Pollutants can be concentrated in the thin film of the surface layer, then transported toward shores by wind, waves, and surface currents. When the tide goes out, that sea surface film may remain on the shore, similar to the bathtub ring that gets left behind when the water is drained from the tub. Previous studies have shown that contaminated sea surface films can be toxic to intertidal organisms. The density of the spores that were recovered from the screen samplers were compared with that of water samples from below the surface taken at the same time. Sea surface films, are a potential source of contamination of intertidal flats.
Further study is needed to establish the nature and extent of contamination over time.
In estuaries like Padilla Bay, suspended sediments come from streams, rivers and sloughs draining into the bay. Our human activity on the land can have a big impact on the amount of sediment that drains into the sloughs and the bay. The amount of suspended sediment in Joe Leary Slough and its tributaries were measured at various times and locations over the course of 13 months. Though the volume of water entering Padilla Bay from Joe Leary Slough is relatively small, the concentration of sediment is substantial. The amount of sediment in the slough fluctuates widely with the tidal cycle and with the seasons.