Dams and Flow in the Cotter River, Australia: Effects on Instream Trophic Structure and Benthic Metabolism

This study assessed benthic macroinvertebrates and periphyton and its responses to managed river-flows, in riffles downstream of three dams on the Cotter River, Australian Capital Territory. Benthic macroinvertebrates and periphyton were also assessed in adjacent tributaries of the river, as well as in a nearby unregulated river and its tributaries. Food sources of four macroinvertebrate taxa (Leptophlebiidae, Elmidae, Glossosomatidae and Orthocladiinae) were determined by stable isotope analysis of the invertebrates and their potential food, in conjunction with examination of the gut contents of individual invertebrates. Components of benthic periphyton were the main food source for the selected taxa. Orthocladiinae consumed primarily amorphous detritus, while Elmidae, Glossosomatidae and Leptophlebiidae consumed diatoms. Enclosed benthic chambers were used to measure the response of benthic metabolism to monthly flow spikes released from one of the dams. The balance of benthic metabolism as measured by the Production/Respiration ratio (P/R) showed a shift towards production after the release of flow spikes. At sites downstream of the dams, there was more periphyton chlorophyll-a in the form of filamentous green algae than at sites in the unregulated river and the tributaries, and macroinvertebrate taxa using periphyton as a food resource were missing or reduced in abundance relative to sites without dams. However, the site downstream of the dam with environmental flow releases had more macroinvertebrate taxa and less periphyton cholorophyll-a content than sites downstream of dams without managed environmental flows, suggesting that a more suitable food supply resulting from environmental flow releases shifted macroinvertebrate communities towards those of unregulated streams.     

Influences of fish on food web structure and function in mountain lakes

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Phosphorus removal from eutrophic lakes using periphyton on submerged artificial substrata

The potential of periphyton for phosphorus removal from lakes has been investigated using a novel method involving polypropylene (PP) substrate carriers submerged in the pelagial. The study area Lake 'Fühlinger See' in Cologne (Germany) is a complex of mesoeutrophic gravel pit lakes. The whole site is intensively used as a recreation area. Visitors are thought to be the most important single contributors to lake eutrophication. Carriers were exposed at different depths (2, 3.5, 5 m), for different time intervals (1–8 months) and from March to November PP-sheets were readily colonised by periphyton and a biofilm consisting mainly of benthic diatoms developed. Seasonal variability of periphyton on substrates was observed since filamentous green algae colonised the artificial substrates mainly between July and November. Chlorophyll a content of periphyton on the PP-fleece was up to 240-fold higher than chlorophyll a concentrations in the same volume in the epilimnion. Up to around 100 mg of total phosphorus per m² PP-fleece was bound and can be eliminated from the lake by removal of the substrate carriers together with the periphyton after four months of exposure. Though large-scale validations are needed, this method may be applicable as a technique to harvest phosphorus from the water column in larger-scale settings.     

Seasonal Dynamics of Periphyton in a Large Tropical Lake

Tropical aquatic systems are generally assumed to have little seasonality in productivity patterns. However, this study indicated that there was substantial seasonal variation in epilithic productivity and biomass in tropical Lake Tanganyika, due primarily to seasonal patterns in lake hydrodynamics that influence nutrient availability. Although they support much of the lake’s biological diversity, epilithic algae made a minor contribution to the total energy budget in Lake Tanganyika. A comparison among large, oligotrophic lakes revealed no significant latitudinal trends in periphyton productivity or biomass. However, Lake Tanganyika has relatively low benthic algal biomass and is therefore more efficient at photosynthesis than the temperate lakes. The influence of wave action and consumer density and diversity may be important in moderating productivity of the epilithic community.     

