Flow regulation by dams affects ecosystem metabolism in Mediterranean rivers

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Transported material in a small river with multiple impoundments

SUMMARY.

• 1 The transport of particulate material in a multiply-impounded southern African river was studied from source to mouth over a period of 2 years during base flow conditions.
• 2 More than 95% of the dissolved and particulate material in transport was ultra fine (<80 μm). We conclude that too much emphasis has been placed on coarse material (>1 mm) in theories of river ecosystem functioning.
• 3 The ratio of CPOM:FPOM (1000–4000:250–1000 μm) in transport decreased with increasing stream order as a result of inputs of FPOM from pollution sources and from plankton blooms discharged from reservoirs.
• 4 The downstream effects of impoundment depended largely on the type of release and the quality of the inflowing water: surface-releasing reservoirs in the clean, upper reaches of the river had the least effect on transported material. A polluted surface-release impoundment in the mid-reaches of the river converted the particle size spectrum of the river from small (<80 μm) to large (250–1000 μm). Bottom-released water carried high concentrations (36–190 g m³) of small (<5 μm) and largely inorganic (86–93%) material.
• 5 The distance required for zooplankton densities to reduce by 95% was between 4 and 8 km downstream of an impoundment, except below a polluted impoundment where zooplankton densities took 32–35 km to reduce by 95%.
• 6 Most of the downstream changes in transported organic matter in the Buffalo River are due to inflows of agricultural and urban effluent. These disturbances to the river cause greater perturbations than do the impoundments.

     

Upper Mississippi River: seasonal and floodplain forest influences on organic matter transport

Seasonal influences and the role of floodplain forest as source or sink of organic matter is relatively unknown for 3arge, temperate rivers. Discharge and fine-particulate (FPOC), dissolved (DOC), and total organic carbon concentrations (TOC) were measured during five sampling periods from November, 1984, to August, 1985, above and below the floodplain-forested area (1054 ha) of Burlington Island in navigation Pool 19, upper Mississippi River. Sampling coincided with autumnal leaf fall of the floodplain forest, peak flood and falling spring flood, and low-flow conditions prior to and during phytoplankton bloom. Greatest TOC transport occurred during peak flood (8.84 × 10⁶ Kg/day) and leaf fall (7.79 × 10⁶ Kg/day). Peak flood transport was dominated by FPOC associated with flushing of material from upland areas. Transport during autumnal leaf fall was predominantly DOC attributed to litter leaching. Seasonal DOC loads generally increased downstream except during the phytoplankton bloom when a decrease was associated with increased microbial metabolic activity. Downstream decline in FPOC and increasing DOC loads during peak flood characterized the mechanism of deposition and processing of FPOC on the floodplain. FPOC concentration was significantly correlated to discharge and DOC concentrations were higher than FPOC except for peak flood. Significant downstream changes in TOC load suggests the importance of riparian vegetation as an influence on organic matter transport in large rivers.     

Comparing the fish assemblages and food‐web structures of large floodplain rivers

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Sediment transport in an inland river in North Queensland

Rivers in northern Queensland are ephemeral and carry water mainly as a direct response to heavy rainfall. Sediment is transported downstream with the runoff and sediment deposition may be a major problem in many proposed reservoirs. Hence information about sediment transport, particularly under high flow conditions, is required for planning and design of water storage reservoirs. In this region, bed material samples can be obtained during low flow periods and suspended sediment sampling during floods is possible but only with difficulty. Little reliable data is available.This paper outlines a possible approach to predicting sediment loads in such rivers. Suspended sediment samples have been analysed to give both particulate concentrations and their grain size distributions. The latter have been compared with bed material size distributions, and the concentrations of suspended bed material and wash load components have been estimated.After investigations of a number of methods for predicting bed material transport, those which treat bed load and suspended load independently have been selected. Field data have been used to determine the wash load and the suspended bed material load. The bed load was then computed so that the total sediment load could be determined.This approach has been applied to the Flinders River at Glendower, based on field data obtained by the Queensland Water Resources Commission in 1982/83.     

