Linda Benedict, Haggard, Beatrix J, Hendrix, James | 7/31/2013 10:01:23 PM
Beatrix Haggard, James Hendrix and Donnie Miller
In northeast Louisiana much of the crop production area has been historically dominated by cotton. Because of low cotton prices and increasing grain prices, however, cotton acreage has steadily decreased. This trend was evident in the 2012 growing season, when producers harvested 533,395 acres of corn, 225,095 acres of cotton and 1,120,527 acres of soybeans. Increased acreage of high-yielding row crops in Louisiana has led to the need of production systems to improve nutrient use efficiency and conservation management practices.
Because of high amounts of rainfall in northeast Louisiana, implementing practices such as sediment trapping is important. To determine the effectiveness of selected conservation practices, baseline water quality data were collected from Lake St. Joseph, a 1,580-acre impaired oxbow lake within the Ouachita River Basin in Tensas Parish. Currently, Lake St. Joseph is not supporting fish and wildlife propagation.
Because of the impaired status of the lake, the LSU AgCenter obtained a grant from Louisiana Department of Environmental Quality to monitor water quality parameters for one year to obtain current baseline data. The goals of this project were to monitor the water quality, identify the main drainage ditches that are substantial pathways for the pollutant load in the lake, and generate an updated baseline of water quality.
An initial project to measure water quality was conducted from February 2012 to January 2013 to obtain a baseline data set for three inflow points, an outflow point and three locations within the main body of the lake (Figure 1). Water samples were taken and measured on site. Further laboratory analysis was completed at the LSU AgCenter W.A. Callegari Environmental Center in Baton Rouge.
A total maximum daily load is a calculation of the maximum amount of a pollutant that a waterbody can receive and still safely meet water quality standards. The total maximum daily load for dissolved oxygen is 5 milligrams per liter annually. Site G, which corresponds with the site the Department of Environmental Quality previously sampled, provides an opportunity to show a change from 2006 – when the dissolved oxygen was 5.04 milligrams per liter – to 2012, when dissolved oxygen was 7.6 milligrams per liter – an improvement. Site D continues to be lower in dissolved oxygen throughout the year because of the cyclical growth and die-off of aquatic vegetation in the northern portion of the lake.
Time of day or weather differences can have an influence on the dissolved oxygen. Researchers have found that dissolved oxygen is much lower right before sunrise and after sunset, with the peak occurring around midday. This is because aquatic vegetation does not synthesize oxygen when clouds or darkness decrease sunlight. The values also are reduced with the depth of the water column, which can have a large influence because of wind, sunlight and the decomposition of plants in the lower levels. This is important to take into account for other nonpoint-source projects.
The next step in this project is a 27-month extension to evaluate the establishment of best management practices on lake water quality. The U.S. Department of Agriculture’s Natural Resources Conservation Service contracted with 15 of the 18 agricultural producers located around the lake to provide funding to implement these practices. Sampling resumed in June 2013 and will continue through June 2015.
The implementation of best management practices is expected to reduce sediment-related issues, including turbidity, total dissolved solids and total suspended solids.
Beatrix Haggard is a soils specialist, Northeast Region, Winnsboro; James Hendrix is a watershed agent, St. Joseph; and Donnie Miller is John B. Baker Professor for Excellence in Weed Science and resident coordinator, Northeast Research Station, St. Joseph, and Macon Ridge Research Station, Winnsboro.
(This article was published in the spring 2013 issue of Louisiana Agriculture magazine.)