralling parameters in spring, summer, and autumn in the study reach in River Gudenå F I G U R E 6 The relative contribution of autotrophic (dark grey) and heterotrophic (light grey) uptake to measured reach-scale uptake (solid points) differed among seasons and between nitrogen (a) and phosphorus (b). Reach-scale N uptake was below detection (BD) in autumn, and heterotrophic assimilation was low in spring (and therefore difficult to visualise on the plot, although the relative contributions are included in the figure) in epiphytic biofilms colonising macrophytes (Alnoe, Riis, & Baattrup-Pedersen, 2016;Levi et al., 2015), while benthic biofilms may be less prevalent as a result of macrophyte shading. ...
... For example, 24% of primary production in a macrophyte habitat was due to epiphytic microalgae (Alnoe et al., 2016); this contribution can be even higher when macrophytes themselves are light-limited, and their role as substrate for epiphytic biofilm increases. Therefore, in this study, the difference in spring and summer GPP might have been due to the increased role of benthic biofilm plus macrophytes in spring, whereas the fully developed epiphytic and benthic biofilm, without significant macrophyte contribution, in summer may have resulted in lower reach-scale GPP. ...
Article
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In low‐gradient, macrophyte‐rich rivers, we expect that the significant change in macrophyte biomass among seasons will strongly influence both biological activity and hydraulic conditions resulting in significant effects on nutrient dynamics. Understanding seasonal variation will improve modelling of nutrient transport in river networks, including annual estimations of export, which could optimise decision‐making and management outcomes. We explored the relationships among seasonal differences in reach‐scale nutrient uptake, macrophyte abundance, solute transport and transient storage in the River Gudenå (Denmark), a large macrophyte‐rich river. We used the minimal pulse addition technique to measure uptake of ammonium, nitrate, soluble reactive phosphorus, as well as reach‐scale metabolism, and surface transient storage in spring, summer, and autumn. We found that riverine uptake changed among seasons and was linked to macrophyte biomass via both biological activity, reflected in reach‐scale metabolism, and through physical processes, as solute transport was influenced by longitudinal dispersion. In this macrophyte‐rich river, seasonal changes in macrophyte biomass affected contact time between the water and biota, which influenced ammonium and soluble reactive phosphorus uptake. Using stoichiometric scaling of reach‐scale metabolism, we found that seasonal variation also influenced the relative contributions of autotrophic and heterotrophic biota in assimilatory uptake. In summary, riverine nutrient uptake was not static, highlighting the importance of seasonality, with significant implications for modelling of nutrient export in river networks. Moreover, current management strategies that remove macrophyte biomass (i.e. weed cutting and dredging) will short‐circuit the positive effects of enhanced nutrient uptake resulting from abundant macrophytes in rivers. In low‐gradient, macrophyte‐rich rivers, we expect that the significant change in macrophyte biomass among seasons will strongly influence both biological activity and hydraulic conditions resulting in significant effects on nutrient dynamics. Understanding seasonal variation will improve modelling of nutrient transport in river networks, including annual estimations of export, which could optimise decision‐making and management outcomes. We explored the relationships among seasonal differences in reach‐scale nutrient uptake, macrophyte abundance, solute transport and transient storage in the River Gudenå (Denmark), a large macrophyte‐rich river. We used the minimal pulse addition technique to measure uptake of ammonium, nitrate, soluble reactive phosphorus, as well as reach‐scale metabolism, and surface transient storage in spring, summer, and autumn. We found that riverine uptake changed among seasons and was linked to macrophyte biomass via both biological activity, reflected in reach‐scale metabolism, and through physical processes, as solute transport was influenced by longitudinal dispersion. In this macrophyte‐rich river, seasonal changes in macrophyte biomass affected contact time between the water and biota, which influenced ammonium and soluble reactive phosphorus uptake. Using stoichiometric scaling of reach‐scale metabolism, we found that seasonal variation also influenced the relative contributions of autotrophic and heterotrophic biota in assimilatory uptake. In summary, riverine nutrient uptake was not static, highlighting the importance of seasonality, with significant implications for modelling of nutrient export in river networks. Moreover, current management strategies that remove macrophyte biomass (i.e. weed cutting and dredging) will short‐circuit the positive effects of enhanced nutrient uptake resulting from abundant macrophytes in rivers.
... The link between aquatic vegetation and characteristics of ecosystem function, in particular metabolic activity, in streams has been receiving increased attention [O'Brien et al., 2013;Levi et al., 2015;Alnoee et al., 2016], however the link between stream flow, vegetation abundance and function has not been explicitly identified in lotic systems previously. Aquatic vegetation is known to influence stream nutrient dynamics and autotrophic metabolism via a number of mechanisms. ...
... Unfortunately, our study is not able to directly distinguish the relative importance to observed metabolic activity of the contribution of the aquatic vegetation itself from that of associated with epiphytic biofilms, nor the relative importance of the vegetated surface water from that of hyporheic sediments. Nevertheless, stream sections dominated by aquatic vegetation have been shown to have higher metabolic activity than those dominated by sediment, in large part due to epiphytic biofilms associated with the vegetation [Alnoee et al., 2016]. Given the high surface area of Ranunculus, the dominant vegetation type in our mesocosms, the contribution of epiphytes to observed metabolic activity could likewise be high. ...
Article
Transient storage zones for water represent potential hot spots for metabolic activity in streams. In lowland rivers, the high abundance of submerged vegetation can increase water transient storage, bioreactive surface areas and, ultimately, in-stream metabolic activity. Changes in flow resulting from climatic and anthropogenic factors that influence the presence of aquatic vegetation can also, thereby, impact in-stream metabolism and nutrient cycling. We investigated the effects of water column depth on aquatic vegetation cover and its implications on water transient storage and associated metabolic activity in stream mesocosms (n=8) that represent typical conditions of lowland streams. Continuous injections of metabolically reactive (resazurin-resorufin) tracers were conducted and used to quantify hydraulic transport and whole-mesocosm aerobic respiration. Acetate, a labile carbon source, was added during a second stage of the tracer injection to investigate metabolic responses. We observed both higher vegetation coverage and resazurin uptake velocity, used as a proxy of mesocosm respiration, with increasing water column depth. The acetate injection had a slight, positive effect on metabolic activity. A hydrodynamic model estimated the water transport and retention characteristics and first-order reactivity for three mesocosms. These results suggest that both the vegetated surface water and sediments contribute to metabolically active transient storage within the mesocosms, with vegetation having a greater influence on ecosystem respiration. Our findings suggest that climate and external factors that affect flow and submerged vegetation of lowland rivers will result in changes in stream respiration dynamics and that submerged vegetation are a particularly important and sensitive location for stream respiration.
... Similarly, Koljonen et al. (2012) found that the retention of leaves at low discharges increased by adding moss, boulder or wood either alone or in combination into channelized streams. Furthermore, the increase in ER with total plant coverage, can also link to higher amount of accumulated fine particulate organic matter at the base of the macrophyte beds because of reduced water velocities (Sand-Jensen and Mebus, 1996), and with that enhanced ER (e.g., Acuña et al., 2011;Alnoee et al., 2016), and also to the epiphytic biofilm canstimulate in-stream processes (Levi et al., 2015). ...
Article
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Restoration has been increasingly applied over the last decades as a way to improve the ecological conditions in stream ecosystems, but documentation of the impact of restoration on ecosystem functions is sparse. Here, we applied a space-for-time approach to explore effects of stream restoration on metabolism and organic matter decomposition in lowland agricultural streams. We included stream reaches that were restored >10 years ago and compared ecosystem functioning in these streams with those in channelized and naturally meandering stream reaches from the same geographical region. Specifically, we tested the following hypotheses: 1) rates of stream metabolism (gross primary production, GPP, and ecosystem respiration, ER) and organic matter decomposition in restored reaches resemble rates in naturally meandering reaches more than rates in channelized stream reaches and 2) higher resemblance in ecosystem metabolism and organic matter decomposition between restored reaches and meandering reaches can be attributed to the improved physical habitat conditions in the restored stream reaches. Overall, we did not find that stream metabolism or organic matter decomposition differed among restored, channelized and naturally meandering stream reaches even though habitat conditions differed among the three stream types. Instead, we found a large variation in ecosystem function characteristics across all sites. When analyzing all stream types combined, we found that GPP increased with increasing plant coverage and that ER increased with increasing stream size and with the coverage of coarse substratum on the stream bottom. Organic matter decomposition, on the other hand, only slightly increased with the number of plant species and declined with increasing concentrations of nutrients. Overall, our findings suggest that physical habitat improvements in restored stream reaches can affect ecosystem functions, but also that the restoration outcome is context-dependent since many of the physical characteristics playing a role for the measured functions were only to some extent affected by the restoration and/or clouded by interference with factors operating at a larger-scale.
