Littoral and shoreline wood in mid‐continent great rivers (USA)

Woody debris has several important roles in running water. Less is known about the ecology of wood in great rivers than in smaller rivers and streams. We used a probability survey to estimate the abundance of littoral and shoreline wood along the following mid‐continent great rivers of the United States in summer 2004–2006: the Missouri River, Upper Mississippi River, and the Ohio River. We counted wood pieces >0.3 m in diameter from a zone between the bank full level out into the river 10 m. We categorized wood according to its origin and function as “beached” (transported from upriver but not providing aquatic habitat), “wet” (origin unknown and providing aquatic habitat; includes snags), or “anchored” (attached to the bank at its current location and providing aquatic habitat). We counted 5900 pieces of wood at 447 sites across rivers. Approximately 56 percent of pieces were beached, 30 percent were wet, and 14 percent were anchored. Overall, mean abundance of wood was 2.6 pieces of wood 100 m^?1 of shoreline (approximately 3.0 m³ 100 m^?1). Abundance of wood (pieces per unit distance of river) was much lower than has been reported for many smaller streams and rivers. There was more wood along the Upper Mississippi River (3.3 pieces 100 m^?1) than elsewhere (≤2.4 pieces 100 m^?1). The mean abundance of wood on the Ohio River decreased significantly between the 2004 and 2005 survey periods due to high flows. Longitudinal patterns in wood abundance were weak. There was less anchored and wet wood along shorelines protected by revetment (e.g., rip rap). There was generally more wood along shorelines where the riparian land use was characterized as forest rather than agriculture or developed. Mean abundance of wood along forested, un‐revetted shorelines was approximately four pieces 100 m^?1 of shoreline (= 80 pieces km^?1 of river). This estimate of mean wood abundance for what amounts to least disturbed riparian and shoreline conditions is relevant for great river bioassessment and management. Published in 2009 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.     

Regulation leads to increases in riparian vegetation,but not direct allochthonous inputs,along the Colorado River in Grand Canyon,Arizona

Dams and associated river regulation have led to the expansion of riparian vegetation, especially nonnative species, along downstream ecosystems. Nonnative saltcedar is one of the dominant riparian plants along virtually every major river system in the arid western United States, but allochthonous inputs have never been quantified along a segment of a large river that is dominated by saltcedar. We developed a novel method for estimating direct allochthonous inputs along the 387 km‐long reach of the Colorado River downstream of Glen Canyon Dam that utilized a GIS vegetation map developed from aerial photographs, empirical and literature‐derived litter production data for the dominant vegetation types, and virtual shorelines of annual peak discharge (566 m³ s^?1 stage elevation). Using this method, we estimate that direct allochthonous inputs from riparian vegetation for the entire reach studied total 186 metric tons year^?1, which represents mean inputs of 470 gAFDM m^?1 year^?1 of shoreline or 5.17 gAFDM m^?2 year^?1 of river surface. These values are comparable to allochthonous inputs for other large rivers and systems that also have sparse riparian vegetation. Nonnative saltcedar represents a significant component of annual allochthonous inputs (36% of total direct inputs) in the Colorado River. We also estimated direct allochthonous inputs for 46.8 km of the Colorado River prior to closure of Glen Canyon Dam using a vegetation map that was developed from historical photographs. Regulation has led to significant increases in riparian vegetation (270–319% increase in cover, depending on stage elevation), but annual allochthonous inputs appear unaffected by regulation because of the lower flood peaks on the post‐dam river. Published in 2010 by John Wiley & Sons, Ltd.     

