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•Lake Erie is heavily impacted by urban and agricultural nutrient loading.•The timing and bioavailability of these nutrient inputs favour toxic cyanobacteria.•High organic production ...exacerbates bottom hypoxia and sediment release of phosphorus, which will delay the lake's response to nutrient management.•Modelling has generated soluble and total P reduction targets for Lake Erie.•Many best management options were identified; their performance should be verified on a watershed basis.
Lake Erie supplies drinking water to more than 11 million consumers, processes millions of gallons of wastewater, provides important species habitat and supports a substantial industrial sector, with >$50 billion annual income to tourism, recreational boating, shipping, fisheries, and other industries. These and other key ecosystem services are currently threatened by an excess supply of nutrients, manifested in particular by increases in the magnitude and extent of harmful planktonic and benthic algal blooms (HABs) and hypoxia. Widespread concern for this important international waterbody has been manifested in a strong focus of scientific and public material on the subject, and commitments for Canada-US remedial actions in recent agreements among Federal, Provincial and State agencies. This review provides a retrospective synthesis of past and current nutrient inputs, impairments by planktonic and benthic HABs and hypoxia, modelling and Best Management Practices in the Lake Erie basin. The results demonstrate that phosphorus reduction is of primary importance, but the effects of climate, nitrogen and other factors should also be considered in the context of adaptive management. Actions to reduce nutrient levels by targeted Best Management Practices will likely need to be tailored for soil types, topography, and farming practices.
Although climate warming is expected to benefit temperate ectotherms by lengthening the summer growing season, declines in reproductive success following short, warm winters may counter such positive ...effects. Here we present long-term (1973-2010) field patterns for Lake Erie yellow perch, Perca flavescens, which show that failed annual recruitment events followed short, warm winters. Subsequent laboratory experimentation and field investigations revealed how reduced reproductive success following short, warm winters underlie these observed field patterns. Following short winters, females spawn at warmer temperatures and produce smaller eggs that both hatch at lower rates and produce smaller larvae than females exposed to long winters. Our research suggests that continued climate warming can lead to unanticipated, negative effects on temperate fish populations.
Relieving phosphorus loading is a key management tool for controlling Lake Erie eutrophication. During the 1960s and 1970s, increased phosphorus inputs degraded water quality and reduced central ...basin hypolimnetic oxygen levels which, in turn, eliminated thermal habitat vital to cold-water organisms and contributed to the extirpation of important benthic macroinvertebrate prey species for fishes. In response to load reductions initiated in 1972, Lake Erie responded quickly with reduced water-column phosphorus concentrations, phytoplankton biomass, and bottom-water hypoxia (dissolved oxygen <2mg/l). Since the mid-1990s, cyanobacteria blooms increased and extensive hypoxia and benthic algae returned. We synthesize recent research leading to guidance for addressing this re-eutrophication, with particular emphasis on central basin hypoxia. We document recent trends in key eutrophication-related properties, assess their likely ecological impacts, and develop load response curves to guide revised hypoxia-based loading targets called for in the 2012 Great Lakes Water Quality Agreement. Reducing central basin hypoxic area to levels observed in the early 1990s (ca. 2000km2) requires cutting total phosphorus loads by 46% from the 2003–2011 average or reducing dissolved reactive phosphorus loads by 78% from the 2005–2011 average. Reductions to these levels are also protective of fish habitat. We provide potential approaches for achieving those new loading targets, and suggest that recent load reduction recommendations focused on western basin cyanobacteria blooms may not be sufficient to reduce central basin hypoxia to 2000km2.
•Lake Erie hypoxia has increased since mid-1990s primarily due to increased agricultural DRP loads•Reducing hypoxic area to 2,000 km2 requires 46% reduction in total phosphorus loads or 78% reduction in DRP•Reductions to these levels are also protective of fish habitat.•Reducing agricultural loads requires more and more targeted BMPs•Climate change will make load reductions more difficult
Human-driven nutrient inputs into aquatic ecosystems must be managed to preserve biodiversity and to ensure that valued fishery and water quality services are not compromised by hypoxia and harmful ...algal blooms. Aiming for nutrient inputs that achieve an intermediate level of ecosystem productivity is expected to provide both high fish yield and good water quality. However, we argue that such an intermediate “optimum” may not exist for many aquatic ecosystems that support multiple fisheries with differing tolerances to eutrophication and that must provide multiple water quality services. We further support this argument with an empirical case study of nearly a century (1915–2011) of change in the productivity of Lake Erie and its lake whitefish ( Coregonus clupeaformis ), walleye ( Sander vitreus ), and yellow perch ( Perca flavescens ) fisheries. We discuss and show how the harvest of each fishery has been historically maximized at different levels of ecosystem productivity. Additionally, we examine how anticipated management efforts to improve water quality by reducing nutrient inputs (i.e., oligotrophication) may favor certain fisheries over others, resulting in no single optimal range of nutrient inputs that achieves all valued fishery and water quality objectives. Our synthesis and case study illustrate how the need to balance multiple services in aquatic ecosystems can create a wicked management problem with inevitable trade-offs. To navigate these trade-offs, we recommend the use of ecosystem-based management approaches, which can help decision makers identify and resolve complex trade-offs by facilitating cooperative research and communication among water quality regulators, fisheries managers, and end users.
Understanding the relative importance of top-down and bottom-up regulation of ecosystem structure is a fundamental ecological question, with implications for fisheries and water-quality management. ...For the Laurentian Great Lakes, where, since the early 1970s, nutrient inputs have been reduced, whereas top-predator biomass has increased, we describe trends across multiple trophic levels and explore their underlying drivers. Our analyses revealed increasing water clarity and declines in phytoplankton, native invertebrates, and prey fish since 1998 in at least three of the five lakes. Evidence for bottom-up regulation was strongest in Lake Huron, although each lake provided support in at least one pair of trophic levels. Evidence for top-down regulation was rare. Although nonindigenous dreissenid mussels probably have large impacts on nutrient cycling and phytoplankton, their effects on higher trophic levels remain uncertain. We highlight gaps for which monitoring and knowledge should improve the understanding of food-web dynamics and facilitate the implementation of ecosystem-based management.
Microcystin (MC), a hepatotoxin that can adversely affect human health, has become more prevalent in freshwater ecosystems worldwide, owing to an increase in toxic cyanobacteria blooms. While ...consumption of water and fish are well-documented exposure pathways of MCs to humans, less is known about the potential transfer to humans through consumption of vegetables that have been irrigated with MC-contaminated water. Likewise, the impact of MC on the performance of food crops is understudied. To help fill these information gaps, we conducted a controlled laboratory experiment in which we exposed lettuce, carrots, and green beans to environmentally relevant concentrations of MC-LR (0, 1, 5, and 10μg/L) via two irrigation methods (drip and spray). We used ELISA and LC-MS/MS to quantify MC-LR concentrations and in different parts of the plant (edible vs. inedible fractions), measured plant performance (e.g., size, mass, edible leaves, color), and calculated human exposure risk based on accumulation patterns. MC-LR accumulation was positively dose-dependent, with it being greater in the plants (2.2–209.2μg/kg) than in soil (0–19.4μg/kg). MC-LR accumulation varied among vegetable types, between plant parts, and between irrigation methods. MC-LR accumulation led to reduced crop growth and quality, with MC-LR persisting in the soil after harvest. Observed toxin accumulation patterns in edible fractions of plants also led to estimates of daily MC-LR intake that exceeded both the chronic reference dose (0.003μg/kg of body weight) and total daily intake guidelines (0.04μg/kg of body weight). Because the use of MC-contaminated water is common in many parts of the world, our collective findings highlight the need for guidelines concerning the use of MC-contaminated water in irrigation, as well as consumption of these crops.
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•Microcystin in irrigation water is a significant pathway for human exposure.•Microcystin accumulated in crops and soil when grown with contaminated water.•Crops lost their quality and productivity from microcystin exposure.•Microcystin from irrigation water persisted in soil after crops were harvested.•Consumption of crops grown with microcystin-tainted water poses a high health risk.
Complete functional descriptions of the induction sequences of phenotypically plastic traits (perception to physiological regulation to response to outcome) should help us to clarify how plastic ...responses develop and operate. Ranid tadpoles express several plastic antipredator traits mediated by the stress hormone corticosterone, but how they influence outcomes remains uncertain. We investigated how predator-induced changes in the tail morphology of wood frog (Rana sylvatica) tadpoles influenced their escape performance over a sequence of time points when attacked by larval dragonflies (Anax junius). Tadpoles were raised with no predator exposure, chemical cues of dragonflies added once per day, or constant exposure to caged dragonflies crossed with no exogenous hormone added (vehicle control only), exogenous corticosterone, or metyrapone (a corticosteroid synthesis inhibitor). During predation trials, we detected no differences after four days, but after eight days, tadpoles exposed to larval dragonflies and exogenous corticosterone had developed deeper tail muscles and exhibited improved escape performance compared to controls. Treatment with metyrapone blocked the development of a deeper tail muscle and resulted in no difference in escape success. Our findings further link the predator-induced physiological stress response of ranid tadpoles to the development of an antipredator tail morphology that confers performance benefits.
We evaluated otolith chemistry as a tool for identifying natal origins of potamodromous fishes using historical Lake Erie water chemistry (1983-2001) and yellow perch (
Perca flavescens
) otolith ...elemental composition (1994-1996) data. Lake Erie's tributaries had stream-specific chemical signatures that were temporally stable. Correspondingly, the otolith microelemental composition of larvae collected from tributary embayments (Sandusky and Maumee bays) was shown to be geographically distinct and the use of known-origin juveniles showed that larval otolith microelemental signatures could be used to accurately identify natal origins and indicate fish movement. Discrimination between offshore spawning locations was relatively difficult, however, indicating limitations to working in systems that are dominated by flow from a single large river (i.e., Detroit River). Interannual variability in otolith microelemental signatures was high such that larvae from one year could not reliably classify natal location of larvae in another year. Development of an annual library of site-specific signatures and exploration of complementary ways to discriminate natal origins would improve the use of otolith microchemistry as a fishery management tool in freshwater systems.
Growth-selective mortality as larvae can influence recruitment in marine fishes. Its importance in freshwater fishes, however, remains speculative. We quantified growth trajectories within annual ...cohorts (2011–2013) of Lake Erie walleye (Sander vitreus) and their relationship with recruitment. We hypothesized that selection against slow or fast growth would be associated with high mortality and poor recruitment, whereas weak or nonexistent growth-selective mortality co-occurring with fast growth would be associated with good recruitment. We used otoliths to reconstruct growth rates during the first 15 days of life from larvae collected during spring and juvenile recruits (survivors) collected during late summer. We documented growth-selective mortality during 2011 and 2013, which exhibited poor recruitment as expected. During 2012, growth selection was absent, but growth was slow when compared to historical averages, resulting in poor recruitment. Growth was also considered slow in 2011 and 2013, due to multiple interacting conditions. Our study indicates that the relationship among larval growth, mortality, and future recruitment is complex, highlighting the need for continued research into how larval processes affect recruitment dynamics in freshwater fishes.
Although previous research has identified ways in which environmental conditions influence population processes in many ecosystems, these relationships often weaken or break down with the inclusion ...of additional years of data, for reasons that remain unclear.
To better understand if and how the relationships between historically important environmental drivers of yellow perch (Perca flavescens) recruitment varied during 1969–2018 in two Lake Erie basins characterised by contrasting productivity, we used dynamic linear modelling, which allows for nonstationary relationships between predictor and response variables to be quantified.
Our analyses revealed that abiotic conditions during egg and larval development (i.e. winter temperature, springtime river inflows, and thermal conditions) were important in the productive west basin, whereas a combination of abiotic (i.e. winter temperature and river inflows) and biotic (i.e. small‐bodied and large‐bodied predators) conditions were important in the less‐productive central basin.
While the importance of most environmental factors to yellow perch recruitment remained static through time, the importance of river inflows changed through time in the west and central basins. Large‐bodied predators (i.e. walleye, Sander vitreus) also varied in their importance through time in the central basin. These changes in recruitment drivers were independent of temporal changes to the environmental conditions themselves, coinciding instead with the timing of major shifts in Lake Erie's nutrient status.
Our results demonstrate that ecosystem change can cause the relationships between environmental conditions and population processes (e.g. recruitment) of aquatic organisms to vary through time and space. They also highlight the value of periodically revisiting their applicability, especially if these relationships are used to help manage or sustain populations in ecosystems experiencing human‐driven environmental change.
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