NOTE: This report was published as Busse, K. 1998. Water Quality and Shellfish Management in Tillamook Bay, Oregon. Coastal Management, 26: 291-301.

A Time to Harvest: Water Quality and Shellfish Management in Tillamook Bay, Oregon

Katherine M. Busse1 and Ralph J. Garono2, Ph.D.

prepared for the

Tillamook Bay National Estuary Project

P.O. Box 493

613 Commercial Ave.

Garibaldi, OR 97118

(503) 322-2222

http://www.orst.edu/dept/tbaynep

1 College of Oceanic and Atmospheric Sciences

Oregon State University

Ocean Admn Bldg 104

Corvallis, Oregon 97330

2 Earth Design Consultants Inc.

800 NW Starker, Suite 31

Corvallis, Oregon 97330

Report presented at the Oregon Academy of Science meeting

February, 1997. Portland, Oregon.

Summary

The Tillamook community is concerned about oyster bed closures, declines in salmonid populations, and decreased recreational use of estuarine resources which have been linked to water quality degradation in the Tillamook Bay. In this study, both spatial and temporal patterns in Tillamook Bay fecal coliform concentrations were examined for designated shellfish management areas using Department of Environmental Quality STORET monitoring data. Using one-way ANOVA statistical analyses, we found (1) a significant spatial difference in Tillamook Bay water quality, (2) a significant decrease in fecal coliform concentrations from the early to mid 80's, and (3) a significant increase in fecal coliform from the mid 80's to early 90's. Monitoring practices need to be re-evaluated in order to draw more refined conclusions about water quality assessments in Tillamook Bay.

Introduction

Estuaries are biologically productive transitions zones between marine and freshwater systems. Natural and human influenced watershed processes can have cumulative effects which include increased sedimentation, degradation in habitat, and water quality all of which combine to stress and alter these ecosystems. The Tillamook Bay estuary is located on the Northwestern coast of Oregon and is the third largest estuary in the state. The Tillamook watershed is made up of five river basins including the Miami, Kilchis, Wilson, Trask, and Tillamook which drain into the bay (Figure 1). Tillamook Bay is approximately 9.5 km long, 4.5 km wide at high tide, and relatively shallow with an average depth of 1.8 m (TBNEP 1996).

Figure 1. View of Tillamook watershed with Miami, Kilchis, Wilson, Trask, and Tillamook subwatersheds

Use of the Tillamook watershed includes agriculture, forestry, and shellfish harvest practices. Land use varies within the watershed; primarily with agriculture on privately owned land in the lower watershed and forestry in publicly owned land of the upper watershed (Strittholt et al. 1997). Over 180 combined animal feeding operation (CAFO) permits have been issued in agricultural areas while six oyster growers and two to three clam divers use the bay for shellfish harvesting (ODA 1995).

Tillamook Bay was designated as an estuary of National significance and included in the US EPA National Estuary Program (NEP) in October, 1992. Designation of environmental priority problems is a key component of the NEP process. The Tillamook Bay National Estuary Project (TBNEP) has identified three priority problems: (1) water-borne pathogen contamination affecting the agricultural and commercial shellfish industries, (2) sedimentation affecting fresh and saltwater flows, and (3) habitat degradation affecting salmon spawning, stream temperatures, and other watershed functions (TBNEP 1994).

Tillamook Bay water quality has been a concern of the Tillamook community since the estuary is one of Oregon's primary shellfish harvest areas covering approximately 1,000 acres or 10% of the bay (Musselman 1986). The concentration of water-borne pathogens in shellfish tissue is a problem because the shellfish are eaten either raw or cooked which is not likely to destroy all pathogens (Dorsey-Kramer 1996; TBNEP 1994). Therefore, it is important to study spatial differences of fecal coliform bacteria since contaminated shellfish are a health risk to the community.

This study examined patterns in fecal coliform concentrations in Tillamook Bay. Fecal coliform concentrations have been used as an indicator of water quality because the origin and transport of these bacteria and of water-borne pathogens are directly related to land use practices (Dorsey-Kramer 1996). Point source pollution of fecal coliform include sewage treatment plants while non-point sources include manure fertilizers, failing septic systems, and animal waste runoff (Musselman 1986; Strittholt et al. 1997). Environmental conditions such as precipitation and bay circulation also influence patterns of fecal coliform concentrations in the Tillamook Bay.

