EileenHemphill-Haley, U.S. Geo ogrca Survey at 1272Department of ceologcal Scences. Universty of Oregon EugeneOregon 974A3 1272 IntertidalDiatoms from Willapa Bay, Washington: Application to Studies of Small-ScaleSea-Level Changes Abstract .sea]ere1leconstnt]ti.lisusiilg(]stUaril. thedjstrjbutionsofmoderniItertida]s|..iljS'{SIlattl)|anon.goings|ud1torussessthebiostlatig .ha|lgcslrjgg{.(ible!rlhquakesnithe|aci1icNord]$est.on)d.jf|inLl.|Lill! tn \\ illapa t3ar. \nashington. Q mode frctor rnah sn iros used t0 rta*ii1- assiJnblas,,s lrom lnlal fllts and boks. shallo* srbtirlal chaMds. lx and high nrurshes along tro inre id:il traDsecc on the \iariakunr Rircr. and in intertirlal sarnples fron dre open ha!. Auto.h oh,n,s raxa rlorninat(1 thc ussr:mbiages. hut in some cases pnrhahle alk,rhthorous tuu scordl relarireh high in rhe .I.lj.r.stl|s.l|hlja|ltYsiSsuggeststhatdiatomscanbeusedtoir1enLi|rLlrnrlr ilaG.(|hannllb!nks'udsh!||oi{Sub1olchannels.belorapproxirnatlm'anlo$(]thjgh\'uLer(MI,H marel'- be ee. ['ll.H$ unrl rran fisho high $rLter {}IHHS]: and {3) high narsbr:s apprxirrrclr bctwccn X'lHH\i rurl ertreme high water iEH\\1. lhc marsilur,hn,l rransirion. near F:Htr. coincides wirh the terminrrs ofrcsularrJiaLon ptuhrcriir' lnd is recos nizable br the disappearance of high marh diatona in soil .li,tl)sirs. dbsolute elerations ofthe ecobgn:al zon.s an, (!'rstrline{l br lo.al tidal range.Becruse ofthe cosmopolitardistributions of n,lnl,l Lhcspocies observed in this studv. thesedata at pn,bab r applicatrle to sturlies of Quaternar,r sea-lere1 rhangc !rd fali,oscismicirv throughour the coastal Pacilic \orth$cst. Introduction along the Cascadiasubduction zone. the boLrnd- ar'_ betwccn thc de I'uca plate and the over- Thc purpose ofthis stud_vis to identify cliatom taxa Juan riding North America plaLe (Figrrrc l). rssociated with verticallv distributcd cstuarinc rvhereas deposits (i.e., high rnarshcs,low marshes,tidal othcrs arc bclicved to have been caused br clis- flats, sloughs.and banks) that can be used to recon- placementson shallowcrustal faults (Nelson. 1992; struct small-scale (< 3 m) palco-sca-lcvel changes Bucknempi ol.. laq2; \elsorrarrd P, r-,,rriu..in llrt, rl to 1'Jeo.ei-micit\nr cu:tatirlro, c-sFi in prcss). Coseismic landJevel changes rnar result in the Pa, ifir'\orthrrr'1. Tlu'itiurr: betrreenrnarine sudden subsidcncc(e.g., Plalker, 1969; Atrvater, ancl freshwater diatoms in co:r.stalcleposrts are com- l9B7:. 1992; Darienzoand Pctcrson. 1990: Nel- monlv used to identify rnajor transgrcssionsand son, 1992; Clarke and Carver, 1992) or uplift regressionsof Quatcrnarr sea level (e.g.. Palmer (Plalker, 1969; Bucknam et al., 1992) of coastal and Abbott. l986; llronen et al.. 1987). but the and estuarinesites. The ecologicalconscquences recognition of srnall-scalcchangcs in paleo-sea-leve1 inr.olveeither a rapid rise or llll in relativc sca lcvcl mrr-tb, Lc-ed on more -uhtle clrange-irr r, rti- strch that vegdatcd dreasnormallv above the reach callv distributedasscmbl:ges. Such studiesare in- oftides are suddenly inundalcd. or-conversely,nor- variably hindered bv the paucitv of detailed data mallv intcrtidal sullaces are elevated out o[ the in- reearLlirrgthe rn, rl.rn,li-triLuliuns ulpedinent I'rra (e.g.. Eroncn er