Implications of the annual macrophyte growth cycle on habitat in rivers

The continuity equation, Manning's equation and an empirically determined relationship between channel roughness and the biomass of macrophytes were used to simulate the effects of weed growth in contrasting channels. Two indices of wetted available habitat, velocity and depth were chosen to illustrate the role of macrophyte in maintaining and modifying instream habitat with particular reference to chalk streams. Plant growth maintained depth within the channels and its effect was modified by channel shape and slope. Weed cutting resulted in very sudden changes in depth and velocity and the loss of a large volume of water from the river. The results indicate that macrophyte growth could be used to maintain wetted habitat while allowing more abstraction, but more data are required on the long-term effects of implementing such policies.     

Influences of environmental conditions on macrophyte communities in drought‐affected headwater streams

A 10‐year study of groundwater‐dominated headwater streams in the chalklands of southern England has highlighted the major influence that stream flow has on the composition of in‐channel macrophyte communities. Macrophytes supply much of the physical structure within these headwater channels, as well as providing habitats for a rich assemblage of higher life forms, some of them specialized and rare. The overall influence of stream flow however, is modulated by many environmental factors operating at diverse spatial scales. Data describing the relevant environmental variables were accumulated for six chalk streams in the Thames basin and related directly to the vegetation record by means of Canonical Correspondence Analysis, correlation tests and other analyses, to reveal the circumstances in which communities would be likely to thrive and those in which they would be negatively impacted by variations in stream flow. It was found that local topography and channel dimensions had a direct influence on the composition of communities at local level and that land use and rates of water abstraction had an underlying, but no less important, influence at catchment level. The species most associated with positive species diversity were those of sluggish flow and damp margins indicating the importance of velocity and moisture gradients across the channel in producing a full manifestation of the flora. Strong negative correlations were produced by non‐aquatic grasses and herbs, which represent prolonged periods of channel desiccation. The environmental parameters most associated with positive diversity were high local water stages, wide channels and a high degree of semi‐natural land use within the catchment. Steep channel gradients were strongly associated with negative diversity. The results have confirmed that optimal channel conditions, as exemplified by the classic ‘winterbourne’ with its low‐flow channel, extensive margins, gently sloping banks and high seasonal inundation, will produce good conditions for species diversity and make communities more resistant to the effects of drought. These conditions can be enhanced through sensitive catchment management that encourages rainfall percolation, limits abstractions and seeks to maintain a low intensity of landcover management. Copyright © 2006 John Wiley & Sons, Ltd.     

Disturbance by aquatic plant management in streams: Effects on benthic invertebrates

The effect of aquatic plant removal on benthic invertebrates and their habitat was studied in two macrophyte-rich streams of the Swiss Plateau. In each stream, habitat conditions (macrophyte biomass, current velocity, water depth) and invertebrate densities were monitored in a control reach and in a reach where plants were removed by cutting. Biological samples were taken and physical parameters measured on three dates before and six dates after plant removal in both reaches. Responses to plant removal were similar in both streams; macrophyte cutting initially decreased mean plant biomass (ca. 85%) and total number of invertebrates (ca. 65%). Variation between replicates was, however, higher in one of the streams, causing fewer effects on plants and invertebrates to be statistically significant. Plant cutting affected mainly taxa that used macrophytes as habitat (e.g. Simuliidae, Chironomidae), whereas highly mobile taxa (e.g. Ephemeroptera) and taxa living on or within the bed sediments (e.g. Trichoptera, Bivalvia) were less affected. Taxa that decreased after plant removal recovered within 4–6 months, although recovery of macrophytes was quite different in both streams. Invertebrate recovery also seemed to be seasonally dependent, with cutting having a less severe impact during summer than spring. Our results suggest that macrophytes in streams should be removed only in summer, preferably leaving some plant beds to act as refugia for phytophilous invertebrates. © 1998 John Wiley & Sons, Ltd.     