... Most studies on biofilm structure in lowland agricultural streams have been on epilithic biofilm, e.g., [6,7] and much less is known about the epiphytic biofilm, although we know it might be the primary site for microalgae growth in macrophyte-rich streams and may be the main contributor to reach-scale metabolism [8] and nutrient uptake [9]. Furthermore, macrophytes as biofilm substrate offer very different conditions for auto-and heterotrophic biofilm compared to gravel, and stones and the communities may therefore differ. ...
Article
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Stream biofilms play an important role in the structure, functioning, and integrity of agricultural streams. In many lowland streams, macrophyte vegetation is abundant and functions as an im-portant substrate for biofilm (epiphyton) in addition to the gravel and stone substrate for epilithon on the stream bed. We expect that reach-scale habitat conditions in streams (e.g., nutrient availa-bility, hydraulic conditions) affect the epiphyton and epilithon biomass and composition, and that this effect will be substrate-specific (macrophytes and stones). The objectives of our study were (i) to describe concurrent changes in epiphyton and epilithon biomass and composition over a year in agricultural streams, and (ii) to determine the substrate specific reach-scale habitat drivers for the epiphyton and epilithon structure. We monitored epiphyton and epilithon biofilm biomass and composition at three-week intervals and reach-scale environmental conditions daily during a year for two agricultural steams. The results showed that epiphyton and epilithon communities differed in biomass, having high substrate specific biomass in epilithon compared to epiphyton. Epiphyton was mainly composed of diatom and green algae, while cyanobacteria were more important in epilithon, and the diatom species composition varied between the two biofilm types. Epiphyton structural properties were less influenced by reach-scale hydrology and nutrient availability compared to epilithon. The overall explanatory power of the measured environmental variables was low, probably due to micro-scale habitat effects and interactive processes within stream bio-films. Knowledge of biofilm control in agricultural streams is important in order to improve management strategies, and future studies should improve the understanding of micro-scale hab-itat conditions, interactive relationships within biofilms and between the biofilm and the substrates.
... Unaccounted for uptake and storage may help to explain strong patterns of enhanced GPP and ER coupled with weaker nutrient storage patterns within vegetated systems. However, macrophyte cover has been shown to enhance GPP and ER rates and contribute proportionally more to ecosystem metabolism than other plant forms; moreover, plant biomass and chlorophyll a have been found to explain the majority of variation in daily GPP (80%) and ER (63%) in agricultural streams [70,71]. Additionally, C assimilation and processing via metabolic processes require nutrient inputs; plant and associated microbial uptake can be a significant nutrient removal mechanism in vegetated aquatic systems [42]. ...
Article
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Agricultural drainage networks within the Lower Mississippi River Basin (LMRB) have potential to attenuate nutrient loading to downstream aquatic ecosystems through best management practices. Nutrient uptake (nitrogen, phosphorus), gross primary production (GPP), ecosystem respiration (ER), and denitrification rates were estimated using a combination of sensor measurements and hourly discrete samples for dissolved nutrients and gases at three hydraulic residence times (2, 4, and 6 h) in three vegetated and three unvegetated ditches. We also measured vegetation and soil nutrient content. GPP and ER were significantly higher in vegetated drainages and increasing hydraulic residence time increased respiration rates. Shorter hydraulic residence times were associated with increased uptake rates for both N and P, and vegetation increased N uptake rates in all hydraulic residence time (HRT) treatments. Vegetation and sediment assimilated N and P over the course of the experiment. Overall, our experimental results demonstrate the strong role of emergent vegetation in nutrient retention and removal processes in agricultural drainage ditch networks.
... These values of stream metabolism are much higher than those of headwater streams with well-developed riparian forests in temperate regions (Fellows et al. 2006, von Schiller et al. 2008, Bernhardt et al. 2017). High metabolism is common in open-channel streams, where light does not limit primary production (Bernot et al. 2010, Alnoee et al. 2016. ...
Article
In-stream nutrient retention is an important ecosystem function because it can regulate nutrient fate and export to downstream ecosystems. Temporal variation in nutrient retention in streams has been studied extensively at the annual and seasonal scale but less thoroughly at the diel scale. However, understanding temporal variability in nutrient uptake at the diel scale can increase understanding of the role of photoautotrophic primary production on nutrient uptake in streams, especially open-canopy streams. We hypothesized that nutrient retention mostly de�pends on autotrophic demand in open-canopy streams and that it varies following the diel pattern of gross primary production (GPP). We therefore evaluated the temporal variation in phosphate (PO432) and ammonium (NH41) up�take at a daily scale in a highly-productive Pampean stream that is dominated by a dense assemblage of macrophytes and filamentous algae. We conducted 6 slug additions of PO432 and NH41 over a 24-h period and quantified reach�scale nutrient uptake concurrently with measurements of whole-stream metabolism and chemical variables during additions (including nitrates and nitrites). The study stream had extremely high uptake of PO4 32 and NH41 (>90 and >75% retention of the P and N mass added, respectively). Uptake of PO4 32 did not vary throughout the day. Estimated PO4 32 uptake from GPP accounted for only a small fraction of observed PO4 32 uptake. Thus, another mechanism, such as heterotrophic demand by microbial assemblages or adsorption onto sediments, could also have contributed to PO4 32 uptake in the study stream. In contrast, NH4 1 uptake clearly varied throughout the day. Up to 48% of the observed NH4 1 uptake rate could be explained by NH4 1 estimated from GPP, and NH41 demand was positively as�sociated with GPP, indicating a high dependence on photoautotrophic demand. An increase of nitrite (NO2 2) con�centration during additions (representing up to 70% of the added mass of NH4 1) suggests that nitrification contrib�uted to the diel pattern of NH41 uptake. Our results indicate that nutrient uptake does not always rely on autotrophic demand in open-canopy streams and that other abiotic and dissimilatory mechanisms may explain the diel patterns of nutrient retention. In addition, our study highlights the need to measure uptake metrics throughout the day to obtain an accurate estimate of nutrient retention on a daily scale.
... Linear relationships between GPP and ER always indicated increased heterotrophy in response to increasing GPP, regardless of which approach was used to estimate K (Fig. 7A-C). Slopes describing this response were always higher in vegetated vs unvegetated streams, consistent with previous findings that slopes describing GPP-ER relationships increased in macrophyte dominated habitats relative to unvegetated streams (Alnoee et al. 2016). Additionally, overall patterns of increasing heterotrophy with increasing photosynthetic capacity in these shallow, low-gradient, open-canopy streams were similar among all approaches to estimating K. Patterns within our streams suggest that as GPP increased, ER rates exceeded photosynthetic capacity, which is similar to results from highly-productive, open-canopy streams (Rosenfeld and Mackay 1987, Frankforter et al. 2010, Marcarelli et al. 2011, Roley et al. 2014. ...
... Our results suggest that fine sediment removal lowered GPP in Fawn River by removing macrophytes associated with fine sediment deposits and preventing their recolonization. Macrophytes directly increase GPP in freshwater ecosystems (Allen 1971, Likens 1975, Alnoee et al. 2016) and they can indirectly increase primary productivity by providing an attachment surface for epiphytic algae (Hooper andRobinson 1976, Cattaneo andKalff 1980). ER was lower in the restored reach on all sampling dates but September, suggesting that fine sediment removal also reduced ER by removing macrophytes. ...
Article
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The transport and processing of nutrients and organic matter in streams are important functions that influence the condition of watersheds and downstream ecosystems. In this study, we investigated the effects of streambed sediment removal on biogeochemical cycling in Fawn River, a gravel-bottomed river in Indiana, U.S.A. We measured stream metabolism as well as nitrogen (N) and phosphorus (P) retention in both restored and unrestored reaches of Fawn River to examine how sediment removal affected multiple biogeochemical functions at the reach scale. We also assessed the properties of restored and unrestored streambed sediments to elucidate potential mechanisms driving observed reach-scale differences. We found that sediment removal led to lower rates of primary productivity and ecosystem respiration in the restored reach, likely due to macrophyte removal and potentially due to changes to sediment organic matter quality. We found minimal differences in N and P retention, suggesting that these processes are controlled at larger spatial or temporal scales than were examined in this study. Denitrification enzyme activity was lower in sediments from the restored reach compared to the unrestored reach, suggesting that restoration may have decreased N removal. Our results indicate that most near-term changes in biogeochemical function following restoration could be attributed to macrophyte removal, although effects from sediment removal may emerge over longer timescales.
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The unique hydrology and physicochemistry of alpine streams provide an important influence on the structure and function of inhabiting biological communities. A substantial body of research exists on alpine streams across many regions of the globe (e.g. Europe, North and South America and Greenland). To date, however, there have been few studies investigating the environmental conditions present in alpine streams across the Japanese archipelago. The lack of information on alpine streams in Japan is problematic as unique regional climates, e.g. some of the highest levels of snowfall globally, are likely to have repercussions for morphological, hydrological, physicochemical and metabolic signatures, causing them to differ from those observed in other regions. In this study we compare the morphology, hydrology, physicochemistry and metabolic activity of snowmelt and groundwater fed streams in the Kamikochi region of the Japanese Alps. Stream discharge, water chemistry (major ions, silica, dissolved oxygen), water temperature and channel stability were measured over a period of 16 months in 2017–2018. Metabolic activity was determined using Resazurin-Resorufin (Raz-Rru) Smart Tracer and variation in the Raz transformation rate was assessed to understand the effects of hydrology and physicochemistry on ecosystem functioning. Snowmelt streams were characterised by higher variability of water temperature, water chemistry and stream discharge, both, within and between sites. Indeed, two of the snowmelt streams experienced no flow conditions for several periods and also floods. In comparison, water chemistry, water temperature and stream discharge in groundwater fed streams were more temporally stable. Metabolic activity was higher in one groundwater fed stream, attributed to significant growth of macrophytes. These findings indicate that the patterns of morphology, hydrology, physicochemistry and metabolic activity across streams in the Japanese Alps largely resemble those identified elsewhere, although there were higher levels of inter-stream variation. The diversity and inter-site variation of hydrological and physicochemical conditions are likely responsible for the unique flora and fauna in the streams. This study therefore indicates the potential importance of habitat templates for the aquatic biodiversity hotspot in this region.
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Urban rivers worldwide are affected directly by macrophyte growth, causing reduced flow velocity and risks of flooding. Therefore, cutting macrophytes is a common management practice to ensure free drainage. The impacts of macrophyte removal on transient storage dynamics and microbial metabolic activity of wastewater-fed urban streams are unknown, preventing any assessment of the hydrodynamic and biogeochemical consequences of this management practice. Slug tracer injections were performed with the conservative tracer uranine and the reactive tracer resazurin to quantify the implications of macrophyte cutting on stream flow dynamics and metabolism. Macrophyte cutting reduced mean tracer arrival times in managed stream reaches but did not significantly decrease whole-stream microbial metabolic activity. In fact, transient storage indices were found to have increased after cutting, suggesting that macrophyte removal and the resulting increase in flow velocity may have enhanced hyporheic exchange flow through streambed sediments. Our results evidence that macrophyte cutting in nutrient-rich urban streams does not necessarily lead to lower in-stream storage and metabolism but that the gain in hyporheic exchange and streambed microbial metabolic activity can compensate for reduced in-stream storage. Increased stream flow resulting from macrophyte removal may therefore even enhance nutrient and pollutant attenuation capacity of streambed sediments.
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• Understanding the mechanisms that control gross primary production (GPP) and ecosystem respiration (ER) is important in open‐canopy streams, particularly as their prevalence increases across the landscape with the expansion of human land use. • We measured resazurin (raz) transformation to resorufin (rru) as an indicator of ER in two contrasting experimental stream systems to examine the linkages between underlying substrate, biofilm colonisation and stream metabolism in open‐canopy systems. • We implemented a gradient of biofilm coverage (0%–100%) in 20 recirculating streams and found that raz transformation (kτ) increased proportionally with algal biomass and gross primary production (GPP). We then conducted multiple short‐term additions of raz over a 5‐month biofilm colonisation sequence in four groundwater‐fed, experimental streams (Q = 1.5 L/s, 50 m long) at the Notre Dame Linked Experimental Ecosystem Facility (ND‐LEEF). Streams at ND‐LEEF were lined with two different substrate sizes (pea gravel vs. cobble) and two levels of heterogeneity (alternating sections vs. well‐mixed). • We found that longitudinal patterns of kτ varied with substrate type and heterogeneity on the majority of sampling days. Temporal patterns of kτ over the trajectory of biofilm growth were similar among streams, with “peak” kτ occurring after three months of biofilm growth; kτ decreased with the onset of algal senescence and decreasing temperatures. Raz transformation was also positively correlated with algal biomass and GPP in the streams at ND‐LEEF, which varied with substrate composition. • Overall, the raz‐rru method identified spatial and temporal variability in the linkages between substrate, algal biofilms, and metabolism in open‐canopy streams.
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We quantified oxygen flux in a coastal stream in Virginia using a novel combination of the conventional open water technique and the aquatic eddy covariance technique. The latter has a smaller footprint (sediment surface area that contributes to the flux; ∼ 10 m2), allowing measurements to be made at multiple sites within the footprint of the open water technique (∼ 1000 m2). Sites included an unvegetated stream pool with cohesive sediment, a macrophyte bed with sandy sediment, and an unvegetated sand bed with rippled bedforms. Nighttime eddy covariance oxygen uptake was always smaller than uptake produced by the open water technique. At the pool and unvegetated sand bed sites, nighttime eddy covariance uptake was 20-fold smaller than open water uptake. At the macrophyte bed site, gross primary production quantified with the two techniques was similar but eddy covariance uptake was 2.4-fold smaller. The difference in oxygen uptake between eddy covariance and open water techniques could not be accounted for by uncertainties in the gas transfer velocity but could be accounted for by anoxic groundwater inflow through stream banks outside of the eddy covariance footprint. Nighttime oxygen uptake was also measured with eddy covariance in a tidal freshwater part of the stream, where pore space in the sandy sediment near the sediment–water interface was flushed with stream water at peak water velocities. As a result of this advective hyporheic exchange, nighttime oxygen flux increased fourfold with a doubling of water velocity.
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Disturbance by floods is believed to be 1 of the fundamental controllers of temporal and spatial patterns in stream periphyton. However, the exact causes of biomass losses are still poorly understood and discharge measures of disturbance often only explain limited variance in periphyton development. We investigated the effects of 2 of the main mechanisms of flood disturbance to periphyton - frequency of high-velocity events and frequency of bed sediment movement - in an effort to better understand disturbance processes and improve the quantification of flood disturbance regimes for studies of stream periphyton. Three sites were selected in headwater streams in each of 4 groups according to a 2-way factorial design of frequency of high-velocity events and sediment stability, giving a total of 12 sites. Periphyton were sampled monthly for 15 mo and analyzed for chlorophyll a. Maximum photosynthetic rates (P(max)), chlorophyll-specific P(max), community respiration (CR), and P(max):CR ratios were determined seasonally. Nutrient concentrations were generally low and did not vary as a function of disturbance regime. Peaks in chlorophyll a were usually low reflecting the low nutrients. Chlorophyll was 2-10x higher where bed sediments moved <15x/y and with seasonal maxima most often in autumn. Frequency of bed movement, soluble reactive P, and the frequency of velocity perturbations were significant predictors of mean monthly chlorophyll a (r2 = 0.88). Chlorophyll a and water temperature were major correlates of P(max), specific P(max), and CR, and thus the metabolic variables partly reflected changes in biomass among the disturbance regimes. With chlorophyll and temperature removed as covariates, the main factor influencing all metabolic parameters was season. P(max) was 7x higher in summer than in spring when minima occurred, chlorophyll-specific P(max) was 10x higher in summer than in spring, and CR was 4x higher in autumn than in spring. P(max):CR ratios indicated that the communities were generally autotrophic at times of maximum photosynthesis with the highest ratios in summer (3x higher than winter). The frequency of velocity perturbations also had a significant effect on P(max):CR ratios with highest ratios at sites where there was a low frequency of high-velocity events. Our results suggest that sediment instability greatly increases disturbance intensity for periphyton. It is therefore essential to assess not just the frequency of floods, but also the degree of bed movement when quantifying disturbance regimes for periphyton in headwater streams.