ol., l987). tertidal zone. Estimalesof coseismicsubsidence r:aused bv the earthquakc about 300 years ago CompelJingstratigraphic. evidcncc now suggests range liom about 0.5 m (Clarke and Carr,cr; 1992; that some changcs in relative sea-level in the Pa- Da|ienzo and Pctcrson, 1990) to 2 m (Atnater. cilic Northwest drrling the l{oloccnc mav har.e 1987; Atwaterand Yamaguchi,1991). This range resuitedfrom large earthquakes,inclucling a rno- in clcvatioral change tould be enough ment magnitude (XI.)) {} event as rcccntlv as about to quicklv i300 years ago (Atrvatcr.1987, 1992r Darienzo transforrn a lorvland coastal meadow or forest inlo and Pctcrson. I990; Attater and Yamaguchi. a tidal flat. Basccl on strati;paphic and biostrati- l99l: Att'ater er al., 1991; Nelson, J992: Clarkc graphic evidence in south*estern Washington, this an,l Can.r. lqq2. \, l.un .rnd Per-orriu-.in lre..: process mav havc bccn repeated at least six times Clague and Bobrowsky, 1994). Some of the in about the lasL 3500 ycars (Atvater, 19BB: palco-ea hquakcs have been attributed lo fopture Hcmphill-Hale,v. unpub. data). \orlhrvest Science.Vol. 69, No. l. 1995 29 t 24'1svv |igun. 1. \tl illupr Bav. a nisotidal ,istulri iii sodth{estern Washhgton. -samphrg localities: BC Bav Center tidal llat: BR Bone Rivir tidal n!L: \l-traDse(r Nl. l,^'er Nia$ialum Rirer; -sP Stonl Point; Nu bansect \u. upper Niairiakun Riveu '1t'- li,L. l'(,nrr. Various kinclsoI coastalcnvironmenls can be Riznyk and Phinney. 1972; Rizn_,-k,1973; l\lain idcntficd bascclon thc classificationolcliatoms into anclMcJntire. 1974; Moore and McTntire,1977; ecologicalgroups (Vos rnd clcWol[. 19138;1993; Amspoker and Mclntire, J97B). but othcl than Kosugi. 19BB). ln this papcr. Q-modcfactor anal- \el-on rn,l Kr-himr t 19031.rlifference- in a--em vsis is uscd to clustcr samplcswith similar diatom blages betrveen tidal llats, marshes. and uplands asscmbllgcs from thc modcm surfacesoftidal flats, have not been documented. and there are no such intertidal ri,'er banks. shallowsrrbtidal channels, pre\.ious studies fbr coastal south$'estern low rnarshes, and high marshes in northern Wil- Washinplon. lapa Bay. WashinSon (!igure l). Upland samples. iound to be barren of in situ diatonrs.were ex- Background cluded liom the factor analvsis. GeneralEco ogical Zonat on Reative to T da Studies ol modern estuarine diakrms have LEVEI (i.e.. shown lhat manv taxa are cosmopoiitan have The mixed tides oi the Pacilic coast along south- (Mclntirc a rvorldrddc clistlibution) and frloorc. wcstcm Washinlfon cause a fairly predictablc 1977; T,vnni. l986) and usuall,vcxhibit bloadcr thrcc-ticrcd ;ntcrtidal zonation.with lowcr inter'- tolcranccs for salinity (Xloorc and Mclntirc. 1977; ticlal flats. "lot"'marshcs. and "high" marshcs Mclntirc. l97B; Amspoker and Mclntirc, l97B; (Macdonald, 1977at Macdonald and Barbour. Admiraal. 1979) than ltrr othcr factorssuch as ex- 1977; Frc,v and Basan. l9B5). Thc clcrational posL.rre(Caslenholz. 1963; Sullivan, 197tl) and rangesof thesc zonesdepends on the local tidal subslrale (Amspoker and N{cIntire, 1978; Whit- range, $hich vades both along the r:oastin the Pa- ing. I983: Whitingand Mclntirc.l9B5: Kosugi, cific Northvest and t'ithin individual estuaries. In 1987). A series of er:ologicalstudies in Oregon Willapa Ba,v,thc tidal rangc bctwccn mcan high documented the rnodern r.ertical distributions of r,ater (MHS ) and mean lorv waler (llLS ) rangcs attached or sediment-associatedspecies in thc from 2.3 m ncar thc mouth of the estuaryto 3.4 lower part of the intertidal zone (Castenholz,1963; m at jts soulhcrnmostrcachcs (Nlajor, l9B9). :'i0 Hemphill-Haley Thc initiation of lorv mamh \'rgetation in thc Pa matelr 800.500, and 200 m liom shore. resJrec- 'l'he cific Northu'estis approximatelyecFivalent to lhe tivciv. llat is vegetated rrilh sparse Zosterz r:lo'ation of mean lower high water (l\{T,HS ) (Mac- rdrra al the locat;onsof samplesB(l 2 :rnd BC-iJ. donald and Barlnur'. 1977) ancl cxtends to approx- -qaml)lesBR-l unclBR-2 r'ere collectedffom thc irnatel;-rncan highcr high t'ater (SIHHW). although Lrnlcgetatedsu ece of a siltv tidal flatnorthofthe lcgctrtion is genefallvthicker betwccn mcan high Bone River, approximatcl,-v150 and 300 m fitrrn uaLer'(N'[HS ) and frlHHW. Low marshesare com- shorc. Samplesrrere collected lrorn thc marsh and monlv suhmergedoncr: cach tidal dav (l'rev and adjacenLticlal tlat at Ston,vPoint: SP-l and SP-2 Basan.l985) and thus supportmacrophvtcs cupa- are liom tlre un,regetatedflat; SI'-3 is from the flat ble of legular subrnergt:ncc.Sa,vce (l9BB) lisred adjacenL to a Jratchcrf Tiglochin mo.itino: SP-A the dorninantlol-marsh macrophvlesin S illapa is frorn a lot' marsh thicklv regetaLedwith Tnglo- chin maitinn ancl Salirnmio t:irginica; and SP-5 Bav trs ^Salicorzia rirgi.niut. Jou.nrea camosa. 'Ihglochi.rt is lrom a high marsh marititrtu. nnLlPlantago mtLtitima. High in a thick stand ol Potentillo. pu,i.liro-3 m liom tlr" ha-- nf r Pl, i-tu,nne ter m rshes e\tend liom NIHHST to nc:l crtreme high race. Samplcslvcrc collected liom a marsh and water (EI{S ) (l'lacdonald ancl Barlmur. 1977) anrJ tidal slough at Toke Point : TIJ-I is from the 1loor are slrbmerge.l only (luring highcst spring tides and o[ a sardr tidal slough colered $,ith Ztttertt m.a- -ctorrnsurgcs. According to l-re1and Basan(1985), 'll'2 dna beds; from a l-m-diamctcr patch oi high m:tshes are prone to desi<rcationbccause thev 'lhgLochin "mav mrtiLirrut aLthc mar.sh-to-11attran-ririon: rcmain continuouslv exposcd lbr pcriods ex and TP-3 is from thc lov marsh thicklv vegetatcd ceedinEll0 clavs.betr,'rcn tidal inuntlations." Tvpi- with T. nruitimo and S. r,irgrnirra. cal high-marsh macrophvtesof Willapa Bav incluclc Distic hli.s spiru o. Dest:harLpsitt ( aespitosa. and Samplesfrom t*o intcrtidaltransects along tlrr Niatiakurn lliver (Nl ancl Nu) u,erc analvzed in acl Agrostiso[ba" nith "/rrncasba,ltictts anclPotentillo. dition to the intertidal pttcifittt ttr the highest le,'els (Sayce, l9BB). sarnplesliom the open bav. Transect Nl cxtends liom the channel floor to thc 'l'idal llats of the open cstuarv dnd channel transition liom marsh t() forested uplancl in the banks oi tidal rivers ieeding thc cstuary e)itend lower Niawiakum Rivcr vallc,v(!igure t. 2). The dornrard irom \ILHW to appro\imalelv mean channcl floor is approximately 3.5 m belorr lot'er lot tater (N'ILLSl. Thcsc fiats ard banks \'lLLV. sr,l th- mrrsh-rrplnnrltrcn-itinn i- r-t.- ,',mpri-. a Lr,'r,l- mu-th ,rn\eeclnlcdregiorr po1'rr- mated at 3.,Xm above MLLW.