Responses to Riparian Restoration in the Spring Creek Watershed, Central Pennsylvania

Riparian treatments, consisting of 3‐ to 4‐m buffer strips, stream bank stabilization, and rock‐lined stream crossings, were installed in two streams with livestock grazing to reduce sediment loading and stream bank erosion. Cedar Run and Slab Cabin Run, the treatment streams, and Spring Creek, an adjacent reference stream without riparian grazing, were monitored prior to (1991–1992) and 3–5 years after (2001–2003) riparian buffer installation to assess channel morphology, stream substrate composition, suspended sediments, and macroinvertebrate communities. Few changes were found in channel widths and depths, but channel‐structuring flow events were rare in the drought period after restoration. Stream bank vegetation increased from 50% or less to 100% in nearly all formerly grazed riparian buffers. The proportion of fine sediments in stream substrates decreased in Cedar Run but not in Slab Cabin Run. After riparian treatments, suspended sediments during base flow and storm flow decreased 47–87% in both streams. Macroinvertebrate diversity did not improve after restoration in either treated stream. Relative to Spring Creek, macroinvertebrate densities increased in both treated streams by the end of the posttreatment sampling period. Despite drought conditions that may have altered physical and biological effects of riparian treatments, goals of the riparian restoration to minimize erosion and sedimentation were met. A relatively narrow grass buffer along 2.4 km of each stream was effective in improving water quality, stream substrates, and some biological metrics.     

Herbs and grasses as an allochthonous resource in open-canopy headwater streams

1. The organic matter dynamics of streams dominated by herbs and grass on their banks are poorly understood, despite the fact that such streams are common worldwide. Further, herbs and grasses can provide large quantities of detritus to stream food webs, and particularly small streams can be heavily shaded by overhanging vegetation, perhaps limiting in‐stream primary production. 2. We quantified the standing crop of edge vegetation and associated macroinvertebrate communities along three headwater streams with herbaceous and grass riparian vegetation on agricultural land in the Piedmont of Maryland, U.S.A., measured the decomposition of four common species of herbs and grasses using experimental leaf packs, and removed edge vegetation experimentally to determine the effect of shading on benthic algal production. 3. Large standing crops of plant material (average range: 68–276 g ash‐free dry mass per m⁻²), composed largely of monocotyledons, were found at all three study streams. These values are similar to those for coarse particulate organic matter in deciduous forested streams in the eastern U.S.A. In addition, diverse assemblages of shredding macroinvertebrates were observed at all three study sites. 4. Decomposition of the herbs was faster than that of the grasses, and both decomposed faster than most deciduous tree leaf litter. The decomposition rates of the herbs and grasses were significantly related to leaf quality as measured by leaf nitrogen content. Macroinvertebrate shredders colonized all experimental leaf packs, and the colonization of the herbs was faster than that of the grasses. 5. The accrual of chlorophyll‐a after the removal of shading vegetation was faster than that measured prior to removal as well as that in an unmanipulated control reach. 6. Given that the standing crop of organic matter in streams with herbs and grass along their banks was similar to that in forested streams, that the organic matter was rich in nitrogen and used by detritivores, and riparian shading limited algal growth, we suggest that herbaceous and grass plant material may be an important allochthonous food resource in such systems.     

Differences in litter characteristics and macroinvertebrate assemblages between litter patches in pools and riffles in a headwater stream

We compared the abundance of litter categories (coarse particulate organic matter 1–16 mm, leaves >16 mm, and small woody detritus 16–100 mm) and macroinvertebrate assemblages between natural litter patches in pools and riffles in a headwater stream. Litter patches in pools were formed under conditions of almost no current (<6 cm s⁻¹), but in riffles they were formed under variable current velocities (13–89 cm s⁻¹). Although the abundance of each litter category exhibited seasonal change, leaves were more abundant in riffles, and coarse particulate organic matter and small woody detritus were more abundant in pools throughout the study period. Macroinvertebrate assemblages in pools and riffles also changed seasonally but distinctly differed from each other. Shredders, collector-gatherers, and predators were the dominant functional groups in abundance in both pools and riffles, but the dominant shredders were caddisflies in pools and stoneflies in riffles. It is considered that the hydraulic conditions affected macroinvertebrate assemblages directly and indirectly through influences on the characteristics of litter retained in the patches. Our results suggest that the relative abundance of litter patches in pools and riffles largely affects the macroinvertebrate community structure of the headwater stream. Received: July 19, 2001 / Accepted: December 19, 2001     