The Oregon Department of Agriculture (ODA) regulates the commercial harvest of shellfish in Tillamook Bay and is responsible for notifying the public of shellfish safety closures based on the Food and Drug Administration's National Shellfish Sanitation Program (TBNEP 1994). This program sets classification standards for shellfish harvest areas based on water quality samples taken during adverse pollution conditions (sewage spills) or heavy rainfall. The highest classification or an "approved" area must have a geometric mean of fewer than 14 fecal coliform bacteria (FCB) per 100 ml, with not more than 10% of the samples exceeding 43 organisms per 100 ml (DEQ 1994; TBNEP 1994). Most Tillamook Bay harvest areas are classified as "conditionally approved" which allows fecal coliform geometric means to exceed 14 FCB/100 ml. When fecal coliform counts exceed the standard, shellfish harvesting is restricted or banned in the bay (TBNEP 1994).

Ideally, the ODA Commercial Shellfish Harvest Plan is a management plan that opens and closes commercial harvest based on water quality. Oyster beds are closed by ODA an average of 50-60 days per year (TBNEP 1994). The management plan separates the bay into two prohibited, two conditionally approved, and one restricted management area (Figure 2) (TBNEP 1994).

Figure 2. ODA shellfish management areas in Tillamook Bay

P = prohibited, R = Restricted, C = Conditional

= DEQ water quality sampling stations for rivers and bay

Since most shellfish harvest occurs in conditional areas (Figure 3), it is especially important to detect water quality trends and minimize the health risk of fecal coliform contamination in these regions (Figure 3).

Figure 3. Oyster Plot locations and shellfish management areas in Tillamook Bay

blocks = oyster plots

P = prohibited, R = restricted, C = conditional shellfish management areas

Prohibited regions are areas where no harvest is allowed while conditional and restricted areas ban harvest based on the Wilson River gauge and precipitation patterns (TBNEP 1994). Rather than using fecal coliform water quality monitoring data, gauge and precipitation levels are used as standards for harvest because they provide more instantaneous results. When the Wilson River gauge rises to 7 feet, all conditionally approved areas are closed. When more than 1" of rainfall occurs within a 24-hour period, one of the conditional areas is closed while the other remains open provided the Wilson gauge is not above 7 feet and there is not a sewage or toxic spill (TBNEP 1994). However, there is no evidence to suggest that the Wilson River gauge is correlated with fecal coliform bacteria concentrations in the bay. Although bacterial counts usually decrease in 48 hours, management areas remain closed to commercial harvesting for at least 5 days after the period of heavy precipitation (Laimons et al. 1976; TBNEP 1994). When harvest areas are re-opened, it is the responsibility of the ODA to notify agencies, commercial harvesters, and the local media.

Study Objectives

Since ODA shellfish management area designations and harvest closures are based on river gauge and precipitation patterns, it is important to determine if these management areas differ with respect to water quality. To address the issue of water quality in Tillamook Bay, this study focused on three questions:

1. Do fecal coliform concentrations differ between ODA prohibited, restricted, and conditional shellfish management areas?

2. How do fecal coliform concentrations in these management areas specifically differ from one another?

3. How do fecal coliform concentrations change through time in each management area?

Methods

In this study, fecal coliform bacterial (FCB) counts from the Department of Environmental Quality STORET database were analyzed. To determine trends in water quality on a spatial and temporal basis, we examined 15 years of data between 1979-1993 from 14 sampling stations in the bay with a total of 1835 observations for all three regions. Since station sampling was unreplicated for each date, water quality data were grouped by prohibited, restricted, and conditional management areas. Areas which had the same prohibited and conditional designations were grouped together. Each region was assumed to be well-mixed (homogenous) and adequately represented by existing STORET sampling stations.

To examine spatial patterns in water quality, we used the 15 years of data to determine an overall trend of FCB concentrations between prohibited, restricted, and conditional management areas. We then broke the 15 years of fecal coliform data into three distinct five year periods (early 80s, mid 80s, and early 90s) to examine temporal trends in water quality for each of the management areas.

