崇明东滩盐沼植被变化对滩涂湿地促淤消浪功能的影响

30年来在海平面上升、人类围垦、自然保护、外来物种入侵等自然与人为作用共同影响下,崇明东滩盐沼植被群落结构发生了巨大变化。基于长江口四期遥感影像解译结果,得到盐沼植被群落结构变化,结合对盐沼植被促淤消浪功能已有研究成果,量化崇明东滩盐沼植被促淤消浪功能潜力及其变化。研究表明:1980、1990、2000和2010年崇明东滩芦苇、互花米草、藨草群落面积比例分别为23∶0∶77、73∶0∶27、33∶9∶58、34∶34∶32,同期总植被覆盖面积分别为51、83、37、44 km2。30年来滩涂湿地促淤消浪能力均有下降,1990—2000年变化最大。其中,植被黏附悬浮颗粒物量分别为1976、4645、2192、4695 t;沉积量分别为960、1579、195、286万m3;常规波高情况下堤外没有足够植被保护的岸段长度分别为5、0、7、6 km;风暴潮情况下堤外没有足够植被保护的岸段长度分别为19、5、26、20 km。因此保护堤外盐沼植被对消浪促淤,特别是抵御风暴潮等恶劣气候灾害的影响具有重要意义。

The impact of salt marsh change on sediment accumulation and wave attenuation at the East Chongming Island

As a key part of substance and energy exchange between land and ocean, estuarine wetland is the hotspot and focus of multiple disciplines. Under natural and artificial influences such as sea level rising, human reclamation, nature conservation, and exotic species invasion, salt marsh in the East Chongming wetlands had undergone severe changes during the past decades. Based on field investigation, remotely sensed images were classified and corrected for the periods of 1980, 1990, 2000 and 2010 at the East Chongming Island. In combination with existing research results, the impact of salt marsh change on sediment accumulation and wave attenuation of the East Chongming wetlands were quantified. The results showed that: the area ratio of Phragmites/Spartina/Scirpus were 23:0:77, 73:0:27, 33:9:58 and 34:34:32 in 1980, 1990, 2000 and 2010, respectively, with the total area of salt marsh vegetation changed from 51 km² to 83 km², 37 km² and 44 km². Under constant sedimentation during 1980-1990, the total amount of suspended particulate matter adhered by vegetation increased by 2669 t, while the amount of sediment accumulation increased by 619×10⁴m³. The length of seawall without enough vegetation protection under normal tidal heights and under storm surge decreased by 5 km and 14 km, respectively. Due to intensive human reclamation during 1990-2000, the total amount of suspended particulate matter adhered by vegetation decreased by 2453 t, the amount of sediment accumulation decreased by 1384×10⁴m³. The length of seawall without enough vegetation protection under normal tides and under storm surge increased by 7 km and 21 km, respectively. With the influences of constant sedimentation and exotic species invasion during 2000-2010, the total amount of suspended particulate matter adhered by vegetation increased by 2503 t, and sediment accumulation increased by 91×10⁴m³. The length of seawall without enough protection under normal tides and under storm surge decreased to 6 km and 20 km, respectively. Saltmarsh vegetation protection is of great importance for land accretion and for the safety behind the seawall, in addition to its importance for a number of other ecological functions such as bio-productivity, biodiversity, and purification.