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A sample from a 2019 cyanobacterial bloom in a freshwater reservoir in eastern Oregon, USA, was used to produce a metagenome from which the complete, circular 7.3 Mbp genome of Limnoraphis sp. WC205 was assembled. The Limnoraphis sp. WC205 genome contains gas vesicle genes, genes for N

Burnet SH, Wilhelm FM. 2021. Estimates of internal loading of phosphorus in a western US reservoir using 3 methods. Lake Reserv Manage. XX:XXX–XXX. We used 3 methods to estimate internal loading of total and dissolved phosphorus (TP/DP) in 2 years in a stratified eutrophic western US reservoir with high internal loading of phosphorus. We calculated the internal load from (i) net increases of TP/DP from reservoir water column samples, (ii) gross TP mass balances, and (iii) gross TP/DP loading estimated from laboratory-incubated sediment cores and the anoxic reservoir area. We also present a cost comparison and spreadsheet to allow managers to estimate costs for each method. The highest internal loads were estimated in 2015 from the net in situ samples (999 mg/m2/yr) and the gross annual mass balance (850 mg/m2/yr). Gross estimates from sediment cores were 1.2× higher in 2015 than in 2014 due to differences in anoxic area resulting from a drought and record reservoir drawdown. Costs were highest for the mass balance method and lowest for the sediment core method. Given the small monetary difference between the sediment core and in situ methods, we suggest managers obtain in situ data to estimate internal loading because this yields a net estimate most reflective of whole-lake dynamics. Our data provide an important benchmark of internal loading in a human-made reservoir given the general paucity of such estimates in this large geographic region.

The oxidation state of sulfur [S] is a primary control on mobility of metals in sediments impacted by legacy mining practices. Coeur d&rsquo, Alene Lake of northern Idaho, USA, has been impacted by upstream legacy mining practices that deposited an estimated 75 Mt of metal(loid)- and S-rich sediments into the lake. Future lake conditions are expected to include algal blooms, which may alter S and metal remobilization during the seasonal euxinic environment. Cores of the lake sediments were exposed to anoxic and anoxic + algal detritus conditions for eight weeks at 4.5 &deg, C through introduction of a N2 atmosphere and addition of algal detritus. At a location 2.5 cm below the sediment-water interface, anoxic conditions promoted a shift in S species to continually larger concentrations of reduced species and an associated shift in the bonding environment reflective of increased S&ndash, metal bonds. Anoxic + algal detritus conditions suppressed the increasing trend of reduced S species and induced greater release of Mn compared to the anoxic-only conditions but did not appear to enhance the release of As, Cd, or Fe. The addition of algal detritus to the sediment-water interface of these Fe- and S-rich sediments enhanced mobilization of Mn likely because of dissimilatory metal reduction where the anaerobic oxidation of the algal detritus stimulated Mn reduction. Results of the study indicate that future metal release from the lake sediments will be altered with the likely deposition of algal detritus, but the effect may not enhance the release of acutely toxic metals, such as As or Cd, or substantially impact Fe cycling in the sediments.

Establishment of non-native species can alter native species populations and restructure lake food webs through complex tropic interactions such as intraguild predation or classic trophic cascades. Although the freshwater shrimp Mysis diluviana is well known for its ability to impact both primary and secondary productivity through omnivorous feeding in aquatic ecosystems in which it has been introduced, empirical evidence of mysid consumption of zooplankton prey and associated impacts on cladoceran communities from the same lake is uncommon. Furthermore, recent literature has suggested that mysids may impact other zooplankton populations outside of cladocerans. To test the hypothesis that introduced mysids negatively affect the seasonal abundance of cladocerans in Lake Pend Oreille, a large and deep (348 km2, max. depth: 352 m) lake in Idaho, USA, we quantified the seasonal diet and consumption rates of mysids and compared them with cladoceran production rates. During isothermal conditions, mysids opportunistically fed on copepods, diatoms, and rotifers. However, during stratification, mysids strongly selected cladocerans. In addition, during isothermal conditions, mysids consumed 100% of cladoceran production and selected reproductive-sized individuals. We interpret this to show that mysids regulate the production of cladocerans when the lake is not stratified. The suppression of cladocerans in the spring coincides with the appearance of kokanee (Oncorhynchus nerka) fry whose growth and survival may be negatively affected by the lack of abundant cladocerans, a preferred prey. This suggests a possible cascading effect to higher trophic levels.

Nitrate is a significant water pollutant with potential environmental impacts ranging from eutrophication to health risks to infants. But under certain circumstances nitrate may enhance water quality through a number of mechanisms, including enhancing oxidant capacity, regulation of redox potential, and suppression of nitrogen-fixing cyanobacteria. In this review the authors explore a range of case studies in which nitrate addition enhanced surface water quality including: purposeful addition of nitrate salts to lakes to repress internal phosphorus (P) loading, enhance organic matter oxidation, or impede bottom-water accumulation of methylmercury; purposeful and incidental addition of nitrate from point and nonpoint discharges to reservoirs and lakes; nitrogen (N) addition to lakes to affect phytoplankton and zooplankton composition; and nitrate addition to estuary sediment to repress hydrogen sulfide production. Nitrate addition decreased internal P and methylmercury loading, repressed sulfide pr...

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A global dataset was compiled to examine relations between the total nitrogen to total phosphorus ratio (TN:TP) and microcystin concentration in lakes and reservoirs. Microcystin concentration decreased as TN:TP ratios increased, suggesting that manipulation of the TN:TP ratio may reduce microcystin concentrations. This relationship was experimentally tested by adding ammonium nitrate to increase the TN:TP ratio in large-scale (70 m3), in situ mesocosms located in a eutrophic reservoir that routinely experiences toxic blooms of cyanobacteria. At a TN:TP ratio >75:1, chlorophytes dominated the phytoplankton community in the mesocosms, while cyanobacterial biovolume was significantly reduced and microcystin was not detected. In contrast, the unmanipulated reservoir was dominated by cyanobacteria, and microcystin was detected. Secchi depths were 1.1 to 1.8 times greater in the mesocosms relative to the reservoir. Cladoceran zooplankton had a larger body size (0.14 mm on average) in the mesocosms com...

Recent studies suggest that nitrogen additions to increase the total nitrogen:total phosphorus (TN:TP) ratio may reduce cyanobacterial biovolume and microcystin concentration in reservoirs. In systems where TP is >100 μg/L, however, nitrogen additions to increase the TN:TP ratio could cause ammonia, nitrate, or nitrite toxicity to terrestrial and aquatic organisms. Reducing phosphorus via aluminum sulfate (alum) may be needed prior to nitrogen additions aimed at increasing the TN:TP ratio. We experimentally tested this sequential management approach in large in situ mesocosms (70.7 m3) to examine effects on cyanobacteria and microcystin concentration. Because alum removes nutrients and most seston from the water column, alum treatment reduced both TN and TP, leaving post-treatment TN:TP ratios similar to pre-treatment ratios. Cyanobacterial biovolume was reduced after alum addition, but the percent composition (i.e., relative) cyanobacterial abundance remained unchanged. A single ammonium nitrate...

Amenity value of water resources has become a major driving force of recent population growth in the region centered on Coeur d’Alene Lake in northern Idaho, USA. Despite regulatory measures aimed to protect lake water quality, surface water quality is increasingly threatened by lakefront development and invasions of Eurasian watermilfoil (Myriophyllum spicatum), a non-indigenous aquatic plant species. We used hedonic modeling to estimate the effects of ambient water quality and the presence of Eurasian watermilfoil on lakefront property values of single-family homes in the Coeur d´Alene area. We find that property values are positively associated with Secchi depth (a proxy of water quality or clarity), and negatively related to the presence of watermilfoil. Results of spatial regime analysis indicate the geographical variations of these associations. The presence of watermilfoil was related to a 13% decline in mean property value, corresponding to $64,255 USD, on average, lower property sales price. Our study demonstrates that proactive mitigation approaches to cope with potential environmental degradation in lake ecosystems could have significant economic benefits to owners of lakefront properties and local communities.

To analyze the stable isotope ratios of small-bodied invertebrates, the entire animal is typically sacrificed and processed, which is problematic for threatened or endangered species. Appendages which are regenerated could be used to infer whole-body isotope ratios, but differences in turnover rates and isotopic signatures among tissues may confound such an approach. We tested the hypothesis that the δ13C and δ15N of whole-body tissue for freshwater amphipods could be predicted from the δ13C and δ15N of walking legs, with the goal of estimating body δ13C and δ15N of Gammarus acherondytes, a United States federally endangered species. To test this, we analyzed the δ13C and δ15N of walking legs and bodies of five species of amphipods from geographically distant areas (Idaho, Illinois, and Washington) in the United States. The general relationships of whole-body isotope ratios of C and N as a function of leg isotope ratios were linear and had slopes of one. In the range of the data, leg δ13C was slightly lower than body δ13C, indicating some tissue-specific fractionation, while δ15N was similar for legs and bodies. Our data suggest that legs can be used to predict body isotope ratios in freshwater amphipods. This approach provides an additional tool to help researchers understand the biology of small, endangered invertebrates without sacrificing individuals. This is especially useful in cave ecosystems where populations are naturally sparse.

Amphipods play important roles in the cycling of nutrients and energy in many aquatic systems where they display a wide range of feeding modes ranging from detritivore to predator. Although the biology of many amphipod species has been examined, little is known of hypogean amphipods inhabiting cave streams. Gammarus troglophilus is a stygophilic amphipod that co-occurs with the federally endangered stygobiont G. acherondytes in cave streams of the Salem Plateau Karst Region of southwestern Illinois. With the goal to establish a self-sustaining laboratory population of cave amphipods to obtain amphipods for lethality experiments, we tested hypotheses relating the survival and growth rates of G. troglophilus collected from cave streams to different laboratory conditions of food and water velocity. We used a series of microcosm experiments to test the hypotheses that survival and growth are not affected by type of water (cave water vs. amended water), water velocity (static vs. dynamic/recirculating...

The ability to distinguish sex using secondary rather than primary sexual characteristics allows the reduction or elimination of handling organisms, an advantage with rare and/or fragile species. Based on observations of differences in the morphology of gnathopods 1 and 2 of male and female cave amphipods, Gammarus acherondytes and Gammarus troglophilus, we tested the hypothesis that gnathopod morphology could be used to identify sex. To examine the size at which gnathopod metrics allowed reliable identification of sex and to establish predictive relationships, we recorded sex, total body length, and the length and width of propodi from museum collections. In an attempt to test these predictive relationships with an independent data set, we discovered that relationships were species and population specific, even after accounting for shrinkage in the preserved samples. Sex could be most successfully distinguished for G. acherondytes from Reverse Stream Cave using propodus 1 length, while for G. troglophilus it was propodus 2 length. Because regression lines of relationships diverged for G. troglophilus from Fogelpole Cave, all metrics except propodus 1 length were predictive. Although gnathopod dimorphism was limited to large individuals, it was much faster than examining individuals for the presence of penal papillae or oostegites. Thus, using gnathopod morphology to determine sex may be adequate for some studies.

Worldwide, conservation personnel must balance the needs of endangered species and humans. Studies that provide information of a species’ genetic structure can identify conservation units and help prioritize populations. We used a region of the cytochrome c oxidase subunit I gene to examine the population genetics of the U.S. federally listed Illinois cave amphipod, Gammarus acherondytes. Eleven unique haplotypes were identified from nine populations in two hydrologically separate subregions, each of which contained genetically distinct populations. This conclusion is based on (i) subregions form clades in the interspecific phylogeographic analyses; (ii) the between-subregions component in the Analysis of Molecular Variance accounted for a significant fraction (81.45%) of the genetic variation; and (iii) no haplotypes were shared between subregions. These results coincide with the known distribution of G. acherondytes and regional hydrology. We recommend future recovery efforts avoid mixing individuals between subregions to prevent the breakdown of local adaptive gene complexes.