Spatially heterogeneous trends in nearshore and offshore chlorophyll a concentrations in lakes Michigan and Huron (1998–2013)

1. Nutrient abatement programmes have been successfully implemented around the globe to reduce nutrient loading into aquatic ecosystems. Concurrently, the worldwide spread of invasive filter feeders, such as dreissenid mussels, may alter nutrient dynamics in invaded systems by sequestering nutrients away from pelagic zones and reducing primary production in offshore areas. Such is the case in the Laurentian Great Lakes of North America, where decades of nutrient abatement and the establishment of dreissenid mussels have seemingly resulted in more oligotrophic conditions and altered spatial patterns of nutrient availability and primary production.
2. Recent studies have focused on whole lake trends in primary production despite spatial differences in tributary inputs, bathymetry, and other environmental conditions that can affect primary production in nearshore areas. Thus, we hypothesised that trends in nearshore chlorophyll concentrations in different areas may diverge in a manner consistent with spatial differences in nutrient input. To evaluate these differences in surface chlorophyll responses, we assessed temporal trends in four different areas of Lake Michigan and three different areas of Lake Huron.
3. We hypothesised that in lakes Huron and Michigan, nearshore zones have experienced slower declines of chlorophyll concentrations relative to offshore zones. To assess this hypothesis, we estimated temporal trends of surface water chlorophyll concentrations (a proxy for primary production) from satellite imagery from 1998 to 2013. We calculated average surface chlorophyll concentrations for 10-m depth intervals ranging from the shore (0–10 m) to offshore (>90 m) during representative months of May, July, and September. We then analysed these data to determine if long-term trends in surface chlorophyll varied by season, proximity to the shoreline, and water depth.
4. The rates of annual change in chlorophyll concentrations in nearshore areas were markedly different to offshore trends in both lakes. Chlorophyll concentrations declined overtime in offshore areas, but nearshore chlorophyll concentrations were either stable (in May) or increased (in July and September) throughout the time series.
5. Differences in chlorophyll concentrations among areas were prominent in Lake Michigan. While differences between the northern and southern basin have been previously documented, trends in chlorophyll concentrations also differed between the eastern and western sides of Lake Michigan. Despite similar bathymetry and geographic features to Lake Michigan, regional trends were not observed in Lake Huron.
6. The results of this study are generally consistent with the nearshore shunt hypothesis, which predicts that dreissenid filtering, nutrient re-suspension, and continued nutrient loading from tributaries can cause an increase in primary production in nearshore areas during periods of offshore oligotrophication. Thus, the localised effects of nutrient abatement programmes in a given lake will be influenced by complex interactions between lake bathymetry and the presence of non-native filter feeding organisms.

     

Periphyton in the Volta Lake. II. Seasonal changes on wooden blocks with depth

A seasonal study of the periphyton developed on wooden blocks suspended at five constant depths (0, 0.5, 1, 2, 5 m) in the Pawm-pawm arm of the Volta Lake is reported. The early colonizers at all depths were diatom species, they gradually declined in diversity and numbers and blue-green algae and green algae became more common. After one year the shallower (0–1 m) blocks were covered by a luxuriant growth of filamentous green algae though at lower levels diatoms predominated. Diversity and cell numbers of algae decreased with depth, this was most pronounced below 2 m. It appears that filamentous green algae eventually come to dominate wooden surfaces floating at relatively shallow depths in the Volta Lake.     

Long‐term impacts of invasive species on a native top predator in a large lake system

1. Declining abundances of forage fish and the introduction and establishment of non‐indigenous species have the potential to substantially alter resource and habitat exploitation by top predators in large lakes. 2. We measured stable isotopes of carbon (δ¹³C) and nitrogen (δ¹⁵N) in field‐collected and archived samples of Lake Ontario lake trout (Salvelinus namaycush) and five species of prey fish and compared current trophic relationships of this top predator with historical samples. 3. Relationships between δ¹⁵N and lake trout age were temporally consistent throughout Lake Ontario and confirmed the role of lake trout as a top predator in this food web. However, δ¹³C values for age classes of lake trout collected in 2008 ranged from 1.0 to 3.9‰ higher than those reported for the population sampled in 1992. 4. Isotope mixing models predicted that these changes in resource assimilation were owing to the replacement of rainbow smelt (Osmerus mordax) by round goby (Neogobius melanostomus) in lake trout diet and increased reliance on carbon resources derived from nearshore production. This contrasts with the historical situation in Lake Ontario where δ¹³C values of the lake trout population were dominated by a reliance on offshore carbon production. 5. These results indicate a reduced capacity of the Lake Ontario offshore food web to support the energetic requirements of lake trout and that this top predator has become increasingly reliant on prey resources that are derived from nearshore carbon pathways.     

Hydrophyte-macroinvertebrate interactions in Zwemlust,a lake undergoing biomanipulation

In two years after biomanipulation of Lake Zwemlust (The Netherlands), macrophytes (helophytes, elodeids) and filamentous algae developed luxuriantly in the lake. They influenced the structure of macroinvertebrate communities inhabiting them. Macrophytes and algae, by changing environmental and trophic conditions, also affected the composition of macrozoobenthos. Vascular plants served as an important source of food for zoobenthos and phytofauna, mainly after they were decomposed. Filamentous algae were consumed readily alive by many animals. Invertebrates appeared to be important as a potential nutrient source for hydrophytes.     

Periphyton on artificial substrata from three lakes of different trophic status at Hope Bay (Antarctica)

The nutrient characteristics of aquatic environments at Hope Bay (Antarctica) depend on different factors, penguin enrichment being one of the most important. In this study we surveyed three water bodies of different morphometry and trophic status: Esperanza Lake (oligotrophic), Boeckella Lake (meso-eutrophic), and Pingüi Pond (hypereutrophic). This research provides a preliminary characterization of the periphyton colonization on artificial substrata (glass slides) of these water bodies from the end of January to mid-March 2000. Qualitative and quantitative analyses of the algae, chlorophyll a, dry weight, ash-free dry weight, and physical and chemical variables of the lakes were assessed. The Autotrophic Index and the Lakatos system of classification were also applied. All three lakes differed clearly in all the variables considered. The periphyton from Esperanza Lake was first dominated by Bacillariophyceae and subsequently by the chrysophyce Phaeogloea mucosa. P. mucosa was the dominant species at Boeckella Lake and Chlamydomonas subcaudata was dominant at Pingüi Pond. Highest mean maximum density values were reached at Pingüi Pond, followed by Boeckella and Esperanza Lakes. Highest biomass figures were registered with increasing trophic status. According to the Lakatos index, the periphyton of Esperanza Lake was the least developed and it was mainly organic and heterotrophic; Boeckella Lake showed intermediate development in periphyton mass, which was autotrophic and mainly inorganic whereas Pingüi Pond showed the highest development in periphytic mass, and it was mainly autotrophic.     

Effects of Multi-chain Omnivory on the Strength of Trophic Control in Lakes

Omnivory has been implicated in both diffusing and intensifying the effects of consumer control in food chains. Some have postulated that the strong, community level, top-down control apparent in lakes is not expressed in terrestrial systems because terrestrial food webs are reticulate, with high degrees of omnivory and diverse plant communities. In contrast, lake food webs are depicted as simple linear chains based on phytoplankton-derived energy. Here, we explore the dynamic implications of recent evidence showing that attached algal (periphyton) carbon contributes substantially to lake primary and secondary productivity, including fish production. Periphyton production represents a cryptic energy source in oligotrophic and mesotrophic lakes that is overlooked by previous theoretical treatment of trophic control in lakes. Literature data demonstrate that many fish are multi-chain omnivores, exploiting food chains based on both littoral and pelagic primary producers. Using consumer-resource models, we examine how multiple food chains affect fourth-level trophic control across nutrient gradients in lakes. The models predict that the stabilizing effects of linked food chains are strongest in lakes where both phytoplankton and periphyton contribute substantially to production of higher trophic levels. This stabilization enables a strong and persistent top down control on the pelagic food chain in mesotrophic lakes. The extension of classical trophic cascade theory to incorporate more complex food web structures driven by multi-chain predators provides a conceptual framework for analysis of reticulate food webs in ecosystems.     

