Wetland soils contain a reservoir of dormant plant seeds and invertebrate eggs, collectively termed the seed or propagule bank, which integrate spatiotemporal variation at various levels of biology (genetic, phenotypic, species, and community). Several recent studies suggest that anthropogenic physical or chemical stressors may disrupt the process of emergence from propagule banks. This process is often the single most important colonization process in wetlands isolated geographically from other water bodies. The potential for disruption of emergence can be exploited as a useful indicator of anthropogenic stress. The aim of our paper is to provide a conceptual framework that shows the advantages and limitations of wetland propagule banks as indicators of anthropogenic stress or ecological integrity. This framework describes mechanistic responses of propagule banks to stressors and makes recommendations on experimental approaches for the evaluation of cause–effect relationships between stressors and propagule bank responses. This indicator could help bridge the current gap between basic and applied wetland ecology and could find application in future wetland management and restoration strategies.

Nitrification, the chemoautotrophic process by which NH₄-N is converted to NO₃-N, is an integral biogeochemical transformation in stream ecosystems. Previous research has shown that experimental addition of dissolved organic C inhibits rates of nitrification, and that NH₄-N addition stimulates rates of nitrification. In many streams, large amounts of C and N may be present in particulate and sorbed forms. Hugh White Creek, a headwater stream located in the southern Appalachian mountains of North Carolina, USA, has very low concentrations of dissolved N and receives large inputs of allochthonous particulate organic matter (POM) each autumn. We conducted a seasonal survey of organic matter (OM) standing stocks and nitrification rates, and we experimentally manipulated dissolved C and N supplies in stream-sediment microcosms to determine: 1) how rates of nitrification compare across seasons, and 2) to what extent nitrification rates are influenced by seasonal changes in standing stocks and relative abundances of particulate, sorbed, and dissolved forms of C and N. Rates of nitrification were closely and positively related to rates of ammonification which, in turn, were negatively related to C:N ratios of fine benthic organic matter (FBOM). Uniform additions of dissolved C and N had varying effects on sediment N-transformation rates during different seasons. Variable responses to experimental additions probably reflected the changing relative importance of C and N as sediment OM stocks were depleted and underwent changes in quality. Slow rates of nitrification for much of the year may be attributed to colder temperatures and large quantities of particulate C relative to N. To the extent that changes in POM stocks dictate changes in C and N availability, seasonal OM dynamics are closely linked to rates of nitrification.

Gradients in photosynthesis (P) and respiration (R) were measured on an unperturbed portion of the Rio Mameyes, a tropical stream in the Luquillo Experimental Forest, northeastern Puerto Rico. Rates of P, which were similar to those of streams in temperate-deciduous forests, were low in the heavily canopied headwaters (<70 g O₂ m⁻² y⁻¹) and were higher (453–634 g O₂ m⁻² y⁻¹) in middle and lower reaches. Periphyton biomass did not show the expected increase as the canopy opened downstream, probably because of increasing herbivory in downstream reaches. Rates of R, which were much higher than in most temperate streams, also were lower in the headwaters (767 g O₂ m⁻² y⁻¹) than in the middle and lower reaches (1550–1660 g O₂ m⁻² y⁻¹). High rates of R and suppressed periphyton abundance caused annual P/R to be ≪1 from headwaters to lower reaches. Results for the Rio Mameyes suggest that intense herbivory, which is favored by the presence of large herbivores and consistently high temperatures, may be more typical of tropical than temperate streams. Results also show that the tropical rainforest provides the stream with sufficient amounts of labile organic C to support high rates of respiration over long distances across the basin.

