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Abiotic controls and temporal variability of river metabolism: Multiyear analyses of Mississippi and Chattahoochee River data
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Whole-ecosystem metabolism is an important indicator of the role of organic matter, C cycling, and trophic structure in rivers. Ecosystem metabolism is well studied in small streams, but less is known about metabolism in large rivers. We estimated daily whole-ecosystem metabolism over 2 y for 1 site each at the Mississippi and Chattahoochee Rivers in the USA to understand factors influencing temporal patterns of ecosystem metabolism. We estimated rates of gross primary production (GPP), community respiration (CR), and net ecosystem production (NEP) with a curve-fitting approach with publicly available discharge (Q), dissolved O2, temperature, and photosynthetically active radiation (PAR) data. Models were run for week-long blocks, and power analyses suggested that rates should be established at least once for each 10-wk period throughout the year to characterize annual rates of metabolism accurately in these 2 rivers. We analyzed weekly rates averaged over 10-wk periods with Spearman rank correlation to identify potential drivers and with path analyses to identify interactions among variables driving GPP, CR, and NEP. Both rivers had an overall negative NEP, and the Mississippi River had stronger seasonal trends. In the Mississippi River, CR was strongly positively correlated with Q, which suggests variation in seasonal availability of allochthonous C. In the Chattahoochee, CR was most strongly positively correlated with GPP, whereas GPP was negatively correlated with Q, which suggests that autochthonous processes and water-column light attenuation played important roles in C dynamics. Our results suggest that these large rivers were net heterotrophic at annual time scales but autotrophy can be important seasonally.
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... Our budget further suggests that river NEP is the source of approximately 12% (LB: 4%, UB: 14%) of the global river C emissions (2.3 Pg C year −1 , including reservoir emissions; UB: 2.9 Pg C year −1 ). This estimate is lower than the contributions reported from US rivers (19% to 39%) 3 , the Amazon River and its floodplains (20%) 74 and Mississippi River (22%) 75 . NEP contributions to CO 2 evasion seem higher in small Arctic (>80%) 76 and boreal (75%) 77 rivers draining catchments with OC-rich soils. ...
... NEP contributions to CO 2 evasion seem higher in small Arctic (>80%) 76 and boreal (75%) 77 rivers draining catchments with OC-rich soils. This apparent 'mismatch' between our global budget approach and local field studies may be attributable to the high contributions of terrestrial CO 2 to the emissions from small headwaters 3 , not included, for instance, in the study on the Mississippi River 75 . The broad range of river NEP contributions to CO 2 emissions further highlights current difficulties in closing the terrestrial-aquatic continuum C budget. ...
River networks represent the largest biogeochemical nexus between the continents, ocean and atmosphere. Our current understanding of the role of rivers in the global carbon cycle remains limited, which makes it difficult to predict how global change may alter the timing and spatial distribution of riverine carbon sequestration and greenhouse gas emissions. Here we review the state of river ecosystem metabolism research and synthesize the current best available estimates of river ecosystem metabolism. We quantify the organic and inorganic carbon flux from land to global rivers and show that their net ecosystem production and carbon dioxide emissions shift the organic to inorganic carbon balance en route from land to the coastal ocean. Furthermore, we discuss how global change may affect river ecosystem metabolism and related carbon fluxes and identify research directions that can help to develop better predictions of the effects of global change on riverine ecosystem processes. We argue that a global river observing system will play a key role in understanding river networks and their future evolution in the context of the global carbon budget. A review of current river ecosystem metabolism research quantifies the organic and inorganic carbon flux from land to global rivers and demonstrates that the carbon balance can be influenced by a changing world.
... Understanding the drivers of carbon cycling in rivers is needed to predict the effects of modification by stressors such as warming, land use changes, and flow regulation . Unlike terrestrial systems, carbon processing in rivers may not be synchronized with subsequent emissions of the produced GHG due to the dynamic nature and spatiotemporal variability in their physicochemical and biological characteristics (Dodds et al., 2013). Continuous measurements of the key drivers of metabolism in rivers (e.g. ...