Impact of mechanical cutting on the channel roughness

The impact of mechanical cutting for weed control along vegetated irrigation canals in terms of Manning's n, is discussed. Flow resistance was measured in channels completely infested by submerged macrophytes. Next, a path was cut along one or both canal banks by mechanical means and the measurement of flow resistance was repeated. The experiments and measurements carried out during only one seasson are described. A series of relationships between the flow resistance and a cross-section of areas both free from vegetation and with vegetation density, respectively, were found. Clearly, the elucidation of such relationships will be useful in assessing the frictional effects of submerged macrophyte growths in relation to the design and management of irrigation and drainage channels.     

Mitigation of impacts of cattle access on stream ecosystems: Efficacy of fencing

Headwater streams can constitute up to 80% of river channel length and are vulnerable to anthropogenic pressures due to their high connectivity to adjacent land, large relative catchment size and low dilution capacity. In these environments, unrestricted cattle access is a potentially significant cause of water quality deterioration, resulting from increases in stream bank erosion, riparian damage and sediment deposition among others. Several studies have reported improvements in the physico-chemical and hydromorphological conditions of streams following the elimination of cattle access; few, however, have focussed on the ecological impacts of such management practices. Here, such impacts are assessed. The study explores the short-term effects of cattle exclusion by comparing habitat conditions, sediment deposition and instream macroinvertebrate communities upstream and downstream of cattle access points prior to, and 1 year following exclusion via fencing. The long-term effects are also measured by reassessing a small stream catchment entirely fenced off from cattle access in 2008 under a dedicated management plan. In the short term, cattle exclusion led to a reduction in deposited sediment downstream of cattle access points and a related homogenisation of macroinvertebrate community structure between upstream and downstream of cattle access points. Increased abundances of specific indicator taxa (Ancylus fluviatilis, Glossosomatidae and Elmidae) in the fenced catchment following 9 years of exclusion highlight the long-term ecological benefits of such mitigation practices. These findings highlight the importance of incentivised agri-environment measures in reducing the negative impacts of cattle access to vulnerable aquatic ecosystems.     

Assessing the effectiveness of enhancement activities in urban streams: II. Responses of invertebrate communities

The effects of habitat enhancement on the invertebrate communities in five urban streams in Christchurch, New Zealand, were investigated. All streams underwent riparian planting, while extensive channel modifications were made at two streams, where a concrete dish channel and a wooden timber‐lined stream were removed and natural banks reinstated. Benthic invertebrates were collected before enhancement and 5 years after from the same locations. Invertebrates were also collected from control sites in each stream in 2001. Desired goals of enhancement activities included increasing the densities of mayflies and caddisflies, and decreasing densities of oligochaetes, snails and midges. Enhancement activities changed riparian vegetation and bank conditions, as well as substrate composition, instream organic matter and variability of instream velocities. Invertebrate communities prior to enhancement were typical of those in urban environments, and dominated by snails (Potamopyrgus, Physa), the amphipod Paracalliope, the hydroptilid caddisfly Oxyethira, oligochaetes and chironomids. Stream enhancement caused only small changes to the invertebrate community, with subtle shifts in overall abundance, species evenness, diversity, and ordination scores. Lack of a consistent strong response by invertebrates to enhancement activities, and continued absence of caddisflies and mayflies from enhanced sites may reflect lack of sufficient change to instream conditions as a result of stream enhancement, colonization bottlenecks for aerial stages of these animals, and the inability of individuals outside the urban watershed to perceive these enhanced ‘islands’ of good habitat. Alternatively, contamination of streambed sediments, excess sedimentation and reduced base flows may be limiting factors precluding successful invertebrate colonization in enhanced sites. These results highlight the importance of setting clear goals and objectives necessary to meet these goals. Enhancement of riparian zones in urban streams may not be adequate to improve benthic invertebrate communities. Identifying over‐arching factors that potentially limit invertebrate communities will enable the enhancement potential of streams to be better assessed, and allow managers to identify sites where recovery of biological communities is possible, and where such recovery is not. Copyright © 2005 John Wiley & Sons, Ltd.     