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The aim of this study was to determine the species composition, biodiversity and, relative abundance of epiphytic algae and their relationship with environmental variables on three different macrophytes (Nymphaea alba, Ceratophyllum demersum, Typha latifolia ) at Acarlar Floodplain Forest (AFF). Epiphytic algae were gathered monthly by collecting aquatic plants between November 2011 and October 2012, except in winter when there were no plants. In this study, 67 taxa on N. alba, 66 taxa on C. demersum and 66 taxa on T. latifolia were identified as epiphytic algae. The mean value of species richness was 17, that of diversity was 1.5 and that of evenness was 0.54 for epiphytic algae on N. alba, 17, 1.1, and 0.39 on C. demersum, and 18, 1.64, and 0.56 on T. latifolia, respectively. Oscillatoria sp. and Komvophoron crassum (Vozzen) Anagnostidis and Komárek were the most abundant and consistent epiphytic algal species, occurring in high abundance on all macrophytes. Results show that species composition of epiphytic algae was different, but diversity values were similar on all the macrophytes. The hydrological pulse is one of the most important factors determining the physical and chemical environment of the epiphytic algal community. However, substrate type also affected the colonization by F. capucina, O. sancta, P. catenata, and L. truncicola more than the epiphytic algal seasonality.
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The metabolism (gross primary production, GPP; respiration, R; and net metabolism, NM) of epilithon was measured by incubating randomly selected cobbles in recirculatory chambers in 21 Basque streams running to the Atlantic coast. The studied streams spanned a broad range of environmental conditions and ranged in ecological status from excellent to poor. The GPP ranged from negligible to 35 g O2m-2d-1, and the R ranged from 1 to 17 g O2m-2d-1. The NM showed that the epilithon was autotrophic in 15 sites and heterotrophic in the rest. None of the measured environmental variables was significantly correlated with R. Stepwise analyses showed that both the GPP and the NM were related to the epilithic chlorophyll a and phosphate concentrations. The metabolism values obtained were lower than those previously published from open-channel method, the number of autotrophic sites higher, and the controlling environmental variables different. The difference between open-channel and chamber methods was not related to the area covered with cobbles in the study sites. Although chamber measurements yield results in sites where open-channel methods do not work, they seem to overestimate the importance of autotrophy.
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Stream metabolism at both ecosystem and functional-compartment scales was measured in a low-order Pampean stream (La Choza) over a 3-wk period to characterize metabolic rates and discern the contribution of each functional compartment (submerged macrophytes, benthos, floating macroalgae, water column, and hyporheic zone) to ecosystem metabolism. La Choza stream is an autotrophic ecosystem during low flows and has gross primary production rates of up to 22 g O2 m−2d−1, which are among the highest reported in the literature and set an upper bound on how productive streams can be in the absence of light and nutrient limitations. Floating macroalgae provided most of the primary production (30–90%), whereas the hyporheic zone provided most of the ecosystem respiration (40–80%). The differential effects of high flows on the different functional compartments depressed the production∶respiration ratio, suggesting a strong relationship between flow and metabolism. Thus, low flows enhanced primary production and led to diel dissolved O2 concentration oscillations between 0 and 25 g O2/m3. In contrast, high flow depressed primary production by an order of magnitude and increased ecosystem respiration. High production rates during the low-flow period and extreme physicochemical conditions (anoxia for 7–8 h on a daily basis) may be typical in this type of ecosystem during extended low-flow periods.
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Weather variations change stream hydrological conditions, affecting the stream function. A seasonal study in three well-conserved first-order Pampean streams was carried out to test the hypothesis that rainfalls are the main drivers of whole-stream metabolism, through their effects on hydrology. We estimated the stream metabolism and metabolic contribution of six relevant communities (angiosperms, macroalgae, seston, epiphyton, epipelon, and hyporheos) during late spring, summer, and winter and examined the relation between gross primary production (GPP) and photosynthetic active radiation (PAR). Our results showed that the decrease in available streambed light due to the dissolved organic carbon after rainfalls was the main factor related to the decrease in the ecosystem and community metabolisms. For instance, GPP oscillated from ~10 gO2 m−2 d−1 in early spring (low flows) to ~3 gO2 m−2 d−1 in summer (high flows). Ecosystem respiration (ER) was less sensitive than GPP to rainfalls due to the increase of hyporheic respiration. Rainfalls also caused a significant loss of downstream macroalgal biomass. At a day scale, the high PAR of late spring and summer saturated GPP during the afternoon, and the low temperature of winter mornings constrained GPP. Hence, the knowledge of weather changes is key to understanding the main hydrological drivers of stream function.
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Mesoscale spatial (centimeters–meters) and temporal (days–weeks) flow variability plays an important role in stream ecosystem structure and function. The structural effects of flow variability have been widely tested but its influence on ecosystem processes is less well understood. Our study examined the influence of mesoscale flow variability on cobble biofilm metabolism in an Australian regulated upland stream that had been subjected to severe catchment disturbance as a result of extensive fire 10 mo before the study. Rates of primary production and respiration were calculated from changes in dissolved O2 over 24 h in benthic chambers containing stream cobbles sampled before and after high-discharge events in areas with differing surface-flow types. Overall, cobble biofilm communities were strongly autotrophic (primary production » respiration), probably because of reduced shading and increased nutrient influx caused by the recent fire. Differences in production and respiration before and after individual high-discharge events were inconsistent and, therefore, not statistically significant. The effect of high discharge on respiration was greater when high-discharge events were preceded by long periods of low discharge, but the number of events sampled was limited and this result could not be tested statistically. Rates of respiration and concentrations of organic material, chlorophyll a, and pheophytin a also varied spatially, and these variables were affected more by mesoscale variation in hydraulic conditions than by reach-scale variation in hydraulic conditions. Our results suggest that flow management has the potential to alter benthic metabolism.
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We carried out a first study of Lake Baikal epiphyton on six species of submerged macrophytes: Myriophyllum spicatum L., Potamogeton perfoliatus L., Potamogeton sp., Sparganium gramineum Georgi, Ceratophyllum demersum L., and Elodea сanadensis Michaux. We identified 70 epiphyton species and intraspecific taxa belonging to 3 phyla, viz. Ochrophyta, Cyanobacteria, and Chlorophyta. Nine species of Cyanobacteria were new records for Lake Baikal. Epiphyton communities differing in species composition and quantitative characteristics grew on diverse species of submerged macrophytes. High levels of species richness were recorded on Sparganium gramineumand Potamogeton sp., whereas low diversity of epiphyton was observed on Myriophyllum spicatumand Elodea canadensis. A monodominant community was revealed on the invasive Elodea canadensisrepresented by Cocconeis placentula var. placentula. Specific characteristics of morphology of submerged macrophytes influenced the structural organization and quantitative evelopment of epiphyton. Epiphyton abundance and biomass were higher on upper sections of most plants than on lower sections, probably because of canopy shading of macrophyte lower portions.
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Obtaining a better knowledge of how flow variability affects lotic biota is of considerable importance to stream and river management. We contend that processes at different hierarchical levels of organization in lotic ecosystems are sensitive to variation in flow at related hierarchical temporal scales. Ecosystem disturbance caused by large-scale events (i.e. infrequent, but high magnitude flow events with a recurrence interval of years to many days) tend to determine high-level characteristics of ecosystem structure (e.g. determining species pools, periphyton versus macrophyte dominance) and function (e.g. balance between auto- and heterotrophy). The high-level ecosystem characteristics then set the stage for processes that are influenced by flow variation that occurs at smaller temporal scale (i.e. minutes to milliseconds) such as colonization, biotic interactions and mass transfer enhancement of production. We contend that large-scale temporal events predominantly affect lotic ecosystems through physical drag processes (‘drag-disturbance’), whereas small-scale flow variations affect ecosystems through mass-transfer processes (including invertebrate and fish food-uptake). Drag-disturbance and mass-transfer related processes mark the opposite ends of a continuum of flow variability controlled processes, with moderate temporal scale flow variability events affecting ecosystems through both drag-disturbance and mass-transfer processes in similar proportions. Flow variability, and associated effects on ecosystems, across these scales is discussed with reference to New Zealand rivers. We suggest that these concepts can be integrated across the full range of temporal scales based on a spectrum of velocity variations. This may provide a unifying conceptual model for how the structure and functioning of lotic ecosystems are linked to flow variability. Copyright © 2005 John Wiley & Sons, Ltd.
