Hydrologic,vegetation, and substrate characteristics of floating marshes in sediment-rich wetlands of the Mississippi river delta plain,Louisiana, USA

Floating marshes occur over 70% of the western Terrebonne Basin, Louisiana, USA, freshwater coastal wetlands. They are of several types: A free-floating thick-mat (45–60 cm) marsh dominated by Panicum hemitomon and Sagittaria lancifolia; a thick mat marsh dominated by Panicum hemitomon and Sagittaria lancifolia that floats part of the year, but whose vertical floating range is damped compared to adjacent water; and an irregularly-floating thin mat (< 30 cm) dominated by Eleocharis spp. in the spring and Ludwigia leptocarpa and Bidens laevis in the summer and fall. Floating mats must be almost entirely organic in order to be buoyant enough to float. The western Terrebonne wetlands receive large winter/spring supplies of suspended sediments from the Atchafalaya River. Even though sediment concentrations in the adjacent bayou are as high as 100 mg l^–1, the Panicum hemitomon/Sagittaria lancifolia free-floating marsh probably receives no over-surface sediments since it floats continuously. The bulk density data of the damped-floating marsh, however, suggest some mineral sediment input, probably during winter when this marsh is submerged. These two types of floating marsh could not have developed in the present sediment regime of the Atchafalaya River, but as long as they remain floating can continue to exist. Thin floating mats are found in areas receiving the least sediment (<20 mg 1^–1 suspended sediment concentration in adjacent bayous). This low sediment environment probably made possible their formation within the past 20 years. They may represent a transitional stage in mat succession from (1) existing thick-mat floating marsh to a degrading floating marsh, or (2) a floating marsh developing in shallow open water.Corresponding editor: D. Whigham     

南水北调与生态平衡

水是人类赖以生存繁衍的重要资源。我国人口逐年增长,而淡水资源数量有限。多变的自然降水及频繁的旱涝灾害,一直决定着我国农业收成乃至整个国民经济的盛衰。     

Sphagna of the 1979 Projeto Flora Amazônica expedition

Within the great expanse of the Brazilian Amazon Basin,Sphagnum has been greatly overlooked, in part because of its scarcity and in part because of the paucity of trained bryological collectors in the area. During a Projeto Flora Amazônica expedition in 1979, seven specimens ofSphagnum were collected, representing six species, five of which are newly described:S. amazonicum, S. dimorphophyllum, andS. subsecundoides in sectionSphagnum;S. curicuriariense andS. ripense in sect.Subsecunda. Also discussed areS. negrense Mitt. andS. sanguinale Warnst.     

Weeds of Kentucky and Adjacent States. A field guide. By Patricia Dalton Haragan The University Press of Kentucky, Lexington, KY 40506-0336

In 1843 S. B. Buckley (1809–1884) traveled up the St. Johns River, Florida in search of plants, shells, and possibly other natural history objects. Buckley encountered many difficulties in interior Florida and his trip did not live up to his original expectations. It was unfortunate that the took years to distribute his plant specimens, since few botanists or naturalists had preceded him into that poorly explored region.     

Intraspecific resource partitioning in a headwaters stream fish,the pearl dace Semotilus margarita (Cyprinidae)

Synopsis Pearl dace, Semotilus margarita, are common in slow-moving channels and pools of the headwaters of the Brokenhead River. From May to September age groups 0, 1 and 2+ were partially segregated in space based on water depth with age 0 occupying shallow pools and shallow channels. Age 1 were abundant in shallow pools and deep channels while age 2+ occurred in deep channels and deep pools. In November all age groups coexisted in deep pools. Pearl dace are omnivorous consuming invertebrates, plant material, and detritus. From May to September age groups 0 and 1 consumed mainly terrestrial invertebrates (Diptera, Hymenoptera, Thysanoptera) but age 1 consumed more detritus than age 0. Age 2+ consumed mainly aquatic Diptera larvae. Although all ages consumed aquatic insects almost exclusively in November differences in diet between age groups still existed. Younger fish fed higher in the water column than older fish. Intraspecific resource partitioning of food and space occurs between age groups and this combined with the omnivorous diet is highly adaptive to the headwaters of streams.     

The populations of fish in tributaries of the River Eden on the Moor House National Nature Reserve,northern England

The population dynamics of trout (Salmo trutta L.) were studied in two high-altitude streams flowing westwards into the River Eden in northern England. The results from one (Knock Ore Gill), which is accessible to spawners from downstream, were compared with published data from an isolated population in a nearby stream which flows eastward into the River Tees. The Knock Ore Gill trout had a population density of 0.4–0.9 fish m^–2, a biomass of 12.4 g m^–2, annual production of 12–14 g m^–2 year^–1 and an instantaneous mortality rate of 0.97 year^–1. Comparable values from the Tees tributary were 0.2, 3.3, 2.3 and 0.66 respectively. The Knock Ore Gill population also contrasted with that of the Tees tributary in having reliable recruitment from year to year. These differences were related to differences in the chemistry and spate characteristics of the two streams and to the fact that immigrants from downstream were responsible for over 30% of the annual oviposition in Knock Ore Gill.     

Evidence of a genetically distinct population of Vrljika softmouth trout Salmo obtusirostris Heckel evolved by vicariance

Mitochondrial DNA haplotypes (control region, partial cytochrome b and ATPase6 genes) indicate a sister relationship between Vrljika and Neretva softmouth (Adriatic) trout Salmo obtusirostris . This relationship was supported by a tree of individuals based on microsatellite results [allele sharing distances ( D _AS)], which revealed three distinctive clusters, corresponding to Jadro softmouth, Neretva brown trout Salmo trutta and Neretva softmouth trout. Within the latter taxon, Vrljika trout are clearly separated from other trout. The genetic results contradict the synonymy of Jadro with Vrljika softmouth trout, as recently proposed in the Red Book of Freshwater Fish in Croatia. Vrljika softmouth trout appear to have originated from a vicariance that split a common ancestor into large (Neretva) and small (Vrljika) fragmented populations 135 000–270 000 years ago. Vrljika softmouth trout can be distinguished by an array of derived phenotypic and molecular character states. For conservation, this population should be recognized formally at the same taxonomic level as the other geographically separated populations of softmouth trout.