Response of secondary production by macroinvertebrates to large wood addition in three Michigan streams

1. We measured responses in macroinvertebrate secondary production after large wood additions to three forested headwater streams in the Upper Peninsula of Michigan. These streams had fine‐grained sediments and low retention capacity due to low amounts of in‐channel wood from a legacy of past logging. We predicted that wood addition would increase macroinvertebrate secondary production by increasing exposed coarse substrate and retention of organic matter. 2. Large wood (25 logs) was added haphazardly to a 100‐m reach in each stream, and a 100‐m upstream reach served as control; each reach was sampled monthly, 1 year before and 2 years after wood addition (i.e. BACI design). Macroinvertebrate secondary production was measured 1 year after wood addition in two habitat types: inorganic sediments of the main channel and debris accumulations of leaf litter and small wood. 3. Overall macroinvertebrate production did not change significantly because each stream responded differently to wood addition. Production increased by 22% in the main‐channel of one stream, and showed insignificant changes in the other two streams compared to values before wood addition. Changes in main‐channel macroinvertebrate production were related to small changes in substrate composition, which probably affected habitat and periphyton abundance. Macroinvertebrate production was much greater in debris accumulations than in the main‐channel, indicating the potential for increased retention of leaf litter to increase overall macroinvertebrate production, especially in autumn. 4. Surrounding land use, substrate composition, temperature and method of log placement are variables that interact to influence the response of stream biota to wood additions. In most studies, wood additions occur in altered catchments, are rarely monitored, and secondary production is not a common metric. Our results suggest that the time required for measurable changes in geomorphology, organic matter retention, or invertebrate production is likely to take years to achieve, so monitoring should span more than 5 years, and ecosystem metrics, such as macroinvertebrate secondary production, should be incorporated into restoration monitoring programs.     

钱塘江中游流域不同空间尺度环境因子对底栖动物群落的影响

溪流底栖动物群落结构受不同空间尺度环境因子的共同作用。基于2010年钱塘江中游流域60个样点的大型底栖无脊椎动物和环境变量数据,寻找与研究流域底栖动物群落结构变化密切相关的关键环境变量,解析流域尺度和河段尺度的环境因子对底栖动物群落的相对影响。PCA分析表明该区域的主要环境梯度是流域内的土地利用类型及其引起的溪流物理生境退化程度和水体营养状态。CCA分析发现影响底栖动物群落的流域尺度的关键环境变量是纬度、海拔、样点所在流域大小、森林用地百分比,河段尺度是总氮、总磷、钙浓度、二氧化硅浓度和平均底质得分。偏CCA分析得到两种尺度环境因子对底栖动物变异的总解释量为26.4%,流域尺度和河段尺度变量分别为总解释量的50%和31%;方差分解结果表明研究区域大型底栖无脊椎动物受到两种尺度环境因子的综合影响,且流域尺度环境因子较河段尺度环境因子更为重要,体现了其在溪流生态系统保护、恢复、监测和评价中的重要参考价值。     

Factors Influencing Bank Geomorphology and Erosion of the Haw River,a High Order River in North Carolina,since European Settlement