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An in situ chamber technique was used to obtain seasonal estimates of benthic community metabolism at three stations in an agriculturally disturbed stream. Two stations with open canopies were examined. Sand was the dominant substrate at one site, cobble at the other. The third station was shaded by riparian vegetation and had a sand substrate. Seasonal estimates of net community productivity (NCP) and community respiration (CR) at the cobble section were significantly higher than those calculated for the sand sections (p>0.05). Ratios of gross community productivity (GCP) to 24 h respiration indicated autotrophic conditions in the cobble and extreme heterotrophy in the sand. NCP was significantly higher (p<0.05) in the open canopy sand than in the riparian shaded sand only when turbidity and discharge were low. Measurements of periphyton ash-free dry mass (AFDM) and chlorophyll a support metabolism estimates. Measurements of loose detrital AFDM were very low and variable compared to others reported in the literature. Therefore, allochthonously derived detritus may not be an important energy source for the benthic community.
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Benthic community metabolism was studied on four stream systems located in different biomes in the United States: the eastern deciduous forest (Pennsylvania, PA, and Michigan, MI), the high desert (Idaho, ID), and the coniferous forest (Oregon, OR). Studies were designed to test the hypothesis advanced within the River Continuum Concept that a transition in community metabolism will occur from a predominance of heterotrophy in headwaters to a predominance of autotrophy in mid-sized reaches, with a return to heterotrophy further downstream. Both gross primary productivity (GPP) and community respiration (CR24) increased with downstream direction on all systems. Net daily metabolism (NDM, or GPP – CR24) shifted from heterotrophy (–NDM, GPP 24) to autotrophy (+NDM, GPP > CR24) with downstream direction at all sites, supporting the hypothesis. Annual metabolism in the most upstream reach of all sites was dominated by respiration; however, the farthest downstream reach was not necessarily the most autotrophic. Site-specific factors affected manifestation of the trend. Photosynthesis predominated annual metabolism in reaches (designated 1–4 in order of increasing size) 2–4 in ID, 3 and 4 in OR, and 4 in MI. In PA annual photosynthesis was slightly greater than respiration only at Station 3. Photosynthesis was predominant most consistently in ID and respiration most often in PA. About half the reaches that were heterotrophic annually were autotrophic at one or more seasons. Annual means of benthic GPP, CR24 and NDM ranged from 0.16 to 3.37, 0.36 to 2.88 and –0.73 to 0.50 g O2 m2 d1, respectively. Metabolic rates were usually high in PA and MI (and sometimes ID) and almost always lowest in OR. Parameters accounting for most variance in multiple linear regression analyses of the combined metabolism data from all sites were indicators of stream size, photosynthetically active radiation, temperature, and chlorophyll a concentration.
Book
This revised and updated edition of the bestselling Methods in Stream Ecology reflects the latest advances in the technology associated with ecological assessment of streams. In this second edition, all chapters have been updated and modified to reflect the most contemporary protocols covering 6 vital areas of stream ecology: Physical Stream Ecology; Material Transport, Uptake, and Stora Stream B Community Interactions; Ecosystem Processes; and Ecosystem Quality. Each chapter contains basic methods suitable for teaching undergraduate or graduate students and advanced methods for conducting state-of-the-art research. Suitable as a textbook for a course in stream or river ecology, this book is also a critical reference for professional aquatic ecologists, natural resource managers, and for those entering the field of stream ecology who wish to evaluate the condition of streams or their watersheds.
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In shaded woodland streams, sediment community respiration is an important measure of decomposition of organic matter. In situ rates of community respiration were measured in sediments from shaded woodland streams at the Hubbard Brook Experimental Forest (HBEF), USA, by estimating rates of CO2 production in low-disturbance benthic chambers. Rates of sediment community respiration (range: 26-340 mg C· m-2· d) were closely correlated with amounts of sediment organic matter, but not with water column DOC or sediment size structure. Analysis of literature data indicated similar couplings between community respiration and sediment organic matter in other streams and in lakes and marine systems. However, respiration per unit organic matter was 23-fold higher in lakes and marine systems than in woodland streams, apparently due to differences in quality of organic matter (algae and macrophytes vs terrestrial detritus). In HBEF streams, community respiration was elevated in sediments of organic debris dams, suggesting that organic debris dams are focal sites of metabolism and nutrient regeneration in the stream channel.
Article
This revised and updated edition of the bestselling Methods in Stream Ecology reflects the latest advances in the technology associated with ecological assessment of streams. In this second edition, all chapters have been updated and modified to reflect the most contemporary protocols covering 6 vital areas of stream ecology: Physical Stream Ecology; Material Transport, Uptake, and Stora Stream B Community Interactions; Ecosystem Processes; and Ecosystem Quality. Each chapter contains basic methods suitable for teaching undergraduate or graduate students and advanced methods for conducting state-of-the-art research. Suitable as a textbook for a course in stream or river ecology, this book is also a critical reference for professional aquatic ecologists, natural resource managers, and for those entering the field of stream ecology who wish to evaluate the condition of streams or their watersheds.
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Catchment characteristics determine the inputs of sediments and nutrients to streams. As a result, natural or anthropogenic disturbance of upland soil and vegetation can affect instream processes. The Fort Benning Military Installation (near Columbus, Georgia) exhibits a wide range of upland disturbance levels because of spatial variability in the intensity of military training. This gradient of disturbance was used to investigate the effect of upland soil and vegetation disturbance on rates of stream metabolism (ecosystem respiration rate [ER] and gross primary production rate [GPP]). Stream metabolism was measured using an open-system, single-station approach. All streams were net heterotrophic during all seasons. ER was highest in winter and spring and lowest in summer and autumn. ER was negatively correlated with catchment disturbance level in winter, spring, and summer, but not in autumn. ER was positively correlated with abundance of coarse woody debris, but not significantly related to % benthic organic matter. GPP was low in all streams and generally not significantly correlated with disturbance level. Our results suggest that the generally intact riparian zones of these streams were not sufficient to protect them from the effect of upland disturbance, and they emphasize the role of the entire catchment in determining stream structure and function.
Article
Studies were conducted at three locations in the Lower Salmon River, Idaho (USA) and at one Upper Salmon "calibration" site to extend results of previous research (headwater through 5-6th-order [1-814 links] streams) to an 8th-order (15,000 links) river. Transported organic matter (TOM) generally increased downstream. Coarse TOM was prevalent only in the upper 50 km of the system, and ultrafine was the predominant particulate component throughout the system. Stored (benthic) organic matter (OM) was highest in the headwaters and showed a progressive downstream decrease. The headwaters were highly retentive of coarse particulate organic matter (CPOM) but much less so of the fine and ultrafine fractions. Transported and stored OM approached a balance only in the lowermost (deeper) reaches of the river system. Analyses of the components of ecosystem metabolism revealed that gross primary production and respiration (R) both showed a general downstream increase. Overall, the net metabolism measurements showed that R was predominant in the upstream reaches, autotrophy prevailed in the middle reaches, and R was again predominant at the farthest downstream site. Insect functional feeding-group patterns apparently were altered in their relative abundances from that predicted by the River Continuum Concept by lower than expected deciduous CPOM-loading in the headwaters and high sediment transport into the mid-reaches from a major tributary (East Fork). Although shredders were prevalent in headwater reaches, they were less abundant than predicted. Gatherers were dominant in the upper reaches and filterers in the mid-sized reaches above East Fork. Scrapers increased progressively downstream in relative abundance. Spiraling and retention measurements revealed a general downstream increase in the rate of movement of OM; turnover length of carbon increased progressively downstream. The ratio of mean water velocity: rate of downstream movement of OM indicated that the export of organic carbon was reduced 3500-fold in headwaters relative to that of mean water velocity whereas the lower reaches behaved more like a conduit with carbon atoms passing through at a rate comparable to water velocity. In spite of the cold and arid climate in which the Salmon River Basin is located and the low allochthonous input from deciduous plants, the data generally support the basic premises of the River Continuum Concept.
