Showing papers in "Freshwater Biology in 1997"

How much water does a river need

Abstract: > * SUMMARY 1. This paper introduces a new approach for setting streamflow-based river ecosystem management targets and this method is called the 'Range of Variability Approach' (RVA). The proposed approach derives from aquatic ecology theory concerning the critical role of hydrological variability, and associated characteristics of timing, frequency, duration, and rates of change, in sustaining aquatic ecosystems. The method is intended for application on rivers wherein the conservation of native aquatic biodiversity and protection of natural ecosystem functions are primary river management objectives. 2. The RVA uses as its starting point either measured or synthesized daily streamflow values from a period during which human perturbations to the hydrological regime were negligible. This streamflow record is then characterized using thirty-two different hydrological parameters, using methods defined in Richter et al. (1996). Using the RVA, a range of variation in each of the thirty-two parameters, e.g. the values at t 1 standard deviation from the mean or the twenty-fifth to seventy-fifth percentile range, are selected as initial flow management targets. 3. The RVA targets are intended to guide the design of river management strategies (e.g. reservoir operations rules, catchment restoration) that will lead to attainment of these targets on an annual basis. The RVA will enable river managers to define and adopt readily interim management targets before conclusive, long-term ecosystem research results are available. The RVA targets and management strategies should be adaptively refined as suggested by research results and as needed to sustain native aquatic ecosystem biodiversity and integrity.

The ecological significance of exchange processes between rivers and groundwater

Abstract: 1. This review focuses on the connectivity between river and groundwater ecosystems, viewing them as linked components of a hydrological continuum. Ecological processes that maintain the integrity of both systems and those that are mediated by their ecotones are evaluated. 2. The hyporheic zone, as the connecting ecotone, shows diverse gradients. Thus it can be characterized by hydrological, chemical, zoological and metabolic criteria. However, the characteristics of the hyporheic zone tend to vary widely in space and time as well as from system to system. The exact limits are difficult to designate and the construction of static concepts is inadequate for the representation of ecological processes. The hyporheic interstices are functionally a part of both the fluvial and groundwater ecosystems. 3. The permeability of the ecotone depends on the hydraulic conductivity of the sediment layers which, because of their heterogeneity, form many flowpath connections between the stream and the catchment, from the small scale of a single microhabitat to the large scale of an entire alluvial aquifer. Local up- and downwellings are determined by geomorphologic features such as streambed topography, whereas large-scale exchange processes are determined mainly by the geological properties of the catchment. Colmation—clogging of the top layer of the channel sediments—includes all processes leading to a reduction of pore volume, consolidation of the sediment matrix, and decreased permeability of the stream bed. Consequently, colmation can hinder exchange processes between surface water and groundwater. 4. Physicochemical gradients in the interstices result from several processes: (i) hyporheic flow pattern and the different properties of surface and groundwaters; (ii) retention, caused by the filtering effect of pore size and lithologic sorption as well as the transient storage of solutes caused by diminished water velocities; (iii) biogeochemical transformations in conjunction with local residence time. Each physicochemical parameter may develop its own vertical dynamics laterally from the active channel into the banks as well as longitudinally because of geomorphologic changes. 5. The river–groundwater interface can act as a source or sink for dissolved organic matter, depending on the volume and direction of flow, dissolved organic carbon concentrations and biotic activity. Interstitial storage of particulate organic matter is influenced mainly by grain size distribution and by spates involving bedload movement that may import or release matter, depending on the season. After initial transient and abiotic storage, hyporheic organic matter is mobilized and transformed by the biota. Micro-organisms account for over 90% of the community respiration. In subterranean waters most bacteria are attached to surfaces and remain in a biofilm. 6. Hyporheic interstices are functionally significant for phreatic and riverine metazoans because they act as a refuge against adverse conditions. The net flow direction exerts a dominant influence on interstitial colonization, but many other factors also seem to be important in structuring the hyporheos. 7. The hyporheic corridor concept emphasizes connectivity and interactions between subterranean and surface flow on an ecosystem level for floodplain rivers. It is a complementary concept to others which focus on surficial processes in the lateral and longitudinal dimensions. 8. The ecological integrity of groundwater and fluvial systems is often threatened by human activities: (i) by reducing connectivity; (ii) by altering exchange processes; and (iii) by toxic or organic contamination.

The influence of catchment land use on stream integrity across multiple spatial scales

Abstract: 1. Despite wide recognition of the need for catchment-scale management to ensure the integrity of river ecosystems, the science and policy basis for joint management of land and water remains poorly understood. An interdisciplinary case study of a river basin in south-eastern Michigan is presented. 2. The River Raisin drains an area of 2776 km2, of which some 70% is agricultural land. The upper basin consists of till and outwash, and both topography and land use/cover are diverse. The lower basin consists of fine textured lake deposits, is of low relief, and land use is primarily agricultural. 3. The River Raisin basin historically was a region of oak-savannah and wetlands. It was deforested, drained and converted to farmland during the mid-nineteenth century. Human population reached a plateau at about 1880, and then underwent a second period of growth after 1950, mainly in small urban areas. More recently, the amount of agricultural land has declined and forested land has increased, in accord with a general decline in farming activity. 4. It could be suggested that the influence of land use on stream integrity is scale-dependent. Instream habitat structure and organic matter inputs are determined primarily by local conditions such as vegetative cover at a site, whereas nutrient supply, sediment delivery, hydrology and channel characteristics are influenced by regional conditions, including landscape features and land use/cover at some distance upstream and lateral to stream sites. 5. Sediment concentrations measured during low flows were higher in areas of greater agriculture. In a comparison of two subcatchments, sediment yields were up to ten times greater in the more agricultural location, in response to similar storm events. A distributed parameter model linked to a geographical information system predicted that an increase in forested land cover would result in dramatic declines in runoff and sediment and nutrient yields. 6. Habitat quality and biotic integrity varied widely among individual stream sites in accord with patterns in land use/cover. Extent of agricultural land at the subcatchment scale was the best single predictor of local stream conditions. Local riparian vegetation was uncorrelated with overall land use and was a weak secondary predictor of habitat quality and biotic integrity. 7. Investigation of the regulatory agencies involved in land and water management in the basin revealed a complex web of overlapping political jurisdictions. Most land-use decision-making occurs at the local level of township, city or village. Unfortunately, local decision-making bodies typically lack the information and jurisdictional authority to influence up- and downstream events.

The role of highly unsaturated fatty acids in aquatic foodweb processes

Abstract: 1. Polyunsaturated fatty acids (PUFA) are almost exclusively synthesized by plants. Animals can convert from one form of PUFA to another through elongation and desaturation, but very few can synthesize PUFA de novo. PUFA play an important role in regulating cell membrane properties, serve as precursors for important animal hormones and are essential for animals. 2. In aquaculture studies, highly unsaturated fatty acids (HUFA), a subset of PUFA, have been found to be critical for maintaining high growth, survival and reproductive rates and high food conversion efficiencies for a wide variety of marine and freshwater organisms. 3. The plankton literature suggests high food-quality algae species are rich in HUFA and low food-quality algae are poor in HUFA. Adding semi-pure emulsions of HUFA to algae monocultures can markedly increase the growth rates of zooplankton feeding on these mixtures. 4. A study measuring zooplankton biomass accrual when feeding on natural phytoplankton found a strong correlation between phytoplankton HUFA (specifically eicosapentaenoic acid) content and herbivorous zooplankton production. 5. The aquatic ecology literature suggests that planktonic foodwebs with high HUFA content phytoplankton have high zooplankton to phytoplankton biomass ratios, while systems with low HUFA phytoplankton have low zooplankton biomass. Also, the seasonal succession of plankton in many temperate lakes follows patterns tied to phytoplankton HUFA content, with intense zooplankton grazing and ‘clear-water-phases’ characteristic of periods when the phytoplankton is dominated by HUFA-rich species. 6. Herbivorous zooplankton production is constrained by the zooplankton’s ability to ingest and digest phytoplankton. It is becoming increasingly clear, however, that much of the phytoplankton which is assimilated may be nutritionally inadequate. HUFA may be key nutritional constituents of zooplankton diets, and may determine energetic efficiency across the plant–animal interface, secondary production and the strength of trophic coupling in aquatic pelagic foodwebs.

Landscape influences on water chemistry in Midwestern stream ecosystems

Abstract: 1. Landscape characteristics of sixty-two subcatchments within the Saginaw Bay Catchment of central Michigan were examined to identify relationships with stream water chemistry. Land use, land cover and elevation were quantified for both entire catchments and the upland–river ecotone (100 m stream buffer strip). Catchment and ecotone data were then empirically compared with stream water chemistry using multivariate and regression analyses. Redundancy analysis was used to partition variance among land use, geology, and the shared influence of land use and geology. 2. Major catchments dominated by rowcrop agriculture had the highest alkalinity, total dissolved solids and nitrate + nitrite concentrations. 3. Strong seasonal differences were observed in total nitrogen and nitrite + nitrate, but not in total phosphorus or suspended solids. Land use and landscape structure factors such as slope and patch density (number of land use patches per km2) accounted for most of the observed variance in summer. 4. In both autumn and summer, landscape factors accounted for much of the observed variation in total dissolved solids and alkalinity. During autumn, geological factors and the shared influence of geology/landscape structure plus land use exerted more influence than did land use alone. 5. Total phosphorus and total suspended solids were much better explained by land use within the stream ecotone in summer than in other seasons. However, total nitrogen, nitrate, orthophosphate and alkalinity were equally well explained by land use within the ecotone and throughout the whole catchment. Only total dissolved solids in summer and ammonium in autumn were explained better by the whole catchment than the ecotone. 6. Our results show that relatively coarse spatial databases can provide useful descriptors of regional water quality.

Catchment and reach‐scale properties as indicators of macroinvertebrate species traits

Abstract: 1. We used catchment and reach-scale physical properties to predict the occurrence of specific species life history and behaviour traits of aquatic insects across fifty-eight catchments in a mixed land use basin. Catchment-scale attributes were derived using a geographical information system (GIS). Logistic regression techniques were used to model the relationships. 2. The reach-scale properties were highly predictive of species traits. Fourteen of the fifteen traits had significant models with concordance values greater than 68%. Cross-sectional area at bank full discharge, % shallow, slow-water habitats, and % fines were the most important variables. 3. Life history and behavioural attributes were best related to reach-scale physical features. This suggests that species traits exhibit strong relationships to local environmental conditions. 4. Catchment-scale variables had fewer significant models with species traits (four of fifteen), however these variables may have direct or indirect influence on reach-scale properties. 5. Catchment features, in particular surficial geology, influence macroinvertebrate assemblages through their control over channel morphology and hydrologic patterns. 6. The effects of land use were masked by geology (i.e. lacustrine clay geology and rowcrop agriculture were correlated), lack of detail in land use data and the aggregation of the species data. 7. These models reflect the coupling of local environmental conditions and the set of adaptations among the local taxa. These observations underscore the idea that habitat plays a major role in organizing stream assemblages. 8. Using these approaches, predictions can be made about the ability of various taxonomic groupings to track environmental change through time, or for projecting the impact of alternative land management scenarios. Identifying fundamental life history and other traits can improve the selection and evaluation of such indicators.

The role of food quality for zooplankton: remarks on the state‐of‐the‐art, perspectives and priorities