The Haw River, a high order river in the southeastern United States, is characterized by severe bank erosion and geomorphic change from historical conditions of clear waters and connected floodplains. In 2014 it was named one of the 10 most threatened rivers in the United States by American Rivers. Like many developed areas, the region has a history of disturbance including extensive upland soil loss from agriculture, dams, and upstream urbanization. The primary objective of this study was to identify the mechanisms controlling channel form and erosion of the Haw River. Field measurements including bank height, bankfull height, bank angle, root depth and density, riparian land cover and slope, surface protection, river width, and bank retreat were collected at 87 sites along 43.5 km of river. A Bank Erosion Hazard Index (BEHI) was calculated for each study site. Mean bank height was 11.8 m, mean width was 84.3 m, and bank retreat for 2005/2007-2011/2013 was 2.3 m. The greatest bank heights, BEHI values, and bank retreat were adjacent to riparian areas with low slope (<2). This is in contrast to previous studies which identify high slope as a risk factor for erosion. Most of the soils in low slope riparian areas were alluvial, suggesting sediment deposition from upland row crop agriculture and/or flooding. Bank retreat was not correlated to bank heights or BEHI values. Historical dams (1.2–3 m height) were not a significant factor. Erosion of the Haw River in the study section of the river (25% of the river length) contributed 205,320 m³ of sediment and 3759 kg of P annually. Concentration of suspended solids in the river increased with discharge. In conclusion, the Haw River is an unstable system, with river bank erosion and geomodification potential influenced by riparian slope and varied flows.     

Effects of livestock exclusion on in‐stream habitat and benthic invertebrate assemblages in montane streams

1. Stream and riparian ecosystems in arid montane areas, like the interior western United States, are often just narrow mesic strands, but support diverse and productive habitats. Meadows along many such streams have long been used for rangeland grazing, and, while impacts to riparian areas are relatively well known, the effect of livestock grazing on aquatic life in streams has received less attention. 2. Attempts to link grazing impacts to disturbance have been hindered by the lack of spatial and temporal replication. In this study, we compared channel features and benthic macroinvertebrate communities (i) between 16 stream reaches on two grazed allotments and between 22 reaches on two allotments where livestock had been completely removed for 4 years, (ii) before and after the 4‐year grazing respite at a subset of eight sites and (iii) inside and outside of small‐scale fenced grazing exclosures (eight pairings; 10+ year exclosures) in the meadows of the Golden Trout Wilderness, California (U.S.A.). 3. We evaluated grazing disturbance at the reach scale in terms of the effects of livestock trampling on per cent bank erosion and found that macroinvertebrate richness metrics were negatively correlated with bank erosion, while the percentage of tolerant taxa increased. 4. All macroinvertebrate richness metrics were significantly lower in grazed areas. Bank angle, temperature, fine sediment cover and erosion were higher in grazed areas, while riparian cover was lower. Regression models identified riparian cover, in‐stream substratum, bank conditions and bankfull width‐to‐depth ratios as the most important for explaining variability in macroinvertebrate richness metrics. 5. Small‐scale grazing exclosures showed no improvements for in‐stream communities and only moderate positive effects on riparian vegetation. In contrast, metrics of macroinvertebrate richness increased significantly after a 4‐year period of no grazing. 6. The success of grazing removal reported here suggests that short‐term removal of livestock at the larger, allotment meadow spatial scale is more effective than long‐term, but small‐scale, local riparian area fencing, and yields promising results in achieving stream channel, riparian and aquatic biological recovery.     

Variable effects of sediment addition on stream benthos

Two upper Piedmont streams were studied to determine the effects of road construction, especially sediment inputs. Benthic macroinvertebrate data suggest that the stream community responded to sediment additions in two different ways. Under high flow conditions the benthic fauna occurs mainly on rocky substrates. As sediment is added to a stream the area of available rock habitat decreases, with a corresponding decrease in benthic density. There is, however, little change in community structure. Under low flow conditions, stable-sand areas may support high densities of certain taxa. Density of the benthic macroinvertebrates in these areas may be much greater than the density recorded in control areas, and there are distinct changes in community structure.     

