Stream Water Quality

Evaluation: Some Action Needed/Closely Monitor

Issue Summary:

Bacteria: Overall, bacteria counts fall below DEQ standards for recreational freshwater and estuarine waters (non-shellfish growing areas). Nutrients: Nutrient levels do not exceed DEQ standards, but occasionally exceed EPA-recommended levels. Temperature: Streams in the project area do not appear to exceed stream temperature standards and so would not be a limiting factor for fish habitat.

Why do we care:

Stream water quality affects ecological functions in stream and riparian habitats. Fully functioning stream systems support a wide variety of commercial and recreational fish species in various parts of their life cycles.

 Stream temp, nutrient and bacteria collection locations
 Stream temp collection locations
Assessment stream systems shown in yellow.

What’s Happening?

The monthly sampling for E. coli bacteria counts using IDEXX (IDEXX Water Testing Laboratories, Westbrook, ME) methods shows variability between sites (Figure 1). There is, however, a general pattern of higher counts observed in the summer season (May-Oct) than in the winter (Nov-Apr). This may be due to higher water temperatures in the summer, which can increase counts of bacteria as well as an increase in wildlife activity during summer times. Typically, bacteria counts are higher with higher flows and rainfall / storm events. At some sites there are increases in counts associated with decreases in daily rainfall data and at other sites there are increases in counts following rainfall events. There are lower counts of E. coli at the Whiskey Run site than all other sites and this is likely due to the proximity of this site to the ocean and relative isolation in comparison to the other streams sites.

For coastal basin fresh water and estuarine waters (non-shellfish growing areas), regulatory criteria for Oregon Department of Environmental Quality E. coli bacteria concentrations include two conditions:  1) a minimum of five samples may not exceed the 30-day log mean of 126 organisms per 100 ml; and 2) no single sample may exceed 406 organisms per 100 ml.  Our bacteria concentration data are presented as the average most probable number (MPN)/100 mls of 3 replicate samples per month at 6 sampling sites.  Despite the differences in sample collection methods (sampling frequency, sample number) we have applied the second condition to our data in Figure 1 to provide a “ballpark” guide for evaluating stream bacteria levels.

There appear to be only two sampling events where bacteria counts exceed the single sample condition (Figure 1)(Three mile 8/3/11 and Joe Ney 7/28/11).  However, these two sampling events represent three average replicate samples.  The number of single samples (not presented in this graph) that exceed the standard is 10 out of 226 samples.

Overall, bacteria counts appear to fall below the standards set by DEQ for recreational freshwater and estuarine waters (non-shellfish growing areas).

Figure 1. Monthly E. Coli bacteria levels and daily rainfall in South Slough and Coastal Frontal streams. Dashed red line indicates the Oregon Department of Environmental Quality standard for a single E. Coli sample (406 organisms/100mL).

Figure 2. Monthly total coliform bacteria levels and daily rainfall in South Slough and Coastal Frontal streams.

The counts for total coliforms follow the same general pattern as the E. coli colonies with higher numbers of bacteria counts occurring during the summer season (May – October) than the winter season (November – April) (Figure 2). The counts are much higher overall since this group includes all fecal coliforms and is not specific to humans or wildlife.

Stream Nutrients
Nutrients such as phosphorus and nitrogen are essential for plant growth; indeed, these elements are key components of chemical fertilizers used in agriculture and on lawns. However, because these nutrients are highly soluble and readily mobilize in surface runoff and in groundwater, excess levels can contribute to eutrophication and a decline in dissolved oxygen levels, contributing to deterioration of coastal water quality and fish habitat.

Phosphorus, ammonium, nitrate, nitrite, and silicate were monitored in six South Slough and coastal frontal streams from September 2010 to January 2012 (Figures 3-6). Of these, maximum acceptable levels have been established by the Oregon DEQ for nitrate only (10 mg/l; Oregon Administrative Rule 340-041). For this region, however, the US EPA recommends nitrate + nitrite levels not exceed 0.09 mg/l based on 25th percentile of values reported for an ecoregion-wide assessment of unimpaired streams (US EPA 2000). Nitrite comprises a very small proportion of the nitrogen-containing compounds in a stream. We combined nitrate and nitrite for our analyses to enable comparison with the EPA recommendation. Additionally, phosphorus was analyzed for orthophosphate (PO4), which is not all-inclusive for phosphorus in this system so direct comparison with EPA recommendations for total phosphorus (0.01 mg/l) are not possible with these data. Ammonium enters the system from decomposing plant and animal waste, and silicate can indicate phytoplankton metabolism of nutrients in the water.