The distribution of fecal coliform concentrations (CFU/100 ml) was first tested with the Levene test. Data were not normally distributed and required a log transformation before doing a one way ANOVA (Marija 1993). A one way ANOVA was used to determine differences in the log transformed mean of FCB concentrations between management areas. The ANOVA was used to test for the null hypotheses that (1) there is no significant difference in the mean of fecal coliform concentrations between shellfish management areas and (2) there is no change in fecal coliform through time for each of the three management areas. The Tukey multiple comparison test a posteriori was used to determine between which regions and time periods differences existed (Zar 1984).

Results

Spatial

Figure 4 illustrates results of water quality compared between the three management regions. In this analysis, comparisons were made between 15 years of fecal coliform data grouped by prohibited, restricted, and conditional regions. We found no statistical difference in water quality (p = 0.507) between the prohibited and restricted regions

(Figure 4: indicated by A). However fecal coliform levels were significantly lower in the conditional management area (p << 0.001) than in the other two regions (Figure 4: indicated by A/B).

Figure 4. Comparisons of mean fecal coliform concentrations between P = prohibited, R = restricted, and C = conditional shellfish management areas in Tillamook Bay.

= log mean of fecal coliform

bar = standard error bars

letters = multiple comparison test results (different letters represent significant difference)

Temporal

Figure 5 illustrates how the log transformed mean of fecal coliform counts have changed through time for each management area. Note that each of these graphs now represents a different management area with the x axis labeled as time. In this analysis, the 15 years of fecal coliform data were broken into three five year periods: 1979-83, 1984-88, and 1989-93.

Figure 5. Comparisons of mean fecal coliform concentrations between time (1979-83, 1984-88, 1989-93) for prohibited, restricted, and conditional shellfish management areas in Tillamook Bay.

Prohibited

1979-83 1984-88 1989-93

time (year)

Restricted

1979-83 1984-88 1989-93

time (year)

Conditional

1979-83 1984-88 1989-93

time (year)

Figure 5. Comparisons of mean fecal coliform concentrations between time (1979-83, 1984-88, 1989-93) for prohibited, restricted, and conditional shellfish management areas in Tillamook Bay.

= log mean of fecal coliform

bar = standard error bars

letters = multiple comparison test results (different letters represent significant difference)

We found an overall decrease in FCB concentrations from 1979-83 to 1984-88. However, FCB concentrations increased from the 1984-88 to 1989-93. Prohibited and conditional results show that all three time periods are significantly different from one another (Table 1) (Figure 5: indicated by A/B/C). In the restricted region, early 80's and 90's concentrations of fecal coliform are not significantly different from one another while they are different from concentrations of the mid 80's (Table 1) (Figure 5: indicated by A/B). Finally, the conditional region has the lowest count of FCB through all three time periods.

Table 1. Multiple comparison statistical p value results for P = prohibited, R = restricted, and C = conditional shellfish management areas.

NS = no significant difference between time periods

* = p <0 .05 or significant difference between time periods

Conclusions

This study examined both spatial and temporal patterns in FCB concentrations in Tillamook Bay. Spatial results show that differences in water quality exist between prohibited, restricted, and conditional areas: the conditional management area has significantly lower concentrations of fecal coliform than the prohibited and restricted regions. Spatial results suggest that (1) to decrease the high degree of variance in the restricted area, there needs to be more than one sample site, (2) if prohibited and restricted regions are not significantly different, it might be appropriate to designate them as the same management area, (3) allowing shellfish harvest from the conditional area where fecal coliform concentrations are significantly lower is more appropriate than harvesting from the prohibited or restricted regions, and (4) monthly sampling may not be adequate to record episodic precipitation events.

Temporal results show an overall reduction in fecal coliform concentrations between 1979 -83 and 1984-88. Results from a similar water quality study for tributaries in the Tillamook watershed also documented a significant decrease in fecal coliform concentrations after 1985 (Dorsey-Kramer 1996). Researchers attributed tributary water quality improvements to the installation of manure handling facilities and other Best Management Practices (BMP) implemented in 1982 (Dorsey-Kramer 1996; Wiltsey 1990). BMPs such as improving fencing and off-site watering sources were designed to reduce the number of cattle from entering streams and thus thought to reduce fecal coliform inputs.

