8
R.1. Fletcher
their world-wide distribution, ecological requirements, floristic composition, influence on the local ecology and methods of their control and
utilization.
1.2 Eutrophication - The Background
Primary production in the sea is governed primarily by the natural cycles of
nutrients. In general, nutrient levels are higher in the winter and lower in
the summer (Nasr and Aleem 1948; Fonselius 1978) with the cycle largely
controlled by the activity of phytoplankton which removes much of the
available nitrogen and phosphorous from seawater during the spring
bloom period (Wallentinus 1981,1991). Nutrients can, therefore, be in
short supply for benthic algae during the spring/summer period with
nitrogen being the most likely nutrient limiting plant growth (Foster 1914;
Alfimov 1959; Ryther and Dunstan 1971; Prince 1974; Wallentinus 1981;
Sfriso et al. 1988a,b). Whilst some perennial algae are known to be capable
of binding large quantities ofN and P in their biomass [e.g. a bioaccumulation factor for nitrate of 28000 was reported by Chapman and Craigie (1977)
for the large kelp alga Laminaria longicrurisl which can be utilized during
periods of low ambient levels, the growth and seasonal response of many
algae largely revolves around the natural availability of the nutrients. Not
surprisingly, therefore, any additional inputs of these nutrients will upset
the natural seasonal cycles of growth and development.
Although there are a number of natural mechanisms outside the growth
cycle of phytoplankton by which nutrients are released into the marine
environment e.g. the release of nutrients from sediments disturbed by
storms, from rotting benthic seaweed and as a result of upwelling systems
(Fujita etal. 1989), many reports relate to man's activities. These include:
the release of nutrients from "disturbed" sediments as a result of dredging
activities, coastal construction works etc. (Perez-Ruzafa et al. 1991);
nutrients derived from atmospheric fall-out, which usually occurs in
coastal waters down-line from industrial areas (considered by Rosenberg
1985,1990 and Wilson et al. 1990 to be a source of nutrients entering the
Kattegat region of the Baltic and Dublin Bay, Ireland, respectively);
nutrient-containing effluents discharged from various coastal refuge tips;
nutrients originating from the growing number of fish farms which are in
operation (Lumb and Fowler 1989; Tsutsumi et al. 1991); nutrients from
river input (runoff) and percolating groundwater coming from agricultural
land treated with fertilizers (Fitzgerald 1978; Rosenberg 1985; Wilson et al.
R.1. Fletcher
their world-wide distribution, ecological requirements, floristic composition, influence on the local ecology and methods of their control and
utilization.
1.2 Eutrophication - The Background
Primary production in the sea is governed primarily by the natural cycles of
nutrients. In general, nutrient levels are higher in the winter and lower in
the summer (Nasr and Aleem 1948; Fonselius 1978) with the cycle largely
controlled by the activity of phytoplankton which removes much of the
available nitrogen and phosphorous from seawater during the spring
bloom period (Wallentinus 1981,1991). Nutrients can, therefore, be in
short supply for benthic algae during the spring/summer period with
nitrogen being the most likely nutrient limiting plant growth (Foster 1914;
Alfimov 1959; Ryther and Dunstan 1971; Prince 1974; Wallentinus 1981;
Sfriso et al. 1988a,b). Whilst some perennial algae are known to be capable
of binding large quantities ofN and P in their biomass [e.g. a bioaccumulation factor for nitrate of 28000 was reported by Chapman and Craigie (1977)
for the large kelp alga Laminaria longicrurisl which can be utilized during
periods of low ambient levels, the growth and seasonal response of many
algae largely revolves around the natural availability of the nutrients. Not
surprisingly, therefore, any additional inputs of these nutrients will upset
the natural seasonal cycles of growth and development.
Although there are a number of natural mechanisms outside the growth
cycle of phytoplankton by which nutrients are released into the marine
environment e.g. the release of nutrients from sediments disturbed by
storms, from rotting benthic seaweed and as a result of upwelling systems
(Fujita etal. 1989), many reports relate to man's activities. These include:
the release of nutrients from "disturbed" sediments as a result of dredging
activities, coastal construction works etc. (Perez-Ruzafa et al. 1991);
nutrients derived from atmospheric fall-out, which usually occurs in
coastal waters down-line from industrial areas (considered by Rosenberg
1985,1990 and Wilson et al. 1990 to be a source of nutrients entering the
Kattegat region of the Baltic and Dublin Bay, Ireland, respectively);
nutrient-containing effluents discharged from various coastal refuge tips;
nutrients originating from the growing number of fish farms which are in
operation (Lumb and Fowler 1989; Tsutsumi et al. 1991); nutrients from
river input (runoff) and percolating groundwater coming from agricultural
land treated with fertilizers (Fitzgerald 1978; Rosenberg 1985; Wilson et al.