Ecology of small marshes using three different water sources

Waterbird use and aquatic vegetation were studied during seven seasons and in five units representing three water types at Arcata Marsh and Wildlife Sanctuary (AMWS), 1 July 1990-30 June 1991. Dominant vegetation types were cover-mapped and sampled for species composition, biomass, and stem density. The PH, salinity, turbidity, and water depth measurements also were taken at appropriate vegetation plots. The five study units represented, a saline basin (Klopp Lake) filled with water from Humboldt Bay, a freshwater unit (Butcher Slough Log Pond, BSLP) filled with well water; and three freshwater units filled with treated domestic wastewater effluent. The PH was greatest in the units in late spring except BSLP where it was highest in late fall. Salinity was greatest in Klopp Lake in mid fall. All four freshwater units had salinities of less than one ppt. The BSLP was significantly less (p0.05) turbid than the wastewater units from late fall through summer. Dominant vegetation types included marsh pennywort (Hydrocotyle ranunculoides), lesser duckweed (Lemna minor), broad-leaved cattail (Typha latifolia), hard-stemmed bulrush (Scirpus acutus), and sago pondweed (Potamogeton pectinatus). Marsh pennywort and lesser duckweed also commonly occurred as understory species in the emergent cover types. Mean stem densities of broad-leaved cattail and hard-stemmed bulrush were greatest in summer and were greater in the wastewater units (p0.05) than in BSLP. Biomass of sago pondweed was greatest in all freshwater units during mid fall. BSLP maintained submergent beds later into the fall than the wastewater units. The wastewater units developed heavy mats of lesser duckweed over most of their surfaces in the fall. Coverage of marsh pennywort mats peaked in early fall in Gearheart Marsh and BSLP and in summer in Allen and Hauser Marshes. Ninety-four species of birds were recorded. There was an annual total of 768,586 bird use-days on the five units. Almost 1/3 of the annual bird use-days occurred during late fall. Shorebirds (58.1 percent) and waterfowl, coots and rails (35.2 percent) accounted for 93.3 percent of annual bird use-days. Lowest bird use occurred in summer. Bird densities were greatest on Klopp Lake for diving ducks, large and small shorebirds, gulls, and terns. Based on relative area use, great blue herons (Ardea herodias) and ospreys (Pandion haliaetus) used Klopp Lake at greater than expected rates. BSLP and Allen, Gearheart, and Hauser units had similar patterns of annual bird use. Densities were greatest on these units for herons, egrets, puddle ducks, coots, rails and raptors. Annually, fish-eating divers, represented mostly by some resident pied-billed grebes (Podilymbus podiceps) used BSLP more than either Klopp Lake or the wastewater units. Black-crowned night-herons (Nycticorax nycticorax) used BSLP at more than twice expected rates but other herons used BSLP at less than expected rates. Cinnamon teal (Anas cyanoptera) and mallards (A. platyrhynchos) were most common on BSLP. The wastewater units were used at or more than 1.5 times than expected rates by herons, all puddle ducks, dowitchers (Limnodromus spp.), and Bonaparte's gulls (Larus philadelphia). The lesser scaup (Avthya affinis) was the only diving duck present on the wastewater units at expected or greater than expected rates. American coots (Fulica americana) and rails used all four freshwater units at least 1.5 times more than expected. Continued annual marsh pennywort removal is strongly recommended, and guidelines should be established to stop encroachment of emergent vegetation into open water and submergent beds. If possible, a freshwater source should be routed into Klopp Lake to reduce high salinities and to allow for possible introduction of additional aquatic vegetation into the water column. An alternative to freshwater would be to introduce eelgrass (Zostera marina) into Klopp Lake.