The effects of water-quality degradation caused by urbanization, agricultural, and industrial activities on leaf litter breakdown and associated communities of invertebrates and microorganisms were examined at 1 reference and 2 downstream polluted sites in the Ave River (northwestern Portugal). Conductivity, concentrations of NH₄ -N, NO₃⁻-N, and PO₄³⁻-P, and density of culturable microorganisms were high at the polluted sites. Rates of leaf breakdown also were high, and the highest value was found at the most-downstream, nutrient-enriched polluted site. However, the other polluted site had low current velocity and sedimentation, and nutrient enrichment did not lead to rapid leaf breakdown. Shredders were scarce or absent at all sampling sites, and low shredder density probably explained the lack of differences in leaf breakdown rates between fine-mesh and coarse-mesh bags. High fungal and bacterial production on leaves supported high leaf breakdown rates. Bacterial production was greater at both polluted sites than at the reference site, but it did not exceed 11% of the total microbial production. Fungal biomass and production were markedly different between polluted sites, with the highest values corresponding to the fastest leaf breakdown. Our findings indicate that fungi were the major decomposers in this polluted river. We encourage further research on the effects of multiple stressors on the activity of fungal decomposers to help us better understand the mechanisms underlying leaf litter breakdown in streams under stress.

Several studies in the past decade have shown that rates of ecosystem processes may be affected by the number of species involved in the processes. However, how products, such as frass and feces, that are derived from those processes indirectly affect other functional feeding groups (FFGs) and whether such effects vary with species number are not well understood. We manipulated presence/absence and species richness of shredding larval stoneflies in laboratory microcosms containing leaf litter to test whether the number of species affected the growth of suspension-feeding black fly larvae. The presence of shredders increased the production of particles (>0.1 mm) and contributed to 30 to 56% higher black fly growth than in the absence of shredders. In addition, species richness and composition of shredders significantly affected black fly growth. Thus, our results show that species richness and composition in one FFG may affect FFGs further down the processing chain, most likely via effects on both quantity and size distribution of products derived from the process.

The landscape position of a lake relative to local and regional groundwater flow patterns has important ecosystem consequences. The local hydraulic gradient sets up seepage regimes, influences hydrologic and nutrient budgets, and alters site stoichiometry (molar N:P). However, little is known about the biotic (ecological) consequences of groundwater–lake coupling. We investigated the relationship between groundwater flux (resource supply rates), resource supply ratios, and species patterns of benthic algae in Sparkling Lake, Wisconsin, USA, a north-temperate flow-through seepage lake. Nutrient fluxes of seepage waters influenced both local benthic algal biomass and species composition. Sites of high groundwater discharge (HGD) were characterized by low N:P flux, high algal biovolume, and low species richness and diversity. In contrast, low groundwater discharge (LGD) and low groundwater recharge (LGR) sites had high N:P, low algal biovolume, and high richness and diversity. HGD sites were dominated by diatoms and cyanobacteria characteristic of high P, whereas LGD and LGR sites were characterized by taxa associated with low P. Many species were unique to the local flow regimes, increasing overall benthic algal species richness in Sparkling Lake.

We examined the effects of ultraviolet radiation (UVR) (280–400 nm) on epilithic algal metabolism, biomass, and taxonomy from early June to mid August 1999 (66 d) in Lake 224, an oligotrophic lake in the Experimental Lakes Area, northwestern Ontario, Canada. Epilithon colonized bare clay tiles placed under UVR-transparent (UVR ) and UVR-shielding (UVR−) acrylic filters, at depths of 0.5, 0.8, and 1.4 m. Filamentous chlorophytes and cyanophytes were the dominant algal taxa at 0.5 and 1.4 m depths, respectively, on day 28. Biovolumes did not differ between UVR treatments for any major algal class. We measured epilithic metabolism on days 28, 45, and 66 after the tiles were deployed. Photosynthesis was not affected by UVR on any date. On day 28, dark respiration was 33 to 49% greater in UVR than in UVR− treatments at all depths. On day 45, respiration was 11% greater in UVR than in UVR− treatments only at 0.5 m, and by day 66, respiration did not differ between treatments at any depth. Thus, the effects of UVR on respiration diminished with depth and over time and were strongest when epilithic biofilms were least developed. UVR probably has little impact on naturally colonized, fully developed epilithon deeper than 0.5 m in Lake 224, i.e., UVR affects <6% of the littoral zone. Comparison of our findings with those of an earlier study in Lake 224 suggests that the intensity and specific nature of UVR effects depend on the taxonomic composition of the benthic algal assemblage.