... The location of such friction zones in the coastal zone is quite different and depends on the morphology of the river channel. In the case of the Mekong River, which naturally has a high concentration of mineral suspension [12], this results in increased sedimentation of the suspension. Thus, it is next to the front of saline water inflow, another process accelerating the sedimentation of the suspension in the delta branches. ...
This work is licensed under Creative Commons Attribution 4.0 License AOMB.MS.ID.000571. Abstract Evaluation of short-time freshwater habitat fluctuations was provided in the period October 2019-February 2020 in the Mekong River delta in Vietnam. Three phases of water flow direction were documented in the diurnal tide cycle. In the middle-"stagnation" state, a daily maximal oxygen concentration in the river occurs, regardless of the sun's position above the horizon. Each tide cycle also creates a periodic water mass friction zone in the nearshore part of the riverbed and increases the sedimentation rate within the opposite direction of water mass flow. The biotic effects of freshwater habitat modification in the river branches are discussed.
... The sensor was deployed in the same location in each mesocosm pool near the observation window (Figure 1). These rates were corrected for variation in temperature, dissolved oxygen saturation, light, atmospheric pressure, and stream mesocosm morphology based on the singlestation modeling technique outlined in Riley and Dodds (2013) and Dodds et al. (2013). In short, this method uses a standard equation (Marzolf et al., 1994) to predict dissolved oxygen concentration. ...
Losses in freshwater fish diversity might produce a loss in important ecological services provided by fishes in particular habitats. An important gap in our understanding of ecosystem services by fishes is the influence of individuals from different size classes, which is predicted based on known ontogenetic shifts in metabolic demand and diet. I used 20 experimental stream mesocosms located at Konza Prairie Biological Station (KPBS), KS, USA, to assess the influence of fish size on ecosystem properties. Mesocosms included two macrohabitats: one riffle upstream from one pool filled with consistent pebble and gravel substrate. There were four experimental and one control treatment, each replicated four times ( N = 20). I used two size classes of central stonerollers ( Campostoma anomalum ) and southern redbelly dace ( Chrosomus erythrogaster ). Five ecosystem properties were assessed: algal filament length (cm), benthic chlorophyll a (μg/cm ² ), benthic organic matter (g/m ² ), macroinvertebrate biomass (g/m ² ), and stream metabolism (g O 2 /m ² /day ⁻¹ ). Size structure of fish populations affected some, but not all, ecosystem properties, and these effects were dependent upon species identity. Size structure of both species had effects on algal filament lengths where stonerollers of both size classes reduced algal filaments, but only small redbelly dace kept filaments short. A better understanding of the relationship between these prairie stream minnows and their small stream habitats could be useful to both predict changes in stream properties if species are lost (redbelly dace are a Species In Need of Conservation) or size structure shifts.
... Aerobic respiration consumes DO and primary production produces it. Dodds et al. (2013) found that even the largest rivers (e.g., Mississippi -drainage area of 2,900,000 km 2 ) can have oxygen variability driven by photosynthesis. Pollution that alters biotic aspects (e.g., organic carbon inputs, interference with light input) can also be important (Cox 2003;He et al. 2011;Zhi et al. 2021). ...