The effect of land use on channel geometry and sediment distribution in gravel mantled bedrock streams,Illinois River watershed,Arkansas

Headwater stream morphology is a direct reflection of watershed characteristics and therefore can inform our understanding of anthropogenic influence on channel geometry and sediment dynamics. Little knowledge of the geomorphology of headwater streams in the Ozark Plateaus region of northwest Arkansas exists. The Illinois River watershed, in northwest Arkansas, is of critical interest within the region because of land use changes in the headwaters due to rapid population growth. A mixture of forest and agricultural (open pasture and poultry houses) land use dominates the watershed, but urban areas are rapidly expanding. These land use types: forest, agriculture and urban are an effective proxy for increasing anthropogenic disturbance. Analysis of longitudinal profile, cross‐section and sediment distribution in streams from each land use type shows a strong trend of increasing slope and channel cross‐sectional area with a greater degree of anthropogenic disturbance. Additionally, urban streams are characterized by the presence of exposed bedrock in the stream bed, while agricultural and forested streams are gravel mantled. These data have important implications for current and future stream management policies and practices regionally. Copyright © 2010 John Wiley & Sons, Ltd.     

Comparison of blockage factors in modelling the resistance of channels containing submerged macrophytes

The proportion of a river channel containing vegetation (termed the blockage factor) has historically been determined in three ways: cross‐sectional, surface area and volumetric. The first two versions are two‐dimensional measures. Meanwhile, the three‐dimensional volumetric version is biased towards deeper sections of a reach. A fourth version of the blockage factor is proposed that does not have such limitations: the multi‐cross‐sectional blockage factor. Between five and nine cross‐sections were sampled to determine the four blockage‐factor versions for 35 river sites containing the clumped submergent macrophyte, Ranunculus subgenus Batrachium (water‐crowfoot). The ability of these four measures to act as predictors of vegetative channel resistance was then assessed. The vegetated proportion of individual cross‐sections was poorly related to the vegetation resistance of a channel reach, primarily due to the high spatial variability of patch‐forming macrophytes. The weighted median of all cross‐sectional blockage factors measured at each site produced the strongest relationship with vegetation resistance, though this was not significantly better than the volumetric or surface area versions. The resistance model using the surface‐area blockage factor gave a very high residual between predicted and calculated resistance for a mat‐forming macrophyte species, and this model is unlikely to hold for conditions other than baseflow. Likewise, the volumetric version is not expected to hold for sites that have more depth variability than those measured in this study. Copyright © 2005 John Wiley & Sons, Ltd.     

Impact of partial removal of the invasive macrophyte Lagarosiphon major (hydrocharitaceae) on invertebrates and fish

Invasive macrophyte species are a threat to native biodiversity and often grow to nuisance levels, therefore, making control options necessary. Macrophyte control can have pronounced impacts on littoral fish by reducing habitat heterogeneity and the loss of profitable (high density of invertebrates) foraging areas. Yet, there is little known about the impacts of macrophyte removal on invertebrates themselves. We conducted a macrophyte removal experiment, that is the cutting of channels into dense macrophyte beds, to investigate the impact of mechanical macrophyte control on invertebrate and fish communities in a littoral zone dominated by the invasive macrophyte Lagarosiphon major. The effect of macrophyte removal had only a temporary effect on macrophyte areal cover (4 months). Nevertheless, the treatment increased light penetration significantly. However, we could not detect any difference in epiphyton biomass. Invertebrate biomass increased in macrophyte stands 4 months after treatment and there was a shift in the invertebrate community composition. Mechanical control had no effect on invertebrate biodiversity. The higher invertebrate biomass did not translate into a higher fish density in the treated areas. The results of this study indicated that partial mechanical removal is a suitable option to control unwanted macrophyte stands. Copyright © 2008 John Wiley & Sons, Ltd.     

