|Shields Jr, Fletcher|
Submitted to: River Research and Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2011
Publication Date: 3/5/2013
Citation: Shields Jr, F.D., Lizotte Jr, R.E., Knight, S.S. 2013. Spatial and temporal water quality variability in aquatic habitats of a cultivated floodplain. River Research and Applications. 29(3):313-329. DOI:10.1002/rra.1596.
Interpretive Summary: Aquatic habitats within lowland river floodplains are extremely productive and valuable, but are adversely impacted by intensive agriculture. Hydrology, water quality and fish were sampled from five sites representing different habitats along the Coldwater River in the Mississippi Delta for four years. The types of fish and the water quality found in these sites were indicative of degraded conditions, with high levels of turbidity and water temperature and low dissolved oxygen. Since habitat conditions were tightly linked to water depth and pollution of inflowing runoff, one large backwater site was rehabilitated by building a weir to increase water depth and divert runoff. This measure was partially effective, but the rehabilitated backwater continued to experience periods of low dissolved oxygen during hot, dry weather. These findings are useful to others interested in protecting and managing floodplains to conserve ecosystem services.
Technical Abstract: Floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services, but are perturbed when intensively cultivated. Hydrologic, water quality and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi were measured over four years: the river, two severed meanders that functioned as backwaters, a managed wetland and an ephemeral channel draining cultivated fields. Off-channel habitats were connected to downstream regions 0.10-32% of the dry season and 24-67% of the wet season. Median temperatures for the five monitored sites ranged from 18 to 23 oC, average total solids concentrations for all sites was 182 mg/L, and median values of total P and total N were 0.29 mg/L and 1.56 mg/L, respectively. Water quality displayed strong seasonal differences between the wet winter/spring and dry summer/fall periods so that temporal variations were comprised of gradual seasonal trends superimposed on strong diurnal variations. All off-channel habitats exhibited periods of hypoxia and temperatures > 30oC during the dry season. Between-site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. Rehabilitation of one backwater by increasing water depth and diverting agricultural runoff was associated with improved water quality and fish species richness relative to an adjacent untreated backwater. Diversion of polluted local runoff and using water control structures to maintain greater water depth were shown to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity.