The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world's largest freshwater ecosystem, by dreissenid (zebra and ...quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world's largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.
Animal excretion provides nutrients for primary productivity and can be a crucial component of ecosystem nutrient cycling. The concentrations of carbon (C), nitrogen (N), and phosphorus (P) in an ...animal’s excretion are strongly influenced by the C:N:P stoichiometry (molar ratios) of its body and of the food it eats. We measured the C:N:P ratios of quagga mussel (
Dreissena rostriformis bugensis
) tissues and excreta and of seston across wide environmental and spatial gradients in the upper Laurentian Great Lakes. We then investigated how mussel excretion rates were impacted by stoichiometric mismatch—the difference between the C:P ratios of mussel tissues and the C:P ratios their food. Quagga mussel internal C:N:P stoichiometry varied significantly across sites and seasons, driven primarily by changes in tissue P concentrations. When mussel tissues had substantially lower C:P ratios than seston (that is
,
strong stoichiometric mismatch), mussels excreted significantly less N and P relative to C. Excretion C:N ratios varied by nearly threefold, while C:P ratios varied by tenfold. The effect of the stoichiometric mismatch on excretion stoichiometry was more dramatic in the spring, when mussels had higher tissue P concentrations, than in the summer. This suggests seasonality in mussel P demand. Our results challenge the assumption of strict internal homeostasis in consumers and demonstrate that food and tissue stoichiometry need to be considered to predict consumer excretion stoichiometry. These findings help to better understand the impact of consumer-driven nutrient cycling in aquatic environments and quagga mussel contributions to the nutrient budgets of invaded ecosystems.
Ecology under lake ice Hampton, Stephanie E.; Galloway, Aaron W. E.; Powers, Stephen M. ...
Ecology letters,
January 2017, Letnik:
20, Številka:
1
Journal Article
Recenzirano
Odprti dostop
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.
Summary
This study examined the effect of invasive dreissenid mussels on nutrient and carbon dynamics in a large lake (Lake Simcoe, Ontario). We measured rates of nutrient (phosphorus and nitrogen) ...and carbon excretion and biodeposition by zebra and quagga mussels and the P, N and C content of their soft tissues and shells at different depths throughout the open‐water season. Measurements were combined with detailed information about dreissenid biomass and lakewide distribution to examine the impacts of dreissenids on whole‐lake dynamics of P, N and C.
Mussel tissue P, N and C content and rates of excretion and biodepositon varied among species, seasons and depths, apparently driven by metabolic and stoichiometric factors.
Dreissenid mussels excreted, deposited and stored large quantities of P, N and C when compared to lake standing stocks and loadings, and represent an important driver of nutrient cycling in the lake. Living and discarded mussel shell material is shown to represent a potentially important, and hitherto largely overlooked, long‐term sink for P, N and C.
The concentration of dreissenid biomass in the well‐mixed and illuminated littoral portion of L. Simcoe results in redirection of nutrients and carbon from offshore areas to the nearshore zone of the lake.
Changes in nutrient and carbon distribution and cycling patterns caused by dreissenid establishment in L. Simcoe and other ecosystems can have implications for the distribution of primary and secondary production and should be considered in the context of water quality and nutrient input management.
As global surface temperatures continue to rise as a result of anthropogenic climate change, effects in temperate lakes are likely to be more pronounced than in other ecosystems. Decreases in snow ...and ice cover extent and duration and extended periods of summer stratification have been observed in temperate lake systems throughout the Anthropocene. However, the effects of changing snow and ice cover on lacustrine communities remain largely uninvestigated. We examined underwater light climate and associated primary productivity patterns under snow-covered and clear-lake ice in 6 inland lakes in Minnesota, USA, spanning gradients of water column optical properties (blue, green, brown) associated with trophic status and organic material content. In all lakes, snow cover influenced not only the intensity, but also the spectral signature of light penetrating into the water column. Specifically, the wavelength of maximum penetration was shifted towards longer wavelengths under snow cover in green (eutrophic) lakes but was shifted towards shorter wavelengths in blue and brown lakes. Volumetric primary productivity was often higher than anticipated (e.g., ∼1200 mg m
−3
d
−1
; Lake Minnetonka, snow-covered ice). Carbon assimilation rates were lower under snow-covered ice throughout the water column in all lake types except immediately under cleared ice in eutrophic lakes, where phytoplankton were likely photoinhibited because of the penetration of intense, short-wavelength light. These findings suggest that changes to snow and ice cover under ongoing climate change scenarios can affect patterns of phytoplankton primary productivity in sensitive aquatic ecosystems.