The Contribution of Ciliated Protozoa to Zooplankton Biomass in an Acidic, Subtropical Lake

Ciliated protozoa accounted for up to 50% of the mean daily zooplankton biomass in McCloud Lake, a small (5 ha), oligotrophic, acidic (pH 4.7) lake in north-central Florida. Food resources (algae and bacterioplankton) were limiting for crustacean and rotifer zooplankton during much of the year. Myxotrophic ciliates were a dominant component of the planktonic food web. Stentor niger , an uncommon species in the plankton of lakes, dominated the ciliate assemblage and usually comprised >90% of total ciliate biomass. Stentor niger always contained high densities of photosynthetic zoochlorellae and contributed an estimated 30% to the total autotrophic biomass.     

Depth gradients in food‐web processes linking habitats in large lakes: Lake Superior as an exemplar ecosystem

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Littoral mollusc communities and water quality in southern Lake Winnipeg, Manitoba, Canada

Water quality and mollusc communities have been declining in Lake Winnipeg., the tenth largest freshwater lake in the world. Ninety sites were surveyed in the southern half of the lake. Nitrate and total dissolved solids were found to be significantly higher on the west side, while cadmium, copper and lead were higher on the east side. Agriculture, urban effluent, and recreational development were major factors directly affecting nearshore water quality. Human impacts were sporadically aggravated by Red River floodwaters entering the lake. A total of 26 gastropod were currently found in the lake, but 16 of them were found at 5 or fewer sites. Only 6 unionid species were found, compared to at least 11 historical species records. Species richness of both gastropods and unionids was positively correlated with total dissolved solids, and inversely with lead. Gastropod and unionid species richness were also mutually positively correlated. Catchment basin and shoreline management policies affecting Lake Winnipeg need to be reexamined to reduce further habitat decline.     

Limnological characteristics of several lakes on the Lake Wales Ridge,South-Central Florida

Three lakes near the southern terminus of the Lake Wales Ridge of south-central Florida were studied. The lakes, all connected by either natural drainage or canals, vary significantly in terms of shoreline development. All three lakes are soft water systems with low concentrations of dissolved nutrients; however, rates of primary productivity and chlorophyll a appear to be correlated with the degree of shoreline development. Nutrient enrichment bioassay experiments in the laboratory showed that, in general, water from all the lakes responded to additions of nitrogen and phosphorus in combination. Samples from only one lake responded to enrichment with phosphorus alone, and no samples to additions of nitrogen alone.Two of the lakes can be classified as oligotrophic while the third is most probably eutrophic.     

Fossil record of cladoceran and algal responses to fishery management practices

1. We hypothesized that the fishery management practices of toxaphene application and trout stocking would affect non-target organisms in lakes. Because these practices were rarely monitored in the past, cladoceran and algal assemblages were quantified in sediment cores from two lakes treated 30+ years ago to determine the long-term response of organisms near the base of the food chain. 2. Chydorids were remarkably resistant over the short term (a few years) in both the oligotrophic and eutrophic lakes despite toxaphene treatments that extirpated native fish and other invertebrates. In the oligotrophic lake (Annette Lake), six chydorid taxa were less abundant in the years following treatment, although no loss of species richness was detected. In the eutrophic lake (Chatwin Lake), the dominant Chydorus cf. sphaericus declined coincident with toxaphene treatment, but longer-term declines of all taxa were probably related to food web or other changes rather than to toxaphene toxicity. Cause and effect coupling was complicated by the fact that many chydorids were present at low concentrations in some pretreatment samples. 3. The algal communities (as fossil pigments) responded to treatment differently in the two lakes. In the oligotrophic lake, planktonic diatoms, dinoflagellates and chlorophytes were replaced as dominants by deep-water or benthic blooming cryptophytes, chrysophytes and cyanobacteria. This shift occurred along with increases in large daphnids and the ‘grazing indicator’, pheophorbide a. While both lakes appear to have had enhanced pigment preservation following treatment, the eutrophic lake encountered few long-term changes in its fossil pigment assemblage. Redundancy analysis estimated that the presence or absence of stocked trout explained much of the variation in the algal assemblages, particularly in the oligotrophic lake. 4. Toxaphene remained elevated in profundal sediments from these lakes 30 and 35 years after treatment.     

