Coastal and Estuarine Research Federation Plant Growth and Productivity along Complex Gradients in a Pacific Northwest Brackish Intertidal Marsh Author(s): Kern Ewing Source: Estuaries, Vol. 9, No. 1 (Mar., 1986), pp. 49-62 Published by: Coastal and Estuarine Research Federation Stable URL: http://www.jstor.org/stable/1352193 Accessed: 30/07/2010 19:11 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=estuarine. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Coastal and Estuarine Research Federation is collaborating with JSTOR to digitize, preserve and extend access to Estuaries. http://www.jstor.org Estuaries Vol. 9, No. 1, p. 49-62 March1986 Plant Growth and ProductivityAlong Complex Gradients in a Pacific Northwest Brackish IntertidalMarsh KERN EWING Department of Biology McMaster University Hamilton, Ontario L8S 4K1, Canada ABSTRACT: Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22%oat a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m-2 dry weight) was measured at a site with 0-4%o free soil water salinity, dominated by the sedge Carex lyngbyei. In more saline areas (8-12%o), the bulrush Scirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment. C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher. S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental vari- ation was magnified in the population and community responses of the marsh vegetation. Introduction mances which plants are capable of when Environmental gradients have extensive so constrained, combined with environ- effects upon the structure of plant com- mental variability, play a very great role in munities and upon the performance and determining the observed pattern in coastal success of individual species (Chapman and estuarine wetlands. 1976). Although conditions in brackish in- This study was carried out in the inter- tertidal marshes may be stressful to some tidal brackish marsh formed by the Skagit species and only a limited number are able River as it enters the bay system of Puget to survive, production is comparable to the Sound in Washington. At the Skagit Marsh, most productive systems on earth (Chap- substantial environmental gradients exist. man 1960; Odum 1975; Jefferies et al. 1977). Large salinity differences can be found, as Many species reach the limits of their com- can gradients of soil temperature, soil de- petitive ability or of their tolerance to com- velopment, length of tidal inundation, soil bined stresses in parts of any marsh while textures, organic content of the soil, and re- a few are able to adapt across a great range dox potential. These gradients are neither of environmental variation and survive linear nor parallel, and their cumulative ef- (Mason 1957; Ranwell 1972). Plant reac- fect is a complex environmental pattern. tions to variable environments may be Responding to this pattern is a limited num- viewed as the results of their strategies, or ber of dominant plant species of wide North genetically defined and limited responses to American or circumboreal distribution ranges and combinations of environmental (Disraeli and Fonda 1978; Drinnan et al. conditions (Grime 1979). The perfor- 1978; Kistritz 1978; Taylor 1980; Liverman 0 1986 EstuarineResearch Federation 49 0160-8347/86/010049-14$01.50/0 50 K. Ewing 1982; Ewing 1983). The object of the anal- ysis of this system is to measuregrowth and productivity of five common and locally dominant plant species in the family Cyper- aceae across the range of environmental conditions existing in the marsh, and show the relationshipbetween the local environ- ment and species performance. 1- ~~~r~ Study Area 0-1 3 The study area is located along the east shoreof SkagitBay in PugetSound (48?18'N, 122?24'W), where the Skagit River has cre- 0 .5 i km ated a progradingsubaerial and subaqueous delta. The climate along the eastern shore of Puget Sound is maritime, with cool sum- mers, mild winters, moist air and a small daily range of temperatures.There are two high tides and two low tides in each tidal Fig. 1. Locationmap. Area of the intertidalSkagit period. On neap tides, tidal range may be Marshcovered in this study. Survey transectsare in- as low as 2 m; on spring tides, tidal range dicatedby heavy lines and are numbered. increasesto 4 m (U.S. Departmentof Com- merce 1980). The annualrange of day length varies from a minimum of 8 h to almost 16 marily these data presentedhere. The data h, while the sun angle increasesfrom 18?to collected show little variation from year to 65? above the horizon, so potential insola- year. The climatological conditions over tion increases rapidly in spring and early those years were also little different from summer. those recorded in previous years, demon- Salinities in Skagit Bay are as low as 25- strating the evenness of the maritime cli- 28%oat the surface (Collias et al. 1973). mate of the area. These loweredlevels are producedby runoff Four transects 0.8 to 2.0 km apart and from rainfalland melting snow and glaciers 500 to 750 m long were established from in rivers drainingthe Cascadeand Olympic the dike to the seaward edge of intertidal mountainsand by restrictedmixing with the emergentvegetation along a 5 km reach of salt water in the open sound. Within the 5- shoreline(see Fig. 1). Transect1 was located km long band of vegetation where the study near FreshwaterSlough, the main channel was carriedout, surfacewater salinities dur- of the South Fork of the SkagitRiver. Tran- ing the growingseason vary from 0%ooto that sects 2 through 4 were to the north of the of the open bay. Surface water salinity in slough, in areas inundated by waters of in- channels, tidal pools, and on incoming or creasingsalinity. Four environmentalmea- recedingtides varies substantially.Salinities suring stations were established on each generally increase alongshore away from transect,evenly spaced. At each station, in- rivers and out into the bay, and they are tensive sampling of vegetation and mea- seasonally lower during winter rains and surementof environmentalfactors was car- spring snowmelt runoff. ried out at regular intervals during the growing season. Less intensive measure- Methods ment between stations was used to verify the regularityof variation from station to ENVIRONMENTALMEASUREMENT station. That station closest to the dike at Field work was carried out during the the upland end of each transect was desig- growing seasons of 1978, 1979, and 1980. nated station A, and stations B, C, and D A complete data set for all comparisons of were progressivelylower and closer to the plant performanceand environmentalcon- open water of the bay and the seawardedge ditions was obtained for 1980, and it is pri- of emergentvegetation. Environmental data NorthwestIntertidal Marsh Productivity 51 were collected for soil texture, soil organic arated while fresh, then dried at 70 ?C for material content, free soil water salinity, soil 24 h. redox potential, soil column temperature For the measurement of height, dry weight profiles, and site elevations. Soils were sam- and leaf area per shoot, five randomly se- pled with replicate cores at each station. lected samples of each species in the canopy Nested sieve and hydrometer grain-size layer were collected at each station during analyses were performed on samples after every measurement period. Leaf areas were removal of iron and organic material. Or- calculated from measured dimensions. One ganic material was measured by physical surface of laminar leaves is used in the data separation and by use of the Walkley-Black presentation, while for conical, cylindrical method for fines. Free soil water salinity was or pyramidal shaped leaves or photosyn- determined by using a refraction salinom- thetic stems, total external area is reported eter to measure the salinity of water col- (Sestak et al. 1971). lected in standpipes with perforations from 15 to 25 cm below the soil surface. Soil Results redox potential was measured in the labo- ratory using a platinum electrode on soil ENVIRONMENTAL CONDITIONS cores which had been collected, sealed and The four transects established for this transported.