Abstract
Polyphosphate (polyP) is important to phytoplankton ecology, but a unified view of its variability and roles in ecosystem‐scale phosphorus (P) cycling is lacking. We study polyP in the ...world's largest freshwater ecosystem, the Laurentian Great Lakes, covering pelagic to nearshore areas across a wide nutrient gradient. We show that polyP (average 10.99 ± 3.90 nmol L
−1
) constitutes 3.8–30.2% (average 18.1 ± 7.2%) of total particulate P (TPP). PolyP accumulation is higher in low‐P pelagic waters compared with more productive nearshore areas. PolyP is preferentially degraded in the water column of the Great Lakes, enhancing P recycling and relieving the nitrogen (N) : P imbalance. Our data enables a coherent large‐scale freshwater‐to‐oceanic comparison. We show that while different plankton groups accumulate different levels of polyP with smaller plankton accumulating more, P availability is the key driver of polyP variability within and across systems.
Climate warming impacts ecosystems through multiple interacting pathways, including via direct thermal responses of individual taxa and the combined responses of closely interacting species. In this ...study, we examined how warming and infection by an oomycete parasite (Saprolegnia) affect the dominant zooplankter of Russia’s Lake Baikal, the endemic copepod Epischurella baikalensis. We used a combination of laboratory experiments, long-term monitoring data, and population modeling. Experiments showed a large difference in the thermal optima of host and parasite, with strong negative effects of warm temperatures on E. baikalensis survival and reproduction and a negative effect of Saprolegnia infection on survival. Saprolegnia infection had an unexpected positive effect on E. baikalensis reproductive output, which may be consistent with fecundity compensation by females exposed to the parasite. Long-term monitoring data suggested that Saprolegnia infections were most common during the warmest periods of the year. Population models, parameterized with experimental and literature data, correctly predicted the timing of Saprolegnia epizootics, but overestimated the negative effect of warming on E. baikalensis populations. Models suggest that diel vertical migration may allow E. baikalensis to escape the negative effects of increasing temperatures and parasitism and enable E. baikalensis to persist in the face of moderate warming of Lake Baikal. Our results contribute to understanding of how warming and parasitism interact to affect the pelagic ecosystems of cold lakes and oceans and how the consequences of these interacting stressors can vary seasonally, spatially, and interannually.
Winter Limnology on the Rise Hampton, Stephanie; Dugan, Hilary; Sadro, Steven ...
Limnology and oceanography bulletin,
August 2024, Letnik:
33, Številka:
3
Journal Article
The “Melosira years” of Lake Baikal Katz, Stephen L.; Izmest’eva, Lyubov R.; Hampton, Stephanie E. ...
Limnology and oceanography,
November 2015, Letnik:
60, Številka:
6
Journal Article
Recenzirano
Odprti dostop
Winter primary production in seasonally ice-covered lakes historically has not been well studied, but it is increasingly recognized as an important component of lake metabolism. Lake Baikal in ...Siberia is not only the World’s oldest, deepest, and most biologically diverse lake, but also where large under-ice blooms of the diatom Aulacoseira baicalensis (formerly Melosira) occur in some years. The phenomenon of “Melosira years” is noteworthy both for the intensity of the diatom blooms, in which total under-ice production can be a majority of total annual production, and for the enigmatic regularity of their occurrence every 3–4 yr. The degree to which these episodic blooms might be controlled by external forcing and endogenous lake processes has been debated for decades. We used a 50-yr time series of phytoplankton observations to statistically model the occurrence of Aulacoseira blooms as a function of meteorological and climatological predictor variables. The results support the hypothesis that a confluence of meteorological conditions in the preceding fall season, which favor clear ice formation withminimal snow cover, also favor Aulacoseira blooms in the following spring. Further, we observe that this confluence of factors is related to relatively strong states of the Siberian High which, while not strictly periodic, do explain a significant fraction of the interannual bloom pattern. Finally, our analyses show that the timing of the peak abundance of A. baicalensis shifted 1.6 months later across the 50-yr time series, corresponding with the delay in ice-on timing that has been associated with climate change.
Little is known about the history of heavy metal pollution of Russia’s Lake Baikal, one of the world’s largest lakes and a home to numerous endemic species, including the Baikal Seal, Pusa sibirica. ...We investigated the history of heavy metal (V, Cu, Zn, Cd, Hg, Tl, Pb, U) pollution in Lake Baikal seals over the past 8 decades. C and N stable isotope analysis (SIA) and laser-ablation ICP-MS of seal teeth were used to examine changes in feeding ecology, heavy metal levels associated with life history events and long-term variation in metal exposure. SIA did not suggest large changes in the feeding ecology of Baikal seals over the past 80 years. LA-ICP-MS analyses revealed element-specific ontogenetic variability in metal concentrations, likely related to maternal transfer, changes in food sources and starvation. Hg and Cd levels in seals varied significantly across the time series, with concentrations peaking in the 1960s - 1970s but then declining to contemporary levels similar to those observed in the 1930s and 1940s. Trends in atmospheric emissions of Hg suggest that local sources as well as emissions from eastern Russia and Europe may be important contributors of Hg to Lake Baikal and that, despite the size of Lake Baikal, its food web appears to respond rapidly to changing inputs of contaminants.
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