Organic matter breakdown and ecosystem metabolism: functional indicators for assessing river ecosystem health (original) (raw)
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Freshwater Biology, 2003
Summary1. Leaf breakdown rates of Alnus glutinosa were determined and the structure of decomposer assemblages associated with leaves were analysed to assess the effect of pollution on the ecological condition of the Ave River (North‐west Portugal).2. Increase in organic and inorganic nutrients was associated with an increase in density and a decrease in richness of macroinvertebrates, a dramatic decline in the conidial production of aquatic hyphomycetes, but no major change in the richness of aquatic hyphomycetes.3. Downstream nutrient enrichment was correlated with accelerated leaf breakdown rates.4. The degree of functional impairment assessed by the ratio of leaf breakdown rates in coarse‐mesh and fine‐mesh bags was in accordance with the gradient of pollution defined by two biotic indices.5. This study supports the contention that leaf breakdown experiments are a valuable tool to assess the effect of pollution on the ecological condition of rivers.
Ecosystem measures of river health and their response to riparian and catchment degradation
Freshwater Biology, 1999
1. Measurements of ecological patterns are often used as primary biological indicators of river health. However, these patterns provide little information about important stream ecosystem processes (e.g. the sources and fate of energy and nutrients). The direct measurement of these processes is considered fundamental to the determination of the health of stream and river ecosystems. 2. In this paper we used two basic approaches to assess stream ecosystem response to catchment disturbance and, particularly, to the loss of riparian vegetation in different forested biomes across Australia. Benthic gross primary production (GPP) and respiration (R 24 ) provided measures of the amounts of organic carbon produced and consumed within the system, respectively. Stable isotope analysis was used to trace the fate of terrestrial and instream sources of organic matter in the aquatic food web. In a focal catchment in SE Queensland, additional measurements were taken of riparian attributes, catchment features and water quality. 3. Baseline measurements of GPP and R 24 from undisturbed forest streams provided reference values for healthy streams for comparison with sites where the catchment or riparian vegetation had been disturbed. These values of metabolism were low by world standards in all biomes examined. Preliminary data from the Mary River catchment in SE Queensland indicated that these parameters were sensitive to variations in riparian canopy cover and, to a lesser extent, catchment clearing, and predictive models were developed. The ratio P : R (GPP : R 24 ) was used to determine whether sites were net consumers (P < R) or producers (P > R) of carbon but this was not considered a reliable indicator of stream health on its own. 4. Although forest streams were typically net consumers of carbon (P < < R), stable isotope analysis of metazoan food webs indicated a high dependence on inconspicuous epilithic algae in some biomes. 5. A dramatic decline in the health of forest streams was observed when GPP substantially exceeded R 24 , especially when instream primary producers shifted from palatable unicellular algae to prolific filamentous green algae and macrophytes. These sources of instream production do not appear to enter aquatic food webs, either directly through grazing or indirectly through a detrital loop. Accumulation of these plants has led to changes in channel morphology, loss of aquatic habitat and often a major decline in water quality in some of the streams studied.
Limnology and Oceanography Letters, 2017
Abundant living roots can be found in some streams and other shallow marine and freshwater habitats. A reach of a small Brazilian forested stream had 28% cover by live roots and exhibited diurnal trends in dissolved oxygen that could be attributed to gross primary production, but we hypothesized that activity of riparian tree roots in the channel caused this pattern. During sunny periods, trees transpire deoxygenated water from roots to the canopy but not in the dark, resulting in diurnal cycles of dissolved oxygen. Wholestream shading experiments showed that photosynthesis in the stream is not responsible for the pattern. Sealed chamber measurements showed living roots of riparian vegetation had substantial respiratory activity and ammonium and nitrate uptake, and rates per unit area were greater than sand and less than silt (the other two dominant substrata), indicating roots can substantially alter in-stream biogeochemistry. Whole-system metabolism (ecosystem respiration, ER, and gross primary production, GPP) is a central aquatic ecosystem function and is often used as an index of stream ecosystem health (Fellows et al. 2006; Correa-Gonz alez et al. 2014) and the trophic state (Dodds 2006, 2007). Metabolism is affected by natural features of the aquatic and terrestrial ecosystems (e.g., biofilms, light availability, canopy cover and rainfall) as well as by the impacts from anthropogenic activities (Wang et al. 2003; Frankforter et al. 2010). However, we know of little work on an additional biological component in some streams, living tree roots in the open channel. Streams and other aquatic habitats (e.g., lake shores, estuarine environments) can have exposed living roots associated with nearby vegetation. These roots and their associated biofilms might be an important component of benthic metabolism but their importance to whole systems is not well
River management alters ecosystem metabolism in a large oligotrophic river
Freshwater Science
Algae and aquatic plants support river food webs through in-situ primary production. However, gross primary production (GPP) and ecosystem respiration (ER) are rarely evaluated in the context of river management or habitat restoration. We estimated daily GPP and ER during 2 growing seasons for 7 reaches in the Kootenai River and 1 reach in the Elk River, spanning 290 river km across British Columbia, Canada, and Montana and Idaho, USA. We characterized responses of GPP and ER to river management, including reaches with unregulated flow, regulated flow, nutrient addition, and habitat restoration. Downstream GPP and ER generally increased after changes in river management, and higher management intensity led to greater increases. GPP and ER followed a seasonal pattern with low initial values in spring, elevated values in midsummer , and a return to low values in late summer and autumn. Timing and duration of the elevated period for GPP and ER also differed among reaches following changes in river management. Our results suggest that river management affects GPP and ER, likely through reducing turbidity and the frequency and magnitude of extreme flow events, nutrient additions, and enhanced floodplain connectivity, thereby altering the timing and amount of autochthonous carbon available to the food web.
