Eutrophication effect on production and transfer of omega-3 fatty acids in boreal lake food webs

Climate-Driven Deoxygenation of Lakes Alters the Nutrient-Toxin Profile of a Food Fish

Climate change is rapidly altering fisheries supporting aquatic ecosystems. The implications for food security depend not only on harvest biomass but also concentrations of nutrients and toxins in fish. Using brook trout from Adirondack lakes (New York, USA), we tested whether ongoing lake deoxygenation trends will affect fish muscle omega-3 fatty acids, selenium, and mercury concentrations. Across space (16 lakes: 1 year) and time (6 years: 1 lake), anoxia decreased selenium and was associated with elevated fish mercury, with no effect on omega-3 content. Because selenium may mitigate some end points of mercury toxicity, highly variable Se:Hg molar ratios (0.70-35.79) in neighboring lakes may have health risk implications. For fish consumers, ongoing lake deoxygenation under climate change could potentially reduce selenium intake while enhancing mercury exposure. Simultaneous alteration of beneficial compounds and toxins by environmental change complicates the development of fish consumption advisories to safeguard public health in a warming world.

Differentiated fatty acid allocation of Daphnia magna helped to maintain their population under food quality deterioration

Polyunsaturated fatty acids (PUFAs) are vital to the physiological functioning of crustacean zooplankton. However, cyanobacteria blooms frequently lead to PUFA deficiencies, which poses a substantial challenge to population fitness. Therefore, we hypothesize that D. magna adapt to PUFA-deficient conditions by prioritizing PUFA allocation to somatic growth, and then to offspring during reproduction to ensure population persistence. To test this hypothesis, we applied (compound-specific) 13C labeling to compare the turnover of total carbon and certain groups of fatty acids in Daphnia magna fed with Scenedesmus bijuba for 6 days and then switching to a diet of 13C labeled Microcystis wesenbergii for 6 days (with food quality deterioration) or to a diet of 13C-labeled Scenedesmus (without food quality deterioration), respectively. Fatty acid profiles of D. magna mothers and offspring were also analyzed to reveal their PUFA allocation strategies. Life table parameters from D. magna-feeding Scenedesmus switching to Microcystis were compared with D. magna fed with only Scenedesmus or Microcystis to reveal the effect of PUFA allocation on D. magna performance. Our results showed that with food quality deterioration, D. magna exhibited a significantly lower PUFA and carbon turnover and higher offspring: mother ratios in their PUFA contents. Despite this reduced reproduction, the D. magna switching diets showed no significant different intrinsic increasing rate of populations with those fed only Scenedesmus. Meanwhile, the D. magna switching diets performed significantly better than D. magna fed only Microcystis. These results suggest that differential fatty acid allocation of consumers may serve as an adaptive strategy for population maintenance in food quality deterioration and provide ecological implications with cyanobacterial bloom management and Daphnia reproductive plasticity, which needs further explorations.

Reservoir eutrophication in the Brazilian semiarid: modeling of sediment removal and control of external loads as remediation measures

Eutrophication, driven by nutrient enrichment, poses a global challenge, impacting the ecosystem, water supply systems, and ultimately, human health. In this research, water unavailability due to phosphorus pollution was assessed in Brazilian semiarid reservoirs with data measured over a decade. Management strategies to control eutrophication were simulated using physical-mathematical modeling of the phosphorus budget in the water and sediment layers. The model parameters were calibrated from 1976 to 2021, and the results were validated by comparing measured and modeled duration curves of phosphorus concentration. Water unavailability due to phosphorus pollution occurred approximately 61% of the time, indicating the need for effective control strategies. Simulation of sediment removal when the reservoirs dry up showed potential to contribute to water quality in reservoirs with high emptying frequency, while external phosphorus load reduction proved to be more widely efficient. The variation in the effectiveness of the techniques among the studied reservoirs emphasizes the need for approaches adapted to the specific conditions. This work contributes to improve the understanding of phosphorus dynamics in reservoirs with high water level fluctuations and appropriate management measures to control eutrophication in dry environments.

Foraging in contrasting oceanographic regions impacts the fatty acid profile of two closely related pelagic seabirds

Coastal urbanisation negatively affects marine ecosystems through habitat degradation and pollution. Cory's (Calonectris borealis) and Scopoli's (C. diomedea) shearwaters are closely related species inhabiting the Northeast Atlantic Ocean and the Mediterranean Sea, respectively. This study assesses the fatty acid profile, with the trophic and foraging ecology, of Cory's and Scopoli's shearwaters breeding at Berlenga (Atlantic Ocean) and Chafarinas (Mediterranean Sea) Islands. The diet quality of Scopoli's shearwaters is expected to be generally lower, characterised by reduced levels of ω-3 fatty acids. Additionally, higher concentrations of specific fatty acid trophic markers are anticipated, reflecting the Mediterranean's semi-enclosed environment, low productivity, and pollution challenges. These markers include oleic acid, vaccenic acid, trans fatty acids (indicative of urban and industrial discharges), and odd-chain fatty acids (indicative of bacterial presence). This study supported these predictions, with Scopoli's shearwaters foraging in the Mediterranean having higher concentrations of oleic and vaccenic acids, odd-chain fatty acids, and trans-palmitoleic acid in their plasma. Yet, concentrations of ω-3 were also higher in Scopoli's shearwaters. This may result from diverse prey availability and selection, and different habitat exploitation, partially supported by differences in the trophic ecology and foraging patterns of both species; or from an enhanced immunological basal response of Scopoli's shearwaters to cope with higher anthropogenic pressure in the western Mediterranean Sea. Further studies including specific diet and contaminant analyses are crucial to understand differences in fatty acid profiles of seabirds inhabiting both oceanic basins and the implications of diet quality for seabird populations.

The Implications of Atlantic Salmon (Salmo salar L.) Fatty Acid Profiles for Their Thiamine Status

Thiamine deficiency is an ongoing issue across the Northern Hemisphere, causing reproductive failure in multiple salmonid populations. In the Baltic Sea, a large brackish water system in northern Europe, previous research has suggested that this deficiency is associated with lipid-rich diets with a high proportion of docosahexaenoic acid (DHA, 22:6n-3). The mechanism proposed is that a diet abundant in highly unsaturated fatty acids, such as DHA, depletes thiamine as an antioxidant defense in adult salmonids, rather than allocating thiamine to the offspring. In light of this existing hypothesis, we here explore the relationship between diet history and the related fatty acid (FA), profiles, and thiamine status of Atlantic salmon (Salmo salar L.) in three systems: the Baltic Sea, the North Atlantic Ocean, and Lake Vänern. Atlantic salmon inhabiting each system is known to have unique feeding histories and thiamine status. Our results showed that despite extensive sampling effort and distinct FA profiles, indicative of their diverse diets, there were no correlations between any FAs, including DHA, and the thiamine status of these populations. This finding does not support the above-mentioned hypothesis that diets rich in easily oxidized FAs would lead to lower thiamine concentrations in salmon tissues. Additionally, we found that changes in the salmon FA profiles throughout their life cycle are consistent for both low-thiamine populations from the Baltic Sea and medium-thiamine populations from North Atlantic Ocean, suggesting that these changes might not be involved in thiamine deficiency development.

Risk and mechanisms of phosphorus release at the sediment-water interface of lakes in cold and arid regions during non-frozen seasons

In recent years, the eutrophication of lakes has accelerated in cold arid regions; the release of nutrients from sediments is an important contributor. The sequential extraction method, high-resolution peeper (HR-Peeper), and diffusive gradients in thin films (DGT) techniques were used to study the occurrence characteristics, release risk, and release mechanism of phosphorus (P) at the sediment-water interface (SWI) of Ulanor Wetland in the Hulun Lake Basin, Inner Mongolia, China. The mean total P concentration in overlying water was lower in August than that in May. Dissolved organic P (DOP) or particulate P (PP) was the main form of P in the overlying water. PP dominates in May and DOP in August. Refractory P was the main form of P in sediments. The concentrations of soluble reactive P and DGT-active P in the pore water of the sediment column were higher than those in the overlying water, and the concentrations were higher in August than those in May. Release of P in the wetland sediments occurred during the non-frozen seasons, with a higher risk in August than in May. The good linear correlation between dissolved P, Fe, and Mn in the DGT profiles verified their co-release due to the anaerobic reduction of Fe/Mn oxides. Moreover, alkaline sediments are also conducive to the release of sediment P. This study can provide data and theoretical support for eutrophication control in Ulanor Wetland and other similar water bodies in cold and arid regions.

How do small dams alter river food webs? A food quality perspective along the aquatic food web continuum

Damming of rivers poses a significant threat to freshwater ecosystems. Previous studies about the impact of damming on river ecosystems have mostly focused on large dams, with the impact of small dams largely unknown. Further, while the impacts of dams on aquatic communities have been widely studied, the effect on energy flow across river food webs remains unclear. In recent years, long-chain polyunsaturated fatty acid analysis (LC-PUFA) has emerged as a promising technique for assessing food quality and trophic interactions. In this study, LC-PUFA was applied to explore the nutritional effects of small dams on river food webs. A field investigation was conducted at upstream and downstream areas of three small dams in the headwaters of Dongjiang River, China, to evaluate the impact of small dams on the nutritional quality of basal food sources, and their consequent impacts on aquatic consumers and trophic links. Basal food sources (i.e., submerged leaves, macrophytes and periphyton) and aquatic consumers (i.e., macroinvertebrates and fish) were collected, and their fatty acid (FA) composition was measured. Our results showed that periphyton, rather than submerged leaves and macrophytes, was the primary high-quality food source for aquatic consumers, providing them with LC-PUFA, irrespective of whether sites were upstream or downstream. Damming the streams induced changes in aqueous nutrient concentrations (TP, PO4-P, DIN, and TN) from upstream to downstream of the dams, leading to significant variation in periphyton FA content. Compared with periphyton collected at downstream sites, periphyton at upstream sites contained higher LC-PUFA, but lower short-chain PUFA. Differences in periphyton LC-PUFA between the upstream and downstream areas of dams were reflected in the FA profiles of invertebrate grazers and filterers, and further transferred to fish. Furthermore, decreased periphyton nutritional quality at the downstream of the dams was one of the reasons for the simplification of stream food webs. Our results indicated that small dams negatively affected food webs, emphasizing the importance of high-quality food sources for stream ecosystems. We suggest that the trophic integrity of river food webs hinges on the dietary availability of periphyton supplying physiologically highly required nutrients for consumers and must thus not be compromised by damming of streams or other alterations.