Digital Signal Processing Reference
In-Depth Information
particularly nitrogen and phosphorus. The phytoplankton state is often associated with poor water
quality, an unappealing 'pea-soup' appearance, and a loss of biodiversity as plant species become
fewer, along with the animals that depend on them. Unfortunately, reducing the nutrient load of the
lake doesn't necessarily result in a switch back to the more desirable plant-dominated state. This is
because restoration of the necessary species of macrophytes in shallow lakes depends on several
conditions;
Water clarity
Light is fundamental for plant growth. A decline in water clarity due to increased matter in the water
column (such as particles, phytoplankton, dissolved organic matter) limits the depth to which plants
can grow. However, water clarity can improve over time in some situations, such as when catchment
initiatives are undertaken.
Plant inocula
There need to be inocula (seeds or plant fragments from other areas) that can respond to improving
conditions in a lake. Seed banks that are old or depleted and have a poor germination response can be
a barrier to plant restoration.
Wave action
Wind-driven wave re-suspension of bed sediments can be a barrier in shallow lakes with large fetches,
where plants are uprooted, buried, or shaded out by high levels of re-suspended matter in the water
column.
Pest fish
Certain alien fish can adversely affect plants by eating, damaging, or uprooting them and by
promoting turbid conditions through foraging in lake bed sediments.
Catchment initiatives
Various measures can enhance a lake's chance of regaining vegetation. These include sediment traps
or buffering vegetation along streams and lake edges to improve clarity and water quality.
In this research the focus is on shallow lakes of the type “Shoreline” brackish water in which there are
different aquatic species dominating in both the littoral and limnitic zones. Despite major disturbances,
the Delta lakes, which are of this type, are still primarily characterized by extensive stands of emergent
macrophytes (Khedr & Lovett, 2000) that form valuable refuges for wild-life. At
Edko Lake
, the
dominant emergent plants were
Phragmites communis
and
Typha domingensis. T. domingensis
was
frequently present as fringing growth along the edges of the main
Phragmites
stands. Frequent
channels enclosed by emergent vegetation were colonized by water hyacinth
Eichhornia crassipes
and
Potamogeton pectinatus
. Patches of
P. pectinatus
were occasionally common beyond the reed beds.
This plant species was formerly much more common (Farinha
et al.,
1996). Nowadays it still exists
around the drain inlets into the lake and close to the south-north and south-east shores of the lake. A
detailed description of the vegetation types and their photos is given in
Chapter 6
.
Fisheries (Aquaculture)
Various types of aquaculture form an important component within agricultural and farming systems
development. These can contribute to the alleviation of food insecurity, malnutrition and poverty
through the provision of food of high nutritional value, income and employment generation, decreased
risk of monoculture production failure, improved access to water, enhanced aquatic resource
management and increased farm sustainability (e.g. FAO 2000a, Prein and Ahmed 2000). Inland
fisheries and fish ponds surrounding lakes and drainage systems within agricultural areas, may yet be
able to yield more fish as effort increases, but the increased effort required will become increasingly
challenging. Inland fisheries are also vulnerable to environmental impacts, such as watershed
degradation, development of water control structures and pollution. All features of the changing rural
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