LARGE WOODY DEBRIS IN URBAN STREAM CHANNELS: REDEFINING THE PROBLEM

Large woody debris (LWD) is an important ecological element in rivers and streams. Despite its importance, LWD is often removed from urban stream channels for flood control or road maintenance purposes, an approach with high economic and ecological costs and one that is largely unsuccessful. We propose an approach to conserve LWD in channels by modifying infrastructure (culverts and bridges) to allow LWD passage, maintaining aquatic habitat and reducing flooding and road maintenance costs. In Soquel Creek (California, USA), which has a history of LWD‐related flooding, we compared long‐term LWD management costs of historical, current and a LWD‐passing approach whereby infrastructure is enlarged to accommodate LWD passage downstream. We estimated costs of infrastructure replacement, programmatic flood control (LWD removal), LWD‐related flood damage and lost aquatic habitat. The amount of lost aquatic habitat was determined by comparing LWD loading (pieces m^?1) in Soquel Creek (0.007 pieces m^?1) to nearby unmanaged streams (0.054 to 0.106 pieces m^?1). Estimated costs of infrastructure able to pass LWD were nearly double that of historical costs but comparable to current costs. The LWD‐passing approach was comparable to removal approaches in the short term (1 to 50 years) but much less in the long term (51 to 100 years), as expenditures in infrastructure replacement to accommodate LWD yielded reductions in flooding costs and habitat loss. Given the urgency to maintain and restore aquatic habitat, the proposed approach may be broadly applicable. Copyright © 2011 John Wiley & Sons, Ltd.     

Quantity,controls and functions of large woody debris in Midwestern USA streams

Large woody debris (LWD) can increase stream habitat heterogeneity by providing structure, altering flow patterns, enhancing sediment deposition, forming pools and retaining organic matter. In North America, the role of LWD has been studied extensively in streams of mature forests (e.g. Pacific Northwest), but few studies have assessed LWD in streams of younger forests (e.g. Midwestern USA). Our objectives were to: (1) quantify the volume and abundance of LWD in a set of Midwestern streams; (2) evaluate possible factors influencing LWD quantity; (3) identify the functional roles of LWD; and (4) compare LWD levels in the upper Midwest to those elsewhere in North America. In 2002 and 2003, we measured LWD and geomorphological variables in 15 low‐gradient streams draining previously logged watersheds in the Upper Peninsula of Michigan. Mean (±SE) LWD volume (0.77 ± 0.12 m³ 100 m⁻²) and abundance (33 ± 3 pieces 100 m⁻¹) were 71% and 10% lesser, respectively, than in streams of similar gradient elsewhere in North America. Channel shape (width:depth ratio) explained 30% of the variation in LWD volume (multiple stepwise regression, P = 0.015) while LWD length and length:channel width combined, explained 72% of the variation in LWD density (multiple stepwise regression, P < 0.0001). About 50% of the LWD either stored sediment or stabilized banks and 14% of the LWD formed pools, although pool density was not significantly related to LWD volume or density. LWD levels, overall, were low in upper Midwestern streams, but the relative importance of that LWD to ecosystem function may be magnified in these wood‐poor systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Fish community structure associated with stabilized and unstabilized shoreline habitats,Coeur d'Alene River,Idaho, USA

Stabilization of riverbanks and lake shorelines has become widely used to reduce erosion. Studies on effects of stabilization on fish species and communities have indicated highly variable effects from beneficial to detrimental. Bank stabilization implemented to reduce shoreline erosion of metals‐contaminated sediments in the lower Coeur d'Alene River, Idaho, prompted concern of possible effects on the fish community. Fish sampling (electrofishing and gillnetting) and habitat assessment were conducted at 24 sites in the lower 54 km of river during 2005 and 2006 to assess differences in the fish community (relative abundance, species diversity and community composition) at stabilized and unstabilized shorelines. Within stabilized and unstabilized shorelines we evaluated seasonal differences as well as upstream and downstream differences. We captured 3511 fish from 17 species and 7 families; 83% of fish were captured by electrofishing. Fish relative abundance was significantly higher at stabilized than unstabilized sites for electrofishing. We also found positive correlations between relative abundance and diameter of rock at stabilized sites for both sampling gears. Three species (brown bullhead Ameiurus nebulosus, northern pike Esox lucius and pumpkinseed Lepomis gibbosus) were captured more readily at stabilized shoreline sites. Seasonally, the differences in relative abundance among habitat types indicate that stabilized structures are providing stable habitat year‐round. Overall, stabilized shorelines on the lower Coeur d'Alene River were not found to be adversely affecting overall fish relative abundance, diversity and species composition under the existing low fraction (2.5%) of bank stabilization. Based on these results and reviews of other studies, we suggest that two factors affecting the results of bank stabilization studies are (i) the habitat quality of the unstabilized river, and (ii) the percentage of the river that has been stabilized. Copyright © 2010 John Wiley & Sons, Ltd.     