Response of fishes and aquatic habitats to sand-bed stream restoration using large woody debris

Effects of habitat rehabilitation of Little Topashaw Creek, a sinuous, sand-bed stream draining 37 km² in northwest Mississippi are described. The rehabilitation project consisted of placing 72 large woody debris structures along eroding concave banks and planting 4000 willow cuttings in sandbars. Response was measured by monitoring flow, channel geometry, physical aquatic habitat, and fish populations. Initially, debris structures reduced high flow velocities at concave bank toes, preventing further erosion and inducing deposition. Physical response during the first year following construction included creation of sand berms along eroding banks and slight increases in base flow water width and depth. Fish collections showed assemblages typical of incising streams within the region, but minor initial responses to debris addition were evident. Progressive failure of the structures and renewed erosion were observed during the second year after construction.     

The Effect of Riffle-Scale Environmental Variability on Macroinvertebrate Assemblages in a Tropical Stream

In a tropical stream (at the Soberaní;a National Park, Panama), different environmental factors were quantified in riffle habitats (water characteristics: velocity, depth, turbulence, and direction; stone characteristics: surface area, sphericity, and degree of burial; and others: substrate type, and canopy cover). Characteristics of macroinvertebrate assemblages (mean density of individuals, mean taxon richness, and cumulative taxon richness in three stones at each riffle) were related to both mean values and variability of these environmental factors at riffle scale. Macroinvertebrate density was higher in shallow, fast flowing, stony riffles, with low variability in dominant substrate type. Taxon richness was also higher in shallow riffles with loose, not buried stones, and water direction more or less parallel to the bank. Environmental variability resulted as important as mean values of environmental factors to explain variation in macroinvertebrate assemblages. This is the first study, to our knowledge, that quantifies substratum variability and demonstrates its influence on macroinvertebrate assemblages in a tropical stream.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Decreased habitat specialization in macroinvertebrate assemblages in anthropogenically disturbed streams

Habitat specialists are considered to be more sensitive to anthropogenic disturbance than habitat generalists. However, a number of studies have shown that habitat specialists can be tolerant to or even benefit from environmental degradation, suggesting that the effect of disturbance on distributions and abundances of habitat generalists and specialists can be unpredictable. In this study, we assessed the effects of anthropogenic disturbance on the degree of specialization of stream macroinvertebrates in boreal streams. We first measured the niche width for each macroinvertebrate species using the Outlying Mean Index (OMI) analysis and then, using independent data sets of near-pristine and anthropogenically altered streams, we examined the effects of human disturbances on stream macroinvertebrates with different tolerances to environmental conditions. As expected, human disturbance significantly decreased the level of the specialization in stream macroinvertebrate assemblages, and taxa with narrow environmental tolerances were more sensitive to disturbance than taxa with wide tolerances. Despite being more sensitive to disturbance, taxa with narrow environmental tolerances were locally more abundant than tolerant taxa in near-pristine streams, indicating their better performance in their optimal environments. However, many tolerant taxa decreased in their occurrence in disturbed streams, suggesting that habitat generalists also tend to negatively respond to disturbance. Species-rich assemblages harboured more taxa with narrow tolerances compared with species poor assemblages, suggesting a high conservation value of streams with diverse macroinvertebrate assemblages. Consistent with findings for many biological groups, our results indicate that macroinvertebrate species specialised in certain habitats are more sensitive to environmental degradation than habitat generalists. However, contrary to many previous studies, our results suggest that only a few species are likely to benefit from anthropogenic disturbance and, therefore, environmental degradation does not necessary result in macroinvertebrate assemblages composed of a few tolerant taxa.     

Relationships between deforestation, riparian forest buffers and benthic macroinvertebrates in neotropical headwater streams

