Water clarity of the Colorado River—Implications for food webs and fish communities

<p>The ice-covered period in lakes is increasingly recognized for its unique hydrodynamic and biogeochemical phenomena and ecological relevance yet it remains poorly studied compared to the ice-free season. Knowledge gaps exist where research areas &#8211; hydrodynamics, biogeochemistry and biology &#8211; intersect. For example, density-driven circulation under ice coincides with an expansion of the anoxic zone, but abiotic and biotic controls on oxygen depletion have not been disentangled. While heterotrophic microorganisms and migrating phytoplankton often thrive at the oxycline, the extent to which physical processes induce fluxes of heat and substrates that further support under-ice food webs is uncertain. Similarly, radiatively-driven convection under ice in spring can promote growth of motile phytoplankton or diatoms depending on flow velocity, water clarity and mixing depth, but links between functional trait selection, trophic transfer to zooplankton and fish and the prevalence of microbial versus classical food webs in seasonally ice-covered lakes remain unclear. Under-ice processes cascade into and from the ice-free season, and are relevant to annual cycling of energy and carbon through aquatic food webs. Understanding the coupling between state transitions and the reorganization of trophic hierarchies is essential for predicting complex ecosystem responses to climate change. In this presentation, we briefly review existing knowledge regarding physical processes in lakes in winter and the parallel developments in under-ice biogeochemistry and ecology. We then illustrate interactions between these processes, identify extant knowledge gaps whose solution requires interdisciplinary approaches, and present (novel) methods to address outstanding questions.</p>

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Effects of water quality and habitat on composition of fish communities in the Upper Colorado River Basin

Fact Sheet ◽

10.3133/fs12297 ◽

1997 ◽

Cited By ~ 3

Author(s):

Jeffrey R. Deacon ◽

Scott V. Mize

Keyword(s):

Water Quality ◽

River Basin ◽

Colorado River ◽

Fish Communities ◽

Colorado River Basin ◽

Upper Colorado River Basin

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Role of ambient light in structuring north-temperate fish communities: potential effects of increasing dissolved organic carbon concentration with a changing climate

Environmental Reviews ◽

10.1139/a2012-010 ◽

2012 ◽

Vol 20 (3) ◽

pp. 173-190 ◽

Cited By ~ 27

Author(s):

Ashley D. Stasko ◽

John M. Gunn ◽

Tom A. Johnston

Keyword(s):

Climate Change ◽

Organic Carbon ◽

Dissolved Organic Carbon ◽

Fish Communities ◽

Water Clarity ◽

Smallmouth Bass ◽

Boreal Lakes ◽

Light Environment ◽

Individual Species ◽

Terrestrial Organic Matter

The vertical light environment in freshwater lakes is sensitive to changes in dissolved organic carbon (DOC) concentrations, and DOC concentrations in most boreal lakes appear to be increasing as the climate changes. Understanding how DOC dynamics in lakes and watersheds are then linked to fish habitat is therefore critical to assessing the effects of climate change on fish communities. This paper reviews the evidence for climate-induced alterations to DOC in north-temperate watersheds and assesses the potential consequences of the resultant decreases in water clarity on fish production and community structure in small boreal lakes (<500 ha). Although DOC increases are forecast for most boreal lakes, complex interactions between local climate, rates of terrestrial organic matter decomposition and runoff, existing water quality, species shifts in forest communities, and changing season lengths can all combine to affect the magnitude of water clarity declines that will occur in individual lakes. Elevated DOC concentrations will affect the availability of coldwater versus warmwater habitat and niche characteristics that are dependent on lake depth, water clarity, and the preferences and physiological tolerances of the individual species. The shifts in availability of suitable thermal habitat will in turn affect fish growth, production, and community composition. Range expansions for warmwater species and range reductions for coldwater species will likely occur in warmer, darker environments, with adverse consequences for some native species and likely advantages for invasive species such as smallmouth bass. Likewise, major shifts in trophic dynamics would accompany the darkening of boreal lakes as species-specific feeding efficiencies change and primary and secondary production are altered. From a beneficial perspective, elevated DOC concentrations will likely relieve some physiological stress in biota via protection against contaminant toxicity and ultraviolet radiation (UVR) exposure. As with many other disturbances, we need to view climate change impacts on fish communities as a multiple stressor problem and the potential impacts of the changing light environment needs to be given as much prominence as the study of stressors such as eutrophication and trace contaminants.

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Food web controls on mercury fluxes and fate in the Colorado River, Grand Canyon

Science Advances ◽

10.1126/sciadv.aaz4880 ◽

2020 ◽

Vol 6 (20) ◽

pp. eaaz4880 ◽

Cited By ~ 1

Author(s):

D. M. Walters ◽

W.F. Cross ◽

T.A. Kennedy ◽

C.V. Baxter ◽

R.O. Hall ◽

...

Keyword(s):

Food Web ◽

Food Webs ◽

Species Interactions ◽

Colorado River ◽

Grand Canyon ◽

Terrestrial Ecosystems ◽

Species Traits ◽

Functional Trait ◽

Contaminant Exposure ◽

Aquatic Food

Mercury (Hg) biomagnification in aquatic food webs is a global concern; yet, the ways species traits and interactions mediate these fluxes remain poorly understood. Few pathways dominated Hg flux in the Colorado River despite large spatial differences in food web complexity, and fluxes were mediated by one functional trait, predation resistance. New Zealand mudsnails are predator resistant and a trophic dead end for Hg in food webs we studied. Fishes preferred blackflies, which accounted for 56 to 80% of Hg flux to fishes, even where blackflies were rare. Food web properties, i.e., match/mismatch between insect production and fish consumption, governed amounts of Hg retained in the river versus exported to land. An experimental flood redistributed Hg fluxes in the simplified tailwater food web, but not in complex downstream food webs. Recognizing that species traits, species interactions, and disturbance mediate contaminant exposure can improve risk management of linked aquatic-terrestrial ecosystems.

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