Fate of Artificially Injected Oxygen in the Hypolimnion of a Two-Basin Lake: Amisk Lake, revisited

The first author visited Texas A&M University funded by U.S. National Science Foundation grant CBET 1033514. It was during that visit that, under the supervision of Scott Socolofsky, the double-plume model was implemented into the 3D hydrodynamic model. Meteorological data for Atmore AGDM station was provided by the Alberta Climate Information Service, found at https://acis.alberta.ca. The data displayed in the figures can be accessed at https://zenodo.org/record/4565311.Bubble-plume diffusers are increasingly used to add dissolved oxygen (DO) to the hypolimnion of lakes and reservoirs. Bubble plumes are successful at replenishing hypolimnetic DO, but they also introduce mixing energy that induces subtle changes in the thermal structure of the reservoir, driving changes in plume behavior. To account for this complex plume-reservoir interaction, a double bubble-plume model is coupled with a three-dimensional hydrodynamic model. The coupled model is used to reassess a field-scale analysis of the bubble-plume diffuser in two-basin Amisk Lake, aiming at evaluating the relative role of bubble-induced circulation and internal-seiching in driving inter-basin transport under stratified conditions. A large-scale plume-induced circulation was previously thought to be the main driver of inter-basin oxygen transport. This interpretation was based on the attribution of the time-averaged circulation in the channel due to plume operation. However, the intrinsic complexity of the hydraulic system and the sparseness of the field data introduced large uncertainties in the previous analysis. Here, we demonstrate that the time-averaged circulation is primarily the result of wind-driven internal seiches. Oxygen exchange is shown to be controlled by the interaction between internal seichedriven horizontal transport along the channel, and, the rate at which added oxygen reaches the layers above the sill, which is mainly controlled by plume-induced circulation. Internal-seiche driven transport through basin constrictions will vary depending on the magnitude of the wind forcing, depth of the thermocline and the channel geometry. These results highlight the importance of understanding water movement prior to introducing restoration actions in lakes.National Science Foundation (NSF) CBET 103351

Responses of food web to hypolimnetic aeration in Lake Vesijärvi

We studied the responses of a food web, especially fish and zooplankton, to summertime aeration, pumping of oxygen-rich epilimnetic water to the hypolimnion in Lake Vesijärvi, southern Finland. The aim of hypolimnetic aeration was to reduce internal loading of phosphorus from sediment. The population of smelt (Osmerus eperlanus L.), the main planktivore of the pelagial area, collapsed during the two 1st years of aeration due to increased temperature and low oxygen concentrations in the hypolimnion. The population recovered after the 4th year of hypolimnetic aeration, when oxygen conditions were improved. Despite elevated hypolimnetic temperature, smelt reached exceptionally high abundance, which led to a significant reduction in cladoceran body size. The density of perch (Perca fluviatilis L.) increased at first, but then decreased when the proportion of smelt and cyprinids increased. Biomasses of Daphnia decreased probably as a result of the disappearance of dark, low-oxygen deep-water refuge against fish predation and low availability of nutritionally high-quality algae. Occasionally filamentous cyanobacteria, such as turbulence tolerant Planktothrix agardhii (Gomont), were abundant, suggesting deteriorated food resources for zooplankton. The responses of food web were controversial with respect to the aim of the management, which was to prevent the occurrence of harmful algal blooms.Peer reviewe

Ecological Consequences of Hypoxia for Yellow Perch (Perca Flavescens) in Lake Erie.