Calcareous floating periphyton mats in the southern Everglades provide habitat for a diverse macroinvertebrate community that has not been well characterized. Our study described this community in an oligotrophic marsh, compared it with the macroinvertebrate community associated with adjacent epiphytic algae attached to macrophytes in the water column, and detected spatial patterns in density and community structure. The floating periphyton mat (floating mat) and epiphytic algae in the water column (submerged epiphyton) were sampled at 4 sites (∼1 km apart) in northern Shark River Slough, Everglades National Park (ENP), in the early (July) and late (November) wet season. Two perpendicular 90-m transects were established at each site and ∼100 samples were taken in a nested design. Sites were located in wet-prairie spikerush-dominated sloughs with similar water depths and emergent macrophyte communities. Floating mats were sampled by taking cores (6-cm diameter) that were sorted under magnification to enumerate infauna retained on a 250-μm-mesh sieve and with a maximum dimension >1 mm. Our results showed that floating mats provide habitat for a macroinvertebrate community with higher densities (no. animals/g ash-free dry mass) of Hyalella azteca, Dasyhelea spp., and Cladocera, and lower densities of Chironomidae and Planorbella spp. than communities associated with submerged epiphyton. Densities of the most common taxa increased 3× to 15× from early to late wet season, and community differences between the 2 habitat types became more pronounced. Floating-mat coverage and estimated floating-mat biomass increased 20 to 30% and 30 to 110%, respectively, at most sites in the late wet season. Some intersite variation was observed in individual taxa, but no consistent spatial pattern in any taxon was detected at any scale (from 0.2 m to 3 km). Floating mats and their resident macroinvertebrate communities are important components in the Everglades food web. This community should be included in environmental monitoring programs because degradation and eventual loss of the calcareous periphyton mat is associated with P enrichment in this ecosystem.

Caridina cantonensis Yu 1938 is an atyid shrimp that is widespread in southern China, including Hong Kong. It is a fully freshwater species with an abbreviated larval development lacking planktonic stages. The population genetics of C. cantonensis in Hong Kong streams was studied at inter- and intradrainage scales using random amplified polymorphic DNA (RAPD) markers. Shrimps displayed low levels of within-population genetic variation (≤20% of total genotypic variance) but high levels of among-population variation (>50% of total genotypic variance) at both scales. High interdrainage genetic differentiation indicated that dispersal among catchments was limited, whereas high differentiation among populations at the intradrainage scale mainly resulted from natural barriers such as waterfalls. The effect of man-made barriers on population differentiation at the intradrainage scale was less marked than at the interdraineage scale. Levels of gene flow among populations within and among drainage systems were low, the estimated number of effective migrants/generation (N_em) was <0.1, and there was a trend toward relatively fewer alleles and lower heterozygosity in upstream populations than in downstream populations. Genetic differentiation between lowland populations from adjacent drainages was lower than for other pairwise combinations of populations, suggesting that interdrainage dispersal is likely during floods. The genetic structure of C. cantonensis populations in Hong Kong streams indicates that adaptation to local conditions in individual streams or sites within streams probably occurred. At a regional scale, this process might account for the large number of stenotopic species of Caridina in Asia.

Many shallow aquatic ecosystems with high nutrient loads experience periods of O₂ depletion that evoke behavioral responses by macrobenthic organisms. The sediment-dwelling midge larva Chironomus riparius reduces its deposit-feeding activity and allocates more time to burrow ventilation during periods of hypoxia. We investigated another striking behavioral adaptation of this species, i.e., the elongation of U-shaped sediment burrows to chimneys that tower above the sediment surface. Chironomus riparius larvae gradually abandoned burrow construction and took up chimney construction when exposed to hypoxic conditions in laboratory microcosms. Microsensors were used to show that the chimneys were oxic sediment compartments that were periodically irrigated by the larvae with oxygenated surface water. O₂ uptake rates per unit interface area were significantly higher for chimneys than for the flat sediment surface. This observation was consistent with the dense colonization of the chimneys by bacteria. Chimneys may facilitate the larval acquisition of both O₂ for respiration and microbial biomass for food. Given the mass abundance of C. riparius in many polluted and O₂-deficient habitats, the chimneys also may contribute significantly to the patchiness of the benthic microbial community in terms of structure and function. In particular, the presence of chimneys might favor aerobic bacterial populations and their metabolism.

