Tillamook Bay and its watershed, which are located on the north coast of Oregon, have a long history of water quality problems. Despite progress in restoring water quality over the past two decades, both fresh and saline waters sometimes fail to meet water quality standards for bacteria, frequently causing the cessation of oyster harvesting in the bay. Among the proposed solutions to this problem are regulations designed to curb nonpoint pollution from upstream dairy farms.
E&S Environmental conducted a demonstration project to quantify reduction in fecal coliform bacteria (FCB), suspended solids, and water temperature in response to best management practices (BMPs) that included streamside fencing, riparian planting, water diversion, enhancement of multiple small wetlands, and changes in manure management practices in a stream draining forest and farmlands. We monitored water quality for four years during storm events both above and below the BMP treatment areas and in a reference subbasin. Prior to any treatments, we found substantial bacterial contamination in stream waters at both the reference site and the treatment site. The conditions we found prior to the experiment remained the same in the reference watershed. The levels of FCB downstream from the treatment areas, on the other hand, were reduced by 75% after implementation of restoration actions and management changes. Sediment flux and stream temperature also decreased.
Our restoration and management activities improved water quality in Beaver Creek. Our ability to measure such changes holds important implications for setting constructive, but not restrictive, regulatory policy as regards nonpoint pollution and dairy farming. Moreover, we expect that such management strategies will help reduce bacterial contamination and sediment contributions to Tillamook Bay.
E&S Environmental conducted an experimental study on pasture land in Tillamook, Oregon to quantify the effectiveness of edge-of-field vegetated buffers for reducing transport of fecal coliform bacteria (FCB) from agricultural fields amended with dairy cow manure. Installation of vegetated buffers on loamy soils dramatically reduced the bacterial contamination of runoff water from manure-treated pasturelands, but the size of the vegetated buffer was not an important determinant of bacterial removal efficiency. Only 10% of the runoff samples collected during multiple rain storms from treatment cells having vegetated buffers exhibited FCB concentrations >200 colony forming units (cfu)/100 mL (a common water quality standard value), and the median concentration for all cells containing vegetated buffers was only 6 cfu/100 mL. The presence of a vegetated buffer of any size, from 1 to 25 m, generally reduced the median FCB concentration in runoff by more than 99%.
Results for FCB load calculations were similar. Our results suggest that where substantial FCB contamination of runoff occurs from manure-treated pasturelands, it might be disproportionately associated with specific field or management conditions, such as the presence of soils that exhibit low water infiltration and generate larger volumes of surface runoff or the absence of a vegetated buffer. Buffer size regulations that do not consider such differences might not be efficient or effective in reducing bacterial contamination of runoff.
E&S Environmental Chemistry collected and analyzed water quality data as part of the Tillamook Bay National Estuary Project (TBNEP) to determine the effects of various land use practices on the water quality within the Tillamook Bay Watershed, Oregon. Streamwater in tributaries to the bay frequently exceeded common standards for fecal coliform bacteria (FCB) and temperature. Nutrient and sediment contributions to streams and to Tillamook Bay are also of concern. FCB inputs to the bay have forced periodic closure of the oyster shellfish industry. In addition, impaired water quality may be contributing to reduced salmonid populations in the bay and its tributaries through reduction in the quality of the habitat.
Water quality was measured at dozens of locations via monthly and storm-based sampling. Loads to the estuary were calculated for each of five rivers that flow into the bay. Storms that exhibited the highest FCB concentrations tended to be those that occurred during fall and/or those that were preceded by relatively dry conditions and included high rainfall intensity. Implementation of storm-based monitoring and classification of storms according to season, intensity, and antecedent wetness were recommended to effectively reduce the large variability inherent in the FCB monitoring data, thereby facilitating future trends analysis. Continued storm-based monitoring of FCB and total suspended solids (TSS), and also continued collection of rainfall and river discharge data, were also recommended to provide a database that will help determine to what extent on-the-ground remediation actions and best management practices (BMPs) within the Tillamook Basin are having their desired effects.
Frequent-interval sampling of river water during storm events helped locate portions of the watershed that contributed major sources of fecal bacteria to the rivers and the bay. The largest source areas were associated with urban land use. Rural residential housing and agricultural land use were also associated with bacterial loading to the waters in the Tillamook Bay watershed.