When fertilisers are used on crops to help them grow, often these fertilisers drain into ponds and lakes. This can cause algae to crow very fast, creating a blanket over the surface. What do we call this?
Answers
Answer:
Eutrophication" is the enrichment of surface waters with plant nutrients. While eutrophication occurs naturally, it is normally associated with anthropogenic sources of nutrients. The "trophic status" of lakes is the central concept in lake management. It describes the relationship between nutrient status of a lake and the growth of organic matter in the lake. Eutrophication is the process of change from one trophic state to a higher trophic state by the addition of nutrient. Agriculture is a major factor in eutrophication of surface waters.
The most complete global study of eutrophication was the Organization for Economic Cooperation and Development (OECD) Cooperative Programme on Eutrophication carried out in the 1970s in eighteen countries (Vollenweider et al., 1980). The sequence of trophic state, from oligotrophic (nutrient poor) to hypertrophic (= hypereutrophic [nutrient rich]) is shown in Table 12.
Although both nitrogen and phosphorus contribute to eutrophication, classification of trophic status usually focuses on that nutrient which is limiting. In the majority of cases, phosphorus is the limiting nutrient. While the effects of eutrophication such as algal blooms are readily visible, the process of eutrophication is complex and its measurement difficult. This is not the place for a major discussion on the science of eutrophication, however the factors noted in Table 13 indicate the types of variables that must be taken into account.
Because of the complex interaction amongst the many variables that play a part in eutrophication, Janus and Vollenweider (1981) concluded that it is impossible to develop strict boundaries between trophic classes. They calculated, for example, the probability (as %) of classifying a lake with total phosphorus and chlorophyll-a concentrations of 10 and 2.5 mg/m3 respectively, as:
Phosphorus
Chlorophyll
Ultra-oligotrophic
10%
6%
Oligotrophic
63%
49%
Mesotrophic
26%
42%
Eutrophic
1%
3%
Hypertrophic
0%
0%
The symptoms and impacts of eutrophication are:
· Increase in production and biomass of phytoplankton, attached algae, and macrophytes.
· Shift in habitat characteristics due to change in assemblage of aquatic plants.
· Replacement of desirable fish (e.g. salmonids in western countries) by less desirable species.
· Production of toxins by certain algae.
· Increasing operating expenses of public water supplies, including taste and odour problems, especially during periods of algal blooms.
· Deoxygenation of water, especially after collapse of algal blooms, usually resulting in fish kills.
· Infilling and clogging of irrigation canals with aquatic weeds (water hyacinth is a problem of introduction, not necessarily of eutrophication).
· Loss of recreational use of water due to slime, weed infestation, and noxious odour from decaying algae.
· Impediments to navigation due to dense weed growth.
· Economic loss due to change in fish species, fish kills, etc.
TABLE 12: Relationship between trophic levels and lake characteristics (Adapted from Janus and Vollenweider, 1981)
Trophic status
Organic matter mg/m3
Mean total phosphorus1 mg/m3
Chlorophyll maximum1
mg/m3
Secchi depth1
m
Oligotrophic
low
8.0
4.2
9.9
¯
Mesotrophic
medium
26.7
16.1
4.2
¯
Eutrophic
high
84.4
42.6
2.45
¯
Hypertrophic
very high
750-1200
0.4-0.5
Explanation:
Answer:
Composting is a microbial process that converts plant materials such as grass clippings and leaves to a more usable organic soil amendment or mulch. Gardeners have used compost for centuries to increase soil organic matter, improve soil physical properties, and supply some of the essential nutrients for plant growth.
What is compost?
Compost is the partially decomposed remains of plants. In its final state of decomposition it is referred to as humus.
Does compost have any value as a fertilizer?
Yes, because decomposed materials have some nitrogen, phosphorous, and potassium content even though in small amounts. The addition of garden fertilizers to speed up decomposition supplies some of the nutrients as well.
Can compost be used as a substitute for fertilizer in the garden?
It can be used as a source of nutrients, however, there are not enough nutrients present in the compost to supply the needs of vegetable crops and ornamental plants. The lack of large amounts of nutrients in compost is far outweighed particle size of the material being composted depends on the final use of the compost.
However, on farms and large gardens, it is doubtful whether the advantages of shredding will be sufficient to justify the additional cost and labor. In ordinary composting any particles that are too large can be forked or screened out and broken up when necessary. If the material is to be used on lawns or flower gardens, it can be screened after composting through a 1-inch or smaller screen to give it a better appearance and to make it easier to apply and work into the soil. The individual farmer or gardener may not be necessarily particular about the uniformity of the compost structure when preparing the compost. Nor is the uniformity as important for agriculture fields as for the hobby gardener.
Initial shredding of all the material is not necessary in the composting operation. It is often the best practice to limit the initial shredding to large pieces of organic materials. Some composters believe that permitting some larger irregular pieces to remain tends to create greater air spaces in the mass and entrap more oxygen. Undecomposed pieces can be screened out of the final compost and put back through the decomposing process.
Vegetative and herbaceous matter should not be ground because it becomes soggy. The high moisture content of these materials makes them useful in small quantities throughout the composting process.
Aerobic decomposition proceeds best between 40% and 70%.