1. Few studies have evaluated the effectiveness of riparian buffers in the tropics, despite their potential to reduce the impacts of deforestation on stream communities. We examined macroinvertebrate assemblages and stream habitat characteristics in small lowland streams in southeastern Costa Rica to assess the impacts of deforestation on benthic communities and the influence of riparian forest buffers on these effects. Three different stream reach types were compared in the study: (i) forested reference reaches, (ii) stream reaches adjacent to pasture with a riparian forest buffer at least 15 m in width on both banks and (iii) stream reaches adjacent to pasture without a riparian forest buffer. 2. Comparisons between forest and pasture reaches suggest that deforestation, even at a very local scale, can alter the taxonomic composition of benthic macroinvertebrate assemblages, reduce macroinvertebrate diversity and eliminate the most sensitive taxa. The presence of a riparian forest buffer appeared to significantly reduce the effects of deforestation on benthic communities, as macroinvertebrate diversity and assemblage structure in forest buffer reaches were generally very similar to those in forested reference reaches. One forest buffer reach was clearly an exception to this pattern, despite the presence of a wide riparian buffer. 3. The taxonomic structure of macroinvertebrate assemblages differed between pool and riffle habitats, but contrasts among the three reach types in our study were consistent across the two habitats. Differences among reach types also persisted across three sampling periods during our 15‐month study. 4. Among the environmental variables we measured, only stream water temperature varied significantly among reach types, but trends in periphyton abundance and stream sedimentation may have contributed to observed differences in macroinvertebrate assemblage structure. 5. Forest cover was high in all of our study catchments, and more research is needed to determine whether riparian forest buffers will sustain similar functions in more extensively deforested landscapes. Nevertheless, our results provide support for Costa Rican regulations protecting riparian forests and suggest that proper riparian management could significantly reduce the impacts of deforestation on benthic communities in tropical streams.     

Modifying the Bank Erosion Hazard Index (BEHI) Protocol for Rapid Assessment of Streambank Erosion in Northeastern Ohio

Understanding the source of pollution in a stream is vital to preserving, restoring, and maintaining the stream’s function and habitat it provides. Sediments from highly eroding streambanks are a major source of pollution in a stream system and have the potential to jeopardize habitat, infrastructure, and stream function. Watershed management practices throughout the Cleveland Metroparks attempt to locate and inventory the source and rate the risk of potential streambank erosion to assist in formulating effect stream, riparian, and habitat management recommendations. The Bank Erosion Hazard Index (BEHI), developed by David Rosgen of Wildland Hydrology is a fluvial geomorphic assessment procedure used to evaluate the susceptibility of potential streambank erosion based on a combination of several variables that are sensitive to various processes of erosion. This protocol can be time consuming, difficult for non-professionals, and confined to specific geomorphic regions. To address these constraints and assist in maintaining consistency and reducing user bias, modifications to this protocol include a “Pre-Screening Questionnaire”, elimination of the Study Bank-Height Ratio metric including the bankfull determination, and an adjusted scoring system. This modified protocol was used to assess several high priority streams within the Cleveland Metroparks. The original BEHI protocol was also used to confirm the results of the modified BEHI protocol. After using the modified assessment in the field, and comparing it to the original BEHI method, the two were found to produce comparable BEHI ratings of the streambanks, while significantly reducing the amount of time and resources needed to complete the modified protocol.     

Transport and settlement of organic matter in small streams

1. After it enters streams, terrestrially derived organic matter (OM) rapidly absorbs water. Using field and laboratory experiments, we examined how this process affected the buoyancy, settling velocity, transport distance and retention locations of four types of organic matter typically found in Pacific coastal streams (‘flexible’ red alder leaves and three ‘stiff’ particle types – Douglas‐fir needles, red cedar fronds and Douglas‐fir branch pieces). 2. Immersion in water rapidly changed the physical characteristics of alder leaves, Douglas‐fir needles and red cedar fronds, which all reached constant still‐water settling velocities after only a few days of soaking. In contrast, the settling velocity of branch pieces continued to increase for 13 days, eventually reaching much higher values than any other OM type. Dried alder leaves became negatively buoyant after only two days of immersion, while other types took substantially longer (up to 24 days) before the specific gravity of all particles was >1. 3. We released saturated OM particles in an experimental channel and found that all particle types travelled further in a fast, shallow ‘riffle’ than a slow, deep ‘pool’. Comparisons with a passive settlement null model indicated that leaves were retained more rapidly than expected in the riffle (by large protruding stones), while the three stiff particle types travelled further than expected (probably due to turbulent suspension) and were retained when they settled in deeper water between larger stones. In pools, passive settlement appeared to dominate the retention of all OM types, with leaves travelling furthest. 4. These retention patterns corresponded well with those observed when saturated OM particles collected in the field were released in two pools and two riffles in a second‐order coastal stream. 5. When the experimental channel and in‐stream data were combined, the retention rates of the three stiff OM types were closely related to calculated Rouse numbers (Rouse number = particle settling velocity/shear velocity), whereas the retention rate of alder leaves was not. This suggests that different physical mechanisms are responsible for the retention of leaves and stiff OM types in shallow streams.     

