The importance of hyporheic sediment respiration in several mid-order Michigan rivers: comparison between methods in estimates of lotic metabolism

Metabolism was measured in four Michigan streams, comparing estimates made using a flow-through chamber designed to include the hyporheic zone to a 20 cm depth and a traditional closed chamber that enclosed to a 5 cm depth. Mean levels of gross primary productivity and community respiration were consistently greater in the flow-through chamber than the closed chamber in all streams. Ratios of productivity to respiration (P/R) were consistently greater in the closed chambers than the flow-through chambers. P/R ratios were consistently <1 in all streams when estimated with flow-through chambers, suggesting heterotrophic conditions. Maintenance of stream ecosystem structure and function therefore is dependent on subsidies either from the adjacent terrestrial system or upstream sources. Our results suggest that stream metabolism studies that rely on extrapolation of closed chambers to the whole reach will most likely underestimate gross primary productivity and community respiration.     

A new chamber design for measuring community metabolism in a Michigan stream

We designed an open-ended community metabolism chamber to simultaneously measure surface and hyporheic metabolism. Our chamber design eliminated reaeration, compartmentalized metabolism, maintained ambient conditions and included hyporheic respiration. We compared results from our hyporheic chamber to results obtained from: (1) closed benthic community metabolism chambers constructed as recommended by Bott et al. (1978), and (2) whole-stream metabolism techniques as modified by Marzolf et al. (1994). Simultaneous comparisons of all three procedures were made for a 35 m riffle section of Augusta Creek, a 3rd-order Michigan stream, in July 1997 and repeated in July 1998. Simultaneous comparisons of all three procedures were also made for a 30 m sandy run section of Augusta Creek in September 1997, and repeated in September 1998. Our hyporheic chamber estimates for community respiration (CR₂₄) were similar to those obtained using the whole-stream metabolism procedure but were considerably higher than estimates obtained using the closed benthic chambers in three of the four experiments. These data suggest that our chamber design provided estimates of community metabolism which included both benthic and hyporheic respiration. The chamber incorporates several positive aspects of both closed chambers and the whole-stream method. This new method can be replicated, eliminates the need for a reaeration coefficient, ambient conditions are better approximated since it remains an open system, and it appears to provide more realistic estimates of whole-stream metabolism compared to the traditional chamber approach.     

Effects of inorganic sedimentation and riparian clearing on benthic community metabolism in an agriculturally-disturbed stream

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.     

Benthic community metabolism in three habitats in an Ozark stream

Benthic community metabolism was measured in three habitats (riffles, runs and pools) during spring (May), summer (July) and fall (October) in the Jacks Fork River, Missouri, using an in situ chamber technique. Net community productivity (NCP) and gross community productivity (GCP) were highest in riffles, lowest in pools and intermediate in runs. Rates of NCP and GCP during spring and fall were similar for both riffles and runs, but NCP and GCP increased significantly during summer in both habitats. Pool substrates were always heterotrophic and exhibited no significant seasonal changes in NCP or GCP. Community respiration (CR) was highest in riffles, intermediate in runs and lowest in pools, but interhabitat differences in CR were generally smaller than for NCP. Rates of CR during spring and fall were similar, but CR increased significantly during summer. Results indicate that the physical conditions associated with each habitat strongly affect benthic community metabolism in this stream and that the relative proportions of these habitats will influence the ratio of living algal:detrital organic matter potentially available for consumers.     

Base Cation Cycling in a Pristine Watershed of the Canadian Boreal Forest

In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO₂ efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO₂ efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO₂ effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R _soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO₂ efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO₂ efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO₂ efflux rates provides a level of temporal resolution that permits investigation of short- to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R _soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization.     