We compared historical (1977–1980) and recent (1997–2001) abundance, catch-per-unit-effort (CPUE), and growth data to assess whether the implementation of restrictive sportfishing regulatory regimes in the 1990s led to changes in abundance and population structure of bull trout Salvelinus confluentus in two small Rocky Mountain lakes in Alberta, Canada. For remote Harrison Lake, we used changes in gill-net CPUE to infer a fivefold increase in bull trout abundance after closure of an access road and implementation of catch-and-release (CR) regulations. Bull trout growth rates decreased as their abundance increased. All large (fork length > 420 mm), old (age >12) bull trout were eliminated after regulatory changes were imposed. Reductions in prey abundance and size as bull trout abundance increased probably contributed to the demise of the large bull trout. For road-accessible Osprey Lake, no change in bull trout mark–recapture abundance estimates or growth rates were observed despite implementatio...

We examined the seasonal diet of juvenile (≤32 mm total length) common bullies, Gobiomorphus cotidianus, in Lake Waihola, South Island, New Zealand and whether they preyed selectively on the amphipod, Paracalliope fluviatilis, which was a dominant prey item. Generally, ≥75% of all fish sampled had consumed amphipods, which comprised 80%, or more, of the total prey volumes in fish stomachs over most of a year except on one sampling occasion. Copepods, snails, chironomids, Daphnia, mysids and isopods also contributed to the diet. Comparisons of the size distribution of amphipods in fish stomachs and the lake on the date of sampling showed that on four occasions, juvenile bullies selectively consumed small amphipods. No selective feeding was detected on the other occasions. The dominance of primarily benthic amphipods in the diet of juvenile bullies which, in turn, are preyed on by piscivores, suggests a strong benthic-pelagic link in the transfer of energy in Lake Waihola.

Many cave species exhibit k-selected life history characteristics, i.e., long life span, slow growth, and low reproductive effort, which can reduce their ability to survive rapid changes in environmental conditions and their potential for recovery from events that reduce their densities. In this study, we examined aspects of the life history, growth rate, and reproductive timing of the U.S. federally listed Illinois cave amphipod, Gammarus acherondytes, to assess its potential for recovery. Sampling between October 2003 to March 2005 with non-lethal techniques in Reverse Stream Cave, Illinois, U.S.A. showed that pre-juveniles and juveniles generally constituted > 50% of the population and thus strongly influenced fluctuations in population density. Except in September 2004, ovigerous females were collected every month, indicating that reproduction occurred year-round. Distinct peaks of pre-juveniles were observed from February to May and August to October. The seasonal recruitment of young appear...

The use of clove oil as a potential anaesthetic for freshwater amphipods was examined at 20 °C. Individuals of Gammarus minus, a common species in southern Illinois, USA, spanning the entire body size range (4.3–14.3 mm), were used to test four anaesthetic concentrations varying from 1.48 × 10−4 ml ml−1 to 5.9 × 10−4 ml ml−1. Small-bodied individuals (mean size = 5.4 mm ± 0.27SE) were used to test additional concentrations, up to 14.7 × 10−4 ml ml−1, a 10-fold span, to identify potential lethal concentrations. At the lowest concentration, time to anaesthesia and recovery was constant at all body sizes. For the three next higher concentrations, time to anaesthesia decreased with increasing concentration while recovery time increased. Activity of amphipods was not affected by the ethanol carrier. In addition, activity did not differ between amphipods that had recovered from anaesthesia and unexposed amphipods. At clove oil concentrations of 8.84 × 10−4 ml ml−1 and 14.7 × 10−4 ml ml−1, mortality was 7 and 40%, respectively, indicating, that 5.9 × 10−4 ml ml−1 was a safe working concentration. No mortality was observed with Gammarus acherondytes, a federally endangered cave amphipod on which the protocol with 80 μl of stock was used in the field. The method enabled us to obtain information on the endangered amphipod which normally would have required the sacrifice of individuals. Thus, research can continue on species for which population numbers are low and for which basic information is needed to formulate meaningful recovery plans.