Ceraclea joannae, new species, feeds on the freshwater snail Somatogyrus virginicus Walker (Hydrobiidae). Our study is the first report of prey other than sponges for a Ceraclea species and the first report of snail predation by Trichoptera larvae in North America. Ceraclea joannae larvae and adults resemble those of C. diluta (Hagen); however, the larva of the new species has a dark head, sickle-shaped mandibles, and a dark pronotum except for a pair of unique, conspicuous, oblique, white bands; the male differs in the slightly longer superior appendages, more nearly straight ventral margins of tergum X, slightly stouter inferior appendages, and the more-tapered apex and less-pronounced ventral notch of the phallus. This new species of Ceraclea is known from only 3.2 km of the Little River (Montgomery County, North Carolina, USA), downstream of the developing town of Asheboro. Because of its rarity and limited distribution, Ceraclea joannae may be highly vulnerable to changes in water or habitat quality.

We measured shell length, hinge length, and height of glochidia from 21 freshwater mussel species occurring in the Sipsey River, Alabama, to test our ability to identify species based on these glochidial morphometrics. Glochidial size and shape differed widely among species; for all 3 dimensions, mean values for the largest species were 5 to 7× greater than for the smallest species. Within-species variation in glochidia size was low for all species with the exception of Pleurobema decisum, which was represented by 2 glochidial morphotypes; variation within each morphotype was similar in magnitude to variation within other species. We were able to classify 72 to 79% of total glochidia (n = 870 or 750, respectively) to the correct species with discriminant function analysis. Percentage of correct classification ranged from 40 to 100% for individual species. Misclassifications were caused by overlap in shell dimensions between some species, but even species with poor classification success were confounded with an average of only 2.2 to 3.0 other species. Unlike previous studies, we found that glochidia of closely related species were not necessarily more similar to each other than to glochidia of more distantly related species. For example, species in the tribe Quadrulini were widely divergent in glochidium size and represented some of both the smallest and largest glochidia in our study. These 3 shell measurements and subsequent application of discriminant function analysis can be useful for identification of unknown glochidia or for rapidly narrowing the range of potential species identifications to smaller groups of species with similar glochidia.

Meiofauna are potentially capable of controlling microphytobenthic biomass. Grazing by copepods in high densities has been hypothesized to lead to successional changes in algal assemblages toward less-edible algal species with consequent effects on copepod survival and growth. In our study, adult Attheyella trispinosa were offered monospecific algal films of 3 benthic diatom species and 1 benthic cyanobacterial species and algal assemblages consisting of different combinations of these species. Changes in abundances of algal species were observed over 17 d. Nauplii of A. trispinosa and Bryocamptus minutus were grown with a similar range of algal assemblages supplied as food, and their survival and development rates were measured. Feeding by A. trispinosa decreased the density of the diatom Nitzschia perminuta, whereas biomass of all other diatom species generally was unaffected by copepod feeding. The biomass of the cyanobacterium Leptolyngbya foveolarum was either unaffected or slightly enhanced by copepod feeding. Nevertheless, the architecture of the algal assemblages changed. Leptolyngbya foveolarum was ingested and partly digested by the copepods, and copepods were able to develop on this diet. However, L. foveolarum alone or combined with diatoms reduced the survival and development rate of nauplii and diminished copepodid sizes of A. trispinosa and B. minutus. Our results suggest that these algal species can exert a strong effect on harpacticoid copepods. Specific effects of copepod grazing on bispecific algal assemblages were masked to a large extent by the interactions among autotrophic species. In contradiction to our hypothesis, copepods grazing on L. foveolarum altered the physiognomy of algal assemblages and promoted the persistence of (edible) diatom species otherwise overgrown by L. foveolarum of lower food quality.

