Long‐term changes in flow regime and fish assemblage composition in the guadalupe and san marcos rivers of texas

Riverine flow regimes are naturally dynamic, but become increasingly homogenized following anthropogenic flow alteration. Loss of dynamism disrupts naturally occurring structuring mechanisms within the associated biotic communities, at times causing shifts in composition. Here we considered how stream fish assemblages in two Central Texas rivers changed after alteration of flow regime by either construction of a mainstem, deep storage reservoir or flood‐retaining structures. Following impoundment, number of large and small floods increased from 0.81 to 1.07 floods per year (FPY) in the upper Guadalupe River, decreased from 0.84 to 0.42 FPY in the lower Guadalupe River and decreased from 0.87 to 0.7 FPY in the San Marcos River. Historical ichthyofauna data ranging from 1938 to 2006 were used to assess changes in assemblage composition and species abundance. Assemblages did not differ in the upper Guadalupe River (Bray–Curtis index = 37.4%; ANOSIM global R = 0.079, p = 0.08), but did differ in the lower Guadalupe River (25%; global R = 0.409, p < 0.01) and San Marcos River (27%; global R = 0.19, p < 0.01). In general, habitat generalist species dominated assemblages during periods of reduced flood frequencies (i.e. drought of record; following impoundment), whereas regionally endemic species (N = 3) and substrate and broadcast spawning species (N = 5) declined (b₁ < 0; α = 0.05). Based on the results from this study, managing flows in the lower Guadalupe River to mimic historical timing of flood pulses might attenuate contemporary disruption of natural assemblage composition. Copyright © 2010 John Wiley & Sons, Ltd.     

ESTIMATION OF JUVENILE SALMON HABITAT IN PACIFIC RIM RIVERS USING MULTISCALAR REMOTE SENSING AND GEOSPATIAL ANALYSIS

We conducted a regional classification and analysis of riverine floodplain physical features that represent key attributes of salmon rearing habitats. Riverine habitat classifications, including floodplain area and river channel complexity, were derived at moderate (30 m) spatial resolution using multispectral Landsat imagery and global terrain data (90 m) encompassing over 3 400 000 km² and most North Pacific Rim (NPR) salmon rivers. Similar classifications were derived using finer scale (i.e. ≤ 2.4‐m resolution) remote sensing data over a smaller set of 31 regionally representative flood plains. A suite of physical habitat metrics (e.g. channel sinuosity, nodes, floodplain width) were derived from each dataset and used to assess the congruence between similar habitat features at the different spatial scales and to evaluate the utility of moderate scale geospatial data for determining abundance of selected juvenile salmon habitats relative to fine scale remote sensing measurements. The resulting habitat metrics corresponded favorably (p < 0.0001) between the moderate scale and the fine scale floodplain classifications; a subset of these metrics (channel nodes and maximum floodplain width) also were strong indicators (R² > 0.5, p < 0.0001) of floodplain habitats defined from the finer scale analysis. These relationships were used to estimate the abundance and distribution of three critical shallow water floodplain habitats for juvenile salmon (parafluvial and orthofluvial springs, and shallow shore) across the entire NPR domain. The resulting database provides a potential tool to evaluate and prioritize salmon conservation efforts both within individual river systems and across major catchments on the basis of physical habitat distribution and abundance. Copyright © 2011 John Wiley & Sons, Ltd.     

Assessing the Impacts of Four Land Use Types on the Water Quality of Wetlands in Japan