SUMMARY 1. Reduced metabolic rate among cave organisms compared with surface species has long been suggested as an adaptation to food shortage in cave environments. However, comparisons of metabolic rates between species have not often included closely related surface and cave species. By measuring metabolic rate across three seasons and over a range of body sizes, we examined the hypothesis that the routine metabolic rate of Gammarus acherondytes, a federally listed stygobitic amphipod, is lower than that of the closely related stygophilic Gammarus troglophilus. To determine if human activities increased the supply of organic matter to caves, we also examined the relationship between residential development and bacterial contamination in water wells. 2. For G. acherondytes, the slope of the overall relationship between oxygen consumption and body dry mass did not differ from zero and did not vary seasonally, whereas for G. troglophilus it was positive and higher in summer than in winter and spring. These results provide insights into a potential novel metabolic adaptation among stygobites. Higher metabolic rate in young G. acherondytes would allow efficient use of typically transient energy sources and a low metabolic rate at larger body sizes would increase survival through periods of food scarcity. 3. The number of wells with faecal coliform contamination was weakly but positively correlated with the number of residential building permits, indicating that surface landuse changes probably increase the availability of energy in groundwater systems inhabited by G. acherondytes. This may give stygophilic animals, with higher metabolic rates, a competitive advantage in the caves, thus reducing the abundance of stygobites such as G. acherondytes.

The removal of rare or endangered individuals from wild populations for evaluation of genetic composition may have deleterious consequences to these populations. As a viable alternative, we recommend limb removal as a means to obtain tissue for genetic analysis of rare amphipods. The effect of limb amputation on the survival of amphipods has not been previously studied. Our experiments showed that survival of Gammarus troglophilus, a common amphipod of Midwest caves and springs, was similar (p=.74) between control (unmanipulated) and experimental (amputation of 1 or 2 of the walking legs, pereopods 5 through 7) groups of amphipods. After 42 d, 25 of 26 amphipods in the experimental group had regenerated limbs that were half the size of the original appendage. Post-amputation survival could allow sampling of tissue for genetic analyses without sacrificing individuals, an important asset when working with species that are endangered or for which population sizes are very small.

Invertebrates that brood eggs or offer parental care to developing embryos incur a cost of reproduction in addition to that associated with the production of eggs. This additional cost is difficult to quantify but it is important in shaping the reproductive strategy of organisms and for evaluating their life history trade-offs. I used lipid analyses to determine the energy expended by female amphipods during the incubation of eggs. Lipid levels in female Gammarus lacustris during incubation of eggs dropped from 18.2% after egg deposition into the brood pouch to 8.4% when young were released. This decrease equalled 13.0 J and was similar to the 14.6 J in lipid energy in the eggs.

Interactions between mysids and invertebrates other than pelagic zooplankton have not been well studied. We tested the hypothesis that the mysid Tenagomysis chiltoni preys on the co-occurring amphipod Paracalliope fluviatilis in laboratory experiments. In prey size preference experiments with single prey species, male and female T. chiltoni consumed more small than large amphipods in the absence of the macrophyte Elodea canadensis, but were not selective when macrophytes were present. When offered small and large Daphnia, T. chiltoni males consumed more small than large Daphnia, whereas female T. chiltoni did not show any preference. When amphipods and Daphnia of similar size were presented together, male T. chiltoni strongly selected Daphnia in the presence and absence of E. canadensis, whereas female mysids did so only in the presence of macrophytes. The total number of prey consumed by each sex did not differ between macrophyte treatments. However, female T. chiltoni, which are larger than males, consumed more prey than males. These data suggest that mysids may be an important source of mortality to the amphipod P. fluviatilis. Mysids may also prey on amphipods in other aquatic systems where they co-occur.