Inter‐habitat variation in the benthos of the Upper Missouri River (North Dakota,USA): implications for Great River bioassessment

We examined inter‐habitat variation in benthic macroinvertebrate assemblages in the 180‐km Garrison Reach of the Upper Missouri River, North Dakota (USA) in 2001–2003. The Garrison Reach is unchannelized with a mostly rural setting. Flows are regulated by Garrison Dam. We sampled benthos from three habitats defined a priori: channel, shoreline, and backwater. Benthic assemblages were different in each habitat. Average Bray‐Curtis dissimilarity in assemblage composition ranged from 89% for backwater versus channel habitat to 70% for backwater versus shoreline habitat. There were distinct intra‐habitat groups within a priori habitats: channel assemblages included moving‐sand assemblages and other‐substrate channel assemblages; backwater assemblages included connected (to the river channel) and unconnected backwater assemblages; shorelines assemblages varied between natural (unprotected) and riprap (rock revetment) shorelines. Abundance and taxa richness were lowest and spatial variability highest for moving‐sand channel assemblages. Abundance was highest in backwaters. Taxa richness in backwaters and along channel shorelines were similar. Assemblages in all three habitats were dominated by Nematoda, Oligochaeta and Chironomidae. Taxa in these groups comprised at least 80% of mean abundance in all three habitats. Taxa that discriminated among habitats included the psammophilic chironomid Chernovskiia for moving‐sand channel substrates versus all other habitats; Hydroptila (Trichoptera) for riprap vs natural shorelines, Aulodrilus (Oligochaeta) for connected versus unconnected backwaters; and Nematoda for backwater versus channel and shoreline versus channel. Based on overlap patterns in benthic assemblages among habitats, we concluded that sampling main channel shorelines should also capture much of the natural and stressor‐induced variation in connected backwater and channel habitat exclusive of moving‐sand channel habitat. Published in 2006 by John Wiley & Sons, Ltd.     

An Estimate of Basin‐Wide Denitrification Based on Floodplain Inundation in the Atchafalaya River Basin,Louisiana

Maximizing the reduction of nitrate to dinitrogen gas (denitrification) has been advocated as a means to decrease nitrate pollution that causes eutrophication and hypoxia in estuaries worldwide. Managing this flux in bottomland forest wetlands of the Mississippi River could potentially reduce the world's second largest hypoxic zone. We used published denitrification rates, geospatial data on habitat area and inundation frequency, water level records (1963–2011), and average monthly temperatures to estimate annual denitrification in the Atchafalaya River Basin, the principal distributary of the Mississippi River. Denitrification rates ranged from 5394 kg N year^?1 (3.07 kg N km^?2 year^?1) in 1988 to 17 420 kg N year^?1 (9.92 kg N km^?2 year^?1) in 1981, and rates were consistently higher in fall compared with those in spring. Total NO₃^? denitrified in the basin was negligible compared with total NO₃^? entering the Gulf of Mexico. If all N denitrified in the basin instead entered the Gulf, the hypoxic zone was predicted to increase only 5.07 km² (0.06%). This negligible effect of the basin on N dynamics in the Gulf agrees with other mass balance and isotopic studies in the region. Copyright © 2014 John Wiley & Sons, Ltd.     

