Abstract
Many agricultural watersheds in the United States have impaired waterbodies due to nonpoint source pollution from agricultural activities and related processes. To understand the physical, chemical, and biological integrity of surface water in a coastal agricultural watershed, spatial and seasonal patterns of physicochemical and biological properties were investigated in Bayou Lacassine watershed (BLW) in Louisiana, United States. The relationship between the physicochemical and biological properties were also investigated. Sampling sites were located in the Bayou Chene and Lacassine Bayou subwatersheds within the BLW. Dissolved oxygen (DO), turbidity, conductivity, temperature, pH, total suspended solids (TSS), total dissolved solids (TDS), total solids (TS), five-day biological oxygen demand (BOD5), nitrate and nitrite-nitrogen (NO3/NO2-N), total Kjeldahl nitrogen (TKN), soluble reactive phosphorus (SRP), total phosphorus (TP), chloride (Cl−), fluoride (F−), and sulfate (SO4) were determined weekly from samples collected during 2012 to 2015. Fish and benthic invertebrate diversity and abundance in the two subwatersheds were determined in early summer and in fall of 2012 and 2013 at nine sites. Water quality was generally better at the most downstream site than at the most upstream site where agricultural intensity was highest, with significant differences in turbidity, TSS, TDS, TS, NO3/NO2-N, TKN, TP, and BOD5. There was also seasonal variation for the water quality parameters due to variability in agricultural activities and climatic conditions within the watershed. Results of the relationship between physicochemical properties and fish community variables showed that species richness, diversity, and abundance were negatively affected by elevated TS, NO3/NO2-N, and conductivity. For the benthic invertebrates, diversity was negatively related to BOD5. This study demonstrated unexpected longitudinal and seasonal patterns in physicochemical and biological properties of surface waters in a coastal agricultural watershed. This information is valuable in developing nonpoint source pollution control strategies for these subwatersheds.
- Key words
- agriculture
- fish and macroinvertebrates
- nonpoint source pollution
- physicochemical and biological properties
- water quality
- watershed
- © 2020 by the Soil and Water Conservation Society