腾格里荒漠红砂-珍珠群落CO2收支变化及其不同观测方法间的比较

由于荒漠生态系统植被覆盖度低、生产力低下,其在全球碳循环中的作用被长期忽视。为探讨荒漠生态系统碳收支各组分的变化规律,以腾格里荒漠红砂(Reaumuria soongorica Maxim.)-珍珠(Salsola passerina Beg.)群落为研究对象,采用静态箱式法研究了该群落的净生态系统CO2交换量(NEE)、生态系统呼吸、土壤呼吸的日变化规律,同时将该方法所获得的NEE结果与涡动相关法观测的结果进行了比较。结果表明:(1)红砂-珍珠群落NEE的日变化表现为,在6:00—9:00左右出现一个CO2吸收的高峰值,随后在12:00—15:00左右出现一个CO2释放高峰值。红砂种群、珍珠种群和整个群落NEE的平均值分别为0.018、0.020和0.028 mg CO2m-2s-1;(2)红砂种群、珍珠种群、土壤及整个群落生态系统呼吸速率的日变化规律一致,均表现为明显的单峰变化趋势,在12:00—15:00左右出现一个CO2释放的高峰值。红砂种群、珍珠种群、土壤和整个群落的生态系统呼吸的平均值分别为:0.121、0.062、0.029和0.040 mg CO2m-2s-1。以盖度为加权因子计算得到红砂种群、珍珠种群和土壤呼吸占生态系统呼吸的比例分别为:9%、21%和70%,由此可见,生态系统呼吸主要来源于土壤呼吸。(3)将箱式法和涡动相关法观测的NEE进行比较,结果表明两种方法观测的NEE变化规律基本一致,相关系数达到0.7。采用箱式法观测的NEE高于涡动相关法观测的结果,平均值分别0.028 mg CO2m-2s-1(箱式法)和0.015 mg CO2m-2s-1(涡动相关法),涡动相关法的观测结果与箱式法观测结果的比值为0.54。综上可得,荒漠生态系统土壤呼吸的变化速率决定了生态系统呼吸的变化规律,采用箱式法可能高估了荒漠生态系统CO2的释放量。     

The effects of nutrient limitation and stream discharge on the epilithic microbial community in an oligotrophic Arctic stream

Nutrient limitation of epilithic microbial activity is modified by stream discharge and drainage from the tundra surrounding the Kuparuk River, Alaska, USA. During 1984, after three weeks of whole stream enrichment with phosphorus, autotrophic activity per unit biomass had increased in the enriched section of the stream suggesting that phosphorus availability was limiting productivity. In contrast, after three weeks of phosphorus enrichment during 1985, heterotrophic and autotrophic activity was similar in the control and enriched sections of the stream. However, when ammonia or nitrate and phosphorus were added to an in situ bioassay chamber for two weeks, higher community biomass and heterotrophic activity resulted. Ten days later biomass significantly dropped in the unenriched section. Nitrate levels over this period increased four fold concomitantly with decreased stream discharge. Apparently during 1985, nitrogen was limiting epilithic microbial community in the phosphorus enriched section of the Kuparuk River. The significant negative relationship between nitrate concentration and stream discharge observed during 1984 supported the trends seen in 1985. These data suggest that nutrient concentrations which limit epilithic microbial activity and biomass are regulated by the stream discharge and drainage from the surrounding tundra.     

Probing whole‐stream metabolism: influence of spatial heterogeneity on rate estimates

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A comparison of periphyton community structural and functional responses to heavy metals

This study evaluates the effectiveness of community production and respiration measurements as monitoring tools for environmental impact evaluations and compares these data to community structural data.In Prickly Pear Creek, Montana, production and respiration rates were determined for periphyton communities in control, impact and recovery reaches using colonized granite substrates and sealed plexiglas chambers. Values for gross primary productivity (GPP), community respiration (CR₂₄), ash-free dry mass (AFDM) and chlorophyll a content (Chla) were obtained for each granite slab. Of these, AFDM, Chla and CR₂₄ were statistically significant among sites (P0.01). Although mean values for GPP appeared to differ among reaches, statistical differences could not be inferred because of large variances associated with this measure. These data indicate that inherent variability may limit the use of community function measures in routine environmental monitoring. However, production/respiration methods provide valuable data about emergent properties of aquatic communities that cannot be derived from routine population censuses.     

Forest ecosystem respiration estimated from eddy covariance and chamber measurements under high turbulence and substantial tree mortality from bark beetles