This study examined how changes in the composition of land use can affect wetland water quality. Twenty-four wetlands located in Hiroshima prefecture in the western part of Japan were selected for this purpose. The water quality parameters that were explored include: pH, electrical conductivity, turbidity, dissolved oxygen, total dissolved solid, temperature and different forms of nitrogen. These important indicators of the water quality in the study area were measured from December 2005 to December 2006. The composition of land uses was determined for the catchments of the wetlands. They were then categorized into three classes, including non-disturbed, moderately-disturbed and highly-disturbed wetlands, based on the extent of urban area (as the most disruptive land use type within the catchment of the wetlands). The relationship between land use types and water quality parameters for the wetlands was statistically examined. The findings indicated that there were significant positive relationships between the proportion (%) of urban areas within catchments of the wetlands and EC (r?=?0.67, p?<?0.01), TDS (r?=?0.69, p?<?0.01), TN (r?=?0.92, p?<?0.01), DON (r?=?0.6, p?<?0.01), NH₄ ⁺(r?=?0.47, p?<?0.05), NO₂ ^? (r?=?0.50, p?<?0.05), while negative relationships were observed between the proportion (%) of forest area in these wetlands and EC (r?=??0.62, p?<?0.01), TDS (r?=??0.68, p?<?0.01), TN (r?=??0.68, p?<?0.01), DON (r?=?-0.43, p?<?0.05), and NH₄ ⁺ (r?=??0.55, p?<?0.01). Analysis of the variance also revealed significant differences within the wetland groups in terms of the annual mean of electrical conductivity, total dissolved solids, total nitrogen, nitrite, dissolved inorganic nitrogen and dissolved organic nitrogen in the study area. Moreover, the study also indicated that the forest area plays a significant role in withholding nutrient loads from the wetlands, and hence, it can act as a sink for surface/subsurface nutrient inputs flowing into such water bodies from the watersheds.     

Assessing channel geometry in response to land use disturbance in a low-relief,glacially conditioned setting

Bankfull stage, the highest flow elevation contained by a river channel before overbank flooding occurs, is the presumed threshold for channel morphological change. At bankfull, the channel boundary experiences the highest shear stress, producing somewhat predictable hydraulic relationships and a cross-sectional form. However, land use and glacial conditioning can profoundly impact a channel's geomorphic responses. Two common methods characterize bankfull flow: one based on flow frequency and other based on channel form. This study considers a simplified approach to identify upstream land use relative to estimates of bankfull flow versus a channel's geometric form. The approach compares archived geomorphic surveys of 140 river reaches in southern Ontario, Canada, to 2-year flood quantiles modelled from historical flood data of 207 gauge stations. Flood frequency analysis determines that annual maximum series (AMS) datasets, fitted to optimized probabilistic distributions, underestimate discharge for low-magnitude, high-frequency flood events compared to partial duration series (PDS) datasets. For smaller drainage areas (<100 km²) associated with an extensive agricultural activity and/or urbanization, the estimates of bankfull discharge (Q_bf) generated by cross-sectional channel geometry are greater than the gauge-derived Q₂ values. Channels impacted by high levels of upstream land use disturbance show statistically significant lower width-to-depth ratios (p < 0.001) and a trend towards a finer D₅₀ bed material, suggesting enhanced surface runoff delivering more mobile finer sediments and channel confinement or incision. This research quantifies the formative bankfull stage to better understand the link between land use and a channel's ‘natural’ hydrogeomorphic response in a low-relief, glacially conditioned setting.     

Rehabilitation of bedrock stream channels: the effects of boulder weir placement on aquatic habitat and biota

The placement of boulder weirs is a popular method to improve fish habitat, though little is known about the effectiveness of these structures at increasing fish and biota abundance. We examined the effectiveness of boulder weir placement by comparing physical habitat, chemical and biotic metrics in 13 paired treatment (boulder weir placement) and control reaches in seven southwest Oregon watersheds in the summer of 2002 and 2003. Pool area, the number of boulders, total large woody debris (LWD) and LWD forming pools were all significantly higher in treatment than control reaches (p < 0.05). No differences in water chemistry (total N, total P, dissolved organic carbon) or macroinvertebrate metrics (richness, total abundance, benthic index of biotic integrity etc.) were detected. Abundance of juvenile coho salmon (Oncorhynchus kisutch) and trout (O. mykiss and O. clarki) were higher in treatment than control reaches (p < 0.05), while dace (Rhinichthys spp.; p < 0.09) were more abundant in control reaches and no significant difference was detected for young‐of‐year trout (p > 0.20). Both coho salmon and trout response to boulder weir placement were positively correlated with difference in pool area; p < 0.10), while dace and young‐of‐year trout response to boulder weir placement were negatively correlated with difference in LWD (p < 0.05). The placement of boulder weirs appears to be an effective technique for increasing local abundance of species that prefer pools (juvenile coho and trout >100 mm). Based on our results and previous studies on bedrock and incised channels, we suggest that the placement of boulder structures is a useful first step in attempting to restore these types of stream channels. Published in 2006 by John Wiley & Sons, Ltd.     

Reproductive success of the interior least tern (Sterna antillarum) in relation to hydrology on the Lower Mississippi River

The annual hydrograph of large rivers, including flood pulses and low‐flow periods, is believed to play a primary role in the productivity of biota associated with these ecosystems. We investigated the relationship between river hydrology and Interior least tern (Sterna antillarum) reproductive success on the Lower Mississippi River from April to July 1986–1993. The number of fledglings produced per adult pair was negatively correlated with July mean (r=?0.95, p=0.0004) and July maximum river elevation (r=?0.97, p=0.0001), but no other aspects of river hydrology were related to tern reproduction. Low‐water elevations in July may benefit least tern reproductive success by increasing sand island area or the area of shallow‐water habitat that surrounds islands. Loss of deep‐water habitats in conjunction with an increase in shallow habitat during stage decreases may concentrate fish prey in shallow‐water habitats and backwater areas, thereby increasing food availability during chick‐rearing. Copyright © 2002 John Wiley & Sons, Ltd.     

A dynamic model to predict responses of millets (Echinochloa sp.) to different hydrologic conditions for the Illinois floodplain–River

Millets grow on floodplain mud flats exposed when seasonal floods recede, and the seeds of this plant are an important food source for waterfowl during their spring and autumn migrations in the Mississippi Flyway. Productivity of millets along the Illinois River has declined because of unnaturally frequent floods that inundate the mud flats and drown the plants during the summer growing season. These small floods are caused by operation of the navigation dams on the main channel and by alterations of the floodplain and tributary watersheds and channels. Predictive models are needed to evaluate the most cost‐effective combination of approaches for restoring plant productivity. We developed a moist‐soil plant model that simulates millet growth on 1 m² in response to daily water levels during the summer growing season. The model responds to daily water depth, flood timing (within the growing season), and flood duration, and was qualitatively verified using historical (1938–1959) water levels and plant coverage for three areas along the Illinois River. In the absence of untimely floods, the model predicts net above‐ground primary productivity of ～500 g m^?2 yr^?1 and plant heights of up to 130 cm by the end of the growing season. As expected, growth declines with decreasing land elevation or with more frequent flooding (or a shorter duration of the dry period) at the same elevation. A dry period of >85 days is required to achieve at least 50% of maximum production during the growing season, which is somewhat longer than the 70‐day recommendation based on reported field observations. The model predictions of plant success or failure agree with historical observations, indicating that water regime is a major factor limiting plant success. Copyright © 2004 John Wiley & Sons, Ltd.     

Long-term and seasonal nitrate trends illustrate potential prevention of large cyanobacterial biomass by sediment oxidation in Hamilton Harbour,Lake Ontario

Several studies have shown that large, experimental additions of nitrate (NO₃) to eutrophic systems can mitigate large populations of nuisance cyanobacteria and that high NO₃ concentrations can oxidize anoxic sediments. These studies are consistent with observations from numerous aquatic systems across a broad trophic range showing development of reduced surficial sediments precedes the formation of large cyanobacteria populations. We use 50+ years of data to explore whether high NO₃ concentrations may have been instrumental both in the absence of large populations of cyanobacteria in eutrophic Hamilton Harbour, Lake Ontario in the 1970s when total phosphorus (TP) and total nitrogen (TN) concentrations were high, and in delaying large populations until August and September in recent decades despite much lower TP and TN. Our results indicate that large cyanobacteria population events do not occur at the central station in July-September when epilimnetic NO₃ > 2.2 mg N L^?1. The results further suggest that remedial improvements to wastewater treatment plant oxidation capacity may have been inadvertently responsible for high NO₃ concentrations > 2.2 mg N L^?1 and thus for mitigating large cyanobacteria populations. This also implies that large cyanobacteria populations may form earlier in the summer if NO₃ concentrations are lowered.     

Nitrogen cycling in large temperate floodplain rivers of contrasting nutrient regimes and management

Hydraulic connection between channels and floodplains (“connectivity”) is a fundamental determinant of ecosystem function in large floodplain rivers. Factors controlling material processing in these rivers depend not only on the degree of connectivity but also on the sediment conditions, nutrient loads, and source. Nutrient cycling in the nutrient‐rich upper Mississippi River (MISS) is relatively well studied, whereas that of less eutrophic tributaries is not (e.g., St Croix River; SACN). We examined components of nitrogen cycling in 2 floodplain rivers of contrasting nutrient enrichment and catchment land use to test the hypothesis that N‐cycling rates will be greater in the MISS with elevated nutrient loads and productivity in contrast to the relatively nutrient‐poor SACN. Nitrate (NO₃^?‐N) concentrations were greatest in flowing habitats in the MISS and often undetectable in isolated backwaters except where groundwater inputs occurred. In the SACN, NO₃^?‐N concentrations were greatest in the flowing backwater where groundwater inputs were high. Ambient nitrification in the MISS was twice that in the SACN and tended to be lowest in the main channel. Denitrification was 3× greater in the MISS than that in the SACN, N‐limited in both rivers. Community production/respiration was >1 in the MISS and likely provisioned labile C to fuel microbial metabolism and dissimilatory NO₃^?‐N reduction, whereas the heterotrophic (production/respiration < 1) nature of the SACN likely limited microbial metabolism and NO₃^?‐N dissimilation. It appears that N‐cycling in the SACN was driven by groundwater, whereas that in the MISS was supported mainly by water column N‐sources.     

Evidence supporting the importance of nutrient regeneration by nano- and micrograzers for phytoplankton photosynthesis in Lake Malawi/Nyasa

Photosynthesis and nutrient status measurements were compared in size fractioned water samples collected in southern Lake Malawi in three different seasons. The size fractions analyzed were 0–2.0 μm, 0–20 μm, and 0–200 μm. Total chlorophyll concentrations were relatively invariant at about 1 μg L^?1 in all seasons (wet stratified, deep mixing, dry stratified). Over 90% of total chlorophyll was < 20 μm and 40–50% < 2 μm. Stoichiometric ratios of carbon (C):nitrogen (N) and C:phosphorus (P) for the < 2-μm seston were similar to < 20-μm and < 200-μm seston samples and indicated that all size fractions were moderately N and P deficient in all seasons. N and P uptake experiments demonstrated that when the < 2-μm picoplankton were isolated from the larger sizes, they showed high N and P nutrient debts, apparently in response to the removal of nano- and micrograzers. This effect was strongest for N debt in the dry stratified season, but was apparent for P debt in all seasons. The chlorophyll-normalized light saturated rate of photosynthesis, P^b_m, was always higher in whole water samples compared to the rates of the isolated picophytoplankton which were lowest in the dry season. We infer that nano- and micrograzers were an especially important source of regenerated nutrients when the lake was stratified although their removal as a source of nutrient to the picophytoplankton may affect P^b_m in all seasons. Nitrogen regeneration was especially critical to the picophytoplankton in the dry stratified season but less important in the windy deep mixing season.     

Can the Regeneration of Vegetation from Riparian Seed Banks Support Biogeomorphic Succession and the Geomorphic Recovery of Degraded River Channels?