Abstract: 1. This paper summarizes the salient features of the contributions to the workshop on The Role of Food Quality for Zooplankton. In this paper we attempt critically to evaluate our present knowledge in the light of new studies. 2. For the growth and reproduction of zooplankton, the existing literature considers two main Limiting factors in the diet, i.e. phosphorus (homeostasis theory) and fatty acids. Nevertheless, interpretations and opinions regarding the importance of these two factors are the subject of controversy in the literature. No attempts have been made to link these two potentially limiting factors, let alone give a coherent view based on the mechanisms behind limitation. Aquaculture studies provide some direct evidence of the importance of the long-chained poly unsaturated fatty acids (PUFA) for zooplankton. The presence of PUFA in phytoplankton is reported to affect the growth rates of zooplankton significantly. 3. Field data on carbon and phosphorus indicate a greater constancy of the C:P ratios of zooplankton than of their food. Empirical data and modelling studies suggest that zooplankton, especially Daphnia spp., may maintain nutrient homeostasis by incorporating a greater proportion of the Limiting nutrients ingested and releasing more of nutrients in excess supply. The need for conserving nutrients in short supply increases with the increase in growth rates. 4. Phosphorus certainly influences zooplankton food directly. Direct supplementation of of the P-insufficient algal diet with PO4-P alone discernibly improves the growth in daphnids. It is highly plausible that P limitation and fatty acid limitation are not mutually exclusive alternatives. The two, separately or in conjunction, can control growth of at least some lake zooplankters, especially daphnids. 5. Besides a shortage of nutrient (P), other environmental factors (irradiance, UV-radiation, temperature) can also adversely affect the zooplankton diet, including its digestibility and assimilation efficiency. 6. It is not yet clear if PUFA deficiency in the diet is in some way related to or caused by P deficiency. It is, however, now known that the EPA (eicosapentaenoic acid, 20:5 omega 3) content of certain algae is markedly reduced under P-limitation and that it differs significantly among the different taxonomic groups of phytoplankton. Diatoms and flagellates are generally considered as good-quality foods because of their high EPA content. On the contrary, cyanobacteria are low-quality food, having both low EPA and P content. 7. Recent experiments reveal that the relative importance of fatty acids for daphnids increases with a decreasing C:P ratio in the food, i.e. if P is no longer limiting, and vice versa. For daphnids, there is possibly a switch between P-limitation and PUFA limitation at intermediate C:P ratios. At higher C:P ratios, P is more important but at lower ratios PUFA are more crucial for growth and reproduction. 8. Lastly, the accumulating evidence for P limitation is stronger than that for fatty acid limitation. [KEYWORDS: Blue-green-algae; nutrient element limitation; planktonic cladocerans; mineral limitation; lipid-composition; daphnia growth; p-limitation; fatty-acids; phosphorus; phytoplankton]

Species traits in relation to temporal and spatial heterogeneity in streams: a test of habitat templet theory

Abstract: 1 The habitat templet approach depends on defining templet axes appropriate to the organism(s) of interest, predicting the traits of species associated with different parts of the templet, and testing these predictions in a range of habitats whose positions in the templet have been determined 2 In this study of thirty-five benthic insect taxa at fifty-four tributary sites of the Taieri River on the South Island of New Zealand, we chose as the temporal axis the intensity/frequency of disturbance, defined in terms of bed movement during high discharge events As the spatial axis, we postulated that three features would provide refugia and therefore ameliorate disturbance—percentage of the bed with low shear stress, percentage of the bed made up of large substratum particles and availability of interstitial space in the bed—from which we derived a combined multivariate refugium axis 3 More disturbed communities contained a significantly higher percentage of individuals possessing the following traits: small size, high adult mobility, habitat generalist (each predicted to confer resilience in response to disturbance), clinger, streamlined/flattened and with two or more life stages outside the stream (each predicted to confer resistance in the face of disturbance) When analyses were performed on the percentage of taxa having particular traits, the predicted positive relationships with average bed movement were found for high adult mobility and habitat generalist traits 4 The percentage of variance in trait scores explained by intensity of disturbance was generally higher in sites with less refugia available and lower in sites further from the headwaters The percentage of variance explained was higher in sites recently subject to a major high discharge disturbance, suggesting that disturbances tend to strengthen the pattern of preponderance of resilience/resistance traits 5 We mapped insect taxa onto the two-dimensional templet, following Grime et al’s triangular terrestrial plant classification The full variety of resistance and resilience traits were represented in insect species throughout the templet, but taxa associated with more disturbed conditions generally displayed a larger number of resilience and resistance traits, combined, than taxa associated with more stable stream beds

Depth limits and minimum light requirements of freshwater macrophytes

Abstract: 1. Data for maximum colonization depth (Zc) of five groups of submerged macrophytes and light attenuation were collected for forty-five Danish lakes and 108 non-Danish lakes. The macrophyte groups were bryophytes, charophytes, caulescent angiosperms, rosette-type angiosperms and Isoetes spp. 2. The data showed systematic differences among the groups in the relationship of Zc to water transparency. In lakes with low transparency (Secchi disc transparency (Zs) less than 7 m) caulescent angiosperms and charophytes penetrated deepest followed by bryophytes and Isoetes spp. In more transparent lakes bryophytes grew deepest, followed by charophytes, caulescent angiosperms and Isoetes spp. Rosette-type angiosperms had the lowest Zc in all types of lakes. Charophytes and caulescent angiosperms had similar depth limits in lakes with Zs < 4 m but charophytes grew deeper in more transparent lakes. The depth limits of both groups were independent of light penetration in lakes with very low transparency (Zs < 1 m). The annual light exposure for the deepest growing macrophytes (bryophytes) was 20–95 mol photons m–2. 3. The relationship between Zc, macrophyte type and lake transparency could be explained by three distinct processes regulating Zc. In lakes with low transparency (Zs < 1 m), tall macrophytes (caulescent angiosperms and charophytes) compensate for light limitation by shoot growth towards the water surface and Zc is therefore independent of transparency. In lakes with medium transparency (1 m < Zs < 4 m) Zc for angiosperms, charophytes and Isoetes spp. is constrained by light attenuation in the water column, corresponding to a linear relationship between Zc and Zs. This pattern also applies to bryophytes, despite lake transparency. In transparent lakes, the minimum light requirement at Zc increased with increasing transparency for angiosperms, charophytes and Isoetes spp. 4. The minimum light requirements among submersed macrophytes (including marine macroalgae) depend on their plant-specific carbon value (plant biomass per unit of light-absorbing surface area) for the species/group, indicating that the light requirements of submersed plants are tightly coupled to the plants’ possibility to harvest light and hence to the growth form. 5. The light requirements increased on average 0.04% surface irradiance per degree increase in latitude corresponding to an average decrease in Zc of 0.12 m per degree latitude.

Relationships between benthic biota and hydrological indices in New Zealand streams

Abstract: SUMMARY 1. The objective of this study was to identify the most ecologically relevant hydrological indices for characterizinghydrological regimes in New Zealand streams' To do this we related measures of periphyton chlorophyll o, ash-free dry mass (AFDM' species richness, and diversity and invertebrate density, species richness and diversity, ta thirty-four hydrological variables derived from daily flow records at eighty-three sites. Tire hydrologicai variables included some describing average flow conditions, flow variability, floods, and low-flow characteristics' Z. A principal components analysis showed that the interrelationship between many of the hyarological variables was high, and most variables correlated significantly with princlpil Component 1 (PC1). The flood frequency variables formed a distinct component of the flow regime and were the main contributor to PC2' g. We found that both the average flow conditions and some rieasure of variability were significantly related to most of the biological variables, and these individual hydrolo-gical variables were more strongly correlated to the biological measures than the "amposit" principal components. Only four of the thirty-four flow variables were signi-ficantþ "ortalut"d 1Þ < O.OSi with measures of periphyton biomass (chlorophyll o utia epiVf), whereas twenty-four variables were correlated with periphyton diversity' Conversely, thirty-one of the thirty-four flow variables were correlated with total invertebraie density, whereas only four variables correlated with diversity' 4. We selected the flood frequency (FRE3), where a flood is defined as flows higher than three times the median flow, as the most ecological useful oaerall flow variable in New Zealand streams becausq it explained a significant amount of the variance in four out of the six main benthic community measures, and it had a clear mechanism of control of the biota which was commensurate with current stream ecosystem theory' Periphyton biomass decreased with increasing FRE3, whereas invertebrate density had an increasing/curvilinear relationship with FRE3. Periphyton species richness and diversity decreased with increasing FRE3.

Structure and diversity of stream invertebrate assemblages : the influence of temperature with altitude and latitude

Abstract: 1. Structure and diversity of the macroinvertebrate fauna were studied in relation to altitude and latitude among three groups of streams from Ecuador (lowland: 100–600 m, Central Valley: 2600–3100 m, paramo: 3500–4000 m), and one group from the temperate lowland region of Denmark. The streams in the four regions were comparable with regard to physical characteristics such as size, current and substratum. 2. In terms of faunal composition the Ecuadorian highland streams bore more resemblance to the Danish lowland streams than the Ecuadorian lowland streams. The greater similarity between the Ecuadorian highland and the Danish streams, however, was due to the large number of insect families in the Ecuadorian lowlands, many of which were not found in the other regions. Of ten physico-chemical parameters measured, maximum stream temperature explained by far the most variability in faunal composition. 3. The number of insect orders and families increased linearly with maximum stream temperature and therefore decreased with altitude and latitude. A compilation of literature data on insect richness and maximum water temperature from streams around the world confirmed this pattern, yielding a common linear relation for both temperate and tropical streams. This pattern may arise due to a direct temperature effect on speciation but is probably also related to geological history and the influence of climatic changes on stream ecosystems. We estimate that small, tropical, lowland streams have, on average, a two- to fourfold higher species richness than temperate lowland streams.

Response of invertebrates to lotic disturbance: is the hyporheic zone a patchy refugium?

Abstract: 1. Natural experiments, in the form of disturbance from spates, were used to study the resistance and resilience of interstitial communities. Investigations were conducted in a by-passed section of the Rhone River characterized by an artificial hydrology with frequent spates separated by regular minimum discharge of 30 m3 s–1. 2. Three areas of a bar were studied, upwellings at the head of the bar (stations 1 and 2), and downwelling at the tail of the bar (station 3). In the head of the bar the substratum was characterized by stable cobbles, while mobile gravels dominated in the tail of the bar. At each station, samples were derived from four depths (0.5, 1.0, 1.5 and 2.0 m below the surface of the substratum). Fifteen spates occurred during the study period whose peak discharge ranged from 50 to 1640 m3 s–1. Temporal variations of the fauna were studied by comparing the spate effect observed 1 day (resistance), 7 days (resilience) and 17 days after the spate. Within-class correspondence analysis was used to compare the temporal variability of the fauna within each class {station/depth}. 3. The fauna differed markedly between the three stations, and the relative density of stygobionts (i.e. hypogean fauna) decreased from 55% at station 1 to 4% at station 3. The spatio-temporal variability increased dramatically from station 1 to station 3. 4. The results suggest that the hyporheic zone acts as a patchy refugium: the stations were more or less active refugial zones, depending on hydrology (upwelling or downwelling), substratum stability and spate amplitude. 5. The downwelling station was the main refugium area for benthic taxa. Important migrations of benthic groups (e.g. Gammarus, Cladocera) or hyporheic taxa (e.g. Cyclopoida and Harpacticoida) were observed deep into the sediment (2 m). Vertical movements of stygobionts (Niphargus, Niphargopsis) were also observed at high amplitude spates. These movements were very important (great numbers of individuals migrated) at low and medium magnitude spates, but were unimportant at high discharge, when the threshold of sediment instability was exceeded. In this case the substratum became mobile and induced drift of benthic organisms. 6. Conversely, in the upwelling stable stations, accumulation was less important (lower number of species and lower densities) but more constant with increasing discharge, suggesting that substratum stability is also a key factor. 7. Generally recovery was rapid at all stations (within 7 days) but no relationships were found between resilience (rate of recovery) and the amplitude of spates.

The influence of landscape position on lakes in northern Wisconsin

Abstract: 1. Using data from the North Temperate Lakes Long-Term Ecological Research site in northern Wisconsin, we present a series of examples illustrating how landscape setting can influence the static and dynamic aspects of many physical, chemical and biological properties of lakes. 2. One important landscape attribute is the hydrologic position of a lake within the regional flow regime. Lake position determines the relative importance of groundwater and precipitation input to a lake, with lakes high in the landscape receiving a greater proportion of their input waters from precipitation than lakes lower in the landscape. Landscape position is strongly correlated with the concentration of base cations such as calcium and magnesium. 3. Landscape position also influences how lakes respond to drought conditions. Lakes high in the landscape responded to a 4-year drought with decreases in calcium mass, whereas lakes low in the landscape increased in mass of calcium. During extended dry conditions, these differential responses of lakes suggest that lakes already low in calcium (i.e. in a high position in the flow system) will have further reductions in calcium concentrations. These reductions could decrease the number of lakes offering suitable habitat for organisms such as crayfish and snails whose distributions are limited by calcium. 4. Landscape position also affects silica concentrations in lakes, with lakes low in the landscape having silica concentrations up to three orders of magnitude greater than lakes high in the landscape. Differences in silica concentration affect robustness of freshwater sponge spicules which can potentially alter some aspects of the dynamics of littoral zone food webs. 5. Landscape position can influence the vertical distribution of primary production. Concentrations of dissolved organic carbon are affected by landscape setting and can influence vertical light penetration, thus affecting the depth at which primary production can occur. 6. Lake area and fish species richness are correlated with landscape position: larger, species-rich lakes are low in the landscape, whereas smaller lakes with fewer species tend to be high in the landscape. 7. By taking a landscape-scale view, in addition to the more usual lake-specific view, it is possible to reach a more robust understanding of lake dynamics and avoid some of the problems associated with extrapolating from single lake results.