Eddy covariance nighttime fluxes are uncertain due to potential measurement biases. Many studies report eddy covariance nighttime flux lower than flux from extrapolated chamber measurements, despite corrections for low turbulence. We compared eddy covariance and chamber estimates of ecosystem respiration at the GLEES Ameriflux site over seven growing seasons under high turbulence [summer night mean friction velocity (u*) = 0.7 m s^?1], during which bark beetles killed or infested 85% of the aboveground respiring biomass. Chamber‐based estimates of ecosystem respiration during the growth season, developed from foliage, wood, and soil CO₂ efflux measurements, declined 35% after 85% of the forest basal area had been killed or impaired by bark beetles (from 7.1 ± 0.22 μmol m^?2 s^?1 in 2005 to 4.6 ± 0.16 μmol m^?2 s^?1 in 2011). Soil efflux remained at ~3.3 μmol m^?2 s^?1 throughout the mortality, while the loss of live wood and foliage and their respiration drove the decline of the chamber estimate. Eddy covariance estimates of fluxes at night remained constant over the same period, ~3.0 μmol m^?2 s^?1 for both 2005 (intact forest) and 2011 (85% basal area killed or impaired). Eddy covariance fluxes were lower than chamber estimates of ecosystem respiration (60% lower in 2005, and 32% in 2011), but the mean night estimates from the two techniques were correlated within a year (r² from 0.18 to 0.60). The difference between the two techniques was not the result of inadequate turbulence, because the results were robust to a u* filter of >0.7 m s^?1. The decline in the average seasonal difference between the two techniques was strongly correlated with overstory leaf area (r² = 0.92). The discrepancy between methods of respiration estimation should be resolved to have confidence in ecosystem carbon flux estimates.     

Activity of the Respiration Electron Transport System (ETS) Different Size Particles as a Measure of Carbon Losses from Primary Producers

In situ ETS-activity of size-fractionated natural phytoplankton communities was studied to determine the relative rate of respiration of different size fractions. Different lakes of varying trophic levels were examined. This study suggested that <35 μm organisms are the major contributes of respiratory-enzyme activity to the total community respiration. The results of this study indicate that half or more of the losses of primary productivity in different particle sizes are from respiratory activity. The data collected during this research on the photosynthetic rates and P/R ratio of different size particles give better information than primary productivity alone on community metabolic rates for evaluating productivity measurements.     

Characteristics of nighttime respiration in outdoor mesocosms

To better understand the patterns and regulation of nighttime community respiration, dissolved oxygen (DO) and pH were simultaneously measured at 5-min intervals for 37 days in each of three outdoor mesocosms with different fish stocking levels. Nighttime decreases in community respiration rates were estimated fairly well by an exponential function of time and slightly worse by a linear one, irrespective of ecosystem differences, but smaller time coefficients were obtained for dissolved inorganic carbon (DIC) than for DO. Respiratory quotients increased significantly from nightfall to the hour before dawn. To roughly estimate gross productivity from net productivity measurements, we extrapolated nighttime respiration from various parts of the night to the daytime; among the models evaluated, that extrapolating the respiration rate averaged over the whole nighttime to the previous day led to the highest correlation between irradiance and estimated gross productivity. Significant correlations were found between estimated daytime gross production rates and respiration rates just after sunset, whereas respiration before sunrise seemed quite constant and close to minimum metabolic rates of the ecosystems. Nighttime respiration was also affected by the composition and/or metabolic state of the system, expressed here by daily net community productivity. Multiple regression analysis showed that more than 75% of daily and between-pond variation in respiration rates just after sunset was explained by daytime gross productivity, planktonic and detrital carbon concentrations, and daily net community productivity. Received: July 5, 1999 / Accepted: November 17, 1999     

Metabolic balance of streams draining urban and agricultural watersheds in central Japan

Empirical data that describe the metabolic balance of stream ecosystems in human-dominated watersheds are scarce. We measured ecosystem metabolism in 23 open-canopied lowland streams draining urban and agricultural areas in the Fuji River Basin, central Japan. Gross primary production (GPP) and community respiration (CR) were estimated using the diurnal dissolved oxygen (DO) change technique, with the reaeration coefficient (K ₂) determined from seven empirical depth-velocity equations. Because the predicted values of K ₂ showed variation among the depth-velocity equations, the estimates of stream metabolism also varied according to the equations. However, CR was almost always greater than GPP, resulting in negative net ecosystem production (NEP) and GPP/CR ratios below unity for most of the study reaches. Highly heterotrophic streams were found in intensively farmed watersheds, suggesting that organic matter loading from agricultural lands is likely to be a source of allochthonous carbon fueling excess respiration in the study streams. In contrast, streams draining more urbanized areas were less heterotrophic. The present results suggest that lowland streams in agriculturally developed watersheds are associated strongly with terrestrial ecosystems as a source of organic carbon. The resultant strong respiration might become the dominant process in ecosystem metabolism, as reported for headwater streams, large downstream rivers, and estuaries.     

Abundance and productivity of protozoa in chalk streams

The distribution and abundance of protozoa in two chalk streams were studied. Particular attention was given to the ciliates and amoebae associated with the dominant submerged macrophyte, Ranunculus penicillatus . Highest numbers of protozoa occurred in habitats in the stream where the current velocity was reduced. Mean standing crops of ciliates, flagellates and amoebae were 32.5, 2.9 and 2.0 mg dry wt m⁻² of stream bed respectively. Estimates of production and respiration rates by field populations of ciliates and amoebae were made for one type of habitat within the streams. The results are compared with published data on the productivity of protozoa in other habitats and of other invertebrates within the chalk stream ecosystem. The limitations of such productivity estimates are discussed.     

Comparison of soil respiration methods in a mid-latitude deciduous forest

In forest ecosystems the single largest respiratory flux influencing net ecosystem productivity (NEP) is the total soil CO₂ efflux; however, it is difficult to make measurements of this flux that are accurate at the ecosystem scale. We examined patterns of soil CO₂ efflux using five different methods: auto-chambers, portable gas analyzers, eddy covariance along and two models parameterized with the observed data. The relation between soil temperature and soil moisture with soil CO₂ effluxes are also investigated, both inter-annually and seasonally, using these observations/results. Soil respiration rates (R _soil) are greatest during the growing season when soil temperatures are between 15 and 25 °C, but some soil CO₂ efflux occurs throughout the year. Measured soil respiration was sensitive to soil temperature, particularly during the spring and fall. All measurement methods produced similar annual estimates. Depending on the time of the year, the eddy covariance (flux tower) estimate for ecosystem respiration is similar to or slightly lower than estimates of annual soil CO₂ efflux from the other methods. As the eddy covariance estimate includes foliar and stem respiration which the other methods do not; it was expected to be larger (perhaps 15–30%). The auto-chamber system continuously measuring soil CO₂ efflux rates provides a level of temporal resolution that permits investigation of short- to longer term influences of factors on these efflux rates. The expense of building and maintaining an auto chamber system may not be necessary for those researchers interested in estimating R _soil annually, but auto-chambers do allow the capture of data from all seasons needed for model parameterization.     

Seasonal and annual respiration of a ponderosa pine ecosystem

The net ecosystem exchange of CO₂ between forests and the atmosphere, measured by eddy covariance, is the small difference between two large fluxes of photosynthesis and respiration. Chamber measurements of soil surface CO₂ efflux (F_s), wood respiration (F_w) and foliage respiration (F_f) help identify the contributions of these individual components to net ecosystem exchange. Models developed from the chamber data also provide independent estimates of respiration costs. We measured CO₂ efflux with chambers periodically in 1996–97 in a ponderosa pine forest in Oregon, scaled these measurements to the ecosystem, and computed annual totals for respiration by component. We also compared estimated half-hourly ecosystem respiration at night (F_nc) with eddy covariance measurements. Mean foliage respiration normalized to 10 °C was 0.20 μmol m^–2 (hemi-leaf surface area) s^–1, and reached a maximum of 0.24 μmol m^–2 HSA s^–1 between days 162 and 208. Mean wood respiration normalized to 10 °C was 5.9 μmol m^–3 sapwood s^–1, with slightly higher rates in mid-summer, when growth occurs. There was no significant difference (P > 0.10) between wood respiration of young (45 years) and old trees (250 years). Soil surface respiration normalized to 10 °C ranged from 0.7 to 3.0 μmol m^–2 (ground) s^–1 from days 23 to 329, with the lowest rates in winter and highest rates in late spring. Annual CO₂ flux from soil surface, foliage and wood was 683, 157, and 54 g C m^–2 y^–1, with soil fluxes responsible for 76% of ecosystem respiration. The ratio of net primary production to gross primary production was 0.45, consistent with values for conifer sites in Oregon and Australia, but higher than values reported for boreal coniferous forests. Below-ground carbon allocation (root turnover and respiration, estimated as F_s– litterfall carbon) consumed 61% of GPP; high ratios such as this are typical of sites with more water and nutrient constraints. The chamber estimates were moderately correlated with change in CO₂ storage in the canopy (F_stor) on calm nights (friction velocity u* < 0.25 m s^–1; R² = 0.60); F_stor was not significantly different from summed chamber estimates. On windy nights (u* > 0.25 m s^–1), the sum of turbulent flux measured above the canopy by eddy covariance and F_stor was only weakly correlated with summed chamber estimates (R² = 0.14); the eddy covariance estimates were lower than chamber estimates by 50%.     