Trophic complexity of small fish in nearshore food webs

Small nearshore fishes are an important part of lacustrine and functional diversity and link pelagic and benthic habitats by serving as prey for larger nearshore and offshore fishes. However, the trophic complexity of these small nearshore fishes is often unrecognized and detailed studies of their role in food webs are lacking. Here, we examined niche space patterns of small nearshore fish species using Bayesian analyses of carbon and nitrogen stable isotope data in nine freshwater lakes that are among the largest lakes in Minnesota. We found considerable variability in niche areas within species and high variability in niche overlap across species. At the assemblage level, niche overlap (average diet overlap of all species pairs at a lake) decreased as whole-lake species richness increased, possibly indicating a greater degree of resource specialization in more speciose lakes. Overall fish niche space was weakly but significantly related to niche space of their invertebrate prey. Although nearshore benthic resources contributed to fish diets in all lakes, all fish species also had non-negligible and variable contributions from pelagic zooplankton. This inter- and intraspecific variability in trophic niche space likely contributes to the multi-level trophic complexity, functional diversity, and potentially food web resilience to ecosystem changes.

     

Cost of predation avoidance in young-of-year lake trout (Salvelinus namaycush): growth differential in sub-optimal habitats

Selection of habitat to avoid predation may affect the diet of young-of-year (YOY) lake trout (Salvelinus namaycush). YOY lake trout may use inshore habitat to avoid predation; this habitat may be sub-optimal for growth. To test this, YOY lake trout were penned in nearshore and offshore pelagic areas of two arctic lakes. Toolik Lake had a lake trout population, the other lake, S6, did not. YOY lake trout in Toolik Lake lost weight, but those offshore lost less weight. The YOY lake trout in Lake S6 gained weight and those offshore gained more weight. The primary diet item of the YOY lake trout in both lakes during this experiment was the zooplankter Diaptomis probilofensis; it was also one of the most abundant species. However, its density inshore in Lake S6 was similar to inshore and offshore densities in Toolik Lake. The increased availability of alternative zooplankton prey in Lake S6 may account for the growth differential of YOY lake trout in Lake S6 relative to Toolik Lake. Bioenergetic modeling of YOY lake trout suggests that growth similar to that in the offshore of Lake S6 would be necessary for successful recruitment. If the reduced zooplankton availability in Toolik Lake leads to the reduced growth of YOY in the inshore and offshore pelagic areas, then these fish will be more susceptable to winter predation/starvation. For YOY lake trout to survive in Toolik Lake they most likely shift to feeding on benthic prey before the end of their first summer. Dept. of Chemical Engineering     

Variations in the periphytic community structure and dynamics of Lake Nahuel Huapi (Patagonia,Argentina)

Little is known about periphyton community in Patagonia and the influence that urban development has on a particular water body. Lake Nahuel Huapi is located in a National Park with little industrial or agricultural activity in the basin, but it is influenced by urban discharges from San Carlos de Bariloche, a town of 80000 inhabitants located on its south shore. Variations in structure and dynamics of the periphyton community in Lake Nahuel Huapi were studied during 1 year, to examine the influence of urban discharges on this community. Periphyton samples were collected on the shoreline of the lake and evaluated for biomass (as chlorophyll a concentration) and cell density of the main algal groups, at sites with and without urban influence. Results indicated the major influence of pollution from urban sources on periphyton at the most impacted sites, as well as the effect of different local events at each site (degree of contamination, type of coast, wind exposure, etc.). Higher biomass and cell densities at contaminated sites were evident, but the variation of main algal groups through the year was similar in all the sites. Periphyton in Lake Nahuel Huapi proved to be an important bioindicator of urban impacts on this water body.     