The influences of climatic variation and vegetation on stream biota: lessons from the Big Dry in southeastern Australia

Aquatic biodiversity faces increasing threats from climate change, escalating exploitation of water and land use intensification. Loss of vegetation in catchments (= watersheds) has been identified as a substantial problem for many river basins, and there is an urgent need to better understand how climate change may interact with changes in catchment vegetation to influence the ecological condition of freshwater ecosystems. We used 20 years of biological monitoring data from Victoria, southeastern Australia, to explore the influences of catchment vegetation and climate on stream macroinvertebrate assemblages. Southeastern Australia experienced a severe drought from 1997 to 2009, with reductions of stream flows >50% in some areas. The prolonged drying substantially altered macroinvertebrate assemblages, with reduced prevalence of many flow‐dependent taxa and increased prevalence of taxa that are tolerant of low‐flow conditions and poor water quality. Stream condition, as assessed by several commonly used macroinvertebrate indices, was consistently better in reaches with extensive native tree cover in upstream catchments. Prolonged drought apparently caused similar absolute declines in macroinvertebrate condition indices regardless of vegetation cover, but streams with intact catchment and riparian vegetation started in better condition and remained so throughout the drought. The largest positive effects of catchment tree cover on both water quality and macroinvertebrate assemblages occurred above a threshold of ca. 60% areal tree cover in upstream catchments and in higher rainfall areas. Riparian tree cover also had positive effects on macroinvertebrate assemblages, especially in warmer catchments. Our results suggest that the benefits of extensive tree cover via improved water quality and in‐channel habitat persist during drought and show the potential for vegetation management to reduce negative impacts of climatic extremes for aquatic ecosystems.     

Ecosystem engineering by invasive exotic beavers reduces in-stream diversity and enhances ecosystem function in Cape Horn,Chile

Species invasions are of global significance, but predicting their impacts can be difficult. Introduced ecosystem engineers, however, provide an opportunity to test the underlying mechanisms that may be common to all invasive engineers and link relationships between changes in diversity and ecosystem function, thereby providing explanatory power for observed ecological patterns. Here we test specific predictions for an invasive ecosystem engineer by quantifying the impacts of habitat and resource modifications caused by North American beavers (Castor canadensis) on aquatic macroinvertebrate community structure and stream ecosystem function in the Cape Horn Biosphere Reserve, Chile. We compared responses to beavers in three habitat types: (1) forested (unimpacted) stream reaches, (2) beaver ponds, and (3) sites immediately downstream of beaver dams in four streams. We found that beaver engineering in ponds created taxonomically simplified, but more productive, benthic macroinvertebrate assemblages. Specifically, macroinvertebrate richness, diversity and number of functional feeding groups were reduced by half, while abundance, biomass and secondary production increased three- to fivefold in beaver ponds compared to forested sites. Reaches downstream of beaver ponds were very similar to natural forested sections. Beaver invasion effects on both community and ecosystem parameters occurred predominantly via increased retention of fine particulate organic matter, which was associated with reduced macroinvertebrate richness and diversity (via homogenization of benthic microhabitat) and increased macroinvertebrate biomass and production (via greater food availability). Beaver modifications to macroinvertebrate community structure were largely confined to ponds, but increased benthic production in beaver-modified habitats adds to energy retention and flow for the entire stream ecosystem. Furthermore, the effects of beavers on taxa richness (negative) and measures of macroinvertebrate biomass (positive) were inversely related. Thus, while a generally positive relationship between diversity and ecosystem function has been found in a variety of systems, this work shows how they can be decoupled by responding to alterative mechanisms. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Seabed mapping in the southern Irish Sea: predicting benthic biological communities based on sediment characteristics

