Macrophyte removal affects nutrient uptake and metabolism in lowland streams
2023 - Ada Pastor, Cecilie M.H. Holmboe, Olatz Pereda, Pau Giménez-Grau, Annette Baattrup-Pedersen, Tenna Riis

Macrophytes provide essential ecosystem services in lowland streams, including nutrient uptake that can reduce downstream transport to vulnerable coastal areas. Despite that, to ensure water conveyance and effective run off from agricultural fields, aquatic plant biomass is removed regularly in many European streams (i.e. weed cutting practices). However, the impacts of weed cutting on stream ecosystem processes are not yet well documented. Here, we studied the effect of weed cutting on nutrient retention and ecosystem metabolism in three lowland streams with contrasting dominant vegetation communities (submergent and emergent plants) during summer in Denmark. Our results showed a decrease in nutrient retention; uptake velocity of ammonium decreased 34–77 % and of phosphate decreased 50–77 %. Ecosystem metabolic rates also decreased after weed cutting, both in gross primary production (9 %, 60 % and 85 %) and respiration (47 %, 69 % and 76 %). The effects of weed cutting on these ecosystem processes prevailed three weeks after the cutting occurred. Understanding the effects of weed cutting on stream ecosystem functioning can improve nature-based management strategies to control eutrophication of downstream coastal areas.
Remediation of marine dead zones by enhancing microbial sulfide oxidation using electrodes
2023 - Andreas Libonati Brock, Kristin Kostadinova, Emma Mørk-Pedersen, Fides Hensel, Yifeng Zhang, Borja Valverde-Pérez, Colin A. Stedmon, Stefan Trapp

Marine dead zones caused by hypoxia have expanded over the last decades and pose a serious threat to coastal marine life. We tested sediment microbial fuel cells (SMFCs) for their potential to reduce the release of sulfide from sediments, in order to potentially protect the marine environment from the formation of such dead zones. Steel electrodes as well as charcoal-amended electrodes and corresponding non-connected controls of a size of together 24 m2 were installed in a marine harbour, and the effects on water quality were monitored for several months. Both pure steel electrodes and charcoal-amended electrodes were able to reduce sulfide concentrations in bottom water (92 % to 98 % reduction, in comparison to disconnected control steel electrodes). Also phosphate concentrations and ammonium were drastically reduced. SMFCs might be used to eliminate hypoxia at sites with high organic matter deposition and should be further investigated for this purpose.
Disturbance of primary producer communities disrupts the thermal limits of the associated aquatic fauna
2023 - J.M. Booth, F. Giomi, D. Daffonchio, C.D. McQuaid, M. Fusi

Environmental fluctuation forms a framework of variability within which species have evolved. Environmental fluctuation includes predictability, such as diel cycles of aquatic oxygen fluctuation driven by primary producers. Oxygen availability and fluctuation shape the physiological responses of aquatic animals to warming, so that, in theory, oxygen fluctuation could influence their thermal ecology. We describe annual oxygen variability in agricultural drainage channels and show that disruption of oxygen fluctuation through dredging of plants reduces the thermal tolerance of freshwater animals.
The effect of water management and ratoon rice cropping on methane emissions and yield in Arkansas
2023 - Marguerita Leavitt, Beatriz Moreno-García, Colby W. Reavis, Michele L. Reba, Benjamin R.K. Runkle

Sustainable intensification of rice farming is crucial to meeting human food needs while reducing environmental impacts. Rice production represents 8% of all anthropogenic emissions of CH4, a potent greenhouse gas. Cultivation practices that minimize the number of days the rice fields are flooded, such as irrigation using the alternate wetting and drying (AWD) technique instead of continuous flooding (DF) can potentially reduce CH4 emissions. Ratoon cropping, wherein a second crop of rice is grown from the harvested stubble of the first crop, can produce additional yield with minimal labor but may generate more CH4 than single cropping.
Experimental reductions in subdaily flow fluctuations increased gross primary productivity for 425 river kilometers downstream
2022 - Bridget R Deemer, Charles B Yackulic, Robert O Hall, Jr, Michael J Dodrill, Theodore A Kennedy, Jeffrey D Muehlbauer, David J Topping, Nicholas Voichick, Michael D Yard