We examined the effect of experimental scale on the predation rate of Gammarus lacustris preying on Daphnia middendorffiana in 20 l cubitainers, 2800 l mesocosms and diurnal whole-lake surveys. The predation rate differed significantly among experimental scales. It was highest in the 20 l cubitainers, intermediate in the 2800 l mesocosms and lowest in the lake. At all experimental scales, the predation of G.lacustris on D.middendorffiana increased as a linear function of prey density (Type I functional response). Very different predation rates were calculated for the whole lake depending on whether D.middendorffiana densities were estimated from whole-water column hauls or stratified depth hauls. This highlights the importance of accurately determining the spatial distribution of prey for estimating reliable in situ predation rates. We also determined prey selection by G.lacustris. Daphnia middendorffiana was strongly selected over the calanoid copepod Hesperodiaptomus arcticus. When presented with different sized Daphnia, G.lacustris preyed size selectively on indi- viduals ≥2 mm. Our results show that the predation rate of small invertebrate predators is sensitive to a wide range of experimental conditions and needs to be corroborated at a variety of scales. We conclude that the impact of G.lacustris on zooplankton communities would be strongest in small fishless lakes or ponds.

1. The number of eggs, their size, mass and development time, and the starvation time of newly hatched young, was examined in four populations of Gammarus lacustris along an elevation gradient from prairie to alpine lakes (730 m to > 2300 m above sea level). Water temperature and ice-free season decreased with increasing altitude. 2. Females in the alpine lake produced fewer but larger and heavier eggs than females in the prairie lake. Eggs produced by females in montane and subalpine lakes were intermediate in size, mass and number. Within populations, egg size was not related to the number of eggs or female size. 3. The development time of eggs declined with an increase in incubation temperature. At all incubation temperatures, large eggs had a longer incubation time than small eggs. All eggs incubated at 4 °C failed to produce young. Young from large eggs were larger in size than young from small eggs. 4. The starvation time of newly hatched young increased with decreasing temperature. However, slopes of regressions relating starvation time to temperature differed among populations. At 4 °C young from large eggs survived longer than young from small eggs. 5. The high phenotypic plasticity in reproductive traits contributes to the success of G. lacustris in a wide range of aquatic habitats. It is predicted that in response to climate-induced warming, populations in currently cold montane and alpine lakes would shift their reproduction to produce more eggs of smaller size. However, the accurate prediction of the fate of populations between ecoregions will require knowledge of the extent to which these traits are under genetic control.

We investigated the seasonal diet of a native, undisturbed population of bull trout Salvelinus confluentus in an alpine lake to examine predation patterns between fish size-classes and in relation to available invertebrate prey. The diets of small (≤250 mm in fork length, FL) and large (>250 mm FL) bull trout were similar. Bull trout fed on seasonally abundant prey species. After ice-out in July, the diet was dominated by chironomid pupae. Daphnia pulex var. and the amphipod Gammarus lacustris dominated the diet in August and September. Both Daphnia and Gammarus reproduced before bull trout switched to preying on them in early August. Bull trout fed size-selectively on large individuals of both Daphnia and Gammarus. Large bull trout preyed on larger Daphnia than did small bull trout. Fish of both size-classes consumed large Gammarus. Bull trout were spatially segregated; small fish occupied shallow water (

We estimated the net P transport by Gammarus lacustris from the benthic to pelagic regions of a fishless alpine lake and compared it with P regeneration by the entire plankton community. Gammarus lacustris released between 5.2 and 18.1 ng P·L-1·h-1 (adults only and adults plus immatures, respectively) in the pelagic region during nighttime vertical migration. Additional P released into and removed from the water column due to predation on zooplankton was estimated at 1.87 and 2.3 ng P·L-1·h-1, respectively. The net daily regeneration of 52.2-181.4 ng P·L-1·day-1 by the G. lacustris population represented 9.5-32.9% of the total P regenerated by the planktonic community. The majority of the P released by G. lacustris represents "new" P to the pelagic zone because it originated in sediments. We conclude that G. lacustris can represent an important link in benthic-pelagic coupling in oligotrophic mountain lakes.

[Amphipod body lengths and weights are important variables in life history, biomass and production determinations. Length and weight are often estimated from head capsule length-body length or weight relationships based on a single field collection. Possible seasonal variation in these relationships is rarely considered. We used seasonal data for two amphipod species (Gammarus lacustris and Diporeia hoyi) to test the hypothesis that head capsule length-body length/weight relationships remain seasonally constant. Slopes of monthly relationships were significantly different (ANCOVA). However, the differences in slope and intercept were trivial, and all monthly regressions yielded similar predictive results. Regressions based on pooled seasonal samples underestimated measured biomass by 5%, while predicted lengths varied between 0 to ± 2 mm from measured lengths. We conclude that head capsule length-body length/weight relationships for these amphipods are seasonally robust, and may be estimated from single collections provided all size classes are obtained. If all size classes can not be obtained from one sample, relationships should be based on pooled samples., Amphipod body lengths and weights are important variables in life history, biomass and production determinations. Length and weight are often estimated from head capsule length-body length or weight relationships based on a single field collection. Possible seasonal variation in these relationships is rarely considered. We used seasonal data for two amphipod species (Gammarus lacustris and Diporeia hoyi) to test the hypothesis that head capsule length-body length/weight relationships remain seasonally constant. Slopes of monthly relationships were significantly different (ANCOVA). However, the differences in slope and intercept were trivial, and all monthly regressions yielded similar predictive results. Regressions based on pooled seasonal samples underestimated measured biomass by 5%, while predicted lengths varied between 0 to ± 2 mm from measured lengths. We conclude that head capsule length-body length/weight relationships for these amphipods are seasonally robust, and may be estimated from single collections provided all size classes are obtained. If all size classes can not be obtained from one sample, relationships should be based on pooled samples.]

Respiration studies of small benthic invertebrates are generally completed without regard to the inclusion of a substrate or the quantification of activity in the experimental chamber. We describe a new activity monitoring system for continuously recording the activity and oxygen consumption of small benthic invertebrates in water with the presence of a substrate. We used the freshwater amphipod Diporeia hoyi to test the new system. Activity rates were significantly higher without sediment than with sediment, and oxygen consumption was directly related to activity. Future invertebrate respiration studies, especially those with infaunal organisms, will benefit from such a system by allowing researchers to determine possible test condition - treatment interactions.

We present a mechanical method to horizontally section soft bottom sediment cores to minimize the vertical post-sampling redistribution of motile infaunal macroinvertebrates. A clear acrylic core tube for a standard Kajak-Brinkhurst corer was modified by cutting a series of horizontal slits into the side of the core tube to allow the insertion of sectioning plates for physically sealing each section immediately after core retrieval. The modification is simple, inexpensive and easily adapted to any open barrel gravity corer.

Hesperodiaptomus arcticus, a predatory calanoid copepod, was eliminated from two alpine lakes within 6 years of stocking with salmonids. Using historical and contemporary zooplankton and fish data, sediment analysis for diapausing eggs, and experiments on predation of Gammarus lacustris on diapausing eggs of H. arcticus, we assess the fate of these populations 35 years after fish stocking. In Pipit Lake, in which the trout introduction failed within 21 years, we propose that H. arcticus recovered as a result of hatching of diapausing eggs held in the sediments. In Snowflake Lake the diapausing egg bank was exhausted prior to the loss of the fish population 25 years after first stocking and H. arcticus recovery did not occur. Experimental studies indicate that G. lacustris predation on diapausing eggs probably occurs within the sediments. Combined with a 10-fold difference in G. lacustris density between Snowflake and Pipit lakes the results of the predation experiments imply that G. lacustris had a strong negative impact on the abundance of diapausing eggs held in Snowflake Lake sediments and therefore reduced the ability of the population to recover following perturbation. Resume : Hesperodiaptomus arcticus, un copepode calanoi'de predateur, a ete elimine de deux lacs alpins en moins de 6 ans aprks l'introduction de salmonides. D'aprks des donnees anciennes et des donnees contemporaines sur le zooplancton et le poisson, l'analyse des sediments contenant les oeufs en diapause et les resultats d'experiences de predation de Gammarus lacustris sur les oeufs en diapause d'H. arcticus, nous avons pu constater le sort de ces populations 35 ans aprks l'introduction des poissons. Au lac Pipit, ou la population de truites introduites s'est eteinte aprks 21 ans, nous croyons que la population d'H. arcticus s'est relevee par eclosion des oeufs en diapause dans les sediments. Au lac Snowflake, la reserve d'oeufs en diapause s'est epuisee avant la disparition de la population de poissons, 25 ans aprks l'introduction, et la population d'H. arcticus n'est pas reapparue. Des etudes experimentales ont demontre que Gammarus lacustris consomme probablement des oeufs en diapause dans les sediments. Combines a l'enorme difference entre les densites de G. lacustris aux deux lacs, dix fois plus elevee au lac Snowflake qu'au lac Pipit, les resultats des experiences de predation indiquent que G. lacustris a eu un impact negatif important sur l'abondance des oeufs en diapause dans les sediments du lac Snowflake, annihilant les chances de survie de la population aprks la disparition des poissons. (Traduit par la Redaction)

