Coarse Particulate Organic Matter Dynamics Research Articles

Coarse particulate organic matter dynamics in ephemeral tributaries of a Central Appalachian stream network.

Headwater ephemeral tributaries are interfaces between uplands and downstream waters. Terrestrial coarse particulate organic matter (CPOM) is important in fueling aquatic ecosystems; however, the extent to which ephemeral tributaries are functionally connected to downstream waters through fluvial transport of CPOM has been little studied. Hydrology and deposition of leaf and wood, and surrogate transport (Ginkgo biloba leaves and wood dowels) were measured over month-long intervals through the winter and spring seasons (6 months) in 10 ephemeral tributaries (1.3–5.4 ha) in eastern Kentucky. Leaf deposition and surrogate transport varied over time, reflecting the seasonality of litterfall and runoff. Leaf deposition was higher in December than February and May but did not differ from January, March, and April. Mean percent of surrogate leaf transport from the ephemeral tributaries was highest in April (3.6% per day) and lowest in February (2.5%) and May (2%). Wood deposition and transport had similar patterns. No CPOM measures were related to flow frequency. Ephemeral tributaries were estimated to annually contribute 110.6 kg AFDM·km−1·yr−1 of leaves to the downstream mainstem. Ephemeral tributaries are functionally connected to downstream waters through CPOM storage and subsequent release that is timed when CPOM is often limited in downstream waters.

Effect of plant richness on the dynamics of coarse particulate organic matter in a Brazilian Savannah stream

The high plant richness in riparian zones of tropical forest streams and the relationship with an input of organic matter in these streams are not well understood. In this study, we assessed (i) the annual dynamics of inputs of coarse particulate organic matter (CPOM) in a tropical stream; and (ii) the relationship of species richness on riparian vegetation biomass. The fluxes and stock of CPOM inputs (vertical-VI = 512, horizontal-HI = 1912, and terrestrial-TI = 383 g/m2/year) and the benthic stock (BS = 67 g/m2/month) were separated into reproductive parts, vegetative parts and unidentified material. Leaves that entered the stream were identified and found to constitute 64 morphospecies. A positive relationship between species richness and litterfall was detected. The dynamics of CPOM were strongly influenced by rainfall and seasonal events, such as strong winds at the end of the dry season. Leaves contributed most to CPOM dynamics; leaf input was more intense at the end of the dry season (hydric stress) and the start of the rainy season (mechanical removal). Our study show an increase of litter input of CPOM by plant diversity throughout the year. Each riparian plant species contributes uniquely to the availability of energy resources, thus highlighting the importance of plant conservation for maintaining tropical streams functioning.

Measurements of coarse particulate organic matter transport in steep mountain streams and estimates of decadal CPOM exports

Summary Coarse particulate organic matter (CPOM) provides a food source for benthic organisms, and the fluvial transport of CPOM is one of the forms in which carbon is exported from a forested basin. However, little is known about transport dynamics of CPOM, its relation to discharge, and its annual exports from mountain streams. Much of this knowledge gap is due to sampling difficulties. In this study, CPOM was sampled over one-month snowmelt high flow seasons in two high-elevation, subalpine, streams in the Rocky Mountains. Bedload traps developed for sampling gravel bedload were found to be suitable samplers for CPOM transport. CPOM transport rates were well related to flow in consecutive samples but showed pronounced hysteresis over the diurnal fluctuations of flow, between consecutive days, and over the rising and falling limbs of the high-flow season. In order to compute annual CPOM load, hysteresis effects require intensive sampling and establishing separate rating curves for all rising and falling limbs. Hysteresis patterns of CPOM transport relations identified in the well-sampled study streams may aid with estimates of CPOM transport and export in less well-sampled Rocky Mountain streams. Transport relations for CPOM were similar among three high elevation mountain stream with mainly coniferous watersheds. Differences among streams can be qualitatively attributed to differences in CPOM contributions from litter fall, from the presence of large woody debris, its grinding into CPOM sized particles by gravel–cobble bedload transport, hillslope connectivity, drainage density, and biological consumption. CPOM loads were 3.6 and 3.2 t/yr for the two Rocky Mountain streams. Adjusted to reflect decadal averages, values increased to 11.3 and 10.2 t/yr. CPOM yields related to the entire watershed were 2.7 and 4 kg/ha/yr for the years studied, but both streams exported similar amounts of 6.5 and 6.6 kg/ha/yr when taking the forested portion of the watershed into account. To reflect decadal averages, CPOM yields per basin area were adjusted to 8.6 and 12.6 kg/ha/yr and to 21 kg/ha/yr for the forested watershed parts. CPOM yield may be more meaningfully characterized if annual CPOM loads are normalized by the area of a seam along the stream banks together with the stream surface area rather than by the forested or total watershed area.