Identifying Temperature Thresholds Associated with Fish Community Changes in British Columbia,Canada, to Support Identification of Temperature Sensitive Streams

We collected fish samples and measured physical habitat characteristics, including summer stream temperatures, at 156 sites in 50 tributary streams in two sampling areas (Upper Fraser and Thompson Rivers) in British Columbia, Canada. Additional watershed characteristics were derived from GIS coverages of watershed, hydrological and climatic variables. Maximum weekly average temperature (MWAT), computed as an index of summer thermal regime, ranged from 10 to 23 °C. High values of MWAT were associated with large, warm, low relief watersheds with a high lake influence. Measures of community similarity suggested that the fish community changed most rapidly through a lower transition zone at an MWAT of about 12 °C and an upper transition zone at an MWAT of about 19 °C. These results were confirmed using existing fisheries inventory data combined with predictions of MWAT from a landscape‐scale regression model for the Thompson River watershed. For headwater sites in the Chilcotin River watershed (which drains into the middle Fraser River), the relative dominance of bull trout versus rainbow trout (based on inventory data) decreased with increasing predicted MWAT although the distinction was not as clear as for the Thompson River sites. The fish communities in these watersheds can be characterized in terms of very cold water (bull trout and some cold water species), cold water (salmonids and sculpins) and cool water (minnows and some cold water salmonids). The two transition zones (ca 12 and 19 °C) can be used to identify thresholds where small changes in stream temperature can be expected to lead to large changes in fish communities. Such clear, quantifiable thresholds are critical components of a management strategy designed to identify and protect vulnerable fish communities in streams where poor land use practices, alone or in combination with climatic change, can lead to changes in stream temperatures. Copyright © 2015 John Wiley & Sons, Ltd.     

The role of riparian vegetation and woody debris in the development of macroinvertebrate assemblages in streams

Riparian vegetation development and macroinvertebrate assemblages were studied in 16 streams formed between 35 and 230 years ago, following glacial recession in Glacier Bay National Park, southeast Alaska. Riparian vegetation established most rapidly in streams where flow variation in downstream reaches was buffered by a lake. Riparian vegetation development was positively correlated with lower bank stability, but was independent of stream age. Roots and branches of riparian vegetation trailing into streams (trailing riparian habitat—TRH) were shown to be an important habitat for a number of macroinvertebrate taxa. In young and unstable streams, TRH was colonized mainly by Plecoptera whereas in more stable lake‐influenced streams Simuliidae dominated. Significant coarse woody debris (CWD) accumulations were not observed until after approximately 130 years of stream development had occurred when certain channel features, such as gravel bars, were stabilized by dead wood. Where dead wood was present, opportunistic wood taxa were abundant, even in the younger streams. However, a xylophagous species, Polypedilum fallax, was not recorded until streams were over 100 years old. Two‐way indicator species analysis (TWINSPAN) using presence/absence of macroinvertebrate taxa on TRH, initially divided streams into lake and non‐lake systems, but subsequent divisions were consistent with differences in stream age. TWINSPAN of macroinvertebrate assemblages on dead wood again highlighted differences in stream age. Canonical correspondence analysis indicated that bed stability and stream age were the most important environmental variables influencing macroinvertebrate distribution on TRH. Trailing riparian habitat was most abundant in moderately unstable streams where it facilitates invertebrate colonization. CWD contributes markedly to channel stabilization, provides habitat for invertebrate xylophages, and confers additional habitat complexity. Maximum levels of CWD are predicted to occur in non‐lake streams after approximately 300 years, but at least a further 100 years will be required in stable streams below lakes where dead wood entrainment is not enhanced by flooding, channel migration and bank undercutting. A conceptual model summarizing the role of TRH and CWD on stream development in Glacier Bay is presented. Copyright © 2005 John Wiley & Sons, Ltd.     

Cascade macroinvertebrate assemblages for in‐stream flow criteria and biomonitoring of tropical mountain streams