Aquatic primary production is the foundation of many river food webs. Dams change the physical template of rivers, often driving food webs toward greater reliance on aquatic primary production. Nonetheless, the effects of regulated flow regimes on primary production are poorly understood. Load following is a common dam flow management strategy that involves subdaily changes in water releases proportional to fluctuations in electrical power demand. This flow regime causes an artificial tide, wetting and drying channel margins and altering river depth and water clarity, all processes that are likely to affect primary production.
Is All Seagrass Habitat Equal? Seasonal, Spatial, and Interspecific Variation in Productivity Dynamics Within Mediterranean Seagrass Habitat
2022 - Emma A. Ward, Charlotte Aldis, Tom Wade, Anastasia Miliou, Thodoris Tsimpidis, Tom C. Cameron

Seagrass meadows’ ability to capture carbon through sequestering autochthonous carbon via photosynthesis means they could represent a potential nature-based solution to rising carbon emissions. In multispecies seagrass communities, and due to species introduction or predicted range shifts, it is important to know which species deliver different carbon sequestration gains to inform conservation actions. Large benthic chamber experiments (volume = 262L) assessed the seasonal and spatial variation in metabolism dynamics of the endemic and dominant Mediterranean seagrass, P. oceanica whilst small benthic chamber experiments (volume = 7L) compared the dynamics between, P. oceanica the native C. nodosa and non-native H. stipulacea.
Dissolved organic matter mediates the effects of warming and inorganic nutrients on a lake planktonic food web
2022 - Marie-Pier Hébert, Cynthia Soued, Gregor F. Fussmann, Beatrix E. Beisner

Lakes are undergoing striking physicochemical changes globally, including co-occurring increases in dissolved organic carbon and nutrient concentrations, water color, and surface temperature. Although several experimental studies of lake browning and warming have been conducted over the last decade, knowledge remains limited as to the structural and functional responses of multitrophic plankton communities, especially under environmentally relevant physicochemical conditions. Using reverse osmosis to manipulate naturally occurring dissolved organic matter (DOM), we performed an enclosure experiment to evaluate the response of a planktonic food web (zooplankton–phytoplankton–bacterioplankton) to individual and combined increases in DOM and temperature, while accounting for changes in inorganic nutrients associated with DOM enrichment. We found that concomitant increases in DOM and temperature or inorganic nutrients elicited substantially greater biotic effects, but infrequently led to interactive effects. Overall, major plankton groups responded differently to manipulated factors, with most effects observed in standing stocks, community composition, and trophic structure, while metabolic (primary production and respiration) rates appeared to be generally less responsive.
Contribution of boulder reef habitats to oxygen dynamics of a shallow estuary
2022 - Peter A.U. Staehr, Sanjina U. Staehr, Denise Tonetta, Signe Høgslund, Mette Møller Nielsen

We assessed the importance of boulder reefs to the oxygen dynamics of a shallow estuary during two growing seasons in 2017 and 2018. Using open-system diel oxygen measurements and benthic and pelagic incubations, we evaluated the relative contribution of pelagic and benthic habitats to the ecosystem metabolism along a depth gradient in two areas, with (Reef) and without (Bare) boulder reefs in the Limfjorden, Denmark. System integrated areal rates of gross primary production (GPP) and ecosystem respiration (ER) both increased with depth in both areas.
Solar circulator to restore dissolved oxygen in a hypoxic ice-covered lake
2022 - Kyle F. Flynn , Kyle A. Cutting, Matthew E. Jaeger, Jeffrey M. Warren, Theodore Johnson, Darrin Kron, Chace Bell

Hypoxia is common to shallow ice-covered lakes during the winter season, and restorative actions to prevent impacts to aquatic ecosystems are desired yet untested in remote settings. The use of a solar photovoltaic circulator was investigated for reoxygenation in a shallow hypoxic lake in the northern Rocky Mountains. During the fall of 2019, a solar powered lake circulator (SolarBee SB10000LH; hereinafter circulator) was installed near the center of Upper Red Rock Lake, Montana USA (latitude 44° 36’N) and dissolved oxygen (DO), temperature, turbidity, and changes to ice formation were monitored until ice-out the following spring of 2020 using an array of real-time and data logging sondes. Observations indicate the circulator formed a polynya that lasted until late November, did not increase lake turbidity, and facilitated oxygen exchange through the circulator-created-polynya for at least 3 weeks after an adjacent lake became ice covered.
Characterization of the abiotic drivers of abundance of nearshore Arctic fishes
2021 - Noah S. Khalsa, Kyle P. Gatt, Trent M. Sutton, Amanda L. Kelley

Fish are critical ecologically and socioeconomically for subsistence economies in the Arctic, an ecosystem undergoing unprecedented environmental change. Our understanding of the responses of nearshore Arctic fishes to environmental change is inadequate because of limited research on the physicochemical drivers of abundance occurring at a fine scale. Here, high-frequency in situ measurements of pH, temperature, salinity, and dissolved oxygen were paired with daily fish catches in nearshore Alaskan waters of the Beaufort Sea. Due to the threat that climate change poses to high-latitude marine ecosystems, our main objective was to characterize the abiotic drivers of abundance and elucidate how nearshore fish communities may change in the future. We used generalized additive models (GAMs) to describe responses to the nearshore environment for 18 fish species.
Large spatiotemporal variability in metabolic regimes for an urban stream draining four wastewater treatment plants with implications for dissolved oxygen monitoring
2021 - Sarah H. Ledford, Jacob S. Diamond, Laura Toran

Urbanization and subsequent expansion of wastewater treatment plant (WWTP) capacity has the potential to alter stream metabolic regimes, but the magnitude of this change remains unknown. Indeed, our understanding of downstream WWTP effects on stream metabolism is spatially and temporally limited, and monitoring designs with upstream-downstream comparison sites are rare. Despite this, and despite observed spatiotemporal variability in stream metabolic regimes, regulators typically use snapshot monitoring to assess ecosystem function in receiving streams, potentially leading to biased conclusions about stream health.
Testing angular velocity as a new metric for metabolic demands of slow-moving marine fauna: a case study with Giant spider conchs Lambis truncata
2021 - Lloyd W. Hopkins, Nathan R. Geraldi, Edward C. Pope, Mark D. Holton, Miguel Lurgi, Carlos M. Duarte & Rory P. Wilson

Quantifying metabolic rate in free-living animals is invaluable in understanding the costs of behaviour and movement for individuals and communities. Dynamic body acceleration (DBA) metrics, such as vectoral DBA (VeDBA), are commonly used as proxies for the energy expenditure of movement but are of limited applicability for slow-moving species. It has recently been suggested that metrics based on angular velocity might be better suited to characterize their energetics.
Carcass deposition to suppress invasive lake trout causes differential mortality of two common benthic invertebrates in Yellowstone Lake
2020 - Michelle A. Briggs, Lindsey K.Albertson, Dominique R. Lujan, Lusha M. Tronstad, Hayley C. Glassic, Christopher S. Guy, Todd M. Koel

Invasive species require management to mitigate their harmful effects on native biodiversity and ecosystem processes. However, such management can also have negative, unintended consequences on non-target taxa, ecosystem processes, and food web dynamics. In Yellowstone Lake, invasive lake trout (Salvelinus namaycush) have caused a decline in the native Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) population. To suppress the invader, lake trout carcasses are deposited on the species’ spawning sites, causing embryo mortality by reducing dissolved oxygen as they decay. The non-target effects of carcass deposition are unknown, but benthic invertebrates may be sensitive to reductions in dissolved oxygen.
Drought alters the biogeochemistry of boreal stream networks
2020 - Lluís Gómez-Gener, Anna Lupon, Hjalmar Laudon & Ryan A. Sponseller

Drought is a global phenomenon, with widespread implications for freshwater ecosystems. While droughts receive much attention at lower latitudes, their effects on northern river networks remain unstudied. We combine a reach-scale manipulation experiment, observations during the extreme 2018 drought, and historical monitoring data to examine the impact of drought in northern boreal streams. Increased water residence time during drought promoted reductions in aerobic metabolism and increased concentrations of reduced solutes in both stream and hyporheic water.
Organic Pellet Decomposition Induces Mortality of Lake Trout Embryos in Yellowstone Lake
2019 - Todd M. Koel, Nathan A. Thomas, Christopher S. Guy, Philip D. Doepke, Drew J. MacDonald, Alex S. Poole, Wendy M. Sealey, Alexander V. Zale

Yellowstone Lake is the site of actions to suppress invasive Lake Trout Salvelinus namaycush and restore native Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri and natural ecosystem function. Although gill netting is effective (Lake Trout λ ≤ 0.6 from 2012 through 2018), the effort costs more than US$2 million annually and only targets Lake Trout age 2 and older. To increase suppression efficiency, we developed an alternative method using organic (soy and wheat) pellets to increase mortality of Lake Trout embryos on spawning sites.
Oxygen supersaturation protects coastal marine fauna from ocean warming
2019 - Folco Giomi, Alberto Barausse, Carlos M. Duarte, Susana Agusti, Vincent Saderne, Andrea Anton, Daniele Daffonchio

Ocean warming affects the life history and fitness of marine organisms by, among others, increasing animal metabolism and reducing oxygen availability. In coastal habitats, animals live in close association with photosynthetic organisms whose oxygen supply supports metabolic demands and may compensate for acute warming. Using a unique high-frequency monitoring dataset, we show that oxygen supersaturation resulting from photosynthesis closely parallels sea temperature rise during diel cycles in Red Sea coastal habitats.
Environmental parameters of shallow water habitats in the SW Baltic Sea
2019 - Markus Franz, Christian Lieberum, Gesche Bock, and Rolf Karez

The coastal waters of the Baltic Sea are subject to high variations in environmental conditions, triggered by natural and anthropogenic causes. Thus, in situ measurements of water parameters can be strategic for our understanding of the dynamics in shallow water habitats. In this study we present the results of a monitoring program at low water depths (1–2.5 m), covering 13 stations along the Baltic coast of Schleswig-Holstein, Germany.
Thermal dependence of seagrass ecosystem metabolism in the Red Sea
2019 - Celina Burkholz, Carlos M. Duarte, Neus Garcias-Bonet

The Red Sea is one of the warmest seas with shallow seagrass ecosystems exposed to extreme temperatures, in excess of 35°C, during the summer months. Seagrass meadows are net autotrophic ecosystems, but respiration increases faster than primary production with temperature. This may lead to a shift from an autotrophic to a heterotrophic system at the highest temperatures. Although tropical seagrasses are adapted to high temperatures, the metabolic rates of Red Sea seagrasses have not yet been reported. Here we assessed the community metabolism of 2 seagrass ecosystems, an Enhalus acoroides monospecific meadow and a Cymodocea serrulata and Halodule uninervis mixed meadow, located in the central Red Sea.
Oxycline oscillations induced by internal waves in deep Lake Iseo
2019 - Giulia Valerio, Marco Pilotti, Maximilian Peter Lau, and Michael Hupfer

Lake Iseo is undergoing a dramatic deoxygenation of the hypolimnion, representing an emblematic example among the deep lakes of the pre-alpine area that are, to a different extent, undergoing reduced deep-water mixing. In the anoxic deep waters, the release and accumulation of reduced substances and phosphorus from the sediments are a major concern.
A network model for primary production highlights linkages between salmonid populations and autochthonous resources
2018 - W. Carl Saunders, Nicolaas Bouwes, Peter McHugh, Chris E. Jordan

Spatial variation in fish densities across river networks suggests that the influence of food and habitat resources on assemblages varies greatly throughout watersheds. We produced reliable estimates of GPP at sites where DO loggers were deployed using measurements of solar exposure, water temperature, and conductivity measured at each site, as well as surrogates for these data estimated from remote sensing data sources.
Atmospheric stilling leads to prolonged thermal stratification in a large shallow polymictic lake
2017 - R. Iestyn Woolway, Pille Meinson, Peeter Nõges, Ian D. Jones & Alo Laas

To quantify the effects of recent and potential future decreases in surface wind speeds on lake thermal stratification, we apply the one-dimensional process-based model MyLake to a large, shallow, polymictic lake, Võrtsjärv. The model is validated for a 3-year period and run separately for 28 years using long-term daily atmospheric forcing data from a nearby meteorological station. Model simulations show exceptionally good agreement with observed surface and bottom water temperatures during the 3-year period. Similarly, simulated surface water temperatures for 28 years show remarkably good agreement with long-term in situ water temperatures.