As with bacteria counts in South Slough watershed streams, nutrient levels varied over the year across the watershed and were generally well-correlated with precipitation. For some parameters such as phosphate, ammonium, and silicate, nutrient levels tended to increase (concentrate) during periods of low rainfall and decline (dilute) during the rainy season (Figures 3, 4, and 6). Other nutrients, such as nitrate and nitrite, generally followed the opposite pattern with increases and decreases in relative concert with annual precipitation cycles (Figure 5). At all times during the monitoring period the level of nitrate remained well below the maximum acceptable level established by the DEQ, but at some sites (Big Creek, Three Mile Creek, and Winchester Creek), levels exceeded the EPA’s recommendation during winter.

Figure 3. Monthly phosphate levels for all streams from September 2010 to February 2012.

Stream Temperature in the Project Area

Water temperature recorders were placed at twenty one sites in the South Slough and Coastal Frontal streams during the summer of 2010 and 2011. Five units were placed in main-stem Winchester Creek: two in the upper valley (Winchester 2 and 4), one upstream of the stream gage (Winchester 5), one at the stream gage upstream of the SSNERR (Winchester gage), and one in a lower tidal reach about 0.7 kilometers below Hinch Bridge (Winchester 9). Six tributaries of Winchester Creek were also monitored (Anderson Creek, Wasson Creek, and Winchester 1, 3, 6, and 7). Four streams that flow into South Slough below its confluence with Winchester Creek were also monitored (Talbot Creek, John B. Creek, Elliot Creek, and Joe Ney Creek). The five Coastal Frontal streams monitored were Whiskey Run Creek, Two Mile Creek, Three Mile Creek, Five Mile Creek, and Big Creek (Figure 7).

Table 1 provides the 7-day average maximum and minimum temperatures recorded during 2011 and the number of days where temperatures exceeded 55°F and 64°F for each monitoring site in the assessment area. The EPA’s threshold for salmonid spawning and incubation is 55°F, and for rearing the threshold is 64°F (based on the average of daily maximum temperatures recorded during a 7-day period)(EPA 2003).

Fig. 7. Summer 2011 stream temperatures based on 7 day max. temp. averages in S. Slough & Coastal Frontal streams.

Table 1. Seven day average max. & min. temperatures for project area streams.

During the period there were 7-day average maximum temperatures above 64°F observed at Big Creek, Anderson Creek, Talbot Creek, Wasson Creek, and at Winchester Creek segments 2, 7, and 9 (Figure 8).

The highest temperatures in Winchester Creek during the 7-day period were recorded at Winchester Creek segments 2, 7, and 9. The high temperature at Winchester 2 (71.6°F) may be due to the loss of riparian cover associated with a recent nearby timber harvest and potentially the back-water influence from beaver dams downstream.

Figure 8. Comparison of 7 day average maximum and minimum temperatures at monitoring stations during summer 2011. Dotted red line indicates the EPA’s 64° F threshold: the maximum stream temperature juvenile salmonids can tolerate for extended periods of time.

Winchester 7 (71.6°F) is located in a tributary to Winchester Creek (Cox Creek) with a large beaver dam and pond just upstream of the temperature monitoring unit. This pond likely contributes to elevated stream temperatures at this site, because beaver impoundments can cause stream outflow temperatures below the dam to be greater than inflow temperatures above the pond (Alexander 1998).

Winchester 9 (74.4°F) is the most downstream unit. Elevated water temperature values there are probably the result of tidal action. During summer months, ocean water can warm up considerably during incoming tides as it moves over expansive mudflats heated by solar exposure during low tide (M. Graybill, pers. comm.).

Of the Coastal Frontal streams, the temperature units at Big Creek showed the highest stream temperatures. Different land use types may have contributed to elevated stream temperatures there. The Big Creek basin includes agriculture and recreational (golf course) land uses, both of which provide limited shade to the stream. The dominant land use in the other Coastal Frontal stream basins is forestry.

Literature cited

Alexander, M.D. 1998. Effects of beaver (Castor canadensis) impoundments on stream temperature and fish community species composition and growth in selected tributaries of Miramichi River, New Brunswick. Canadian Technical Report of Fisheries and Aquatic Sciences.
Issue: 2227. Pp.: I-IX, 1-44.

Environmental Protection Agency. 2003. EPA Region 10 Guidance for Pacific Northwest State and Tribal Temperature Water Quality Standards. EPA Region 10 Office of Water Report # 910-B-03-002. 57 pp.