Water quality monitoring networks (WQMNs) that capture both the temporal and spatial dimensions are essential to provide reliable data for assessing water quality trends in surface waters, as well as for supporting initiatives to control anthropogenic activities. Meeting these monitoring goals as efficiently as possible is crucial, especially in developing countries where the financial resources are limited and the water quality degradation is accelerating. Here, we asked if sampling frequency could be reduced while maintaining the same degree of information as with bimonthly sampling in the São Paulo State (Brazil) WQMN. For this purpose, we considered data from 2004 to 2018 for 56 monitoring sites distributed into four out of 22 of the state’s water resources management units (UGRHIs, “Unidades de Gerenciamento de Recursos Hídricos”). We ran statistical tests for identifying data redundancy among two-month periods in the dry and wet seasons, followed by objective criteria to develop a sampling frequency recommendation. Our results showed that the reduction would be feasible in three UGRHIs, with the number of annual samplings ranging from two to four (instead of the original six). In both seasons, dissolved oxygen and Escherichia coli required more frequent sampling than the other analyzed parameters to adequately capture variability. The recommendation was compatible with flexible monitoring strategies observed in well-structured WQMNs worldwide, since the suggested sampling frequencies were not the same for all UGRHIs. Our approach can contribute to establishing a methodology to reevaluate WQMNs, potentially resulting in less costly and more adaptive strategies in São Paulo State and other developing areas with similar challenges.
... We expected side channels with greater heterogeneity to have increased adult richness through a diversified forage base. Side channels commonly have greater concentrations of suspended organic solids (Sobotka and Phelps, 2017a) and have greater gross primary productivity relative to the main channel (Dodds et al., 2013;Sobotka and Phelps, 2017b). Side channels provide important sources of invertebrates (Neuswanger et al., 1982) and transport pulses of invertebrate drift derived from backwater habitats (Eckblad et al., 1984). ...
Side channels in large floodplain rivers serve a variety of important ecological roles, particularly in reaches where habitat conditions have been degraded or diminished. We developed hypotheses regarding side channel ecological structure whereby we expected species richness of young of year fishes to generally be higher in shallower, more physically heterogeneous side channels with lower velocities, with differences based on reproductive guild. We also hypothesized species richness of adult fishes to be higher in side channels with greater heterogeneity that could support diverse foraging resources and provide refugia during extreme flow conditions. To test these hypotheses, we used a 28-year fish community dataset from the Upper Mississippi and Illinois Rivers. Across six study reaches, we assessed metrics of side channel physical size, heterogeneity, and connectivity that were hypothesized to explain variance of fish community response, while accounting for site-level factors across 52 side channels using multilevel models. We then used these side channel-level characteristics in a K-means cluster analysis to classify 1126 side channels across 32 reaches of the river system. Our results indicated that the relative explanatory contributions of physical metrics varied by response variable, providing varying evidence in support of our hypotheses, and indicating that different forms of heterogeneity matter in different ways. Side channel-level factors were more explanatory of fish community responses in side channels of upstream reaches compared to downstream reaches and percent wet forest was the most explanatory side channel-level factor of fish community responses across all models. Our classification of side channels indicated strong spatial contrasts in the abundance and diversity of side channels across reaches. Scaling up to understand how the diversity and abundance of different types of side channels contributes to landscape-scale ecological functions and processes would be useful for establishing targets for reach-scale physical heterogeneity.
The removal of the two dams on the Sélune River since 2019 has led to profound changes in the aquatic ecosystem. Lentic habitats bordered by forest had shifted to new conditions (running water and sparsely vegetated riverbanks) therefore shaping organisms’ assemblies. We studied how the reestablishment of aquatic lotic habitats in interaction with riparian vegetation could mediate the restoration of important ecological functions in the new river. Six stations located along the river continuum were surveyed for 3 years after dam removal: two control stations upstream the former reservoir, three restored stations within the former reservoir, and one control station downstream. We monitored physico-chemical characteristics, phytobenthos biomass and the river’s benthic metabolism, and assessed the functional composition of macroinvertebrate communities. We compared the recorded variables among upstream, downstream and restored sampling stations. We observed a rapid recolonization by invertebrates, but a still low phytobenthic primary production in restored stations. Such a low primary productivity was also reflected in the functional composition of invertebrate communities. Three years after dam removal, there was still a significant time lag between communities recovery and expected ecosystem functioning restoration. We observed a quick colonization by aquatic running-water invertebrate communities of new lotic reaches, but a slower recovery of important ecological functions rates such as those observed in control stations.
Although time series in ecosystem metabolism are well characterized in small and medium rivers, patterns in the world's largest rivers are almost unknown. Large rivers present technical difficulties, including depth measurements, gas exchange (, ) estimates, and the presence of large dams, which can supersaturate gases. We estimated reach‐scale metabolism for the Hanford Reach of the Columbia River (Washington state, USA), a free‐flowing stretch with an average discharge of 3173 . We calculated from semi‐empirical models and directly estimated it from tracer measurements. We fixed at the median value from these calculations (0.5 ), and used maximum likelihood to estimate reach‐scale, open‐channel metabolism. Both gross primary production (GPP) and ecosystem respiration (ER) were high (GPP range: 0.3–30.8 g , ER range: 0.8–30.6 g ), with peak GPP and ER occurring in the late summer or early fall. GPP increased exponentially with temperature, consistent with metabolic theory, while light was seasonally saturating. Annual average GPP, estimated at 1500 g carbon , was in the top 2% of estimates for other rivers. GPP and ER were tightly coupled and 90% of GPP was immediately respired, resulting in net ecosystem production near 0. Patterns in the Hanford Reach contrast with those in small‐medium rivers, suggesting that metabolism magnitudes and patterns in large rivers may not be simply scaled from knowledge of smaller rivers.
Wildfires generate hydro-geomorphological disturbances initiated by post-fire precipitation-runoff events. These disturbances are drivers of aquatic impairment over multiple months and years. While the impacts of wildfires on streams and rivers near burned areas have received increased attention in the last decades, it is still unclear how wildfire disturbances propagate longitudinally through fluvial networks. We deployed a rapid response team to install and maintain five high-frequency in-situ sondes to monitor water quality and stream metabolism changes over 190 km along the Gallinas Creek-Pecos River-Santa Rosa Lake fluvial network in response to the Hermit’s Peak - Calf Canyon (HPCC) wildfire, the largest in New Mexico’s recorded history. We assessed how far downstream water quality disturbances propagated along the fluvial network, the role of seasonality in that propagation, and the impact of lakes in mitigating further longitudinal propagation. Monitoring began a few days after the fire started in April 2022 and before any precipitation events had occurred. In the ten months post-fire, there were significant increases in turbidity and fDOM and reductions in gross primary production and ecosystem respiration at all monitoring sites upstream of Santa Rosa Lake. Stream metabolic fingerprints suggest increased scouring, DOC, nutrients, and suspended sediments at these sites. In contrast, the site downstream of Santa Rosa Lake did not have altered turbidity, gross primary production, or ecosystem respiration, and the metabolic fingerprints remained unchanged. These results suggest that Santa Rosa Lake, and associated water operations, buffered the propagation of wildfire disturbances ~180km downstream from the burn scar, resetting water quality parameters and metabolic activity for over ten months post-fire.
Studies of stream ecosystem metabolism over decades are rare and focused on responses to a single factor, e.g., nutrient reduction or storms. Numerous studies document that light, temperature, allochthonous inputs, nutrients, and flow affect metabolism. We use measurements spanning ~ 40 years to examine the interplay of all these influences on metabolism in forested and meadow reaches of a rural stream in southeastern Pennsylvania, USA. Measurements made in 1971–1975 used benthic substrata transferred to chambers (Period 1, P1), and ones in 1997–2010 used open system methodology (P2). Metabolism was greater in the Meadow reach both periods. Gross primary productivity (GPP) was driven primarily by light and chlorophyll, and respiration (R) by temperature and inclusion of hyporheic metabolism. Annually, processes were nearly balanced (Forested reach) or dominated by autotrophy (Meadow reach) in P1. Heterotrophy predominated in both reaches in P2, fueled by litter inputs (Forested reach) and fine particulate organic matter from the agricultural watershed (Meadow reach). Storms reduced GPP, R, and chlorophyll in proportion to storm size, but had less influence than other environmental factors. Riparian-zone reforestation of the P1 Meadow reach resulted in incident light and GPP similar to that in the permanent Forested reach within ~ 20 years.