However, temporal results of this study show that fecal coliform concentrations began to increase between the late 80's and early 90's. Possible causes for increasing fecal coliform concentrations may include doubling cattle numbers since 1980, changing precipitation patterns, shifting agricultural land ownership, decreasing BMP implementation or maintenance, decreasing riparian vegetation, or increasing water flows from clear-cut areas in the upper watershed. Further studies are needed to more closely examine causes for decreased Tillamook Bay water quality.

Recommendations

The goal of all National Estuary Projects is to develop a science-based Comprehensive Conservation Management Plan. The process of coordinating a CCMP requires the production of Scientific-Technical Characterization Reports from existing data (Strittholt et al. 1997). Results from this study of existing water quality data can be used to develop more robust shellfish management strategies for the Tillamook Bay CCMP.

Further monitoring and experimental studies should be conducted to improve assessments of Tillamook Bay water quality. Several management recommendations can be made based on this study's results.

Water quality sampling should be conducted on a regular basis.

Samples should be taken more frequently to examine relationships between precipitation and fecal coliform concentrations since monthly sampling records water quality trends but does not adequately address the impact of episodic rainfall events.

The distribution of sample sites should be re-evaluated and include more sites in the restricted region.

Management area recommendations should be re-evaluated for the restricted area which is not significantly different from prohibited areas.

If management recommendations are to be based on water quality, they should have greater links to land use practices in the upper and lower watersheds (i.e., riparian buffer design and maintenance).

Management plans and data collection points could be based on an existing bay circulation model rather than using gauge and precipitation patterns (TBNEP 1994).

Studies should be designed to monitor the effectiveness of BMP implementation and to determine the possible effects of altering shellfish management area designations.

In conclusion, continued monthly monitoring of the bay is necessary to further assess long-term trends in water quality. However, this study suggests that the pattern and frequency of sampling should be re-evaluated to provide more data for making reliable shellfish management decisions. As data become available, further assessments of Tillamook Bay water quality should be performed.

Acknowledgments

We wish to thank Scott Sloane at the Department of Environmental Quality for his help with STORET data and the Tillamook National Estuary Project for supporting this study.

REFERENCES

DEQ. 1994. Oregon Administrative Rules (OAR). Chapter 340, Division 41. Oregon Department of Environmental Quality. Portland, Oregon. May 1994.

Dorsey-Kramer. 1996. A statistical evaluation of the water quality impacts of best management practices installed at Tillamook county dairies. Bioresource Engineering Dept. Oregon State University, M.S. Thesis, 208 pp.

Laimons, O. and D. Demory. 1976. Classification and utilization of oyster land in Oregon. Oregon Department of Fish and Wildlife, Portland, OR.

Marija J. Norusis. 1993. SPSS for windows: base system user's guide release 6.0. Chicago: SPSS Inc.

Musselman, J.F. 1986. Sanitary survey of shellfish waters, Tillamook Bay, Oregon. Department of Health and Human Services, Public Health Service, Food and Drug Administration, Shellfish Sanitation Branch, Portland, Oregon.

ODA. 1995. ODA Shellfish growing area triennial evaluation. Oregon Department of Agriculture, Portland, Oregon. August 1995.

Strittholt, James R., Ralph J. Garono and Pamela A Frost. 1997. Spatial Patterns in Land Use and Water Quality in the Tillamook Bay Watershed: A GIS Mapping Project. TBNEP Technical Report. Tillamook Bay National Estuary Project. Garibaldi, OR: February, 1997.

TBNEP Technical Advisory Committee. 1994. Issue forum on biochemical water quality issues in Tillamook Bay and Watershed. Tillamook Bay National Estuary Project Report. Garibaldi, OR: December 8, 1994.

TBNEP. 1996. Tillamook Bay National Estuary Project. Online. Internet. February 7, 1997. http://www.orst.edu/dept/tbaynep/.

Wiltsey, Michael R. 1990. Tillamook Bay Watershed Bacterial Trends Assessment. Water Quality Division, Oregon Department of Environmental Quality. Portland, Oregon. September, 1990.

Zar, Jerold. 1984. Biostatistical Analysis. 2nd ed. New Jersey: Simon and Schuster.