The expanding human population and continuing pollution of aquatic resources threaten the survival of life on earth by reducing the quality and quantity of available water. Pollution sources are highly varied but can be categorized as point- and nonpoint source. Point source pollution is highly localized, easily identified, and relatively easily remedied. Nonpoint-source pollution, however, comes from diffuse sources and requires much greater effort to address. Loss of water, oxygen demands, and nutrient effects are examined in detail. Large impacts have been, and are, expected with continued water abstraction. Solutions include litigation and at worst armed conflict. Although oxygen demands from the addition of organic material can be significantly reduced by treating effluents, many parts of the world, especially developing countries, do not have the necessary funds or infrastructure. Significant progress has been made to relieve oxygen demand with in situ methods. These are expensive and require ongoing monitoring and maintenance. Excessive nutrients contribute to eutrophication, loss of oxygen, and ecosystem diversity. The recovery of some significant ecosystems after nutrient reductions is one of the not-so-dim parts of the chapter. Simply preventing aquatic pollution would be the most effective and least costly strategy to deal with it.

We used a simple and inexpensive water-based method to separate live and preserved invertebrates from lake and stream sediments. Sediment samples were emptied onto a large screen and slowly immersed in water which caused the invertebrates to become trapped in the surface film from which they were easily removed. Invertebrates with setae or numerous appendages were separated most successfully, whereas dense organisms had to be removed by hand. On average 74% of all invertebrates per sample were removed by sieving in 23 minutes. We suggest that the time and effort spent sorting samples can be reduced by combining sieving with hand-sorting, especially when samples contain large numbers of invertebrates.

Populations of the amphipod Gammarus lacustris were examined for their concentrations of organochlorine pesticides and polychlorinated biphenyls (PCBs) from seven lakes spanning a 1,300-m elevation gradient in Alberta, Canada. The concentrations of several of the semivolatile organochlorine compounds ([SVOCs], vapor pressure > 0.03 Pa at 20 degrees C) increased at higher altitudes. This pattern was generally not observed among the less volatile organochlorines ([LVOCs]. vapor pressure < 0.03 Pa at 20 degrees C). These same SVOC compounds have been previously shown to increase at high latitudes as a result of their long-range transport and preferential deposition in cold climates. We also show that populations of G. lacustris at high elevations have slower growth rates and store more lipids than populations at lower elevations. To resolve the colinearity of independent variables, we used multiple regression to identify patterns of contaminant concentrations in this data set. Multiple regressions showed that the effect of elevation, lipid content, and temperature on contaminant concentrations was no longer significant once the growth rate of Gammarus was included as an independent variable. This study shows that enrichment of SVOCs occurs in Gammarus at high altitudes in Alberta, Canada, and that growth rate (biodilution) appears to be the primary influence. Because Gammarus is an important trophic link in aquatic foodwebs in these environments, enhanced concentrations of toxicants in prey may increase their biomagnification in top predators of high-altitude lakes.