TRENDS IN WATER AND SEDIMENT QUALITY FOR THE HOUSTON SHIP CHANNEL

摘要

Ambient monitoring data collected by the Texas Natural Resource Conservation Commission from 1971 through 1991 were assessed for five stations located on the Houston Ship Channel mainstem (Turning Basin, Greens Bayou, San Jacinto Monument, Channel Marker 120 and Morgans Point). Water quality was most impacted in the upper channel, especially at the Turning Basin, improving downstream of the San Jacinto River confluence. This is consistent with the more confined physical characteristics and the high degree of point and non-point source pollutant loading in the upper channel. Water quality has improved over the last couple of decades as demonstrated by declining trends for total organic carbon, total suspended solids, fecal coliforms, ammonia nitrogen, ortho-phosphate, total phosphate, total arsenic and total copper. Increases in nitrate nitrogen, over time were found at all sites. Declining trends for total cadmium, mercury, nickel and zinc were found for the upper (industrialized) portion of the channel only. Other findings for total metals indicated site-specific differences for silver, possible increasing trends for selenium and no trends for chromium. Increasing dissolved oxygen and decreasing biochemical oxygen demand and Kjeldahl nitrogen concentrations were evident at the upstream stations but, unexpectedly, trends reversed further downstream. Concentrations of heavy metals and PCBs in bottom sediment were greatest in the Turning Basin and dropped progressively downstream. Levels of arsenic, cadmium, lead and zinc in Turning Basin sediments decreased significantly over time. Improving water and sediment quality has enhanced utilization of the Ship Channel system by aquatic life.