For rivers degraded by erosion and channel widening, the re‐establishment of riparian vegetation is essential. We assess the potential for riparian seed banks to facilitate natural channel contraction through the regeneration of plants involved in the biogeomorphic succession of three discrete geomorphic units of increasing age and height above the channel bed: bars, benches and floodplain. Standing vegetation upon each unit type was surveyed for four river reaches in the Hunter catchment of eastern Australia. Seed bank composition was determined using seedling emergence techniques on sediment sampled from the units. We compared species richness and composition, and longevity, growth form and seed dispersal mechanisms between the standing vegetation and seed bank species. The seed bank was similar across bars, benches and floodplain, containing mostly perennial pioneer herbs, sedges and rushes, dispersed by wind and hydrochory (water transport). While bar vegetation was similar to the seed bank, bench and floodplain vegetation included later successional species such as shrubs and trees, significantly more grasses and vines (benches: χ²_{5, N = 402} = 102.033, p < 0.001; floodplain: χ²_{5, N = 792} = 30.324, p < 0.001) and higher proportions of unassisted and animal‐dispersed seeds (benches: χ²_{5, N = 352} = 89.409, p < 0.001; floodplain: χ²_{5, N = 338} = 56.026, p < 0.001). The results suggest that seed banks may support early stages of biogeomorphic succession, via regeneration of pioneer plants. However, plants, such as shrubs and trees that are observed upon units of increasing age and height above the channel bed (i.e. benches and floodplain), are likely sourced from transient seeds produced by local vegetation, rather than seed banks. Copyright © 2014 John Wiley & Sons, Ltd.     

Post‐flooding distribution and characteristics of large woody debris piles along the semi‐arid Sabie River,South Africa

The formation of large woody debris (LWD) piles has a profound impact on channel patterns and riparian succession in temperate rivers. The opportunity to study LWD along the Sabie River, a river in the semi‐arid region of Kruger National Park, South Africa, arose in February 2000 after a significant flood (c. 100‐year return interval) removed a large proportion of the fully mature riparian forest and other plant communities. Much of the uprooted vegetation was deposited as LWD piles (woody vegetation accumulations deposited on the ground > 0.1 m³) throughout the riparian and upland zones. In this article we describe the spatial distribution patterns of LWD as related to geomorphic channel type and flood frequency zone, and assess pile composition characteristics six months after the flood. Within the areas surveyed there were 68 LWD piles per hectare, the median size of LWD piles was 4.6 m³ but pile sizes (by volume) varied widely. Pool/rapid geomorphic channel types had the highest density of LWD piles (79 ha^?1) and the largest piles (by volume) were in the bedrock anastomosing channels (mean = 124 m³). Piles were larger in the seasonal and ephemeral flood frequency zones (mean = 54 m³ and 55 m³) than piles in the active zone (c. 2 m³). The patterns of distribution and volume of LWD will affect the subsequent development of vegetation communities as debris piles form a mosaic of patches of surviving organisms and propagules that can strongly influence the initial trajectory of succession. The amount, distribution, and subsequent decomposition of LWD are different from that reported for temperate rivers, suggesting that the role of LWD may be different on non‐floodplain rivers such as the Sabie in semi‐arid South Africa. Copyright © 2004 John Wiley & Sons, Ltd.     

Sediment nitrification and denitrification in a Lake Superior estuary

Inorganic nitrogen (N) transformations and removal in aquatic sediments are microbially mediated, and rates influence N-transport. In this study we related physicochemical properties of a large Great Lakes embayment, the St. Louis River Estuary (SLRE) of western Lake Superior, to sediment N-transformation rates. We tested for associations among rates and N-inputs, vegetation biomass, and temperature. We measured rates of nitrification (NIT), unamended base denitrification (DeNIT), and potential denitrification [denitrifying enzyme activity (DEA)] in 2011 and 2012 across spatial and depth zones. In vegetated habitats, NIT and DeNIT rates were highest in deep (ca. 2 m) water (249 and 2111 mg N m^− 2 d^− 1, respectively) and in the upper and lower reaches of the SLRE (> 126 and 274 mg N m^− 2 d^− 1, respectively). Rates of DEA were similar among zones. In 2012, NIT, DeNIT, and DEA rates were highest in July, May, and June, respectively. System-wide, we observed highest NIT (223 and 287 mg N m^− 2 d^− 1) and DeNIT (77 and 64 mg N m^− 2 d^− 1) rates in the harbor and from deep water, respectively. Amendment with NO₃⁻ enhanced DeNIT rates more than carbon amendment; however, DeNIT and NIT rates were inversely related, suggesting the two processes are decoupled in sediments. Average proportion of N₂O released during DEA (23–54%) was greater than from DeNIT (0–41%). Nitrogen cycling rates were spatially and temporally variable, but we modeled how alterations to water depth and N-inputs may impact DeNIT rates. A large flood occurred in 2012 which temporarily altered water chemistry and sediment nitrogen cycling.     