Marine habitat mapping is necessary to comply with European legislation (92/43/EEC, 79/409/EEC and 2001/60/EEC), with international obligations to organizations such as ICES and with agreements such as the OSPAR Convention. Clearly defined habitats are needed before conservation and management practices can be implemented. The BIOM?R, SWISS and HABMAP projects have used sediment particle size, organic matter, organic carbon and nitrogen along with benthic macrofaunal species and abundance to define habitats in the southern Irish Sea. The sea floor of the southern Irish Sea is predominantly sandy gravel, grading down through sand to mud in the deeper parts of the Celtic Sea and similarly in the shallower northern basin beyond Anglesey. The physical gradient in particle size is correlated with organic content and also with biological communities. Nevertheless, there are marked discrepancies between boundaries defined by the Folk sediment characterization trigon, by the chemical characteristics of the sediments and by biological communities. The validity of using continuous physical and chemical sediment characteristics to more accurately predict categorical biological assemblages was tested with use of stepwise backward elimination Binary Logistic Regression (BLR). This method could be used as a tool to predict biological assemblages where there is a paucity of biological data. It lends support to the idea that benthic habitat mapping will have to take more account of biological structuring and system function. Guest editors: J. Davenport, G. Burnell, T. Cross, M. Emmerson, R. McAllen, R. Ramsay & E. Rogan Challenges to Marine Ecosystems     

Space–time interactions and invertebrate assemblage change in stream networks

Streams form hierarchical, dendritic physical networks, but relatively little is known about how this spatial structure affects community assembly. We investigated interactions between changes over time in macroinvertebrate assemblages and their distribution in space (the space–time interaction) in stream networks. Assemblages were sampled from every tributary, and every reach between tributaries, to determine effects of network position on assemblage composition, in four West Coast, South Island, New Zealand, headwater networks. Using canonical redundancy analysis, we found that macroinvertebrate assemblages were significantly spatially structured and species assemblages changed significantly between two sampling periods. The most important environmental variables (averaged over all AIC models) explaining change in assemblage composition were related to disturbance, local habitat/resources and habitat size. The lack of a significant interaction between space and time, however, indicated the spatial pattern of assemblages remained the same over time, regardless of changes in assemblage composition. Consistent spatial structuring could be the result of unchanging processes such as those arising from the universal nature of stream topology and hydrology acting both on habitat‐ and dispersal‐ related community processes. Thus, we conclude that although community assemblages changed over time, the spatial arrangement of communities could potentially be predicted from stream network topology and hydrology.     

Riffle-pool geomorphology disrupts longitudinal patterns of stream benthos

An Ozark Plateau stream was studied to determine the influence of distinct pool and riffle geomorphology on the longitudinal zonation of macroinvertebrate species assemblages and functional group classification. All study sites were dominated by alluvial pool and riffle channel form and the first two orders became intermittent during summer months. Nine benthos samples were collected seasonally from riffles and pools at each of five sites using a vacuum benthos sampler. Diel temperature pulse and coarse particulate organic matter (CPOM) were measured at each site also. Water temperature was most variable in second order, and CPOM on riffles was not more abundant in upstream reaches. Annual average density and biomass of invertebrates were highest in third and fourth orders, respectively. Diversity was depressed in the intermittent headwaters sites. Macroinvertebrate functional groups did not exhibit strong longitudinal trends as predicted by the river continuum model, with species assemblages apparently more strongly affected by the segment-level physical template, although shredders were more abundant in the headwaters during fall and winter. This study indicates that a reach-level perspective based on channel form is a necessary complement to holistic stream ecosystem models, especially in alluvial gravel streams.