Spatial and Temporal Water Quality Variability in Aquatic Habitats of a Cultivated Floodplain

Abstract

The floodplains of lowland rivers contain diverse aquatic habitats that provide valuable ecosystem services but are perturbed when intensively cultivated. Hydrologic, water chemistry and biological (fish) conditions in five aquatic habitats along the Coldwater River, Mississippi, were measured for more than 4 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% to 32% of the dry season and 24% to 67% of the wet season. The median temperatures for the five monitored sites ranged from 18°C to 23°C, the median total solids concentration for all sites was 135 mg L−1, the median total phosphorus was 0.29 mg L−1 and the median total nitrogen was 1.56 mg L−1. Chemical and physical water quality displayed strong seasonal differences between the wet winter/spring and the dry summer/fall periods so that temporal variation consisted of gradual seasonal trends superimposed on strong diurnal variations. All off‐channel habitats exhibited periods of hypoxia and temperatures >30°C during the dry season. Between‐site gradients of water and habitat quality were strongly coupled to water depth and runoff loading. The 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. The diversion of polluted runoff and the use of water control structures to maintain greater water depth were observed to be effective management tools, but the former reduces the water supply to habitats that tend to dry up and the latter reduces connectivity. Published in 2011 by John Wiley & Sons, Ltd.

Sediment Nutrient Flux Rates in a Shallow, Turbid Lake Are More Dependent on Water Quality Than Lake Depth

“…As alluvial floodplain deposits are naturally rich in P and organic materials, the Delta has been converted over time to meet intense agricultural and flood control demands [11]. Today, approximately two-thirds of the region is cultivated in row crops, of which twothirds is irrigated [33], often using both surface water and groundwater. Excess sediment, nutrients, and other contaminants in agricultural runoff have transformed much of the regional lakes and rivers into turbid, hypereutrophic ecosystems.…”

Salinization and sedimentation drive contrasting assembly mechanisms of planktonic and sediment‐bound bacterial communities in agricultural streams

“…The remaining land is ~25% wetland that is too wet for agriculture and 10% primarily consisting of small cities and towns (Yasarer et al, 2020). Compared to other regions in Mississippi, intensive agriculture in the MAP has resulted in elevated concentrations of dissolved ions, OC, and P, but not N in surface waters potentially due to high denitrification rates that remove excess N from agricultural fertilizers (Douglas Shields et al, 2011;Taylor et al, 2015Taylor et al, , 2023.…”

Periphyton responses to nutrient and atrazine mixtures introduced through agricultural runoff

“…The site receives runoff from *100 ha of cultivated land, primarily through an intermittent slough connected to a series of drainage ditches and gullies that drain adjacent cropland. In fall of 2006, the site was modified with the construction of two water control weirs, creating a larger, deeper cell managed as a lake-type aquatic habitat and a smaller, shallower cell, 500 m long, 20 m wide, managed as a riverine wetland (Shields and Pearce 2010;Shields et al 2012). The weir controlling the lake cell was located such that most runoff from adjacent fields is diverted into the wetland cell.…”