Limnological aspects of the St. Clair River

The St. Clair River is a major navigable waterway transporting water southwards for 63 km from Lake Huron to Lake St. Clair at an average flow of 5 100 m3 s^-1. Water entering the river is low in suspended solids, organic carbon, phosphorus and nitrates, typical of clear, oligotrophic waters. In contrast to many large rivers, dissolved and colloidal solids account for 90 to 95 percent of the total solids load transported by the river, giving the river a turquoise colour common of glacial meltwater streams.The river supports a diverse floral and faunal community that includes 20 taxa of submergent macroflora, at least 300 benthic macroinvertebrates and 83 fishes. A number of exotic (European) species, including 3 plants, 4 molluscs and 11 fishes, occur in the river with the macroalga, Nitellopsis obtusa, zebra mussel (Dreissena polymorphora), Asian clam (Corbicula fluminea), and white perch (Morone americana) being the most recent invaders. Production is estimated to be 200 g m^-2 a^-1 ash-free dry mass for submergent macrophytes and periphyton, 7 g for macroinvertebrates and 5 g for fishes.The river also supports a variety of water-oriented recreational activities, is a source of municipal and industrial water, a receiver of municipal and industrial wastes, and a shipping corridor. Industrial discharges have adversely affected aquatic life, particularly in the nearshore areas along the Canadian shoreline south of Sarnia, Ontario. In addition, channel dredging and shoreline modifications (bulk-heading and backfilling) have destroyed large areas of valuable habitat in the main channel and along the shoreline. Improvements in the nearshore benthic macroinvertebrate community of the river over the past 20 years show that the river will respond to reductions in contaminants loadings.     

Comparison of Plankton-Water Chemistry Relationships in Three Acid Stressed Lakes in Nova Scotia,Canada

A field program was conducted in 1980 and 1981 on three lakes in Kejimkujik National Park, Nova Scotia, to study plankton-water chemistry relationships in a region of potential acid precipitation stress. Among lake and between year comparisons were made. The three study sites represent two different types of lakes. Kejimkujik Lake (pH 4.8) and Pebbleloggitch Lake (pH 4.5) are both high-colored, dystrophic acid lakes. Beaverskin Lake is a clear, oligotrophic lake which is not as acidic (pH 5.4). The phytoplankton of Kejimkujik Lake was dominated by diatoms, while Pebbleloggitch Lake was dominated by chlorophytes and chrysophytes, and Beaverskin Lake was dominated by cyanophytes. Kejimkujik Lake had the highest total algal cell volume per liter, and Pebbleloggitch Lake the lowest. Rotifer populations composed the majority of the zooplankton communities, while the crustacean zooplankton were dominated by the acid-tolerant copepod Diaptomus minutus. Kejimkujik Lake had the lowest zooplankton biomass and Pebbleloggitch Lake the highest zooplankton biomass per m³. A pattern of highest algal density in Beaverskin Lake, but highest zooplankton density in Pebbleloggitch Lake emerged in both years. This is likely an effect of abundant, but unsuitable food (blue-green algae) in Beaverskin Lake and important detrital food resources in Pebbleloggitch Lake in both years. Multiple regression analysis of water chemistry variables with plankton species produced many significant effects, but failed to show clear patterns. Cause and effect relationships in aquatic ecosystems are poorly delineated by such techniques.