Recent comparative studies suggest that macroinvertebrates in small Boreal Plains lakes respond to large fluctuations in fish densities caused by winterkill and subsequent recovery even when such fluctuations involve the normally piscivorous northern pike (Esox lucius). We introduced pike into a boreal lake made fishless by a past winterkill to isolate experimentally the effects of pike on littoral macroinvertebrates. We compared postmanipulation macroinvertebrate data from the experimental lake (EXP) to premanipulation data from the same lake, to parallel data from 2 unmanipulated reference lakes (R1 and R2) containing pike, and to data from mesocosms within EXP. Pike in all 3 lakes preyed heavily upon macroinvertebrates; diets consisted predominantly of the amphipod Gammarus lacustris in R1 and R2 and erpobdellid leeches in EXP. Principal components analysis (PCA) of macroinvertebrate communities distinguished between systems with and without fish and detected a shift in the macroinvertebrate community of EXP and predator-exposed control mesocosms away from large conspicuous taxa (e.g., odonates, coleopterans, and leeches) toward less-conspicuous taxa such as dipterans and trichopterans following manipulation. Responses of individual taxa were generally in agreement with PCA; erpobdellid leeches and odonates showed consistent negative responses to pike. Our study provides experimental evidence at the whole-lake scale that northern pike can affect littoral macroinvertebrates in small boreal lakes, and demonstrates the sensitivity that littoral food webs in these systems can have to changes in the density of fish.

The effects of the intensity of seasonal droughts on stream ecosystems were studied in the Fuirosos, an intermittent forested Mediterranean stream. Macroinvertebrate community structure and stream ecosystem metabolism were measured during seasonal summer droughts in 2001, 2002, and 2003. Ecosystem metabolism was profoundly affected by stream intermittency. Organic matter that accumulated during the dry period enhanced ecosystem respiration during the postdrought recovery. Highest biotic diversity was found at low water levels as the stream dried and contracted. Macroinvertebrate community response to drying was stepped and apparently defined by thresholds of transition from drying to cessation of flow and from the dry phase to restoration of flow. Environmental conditions changed markedly with cessation of flow, causing large changes in community structure during 2001 and 2003 (dry years). Drying caused an increase in macroinvertebrate density that peaked in isolated pools soon after flow ceased, but then decreased rapidly because of the physicochemical changes associated with fragmentation of the watercourse. The macroinvertebrate community at the end of the summer dry phase (when flow resumed) differed from the community that had been present before drying began. Differences in community structure during the summer dry period were not as marked in 2002 (a wet year) as in 2001/2003. The influence of drought on the macroinvertebrate community differed across substrata. Drying led to significant changes in density on cobbles and leaves, but not on sand. Few taxa resisted drying, and resilience to drying was the dominant response to disturbance in the Fuirosos.

Although spatial scale, upstream–downstream gradients, environmental variability, and floodplain connectivity and complexity have been recognized as integral components of our understanding of riverine pattern and process, aquatic invertebrate community structure across lateral gradients from headwaters to the lowland of a river has received little empirical documentation. Aquatic invertebrate density, distribution, and richness were investigated at 29 study sites distributed laterally (main channel–floodplain) among 6 geomorphologically distinct river reaches from the headwaters to near the mouth of one of the last seminatural river corridors draining the European Alps, the Tagliamento River in northeastern Italy. Community relationships were examined using multivariate and diversity analyses to investigate patterns of taxonomic richness. Diversity parameters were scaled at the site, reach, and catchment levels to better understand local and regional patterns. Mean invertebrate density increased from 7484 ± 2480 (±1 SE) individuals/m² in the headwaters to 98,811 ± 18,037 individuals/m² on the lowland floodplain. Crustacea, Coleoptera, and Ephemeroptera richness increased and nonchironomid Diptera and Plecoptera richness declined along the corridor. Richness (α diversity) and turnover (β diversity) showed no consistent increase or decrease along connectivity gradients within geomorphic reaches along the river corridor, possibly because each reach had unique characteristics. α diversity was similar among geomorphic reaches along the corridor, whereas β diversity between reaches increased as a function of distance between them. Direct gradient analysis indicated high taxa-to-environment concordance along lateral (i.e., floodplain water bodies) and longitudinal (upstream–downstream) dimensions and indicated distinct floodplain communities. These results demonstrate how lateral gradients (floodplain dimension) structure zoobenthic communities and how this structure can change along the longitudinal dimension (upstream–downstream). Our results highlight the importance of off-channel environments to macroinvertebrate community structure and diversity. Conservation, restoration, and preservation measures must consider the lateral dimension along river corridors as integral to maintaining diversity and community structure.