Article
The fraction of gross primary production (GPP) that is immediately respired by autotrophs and their closely associated heterotrophs (AR(f)) is unknown. This value is necessary to calculate the autotrophic base of food webs, which requires knowing production available for grazers. AR(f) is also necessary for estimating heterotrophic respiration (HR) which is needed to calculate C spiraling in streams and rivers. We suggest a way to estimate AR(f) from daily metabolism data using quantile regression between GPP and 90% quantile of ecosystem respiration (ER). We reasoned that autotrophic respiration represents the lower limit for ER on any one day and used quantile regression to estimate the relationship of the lower quantile of ER with respect to GPP. We examined this approach with simulation modeling and application of quantile regression to estimates of continuous GPP and ER from > 20 streams. Simulation modeling showed that low-uncertainty estimates of AR(f) required large variation in daily GPP. Covariance between HR and GPP, which might be observed if the processes were temperature controlled, biased estimates of AR(f). Seasonal estimates of AR(f) were robust to daily variation in AR(f) as a function of GPP. AR(f) calculated from previously published estimates of daily metabolism from streams averaged 0.44 (SD = 0.19) with high variation among streams. This value is higher than most physiological measurements, probably because of light limitation of algae and from HR closely associated with daily GPP. How much of AR(f) was from algal respiration vs closely associated heterotrophic respiration is not known, but we suggest that the value (1 - AR(f))GPP represents the amount of C available to animals.
Article
Macrophytes influence the physical, chemical, and biological characteristics of lowland streams, so may be critically important in stream management. We investigated the role of macrophytes in regulating metabolism and nutrient cycling in three lowland, agricultural streams. We measured stream metabolism over the growing season and following experimental macrophyte removal, and used short-term nutrient additions of phosphate (P) and ammonium to assess macrophyte influences on nutrient uptake. Primary production was closely correlated with macrophyte cover across all streams and dates, and decreased greatly with macrophyte removal, whereas ecosystem respiration was not correlated with macrophyte cover and was not altered by macrophyte removal. Phosphate uptake velocity was negatively related to primary production, suggesting that macrophyte activity actually slowed P uptake. Ammonium uptake was not correlated with macrophyte cover or metabolism metrics. Stream nitrate concentrations typically exceeded concentrations of incoming groundwater, suggesting little net nitrate retention in these macrophyte-dominated streams. Phosphorous demand by macrophytes was 10-fold lower than observed uptake rates, indicating that macrophyte P demand was much lower than that of other stream biota. Nitrogen demand by macrophytes was nearly equal to ammonium uptake and was not sufficient to affect the high nitrate flux. These results indicate that macrophytes drive ecosystem metabolism but have limited influence on water column nutrient concentrations because macrophyte demand is much lower than the supply available from the water column. Thus macrophytes in our streams had a large impact on stream trophic state, but offered little potential to influence nutrient removal via management.
Article
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Article
Small headwater streams are abundant components of the riverine landscape where critical biochemical processes occur that provide clean water, energy, and nutrients to downstream reaches. Disturbance to these systems as a result of human land use has the potential to affect downstream health. Rates of metabolism and organic matter processing were measured in 22 small forested headwater streams in 2 regions of Tasmania, Australia, to evaluate the effects of forestry disturbance. Twelve of these streams had been subjected to recent clearfell-burn-and-sow (CBS) harvest. Benthic metabolism was measured in small in situ chambers (production ranged from <0.001 to 21.845 mg C m−2 h−1 and respiration from <0.001 to 4.976 mg C m−2 h−1), whole-system metabolism was estimated based on relative habitat abundance (gross primary production ranged from <0.001 to 0.297 g C m−2 d−1 and daily respiration from 0.003 to 0.072 g C m−2 d−1). Algal growth potential was measured on nutrient diffusing pots (chlorophyll a ranged from <1.0 to 40.1 mg/m2), and cellulose decomposition potential was assessed with a cotton-strip assay (cotton tensile strength loss ranged from 17.8% to 38.3% in 28 d). Sometimes an increase in the variability of response is a consequence of disturbance, but in our study, the difference between forested streams and clearcut streams was a significant increase in the mean values of all functional variables. The degree of response depended on the underlying geology (broad-scale spatial variability) of the streams. Current management practices for small headwater streams in Tasmania do not protect instream processes from forestry disturbance in the short-term (i.e., 2–5 y), and we suggest that an investigation of long-term response is warranted.
Article
The rate coefficient K2 for the exchange of oxygen between flowing water and the atmosphere (reaeration) has been studied in six Danish streams covering a relatively wide range of hydraulic conditions, pollutional loading, and macrophyte abundance. 103 K2-measurements were performed in 1978–85. 82 measurements were obtained applying 5 different indirect methods all balancing the sources and sinks of stream dissolved oxygen under conditions of normal operation of the system (3 methods) and under artificial depletion of the oxygen concentration of the stream water by addition of sodium sulphite (2 methods). 21 K2-values were determined directly applying a gaseous tracer (krypton-85) for reaeration. Guidelines for selecting a proper method to determine K2 knowing macrophyte biomass and loading characteristics of the particular stream are provided.
Article
Whole-stream metabolism in a first-order stream was measured using upstream-downstream changes in dissolved oxygen (DO) concentration measured at 1-min intervals over a 40-h period. The measured change in DO was corrected for reaeration flux using a reaeration coefficient determined from injections of conservative and volatile tracers. The whole-stream metabolism measurement was compared in the spring with in situ chamber measurements performed a few days later in the same stream reach. Chamber measurements of community respiration extrapolated to a 24-h period (CR(24)) were about one third the whole-stream measurements, while gross primary production (GPP) measured at midday in the chambers was roughly 20% less than the whole-stream estimate. Whole-stream GPP was higher during the spring just prior to forest canopy closure than in summer or autumn. Community respiration exceeded whole-stream GPP on all dates and was greatest during the summer. Our results suggest that this whole-stream approach provides a measure of total stream metabolism that is relevant to other stream ecosystem processes measured on reach scales, such as nutrient spiralling.
Article
We compared 190 photosynthesis-irradiance (P-E) experiments with single- and multispecies communities of macroalgae and vascular plants from freshwater and marine habitats. We found a typical hyperbolic P-E relation in all communities and no sign of photosaturation or photoinhibition of photosynthesis at the highest irradiances of about 2,000 mmol m22 s21. Macrophyte communities displayed much higher maximum gross production (GPmax), respiration, and light compensation point than separate phytoelements because of the multilayered structure and extensive self-shading in the communities, whereas light use efficiency at low irradiance (a) was the same. Although GPmax and a varied extensively among the 190 communities, their upper limits increased linearly and predictably with community absorption reaching 26.3 mmol m22 s21 O2 and 0.090 mol mol21 photon at 100% absorption. The upper limit of a is close to a realistic limit of O2 of 0.10 mol mol21 photon. The upper limit of GPmax, however, is markedly below the theoretically attainable 180 mol m22 s21 O2, reflecting a suboptimal three-dimensional structure and light distribution. Indirect measures supported this explanation as GPmax increased fourfold from communities with a very uneven to a more even light distribution. Photosynthetic characteristics of communities are strongly influenced by plant density, absorption, and distribution of light and cannot be interpreted from the photosynthetic behavior of phytoelements. Thus, many examples of carbon and nutrient limitation in experiments with separate phytoelements may not withstand at the relevant ecological scale of communities where light almost always constrains photosynthetic production.
Article
Samples from two coastal experimental ecosystems were incubated in vitro and sampled over 24 h. Production rates were measured by the 14C method, the O2 and CO, light-dark bottle methods, and the I80 method. 0, production in the experimental enclosures (volume - 1.3 x lo4 liters) was also measured directly. Photosynthetic and respiratory quotients were close to 1 .O. Gross production values determined by 0, light-dark experiments, CO2 light-dark experiments, and I80 were similar. 14C production ranged from 60 to 100% of gross production measured in CO, light-dark experiments, indicating that 14C uptake is not precisely fixed with respect to other measures of community metabolism. There was no evidence that 14C or any other method underestimated the rate of primary production in vitro by more than 40%. Productivities in vitro ranged from 35 to 100% of those in the mesocosm at similar light intensities. In samples from one of the ecosystems, the rate of respiration in the light (calculated from I80 data) was an order of magnitude greater than the rate in the dark. This difference may be ascribed to either photorespiration or light enhancement of mitochondrial respiration.