Impact of an urban centre on the nitrogen cycle processes of epilithic biofilms during a summer low‐water period *

Nitrogen transformations in epilithic biofilms of a large gravel bed river, the Garonne, France, has been studied upstream (one site) and downstream (four sites) of a large urban centre (Toulouse, 740 000 inhabitants). High biomass, up to 49 g AFDM m^?2 (ashes free dry matter) and 300 mg chlorophyll a m^?2 (Chl. a), were recorded at 6 and 12 km downstream from the main wastewater treatment plant outlet. The lowest records upstream and larger downstream (less than 16 g AFDM m^?2 or 120 mg Chl. a m^?2) could be explained by recent water fall (early summer low‐water period). Measurements of nitrogen exchange at the biofilm–overlying water interface were performed in incubation chambers under light and dark conditions. The addition of acetylene at the mid‐incubation time allowed evaluation of both nitrification (variation in NH₄⁺ flux after the ammonium monooxygenase inhibition) and denitrification (N₂O accumulation related to the inhibition of N₂O reduction). Denitrification (D_w) and nitrification rates were maximum at sites close to the city discharges in dark conditions (up to 9.1 and 5.6 mg N m^?2 h^?1, respectively). Unexpected denitrification activities in light conditions (up to 1.4 mg N m^?2 h^?1) at these sites provided evidence for enhanced nitrogen self‐purification downstream. As confirmed by most probable number (MPN) counts, high nitrification rates in biofilm close downstream were related to enhanced (more than almost 3 log) nitrifying bacteria densities (up to 7.6×10⁹ MPN m^?2). Downstream of an urban centre, nitrogen transformations in the biofilm appeared to be influenced by the occurrence of an adapted microflora which is inoculated or stimulated by anthropic pollution. Copyright © 2002 John Wiley & Sons, Ltd.     

Impact of Flood Spreading on Infiltration Rate and Soil Properties in an Arid Environment

Flood spreading (FS) is one of the suitable methods for flood management and water harvesting that increases the groundwater recharge, makes soil more fertile and increases nutrients in soil. It is also a method for reusing sediment, which is usually wasted. The purpose of this paper is to investigate the impact of flood spreading on physical and chemical soil properties (soil texture, infiltration rate, pH, EC, Na, P, K, Ca, Mg, Cl, HCO₃, and SO₄). It is examined that the soil properties change in the flood spreading projection area (FSP). The physico-chemical properties of soil and infiltration rate were measured in different soil depths at both flood spreading and control area. For the 20 cm of top soil, the amount of clay increased after the flood spreading implementation especially in the first and second dikes. Increasing clay was accompanied by decreasing soil infiltration and sand percentage. The mean differences of the clay, sand and infiltration rate between FSP and the control area were statistically significant (P < 0.01). A significant difference was not observed in 20–30 cm of the depth. Soil pH, Mg, HCO₃, Cl and SO₄ in different soil layers did not show any significant difference between the control and FSP. Soil EC in 0–20 cm depth of FSP and control area was showed a significant difference (P < 0.05) but no significant differences were found in deeper layers (P < 0.05). K, Na and Ca were remarkably different between 0 and 10 cm depths (P < 0.05) whereas no significant differences were found in deeper layers (P < 0.05). Comparison of the physico-chemical properties and infiltration rates between the dikes in the FSP shows that there are the significant differences between the medians of dike 1 with dikes 2, 3, 4 and 5, but the differences were not observed between dikes 3, 4 and 5. Our results show that the flood spreading operation can be influenced by the area that is under this operation. This study allowed us to investigate the mechanisms that regulate the infiltration rate and chemical soil properties throughout a seasonally flooded area.     