Landuse change alters the quantity and supply of stream energy resources from allochthonous (catchment-derived) to autochthonous (stream-derived) sources. This alteration has prompted the need for better understanding of C and N pathways through stream food webs. We added stable ¹⁵N-NH₄ and ¹³C-acetate isotopes as tracers to experimental stream channels containing 1 of 4 key basal food resources: autotrophic epilithon, heterotrophic epilithon, fine particulate organic matter (FPOM), and coarse particulate organic matter (CPOM). Our goal was to evaluate the importance of these foods to 2 scrapers (Deleatidium sp. [mayfly] and Potamopyrgus antipodarum [snail]) and a facultative shredder (Olinga feredayi [caddisfly]). A 5^th potential food source, new heterotrophic biofilm, grew on all surfaces during the course of the experiment. Isotope levels in the food resources and the invertebrates were measured weekly during the 3-wk isotope addition and for 2 wk after the addition. Changes in nutrient concentrations between the channel inflows and outflows provided measures of instream net uptake. Net uptake of P by autotrophic epilithon (mean = 0.09–0.24 mg dissolved reactive P [DRP] m⁻² h⁻¹) was 3× higher than uptake by other basal resources. Autotrophic epilithon removed substantial quantities of dissolved N, predominantly as NO₃-N (2.1–9.3 mg NO₃-N m⁻² h⁻¹), whereas the other basal resource types removed only NH₄-N at a rate that was 2 orders of magnitude slower (mean = 0.04–0.08 mg NH₄-N m⁻² h⁻¹) than uptake by autotrophic epilithon. NH₄-N and dissolved organic C isotope tracers were taken up predominantly by heterotrophic epilithon and new biofilms. We developed a dynamic mixing model to separate the contribution to the invertebrates of each treatment food source relative to the new heterotrophic biolfilm. Mayflies obtained almost 100% of their body C and N from new biofilm except when offered autotrophic epilithon, which contributed >50% to their diets. Olinga and Potamopyrgus obtained most of their C and N from the treatment food sources, but in the particulate organic matter treatments (FPOM and CPOM) the contribution of new biofilm was much larger (∼10–60%). Our results suggest that heterotrophic biofilms are a significant component of stream food webs.

The term rare has spatial and temporal, as well as conservation and management, connotations when applied to ecological surveys. We examined the frequency of temporal occurrence of benthic macroinvertebrates in 19- to 20-y survey collections from 4 sites and 7- to 8-y survey collections from 6 sites in northern California streams. We found that a large proportion of taxa (17–33%) were rare (occurred in only 1 y) in all of the sites examined, regardless of season, and that density increased with increasing temporal commonness. Taxa that could be identified only to higher taxonomic levels, i.e., unresolved taxa, were an additional component (0–7%) of the rare species encountered. The biological traits of the rare and common taxa generally provided explanations for the cause of rarity or commonness, e.g., common taxa tended to have short life cycles with multiple generations per year and rare taxa had low dispersal capabilities. The results of our study clearly demonstrate that temporally rare taxa are common in long-term benthic macroinvertebrate surveys; this prevalence may require re-examination of how long-term surveys are interpreted in both ecological studies and biomonitoring.

We developed an Index of Biotic Integrity (IBI) for the Interior Plateau Ecoregion (IPE), USA, which assessed effects of human disturbance on the biotic condition of stream diatom communities. We selected 7 metrics from 59 diatom attributes at reference and impaired sites (training sites), based on significant differences between site groups using the Mann–Whitney U test, high separation power, and a low coefficient of variation. We calculated IBIs by summing metrics for a site after transforming them to a discrete 1, 3, 5 scale or a continuous 0–10 scale. Both discrete and continuous scaling systems successfully separated reference and impaired sites, and IBI scores were significantly related to agricultural land use in IPE watersheds. We then tested the diatom IBI using a 2^nd data set from IPE streams (test sites), processed by slightly different sampling methods and taxonomic references, and classified sites as reference or impaired based on the same criteria used for the training-site data set. Diatom IBI scores differed significantly between reference and impaired streams and correctly classified 80% of sites in the test-site data set. Compared with other diatom IBIs, our measure showed higher separation power among sites and provided an accurate characterization of stream impairment in study watersheds. The developed diatom IBI can be a useful tool for stream and watershed management.