Impact of Human Activities on Depositional Process of Tidal Flat in Quanzhou Bay of China

Chinese Geographical Science 2007 17(3) 265- 269DOl: 10.07/511769-007-0265-9www .springerlink.comImpact of Human Activities on Depositional Processof Tidal Flat in Quanzhou Bay of ChinaWANG Aijun(Open Laboratry of Ocean and Coast Environmental Geology: Third Institute of Oceanography,State Oceanic Adminisration, Xiamen 361005, China)Abstract: As a very inoportant component of a coastal system, tidal flats come to be a focus of the studies onland-ocean interaction in the coastal zone because those areas are subjected to intense human activities and are highlysensitive to the global change. The Quanzhou Bay, located along the middle part of Fujian coast of China, covers about136.4km', and the area of coastal wetland in the entire bay from intertidal to subtidal with 6m of water depth accountsfor 96% of the total area, Seven short cores were collected and divided in situ with tbe interval of 5cm on the coastalwetlands of Quanzhou Bay on April 19, 2006. The sediment samples were sattred and the grain sizes were measuredby using Mastersizer 2000. Human beings' activities on tidal flat have disturbed the vertical distibution of sedimentsin statigraphic sequence and accelerated the sedimentation rates. Grain size analysis results show tbat the grain sizediameters increase and sediment becomes worse sorted towards tbe sca under the stong human disturbance; Spartinaateriflora can play a role of tapping the fine sediment; but Dear the bank, the sediment becomes coarse and there aretwo peak values on frequency curve influenced by the sandpile. The trough formed by human activities along thecoastine changes the transport path of water and suspended sediment. The sediments are transported through thetough and deposit in it during the flood; the ebb flow is retarded by the flow output through the adjacent trough, andthe deposited sediment can not be re-suspended; then, the sedimentation rate increases. In situ observation show thatthe sedimentation rate is about 8-10cm/yr.Keywords: tidal flat; sediment grain size; human ativitie; sedimentation rate; Quanzhou Bay1 Introductionmaterial cycle and system evolution process under theimpact of human activities and the significance of theAs a very important component of a coastal system,coastal development in the next decade (Crossland et al,tidal flats are formed by tidal action under the condition2005). Under the impact of human activities, the sedi-of abundant fine-grained sediment supply, and they bavementation patterns and geomorphological evolution ofbecome a focus of the studies on land-ocean interactiontidal flat are influenced greatly (Ren, 1989; Wu andin coastal zones which are subjected to intense humanWang, 2005).activities and are highly sensitive to global change. WithAs an early developed bay of the southeast coast ofpopulation growth and economic development, humanChina, the Quanzhou Bay was a perfect area foractivities have become more and, more intense andmariculture in the past, and the main type of thenatural resources and environment have being destroyedmariculture was the cultivation on tidal flat. At present,seriously, which have been concemed by many interna-because of the sedimentation on tidal flat and the reduc-tional organizations and related countries. As one of thetion in inundation depth and time of tidal water, the cul-key matters of the Intermational Geosphere and Bio-tivation area on tidal flat is restricted, and even aban-sphere Program (GBP), Land-ocean Interaction in doned at the middle and upper intertidal flat where theCoastal Zone L0ICZ) put the emphasis on the study of main中国煤化工e wild seafood. TheReceived date: 2006-09-06; accepted date: 2007-06-01| YHCNMHGFoundation item: Under the auspices of the National Natural Science Foundation of China (No. 40606012), the Marine Science YouthFund of State Oceanic Administration of China (No. 2006312), and tbe Natural Science Foundation of Fujian Province (No.D0510025)Corresponding author: WANG Ajun. E-mail: ajwang@163.com.266WANG Aijunstratigraphic sequences are disturbed by buman activi- cial Nature Reserve" to protect wetland ecosystems andties such as cultivation and digging, some are even dis-biodiversity. The bay experiences semi-diurnal tide withturbed so completely that there are DO approaches tothe mean tidal range of 4.27m, and the main type offind the natural deposition records within the stratum. Intidal water movement is the stable to-and-fro current.addition, the introduction of Spartina aterniflora alsoAccordinig to the field observation, there are more thaninfluences the distribution pattern of sediment and the1000 species of organisms including some speciessedimentary structure of tidal flat.adapting to various temperature and salinities (Huang,It is the basic research for coastal resources uilization 2004). The main type of human activities is mariculture,and eco environment restoration that how, the intense hu-especially the production of Sinonavacula constricta. Inman activities impact the modem sedimentary structure2002，the mariculture area in Quanzhou Bay wasand depositional process. Based on the field observation, 8126ha with a production of 194,534t (Huang, 2004).this paper tries to discuss the impact of human activitieis on Today, the sustainable development and utilization ofdepositional processes of tidal flat in the Quanzhou Bay.mariculture have been seriously afected by gates con-struction at the river mouths, reclamation of tidal wet-2 Study Arealands and introduction of Spartina alterniflora.The Quanzhou Bay (24950N, 11840'E), located along3 Sampling and Analyzingthe middle part of Fujian coast, covers about 136.4km'and is divided into inner bay and outer bay. The area of Seven short cores were collected on the intertidal flat atthe inner bay is 79.5km', and the coastal wetlands ac-the conjunction area between the Jinjiang River andcount for 99% of the area (Huang, 2004). The area of Shishi City on April 19, 2006 (Fig. 1). Since the mostcoastal wetland in the entire bay from intertidal to sub-area of intertidal flat are disturbed by artificial maricul-tidal with 6m of water depth accounts for 96% of the ture except for the area near the tidal creek, the samplestotal area. The inner bay is the marine outlet for the Jin- were all collected near the tidal creek. The characteris-iang River and the Luoyangjiang River, and has beentics of geomorphology and sedimentary structure ofdesigned as“Quanzhou Bay Estuarine Wetland Provin- sampling cores are shown in Table 1.Luoyang 72459↑。