Benthic Metabolism as an Indicator of Stream Ecosystem Health
Hydrobiologia, 2006
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 (R 24 ) in benthic chambers in cobble and sediment habitats, algal biomass (as chlorophyll a) 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 R 24 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 R 2 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 R 24 , 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.
Science of The Total Environment, 2017
River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. Structure and functioning respond in contrasting and complementary ways to environmental stressors. Moreover, assessing the response of ecosystem functioning to stressors is critical to understand the effects on the ecosystem services that produce direct benefits to humans. Yet, there is more information on structural than on functional parameters, and despite the many approaches available to measure river ecosystem processes, structural approaches are more widely used, especially in management. One reason for this
Leaf Breakdown Rates: a Measure of Water Quality?
International Review of Hydrobiology, 2001
The breakdown rates of Alnus glutinosa leaves and the structure of macroinvertebrate communities were used to evaluate the impact of the village of Montalegre (Portugal) on the water quality of the Cávado river. Chemical and microbial analyses of stream water indicated a high organic load in the vicinity of the village. The abundance of macroinvertebrates associated with leaves increased along the pollution gradient, whereas richness of the community decreased. Biotic indices and multivariate analysis applied to aquatic macroinvertebrate communities discriminated polluted from non-polluted sites. Exponential breakdown rates of alder leaves were high (0.014 to 0.060 day -1 ) and the differences observed among sites suggested that nutrient enrichment stimulated leaf breakdown significantly. Leaf breakdown rates have not reflected improved biotic conditions as assessed by biotic indices at the most downstream site. These results suggest that both data from the structure and function of a stream are important for assessing water quality.
High Rates of Ecosytem Metabolism in Five Western Rivers
The UW National Parks Service Research Station Annual Reports, 2011
Primary production and respiration are core functions of river ecosystems that in part determine the carbon balance. Gross primary production (GPP) is the total rate of carbon fixation by autotrophs such as algae and higher plants and is equivalent to photosynthesis. Ecosystem respiration (ER) measures rate at which organic carbon is mineralized to CO2 by all organisms in an ecosystem. Together these fluxes can indicate the base of the food web to support animal production (Marcarelli et al. 2011), can predict the cycling of other elements (Hall and Tank 2003), and can link ecosystems to global carbon cycling (Cole et al. 2007).
Science of The Total Environment, 2021
We review the biologically driven decomposition processes that take place in riverine ecosystems. • We identify important gaps in our understanding of decomposition processes in rivers from temperate and tropical biomes. • We propose a novel analytical approach to predict decomposition processes from metabolic scaling theory. • Using metadata from 30 rivers, we demonstrate that the slope of community size spectra can predict rates of decomposition.
1. We investigated the effect of trophic status on the organic matter budget in freshwater ecosystems. During leaf litter breakdown, the relative contribution of the functional groups and the quantity/quality of organic matter available to higher trophic levels are expected to be modified by the anthropogenic release of nutrients. 2. Carbon budgets were established during the breakdown of alder leaves enclosed in coarse mesh bags and submerged in six streams: two oligotrophic, one mesotrophic, two eutrophic and one hypertrophic streams. Nitrate concentrations were 4.5–6.7 mg L)1 and the trophic status of each stream was defined by the soluble reactive phosphorus concentration ranging from 3.4 (oligotrophic) to 89 lg L)1 (hypertrophic). An ammonium gradient paralleled the phosphate gradient with mean concentrations ranging from 1.4 to 560 lg L)1 NH4-N. The corresponding unionised ammonia concentrations ranged from 0.08 to 19 lg L)1 NH3-N over the six streams. 3. The dominant shredder taxa were different in the oligo-, meso- and eutrophic streams. No shredders were observed in the hypertrophic stream. These changes may be accounted for by the gradual increase in the concentration of ammonia over the six streams. The shredder biomass dramatically decreased in eu- and hypertrophic streams compared with oligo- and mesotrophic. 4. Fungal biomass increased threefold from the most oligotrophic to the less eutrophic stream and decreased in the most eutrophic and the hypertrophic. Bacterial biomass increased twofold from the most oligotrophic to the hypertrophic stream. Along the trophic gradient, the microbial CO2 production followed that of microbial biomass whereas the microbial fine particulate organic matter and net dissolved organic carbon (DOC) did not consistently vary. These results indicate that the microorganisms utilised the substrate and the DOC differently in streams of various trophic statuses. 5. In streams receiving various anthropogenic inputs, the relative contribution of the functional groups to leaf mass loss varied extensively as a result of stimulation and the deleterious effects of dissolved inorganic compounds. The quality/quantity of the organic matter produced by microorganisms slightly varied, as they use DOC from stream water instead of the substrate they decompose in streams of higher trophic status.