Hypoxia (<2 mg O2•L-1) is a widespread phenomenon in marine and freshwater systems worldwide, yet the ecological consequences of hypoxia are generally unknown, especially for mobile species such as fish. Areas of hypoxic conditions or “dead zones”, due primarily to eutrophication (i.e. nutrient enrichment), are viewed as a major threat to aquatic ecosystem function worldwide. Areas of bottom water (hypolimnetic) hypoxia have long been documented and are increasing in the Lake Erie ecosystem, an economically and ecologically important water body within the Laurentian Great Lakes. Quantifying the ecological consequences of hypoxia for highly mobile organisms (e.g., yellow perch Perca flavescens) is a complex task. Such organisms are capable of avoiding direct lethal effects of hypolimnetic hypoxia, but may be indirectly affected as they are forced to occupy inferior habitats (i.e., novel prey, predators, competitors and physical conditions). I used field, and laboratory techniques to address the overall hypothesis that hypolimnetic hypoxia in Lake Erie negatively affects yellow perch. Laboratory results suggest yellow perch growth and consumption are negatively affected by low oxygen conditions. However, my field results suggest yellow perch attempt to mitigate these potential consequences by altering their distribution and foraging patterns in the presence of hypoxic conditions. My results also suggest a change in the sub-daily behaviors of yellow perch. This behavioral change involves short-term forays to forage within hypoxic habitats. The largest consequence of hypoxia for yellow perch in LECB is altered distribution patterns due to vertical or horizontal migrations in avoidance of low oxygen conditions. Overall, it appears hypoxia has the potential to negatively affect yellow perch however, behavioral modifications allow yellow perch to mitigate the extent of these consequences in Lake Erie. These results will have management implications for Lake Erie resource agencies and provide important conclusions concerning the ecological consequences of hypoxia for freshwater fishes.Ph.D.Natural Resources and EnvironmentUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75890/1/jjrobert_1.pd

Evidence of hypoxic foraging forays by yellow perch ( Perca flavescens ) and potential consequences for prey consumption

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91146/1/FWB_2753_sm_fS1.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/91146/2/j.1365-2427.2012.02753.x.pd

Effects of Hypoxia on Consumption, Growth, and RNA:DNA Ratios of Young Yellow Perch

As in various freshwater and coastal marine ecosystems worldwide, seasonal bottom water hypoxia is a recurring phenomenon in Lake Erie’s central basin. While bottom hypoxia can strongly affect sessile benthic animals, its effects on mobile organisms such as fish are less understood. We evaluated the potential for bottom hypoxia to affect the growth rates of yellow perch Perca flavescens, a species of ecological and economic importance in the lake. To this end, we (1) conducted laboratory experiments to quantify the effects of reduced dissolved oxygen on consumption, somatic growth, and RNA : DNA ratios (an index of short‐term growth) of young yellow perch and (2) explored the effects of bottom hypoxia on young yellow perch growth in Lake Erie’s central basin by collecting individuals in hypoxicand normoxic regions of the lake and quantifying their RNA : DNA ratios. Yellow perch consumption and growth in our experiments declined under hypoxic conditions (≤2 mg O2/L). While yellow perch RNA : DNA ratios responded strongly to experimental temperature, nucleic acid ratios were not significantly affected by dissolved oxygen or feeding ration. We did, however, observe a positive correlation between yellow perch growth and RNA : DNA ratios at low temperatures (11°C). The nucleic acid ratios of yellow perch collected in Lake Erie varied spatiotemporally, but their patterns were not consistent with hypoxia. In short, while yellow perch consumption and growth rates respond directly and negatively to low oxygen conditions, these responses are not necessarily reflected in RNA : DNA ratios. Moreover, in central Lake Erie, where yellow perch can behaviorally avoid hypoxic areas, the RNA : DNA ratios of yellow perch do not respond strongly to bottom hypoxia. Thus, this study suggests that there is no strong negative effect of bottom hypoxia on the growth of young yellow perch in Lake Erie.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141858/1/tafs1574.pd

A novel model for cyanobacteria bloom formation: the critical role of anoxia and ferrous iron

