SEDIMENTS, NUTRIENTS, AND FECAL MATTERS IMPAIR SURFACE WATER QUALITY IN A COASTAL AGRICULTURAL WATERSHED

In order to understand the extent and the magnitude of nonpoint source pollution in a coastal agricultural watershed we monitored surface water quality from September 24, 2009 to August 9, 2011 in seven locations of the Coulee Baton Microwatershed in southwestern Louisiana. We measured dissolved oxygen (DO), turbidity, conductivity, pH, temperature in the field and determined total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), 5-day biological oxygen demand ( BOD₅), total kjeldahl nitrogen (TKN), nitrate-N (NO₃-N), nitrite-N (NO₂-N), total phosphorus (TP), soluble reactive phosphate (SRP), chloride, fluoride, sulfate, and fecal coliform in the laboratory. Field installation of the monitoring equipment included the installation of 6712 ISCO samplers, 4230 ISCO Bubble Flow Meter, Rain Gauge with tipping 674 bucket, solar panel, and battery. A float system was designed to collect water sample from the main stream. Field measurements were taken using the YSI instrument. Surface water quality of the Coulee Baton microwatershed was affected by sediments, nutrients, and fecal matters. Dissolved oxygen level ranged between 1.2 mg/L to 14.4 mg/L with an average of 6.86 mg/L for the microwatershed. Similarly, BOD₅ levels ranged from 1.98 mg/L to 85.3 mg/L with an average of 23.43 mg/L, documenting high levels of 5-day biological oxygen demand. This high level of BOD₅ indicates the presence of high amounts of organic substances in surface water. While TS concentration ranged between 108 mg/L to 5,719 mg/L with an average 428.1 mg/L for the microwatershed, the TDS concentration ranged between 56 mg/L to 4,356 mg/L with an average concentration of 273.5 mg/L. Average turbidity values for the Coulee Baton microwatershed was 245.2 NTU. Average TKN and TP values were 1.28 mg/L and 0.41 mg/L, respectively. Coulee Baton microwatershed showed highly elevated fecal coliform counts. However, fecal coliform counts were reduced dramatically following the implementation of improved septic systems in the microwatershed, clearly indicating the effectiveness of the new systems in controlling fecal coliform pollution in surface water. These results indicate that landuse types, agricultural practices, and the septic systems contribute to nonpoint source pollution in an agricultural watershed.