Restoring complex vegetation in urban settings: The case of tidal freshwater marshes

Tidal freshwater marshes have diverse plant communities that vary spatially and temporally due to hydrology, animal activity, and other factors. Development of urban centers along rivers of the U.S. Atlantic coast has reduced the historic extent and quality of these and other coastal wetlands. Because the vegetation of these wetlands is more complex than that of salt and brackish marshes (where restoration of vegetation typical of natural systems has sometimes been successful), restoration of tidal freshwater marsh vegetation is likely to be more difficult, particularly in urban areas. Watershed urbanization alters hydrology, sediment load, propagule availability and composition, nutrient status, and other variables that together create an environment different from that of wetlands in less developed areas, possibly precluding restoration of typical marsh vegetation. Tidal freshwater wetlands were historically extensive along the Anacostia River in Washington, DC, but most of these were lost due to filling, dredging, or hydrologic alteration. Over the last decade, the U.S. Army Corps of Engineers has implemented projects designed to restore tidal freshwater wetlands along the Anacostia, which involved increasing elevation with dredged river sediment and planting native vegetation. To illustrate some of the mechanisms affecting vegetation development in restored tidal freshwater marshes in urban areas, I present a case study on one of these wetlands, Kingman Marsh, that also includes research at another restored wetland and two natural reference sites. Studies by my research groups indicate that the restored wetlands undergo essentially a planting-modified process of primary succession. Low densities of seeds are initially present in the substrate, and prolific seed dispersal into the restored sites results in high initial plant diversity comprised of plantings and ruderal (i.e. weedy) natives and exotics. Seed banks develop rapidly at the restored sites, probably due to colonization and early reproduction by ruderal species. Hydrology and disturbance by non-native animals (including resident Canada goose) are important variables controlling establishment of vegetation in these systems. Recent literature and the case study indicate that the environmental conditions of urban settings impose constraints in restored wetlands that result in plant communities more like those of urban natural wetlands than those of wetlands in less urbanized watersheds. This suggests that rather than design wetland restoration projects with the goal of creating pristine wetland vegetation, restorationists must identify, accept, and if possible capitalize on the ecological constraints of the urban environment in setting achievable and desirable restoration goals.     

淡水养殖珍珠的激光拉曼光谱特征与改色珍珠的鉴定

采用激光拉曼光谱对各种颜色的淡水养殖珍珠和辐照改色淡水养殖珍珠进行了研究．发现了天然有色珍珠与辐照改色珍珠间的拉曼光谱的差异，据此建立了快速、无损鉴定改色淡水养殖珍珠的方法．     

淡水底栖硅藻对刺参的饵料效果

采用淡水底栖硅藻舟型藻(Naviculasp.)和刺参专用配合饲料投喂刺参(Apostichopus japonicus),经过45天的生长后测定两组刺参的成活率分别是99.57%、83.83%,平均生长率是:4.3%、-27.7%,用流式细胞仪测定两组刺参体腔液细胞的吞噬活性分别是15%和4%。证明新鲜淡水底栖硅藻的饵料效果优于此配合饲料。     

The seed bank of a restored tidal freshwater marsh in Washington,DC

The species composition of seed banks may be a useful indicator of vegetation structure and dynamics, but seed bank studies have rarely been applied to monitoring of wetland restoration projects. We studied the seed banks and vegetation of three distinct sites within a restored tidal freshwater marsh and of two nearby natural marsh sites. Surface soil samples were collected and subjected to flooded and nonflooded conditions in a greenhouse for enumeration of emerging seedlings. Percent coverage of vegetation was estimated in permanent 1-m² plots at each soil sampling location.Species composition of the seed bank and vegetation differed considerably; only 43% of the species observed were common to both. The seed bank of restored marsh sites had higher species richness and seed density than the natural marsh sites, but both had similar species diversity. Annual species were more important in the seed bank and less important in the vegetation of restored sites than reference sites. Flooding significantly reduced the species richness, diversity, and density of emerging seedlings. Most species planted at the site were rare in the seed bank, with Leersia oryzoides being an important exception. Other species abundant in the seed bank included Cyperus odoratus, Juncus effusus, and the nonindigenous Lythrum salicaria. A possible mechanism explaining the higher densities of seeds in restored areas is that ruderal vegetation colonized the restoration site, reproduced, and set seed shortly following placement of dredge material. Perennial species subsequently colonized and were planted, and expanded to reduce the abundance of annuals in restored marsh vegetation. Our study suggests that the plant regeneration dynamics of the restored marsh sites are considerably different from those of natural marshes. Additionally, we suggest that seed bank studies are a useful technique for assessing the community structure and vegetation dynamics of restored wetlands.     

未来30年我国粮食、淡水、能源需求的系统仿真

本文以系统动力学为主要方法,对未来我国的人口总量和经济水平进行了预测,在此基础上对未来粮食、淡水和能源的需求规模进行了仿真,提炼出人口、经济与粮食、淡水和能源需求的关联模式,并进行了灵敏度分析,探讨了为确保粮食、水、能源安全所能采取的有效措施。     

抚州市淡水贝类初步调查

本文报道了抚州市17种淡水贝类:腹足类11种,瓣鳃类6种,主要分布在河流、水田、溪流、池塘,并提出了它们的经济利用和开发意见。     

Relative importance of direct and indirect interaction among individual snails

Summary Individual organisms interact directly through behavior, and indirectly through resource consumption and environment modification. The effects of different kinds of interactions on individual growth and reproduction will differ. Freshwater snails may interact directly for food resources and indirectly through substances dissolved in water. I separated the effects of the direct behavioral interaction and indirect interaction through waters using laboratory experiments with freshwater snailsPhysa acuta. Behavioral direct interaction have negative effects on the growth, but indirect interaction through water environments has positive effect on the growth. The importance of distinction of different kinds of interactions were discussed.