SUMMARY 1. A novel conceptual model linking anoxia, phosphorus (P), nitrogen (N), iron (Fe) and sulphate to the formation of noxious filamentous and colonial cyanobacteria blooms is presented that reconciles seemingly contradictory ideas about the roles of P, N and Fe in bloom formation. 2. The model has several critical concepts: (i) P regulates biomass and productivity in fresh waters until excessive loading renders a system N-limited or light-limited, but it is the availability of ferrous ions (Fe 2+ ) that regulates the ability of cyanobacteria to compete with its eukaryotic competitors; (ii) Fe 2+ diffusing from anoxic sediments is a major Fe source for cyanobacteria, which acquire it by migrating downwards into Fe 2+ -rich anoxic waters from oxygenated waters; and (iii) subsequent cyanobacterial siderophore production provides a supply of Fe 3+ for reduction at cyanobacteria cell membranes that leads to very low Fe 3+ concentrations in the mixing zone. 3. When light and temperature are physiologically suitable for cyanobacteria growth, bloom onset is regulated by the onset of internal Fe 2+ loading which in turn is controlled by anoxia, reducible Fe content of surface sediments and sulphate reduction rate. 4. This conceptual model provides the basis for improving the success of approaches to eutrophication management because of its far-reaching explanatory power over the wide range of conditions where noxious cyanobacteria blooms have been observed

Bioavailability and Migration Features of Metals in “Bottom Sediments – Water” System under the Action of Different Environmental Factors

This review considers and summarizes findings of the studies on metals’ coexisting forms in bottom sediments of surface water bodies. This makes it possible to assess metals’ migration ability in the “bottom sediments – water” system and their potential bioavailability for hydrobionts. The coexisting forms of metals in bottom sediments depend on their chemical properties and the component composition of the solid phase. Metals are distributed among exchangeable, carbonate, oxide, organic and residual fractions of bottom sediments. The highest migration ability is observed for metals contained in the first three fractions. Metals migration from organic and residual fractions hardly ever takes place. The oxygen regime, pH and redox potential, total dissolved solids and water temperature, concentration and component composition of organic substances affect the exchange of metals between bottom sediments and overlying water. The metal mobility in the “bottom sediments – water” system will increase under conditions of climate change. This is because cases of dissolved oxygen deficiency become more common, the total dissolved solids get higher in concentration, and pH and redox potential is reduced. Therefore, the development of methods to reduce metals migration from bottom sediments is a relevant task, which is discussed in the present paper.

Spatial and temporal trends of phytoplankton and physiochemical variables in a hypertrophic, monomictic lake