EVALUATION OF THE SOUNDING ROD METHOD FOR SAMPLING COARSE RIVERBED SEDIMENTS IN NON‐WADEABLE STREAMS AND RIVERS

The substrate of fluvial systems is regularly characterized as part of a larger physical habitat assessment. These measures are instrumental in meeting the regulatory responsibilities of bioassessment and monitoring programs, and essential to monitoring restoration and rehabilitation success. We describe and validate a commonly used technique for broadly categorizing, and thus characterizing, the substrate in non‐wadeable streams and rivers called the sounding rod method. In brief, a rod, often hollow, is used to probe the substrate of non‐wadeable systems to characterize the substrate. We tested the viability of this method on three different systems by comparing estimated particle class and direct particle measurements. Our results indicate that substrates can adequately be defined into six broad classes (fine‐particle sediment, sand, gravel, cobble, boulder and bedrock) based on size using the sounding rod. Estimated classes were significantly positively correlated to measured classes (τ = 0.83, p < 0.001), and estimates of size class and direct measurements of size were not from significantly different distributions (χ² _0.05,9 = 569.51, p < 0.001). Further, there were significant differences between each category (H = 243.5, 3 d.f., p < 0.001). Although our results affirm that actual substrate class size can be directly inferred from estimated data, it should be noted that soft sediments <200 mm were not always detected. This finding should be carefully considered with individual study objective. Overall, the sounding rod method can be learned quickly, and it is a low‐cost and time‐efficient method for substrate classification. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.     

IMPACT OF CHANGING HYDROLOGY ON NUTRIENT UPTAKE IN HIGH ARCTIC RIVERS

Despite the importance of river nutrient retention in regulating downstream water quality and the potential alterations to nutrient fluxes associated with climate‐induced changes in Arctic hydrology, current understanding of nutrient cycling in Arctic river systems is limited. This study adopted an experimental approach to quantify conceptual water source contributions (meltwater, groundwater), environmental conditions and uptake of NO₃^?, NH₄⁺, PO₄^3? and acetate at 12 headwater rivers in Svalbard and so determine the role of changing hydrology on nutrient uptake in these Arctic river systems. Most rivers exhibited low demand for NO₃^? and PO₄^3?, but demand for NH₄⁺ and acetate was more variable and in several rivers comparable with that measured in sub‐Arctic regions. The proportion of meltwater contributing to river flow was not significantly related to nutrient uptake. However, NH₄⁺ uptake was associated positively with algal biomass, water temperature and transient storage area, whereas acetate uptake was associated positively with more stable river channels. Mean demand for NH₄⁺ increased when added with acetate, suggesting NH₄⁺ retention may be facilitated by labile dissolved organic carbon availability in these rivers. Consequently, nutrient export from Arctic river systems could be influenced in future by changes in hydrological and environmental process interactions associated with forecasted climate warming. Copyright © 2013 John Wiley & Sons, Ltd.     

Shallow and deep water aquatic vegetation potential for a midlatitude pool of the Upper Mississippi River System with drawdown

Prior to navigation dam and levee placement, the Upper Mississippi River (UMR) flowed through a wide floodplain supporting a diverse ecosystem. Diversity was created by variable flood frequencies and water flow, but presently high and static water levels supporting river navigation have caused low diversity of aquatic vegetation in locations within the UMR. A pool‐scale water level drawdown was proposed as a wetland management tool to mimic historic low water flow for UMR Navigation Pool 18, between Oquawka and Keithsburg, IL. The objectives of this research are to determine plant species, density, and diversity expected for a drawdown in Pool 18. A seedbank and propagule assay was used to evaluate drawdown plant species response. Emergence was tested using river bottom substrate samples collected in 2009 from the proposed drawdown area. Samples were treated at two hydrologic levels: shallow (3‐cm depth) and deep (16‐cm depth). Dominant species in the shallow flooded treatment were Gratiola neglecta, Leersia oryzoides, Eleocharis palustris, Sagittaria latifolia, and Ammania coccinea. Deep flooded dominant taxa included G. neglecta, S. latifolia, Vallisneria americana, and A. coccinea. Each treatment indicated a seedbank of moderate diversity with a shallow treatment diversity of D = 0.56 and deep treatment diversity of D = 0.44. Plant density for the shallow flooded treatment was 213 stems/m² (±112; 95% CI), and deep flooded hydrologic treatment, 206 stems/m² (±82; 95% CI). It is expected that this drawdown will provide an intermediate ecological disturbance resulting in greater species diversity and density currently lacking in this portion of the Upper Mississippi River System.     