For a majority of aquatic ecosystems, respiration (R) exceeds autochthonous gross primary production (GPP). These systems have negative net ecosystem production ([NEP]=[GPP]–R) and ratios of [GPP]/R of <1. This net heterotrophy can be sustained only if aquatic respiration is subsidized by organic inputs from the catchment. Such subsidies imply that organic materials that escaped decomposition in the terrestrial environment must become susceptible to decomposition in the linked aquatic environment.
Using a moderate-sized catchment in North America, the Hudson River (catchment area 33500 km²), evidence is presented for the magnitude of net heterotrophy. All approaches (CO2 gas flux; O2 gas flux; budget and gradient of dissolved organic C; and the summed components of primary production and respiration within the ecosystem) indicate that system respiration exceeds gross primary production by ~200 g C m⁻² year⁻¹. Highly ¹⁴C-depleted C of ancient terrestrial origin (1000–5000 years old) may be an important source of labile organic matter to this riverine system and support this excess respiration. The mechanisms by which organic matter is preserved for centuries to millennia in terrestrial soils and decomposed in a matter of weeks in a river connect modern riverine metabolism to historical terrestrial conditions.
This paper presents the results of many field measurements of the actual rates at which river water low in dissolved oxygen (D.O.) but free of organic pollution, absorbs oxygen from the atmosphere. Using dimensional analysis and multiple-regression techniques, the observed reaeration rates have been related to the hydraulic properties of the river channels. The several reaeration formulas thus developed can be used to predict accurately the rate at which oxygen will be absorbed by water flowing in natural stream channels.
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.
The level and diversity of metabolism in lotic ecosystems are largely functions of channel geomorphology and hydrology, making site-specific studies difficult to extrapolate to other parts of the watershed. This paper describes the pattern and distribution of aquatic oxygen metabolism for undisturbed boreal forest watersheds in eastern Quebec, Canada. Metabolism by periphyton, mosses, macrophytes, fine particulate organic matter (FPOM: 0.5 @mm-1mm), an coarse particulate organic matter (CPOM: >1mm) was examined during the ice-free period (April to November) of 1979 and 1980 in First Choice Creek (first order; watershed area: 0.25 km^2), Beaver Creek (second order; 1.83 km^2), Muskrat River (fifth order; 207 km^2), matamek River (sixth order; 673 km^2), and the Moisie River (ninth order; 19 871 km^2). As watershed area increases, primary production and the number of autotrophic groups are augmented with moss and macrophyte communities. Total O"2 metabolism increases downstream, ranging from <1 g@?m^-^2@?d^-^1 in First Choice Creek nearly 5 g@?m^-^2@?d^-^1 during summer in the Moisie River. Autotrophic metabolism is not normally correlated with light or chlorophyll, but annual O"2 production is highly correlated with stream order (r^2 > .76 in most cases). These data are combined with a geomorphological analysis of the watershed to discern the spatial distribution of aquatic metabolism, and to estimate total aquatic metabolism in the Moisie River drainage network. Mosses, occurring only in streams of fourth or higher order, are the most productive autotrophic component in the watershed (3.9 x 10^1^0 g/yr); by comparison, periphyton produce only 2.1 x 10^1^0 g/yr. FPOM is the most active detrital component (6.6 x 10^1^0 g/yr). Geomorphic analyses show that streams of fourth or higher order comprise only 1.2% of the total number and 12.7% of the total length, but have 76.8% of the lotic surface area, and are responsible for 86.3% of the gross production by the entire lotic drainage network. The surface area of lakes is approximately six times that of streams, but their contribution (phytoplankton) to total aquatic ecosystem metabolism is comparable only to that of lotic periphyton. Results demonstrate that the River Continuum Concept can be extended to the watershed level by combining biological measurement with geomorphological analyses of the drainage network, thus allowing a detailed description of spatial and temporal patterns for specific metabolic components and total ecosystem metabolism to be constructed.
