Municipal Guide To Clean Water: Conducting Sanitary Surveys to Improve Coastal Water Quality
words, low salinity levels (larger influence of freshwater) have been linked to high bacteria levels.31, 32, 33, 34, 35, 36, 37
Note the presence and location (including GPS coordinates where possible) of the freshwater inputs including rivers, streams, and storm drain outfalls. In general, there are three types of streams: perennial (steady flow), intermittent (seasonal flow, typically active six to nine months of the year), and ephemeral (short duration following extreme storms). The latter two types of streams will need to be documented during or following wet weather.
Collect water samples at all discharges to the shoreline including storm drains, pipes, river mouths, etc. to determine the level of fecal indicator bacteria. If analysis indicates high bacteria levels, additional monitoring sites should be added upstream or within the storm drainage network to locate potential pollution sources (see Special Studies, Part II). The sanitary survey should be expanded to include the land draining to these freshwater inputs.
What is the relationship between tidal stage and bacteria levels?
The impact of freshwater (and resulting bacteria levels) in the coastal zone can vary according to the tidal stage. In general, freshwater inputs transfer a larger amount of water to coastal areas during an outgoing (ebb) tide compared to an incoming tide. Ebbing tides can drain pollutants and materials from the land, transporting watershed contaminants to the beach. Additionally, bac- teria concentrations have been found to be significantly higher during spring (monthly high) tide conditions when coastal waters reach the upper intertidal zone.36, 38 Incom- ing flood (tidal) conditions can dilute bacteria concentra- tions39 or bring contaminants entrained offshore back to the shoreline.40, 51
What are the natural features of the beach?
There is growing evidence that biological factors such as beach sand and tidal wrack can increase concentrations of bacteria in recreational waters. Beach sand may act as a reservoir, protecting bacteria from the sun’s radiation. Bacteria also adhere to sand grains, and can persist longer
in sand compared to water.8, 41, 42 Similarly, algal mats that accumulate on beaches have been shown to harbor ele- vated levels of Enterococci bacteria, especially if waterfowl, dogs, or deer have defecated in the vicinity. Resuspension of bacteria-laden beach sands and algal mats can contrib- ute to degraded water quality in coastal areas.43, 44
Note the amount of sand and the presence of seaweed and other debris washed ashore, and if and how often the beach is cleaned.
Note the presence of tide pools in the upper area of the beach. Sometimes stagnant tide pools develop over time and do not flush on a regular basis. These areas are prone to high bacteria levels due the lack of water flow and increased water temperatures, especially where they attract small children and waterfowl.
While forests help protect water quality, other areas of wildlife habitat like game reserves and marshes often har- bor large animal and bird populations whose fecal matter can contribute to high bacteria levels in the watershed. Coastal areas with marsh outlets will likely experience el- evated bacteria levels, because marshes are ideal locations to promote bacterial growth due to their soft sediments, bacteria-laden sand, nutrients, decaying seaweed wrack, wildlife populations, etc. The impact of these areas on coastal water quality generally increases during spring tidal conditions when the flooding tide picks up con- taminants from the upper reaches of the high water line.