The role of log jams and exceptional flood events in mobilizing coarse particulate organic matter in a steep headwater stream

Abstract. Coarse particulate organic matter (CPOM) fulfills important functions in the physical and ecological system of a stream. CPOM delivery to and export from the stream has implications for the stream's morphology and sediment transport capacity as well as the energy budget and food availability. Export rates of CPOM from mountain catchments have been observed to strongly increase with rising discharge, but the mechanism leading to this strong relationship is unclear. Here, we show that log jams in the Erlenbach, a steep headwater stream in the Swiss Prealps, are an effective barrier for the transport of CPOM pieces, and thus become sites of storage of large quantities of material over time. Exceptional discharge events with return periods exceeding 20 years play a dual role in CPOM transport in the Erlenbach. First, they appear to destroy existing log jams, releasing the stored material (wood and sediment). Second, they intensify channel–hillslope coupling, thereby recruiting new logs to the channel, around which new jams can form. This allows for the formulation of a new, fully episodic end-member in a four-end-member model of CPOM dynamics of steep mountain streams based on wood delivery and export.

Organic-matter dynamics in the riparian zone of a tropical headwater stream in Southern Brasil

We assessed the dynamics of allochthonous coarse particulate organic matter (CPOM) in a tropical headwater stream in the foothills of the Ouro Branco Sierra (S. Brazil; at 1300m a.s.l.) over a yearly cycle, and the contribution of leaves, twigs, and other plant parts to the different types of input and stock. Additionally, we identified the key species that contribute to each type of input and to seasonal patterns in the input and storage of CPOM (particles>1.00mm). Our study tested (and rejected) the hypothesis that the majority of riparian plant species along tropical headwater streams are perennial, and therefore the input of CPOM tends to be continuous over the course of the year. Leaves contributed 74% of CPOM, with input increasing toward the end of the dry season (September to October). Of the total of 188 plant species identified in the riparian zone, 47 species together contributed over 28% of the detritus to the aquatic ecosystem. The species that contributed most were Protium spp., Cabralea canjerana (Vell.) Mart., and Casearia decandra Jacq. The CPOM dynamics of Garcia Stream showed a highly seasonal pattern due to the influence of precipitation. A number of species characteristic of the Amazon and Atlantic Rain forests were identified, together with species of the Cerrado, indicating that the riparian vegetation should not be considered part of a single forest domain, but rather a unique and integrated system that functions as an ecological corridor for species dispersal. The data obtained here confirmed the ecological complexity of the riparian tropical system, derived from the diversity of plant species and the seasonal dynamics of CPOM, related to the phenology of the plant community.

Environmental heterogeneity affects input, storage, and transformation of coarse particulate organic matter in a floodplain mosaic

Quantifying spatial and temporal dynamics of organic matter (OM) is critical both for understanding ecosystem functioning and for predicting impacts of landscape change. To determine the influence of different habitats and coarse particulate OM (CPOM) types upon floodplain OM dynamics, we quantified aerial input, lateral surface transfer, and surface storage of CPOM over an annual cycle on the near-natural floodplain of the River Tagliamento in NE-Italy. Using these data, we modelled floodplain leaf dynamics, taking account of the spatial distribution and hydrologic connectivity of habitats, and using leaf storage as a response variable. Mean aerial CPOM input to the floodplain was similar from riparian forest and islands, but surface transfer was greater from islands, supporting the suggestion that these habitats act as “islands of fertility” along braided rivers. Leaves were the lateral conveyor of energy to more open parts of the floodplain, whereas CPOM was mainly stored as small wood in vegetated islands and riparian forest. Simulating the loss of habitat diversity (islands, ponds) decreased leaf storage on the whole floodplain, on exposed gravel and in large wood accumulations. In contrast, damming (loss of islands, ponds and floods plus floodplain overgrowth) greatly increased storage on exposed gravel. A random shuffle of habitats led to a storage increase on exposed gravel, while that in large wood accumulations and ponds declined. These results disentangle some of the complexities of CPOM dynamics in floodplain ecosystems, illustrate the value of models in understanding ecosystem functioning at a landscape level, and directly inform river management practice.

Coarse particulate organic matter dynamics in small streams: towards linking function to physical structure

Summary1. Organic matter derived from terrestrial vegetation (detritus) is a key basal resource in many food webs, including those of streams. Once detritus enters a stream, it is either retained or transported, but the rates of within‐reach retention depend on structural characteristics of the stream channel, physical properties of the detrital particles and hydrology. Each of these attributes varies in time and space and the magnitude of variation may be affected by structural changes wrought by land‐use. We developed a heuristic model framework in an attempt to find a minimal model that captures the essential temporal dynamics of coarse particulate detritus in small streams.2. The dynamics of our minimal model are driven by several frequently measured variables. Rate of litter breakdown, average transport distance of a particle, discharge and temperature are the primary variables. In addition, we tested the effects of altering assumptions about the nature of particle type and the effect of channel roughness on transport rates.3. The model produced patterns of detrital standing stocks generally similar to those measured by empirical studies in small streams. Discharge‐dependent transport relations are relatively rare, but our assumed pattern of a sigmoid relationship between transport and discharge produced reasonable outputs.4. We parameterised the model using data for small streams in coastal British Columbia, Canada. The outputs of the model indicate that channel roughness has a more profound effect on small, mobile particles, such as conifer needles, than on angiosperm leaves, such as alder. The model also indicates that the largest proportion of detritus is broken down in situ in all model scenarios.5. A major limitation to this model and the literature is a scarcity of detail of leaf interception and entrainment processes in streams. Progress towards integrating ecosystem functions and the dynamics of hydromorphology require integrating these physical drivers with biological processes. We present our model to emphasise that progress towards generalisable models of detrital dynamics is possible if links between physical structure and function can be made explicit.

Artificial steps to stabilize mountain rivers: a post‐project ecological assessment

AbstractThis paper compares the ecological response of reaches treated with traditional (check dams, CDs) and morphologically based (artificial steps, ASs) grade‐control works installed in a mountain river, where an unmodified reach provided reference conditions. Coarse particulate organic matter (CPOM) retentiveness was measured at the reach scale using artificial leaf release experiments. Macroinvertebrate sampling was carried out by a Surber net at pool‐ and run‐type morphological units within the three reach types, and hydraulic and sediment characteristics were measured at each Surber sampling site. In addition to calculating a variety of parameters to describe hydrodynamic and macroinvertebrate characteristics within reaches and morphological units, biotic (Extended Biotic Index, IBE) and ecological (Fluvial Functionality Index, IFF) index scores were also calculated. Results averaged at the reach scale show that CPOM retention, macrobenthos taxa richness and diversity were higher in the presence of a natural bed morphology, whereas both types of grade‐control works alter CPOM dynamics and macroinvertebrate communities. However, ASs showed CPOM retention dynamics and macroinvertebrate richness and diversity that were closer to the unmodified reach than CDs. Analysis at the unit scale demonstrated strong links between hydraulic variables and macroinvertebrate parameters such as abundance, diversity and proportion of shredders (SHR). Overall, ASs seem to provide a good trade‐off between the need to limit channel incision whilst maintaining aquatic ecosystems. Copyright © 2009 John Wiley & Sons, Ltd.