Population dynamics and biofilm composition in a new three-phase circulating bed reactor

The biofilm characteristics of a novel three-phase reactor, the circulating bed reactor (CBR), were studied using industrial prototype fed with primary and secondary settled effluent in conditions of tertiary N and secondary C+N nitrification. The results showed a high nitrification rate close to the intrinsic values for N and C+N conditions: up to 2 and 0.6 kgN-NH₄ m^-3 d^-1, or 1.88±0.26 and 0.22±0.07 gN g^-1 PR d^-1, respectively. The application of an integrated approach for biofilm analysis enabled the better understanding of biofihn dynamics. The biofilm remained relatively thin, below 100 μm, indicating an effective control of the biofilm development. Protein, measured by the conventional colometric method and pyrolysis-GCMS, was the major fraction accounting for up to 35% of the biomass dry weight and 58% of the biopolymer content. The polysaccharide's fraction remained very low (<3%). The ribosomal RNA probes analysis confirmed the predominance of bacterial cells in the CBR biofilm (80–86% of bacteria versus the universal probe) showing a high proportion of nitrifying bacteria accounting for up to 50% and 27% in the N and C+N removal respectively. Nitrosomonas predominated in tertiary nitrification whereas carbon input led to the appearance of other ammonia oxidizers. This particular composition was characterized by a high state of oxidation of the biomass, expressed by the low COD/DW ratio of about 0.85. In conclusion, it can be stated that this new three-phase bioreactor ensures a high nitrification rate through an effective biofilm control promoting the development of bacterial cells, especially nitrifying bacteria, and minimizing exopolysaccharides production.     

Maximum Grade Approach to Surplus Floodwater of Hyperconcentration Rivers in Flood Season and its Application

The severe soil erosion in the Chinese Loess Plateau has resulted in a considerable wastage of surface runoff (floodwater) in flood season due to high sediment concentration in runoff. To address the water scarcity problem, it is a viable solution to utilize the floodwater. A maximum grade approach (MGA) is presented to calculate the coefficient of surplus floodwater in flood season. The raw data sequences are analyzed in a four-step process. An upper triangle of grades is obtained after the third step. A relationship between coefficient of surplus floodwater and sediment concentration in runoff is achieved in terms of the upper triangle. The surplus floodwater in flood season then can be determined. A case study of water diversion from the Jinghe River (the second tributary of the Yellow River, China) to the Jinghuiqu Irrigation District for irrigation was performed. The monthly data sequences of runoff volume, water diversion and sediment concentration in runoff from May to September for the period 1933–2001 are employed. A 16-grade upper triangle is obtained based on the MGA. A functional relationship between the coefficient of surplus floodwater (y, %) and the sediment concentration in runoff (x, %) is achieved as y = 0.0191x + 0.1516 (R^2\thinspace = 0.9738)y = 0.0191x + 0.1516 (R^{2\thinspace } = 0.9738). Results demonstrate that the average annual surplus floodwater in flood season and available surface water resources in the Jinghe River over 69-year time span are 978 and 909 million cubic meter (mcm), respectively, when the limit of sediment concentration for river water utilization is set as 10%. The irrigation district still has a potential of available water diversion of 509 mcm over 1981–2001 time span. Compared with the traditional methods, the MGA produces more reasonable and effective results. The MGA has the ability of rapidly estimating the surplus floodwater under different limits of sediment concentration and is a useful tool for available surface water resources assessment.