Research On The Inter-Annual Change And Influence Factors Of The Coastal Submerged Aquatic Vegetation Abundance

Submerged aquatic vegetation(SAV)consists of a taxonomically diverse groupof plants that lives entirely beneath the water surface. SAV provides habitat andsupplies food for aquatic life, absorbs excess nutrients, and helps purify the water.Since the1960s, SAV coverage has experienced dramatic decline worldwide due toserious deterioration of water quality in coastal ecosystems.In recent years, landscape analyses have been used to predict direct or indirecteffects of geographic characteristics on aquatic organisms. In this study, we analyzedthe inter-annual change and effects of influence factors on the spatial variation of SAVabundance based on the long-term dataset (2004-2009) from99sub-estuaries andtheir linked coastal sub-watersheds of the Chesapeake Bay in the United States.Coastal watershed land use is an important factor influencing inputs of nutrient andsediment to its associated sub-estuary, and thus indirectly affects SAV abundance. Ourresults showed that:(1)SAV abundance generally arises in1984-2002in developed land, peaked at2.4%in2002, but drops to1.6%in2009. The inter-annual variation of SAV abundance inagricultural land turns on the trend of increasing from0.1-0.9%in1984-2002, andfluctuated up and down in2002-2009. SAV abundance in mixed land rise from0.6%to2.0%in1984-1998, and fluctuated up and down in1998-2009. The inter-annualvariation pattern of SAV abundance in forested land is similar to mixed land,increasing in1984-1998and fluctuated in1998-2009.(2)SAV abundance in different salinity shows an trend of increasing in the overallwith fluctuations in1984-2009.The trend of inter-annual variation of SAV abundancein tidal fresh goes up from0to2.0%in1984-2009; SAV abundance drops greatlyfrom1.6%to0.4%between1999and2000. The trend in mesohaline goes up from0.2%to3.1%in1984-2001, declining weatly from3.1%to1.8%in2001-2009. Thetrend in oligohaline gose up from0to1.7%in1984-1998, declines to0.6%in2001, then declines from2.0%to0.7%in2003-2009. The SAV abundance of polyhalineis generally high in1984-1998,which is different from areas of other salinity, arisingfrom1.1to1.8; it drops from2.0%to0.6%in2002-2003, and then goes up from0.6%to1.3%.(3)The three types of rainfall years have no regularity partition on the abundance ofsubmerged aquatic vegetation.(4)SAV abundance have significantly positive correlations with average waveheight(r=0.306,p=0.002), SAV abundance increases as the average wave heightincrease; SAV abundance have significantly positive correlations with mouth width(r=0.442,p=0.001), SAV abundance increases as the mouth width increase; SAVabundance have weak positive correlations with fractal demension(r=0.290,p=0.004),SAV abundance increases as the fractal demension increase; SAV abundance alsohave weak positive correlations with tidal range(r=0.272,p=0.007), SAV abundanceincreases as the tidal range increase.(5)Using the classification and regression tree (CART) model, I predicted that ratioof watershed area/sub-estuary area had the greatest impact on SAV abundance thatappeared at the highest level of the tree, followed by shoreline fractal dimension,salinity regime, and average wave height. These four geographical variables explained63%of the total spatial variation in SAV abundance across the Chesapeake Bay.