The influence of nutrient and organic enrichment on a community dominated by macrophytes and gastropod molluscs in a eutrophic drainage channel: relevance to snail control and conservation.
Abstract
The effects of increased nutrient and organic loading on a community dominated by submersed macrophytes and gastropods were investigated in a drainage channel in East Sussex, UK, in 1989. Increased organic loading resulted in significant increases in conductivity, decreases in oxygen, pH and chlorophyll values in the water column, and increases and decreases in the cover of Potamogeton crispus and Groenlandia densa, resp., compared with controls. The treatment had no effect on snail numbers but the final biomass of Ceratophyllum demersum was significantly greater than in the control. The rate of phosphate sequestration in the nutrient loading treatment declined with time, whereas that of nitrate increased. Despite this, the concn of both chemicals remained greater than in the control. This treatment resulted in rapid divergence towards either phytoplankton or Lemna dominance and the virtual demise of submersed macrophytes. The nutrient loading treatment as a whole resulted in greater densities of Lymnaea peregra and total numbers of snails than controls. When phytoplankton and Lemna-dominated systems were compared, the former had fewer L. peregra, Planorbis planorbis and total number of snails than the latter, and fewer P. planorbis, Physa fontinalis or Bithynia tentaculata than the controls.
Key words
- agricultural entomology
- aquatic animals
- aquatic invertebrates
- aquatic organisms
- aquatic plants
- aquatic weeds
- biology
- chlorophyll
- control
- drainage channels
- ecology
- eutrophication
- freshwater invertebrates
- freshwater molluscs
- growth rate
- helminths
- nitrate
- nutrient availability
- oxygen
- parasites
- pests
- pH
- phosphates
- phytoplankton
- plankton
- population density
- population dynamics
- population structure
- weeds