|Shields Jr, Fletcher|
Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2011
Publication Date: 2/1/2012
Citation: Shields Jr., F.D., Knight, S.S. 2011. Significance of riverine hypoxia for fish: The case of the Big Sunflower River, Mississippi. Journal of the American Water Resources Association. 48(1):170-186. DOI:10.1111/j.1752-1688.2011.00606.x
Interpretive Summary: Rivers and streams in intensively cultivated, low-relief watersheds often experience periods of extremely low dissolved oxygen concentration, which is a violation of water quality regulations. Ecological literature contains varied information about the effects of such conditions on fish. Fish, habitat, and water quality information were collected from the Big Sunflower River in northwestern Mississippi for three years during high and low flows. Low dissolved oxygen levels were chronic, especially during higher flows in late Spring. Statistical analyses showed some species of fish were sensitive to dissolved oxygen levels, disappearing when oxygen levels were low. These results contribute to ongoing discussions regarding the biological significance of existing stream water quality conditions in agricultural landscapes.
Technical Abstract: Degraded streams draining low-relief, intensively cultivated watersheds may experience periods of hypoxia or anoxia. A three-year study of water quality, fish, and physical habitat in the Big Sunflower River in northwestern Mississippi coupled with continuously logged water quality and hydrology data provided by others showed prolonged periods of hypoxia associated with higher flows. Fish species richness was directly related to dissolved oxygen concentration (DO) (r2 = 0.35, p = 0.00004), and ordination using nonmetric multidimensional scaling indicated strong association between fish community structure and DO. Low-head weirs supported relatively dense and diverse fish assemblages and thus provided local habitat enhancement, but may create stagnant zones upstream due to backwater effects that exacerbate low DO problems. Although hypoxia has been reported for some lightly-degraded rivers and floodplains, our observations suggest hypoxia in Big Sunflower River and similar systems alters fish species composition and should be remediated. Cost effective remediation will require better understanding of autotrophic and heterotrophic processes that control DO and the relationship of these processes to discharge.