TRENDS IN WATER AND SEDIMENT QUALITY FOR THE HOUSTON SHIP CHANNEL

Ambient monitoring data collected by the Texas Natural Resource Conser vation Commission from 1971 through 1991 were assessed for five statio ns located on the Houston Ship Channel mainstem (Turning Basin, Greens Bayou, San Jacinto Monument, Channel Marker 120 and Morgans Point). W ater quality was most impacted in the upper channel, especially at the Turning Basin, improving downstream of the San Jacinto River confluen ce. This is consistent with the more confined physical characteristics and the high degree of point and non-point source pollutant loading i n the upper channel. Water quality has improved over the last couple o f decades as demonstrated by declining trends for total organic carbon , total suspended solids, fecal coliforms, ammonia nitrogen, orthophos phate, total phosphate, total arsenic and total copper. Increases in n itrate nitrogen, over time were found at all sites. Declining trends f or total cadmium, mercury, nickel and zinc were found for the upper (i ndustrialized) portion of the channel only. Other findings for total m etals indicated site-specific differences for silver, possible increas ing trends for selenium and no trends for chromium. Increasing dissolv ed oxygen and decreasing biochemical oxygen demand and Kjeldahl nitrog en concentrations were evident at the upstream stations but, unexpecte dly, trends reversed further downstream. Concentrations of heavy metal s and PCBs in bottom sediment were greatest in the Turning Basin and d ropped progressively downstream. Levels of arsenic, cadmium, lead and zinc in Turning Basin sediments decreased significantly over time. Imp roving water and sediment quality has enhanced utilization of the Ship Channel system by aquatic life.