Few comprehensive studies on stream assessment and biomonitoring have been conducted in tropical, freshwater watersheds. Currently under threat from climate change, urbanization and increasing freshwater demands, there is a need for innovative approaches to tropical watershed assessment and management. This study investigated cascade habitat macroinvertebrate communities among four tropical mountain streams with the goal of enhancing future efforts to identify flow biocriteria for watersheds of Polynesia. Cascade macroinvertebrate communities were compared between streams of differing size and magnitude of flow removal to evaluate the biological effects of water withdrawal on benthic communities. Two cascade microhabitats, identified as torrenticolous and amphibious, were evaluated for macroinvertebrate community differences and presence of native taxa among watersheds. Cascade habitat in general was reduced, by as much as 98%, in downstream reaches, having a significant impact on the stream ecosystem physical template important for native stream communities. In addition, two‐way ANOVA results revealed no main effects, but significant interactions of watershed size and flow removal on mean macroinvertebrate density for torrenticolous microhabitats; however, the opposite was true for the amphibious microhabitat. Diversity was significantly higher under undiverted flow conditions (t = 4.21, df = 272, p = 0.0004) and in torrenticolous microhabitats (t = 3.86, df = 272, p < 0.0001) over the entire study period. The amphibious microhabitat was composed of 39% native taxa, while the torrenticolous microhabitat contained <7%. This study provides new options for biomonitoring of native populations in Polynesian watersheds. Further studies that support the development of in‐stream flow criteria to preserve cascades are important to understanding the role of this habitat in tropical stream ecosystem function. Copyright © 2010 John Wiley & Sons, Ltd.     

Spatial distribution and geomorphic condition of fish habitat in streams: an analysis using hydraulic modelling and geostatistics

Reach‐scale physical habitat assessment scores are increasingly used to make decisions about management. We characterized the spatial distribution of hydraulic habitat characteristics at the reach and sub‐reach scales for four fish species using detailed two‐dimensional hydraulic models and spatial analysis techniques (semi‐variogram analyses). We next explored whether these hydraulic characteristics were correlated with commonly used reach‐scale geomorphic assessment (RGA) scores, rapid habitat assessment (RHA) scores, or indices of fish biodiversity and abundance. River2D was used to calculate weighted usable areas (WUAs) at median flows, Q₅₀, for six Vermont streams using modelled velocity, depth estimates, channel bed data and habitat suitability curves for blacknose dace (Rhinichthys atratulus), brown trout (Salmo trutta), common shiner (Notropis cornutus) and white sucker (Catostomus commersoni) at both the adult and spawn stages. All stream reaches exhibited different spatial distributions of WUA ranging from uniform distribution of patches of high WUA to irregular distribution of more isolated patches. Streams with discontinuous, distinct patches of high score WUA had lower fish biotic integrity measured with the State of Vermont's Mixed Water Index of Biotic Integrity (MWIBI) than streams with a more uniform distribution of high WUA. In fact, the distribution of usable habitats may be a determining factor for fish communities. A relationship between predicted WUAs averaged at the reach scale and RGA or RHA scores was not found. Future research is needed to identify the appropriate spatial scales to capture the connections between usable patches of stream channel habitat. Copyright © 2008 John Wiley & Sons, Ltd.     

Responses of lake macrophyte beds dominated by Eurasian watermilfoil (Myriophyllum spicatum) to best management practices in agricultural sub-watersheds: Declines in biomass but not species dominance

Long-term studies of macrophyte beds growing near streams in Conesus Lake, New York, have revealed a high biomass and continuing dominance of the invasive rooted species Eurasian watermilfoil (Myriophyllum spicatum). We tested whether agricultural best management practices (BMPs) designed to reduce tributary nutrient and soil loss from the watershed could reduce populations of Eurasian watermilfoil downstream in the lake littoral. Six macrophyte beds were monitored during a 3-year baseline period (2001–2003) prior to the implementation of BMPs and for a 4-year experimental period after a variety of agricultural BMPs were implemented in three sub-watersheds. For three macrophyte beds downstream from sub-watersheds managed as part of our project, quadrat biomass decreased by 30–50% and was statistically lower than Pre-BMP baseline values in 7 of 11 experimental sample years. Biomass loss primarily in the form of the dominant Eurasian watermilfoil ranged from 6.2 to 10 t wet weight for each bed. The declines in biomass coincided with significant annual and January–August decreases in the concentrations and fluxes of dissolved nutrients, total phosphorus, and total suspended solids in nearby streams. For three macrophyte beds downstream from watersheds in which landowners applied less extensive or no new agricultural management, biomass was statistically indistinguishable from Pre-BMP baseline values in all 12 experimental sample years. Milfoil remained the overwhelmingly dominant species at all sites during the entire study period. These results provide impetus for the use of watershed nutrient management to control the nuisance growth of Eurasian watermilfoil on a local scale in the lake littoral.     

Estimating channel‐forming discharge in urban watercourses

Several methods of estimating channel‐forming discharge were conducted on 12 quasi‐stable urban stream channels ranging from 9 to 99% urban land use to test their applicability in the urban condition. Bankfull stage was identified at a series of locations along each study reach and it was found that the most consistent observations of bankfull discharge occurred during flood conditions where bankfull stage was identified at the top of point bars along the convex arc of bends. The largest errors in estimation occurred at gauge stations where cross‐sectional geometry had been altered to conform to bridges or culverts rather than the channel morphology. Independent evaluations of channel forming discharge were conducted by 11 practitioners ranging from 10 years to 43 years of experience with similar findings and errors. Various methods of relating frequency return periods were evaluated using annual peak series discharge observations and continuous 15‐min systematic discharge records using partial duration series analysis. Bankfull discharge was observed to occur more than once a year in all of the urban streams studied and often averaged from 4 to 8 bankfull discharge or larger events per year. In one particular case in a single given year 18 events exceeding bankfull discharge were observed. No specific correlations were identified between frequency return periods and land use change. However, based upon the findings of this study, the applicability of employing annual series peak discharge data to evaluate bankfull frequency return in urban stream channels is highly discouraged. Copyright © 2010 John Wiley & Sons, Ltd.     

Physical constraints on the distribution of macrophytes linked with flow and sediment dynamics in British rivers

Aquatic vegetation plays a role in engineering river channels by altering patterns of flow velocity, sediment dynamics and, consequently, development and turnover of habitats. This could potentially aid in the rehabilitation of over‐widened, straightened channels, and, less desirably, reduce channel conveyance and contribute to flooding problems. Therefore, it is important to understand the environmental conditions in which in‐stream and marginal vegetation can reach sufficient abundance for these engineering roles to have a significant impact on the physical environment. Macrophyte and environmental data from 1653 river reaches across Great Britain were collated. Specific stream power (SSP) was calculated to represent hydrological disturbance and a median bed calibre index and percentage sand and finer sediment were used to characterize substrate size, since stream energy and sediment properties are two major physical controls on aquatic vegetation. Correlation and Principal Component Analysis (PCA) revealed subtly different physical habitat ‘preferences’ between species of contrasting morphology. Correlations of additional environmental data with SSP indicated that this physical disturbance variable also reflects gradients in stress variables describing nutrient availability and latitude and so is a useful integrator of a number of important pressures on plant survival. A conceptual model was produced which indicates ranges of SSP which may determine the significance of aquatic macrophytes in channel engineering processes. This model could contribute to predicting the potential for macrophyte growth within a given reach thus indicating its capacity for self‐restoration or the likelihood of weed problems. Copyright © 2010 John Wiley & Sons, Ltd.     

Invertebrate response to impacts of water diversion and flow regulation in high‐altitude tropical streams

Water supply systems are critical infrastructure that provides food and energy security for developed societies. The operation of reservoirs (flow regulation) and water intakes (water diversion) has known negative impacts on aquatic ecosystems; however, quantification of ecological impacts and examination of these two types of flow alteration remain a developing area of research. We investigated the individual and combined impact of flow regulation and water diversion on stream ecosystem integrity, the freshwater macroinvertebrate community, and the population structure of flow‐sensitive insects. For 2 years, we monitored quarterly discharge, physical and chemical stream conditions, and benthic invertebrates of four high‐altitude tropical streams that are part of the water supply system of Quito, Ecuador. Flow regulation caused a loss of the hydrological seasonality of these streams, including a decrease in stream depth and biotic quality. Water diversion caused a decrease in dissolved oxygen and overall ecosystem integrity. Freshwater invertebrate density and richness decreased as a result of water diversion and flow regulation. The combined flow alteration in these streams decreased the density of nymphal stages of the widely distributed mayfly Andesiops peruvianus. Given the societal needs for food and energy security, water management for diversion (e.g., irrigation) and in‐line storage practices (e.g., hydroelectric dams) are anticipated to increase. This research suggests that the negative environmental impacts of flow alteration could be mitigated with discharge releases designed to approximate the natural hydrologic regime of undisturbed streams.     

Physiographic characteristics of bridge‐stream intersections

Bridges that cross streams can be greatly affected by channel instabilities, such as channel widening, lateral migration and channel bed degradation. Attention to channel conditions in the vicinity of bridges is an important aspect of bridge maintenance and safety. Channel stability is also critical to goals of multi‐objective river management. Given that channel stability is important for both river management and the structural stability of bridges, any river management scheme should consider the stability of bridge‐stream intersections. In this paper, the characteristics of bridge‐stream intersections across the United States are described based on existing literature and recent field observations. A set of recommendations for addressing and improving channel stability at bridges is suggested, including: (1) controlling water and sediment discharges at the catchment level; (2) revegetating channel banks with woody vegetation; (3) reshaping the channel cross‐section to a more stable, configuration; (4) removing disturbances from the stream channel, such as cattle and (5) using structures to control flow near channel beds and banks. The physiographic setting is a factor in the solution of at least the first three suggestions in this list. Attention to the physical characteristics of bridge‐stream intersections in the various physiographic regions can lead to sustainable solutions for stabilizing channels at bridge‐stream intersections. Copyright © 2006 John Wiley & Sons, Ltd.     

Management of agricultural practices results in declines of filamentous algae in the lake littoral

Filamentous algal cover was quantified during periods of peak biomass from 2001 to 2007 in six littoral macrophyte beds in Conesus Lake, New York (USA). Three of the study sites were adjacent to streams that drained sub-watersheds where extensive agricultural best management practices (BMPs) designed to reduce nutrient runoff were implemented beginning in 2003. Three other study sites were downstream from sub-watersheds where only a few or no BMPs were implemented by landowners. For the sites that received extensive management, comparisons of the Pre-BMP baseline period (2–3 yrs) to the Post-BMP period (4 yrs) revealed that algal cover was statistically lower than baseline in eight of eleven years (72.7%). For the three sites where limited or no management was implemented, the percent cover of filamentous algae was lower than Pre-BMP baseline levels in only three of twelve years (25%). Where major reductions in cover of filamentous algae occurred, positive relationships existed with summer stream loading of nitrate and soluble reactive phosphorus to the nearshore. In some cases only nitrate loading was significantly correlated with percent cover, indicating that the relative importance of nitrogen and phosphorus to algal growth near streams may be determined by the characteristics and land use within each sub-watershed. Agricultural BMPs targeting nutrient and suspended solid runoff can effectively reduce filamentous algal growth locally along the lake littoral zone on a time scale of months to a few years and with moderate commitment of resources. This work offers a new perspective for management of the growing problem of littoral algal growth in the embayments and drowned river mouths of the Great Lakes.     

Seasonal Rearing Habitat in a Large Mediterranean‐Climate River: Management Implications at the Southern Extent of Pacific Salmon (Oncorhynchus spp.)

Pacific salmon (Oncorhynchus) use a variety of rearing environments prior to seaward migration, yet large river habitats and their use have not been well defined, particularly at the southernmost salmon range where major landscape‐level alterations have occurred. We explored juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) presence along the river continuum and in main‐channel and off‐channel habitats of a regulated California Mediterranean‐climate river. Over an 8‐year period, off‐channels of the lower Mokelumne River exhibited slower and warmer water than the main‐channel. Probability of salmonid presence varied by stream reach and habitat types. Steelhead and Chinook salmon both demonstrated transitional responses to the dry season, with juveniles leaving off‐channels by midsummer. This corresponded to flow recession, increasing water temperatures, salmonid growth and end of emigration period. Main‐channel steelhead observations continued until the following storm season, which brought cool flood flows to reconnect off‐channels and the next juvenile cohort of both species to the river. Within arid climates, low‐gradient off‐channels appear more transiently used than in cooler and more northern humid climate systems. Within a highly regulated Mediterranean‐climate river, off‐channel habitats become increasingly scarce, disconnected or temperature limiting in low‐gradient reaches both seasonally and due to anthropogenic modifications. These observations may provide guidance for future management within large salmon streams. Copyright © 2015 John Wiley & Sons, Ltd.