Role of the floodplain and riparian zone in suspended matter and nitrogen retention in the adour river,south-west France

The retention capacity of the floodplain and riparian zone for suspended matter and nitrogen has been investigated in the Adour River, a seventh order stream in south-west France. Suspended matter and nitrogen fluxes through a 25 km meandering stretch of the river were measured during two flood events and compared with the amount of sediment trapped in the riparian zone (1.1 km²) and the major floodplain (16.8 km²) of the studied area. It was estimated that the floodplain and the riparian zone together retained between 10 and 20% of the suspended matter entering the stretch under study during the two main floods (138 700 Mg). Moreover, they retained about 11% of the total particulate nitrogen fluxes (640 Mg). Although the riparian zones are 15 times smaller than the major floodplain, the total suspended matter and particulate nitrogen deposition were, 50 and 17 times, respectively, larger in the riparian zone. The results obtained on the Adour River floodplain show that large river systems should not be considered only as export systems as riparian zones can retain a significant amount of suspended organic and mineral matter during floods.     

Overlap in Offshore Habitat Use by Double-crested Cormorants and Boaters in Western Lake Erie

Double-crested cormorants (Phalacrocorax auritus) and boats of 2 length classes (≤ 8 m and > 8 m) were counted from a boat along 31 established strip transects in western Lake Erie from 24 April to 1 September 2000. Each transect included only one of the following habitats: (1) offshore of a breeding island or roosting/loafing area for cormorants (“refuge”), (2) reefs or shoals, (3) open water, or (4) offshore of an island shoreline that had evidence of development by humans. Foraging cormorants were recorded most often offshore of refuges and least often on open water. There was no difference between the numbers of foraging cormorants/km² recorded offshore of developed shorelines and on reefs and shoals. More than half of all boats recorded were on transects that were within 1 km of developed shorelines. Among those transects > 1 km from developed shorelines, there were no differences among the habitats for the number of boats of either length class. The respective ranks of the 31 transect means of the numbers of cormorants/km² and the numbers of boats/km² in either length class were uncorrelated. The results suggest that (1) cormorants select foraging habitats based mainly on shoreline type, distance from shoreline, and depth, and (2) the amount of boat traffic is influenced by proximity to port and trip objectives, including sport angling and recreational boating. Although there is overlap in habitat use by cormorants and humans, this overlap is not complete. The perception of cormorants as a threat to fish populations may in part be due to this overlap.     

Effects of large woody debris on surface structure and aquatic habitat in forested streams,southern interior British Columbia,Canada

It is well known that large woody debris (LWD) plays an important functional role in aquatic organisms' life. However, the influence of LWD on channel morphology and aquatic environments at watershed levels is still unclear. The relationships between wood and surface structure and aquatic habitat in 35 first through fifth order streams of southern interior British Columbia were investigated. Study streams in the channel networks of the study watersheds were classified into four size categories based on stream order and bankfull width: Stream size I: bankfull width was less than 3 m, Stream size II: 3–5 m, Stream size III: 5–7 m, Stream size IV: larger than 7 m. We found the number of functional pieces increased with stream size and wood surface area in stream sizes I, II and III (24, 28 and 25 m²/100 m², respectively) was significantly higher than that in stream size IV (12 m²/100 m²). The contribution of wood pieces to pool formation was 75% and 85% in stream sizes II and III, respectively, which was significantly higher than those in stream size I (50%) and size IV (25%). Between 21% and 25% of wood pieces were associated with storing sediment, and between 20% and 29% of pieces were involved in channel bank stability in all study streams. Due to long‐term interactions, LWD in the intermediate sized streams (Size II and III) exhibited much effect on channel surface structure and aquatic habitats in the studied watersheds. Copyright © 2008 John Wiley & Sons, Ltd.     