Article
1. Although macrophytes play a key role in the structure and functioning of lowland rivers, most of the basic plant, hydrodynamic and sediment-water interactions have only been described qualitatively. We therefore studied quantitatively, the seasonal dynamics of matter deposition and mobilisation inside and outside (free path) a representative patch of arrowhead, Sagittaria sagittifolia, in the lowland River Spree, NE Germany, in August 2006. Our in situ study combined resuspension experiments, a hydrodynamically calibrated erosion chamber and concurrent measurements of the prevailing flow characteristics and bed load. 2. Increasing entrainment rates (E) of particles (ESPM) and total P (ETP), with increments of shear velocity (U*) from 0.53 to 2.42 cm s−1, were significantly higher inside the plant patch than outside. Indeed, ESPM and ETP at the lowest U* were 8- and 12-fold higher inside than outside the patch, reflecting the resuspension potential of the upper nutrient-enriched layer and the extent of pulsed P inputs even at small increases in U*. 3. Vertical distribution of velocity (u) revealed a flow pattern of a mixing layer inside the S. sagittifolia patch, and that of a boundary layer in the free path. The highest gradient of u in the mixing layer was located in the water column at about 0.5 m depth, whereas the highest gradient of u for the boundary layer was found near the riverbed. The maximum of U* (1.65 cm s−1) was only 4 mm above the sediment. 4. A plant mosaic provides a low-energetic environment promoting extensive particle trapping and the accumulation of a fine-grained, nutrient-enriched sediment, and forming a large resuspension potential. Consequently, after plant decay and the concomitant increase of U* this material is preferentially entrained at higher rates. Hence, the key role of submerged macrophytes in lowland rivers is more directly related to modifying the dynamic equilibria between vegetation trapping and resuspension, than to the retention of nutrients, particularly P, and the reduction of P loads downstream to other waters.
Article
The interplay between erosion and deposition are fundamental characteristics of river basins. These processes result in the delivery, retention and conveyance of sediment through river systems. Although the delivery of sediment to rivers is a natural phenomenon, in recent years there has been increasing concern about the enhancement of sediment loadings as a result of anthropogenic activities. The presence of macrophytes in river channels tends to increase the retention of fine sediment leading to changes in bed composition. However, a complex relationship exists between macrophytes and fine sediment: macrophytes affect the conveyance of fine sediment and are, in turn, affected by the sediment loading. This review deals with these two reciprocal effects and, in particular, summarizes the available evidence base on the impact of fine sediment on macrophytes. Increased inputs of fine sediment appear to have both direct and indirect impacts on the macrophyte community, altering light availability, and the structure and quality of the river bed. The nature of these impacts depends largely on the rate of deposition and the nature of the material deposited. Changes in macrophyte community composition may ensue where the depositing material is more nutrient rich than the natural river bed. Many of the changes in macrophyte flora that occur with increased fine sediment inputs are likely to closely parallel those that occur with increased dissolved nutrient availability. If attempts to manage nutrient inputs to rivers are to achieve their goals, it is critical that fine sediment-associated nutrient dynamics and transfers are considered. Copyright © 2011 John Wiley & Sons, Ltd.
Article
1. In unshaded, nutrient-rich streams, prolific growth of stream macrophytes often results in flows that over-top the banks and in high primary production and respiration that may result in extreme diel variations in dissolved oxygen. Consequently, water protection authorities commonly remove macrophytes periodically. 2. We investigated the effect of plant removal on stream metabolism and oxygen balance in two Swiss streams with a high macrophyte biomass. We monitored the concentration of dissolved oxygen before and after macrophytes were removed by cutting and dredging, and calculated rates of gross primary production and ecosystem respiration by means of diel oxygen curves. 3. The removal of plants, which had reached a dry biomass of 320–420 g m−2 immediately before plant removal, had a different impact on stream metabolism in the two streams. In the first (plants removed in May), neither primary production nor ecosystem respiration were significantly affected. In the second (plants removed in late July), gross primary production and ecosystem respiration were reduced by about 70%. In this latter stream gross primary production increased in the first 2 weeks after plant removal but never recovered to pre-disturbance levels. 4. The removal of plants coincided with only a moderate increase in nocturnal oxygen concentration (+1 mg L−1). This, and the rapid partial recovery of stream metabolism in the second stream, suggests that an increase in the oxygen concentration after plant cutting is transient in unshaded, nutrient-rich streams.
Article
1. Rates of whole-system metabolism (production and respiration) are fundamental indicators of ecosystem structure and function. Although first-order, proximal controls are well understood, assessments of the interactions between proximal controls and distal controls, such as land use and geographic region, are lacking. Thus, the influence of land use on stream metabolism across geographic regions is unknown. Further, there is limited understanding of how land use may alter variability in ecosystem metabolism across regions.
Article
1. This paper describes a continuous-flow system that we have used extensively for measurement of oxygen exchange and nitrogen transformations in different communities of lowland streams, i.e. the water, the sediment, and the macrophyte—biofilm community. The system, which is set up on the stream bank, consists of several macrophyte and sediment chambers equipped with a double-flow system that ensures an internal water velocity close to that in the stream and which, by continuously renewing the water, mimics diel fluctuation in stream temperature and water chemistry. Water temperature and dissolved oxygen are measured continuously and the data stored on magnetic tape. Water samples are collected in a refrigerator and analysed using standard chemical procedures. 2. The application of the system is illustrated using results obtained during a 2-day summer experiment in a shallow macrophyte—rich stream. The biological processes in the stream were mainly associated with the macrophyte—biofilm community and the sediment, those in the water being negligible. Oxygen release was confined to the macrophyte—biofilm community, the sediment consuming oxygen both by day and by night. Whole-system gross production and dark respiration occurred at similar rates (6–7g O2 m−2 day−1), net balance being about zero. Inorganic nitrogen was consumed both by the sediment and to a greater extent by the macrophytes, the diel average consumption being 1g N m−2 day−1. 3. The sum of the activity in the macrophyte and sediment chambers corresponded to the overall activity of the stream section as determined by upstream/downstream mass balance. This indicates that the results obtained with the continuous-flow chambers realistically describe the oxygen and the nitrogen metabolism of the stream.
Article
1. The extent of spatial and temporal variation of microbial respiration was determined in a first-order, sand-bottomed, blackwater stream on the coastal plain of south-eastern Virginia, U.S.A. 2. Annual mean respiration rates (as g O2 m–3 h–1) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area. 3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates. 4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly. 5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O2 m–2 yr–1. Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non-woody detritus, stored in the stream during the year was lost to microbial respiration.
Article
1. Submerged macrophytes have important physical and structural effects on lowland streams. This study investigated the ability of submerged macrophytes to modify the near-bed flow and to retain mineral and organic particles in patches of four common macrophytes in shallow Danish streams during mid-summer. 2. In dense patches of Callitriche cophocarpa and Elodea canadensis, where near-bed velocity was reduced, the sediment surface was markedly raised and enriched with fine particles. In dense patches of Ranunculus peltatus, fine sediments were deposited among rooted shoots in the upstream part of the patches, while erosion and coarse sediments prevailed in the downstream part of the patches because of the strong vortices that formed at the rear and moved up under the trailing canopy. The open canopy of Sparganium emersum, with its streamlined leaves, had little effect on flow and sediment. 3. Patterns of sediment deposition and composition were closely related to the morphology and canopy structure of plant species and the presence of low velocity above the sediment among the rooted shoots. The mineral particles retained probably originate from bed-load, and the enrichment with finer particles within the patches probably results mainly from size-selective processes during erosion and transport of particles rather than during deposition. The mixed sediment composition within patches suggests that the flow-resistant shoots generate an environment conducive to deposition of all transported particles. 4. Fine sediments within macrophyte beds contained high concentrations of organic matter, carbon, nitrogen and phosphorus. The wide scatter in the relationships between mineral grain size and the content of organic matter and nutrients reflects the spatial and temporal complexity of erosion, transport and sedimentation of mineral and organic particles. 5. Enrichment of sediment within macrophyte beds relative to the surrounding substratum ranged from 780 g organic matter m–2, 30 g N m–2 and 25 g P m–2 for the flow-resistant dense canopies af Callitriche cophocarpa to 150 g organic matter m–2, 6.6 g N m–2 and 3.4 g P m–2 for the open canopies of Sparganium emersum. Retention of nutrient-rich particles within the macrophyte beds is probably of limited importance for plant growth in most lowland European streams, because macrophyte growth is rarely nutrient limited.
Article
1. Australian dryland rivers have among the most variable discharge of any rivers worldwide and are characterized by extended periods of no flow during which aquatic habitat contracts into isolated waterholes. Despite naturally high turbidity, benthic primary production is known to be the main source of carbon to waterhole food webs. The objective of this study was to quantify rates of benthic metabolism and identify factors influencing these rates in two Australian dryland rivers, the Cooper Creek and the Warrego River.