Ecosystem Processes Performed by Unionid Mussels in Stream Mesocosms: Species Roles and Effects of Abundance

Unionid mussels are a guild of freshwater, sedentary filter-feeders experiencing a global decline in both species richness and abundance. To predict how these losses may impact stream ecosystems we need to quantify the effects of both overall mussel biomass and individual species on ecosystem processes. In this study we begin addressing these fundamental questions by comparing rates of ecosystem processes for two common mussel species, Amblema plicata and Actinonaias ligamentina, across a range of abundance levels and at two trophic states (low and high productivity) in stream mesocosms. At both low and high productivity, community respiration, water column ammonia, nitrate, and phosphorus concentrations, and algal clearance rates were all linearly related to overall mussel biomass. After removing the effects of biomass with ANCOVA, we found few differences between species. In a separate series of experiments, nutrient excretion (phosphorus, ammonia, and molar N:P) and biodeposition rates were only marginally different between species. For the species studied here, functional effects of unionids in streams were similar between species and linearly related to biomass, indicating the potential for strong effects when overall mussel biomass is high and hydrologic residence times are long.     

Community photosynthesis and respiration in experimental streams

Changes in relative contribution to total stream photosynthetic and respiratory rates by various community components of an open channel stream were estimated. Rates of photosynthetic production of plankton, benthos and macrophytes (with associated epiphytes) were followed through the growing season and compared with total estimates from a diurnal oxygen technique. Photosynthetic production by macrophytes was extremely high early in the growing season; but later declined and heterotrophic processes became predominant. In contrast, benthos production was initially low but became the primary source of photosynthesis later in the season. Plankton contributed little to stream photosynthesis and respiration.     

Persistent nitrogen limitation of stream biofilm communities along climate gradients in the Arctic

Climate change is rapidly reshaping Arctic landscapes through shifts in vegetation cover and productivity, soil resource mobilization, and hydrological regimes. The implications of these changes for stream ecosystems and food webs is unclear and will depend largely on microbial biofilm responses to concurrent shifts in temperature, light, and resource supply from land. To study those responses, we used nutrient diffusing substrates to manipulate resource supply to biofilm communities along regional gradients in stream temperature, riparian shading, and dissolved organic carbon (DOC) loading in Arctic Sweden. We found strong nitrogen (N) limitation across this gradient for gross primary production, community respiration and chlorophyll‐a accumulation. For unamended biofilms, activity and biomass accrual were not closely related to any single physical or chemical driver across this region. However, the magnitude of biofilm response to N addition was: in tundra streams, biofilm response was constrained by thermal regimes, whereas variation in light availability regulated this response in birch and coniferous forest streams. Furthermore, heterotrophic responses to experimental N addition increased across the region with greater stream water concentrations of DOC relative to inorganic N. Thus, future shifts in resource supply to these ecosystems are likely to interact with other concurrent environmental changes to regulate stream productivity. Indeed, our results suggest that in the absence of increased nutrient inputs, Arctic streams will be less sensitive to future changes in other habitat variables such as temperature and DOC loading.     

Metabolism in a macrophyte-rich stream exposed to flooding

The aim of this study was to investigate the effect of floods on the metabolic autotrophic rates of a Pampean stream. We hypothesized that there would be high productivity because of the macrophyte-rich community and the high nutrient levels but that this productivity would be reduced by flooding. Net community production (NCP) and community respiration (CR) were measured using clear and opaque acrylic chambers in the same reach of the stream. Community metabolism was analyzed in relation to biomass and the colonized streambed surface. Prior to the flood, epiphyton was the most productive compartment of the stream, whereas after the flood, the bottom algae compartment was the most productive one. Therefore, the relative contribution of each compartment to the entire ecosystem was influenced by the varying flow conditions. The primary gross production values of the Las Flores stream communities before the flood were higher than most of those reported in other streams worldwide and sustain the complex trophic web associated to the stream. Consequently, production decrease due to the lower relative contribution of macrophytes and epiphyton would lead to a more simplified trophic network.