Effects of land‐cover transitions on emerging aquatic insects and environmental characteristics of headwater streams in an agricultural catchment

Streams and their adjacent riparian zones are increasingly viewed as interdependent systems linked by reciprocal exchanges of energy, organisms, and materials. We assessed potential associations between the emerging aquatic insect flux and transitions between agricultural land and forest fragments to better understand these stream‐riparian linkages in managed landscapes. We sampled stream environmental conditions and emerging insects at 28 sites distributed along three streams flowing through agriculture‐forest‐agriculture transitions in central Ohio, USA, in the summer of 2012. Ephemeroptera and Trichoptera (ET) taxa had higher flux densities in forests (mean and 95% CI: 0.3 insects m^?2 d^?1 [0.1, 0.8]) compared to agriculture (mean and 95% CI: 0 insect m^?2 d^?1 [0, 0.1]; p = .004), and ET taxa were found in 67% of forested sites compared to only 15% of agricultural sites. In contrast, Dolichopodidae were more strongly associated with agricultural land (mean and 95% CI: 0.6 insect m^?2 d^?1 [0.3 to 1.2]) than forests (mean and 95% CI: 0.1 insects m^?2 d^?1 [0.1, 0.2]; p = .002). Although Chironomidae were the most numerically abundant, ET taxa were among the larger bodied insects and comprised >30% of the total biomass flux, illustrating the importance of taxonomic traits in mediating flux dynamics. Mechanisms driving emerging insect flux were related to substrate grain‐size distribution, channel width, and nutrient concentrations. Overall, our results demonstrate that small forest fragments are strongly related to the aquatic‐to‐terrestrial insect flux and thus have important implications for terrestrial biodiversity and food webs in agricultural landscapes.     

Seed banks and seed survival of submersion for an emerging plant invader in the Colorado River system,USA

Soil seed banks along shorelines and the ability of seeds to survive submersion in water are among potential factors that can influence seed supply, a frequent driver of riparian plant invasions. We investigated germinable soil seed banks and the ability of seeds to germinate after different durations of submersion in water for non-native ravennagrass (Saccharum ravennae), an emerging but poorly understood invader of riparian habitats in the American Southwest, including along the Lake Powell section of the Colorado River where we performed the study. We assessed soil seed bank composition in 27 ravennagrass-invaded plots using the emergence technique and evaluated effects on ravennagrass germination of submersion in river water for up to 15 months in a laboratory experiment. Ravennagrass was sparse in soil seed banks, detected in samples from only one of the 27 plots. Instead, soil seed banks were dominated by the non-native annual cheatgrass (Bromus tectorum) and a mixture of native early colonizers (e.g., Pseudognaphalium stramineum) and shrubs (e.g., Baccharis emoryi). Although ravennagrass seed germination was low (<9%) in the submersion experiment, some seeds retained germinability after 15 months of continuous submersion in water. Results suggest that while ravennagrass may have limited on-site, readily germinable soil seed banks, potential implications of its protracted seed viability in water for dispersal along waterways warrants further attention.     

和田河干流河道径流损失与植被生态需水关系研究

和田河干流植被生态需水量是多少?河道渗漏水量能否满足两岸植被的生态需水?为了回答这两个事关和田河中下游河道整治必要性的基础问题,本研究定量分离河道损耗水量,探究河道渗漏水量与天然植被生态需水之间的定量响应关系,结果表明:(1)多年平均来水条件下,和田河干流河损量约为6.46×10~8m~3,其中,蒸发量与渗漏量分别为3.5×10~8和2.65×10~8m~3,各占河损量的58.88%和41.12%;(2)和田河干流天然植被的生态需水量1.37×10~8m~3,河道渗漏水量可以满足植被生态水量需求。因此,本研究认为开展河道整治,不仅不会影响干流植被生态需水,还可以减少水面蒸发,提高和田河输水能力,更有利于开展生态水量调度,保护和恢复干流天然植被。     

THE SOLAR‐TO‐STREAM POWER RATIO: A DIMENSIONLESS NUMBER EXPLAINING DIEL FLUCTUATIONS OF TEMPERATURE IN MESOSCALE RIVERS

The diel variation of temperature in mesoscale river reaches (catchment area > 1000 km²) is analysed using concurrent measurements of water temperature and of those meteorological (incident short‐wave radiation, air temperature, relative humidity and wind speed variables) and hydraulic variables (streamflow, top width, channel slope and flow depth) controlling the thermal regime. Measurements were taken along two river reaches located in central Chile, on the Itata (11 290 km², Strahler's order 6, reach length 30 km, Q_bankfull = 400 m³ s^?1) and Vergara (4340 km², Strahler's order 5, reach length 20 km, Q_bankfull = 85 m³ s^?1) rivers. The measuring frequency was 15 min. The relevant energy fluxes at the air–water interface, that is, atmospheric long‐wave radiation, net short‐wave radiation, radiation emitted by the water body, evaporation (latent heat) and conduction heat are computed and analysed for four scenarios of 12 days duration each, representing typical conditions for the austral winter, spring, summer and autumn. We find large differences in the diel river temperature range between the two sites and across seasons (and thus, flows and meteorological conditions), as reported in previous studies, but no clear relationship with the controlling variables is overtly observed. Following a dimensional analysis, we obtain a dimensionless parameter corresponding to the ratio of solar‐to‐stream power, which adequately explains the diel variation of water temperature in mesoscale rivers. A number of our own measurements as well as literature data are used for preliminary testing of the proposed parameter. This easy‐to‐compute number is shown to predict quite well all of the cases, constituting a simple and useful criterion to estimate a priori the magnitude of temperature diel variations in a river reach, given prevailing meteorological (daily maximum solar radiation) and hydrologic–hydraulic (streamflow, mean top width) conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Depositional settings of sand beaches along whitewater rivers

The numbers and sizes of sand beaches suitable for recreation along selected whitewater rivers in the western United States depend on sand concentrations, range of discharge and the size, frequency and type of depositional settings. River‐width expansions downstream from constrictions are the predominant depositional setting for sand beaches in the upper Grand Canyon and along five Wild and Scenic Rivers in Idaho, but not along other rivers. Beaches located upstream from constrictions are rare, in general, except in the Grand Canyon. Beaches found in expansions without constrictions dominate depositional sites along the Yampa and Green Rivers, are fairly common along the rivers in Idaho, but are relatively rare in the Grand Canyon. The magnitude of flow expansion is a reliable predictor of beach size. Beaches located on the inside of curves are uncommon, in general, but can be important recreation sites. The mid‐channel bar setting is the least important from a recreation standpoint because that setting is rare and beaches there are typically small, and emergent only at low flow. The frequency of beaches is highly variable among rivers and the concentration of sand in transport is only partially responsible. Of the rivers studied, the unregulated Yampa River carries the highest concentrations of suspended sand and has among the most beaches (1.2 beaches km^?1). Emergent sand beaches are essentially nonexistent along the Deschutes River and are rare along other Oregon rivers, yet these rivers transport some sand. Sand beaches are fairly common (0.8–1.1 beaches km^?1) along the regulated Colorado River, but are comparatively rare (0.6 beaches km^?1) along the unregulated Middle Fork Salmon River. The suspended sand concentrations in study reaches of these two rivers are similar, and the difference in the frequency of beaches may be largely because the processes that create beach‐deposition settings are less active along the Middle Fork Salmon. Published in 2008 by John Wiley & Sons, Ltd.     

Distribution, relative abundance, and prey demand by double-crested cormorants on Manitoulin Island lakes vs. Lake Huron Coast

An aerial distance sampling survey of double-crested cormorants (Phalacrocorax auritus) was conducted in the northern region of Lake Huron (North Channel; four largest lakes of Manitoulin Island; South Shore of Manitoulin Is. facing the main body of the lake) to assess the relative distribution, abundance and prey demand by cormorants on inland lake vs. coastal habitat. On a per area basis, the density (approx. 1-2 cormorants ? km^− 2) and prey demand (approx. 1.2 kg ha^− 1) of cormorants in the four inland lakes matched that of the North Channel. The South Shore had approximately half the density and prey demand as the other two areas. Cormorants on the inland lakes of Manitoulin Island represented 13% early in the season and a high of 33% of the total population for this region of Lake Huron later in the summer. Estimating regional distributions of cormorants within the Great Lakes basin is important because mapped nest colonies and nest counts are not representative of the actual distribution of foraging cormorants during and after the nesting season. There are two general conclusions to emerge from this survey. First, aquatic productivity from both Great Lakes coast and inland lakes contributes to trends in population and distribution of cormorants in the northern region of Lake Huron and perhaps elsewhere. Second, inland aquatic ecosystems are important throughout a season for foraging cormorants from the Great Lakes and may become more important as Great Lake productivity trends downward.     

Nitrate removal in the hyporheic zone of a salmon river in Alaska

Pacific boreal streams and riparian zones are believed to receive significant N loads that are derived from the ocean in the form of decaying sockeye salmon (Oncorhynchus nerka). Using a small stream in south‐central Alaska we examined whether the associated riparian forest could take up the pulse of marine‐derived nitrogen (MDN) entering the hyporheic zone from spawning and dying sockeye salmon. We evaluate the relative importance of riparian uptake and denitrification in nitrate‐N removal in hyporheic sediment. We found that maximum biological removal of nitrate peaked within 1 h of water entering the hyporheic zone, decreasing exponentially with subsurface flow duration. Plant and microbial uptake reached 14 µg NO‐N L^?1 min^?1 and denitrification reached 4 µg NO‐N L^?1 min^?1 during the initial 2 h of transit time. Our results reinforce the hypothesis that MDN from Pacific salmon can be transferred to riparian zone via hyporheic flow. Most nitrate‐N removal along hyporheic flow paths is by plant and microbial uptake (the respective contributions could not be determined). Denitrifying bacteria are present and active in the hyporheic zones of this well‐oxygenated Alaskan stream but their contribution to the nitrate‐N removal is small compared to plant and microbial uptake in such nitrate‐N poor environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Vertical distribution of coarse particulate organic matter in river bed sediments (Morava river,Czech Republic)

The vertical and temporal distribution of coarse particulate organic matter (CPOM) larger than 1 mm from 0 to 70 cm depth within the substrate was observed at two different sites along a riffle in the River Morava. Samples of hyporheal sediments were taken by inserting a steel cylinder and a special grab. The amount of CPOM was determined by combustion. The maximum amount of CPOM was found at a depth of 30-40 cm; lower levels of CPOM were observed in deeper horizons. The average amount of CPOM in 10cm layers (volume 1582.9 cm³) was 232.2 gm^?3 at station A and 691.3 gm^?3 at station B. The content of CPOM showed a maximum during the summer.     

Abundance and function of large woody debris in small,headwater streams in the Rocky Mountain foothills of Alberta,Canada

Large woody debris (LWD) significantly influences the structure and function of small headwater streams. However, what it contributes to geomorphic function depends on where it is located relative to the stream channel. We quantified LWD abundance and tested for associations among decay, position, orientation and function classes in 21 streams near Hinton, Alberta, Canada. LWD was more frequent (64.0 ± 3.3 LWD 100 m^?1) in streams in the Alberta foothills than it was in small streams in mountain, coastal, broadleaf deciduous and boreal forests, likely due to the narrow channel widths and low capacity of our study streams to transport logs downstream. LWD volumes were greater in coastal streams than in the Alberta foothills, likely due to differing tree sizes and decay rates. LWD morphology changed significantly as logs decayed and transitioned to different position and orientation classes. LWD in decay classes I and II were longest, most commonly in the bridge and partial bridge position classes, oriented perpendicular to stream flow, suspended above the channel and contributing least to stream geomorphic functions. LWD length and volume (but not diameter) decreased as decay advanced, making logs less stable. LWD in decay classes III and IV were strongly associated with partially bridged, loose, and buried position classes. They were more commonly diagonal or parallel to stream flow and contributed to bank stability, sediment retention, debris jams and riffle and pool formations. These results have been integrated into a conceptual model of LWD dynamics that provides a framework for future research on the mechanisms and rates of LWD recruitment, decay, transport and function. Copyright © 2010 John Wiley & Sons, Ltd.