Trait-mediated biotic interactions within zooplankton, such as inducible defences against predation, are key determinants of community structure and dynamics in lentic ecosystems. The role of such ...interactions in lotic environments, however, has been rarely investigated, as abiotic constraints related to hydrology are generally thought to impair the occurrence of biotic interactions in rivers. We hypothesize that, under conditions of reduced flow during summer, trait-mediated predator–prey interactions can be significant driving forces in the main channel of a large river, despite the disruptive effect of downstream transport. To verify this assumption, we carried out a field study in the lowland stretch of the Po River (Italy). We analysed temporal patterns of morphometric variation in a population of
Brachionus calyciflorus
, potentially triggered by the predatory rotifer
Asplanchna brightwellii.
Our results indicate that the presence of
Asplanchna
can impact the variability of different morphological traits in
B. calyciflorus
even under the disturbance effect of turbulence and drift.
Asplanchna
feeding electivity on several taxa was also investigated, confirming the predator ability to efficiently and selectively feed under lotic conditions. We suggest that complex interactions and trade-offs might occur among life-history traits, predator–prey relationships and physical constraints imposed by flow within zooplankton communities in large rivers.
Extreme climatic events, such as heatwaves and droughts, are occurring more frequently in many regions of the world. Lakes may be especially vulnerable to climatic perturbations, which can trigger ...sudden ecosystem changes through alterations in the hydrologic regime. However, the nature of lake response to climatic extremes, and associated long-term ecosystem-level implications are difficult to predict, due to the paucity of time series allowing exploration of ecosystem behavior before, during, and after extreme events. We investigated the impacts of the 2003 European heatwave on a small, stratifying lake by analyzing available limnological data between 1986 and 2012. In summer 2003, a shift from an unvegetated to a macrophyte-dominated regime occurred, due to the rapid spread of a benthic charophyte. We explored candidate mechanisms driving the shift by comparing empirical observations with the outcome of a model on lake alternative states parameterized for our study lake. Our results support the hypothesis that enhanced light availability due to a heatwave-induced decrease in water level drove the switch in dominant primary producers. The spread of the charophyte was associated with strong depletion of inorganic nutrients and suppression of the typical summer phytoplankton peak. These bottom-up interactions triggered cascading effects at higher trophic levels, inducing a decline in herbivorous zooplankters with high food requirements and in predatory taxa. Some of the changes in the lake food web persist through the available time series. If incidence of heatwaves increases, as projected across temperate regions, our findings suggest that abrupt and long-lasting ecosystem-level reorganizations may occur in small, stratifying lakes.
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•Estimated nutrient reductions in monitoring data often differ from model expectations.•A TMDL progress indicator was developed for the Chesapeake Bay watershed (USA).•This indicator ...can explicitly quantify the progress toward nutrient reduction goals.•Progress of reduction has varied with nutrient source sectors and watershed locations.•For both nitrogen and phosphorus, long-term progress has been documented.
Eutrophication has been a major environmental issue in many coastal and inland ecosystems, which is primarily attributed to excessive anthropogenic inputs of nutrients. Restoration efforts have therefore focused on the reduction of watershed nutrient loads, including in the Chesapeake Bay (USA). To facilitate watershed management, watershed models are often developed and used to assess the expected impact of scenarios of past and future management policies and practices and the impact of watershed conditions. However, the level of load reductions estimated using monitoring data often does not match with model predictions, which may cast doubt on the effectiveness of the restoration efforts, the reliability of the model, and the prospect of achieving pre-established reduction goals. To better reconcile such inconsistencies between expectation (i.e., modeling estimates) and reality (i.e., monitoring information), a watershed-wide indicator was developed for the Chesapeake Bay watershed to explicitly quantify the progress toward nutrient reduction goals in the context of the Chesapeake Bay Total Maximum Daily Load (TMDL). Results of the indicator show that since 1995 long-term progress has been made toward the TMDL planning targets for both nitrogen and phosphorus. Specifically, management practices that are implemented and realized (in monitoring data) have been increasing over time, whereas management practices that need to be implemented in the future to meet the goals have been decreasing. In addition, the progress of nutrient reduction toward meeting the goals has varied with source sectors and watershed locations: i.e., point source management has been fully or nearly fully implemented, whereas nonpoint source management has been implemented by 50%-70%. In summary, this indicator, which is largely based on monitoring data, can provide at least four benefits: (1) evaluating the validity of the modeled estimates of nutrient reductions by comparing them to monitoring information; (2) placing the monitored riverine trends into a management context; (3) comparing progress between different nutrient source sectors and watershed locations; and (4) facilitating communication of the progress to the Chesapeake Bay Program Partnership and the public. Although we focus on the indicator development and interpretation for the Chesapeake Bay watershed, the framework can be transferred to watersheds within and beyond this watershed, where similar modeling and monitoring information exists, to gauge expectations on the trajectory and pace of the progress toward meeting restoration goals.
The 2010 Chesapeake Bay Total Maximum Daily Load was established for the water quality and ecological restoration of the Chesapeake Bay. In 2017, the latest science, data, and modeling tools were ...used to develop revised Watershed Implementation Plans (WIPs). In this article, we examine the vulnerability of the Chesapeake Bay watershed to the combined pressures of climate change and growth in population, agricultural intensity, and economic activity for the 60‐year period 1995–2055. The results will be used to revise WIPs, as needed, to account for expected increases in loads. Assessing changes relative to 1995 for the years 2025, 2035, 2045, and 2055, mean annual precipitation increases of 3.11%, 4.21%, 5.34%, and 6.91%, respectively, air temperature increases of 1.12, 1.45, 1.84, and 2.12°C, respectively, and potential evapotranspiration increases of 3.36%, 4.43%, 5.54%, and 6.35%, respectively, are projected. Population in the watershed is expected to grow by 3.5 million between 2025 and 2055. Watershed model results show incremental increases in streamflow (2.3%–6.2%), nitrogen (2.6%–10.8%), phosphorus (4.5%–26.7%), and sediment (3.8%–18.8%) loads to the tidal Bay due to climate change. Growth in population, agricultural intensity, development, and economic activity resulted in relatively smaller increases in loads compared to climate change.
A large region of low-dissolved-oxygen bottom waters (hypoxia) forms nearly every summer in the northern Gulf of Mexico because of nutrient inputs from the Mississippi River Basin and water column ...stratification. Policymakers developed goals to reduce the area of hypoxic extent because of its ecological, economic, and commercial fisheries impacts. However, the goals remain elusive after 30 y of research and monitoring and 15 y of goal-setting and assessment because there has been little change in river nitrogen concentrations. An intergovernmental Task Force recently extended to 2035 the deadline for achieving the goal of a 5,000-km² 5-y average hypoxic zone and set an interim load target of a 20% reduction of the spring nitrogen loading from the Mississippi River by 2025 as part of their adaptive management process. The Task Force has asked modelers to reassess the loading reduction required to achieve the 2035 goal and to determine the effect of the 20% interim load reduction. Here, we address both questions using a probabilistic ensemble of four substantially different hypoxia models. Our results indicate that, under typical weather conditions, a 59% reduction in Mississippi River nitrogen load is required to reduce hypoxic area to 5,000 km². The interim goal of a 20% load reduction is expected to produce an 18% reduction in hypoxic area over the long term. However, due to substantial interannual variability, a 25% load reduction is required before there is 95% certainty of observing any hypoxic area reduction between consecutive 5-y assessment periods.
In response to degraded water quality, federal policy makers in the US and Canada called for a 40% reduction in phosphorus (P) loads to Lake Erie, and state and provincial policy makers in the Great ...Lakes region set a load-reduction target for the year 2025. Here, we configured five separate SWAT (US Department of Agriculture's Soil and Water Assessment Tool) models to assess load reduction strategies for the agriculturally dominated Maumee River watershed, the largest P source contributing to toxic algal blooms in Lake Erie. Although several potential pathways may achieve the target loads, our results show that any successful pathway will require large-scale implementation of multiple practices. For example, one successful pathway involved targeting 50% of row cropland that has the highest P loss in the watershed with a combination of three practices: subsurface application of P fertilizers, planting cereal rye as a winter cover crop, and installing buffer strips. Achieving these levels of implementation will require local, state/provincial, and federal agencies to collaborate with the private sector to set shared implementation goals and to demand innovation and honest assessments of water quality-related programs, policies, and partnerships.
Ecology under lake ice Hampton, Stephanie E.; Galloway, Aaron W. E.; Powers, Stephen M. ...
Ecology letters,
January 2017, Volume:
20, Issue:
1
Journal Article
Peer reviewed
Open access
Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, ...due to a historical research focus on summer ‘growing seasons’. We executed the first global quantitative synthesis on under‐ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter‐summer patterns for dissolved organic carbon (DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake‐specific, species‐specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass.
In 2020, the Chesapeake Bay Program moved to offset impacts from climate change for the 30‐year period from 1995 through 2025 by having its seven watershed jurisdictions (Delaware, Maryland, New ...York, Pennsylvania, Virginia, West Virginia, and the District of Columbia) apply additional nutrient pollutant reduction practices. The climate change assessment was performed with integrated models of the Chesapeake watershed, airshed, and estuary. Scenarios run for the years 2025, 2035, 2045, and 2055 estimated effects from the different future climatic conditions. This article presents the results of that assessment and is intended to provide a guide to assist other modeling practitioners in assessing climate change impacts in coastal watersheds. Major influences of climate change that were quantified include increases in precipitation volume, potential evapotranspiration, watershed nutrient loads, tidal water temperature, and sea level. Minor influences quantified in the climate change analysis include changes in nutrient speciation and increases in wet deposition of nitrogen, CO2, rainfall intensity, tidal wetland loss, up‐estuary salt intrusion, and phytoplankton biomass. To offset climate change impacts from 1995 to 2025 on water quality, the scenarios indicate an additional 2.3 million and 0.3 million kg of nitrogen and phosphorus per annum, respectively, will need to be reduced beyond what is called for in the Chesapeake Total Maximum Daily Load.
We present a data set reporting the checklist of the species of the phylum Rotifera for Italy, updating the one previously published in the series ‘Checklist delle Specie della Fauna d'Italia’ in ...1995. The records of the updated checklist refer to the 483 taxa at the species and subspecies level currently known from national Italian territories (119 Bdelloidea, 362 Monogononta, 2 Seisonacea) at the regional level (22 terrestrial and nine marine geographical units). The records refer to various freshwater, limno-terrestrial, and marine coastal habitats. The previous checklist reported 245 taxa (54 Bdelloidea, 189 Monogononta, 2 Seisonacea): three taxa were removed because currently considered not valid and 241 were added, scanning 21 papers we found that were published between 1993 and 2020, expanding the regional records and including four papers older than 1993 with overlooked records in the previous checklist. The Rotifera data are part of the updated Checklist of the Italian Fauna, which is viewable on the LifeWatch Italy platform at https://www.lifewatchitaly.eu/en/initiatives/checklist-fauna-italia-en/checklist and is freely available on the LifeWatch Italy Data Portal (https://dataportal.lifewatchitaly.eu/data). The checklist will be dynamically updated with new records; this paper describes the state of the art of the data set regarding Rotifera on May 2021.
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