Town and villageQuaozbou.... Water lineHouzhiCoast line●Sampling site2500mXibiXibitANhmjlangHaojiangShuiouXiangzi。8ShishiShiou11835/118*47Fig. 1 Location of study area and sampling sitesThe way of sampling is to push the organic glass tube measured by using Mastersizer 2000 (product of Mal-downward slowly, and then vacuumize the tube by pis- vem. UK) which. has a measurement range ofton, and at last pull out the tube and taking out the sam- 0.01中国煤化工of <3% for replicatedple. Due to the short length (about 25- 35cm), the coresmea:|YHC N M H Gameters, i.e. medianwere not compacted on the whole. These short cores grain size, sorting coetficient, skewness and kurtosis,were divided in situ with the interval of 5cm. The sedi- were calculated with moment statistics (McManus,ment samples were scattered and the particle sizes were 1988).Impact of Human Activities on Depositional Process of Tidal Flat in Quanzhou Bay267Table 1 Geomorphologic characteristic and sedimentarythe deposited sediment. In addition, the sediment distri-structure of sediment coresbution patterns of the underground without vegetationSite Geomorphologic characterisic Sedimentary structureare also disturbed by intense human activities, while theH Flat with dense Spartina al- Dark mud along the whole profile,sediment distribution patterms of the underground COV-termifora, near tidal ceekwithout laminac, with more grassrootsered by dense Spartina alerniflora are slight disturbedby human activities. Therefore, the sorting of the sedi-i Flat with dense Sprlina al Dark mud along the whole profile,ternijlora, near tidal creekwithout laminae, with more grassments in the flat with Spartina alteriflora is better. Thevariations of sediment parameters indicate that theFFlat with sparse Spurlina Dark mud along the whole profle,source of tidal flat sediment in Shuitou area is tidal cur-aileriflora, ncar tidal crckwithout laminae, with less grassrent input, and obviously different from the sedimentroosinput by coastal erosion (Wang and Chen, 2006).Bare flat, near tidal creekDarnk mud along the whole profile,without lamineMedian grainSortingSkewnes Kurtosis) Bare fat, near tidal creekDark mud along the whole profile,56'coeficien152.025-2-1012 2.02.53.0without laminac3 Bare flat, ner tidal crekwithout laminae10Tranition zone between flat Dark mud along the whole profle,with Spartina alermiflora and宜15bare flat, near tidal creek其22:4 Results and Discussion304.1 Characteristic of sediment grain size parameter35Grain size analysis results of the sediments in Fig. 240show that the median grain size decreases landward--Site H --Site G -SiteF -+-Site E --Site D Site Bwithin the intertidal flat except the site H near the bank,Fig. 2 Grain size parameters of sediment coresbecause the sediments at the site H partially originatein Shuitou intertidal flatfrom the material of the sandpile near the bank. On theflat with dense Spartina alterniflora (site G), the sedi- 4.2 Impacts of cultivation on sedimentation ratements are the finest along the profile, and the medianSince the 1980s, with the development of cultivation ofgrain size varies from 6.37 to 6.50 with the average razor clam, the tidal flat in Shuitou area was dug byvalue of 6.420. Along the profile, the minimum, maxi- human beings, thus formed a special man-made type ofmum and average values of median grain-size increasegeomorphology which alternated with trough-ridge andseaward. On the bare flat at the lower intertidal flat (siteintersected vertically and horizontally, and the troughB), the sediments are coarser and the median grain-size depth was about lm. Therefore, there was no naturalvaries from 4.76中to 6.22中 with the average value of sedimentary property in the whole flat. Aferwards, the5.850. The sorting of the sediment is better within the sediment deposited gradually in the trough, and the cul-flat with dense Spartina alererifora and with the sorting turits dug the mud ceaselessly in order to maintain con-cofficient of 1.45-1.52 (site G), but the sorting oftinuously the cultivation of razor clam. In the earlysediment becomes worse and the soring coficient in- 1990s, due to the serious deposition, the cultivation ac-creases seaward. Previous researches indicated that the tvities on the middle and upper parts of the intertidalsediments are gradually coarser and the sorting of sedi- flat had to be abandoned. At present, the upper and mid-ments is gradually better towards the sea under the dle pa中国煤化工cd and leveled up onnatural conditions (Evans, 1965; Reineck and Singh, the wi|YHC N M H Gls maintained owing1980; Frey and Basan, 1985), but the sorting of the to ther evoution into tidal ceek. Due to the strong dis-sediments in Shuitou area is gradually worse scaward turbance by human acivities,s the statigaphic se-because the dynamic change of the tidal creek disturbs quences of tidal flat were destroyed too seriously to do268WANG Aijunisotope dating. During the sampling a footpath buriedXibin\under the ground about 1m was found. It is known that之the footpath was built for walk 15 years ago and three tofive years later had to be abandoned. From this an in-ference can be made that the sedimentation rate is about》