Article
We tested direct and indirect measures of benthic metabolism as indicators of stream ecosystem health across a known agricultural land-use disturbance gradient in southeast Queensland, Australia. Gross primary production (GPP) and respiration (R24) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophylla) from cobbles and sediment cores, algal biomass accrual on artificial substrates and stable carbon isotope ratios of aquatic plants and benthic sediments were measured at 53 stream sites, ranging from undisturbed subtropical rainforest to catchments where improved pasture and intensive cropping are major land-uses. Rates of benthic GPP and R24 varied by more than two orders of magnitude across the study gradient. Generalised linear regression modelling explained 80% or more of the variation in these two indicators when sediment and cobble substrate dominated sites were considered separately, and both catchment and reach scale descriptors of the disturbance gradient were important in explaining this variation. Model fits were poor for net daily benthic metabolism (NDM) and production to respiration ratio (P/R). Algal biomass accrual on artificial substrate and stable carbon isotope ratios of aquatic plants and benthic sediment were the best of the indirect indicators, with regression model R2 values of 50% or greater. Model fits were poor for algal biomass on natural substrates for cobble sites and all sites. None of these indirect measures of benthic metabolism was a good surrogate for measured GPP. Direct measures of benthic metabolism, GPP and R24, and several indirect measures were good indicators of stream ecosystem health and are recommended in assessing process-related responses to riparian and catchment land use change and the success of ecosystem rehabilitation actions.
Article
Metabolism is an integrative measurement of stream and river ecosystem functioning, and thus, could be used to assess impairment. Stream metabolism is measured by different methods which often yield contrasting results. Furthermore, open-channel measurements of metabolism, which offer the best potential for continuous monitoring of stream functioning, rely on calculations of gas exchange with the atmosphere, for which a plethora of methods exists. Therefore, to incorporate metabolism in stream monitoring programs, it is necessary to determine which methods yield comparable results under a given set of environmental conditions. We studied 21 streams in the Basque Country (northern Spain), ranging widely in physical characteristics and water quality. We calculated reaeration during summer baseflows using three different approaches: the night-time drop in oxygen, the lag between noon and peak oxygen concentration, and ten empirical equations relating depth and velocity with reaeration coefficients obtained from the literature. Differences among methods were very large, especially at the shallower sites. The results obtained with most empirical equations were highly correlated, but showed little agreement with the night-time and peak lag methods. We then analyzed the response of reaeration rate to river stage: reaeration calculated by the night-time method during 1year of continuous monitoring was regressed against discharge at each site, and the resulting model was compared to the results of empirical equations, using software HecRas 2.2 to model hydraulic conditions at different river stages. The shape of reaeration-discharge plots differed greatly and in a site-dependent manner, and there was little agreement between methods. Finally, we investigated the effects of reaeration rate on estimates of metabolism. The choice of method greatly affected the estimates of both primary production and respiration. The empirical equations, except E7 and E10, yielded the most unrealistic estimations of stream metabolism. Overall, the night-time method, especially when regressed against discharge, seems to be the most robust and reliable among those tested, with the energy dissipation method (E10) appearing to be a viable alternative when the night-time method does not work.
Article
1. We studied whole-ecosystem metabolism in eight streams from several biomes in North America to identify controls on the rate of stream metabolism over a large geographic range. The streams studied had climates ranging from tropical to cool-temperate and from humid to arid and were all relatively uninfluenced by human disturbances. 2. Rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) were determined using the open-system, two-station diurnal oxygen change method. 3. Three general patterns in metabolism were evident among streams: (1) relatively high GPP with positive NEP (i.e. net oxygen production) in early afternoon, (2) moderate primary production with a distinct peak in GPP during daylight but negative NEP at all times and (3) little or no evidence of GPP during daylight and a relatively constant and negative NEP over the entire day. 4. Gross primary production was most strongly correlated with photosynthetically active radiation (PAR). A multiple regression model that included log PAR and stream water soluble reactive phosphorus (SRP) concentration explained 90% of the variation in log GPP. 5. Ecosystem respiration was significantly correlated with SRP concentration and size of the transient storage zone and, together, these factors explained 73% of the variation in R. The rate of R was poorly correlated with the rate of GPP. 6. Net ecosystem production was significantly correlated only with PAR, with 53% of the variation in log NEP explained by log PAR. Only Sycamore Creek, a desert stream in Arizona, had positive NEP (GPP: R > 1), supporting the idea that streams are generally net sinks rather than net sources of organic matter. 7. Our results suggest that light, phosphorus concentration and channel hydraulics are important controls on the rate of ecosystem metabolism in streams over very extensive geographic areas.
Article
We used whole-stream and benthic chamber methods to measure rates of metabolism and determine the contribution of the hyporheic zone to ecosystem respiration (R) in two streams with differing surface–subsurface exchange characteristics, Rio Calaveras and Gallina Creek, New Mexico. We used the difference between whole-stream and benthic R to calculate the rate of hyporheic zone R and coupled this estimate to an independent measure of hyporheic sediment R to estimate the cross-sectional area of the hyporheic zone (AH) for two reaches from each stream. Conservative tracer injections and solute transport modeling were used to characterize surface–subsurface hydrologic exchange by determining values of the cross-sectional area of the transient storage zone (As). The hyporheic zone contributed a substantial proportion of whole-stream R in all four study reaches, ranging from 40 to 93%. Wholestream R, hyporheic R, and percent contribution of hyporheic R all increased as transient storage increased, with whole-stream and hyporheic R exhibiting significant relationships with As. All three measures of respiration and values of AH were much greater for both reaches of the stream with greater surface–subsurface exchange. AH is valuable for cross-site comparisons because it accounts for differences in rates of both benthic and hyporheic sediment R and can be used to predict the importance of the hyporheic zone to other stream ecosystem processes. Yes Yes
Article
Light- and CO(2)-saturated photosynthetic rates of the submersed aquatic plants Hydrilla verticillata, Ceratophyllum demersum, and Myriophyllum spicatum were 50 to 60 mumol O(2)/mg Chl.hr at 30 C. At air levels of CO(2), the rates were less than 5% of those achieved by terrestrial C(3) plants. The low photosynthetic rates correlated with low activities of the carboxylation enzymes. In each species, ribulose 1,5-diphosphate carboxylase was the predominant carboxylation enzyme. The apparent K(m)(CO(2)) values for photosynthesis were 150 to 170 mum at pH 4, and 75 to 95 mum at pH 8. The K(m)(CO(2)) of Hydrilla ribulose 1,5-diphosphate carboxylase was 45 mum at pH 8. Optimum temperatures for the photosynthesis of Hydrilla, Myriophyllum, and Ceratophyllum were 36.5, 35.0, and 28.5 C, respectively. The apparent ability of each species to use HCO(3) (-) ions for photosynthesis was similar, but at saturating free CO(2) levels, there was no indication of HCO(3) (-) use. Increasing the pH from 3.1 to 9.2 affected the photosynthetic rate indirectly, by decreasing the free CO(2). With saturating free CO(2) (0.5 mm), the maximum photosynthetic rates were similar at pH 4 and 8. Carbonic anhydrase activity, although much lower than in terrestrial C(3) plants, was still in excess of that required to support HCO(3) (-) utilization.Hydrilla and Ceratophyllum had CO(2) compensation points of 44 and 41 mul/l, respectively, whereas the value for Myriophyllum was 19. Relatively high CO(2) compensation points under 1% O(2) indicated that some "dark" respiration occurred in the light. The inhibition of photosynthesis by O(2) was less than with terrestrial C(3) plants. Glycolate oxidase activity was 12.3 to 27.5 mumol O(2)/mg Chl.hr, as compared to 78.4 for spinach. Light saturation of photosynthesis occurred at 600 to 700 mueinsteins/m(2).sec in each species grown under full sunlight. Hydrilla had the lowest light compensation point, and required the least irradiance to achieve the half-maximal photosynthetic rate.Field measurements in a Hydrilla mat indicated that in the afternoon, free CO(2) dropped to zero, and O(2) rose to over 200% air saturation. Most photosynthetic activity occurred in the morning when the free CO(2) was highest and O(2) and solar radiation lowest. The low light requirement of Hydrilla probably provides a competitive advantage under these field conditions.
Harvest as a control of sago pondweed (Potamogeton pectinatus L.) in Badfish Creek, Wisconsin: frequency, efficiency and its impact on stream community oxygen metabolism
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