沉积物中微囊藻存活能力及其向水柱提供种源的能力研究

Microcystis is a meroplanktonic cyanobacterium that can accumulate and survive in the sediment. The recruitment of Microcystis spp. from sediments can provide an inoculum for the pelagic Microcystis bloom and promote the formation of Microcystis bloom. Microcystis colonies with higher viabilities have more chances to accumulate in the sediment, resulting in higher biomass of Microcystis in the sediment. The contribution of benthic Microcystis populations to promote the Microcystis bloom formation is decided by their abilities to inoculate the water column. Up to now, the viabilities of benthic Microcystis spp. haven't been deeply studied and no related reports could be found. Present studies on inoculations mainly focused on cyanobacterial spring recruitment. Information about the contribution of the annual recruitment on the formation of Microcystis bloom is unavailable. In order to evaluate the potential contribution of benthic Microcystis on the subsequent Microcystis bloom in the water column, we carry out microcosms laboratory experiments, field survey and in situ investigation. The special objectives of the study are to (1) elucidate the effect and mechanism of environmental conditions and colonial characteristics on the viability of benthic Microcystis, (2) evaluate the monthly ability of benthic Microcystis to inoculate the water column, (3) estimate the annual contribution of benthic inoculation on the Microcystis bloom. We hope the program will promote the understanding of the contribution of benthic Microcystis population to promote the formation of Microcystis bloom in eutrophic lakes.

微囊藻是一种间歇性浮游藻类，微囊藻群体能在沉积物中累积和存活。沉积物中的微囊藻通过向水柱的提供种源，促进水柱中微囊藻水华的暴发。微囊藻的存活能力是其能在沉积物中大量累积的关键，向水柱提供种源的能力则决定其对微囊藻水华的贡献。目前关于沉积物中微囊藻存活能力的系统研究还未见报道，对其供种能力的研究主要集中在春季复苏期，尚缺乏全年尺度供种行为对水华贡献的研究。本项目拟结合野外调查、室内模拟和原位试验，揭示影响沉积物中微囊藻存活能力的因素及机制，量化周年内沉积物中微囊藻对水柱的供种能力，为定量评估沉积物中微囊藻群体对水柱中微囊藻水华的贡献提供科学依据。

本课题主要针对沉积物中微囊藻的存活能力和供种能力开展了研究。.在沉积物中微囊藻的存活方面，定量研究了微囊藻的存活能力。结果表明环境条件和微囊藻自身特性对其存活能力有显著影响。温度是决定沉积物中微囊藻存活最重要的环境因素。温度越低，沉积物中微囊藻的存活能力越强。通过对其存活时间的定量化也表明，在我国暴发严重蓝藻水华的主要浅水湖泊，进入沉积物的微囊藻可以成功越冬，但是在夏季大规模死亡，这也导致其无法经年累积。厌氧和黑暗条件有利于微囊藻的存活。微囊藻群体自身特性，包括微囊藻的种类、群里尺寸以及微囊藻的活性，均会显著影响其在沉积物中的存活。.通过野外调查揭示了滇池草海水柱和沉积物中微囊藻的动态变化。滇池草海微囊藻水华最先出现在东北区域，之后会从湖岸带转移到湖心带，浮游藻的这一时空分布主要受西南风和从东北到西南的水流影响；夏季，底栖藻主要分布在东北区域，之后分布在湖心区域，到冬季时集中在西南区域，底栖微囊藻的时空分布主要受浮游藻的沉降和底栖藻自身的死亡影响；调查中还发现，小群体(20-60 µm)在水柱和沉积物中都占主导地位，小群体也更容易在水柱和沉积物中越冬，此外，底栖微囊藻细胞比浮游微囊藻含有更高的毒素含量。.针对沉积物中微囊藻的供种能力定量研究表明。沉积物中微囊藻群体，仅极少部分（<3%）能复苏进入水柱。沉积物中微囊藻的供种能力主要受微囊藻群体自身活性、群体尺寸、和微囊藻的种类的影响。进入沉积物中的时间越长，越难以复苏。.综合分析沉积物中微囊藻的存活能力、供种能力和存活率，表明，尽管沉积物中微囊藻可以长时间存活，但其向水柱供种能力有限，只可能在局部促进水柱中夏季蓝藻水华的暴发。.本研究的结论对湖泊管理和蓝藻水华控制具有一定的指导意义。在冬季，水柱中越冬的微囊藻是夏季微囊藻水华的主要种源，需要优先控制。特别是冬季水柱中微囊藻浓度为全年最低的时期，在这个时间控制水柱中微囊藻种源，成本最低，处理难度也最低。