摘要:

Invasions and declines of submersed macrophyte communities have been reported worldwide. In general, factors contributing to invasions are most poorly understood. Factors potentially contributing to macrophyte declines are numerous, and include reduced irradiance, nutrient depletion, parasites and pathogens, toxin accumulation, animal damage, climatic fluctuations, and other factors. Attention to these dynamics in submersed macrophyte communities is of more than academic interest, since coordination of macrophyte management policies and procedures with natural controls could improve the efficiency of macrophyte management efforts. Indeed, there is some evidence that intense management may prolong the dominance of invasive exotic submersed macrophyte species. As part of the International Symposium on the Biology and Management of Aquatic Plants, held in July 1992 in Daytona Beach, FL, a workshop was conducted to better understand invasion and decline phenomena, from a regional perspective, within the context of aquatic plant management.

ISSN:1040-2381    

DOI:10.1080/07438149409354163

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

There are no reports of exotic macrophyte species causing management problems in the Canadian prairies. However, the spread ofMyriophyllum spicatumthroughout the U.S. and parts of Canada poses concerns to water managers in the Canadian prairie provinces. Given the wide range of environmental conditions that this species can tolerate, it is unlikely that environmental factors prevent its establishment in prairie waterbodies. It is most likely that climatic and geographic constraints have, to date, prevented introduction ofM. spicatumin to the Canadian prairies. In the event that this or other exotic species are introduced to the Canadian prairies, it is difficult to predict whether they will grow to nuisance levels, since many of these lakes already support high submersed macrophyte biomass. In lakes and large rivers of the Canadian prairies, aquatic macrophyte growth is favored by nutrient-rich sediments and, in rivers, high water clarity. At present there are no provincial or federal agencies whose mandate is aquatic plant control. Since existing aquatic plant problems are caused by native species, these problems are viewed as a natural state.

ISSN:1040-2381    

DOI:10.1080/07438149409354164

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The role of plant disease in determining distribution and abundance of submersed aquatic macrophytes has rarely been studied. The most definitive case of a microbial agent causing decline of a submersed aquatic plant is the wasting disease of eelgrass,Zostera marinaL., which is caused by a marine slime mold. Plant pathogens have also been suggested as a potential cause ofMyriophyllum spicatumdeclines in Chesapeake Bay and in Madison, WI, area lakes. Attempts to identify pathogens for use in biological control of submersed plants have yielded several promising microorganisms, but much effort has been expended on relatively weak pathogens. More attention needs to be given to conditions under which pathogens are evaluated, since characteristics of the chemical and physical environment and of the host population itself may determine the amount of disease which occurs. In the near future, biocontrol efforts may benefit from expected changes in U.S. Department of Agriculture regulations which will allow importation of host-specific pathogens of introduced aquatic plant species collected from the native ranges of the plants.

ISSN:1040-2381    

DOI:10.1080/07438149409354165

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nuisance aquatic plants are found throughout New England. Plant presence or absence in a lake appears to be limited more by dispersal than by inappropriate abiotic or biotic conditions. While some nuisance macrophyte species are still spreading to new lakes, there have also been declines reported forMyriophyllum spicatum and M. heterophyllumin three New England states. The cause(s) of these declines are still unclear. However, in all lakes in which declines have occurred herbivorous macroinvertebrate species known to feed onMyriophyllumspp. have been found.

ISSN:1040-2381    

DOI:10.1080/07438149409354166

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Management of nuisance aquatic plants in New York state is directed toward the exotic species,Myriophyllum spicatum, Potamogeton crispus, Trapa natans, andCabomba caroliniana. Public access to a lake may be the number one factor contributing to invasion byM. spicatum. All types of lakes in the Adirondack Mountain region have been invaded by this species except acid lakes. In shallow, eutrophic lakes the entire littoral zone is often comprised ofM. spicatumgrowing to the surface, whereas populations in more oligotrophic lakes form isolated patches. Native plant species in general appear to be stable, except where exotic species have colonized and are dominating.