The response of benthic macroinvertebrates to pollution in developing countries : a multimetric system of bioassessment

Abstract: 1. A variety of bioassessment metrics were tested using family-level macroinvertebrate data, gathered by standard colonization units, and associated physicochemical data from pollution gradients in three rivers in developing countries. 2. Graphical methods of evaluation were used to evaluate the metrics with respect to these pollution gradients. 3. In general, the macroinvertebrate communities sampled displayed a similar response to pollution to that observed in well-studied temperate areas. 4. Of the twenty metrics tested seven described the pollution gradients adequately. Four of these seven metrics, which do not supply duplicate information, were selected for use in a multimetric system of bioassessment. 5. A multimetric system is proposed and tested using the original macroinvertebrate data. It performs well in the assessment of the pollution status of the study sites and the description of the pollution gradient. However, local modifications are likely to enhance its performance.

The importance of highly unsaturated fatty acids in zooplankton nutrition: evidence from experiments with Daphnia, a cyanobacterium and lipid emulsions

Abstract: 1. We used laboratory growth and feeding experiments to evaluate the role of ω3 highly unsaturated fatty acids (HUFA) in zooplankton nutrition. Polyunsaturated fatty acids (PUFA) comprised 40% of total fatty acids (FA) in the green alga Scenedesmus acutus but only 6% in the cyanobacterium Synechococcus elongatus.Scenedesmus contained modest amounts of the ω3 HUFA eicosapentaenoic acid (EPA, 20 : 5ω3) and docosahexaenoic acid (DHA, 22 : 6ω3), whereas Synechococcus contained only a trace of EPA and no DHA. 2. One-day-old Daphnia maintained high growth rates for 2–3 days on a diet of Synechococcus but exhibited reduced growth or even lost weight over the later part of the 6- or 7-day experiments. Daphnia magna grew better than D. galeata or D. pulicaria on a diet of pure Synechococcus. Daphnids fed the same concentration (0.5 mgC l–1) of green algae or a mixture of green algae and Synechococcus maintained high growth rates. 3. Supplementing Synechococcus with fish oil emulsions rich in ω3 HUFA markedly improved the growth and reproduction of all three Daphnia species. Supplementation with an emulsion of monounsaturated oleic acid (18 : 1ω9), however, did not affect the growth of D. galeata and caused a decrease in the growth of D. magna. 4. Short-term (7 min) and long-term (3 h) feeding trials with 14C-labelled Synechococcus were used to evaluate the effects of acclimation and mixed diets on carbon incorporation. D. galeata that had fed on unlabelled Synechococcus for 3 days exhibited no decline in clearance rate but a marked decline in carbon incorporation in comparison with animals acclimated with Scenedesmus or fed a mixture of Synechococcus and Scenedesmus. 5. Our results support the hypothesis that the poor nutritional quality of a cyanobacterium is at least partially due to a HUFA deficiency. Growth and feeding experiments both suggest that the utilization of Synechococcus is enhanced by HUFA from lipid reserves or a mixed diet.

Landscape approaches to the analysis of aquatic ecosystems

Abstract: 1. In the mid-1970s, Hynes (1975) wrote eloquently about the complex interactions between aquatic and terrestrial systems. Central theories in stream ecology developed thereafter have dealt with the longitudinal flow of energy, materials and organisms in streams, and, with the exception of the flood pulse concept (Junk, Bayley & Sparks, 1989), have largely ignored areas outside the riparian zone. The structure of the upland and activities occurring there play a more important part than previously recognized in regulating community structure and ecosystem processes in streams. 2. These new perspectives are made possible by developments in hierarchy theory, patch dynamics, and the refinement of tools used to quantify spatial and temporal heterogeneity. 3. Geographical information systems (GIS), image processing technology and spatial statistical techniques allow quantitative assessment of lateral, longitudinal and vertical components of the landscape that interact at several spatial and temporal scales to influence streams. When GIS is used in concert with geostatistics, multivariate statistics, or landscape models, complex relationships can be elucidated and predicted. 4. To a certain extent, the tools discussed above have only automated functions that were previously performed manually. This suite of tools has improved the ability of aquatic ecologists to examine relationships and test theories over larger, more heterogeneous regions than were previously possible. 5. At the local, state and federal level, management and regulatory frameworks are currently being re-evaluated to incorporate this new perspective in resource management and policy decision making. 6. We will discuss current and future trends in technologies and tools used for aquatic ecosystem research, and the use of techniques as they are applied in these regional assessments are also discussed.

Reconciling landscape and local views of aquatic communities: lessons from Michigan trout streams

Abstract: 1. Rapidly advancing geographical information systems (GIS) technologies are forcing a careful evaluation of the roles and biases of landscape and traditional site-based perspectives on assessments of aquatic communities. Viewing the world at very different scales can lead to seeming contradictions about the nature of specific ecological systems. In the case of Michigan trout streams, landscape analyses suggest a predictable community shaped by large-scale patterns in hydrology and geology. Most site-based studies, however, suggest these communities are highly variable in structure over time, and are strongly shaped by site-specific physical and biological dynamics. As the real world is comprised of processes operating both at local and landscape scales, an analytical framework for integrating these paradigms is desirable. 2. Decomposition of variances by factorial ANOVA into time, space and time–space interaction terms can provide a conceptual and analytical model for integrating processes operating at landscape and local scales. Using this approach, long-term data sets were examined for three insects and two fishes common in Michigan trout streams. Each taxon had a unique variance structure, and the observed variance structure was highly dependent upon sample size. 3. Both spatially extensive designs with little sampling over time (typical of many GIS studies) and temporally extensive designs with little or no spatial sampling (typical of population and community studies), are biased in terms of their view of the relative importance of local and landscape factors. The necessary, but in many cases costly, solution is to develop and analyse data sets that are both spatially and temporally extensive.

The relationship between land use and physicochemistry, food resources and macroinvertebrate communities in tributaries of the Taieri River, New Zealand: a hierarchically scaled approach

Abstract: 1. The relationship between land use and stream conditions was investigated, including physicochemistry, the availability of primary food resources and species richness, species composition and trophic structure of stream macroinvertebrate communities. The survey involved eight subcatchments of the Taieri River (New Zealand) encompassing reasonably homogeneous examples of four major land uses: native forest, native tussock grassland, plantations of introduced pine and agricultural pasture. 2. Each land use was represented by two subcatchments, each subcatchment by two to four tributaries, and each tributary by two to three sampling sites. These three sampling scales each represent typical designs for stream community studies. By recording responses at all scales, it can be determined explicitly whether the scale of sampling influences interpretation of community structure. 3. Elevation, riffle length, proportion of large substrata in the bed, total phosphorus and alkalinity were significantly related to land use, as were canopy cover and the relative abundance of leaves and wood in the streams. Principal components analysis of invertebrate density data identified nine orthogonal community types, the distributions of two of which were significantly related to land use. The role played by browsers and shredders in the stream community depended on land use. 4. Primary analysis was at the level of the tributary. When it focused on sites within tributaries, more variables were related to land use and at a higher level of significance. This was largely a result of enhanced statistical power due to increased replication. When whole subcatchments were the focus of attention, statistical power was so low, even with six to eleven subsamples to generate overall means, that few significant patterns could be identified. However, the community patterns that were revealed were similar whatever the scale of sampling.

The role of dissolved organic matter, particularly free amino acids and humic substances, in freshwater ecosystems

Abstract: 1. Although the mass of dissolved organic matter (DOM) often exceeds that of living organisms in freshwaters, little is known about the roles of its constituent molecules as sources of energy and information for aquatic organisms. In the present review attention is focused on free amino acids (FAA) and humic substances (HS) as examples of labile and refractory components within DOM. 2. The following questions are addressed. (i) What are spatiotemporal patterns in the distribution of DOM, HS and FAA? (ii) What are the origins of the components of DOM and how are their concentrations regulated? (iii) What is the significance of the spatial and temporal distributional patterns of DOM, HS and FAA to detritivorous invertebrates and other organisms associated with them? (iv) What is the relevance of DOM to the food web concept and to the biochemical ecology of freshwater ecosystems? 3. Concentrations of DOM, FAA and HS within lentic ecosystems are ranked as follows: Sediment pore water > Air–water interface > Midwater column. Comparisons between water bodies show that the concentrations of labile constituents of DOM, such as FAA, are usually positively correlated with base cations, nutrients and biological activity. In contrast, HS concentrations are negatively correlated with base cations or nutrients but positively correlated with the rate of biological degradation (the maximum values occurring in the autumn). The FAA : HS ratios might serve therefore as an indicator of the potential productivity of a water body. 4. External sources of DOM in general, and FAA and HS in particular, include rainwater, windborne material, surface flow and groundwater. The relative importance of these allochthonous sources of DOM decreases along the length of lotic ecosystems and also with increase in size of lentic ecosystems. Internal sources of FAA and HS include synthesis or polymerization from existing organic matter, degradation of organic matter and release from both living and dead organisms. The net accumulation of DOM released by living bacteria, phytoplankton, epilithon, macrophytes and invertebrates is much reduced due to heterotrophic uptake. Hence, most of the allochthonous DOM in freshwater originates from dead organic matter deposited on the sediment. Phytoplankton-dominated ecosystems may, however, differ, as most of their DOM may be recycled within the water column. 5. The factors that determine the external concentrations of DOM, FAA and HS are discussed. Evidence is cited in support of the following testable hypotheses. (i) The rates of production of DOM components will be favoured by increasing base cation and nutrient concentrations. (ii) Colloidal clay, base cations, biopolymers and living organisms, particularly bacteria, facilitate the removal of HS. Consequently, base-rich eutrophic waters tend to have lower HS concentrations than oligotrophic, base-deficient waters. (iii) As a result of higher productivity and selective removal of FAA, eutrophic waters tend to have higher FAA concentrations than those that are oligotrophic. 6. Labile DOM components, such as FAA, act as sources of information for aquatic organisms. More research is needed in this field. There is a consensus that DOM acts as an important source of energy for aquatic bacteria, thus forming the microbial loop. However, higher eukaryotic organisms also utilize DOM, including components released by bacteria and plants as metabolic end-products and photoassimilates, respectively. As a result, these DOM components may be more important as food for macrodecomposers than the microdecomposers themselves. HS may also benefit aquatic organisms by promoting their growth and protecting them from inimical forces. Conversely, the removal of photons and the release of toxins by HS may be detrimental to aquatic organisms. 7. It is concluded that the central dogma of the foodweb, and its implicit assumption that the energy flow in aquatic ecosystems can be quantified solely by measuring rates of photosynthesis, ingestion of solid food and its digestion by higher organisms, is invalid. To extend our understanding of the role of DOM as a source of nutrition and information to aquatic organisms it is suggested that the subject should be studied within the context of ‘modules’ which have the following properties: (i) the components have co-evolved; (ii) the more vulnerable components will have protective mechanisms; (iii) the components will derive mutual benefits from co-existence; (iv) sedentary components will release kairomonal attractants or developmental primers; (v) living components will exchange energy and information; (vi) the module will collapse following the removal of strongly interactive keystone species. An example of a three-component, three-subset module, is provided by tubificid worms, epilithic bacteria and algae. A more complex module consisting of pulmonate snails, associated macrophytes, their epiphytic bacteria and algae has four components and six subsets. The elucidation of the interactive mechanisms within such modules demands an interdisciplinary approach, involving microbiology, biochemistry and behavioural biology.

Modelling interactions of food quality and quantity in homeostatic consumers

Abstract: 1. Boundaries between growth limitation by carbon (C) and phosphorus (P) in homeostatic heterotrophic consumers such as zooplankton will vary as demands on these two elements vary, as they should at different food quantities. At very low food quantity when production is close to zero, metabolic requirements (for carbon) become more important than growth requirements (for carbon and phosphorus in fixed proportion). Thus, the boundary separating C-and P-limited growth should be at a higher C : P ratio at low food quantity than at high food quantity. 2. A model including both metabolism and growth indicates that consumer growth should differ between foods of high vs. low phosphorus concentration only when food quantity is above a certain level. Thus, two foods might give identical consumer growth rates at low food quantity but give different consumer growth at higher quantity. 3. Solution of the model using parameters based on 2 mm Daphnia compared with a survey of C and P in seston of marine and freshwater sites supports earlier conclusions of the potential importance of food quality constraints on Daphnia growth.

Effects of nutrient limitation on biochemical constituents of Ankistrodesmus falcatus

Abstract: 1. Cell size and volume changed as a function of the type of resource limitation, with nitrogen-limited cells being smaller and less dense and phosphorus-limited cells being larger and more dense than non-limited cells. 2. The major biochemical constituents of the green alga Ankistrodesmus falcatus varied as a function of nitrogen or phosphorus limitation (15% of maximum growth rate) compared to cells growing at their maximum rate. Nitrogen-limited cells had much lower protein content and phosphorus-limited cells had higher carbohydrate and lipid contents than cells growing under no limitation. 3. Phosphorus-limited cells had a higher total lipid content than either nitrogen-limited or non-limited cells, but the lipid class composition was similar. 4. The protein : lipid ratio was lowest (0.38) in the nitrogen-limited cells, intermediate in the phosphorus-limited cells (0.44) and highest in the non-limited control cells (1.14).

Use of fatty acids for the assessment of zooplankton grazing on bacteria, protozoans and microalgae

Abstract: 1. The distribution of fatty acids in different groups of bacteria, ciliated protozoans and microalgae is reviewed emphasizing specific fatty acids like odd-branched fatty acids and (n-3) polyunsaturated fatty acids. 2. Odd-branched fatty acids and (n-6) fatty acids appear to be good indicators of zooplankton grazing on bacteria and ciliates when they are detected in microcrustacean triacylglycerols. We give several examples where these fatty acids may be used as markers. The value of (n-3) fatty acids in describing zooplankton grazing on phytoplankton seems to be low.

Wave-induced shear stresses, plant nutrients and chlorophyll in seven shallow lakes

Abstract: 1 Sediment resuspension dynamics were investigated in relation to changes in water column nutrients (TP, TN, PO4-P, NO3-N and NH4-N), chlorophyll a and phaeopigment in seven shallow (Zm < 15 m) lakes in South Island, New Zealand, ranging in area from 01 to 180 km2 2 Benthic shear stress, calculated from wind speed, effective fetch and depth, was a considerably better predictor of nutrient and pigment concentrations than wind speed 3 For TP, TN, chlorophyll a and phaeopigment, sixteen of the possible twenty-eight linear correlations with benthic shear stress were significant at P < 005, with 16–87% of the variation being explained by shear stress 4 Wind decreased the ratios of TN : TP, with ratios exponentially approaching those of the sediments as shear stress increased in four of the lakes 5 Relationships of dissolved inorganic nutrients to shear stress were considerably weaker than those for total nutrients and showed no consistent trend over the seven lakes 6 Estimated annual mean TP inclusive of resuspension was over four times higher than that derived from measured calm samples in two lakes 7 The number of nutrient and pigment parameters that were significantly correlated with shear stress and the strengths of the relationships varied widely from lake to lake We could establish no simple relationships between these effects and any single characteristic of the lake, sediment, or water 8 A function is developed to predict the rate of entrainment of TN and TP in response to an applied shear stress, where the independent variables are sediment nutrient content and particle size, and the macrophyte density in the lake

Changes in the crustacean zooplankton community of Harp Lake, Canada, following invasion by Bythotrephes cederstrœmi

Abstract: 1. Detecting the impacts of invading Bythotrephes cederstrœmi (Crustacea, Onychopoda, Cercopagididae) on zooplankton in North American lakes has been hampered by the brevity of pre-invasion data, and by the difficulty of distinguishing the effects of the invader from other stresses. The data from Harp Lake in Ontario, Canada, circumvent these difficulties. Bythotrephes appeared in the lake in 1993. There is a 15-year pre-invasion data set, and no significant complicating concurrent stresses. 2. The species composition and the size structure of the crustacean zooplankton community of Harp Lake changed after the invasion. Several small species either declined dramatically in abundance (e.g. Bosmina longirostris, Tropocyclops extensus) or disappeared (Chydorus sphaericus, Diaphanosoma birgei, Bosmina (Neobosmina) tubicen). In contrast the abundance of the larger cladocerans Holopedium gibberum and Daphnia galeata mendotae and the hypolimnetic copepod Leptodiaptomus sicilis increased. Several univariate and all multivariate summarizations of zooplankton abundance, biomass and size structure highlighted the uniqueness of the post-invasion community. 3. The alterations in the zooplankton community could not be attributed to changes in lake acidity, thermal regimes, penetration by ultraviolet light, nutrient status, fish stocking or the abundances of native invertebrate predators, but they were correlated with Bythotrephes abundance, both within and among years. Hence, we hypothesize that the invasion by Bythotrephes has significantly altered the crustacean zooplankton community of Harp Lake.

UV‐induced changes in phytoplankton cells and its effects on grazers

Abstract: This review addresses the effects of UV-radiation on the morphology and biochemistry of phytoplankton and the potential effects on grazers. UVA and UVB radiation inhibit the uptake of inorganic nutrients in phytoplankton. Reduced rates of ammonium and nitrate uptake in marine diatoms, and reduced uptake of phosphorus in freshwater flagellates are reported. The effects on cell stoichiometry are not settled. UVA and UVB radiation promote increased cell volumes owing to a decoupling between the photosynthetic processes and cell division. Loss or inactivation of flagellae and loss of motility are also reported for a number of phytoplankton species. UVA and UVB radiation may affect major biochemical constituents. Accumulation of intracellular, photosynthetic products (lipids or carbohydrates) is a common, although not unique, property of UV-stressed algae. Fatty acid (FA) profiles seem susceptible to UV radiation. A relative increase of short-chained, and a decrease in polyunsaturated FA (PUFA) are reported. The important membrane FA like eicosapentaenoic acid (EPA, 20:5 omega 3) and docosahexaenoic acid (DHA, 22:6 omega 3) seem particularl UV-related responses are highly dependent on taxonomy, cell-cycle stage, nutrient-limitation and the UV:PAR (photosynthetic active radiation)-ratio. Nutrient deficiency, cell size, cell wall properties and FA can all have significant impacts on grazers. Thus the reported effects on cell morphology and biochemical constituents could have profound effects on grazers and energy transfer in aquatic foodwebs. [KEYWORDS: ULTRAVIOLET-B RADIATION, FATTY-ACID COMPOSITION, EUGLENA-GRACILIS, OZONE DEPLETION, CHLAMYDOMONAS-REINHARDTII, MONOCHROMATIC LIGHT, NITROGEN STARVATION, NUTRIENT LIMITATION, N-15-NITRATE UPTAKE, ISOCHRYSIS-GALBANA]

The functional trophic role of lotic primary consumers: generalist versus specialist strategies

Abstract: 1. The relative extent of generalist or specialist resource use strategies is an important question in ecology. A community dominated by specialist strategies suggests a high level of interspecific competition for resources, resulting in the evolutionary development of isolating mechanisms between species (e.g. resource specialization to avoid and/or outcompete other species). A community dominated by generalist strategies suggests less interspecific competition for resources, allowing many taxa to utilize the same resources. In stream systems, generalist food habits are a common strategy among primary consumers, but little is known about resource assimilation strategies (resources incorporated into tissue growth). Published data indicate that generalist resource assimilation strategies may prevail in lotic systems as well. 2. Functional feeding groups (FFGs) are often used to infer resource assimilation among lotic macroinvertebrates (e.g. shredder-detritivore, scraper-herbivore). While these groupings are aptly used to describe invertebrate feeding modes and community structure, the use of FFGs to describe resource assimilation among lotic consumers is not appropriate. Sufficient data now exist to seriously question how accurately FFG assignments describe the processes of energy flow and material transfer between trophic levels in stream ecosystems. 3. Because FFGs may not accurately describe functional attributes in lotic systems, an alternative approach is needed. One approach is to determine the amount of secondary production that is derived from autochthonous (e.g. periphyton and algae) and allochthonous (e.g. detritus) resources directly. A simple model of community function based on this approach is presented. The model incorporates trophic generalists into measurement of consumer–resource energetics in lotic systems.

The use of artificial neural networks to predict the presence of small‐bodied fish in a river

Abstract: 1. Discriminant factorial analysis (DFA) and artificial neural networks (ANN) were used to develop models of presence/absence for three species of small-bodied fish (minnow, Phoxinus phoxinus, gudgeon, Gobio gobio, and stone loach, Barbatula barbatula). 2. Fish and ten environmental variables were sampled using point abundance sampling by electrofishing in the Ariege River (France) at 464 sampling points. 3. Using DFA, the percentage of correct assignments, expressed as the percentage of individuals correctly classified over the total number of examined individuals, was 62.5% for stone loach, 66.6% for gudgeon and 78% for minnow. With back-propagation of ANN, the recognition performance obtained after 500 iterations was: 82.1% for stone loach, 87.7% for gudgeon and 90.1% for minnow. 4. The better predictive performance of the artificial neural networks holds promise for other situations with non-linearly related variables.

The role of carbon dioxide in the initiation and maintenance of blue-green dominance in lakes

Abstract: 1. In 1993 the south basin of Squaw Lake, Wisconsin, U.S.A., was artificially circulated and injected with CO2 in an attempt to eliminate the massive quantities of blue-greens normally present during summer. The unmixed, uninjected north basin was the control. Despite a great difference in CO2 concentration and in pH between the two basins, their blue-green maxima began simultaneously and eventually reached the same size. The predominant algae in both basins were Aphanizomenon flos-aquae and Anabaena flos-aquae. 2. From 13 May to 9 September, experiments were done to determine the responses of photosynthesis (oxygen production) of the phytoplankton communities in both basins to changes in pH over the range 7–9. Both the north and south basins underwent two distinct shifts in the slopes of their photosynthetic responses to pH. These shifts paralleled changes in the proportion of blue-greens in their phytoplankton. 3. Experiments with additions of KHCO3 or NaHCO3 showed that the responses to pH were really responses to CO2 concentration. Therefore, the data obtained in the photosynthesis experiments were used to calculate the kinetic parameters Ks* and Vmax*. The Ks* values varied in relation to the proportion of blue-greens, with lower values during the period when blue-greens predominated. The Vmax*values showed no such systematic changes. 4. CO2 compensation and zero photosynthesis concentrations confirm that when the blue-greens dominated, CO2 was taken up much more efficiently than when the phytoplankton comprised mostly non-blue-greens. No evidence appeared suggesting direct use of bicarbonate even at pH values of 10.0. 5. Experiments with water collected seasonally from four other lakes show that Squaw Lake is not unique. In each case the response slopes (and therefore Ks* values) were high during spring when non-blue-greens were dominant, but decreased when the blue-green maximum began. 6. Experiments with individual species of algae confirm that blue-greens generally have better CO2 kinetics than do greens. 7. It is concluded that initiation of the blue-green maximum does not depend upon conditions of low CO2 concentration or high pH. However, once the blue-greens become abundant they ensure their dominance by reducing concentrations of CO2 to levels available only to themselves.

Ceratophyllum demersum hampers phytoplankton development in some small Norwegian lakes over a wide range of phosphorus concentrations and geographical latitude

Abstract: 1. Data on submerged and floating-leafed macrophytes, phytoplankton, nutrients (N, P) and calcium were collected from twenty-four small lakes ( 1 km2) over a wide range of latitudes in Norway. The majority of the investigated lakes were mesotrophic or eutrophic, and most of the lakes were markedly affected by diffuse and point-source runoff from agriculture. According to their macrophyte species composition, the majority of the lakes can be classified as Potamogeton lakes or Chara lakes, or a combination of these. 2. This study is consistent with the ‘two alternative stable states’ hypothesis. We observed clearwater lakes with dense macrophyte cover over a wider range of total P concentration than has been reported previously: from 30 to more than 700 mg P m–3. The clearwater state was only observed in lakes with mean depths of less than 1.9 m. 3. Most clear lakes with high cover of submerged vegetation showed indications of N limitation. 4. In this study nearly all the macrophyte-dominated lakes with P concentrations above 30 mg m–3 had dense stands of Ceratophyllum demersum (L.). This indicates that Ceratophyllum may also play an important role in stabilizing and maintaining a clearwater state at high P concentrations.