Spatial and temporal variations in the physical, chemical and biological composition of Lake Ōkaro were measured over 16 months. Lake Ōkaro is a small (0.32 km2) hypertrophic, monomictic lake located in the Central Volcanic Zone of the North Island, New Zealand. Vertical profiles of temperature, chlorophyll fluorescence, dissolved oxygen concentration (DO), pH, specific conductance, photosynthetically active radiation (PAR) and nutrient species, including ammonium-nitrogen (NH4-N), nitrite-nitrogen (NO2-N), nitrate-nitrogen (NO3-N) and phosphate-phosphorus (PO4-P), were collected at up to nine stations at weekly to monthly frequencies. High-frequency variability was assessed during two separate 24-hour monitoring periods, coinciding with an Anabaena spiroides-dominated surface bloom, and a Ceratium hirundinella-dominated deep chlorophyll maximum. Additional data for wind direction and velocity, incident solar irradiance and rainfall was sourced from a meteorological weather station and a lake monitoring buoy at Rotorua, 20 km north of the lake. Spatial variability was more pronounced during summer. Observed vertical gradients in chlorophyll fluorescence, DO, specific conductance and nutrient species were closely linked to thermal stability of the water column. There were large variations in chlorophyll fluorescence amongst stations in summer, which related to displacement of the metalimnion and associated changes in chlorophyll fluorescence. Winter mixing was characterised by relative homogeneity of the water column. Nutrient concentrations were elevated at all depths whereas high concentrations had previously been confined to lower depth strata (the hypolimnion). Temperature profiles in summer displayed clear vertical gradients with a well-defined metalimnion that increased in depth until winter mixing generated isothermal conditions. Chlorophyll fluorescence profiles were characterised by the formation of a DCM that was recurrent over both summer periods, and was strongly statistically related to the depth of the thermocline for the duration of stratification. Dissolved oxygen, specific conductance and pH were relatively uniform horizontally, though pH was consistently lower at a well-sheltered near-shore station. All variables showed strong variations with depth during the stratified period. Dissolved oxygen was negligible or zero below the thermocline for much of the stratified period while specific conductance was lowest above or at the thermocline. There were also strong vertical gradients in nutrient concentrations in summer, with concentrations below the thermocline often an order of magnitude higher than those above. The representativeness of fluorescence at a central station to a whole-lake scale was assessed using a vertical integrated value and the standard error derived from up to eight other stations. Values at the single station frequently deviated from the mean fluorescence of the wider lake, particularly at the DCM which suggests that extrapolating single-station measurements to a whole lake could provide highly exaggerated values of lake fluorescence. High-frequency sampling during the A. spiroides-dominated surface bloom showed diel temperature variations attributed mostly to solar irradiance. There was high light attenuation from the high phytoplankton biomass and consistently elevated pH and DO. Fluorescence profiles suggested that the phytoplankton population was strongly buoyant and did not undergo diel vertical migration. High-frequency sampling during a period when there was a dinoflagellate-dominated DCM showed two coinciding fluorescence peaks had formed at 6-7 and 7-8 m depth and contained morphologically and physiologically distinct taxa. The 6-7 m DCM was predominantly Ceratium hirundinella, while the 7-8 m DCM was composed of C. hirundinella and unidentified colonial picoplankton. Fluorescence profiles suggested diel vertical migration was not taking place, and strong gradients in light, nutrient availability and the relative biomass of the dominants suggested that the 6-7 and 7-8 m DCM populations potentially differed in their modes of nutrition, light history and susceptibility to grazing. This research illustrates the degree of spatial variability that can exist in a small, monomictic hypertrophic lake at a given time, and highlights some of the potential limitations of using single-site monitoring stations to represent the physical, chemical and biological conditions of a whole lake. This information may be used to critically evaluate the reliability of phytoplankton biomass estimates that have been derived from spatially-limited sampling methods. This study further illustrates the role that thermal stratification plays in creating vertical gradients in a number of biological and chemical variables, and demonstrates that parallels exist with regard to DCM formation in oligotrophic and hypertrophic lakes, relating to the interplay between light, chlorophyll fluorescence and thermal stratification. Evidence is also provided showing that diel-scale variations in phytoplankton biomass can differ markedly between a cyanobacteria-dominated surface bloom and a dinoflagellate-dominated DCM, which further highlights the value of high-frequency sampling when seeking to estimate phytoplankton biomass using in situ methods

Storm impacts on phytoplankton community dynamics in lakes

In many regions across the globe, extreme weather events such as storms have increased in frequency, intensity, and duration due to climate change. Ecological theory predicts that such extreme events should have large impacts on ecosystem structure and function. High winds and precipitation associated with storms can affect lakes via short‐term runoff events from watersheds and physical mixing of the water column. In addition, lakes connected to rivers and streams will also experience flushing due to high flow rates. Although we have a well‐developed understanding of how wind and precipitation events can alter lake physical processes and some aspects of biogeochemical cycling, our mechanistic understanding of the emergent responses of phytoplankton communities is poor. Here we provide a comprehensive synthesis that identifies how storms interact with lake and watershed attributes and their antecedent conditions to generate changes in lake physical and chemical environments. Such changes can restructure phytoplankton communities and their dynamics, as well as result in altered ecological function (e.g., carbon, nutrient and energy cycling) in the short‐ and long‐term. We summarize the current understanding of storm‐induced phytoplankton dynamics, identify knowledge gaps with a systematic review of the literature, and suggest future research directions across a gradient of lake types and environmental conditions