Autochthonous production in shallow littoral zones of five floodplain rivers: effects of flow,turbidity and nutrients

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The distribution of macroinvertebrate assemblages in a reach of the River Allier (France), in relation to riverbed characteristics

Investigations on large canalised rivers, for example the Danube, have shown that transported particulate matter, which is typically inorganic, is predominantly deposited in waters near the river’s main channel. This investigation deals with the lower section of the River Havel (NE Germany), a canalised lowland river with a very flat floodplain. This river is highly polluted by nutrients from urban areas (Berlin) and a long chain of river lakes produces high concentrations of phytoplankton. Due to the high proportion of planktogenic detritus, it was hypothesised that greater quantities of nutrient-rich fine particulate organic matter (FPOM) would be deposited in floodplain waters located further from the main channel than has been reported for large rivers. The total nutrient, P-binding metal (Fe, Al, and Mn), organic and inorganic carbon (TOC, TIC) contents of the upper organic sediment layer (0–4 cm) were analysed in samples collected from 48 floodplain water and river sites. The sediment bulk density, calculated on the basis of dry mass content and loss on ignition, was used to characterise the waters according to the impact of the river current. The results showed that the variability of total phosphorus (TP) was best explained by the variability of total iron (TFe, R² = 0.52). The floodplain water sediments could clearly be separated into two groups on the basis of the sediment particle size composition, and of the element ratios TOC:TP, TN:TP, primarily TFe:TP. The sediments from impounded river sections and from mouth sections of backwaters (approx. 100–200 m) were characterised by a high proportion particles from the 0.1 to 0.5 mm size fraction and by homogeneous, low TFe:TP, TOC:TP and TN:TP ratios. Sediments from distal sections of backwaters and of oxbow lakes tended to exhibit high element ratios with much higher variability. These results were interpreted as a spatially limited impact of the river on the floodplain water sediments. Contrary to expectation, the phosphorus bound in river seston was predominantly and very homogeneously deposited in the impounded river and mouth sections of backwaters. This implies that the inundation of the floodplain waters during spring floods seems to have no important material impact on the sediments in waters of low hydrological connectivity with the River Havel.     

Riverine distribution of mussel environmental DNA reflects a balance among density,transport, and removal processes

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The significance of side-arm connectivity for carbon dynamics of the River Danube, Austria

1. Side‐arms connected to the main stem of the river are key areas for biogeochemical cycling in fluvial landscapes, exhibiting high rates of carbon processing. 2. This work focused on quantifying autochthonous and allochthonous carbon pools and, thereby, on comparing transport and transformation processes in a restored side‐arm system of the River Danube (Regelsbrunn). We established a carbon budget and quantified carbon processing from March to September 2003. In addition, data from previous studies during 1997 to 1999 were assessed. 3. Gross primary production (GPP) and community respiration were estimated by diel oxygen time curves and an oxygen mass balance. Plankton primary production was determined to estimate its contribution to GPP under different hydrological conditions. 4. Based on the degree of connectivity, three hydrological phases were differentiated. Most of the organic matter, dominated by allochthonous carbon, was transported in the main channel and through the side‐arm during floods, while at intermediate and low flows (and thus connectivity), transformation processes became more important and autochthonous carbon dominated the carbon pool. The side‐arm system functioned as a sink for particulate matter [total suspended solids and particulate organic carbon (POC)] and a source of dissolved organic carbon (DOC) and chlorophyll‐a. 5. Autochthonous primary production of 4.2 t C day^?1 in the side‐arm was equivalent to about 20% of the allochthonous inputs of 20 t C day^?1 (POC and DOC) entering the area at mean flow (1% of the discharge of the main channel). Pelagic photosynthesis was generally high at mean flow (1.3–3.8 g C m^?2 day^?1), and contributed up to 90% of system productivity. During long stagnant periods at low discharge, the side‐arm was controlled by biological processes and a shift from planktonic to benthic activity occurred (benthic primary production of 0.4–14 g C m^?2 day^?1). 6. The transformation of the organic matter that passes through the side‐arm under different hydrological conditions, points to the importance of these subsystems in contributing autochthonous carbon to the food web of the main channel.     

Decreasing organic carbon bioreactivity in European rivers

1. European rivers experience increased loading of total organic carbon (TOC) from terrestrial sources due to factors involving changes in land use, climate and soil acidity. However, little is known about how increased TOC is linked to changes in the bioreactivity of organic matter in these rivers on a continental scale.
2. We compiled paired measurements of TOC and biological oxygen demand in 5-day 20°C dark incubations from 3,486 EU monitoring rivers. Assuming first-order decay and a fixed respiratory quotient, annual average TOC and biological oxygen demand values were used to calculate 11,060 values of the decay coefficient k.
3. The k decreased by two orders of magnitude as a power function of increasing TOC. This relationship could partly be explained by carbon quality, as the C:N ratio of the organic matter was the lowest in high-reactivity low-TOC rivers, and vice versa. A trend analysis showed that TOC increased by 18% from 1996 to 2012, while k decreased by as much as 50%. As a consequence, the biological oxygen demand in the water decreased over time in spite of the water browning trend (increased TOC).
4. Together, these results suggest that reactivity is low near terrestrial hot spots for TOC export, and low during years with high terrestrial TOC loading, but increases in rivers with low TOC concentrations where internal processes in the water have high relative influence on bulk TOC quality. Thus, browning of European freshwaters is linked to strong decreases in TOC reactivity on a continental scale, suggesting that the impacts of browning on microbial water deoxygenation and greenhouse gas production are less severe than previously thought.

     

Water abstraction impacts stream ecosystem functioning via wetted‐channel contraction

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Macrophytic Communities Inhabiting the Huveaune (South-East France), a River Subject to Natural and Anthropic Disturbances

Few studies have dealt so far with the macrophytic communities inhabiting the small Mediterranean rivers in South-East France. In order to fill this gap, it was proposed to assess the effects of natural and anthropic disturbances on the biodiversity in the lowland River Huveaune (South-East France). The Mediterranean climate in this region results in strong seasonal variations in the hydrological regime: there is a long dry period and sudden episodes of flooding occur, which greatly affect the plant community dynamics. The River Huveaune is severely polluted by organic matter. Two stations were set up, one in an upstream reference sector and the other in a downstream polluted sector. The standard sampling area of 100 m² was divided into plots 4 m² in size, some of which included part of the river and part of a bank. In addition, plant inventories were drawn up over distances of 50 and 100 m. Seventeen sampling campaigns were carried out from April 2002 to October 2003, resulting in the first systematic list of macrophyte species occurring in small Mediterranean rivers in South-Eastern France. The great variability of the hydrological factors involved leads to considerable spatial and temporal variations in the biodiversity. The upstream station was found to be less severely disturbed and to show a wider range of macrophytes than the downstream station: bryophytes predominate upstream and phanerogams and macroalgae, downstream. The Macrophyte Biological Index for River (IBMR) was tested and found to be a valid means of water quality assessment in small Mediterranean rivers.     

Restricted terrestrial carbon input to the continental shelf during Cyclone Winifred: implications for terrestrial runoff to the Great Barrier Reef Province

Tropical Cyclone Winifred (1 February 1986) provided an ideal opportunity to examine the fate of high river discharge in the Central Great Barrier Reef by producing near-record floods between Townsville and Cairns. Comparison of the carbon isotope ratio of organic matter in shelf sediment collected immediately before and after the cyclone showed that the bulk of terrestrial plant detritus from the Johnstone River was deposited within 2 km of the rivermouth and none moved more than 15 km offshore. By comparing the magnitude of the Johnstone River flow to the maximum recorded flows on other rivers in the Great Barrier Reef Province, we conclude that terrestrial runoff has not reached the Reef in historical times except, perhaps, during rare Burdekin River floods. Terrestrial detritus initially deposited near chore, however, is resuspended during tropical cyclones and may eventually be transported to the Reef.     

Mesoscale Dynamics of Ephemeral Wetlands in the Antarctic Dry Valleys: Implications to Production and Distribution of Organic Matter

ABSTRACT Ephemeral wetlands in the Antarctic dry valleys alternate as sites of in situ net primary production when inundated and sources of organic matter for eolian export when desiccated. Evidence of this switch was obtained from observations made in two field seasons (2001 and 2003), coincidentally separated by a season of exceptionally high water yield from nearby glaciers (2002). In 2001, organic matter on soil surfaces adjacent to several ponds in Taylor Valley often exceeded 500 g C/m². One pond had a total stock of approximately 1,388 kg organic C on soils within 20 m of the shoreline. These materials formed concentric rings around the pond, suggesting historically higher water levels, consistent with aerial photographs taken a decade earlier (1993). In 2003, these materials were submerged by water apparently received during the intervening year. Also in 2003, pitfall traps were placed along the edges of exposed organic matter adjacent to another pond to evaluate organic material erosion by wind. Over 4.5 days, traps collected 0.22 ± 0.12 to 2.91 ± 1.68 g C/m², both confirming and quantifying wind transport. These results indicate that organic matter production and movement, driven by seasonal and decadal patterns of inundation/desiccation of small, ephemeral wetlands, overlay longer term (centuries and millennia) and larger scale (landscape) patterns of production and distribution driven by regional fluctuations in hydrological balance between glaciers and large freshwater lakes.     

How seed traits predict floating times: a biophysical process model for hydrochorous seed transport behaviour in fluvial systems

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Flood pulses drive the temporal dynamics of assemblages of aquatic insects (Heteroptera and Coleoptera) in a temperate floodplain

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Damming interacts with the flood pulse to alter zooplankton communities in an Amazonian river

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Longitudinal variation in food sources and their use by aquatic fauna along a subtropical river in Taiwan

1. River food webs rely on two major food sources: autochthonous primary production within the river and allochthonous organic matter transferred to the river. We characterised the consumer communities and assessed the food sources of dominant consumers along a subtropical mountainous river (the Lanyang River of north‐eastern Taiwan) at the catchment scale from the headwater to the estuary using natural abundances of stable carbon and nitrogen isotopes. 2. The downstream transport of fine particulate organic matter (FPOM) was two orders of magnitude greater than that of coarse particulate organic matter (CPOM). Transport of both materials increased from the headwater and reached a maximum in the midstream reach. CPOM composition exhibited a gradual shift from leaves and branches in the headwater, an area characterised by high canopy cover, to algae in the midstream reaches and marsh plants in the downstream reaches. 3. Consumer communities can be classified into two regional categories: the upland category in the headwater and upstream and midstream reaches and the lowland category comprised of samples from the downstream reach and estuary. The upland category revealed a clear and gradual seasonal shift in community composition, but a seasonal shift was not apparent for the lowland category. Nutrient concentrations and water temperature were the main factors explaining longitudinal and seasonal variations. 4. The use of sources of organic matter by dominant consumers along the Lanyang River was primarily determined by their availability. Riparian C₃ plants were the major food sources in the headwater, upstream reach and estuary, but the contribution of periphyton increased in the upper midstream reach where the river flows through an agricultural area. In the lower midstream and downstream reaches, the contribution of riparian C₄ plants became dominant. 5. The trophic transfer of organic materials in the Lanyang River may be influenced by the fast current velocity and by sewage nutrient loading in the river, both of which have important implications for predicting how the functioning of subtropical river food webs will respond to human‐related changes in land use.     

The organization of macroinvertebrate communities in the major tributaries of the LaTrobe River, Victoria, Australia

SUMMARY.

• 1 Seventeen sites were each sampled six times over 2 years for macroinvertebrates. A range of physicochemical variables was also measured to determine which factors were related to the distribution of species.
• 2 Numerical classification of the faunal data indicated that four groups of sites or communities were distinguishable: lowland sites; sandy upland sites; cobble upland sites from the northern catchment; cobble upland sites from the southern catchment.
• 3 Multiple discriminant analysis and multiple regression analysis demonstrated that particle size of the sediment, concentration of dissolved ions and altitude were the physicochemical features that were most strongly associated with changes in the faunal distribution.
• 4 Abundances of shredders and predators did not vary between the site groups while those of scrapers, gatherers and filterers did: scrapers were most abundant at cobble sites while gatherers and filterers were least abundant on sand and increased in abundance downstream. The distribution of the feeding groups showed some similarity with that predicted by the River Continuum Concept, but the fact that the shredders did not decrease in abundance downstream was a notable difference.
• 5 Abundance of the total fauna at a site was inversely related to the amount of benthic organic matter. This feature is contrary to the pattern usually reported from rivers in the northern hemisphere.

     

Can environmental flows moderate riparian invasions? The influence of seedling morphology and density on scour losses in experimental floods

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