ISSN:1040-2381    

DOI:10.1080/07438149409354167

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Control of nuisance species appears to be the primary goal of aquatic plant management in New York State. The three principal species of concern areMyriophyllum spicatumL. (Eurasian watermilfoil),Potamogeton crispusL. (curly pondweed), andTrapa natansL. (water chestnut). A wide range of lake types are apparently colonized by nuisance macrophyte species; these range from acidic, disturbed, oligotrophic lakes to alkaline, eutrophic lakes. Hand harvesting, mechanical harvesting, drawdown, and herbicides have been used for aquatic plant control in the state. Populations of native aquatic plants are stable to declining. There is no clear relationship between invasion of exotics and decline of native species.

ISSN:1040-2381    

DOI:10.1080/07438149409354168

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In the upper Great Lakes region,Myriophyttum spicatum, Elodea canadensis, Potamogeton crispus, andCeratophyllum demersumare the most significant nuisances.M. spicatumandP. crispushave generally invaded lakes with hard water, abundant nutrients, and a history of disturbance or heavy human use.M. spicatumhas declined in some Wisconsin lakes, but not in all that it invaded. The reason for declines was never satisfactorily explained. Following its decline in Madison, WI, lakes, theM. spicatumpopulation never regained its former predominance. There are no long-term data to determine whether populations of native macrophyte species are expanding, stable, or declining on a regional basis, although diversity of the aquatic plant communities of Madison-area lakes has declined over the last 80 years. Most aquatic plant management in the upper Great Lakes region involves controlling nuisance species. Herbicides and mechanical harvesting are the primary means of management, although drawdowns, bottom blanketing, and other methods are also used. Minnesota and Wisconsin have public education programs intended to promote early detection of nuisance species and to minimize their spread. In Wisconsin, reintroduction of aquatic vegetation to lakes is being attempted on an experimental basis for a variety of reasons, including fish and wildlife habitat and water-quality improvement.

ISSN:1040-2381    

DOI:10.1080/07438149409354169

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Declines in submersed aquatic macrophytes, notablyVallisneria americanaMichx., recently have been observed in portions of the Upper Mississippi River (UMR). Coincidentally,Myriophyllum spicatumL. appears to have become more common, frequently occurring in locations formerly occupied byVallisneriaor other submersed aquatic species. Mechanisms causing these changes in the abundance and composition of aquatic vegetation are unknown. However, a 3-year drought may have affected nutrient transport and phytoplankton production, thereby influencing growth and reproduction ofVallisneriaand other macrophyte species. Other factors may potentially affect populations of submersed macrophytes within the UMRS. Foremost among these are suspended sediment concentrations, flooding, herbicides, and grazing.

ISSN:1040-2381    

DOI:10.1080/07438149409354170

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Long-term changes in biomass, species composition, and distribution of submersed aquatic macrophytes have been documented and studied at two sites in the mid-Atlantic region: the tidal Potomac River and Estuary in Maryland, Virginia, and the District of Columbia, and the Currituck Sound-Back Bay system in Virginia and North Carolina. Additional information based on a shorter time period is available for the Pamlico River Estuary in North Carolina. This paper briefly describes the study areas and summaries the history of declines and increases in each area and factors implicated in these changes. The remainder of the paper is devoted to a discussion of factors influencing invasion/establishment success and the current status of submersed macrophytes in the three areas.

ISSN:1040-2381    

DOI:10.1080/07438149409354171

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In Chesapeake Bay, a baywide decline of all submersed aquatic vegetation (SAV) began in the late 1960s. The decline was related to increasing amounts of nutrients and sediments resulting from shoreline and watershed development. In the bay, SAV are rarely considered a nuisance, since they contribute to high baywide productivity and habitat quality. Because SAV is a critical part of the bay's food chain and is sensitive to water quality, it is considered a potential indicator of the bay's health. A conceptual model was developed, which illustrates water quality parameters that influence SAV distribution and abundance. Environmental factors contributing to light attenuation were used to formulate SAV habitat requirements. SAV habitat requirements based on specific water quality standards represent characteristics minimally necessary to sustain plants in shallow water. Improvements in water quality in the bay are predicted to result in increases in the density and biomass of SAV.

ISSN:1040-2381    

DOI:10.1080/07438149409354172

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor